Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2018 Sep 13;3(9):11062–11070. doi: 10.1021/acsomega.8b01355

Encapsulation of a Water Octamer Chain in a Chiral 2D Sheetlike Supramolecular Coordination Network Composed of Dinickel–Dicarboxylate Subunits

Navnita Kumar †, Sadhika Khullar ‡, Sanjay K Mandal †,*
PMCID: PMC6645534  PMID: 31459215

Abstract

graphic file with name ao-2018-01355d_0011.jpg

Four new chiral supramolecular coordination networks of Ni(II) of general formula [Ni2(Hhissal)2(dicarboxylate)(H2O)2]·nH2O (where Hhissal = histidinesalicylate; dicarboxylate = adipate; n = 8 for 1, succinate; n = 4 for 2, maleate; n = 4 for 3, fumarate; and n = 6 for 4) are reported. On the basis of the single-crystal X-ray study, an unprecedented zig-zag chain structure of water octamer encapsulated in 1 has been identified. The supramolecular network of the dimetal subunits is formed through hydrogen bonding interactions between the amine N–H of Hhissal and the oxygen atom of the coordinated water molecule of one subunit with the uncoordinated oxygen atom and the coordinated oxygen atom of the carboxylate group of Hhissal of the next subunit, respectively. The strength of hydrogen bonding within this water cluster (the range of O···O distances is 2.702–2.760 Å) is similar to that found in ice. These networks are further characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, polarimetry, UV–vis/diffuse reflectance and circular dichroism spectroscopy, and thermogravimetric analysis. A comparison of their properties indicates that these are isostructural with a variation of encapsulated water clusters.

Introduction

Chiral supramolecular networks have been extensively studied in the recent past due to their wide range of applications in asymmetric catalysis, chiral recognition and separation, ferroelectric materials, etc.1−7 For the synthesis of chiral networks, the use of readily available amino acids is the best way out. Because of the presence of various functionalities like carboxyl, amines, hydroxyl groups, etc. in amino acids, these serve as a good candidate for the formation of hydrogen-bonded networks. In recent years, transition metal complexes of reduced Schiff base ligands composed of amino acids and salicylaldehyde have been studied.8−10 Numerous coordination polymers and supramolecular coordination networks (SCNs) of such ligands have also been reported in the literature.11,12 Hydrogen bonding, along with other weak interactions, like π–π and cation−π interactions, is the significant feature of these supramolecular networks.13−18 One such ligand, H2hissal ligand (H2hissal = histidinesalicylic acid), has been used in SCNs of several transition metal ions such as Ni(II), Cu(II), Zn(II), and Fe(III).19−24 This nonplanar ligand is unique with the presence of an imidazole moiety along with a phenolic −OH group in addition to the amino and the carboxylate groups.

On the other hand, over the last few decades, water clusters of different sizes are explored a lot to get insights into the aberrant behavior of water.25−30 The structural elucidation of water clusters in diverse environments with different nuclearities and structures gives an understanding of the nature of water–water interactions.31 Interactions of water molecules play a pivotal role in maintaining the stability and proper functioning of the biological units.32−35 However, till now, many aspects of the water clusters in biological systems, such as the water clusters in various enzymes, water channel proteins of cell membrane, or the water structure energy-transducing protein, are unexplored. Various theoretical calculations have been carried out on these water clusters, giving the most stable conformations in the gas phase for some cases with distinct nuclearity and also expressing the properties of bulk water.36,37 For example, on the basis of such calculations, (H2O)8 should have two closely related isomers of nearly identical energy with S4 and D2d symmetries. In both the isomers, oxygen atoms occupy the corners of a cube and form hydrogen bonds along each edge, but the details of their hydrogen bonding are different.38 There is an upsurge in developing and studying new SCNs that provide suitable environments for water clusters of different sizes through moderate to strong hydrogen bonding interactions due to their potential application in various fields, like host–guest chemistry, sensing, molecular recognition, etc. Experimentally, these octameric water clusters were observed in gas-phase C6H6(H2O)8 clusters39 and in molecular beams.40 Thus far, octameric water clusters observed in organic or organic–inorganic supramolecular assemblies exhibit cubane,41 opened cube,42,43 and baglike conformations.44−46 In this context, a water hexamer with two dangling monomers,47−49 a cyclic tetramer with four dangling monomers,50,51 and a cyclic ring52 have been reported due to different environments imposed by the hosts.

In continuation of our work in the area of unmasking water clusters of diverse nuclearity encapsulated in the SCNs,53,54 we have chosen the Ni(II)–Hhissal system with several aliphatic dicarboxylates as a starting point for generating examples of chiral SCNs constructed from transition metal subunits containing reduced Schiff base derivatives of amino acids and multitopic dicarboxylates and water clusters. To the best of our knowledge, a dicarboxylate linker has never been used, along with the Schiff base ligands of amino acids (shown in Figure 1) with a metal ion, in forming an SCN. In this article, we report the synthesis and structural characterization of four SCNs of Ni(II) of the general formula [Ni2(Hhissal)2(dicarboxylate)(H2O)2]·nH2O (where Hhissal = histidinesalicylate; dicarboxylate = adipate; n = 8 (1), succinate; n = 4 (2), maleate; n = 4 (3), fumarate; and n = 6 (4)). A number of analytical techniques (elemental analysis, IR spectroscopy, powder X-ray diffraction, polarimetry, UV–vis/diffuse reflectance and circular dichroism (CD) spectroscopy, and thermogravimetric analysis (TGA)) have been used for their characterization and establishing a trend in their properties. Despite our numerous efforts, suitable crystals only for 1 were obtained for the single-crystal X-ray structure determination. The water octamer encapsulated within 1 has a zig-zag chain structure which is unprecedented.

Figure 1.

Figure 1

Open in a new tab

Structure of the chiral ligand and dicarboxylates used in this study.

Results and Discussion

Synthesis

The synthesis of the H2hissal ligand was carried out by modifying the procedure reported earlier.23 All four complexes 1–4 were obtained via a one-pot synthesis by stirring a methanolic solution of NiSO4·7H2O, KHhissal, and a dipotassium salt of the respective dicarboxylates (in a 1:1:0.5 ratio) for 12 h at room temperature. In all four cases, the desired product was obtained from the evaporation of the filtrate (the solid by-product K2SO4 insoluble in methanol is the precipitate) under reduced pressure.

Single Crystal Structure Analysis

Crystals of 1 suitable for the single-crystal X-ray study were grown by slow evaporation of its methanolic solution for a week. Despite numerous attempts over a long period of time, crystals of 2–4 suitable for data collection could not be obtained. Compound 1 crystallizes in the chiral monoclinic space group C2 (Table 1). Each discrete dinuclear unit has two equivalent hexacoordinated nickel centers with slightly distorted octahedral geometry and are linked together by one adipate molecule (as shown in Figure 2). A 2-fold axis generates the asymmetric unit. The coordination environment around each nickel center is N2O4-type. The two oxygen atoms binding to Ni(II) are from the phenoxy group and the carboxylate group of Hhissal, whereas the third oxygen binding to Ni(II) is from the carboxylate group of the adipate and the fourth oxygen is from the coordinated water. One nitrogen coordinating to Ni(II) is from the NH of the amino group of the ligand, whereas the other nitrogen is from the imidazole group of the ligand. The carboxylate group of the ligand as well as the carboxylate group of the adipate binds to Ni(II) in a monodentate fashion. Selected bond distances and bond angles for 1 are listed in Tables S1 and S2, Supporting Information. In the literature, the mononuclear complexes of the H2hissal ligand [Ni(Hhissal)2]·H2O21 as well as [Ni(hissal)(H2O)2]47 have been reported, where the metal/ligand ratio (1:2 vs 1:1) is different for the ligand acting as a monoanion vs a dianion, respectively.

Table 1. Crystal Structure Data and Refinement Parameters for 1.

chemical formula C32H52Ni2N6O20
formula weight 962.5
temperature (K) 250(2)
wavelength (Å) 0.71073
crystal system monoclinic
space group C2
a (Å) 20.1803(8)
b (Å) 6.2496(3)
c (Å) 17.1447(8)
a (deg) 90
b (deg) 100.701(2)
g (deg) 90
Z 2
V (Å3) 2124.67(17)
density (mg cm–3) 1.504
μ (mm–1) 0.971
F(000) 1012
θ (deg) range for data coll. 1.21–25.06
reflections collected 7126
independent reflections 3111
reflections with I > 2σ(I) 2781
Rint 0.027
no. of parameters refined 284
GOF on F2 1.015
final R1a/wR2b (I > 2σ(I)) 0.0430/0.1162
R1/wR2 (all data) 0.0514/0.1292
Flack parameter 0.0(0)
largest diff. peak and hole (e Å–3) 0.693 and −0.395
Open in a new tab
a

R1 = ∑||Fo| – |Fc||/∑|Fo|.

b

wR2 = [∑w(Fo2 – Fc2)2/∑w(Fo2)2]1/2, where w = 1/[σ2(Fo2) + (aP)2 + bP], P = (Fo2 + 2Fc2)/3.

Figure 2.

Figure 2

Open in a new tab

Dinuclear unit in 1. Lattice water molecules are omitted for clarity.

On the basis of these two examples, it is inferred that the deprotonation of the phenolic −OH group depends on the intramolecular hydrogen bonding and not on the amount of the base used. Using other neutral or monoanionic ligands, like imidazole, SCN–, or benzoate, three other 1:1 complexes [Ni(hissal)(imidazole)2], [Ni(Hhissal)(SCN)(H2O)]·H2O, and [Ni(Hhissal)(benzoate)(H2O)]·H2O have been reported.21,22 In the case of [Ni(Hhissal)2]·H2O, the ligand acts as a monoanion due to strong intermolecular hydrogen bonding between the phenolic OH group and the carboxylate group of the next molecule. On the other hand, in [Ni(Hhissal)(benzoate)(H2O)]·H2O, the intramolecular hydrogen bonding between one of the oxygens of the benzoate group and the OH group of the ligand is responsible for it to be a neutral species even when 2 equiv of the base is used. In the case of 1, a similar strong hydrogen bonding is observed between the oxygen of the carboxylate group of the adipate and the phenolic −OH (O···O distance: 2.585 Å), and thus preventing deprotonation of the phenolic −OH despite the use of 2 equiv of base (see Figure 2).

The dimeric unit grows in one direction forming a two-dimensional (2D) sheetlike structure via intermolecular hydrogen bonding. The nitrogen of the amine of the ligand and the oxygen atom of the coordinated water molecule of the dinuclear subunit are hydrogen-bonded to the uncoordinated oxygen atom and the coordinated oxygen atom of the carboxylate group of the ligand of the next subunit, respectively, forming a ladderlike structure (as shown in Figure 3). This 2D sheet is further hydrogen-bonded to a similar 2D sheet via hydrogen bonding, giving a three-dimensional (3D) network of intermingled ladders (as shown in Figure 4).

Figure 3.

Figure 3

Open in a new tab

Two-dimensional sheet forming a ladderlike structure in 1 via hydrogen bonding interactions (intramolecular hydrogen bonding is shown in orange, and intermolecular hydrogen bonding is shown in violet).

Figure 4.

Figure 4

Open in a new tab

Intermingled ladders in 1 forming a 3D structure via hydrogen bonding interactions.

The −NH of the imidazole ring of the ligand of the first 2D sheet shows bifurcated hydrogen bonding with the oxygen atom (O6) of the coordinated water and the uncoordinated oxygen atom (O2) of the carboxylate group forming intermingled ladders (as shown in Figure S1). On each side of the ladder, the octameric chain of water was strongly hydrogen-bonded to the dimeric unit (as shown in Figure 5, top). While doing so, the lattice water octamer (O7, O7′, O8, O8′, O9, O9′, O10, and O10′) present in the molecule arranges itself in the form of a 1D zig-zag chain via intermolecular hydrogen bonding. The six water molecules (two O8, two O9, and two O10) form the backbone of this chain, whereas two water molecules (two O7) are just attached to this backbone (as shown in Figure 5, bottom). The octamer of water in 1 shows strong intermolecular as well as intramolecular hydrogen bonding.25,55−58 The hydrogen-bonding parameters found in 1 are summarized in Table 2. The dinuclear units are strongly hydrogen-bonded to octameric water chains on both the ends (as shown in Figure S2). Therefore, it is observed that the octameric chain of water is encapsulated between the hydrogen-bonded 2D sheets of the dimeric units of 1 through strong hydrogen bonding (as shown in Figure 6). In 1, the O···O distance varies from 2.6620 to 2.7492 Å; these parameters are comparable to those for ice, where the O···O distance is 2.783 Å25,48,49 and the O···O···O angles vary from 96.64 to 152.09°. This arrangement enhances the stability of the water chain as evident from the thermal behavior of 1 (vide infra). Even though this chain grows infinitely, there are eight water molecules that are traversed every time to reach the unit cell repeat atom. In all previously reported infinite water chains with octamer as a repeating unit, there are one or more rings, whereas in this case, the whole unit (octamer) is a chain with no rings. This octamer can be classified as C8.57,58 Prior to our work, all reports describing the structure of water octamer have different arrangements. For example, theoretical studies suggested that the water octamer of cubelike arrangement with D2d and S4 symmetries would be the most favorable,39,40,59 whereas the first crystallographic observation of the water octamer was reported for [A2B](H2O)8, where A = κ4-[1,2-bis(2-oxy-2-methylpropanamido)-4,5dimethoxybenzene]cobaltate(III) and B = bis-κ3-(2,6-diacetamidopyridine)cobalt(II), in which the water octamer forms a cubelike structure with Ci symmetry.41 In this structure, O···O···O angles vary from 79.9 to 92.1°, whereas O···O distances vary from 2.750 to 2.929 Å. Similarly, in the case of [Y(dpdo)2(H2O)4][Co(CN)6]·4H2O (where dpdo = 2,2′-dipyridine dioxide), the octameric water cluster has a book-shaped hexamer with two dangling water molecules,47 where the O···O distances within the octamer vary from 2.677 to 2.964 Å and O···O···O angles range from 79.4 to 105.7°. Another puckered water octamer is known in the literature52 in which the O···O distance is 2.745 Å and the O···O···O angles are 109.5 and 116°. Finally, in [{V(phen)2SO4}2O](H2O)4 (phen = 1,10-phenanthroline), the water octamer42 shows a butterfly-shaped or opened cubelike structure, where O···O distances within the octamer range from 2.76 to 2.91 Å. Thus, an encapsulated zig-zag water octamer chain found in 1 is unprecedented.

Figure 5.

Figure 5

Open in a new tab

(Top) Octamers of water (space fill pattern) joining the dimeric units in 1 on both sides. (Bottom) Hydrogen bonding interactions within the water octamer.

Table 2. Hydrogen-Bonding Parameters in 1.

D–H···A (Å) r(D–H) (Å) r(H···A) (Å) r(D···A) (Å) ∠D–H···A (deg) symmetry
N1–H1···O2 0.91 2.14 3.0417 172 x, −1 + y, z
N2–H1···O1 0.86 2.16 2.9969 164 1/2 – x, −1/2 + y, −z
O6–H6B···O1 0.85 2.19 2.7556 123 x, −1 + y, z
O6–H6B···N2 0.85 2.56 3.3463 153 1/2 – x, −1/2 + y, −z
O7–H7A···O9 0.86 1.84 2.6664 162  
O8–H8A···O9 0.86 1.98 2.662 135 1/2 + x, −1/2 + y, z
O8–H8B···O2 0.86 2.04 2.7333 137  
O9–H9B···O10 0.86 2.16 2.7492 125  
O10–H10D···O8 0.87 2.17 2.7391 123 –1/2 + x, −1/2 + y, z
Open in a new tab

Figure 6.

Figure 6

Open in a new tab

Encapsulated water octamer (shown in space fill pattern) within the hydrogen-bonded 2D sheet of 1. (All of the hydrogen atoms of the main framework are omitted for clarity.)

Powder X-ray Data Analysis

Powder X-ray diffraction patterns (intensity vs 2θ) were recorded for the bulk samples of 1–4 at room temperature (as shown in Figure S3). In the case of 1, the experimental and simulated (from the single-crystal data) patterns matched very well, confirming that the single crystal and bulk material are the same. This also confirms the phase purity of bulk. The patterns for 2–4 show their crystalline nature. The powder X-ray diffraction of 2–4 shows a similar pattern as that with a slight variation in some peaks, suggesting a small variation in the crystal structure compared to that of 1.

Fourier Transform Infrared (FTIR) Spectroscopy

The IR spectra of 1–4 (see Figures S4–S7) recorded in the solid state as KBr pellets show two broad bands in the region of 3400–3200 cm–1. For compound 1, the broad peak at 3380 cm–1 is for H-bonded phenolic-OH. For 2, 3, and 4, the corresponding peaks appear at 3375, 3384, and 3381 cm–1, respectively. On the other hand, the peaks at 3251, 3227, 3250, and 3263 cm–1, respectively, for 1–4 are for the water molecules. Generally, the IR spectrum of ice shows the O–H stretching frequency at 3220 cm–1.60 This corroborates well with the O···O distances found in the crystal structure of 1, which are similar to those found in ice. For N–H stretching, the peak for 1 appears at 3008 cm–1, for 2 at 3017 cm–1, for 3 at 3023 cm–1, and for 4 at 2984 cm–1. The asymmetric stretch for the carboxylate group of the ligand appears at around 1592 cm–1 for 1, 1600 cm–1 for 2, 1598 cm–1 for 3, and 1598 cm–1 for 4, whereas the symmetric stretch appears at 1480 cm–1 for 1, 1481 cm–1 for 2, 1480 cm–1 for 3, and 1480 cm–1 for 4. The asymmetric stretch for the dicarboxylates appears at 1567 cm–1 for 1, 1568 cm–1 for 2, 1574 cm–1 for 3, and 1576 cm–1 for 4, whereas the symmetric stretch appears at 1406 cm–1 for 1, 1397 cm–1 for 2, 1401 cm–1 for 3, and 1404 cm–1 for 4. In all four compounds, the C–O stretching for the phenoxo part of the ligand appears at around 1294 cm–1.61 This comparative data indicates that all four compounds are isostructural.

Solid-State Diffuse Reflectance

The diffuse reflectance spectra of 1–4 (as shown in Figure 7) are dominated by the d–d transitions of Ni(II). In all complexes, three absorption edges are observed: 271, 370, and 575 nm (for 1); 281, 376, and 603 nm (for 2); 296, 374, and 603 nm (for 3); and 295, 372, and 593 nm (for 4). The absorption edges at ∼600 and ∼370 nm can be assigned to the following transitions of Ni(II) in a distorted octahedral environment: 2A2g to 2T1g (F) and 2A2g to 2T1g (P), respectively.

Figure 7.

Figure 7

Open in a new tab

Reflectance spectra for 1–4 in the wavelength range from 200 to 1100 nm.

UV–Vis and Circular Dichroism (CD) Spectroscopy

UV–visible and CD studies were carried out using a 1.25 mM methanolic solution of 1–4. In the visible region of the spectrum (325–700 nm), 1 shows a major peak at 590 nm (ε = 79 L mol–1 cm–1) and a hump at 365 nm. For other complexes, corresponding peaks appear as follows: for 2, 599 nm (ε = 65 L mol–1 cm–1) and 355 nm; for 3, 590 nm (ε = 73 L mol–1 cm–1) and 350 nm, and for 4, 590 nm (ε = 80 L mol–1 cm–1) and 350 nm (as shown in Figure 8a). These values are similar to the values reported in the literature for similar compounds.21

Figure 8.

Figure 8

Open in a new tab

(a) UV–vis spectra and (b) CD spectra for 1–4 in the wavelength range from 325 to 700 nm.

All of the above-mentioned peaks are due to d–d transitions. The peaks at around 600 nm are due to the 2A2g to 2T1g (F) transition in Ni(II), whereas the humps at around 360 nm are due to the 2A2g to 2T1g (P) transition.62 In the CD spectrum of 1, in the wavelength range of 325–700 nm, the positive Cotton effect is observed at 389 nm (due to 2A2g to 2T1g (P) transitions) and 567 nm (due to 2A2g to 2T1g (F) transitions). The corresponding peaks for other complexes are as follows: for 2, at 391 and 576 nm; for 3, at 389 and 565 nm; and for 4, at 390 and 567 nm (Figure 8b). The negative Cotton effect for 1 is observed at 353 and 504 nm. The corresponding peaks for other complexes are as follows: for 2, at 343 and 509 nm; for 3, at 354 and 509 nm; and for 4, at 352 and 512 nm.63

In the UV region of the spectrum (200–325 nm), the peaks at 205 nm (π–π*) and a shoulder at around 245 nm are due to the l-histidine part of the ligand and at 290 nm (n−π*) due to the salicylaldehyde part of the ligand (as shown in Figure 9a). In the CD spectrum of 1 in wavelength range of 200–325 nm, the positive Cotton effect is observed at 234 and 270 nm. The corresponding peaks for other complexes are observed: 234 and 271 nm (for 2); 233 and 270 nm (for 3); and 230 and 272 nm (for 4). The negative Cotton effect for 1 is observed at 210, 258, and 289 nm. The corresponding peaks for other complexes are observed: at 208, 258, and 289 nm (for 2); 211, 258, and 289 nm (for 3); and 210, 258, and 290 nm (for 4) (as shown in Figure 9b). The solution-state UV–vis absorption spectra of all four complexes 1–4 show a striking similarity with their solid-state reflectance spectra, suggesting the integrity of the solid-state structure in the solution.

Figure 9.

Figure 9

Open in a new tab

(a) UV spectra and (b) CD spectra of 1–4 in the wavelength range from 200 to 325 nm.

Fluorescence Spectroscopy

The presence of an imidazole group in the H2hissal ligand makes it a fluorophore. On being excited at 250 nm, the emission maximum is obtained at 307 nm for the ligand. However, in the case of all of the SCNs (1–4) synthesized using this ligand, quenching is observed in the fluorescence (as shown in Figure 10). A nonradiative decay caused by a Dexter-type energy transfer between the orbitals of Ni(II) and the Hhissal ligand is responsible for such quenching. Apart from this, another λemi peak at 284 is observed in the case of the SCNs (1–4). In the case of 2, two additional peaks at 343 and 358 nm are observed in the emission spectrum, indicating the variation in the structure of the succinate analogue from the other analogues and thus also confirming a different nonradiative pathway in the case of 2 compared to that in 1, 3, and 4.

Figure 10.

Figure 10

Open in a new tab

Fluorescence spectra of KHhissal, 1–4 in methanol (λexc = 250 nm).

Thermogravimetric Analyses

The thermal stability of compounds 1–4 was studied as a function of temperature in the range of 25–500 °C (see Figures S8–S11, respectively). Each of the SCN shows a three-step weight-loss profile. In each case, the first step shows a loss of the lattice water molecule and the second step shows a loss of mainly the coordinated water molecule and the carbon dioxide molecules. In the case of 1 and 4, the loss of remaining two lattice water molecules also takes place in this step, clearly suggesting an increase in the hydrogen bonding in the case of these two lattice water molecules compared to that in their other counterparts within the octamer (vide supra). This is further confirmed from the single crystal X-ray diffraction structure of 1. In the third step, further degradation of the complex is observed in all of the cases. The detailed TGA of 1 is reported herein as an example: the first weight loss of 11.24% between 50 and 160 °C corresponds to the loss of six lattice water molecules (ca. 11.22%). The second step has a weight loss of 21.89% between 260 and 360 °C for the loss of two lattice water molecules, two coordinated water molecules, and three carbon dioxide molecules (ca. 21.20%). The third weight loss of 57.60% between 370 and 470 °C indicates a further loss of the metal–ligand complex (ca. 56.27%). The TGA of 2–4 is reported in the Supporting Information. The TGA described above for 1–4 not only shows the strength of hydrogen bonding of lattice water molecules with the dinickel subunits but also supports the findings of other characterization techniques. The unusual thermal stability of these SCNs can be attributed to the extensive hydrogen bonding of the respective water cluster with the dimetal subunits.

Conclusions

In this article, the chainlike structure of the water octamer encapsulated in the 2D sheet structure of the dinuclear subunits in [Ni2(Hhissal)2(adi)(H2O)2]·8H2O (1) is described in detail based on the single-crystal X-ray structural studies. The encapsulated water octamer having hydrogen bonding within itself as well as with the carboxylate group of the ligand in the dinuclear unit provides greater stability to 1. Further spectroscopic properties and thermal behavior established for 1 provide additional information for understanding such a system. A comparison of these properties of 1 with those of [Ni2(Hhissal)2(succ)(H2O)2]·4H2O (2) and [Ni2(Hhissal)2(mal)(H2O)2]·4H2O (3), and [Ni2(Hhissal)2(fum)(H2O)2]·6H2O (4) has indicated that these are isostructural with a variation of encapsulated water molecules. The current study may provide a deeper insight into the hydrogen-bonding motif of the aqueous environments in biological systems and help in better understanding of the proton conduction in various living organisms. Results obtained in this study have encouraged us to put more effort in this direction with other metal centers as well as several dicarboxylate ligands to illuminate the rich chemistry for such systems. Further details will be communicated in due course.

Experimental Section

Materials and Methods

All reactions reported in this work were carried out under aerobic conditions using chemicals and solvents from commercial sources without further purification. The H2hissal ligand was made by modifying a literature procedure.23 However, its synthesis and characterization are reported in the Supporting Information.

Physical Measurements

The 1H NMR spectrum of the Na2hissal ligand was recorded in D2O solution at 25 °C on a Bruker ARX-400 spectrometer (chemical shifts are referenced to the residual solvent signals). Elemental analysis (C, H, N) of all compounds was done using a Leco TruSpec CHNS analyzer. For all samples, thermogravimetric analysis was carried out using Shimadzu DTG-60H from 25 to 500 °C (heating rate of 10 °C min–1) under a dinitrogen atmosphere. IR spectra of samples prepared as KBr pellets were recorded in the 4000–400 cm–1 range on a Perkin-Elmer spectrum I spectrometer. The UV–vis spectrum of a methanolic solution of each compound (typical concentration: 1 mM) was recorded in a Cary 60 UV–Vis spectrophotometer using a cuvette of path length 1 cm. Solid-state diffuse reflectance spectra were measured in a Cary 5000 UV–vis–NIR spectrophotometer by Agilent Technology. Optical rotations were measured using a glass cell with 50 mm path length in an Anton Paar modular circular polarimeter (MCP 300). Using a 2 mm path length quartz cuvette, CD spectra of all compounds were recorded on a Chirascan spectropolarimeter (Applied Photophysics, Leatherhead, Surrey, U.K.). Fluorescence spectra were recorded using a Shimadzu RF5301PC fluorescence spectrophotometer.

Synthesis of [Ni2(Hhissal)2(adi)(H2O)2]·8H2O (1)

In a 10 mL round bottom flask, 47 mg (0.18 mmol) of NiSO4·7H2O was dissolved in 3 mL of methanol. To this, a clear mixture of monopotassium H2hissal (KHhissal) (which was prepared using 50 mg (0.18 mmol) of H2hissal and 10 mg (0.18 mmol) of potassium hydroxide in 2.5 mL of methanol) and dipotassium adipate (K2adi) (which was prepared using 13 mg (0.09 mmol) of adipic acid and 10 mg (0.18 mmol) of potassium hydroxide in 2.5 mL of methanol) was added to get a blue color. This was stirred for 12 h. A blue solution was collected via filtration and evaporated under reduced pressure to obtain a blue powder. Yield: 70 mg (75.7%). Anal. Calc. for C32H56N6O20Ni2 (MW 962.20): Calc. C, 39.94; H, 5.87; N, 8.73. Found: C, 39.57; H, 5.92; N, 8.67. Selected FTIR peaks (KBr, cm–1): 3390(br), 3274(br), 2919(w), 1592(w), 1567(s), 1480(s), 1452(s), 1408(s), 1289(s), 1192(w), 1082(s), 874, 761. Specific rotation [α]D20 = −60 (0.02%, CH3OH).

Synthesis of [Ni2(Hhissal)2(succ)(H2O)2]·4H2O (2)

For its preparation, the procedure described above for 1 was followed except that 11 mg (0.09 mmol) of succinic acid was used instead of adipic acid. Yield: 45 mg (62.5%). Anal. Calc. for C30H46N6O16Ni2 (MW 862.09): Calc. C, 41.80; H, 5.14; N, 9.75. Found: C, 41.94; H, 5.08; N, 9.89. Selected FTIR peaks (KBr, cm–1): 3398(br), 3252(br), 2909(w), 1600(w), 1567(s), 1480(s), 1452(s), 1403(s), 1294(s), 1277(s), 1194(w), 1083(s), 878, 756. Specific rotation [α]D20 = −20 (0.02%, CH3OH).

Synthesis of [Ni2(Hhissal)2(mal)(H2O)2]·4H2O (3)

For its preparation, the procedure described above for 1 was followed except that 11 mg (0.09 mmol) of maleic acid was used instead of adipic acid. Yield: 50 mg (56%). Anal. Calc. for C30H42N6O16Ni2 (MW 860.07): Calc. C, 41.89; H, 4.92; N, 9.77. Found: C, 42.79; H, 4.79; N, 9.98. Selected FTIR peaks (KBr, cm–1): 3384(br), 3250(br), 2892(w), 1598(w), 1574(s), 1480(s), 1452(s), 1401(s), 1294(s), 1277(s), 1194(w), 1083(s), 878, 756. Specific rotation [α]D20 = +20 (0.02%, CH3OH).

Synthesis of [Ni2(Hhissal)2(fum)(H2O)2]·6H2O (4)

For its preparation, the procedure described above for 1 was followed except that 11 mg (0.09 mmol) of fumaric acid was used instead of adipic acid. Yield: 55 mg (58%). Anal. Calc. for C30H46N6O18Ni2 (MW 896.10): Calc. C, 40.21; H, 5.17; N, 9.38. Found: C, 40.56; H, 4.96; N, 9.40. Selected FTIR peaks (KBr, cm–1): 3384(br), 3250(br), 2892(w), 1598(w), 1574(s), 1480(s), 1452(s), 1401(s), 1294(s), 1277(s), 1194(w), 1083(s), 878, 756. Specific rotation [α]D20 = +30 (0.02%, CH3OH).

Single-Crystal X-ray Structure Determination

As described before,53 crystals of 1 were evaluated and data were collected on a Kappa APEX II diffractometer using the APEX2 program.55 Data were processed for routine steps: integration by the SAINT55 program, corrections for Lorentz and polarization effects, an absorption correction (SADABS), determination of space group, and generation of files necessary for solution and refinement by subroutine XPREP.55 For structure solution of 1 and further refinement, SHELXTL and SHELXL subroutines56 embedded in APEX2 were used. In 1, all nonhydrogen atoms, except oxygen atoms of uncoordinated water molecules, were refined with anisotropic displacement parameters. Crystal data and structure refinement parameters for 1 are listed in Table 1. All figures were generated using MERCURY V 3.0.57 Hydrogen-bonding parameters were obtained from PLATON.64

Powder X-ray Studies

In each case, using a Rigaku Ultima IV diffractometer (for details, refer to the report previously communicated by this laboratory54), data were collected of a fine powder, which was prepared by a mortar and a pestle and was placed on a glass sample holder, over a 2θ range of 3–50° with a scanning speed of 1° per min with 0.02° step.

Acknowledgments

Funding for this work was provided by IISER, Mohali. N.K. is grateful to MHRD, India, for a research fellowship. Central facilities (X-ray, NMR, and CD) at IISER, Mohali, are gratefully acknowledged.

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b01355.

  • Synthesis of H2hissal, additional Crystallographic Figures, FTIR spectra, TGA scans, selected bond lengths in 1 (PDF)

  • Crystallographic data for 1 (CCDC 962607) (CIF)

Author Present Address

§ Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States (N.K.).

The authors declare no competing financial interest.

Supplementary Material

ao8b01355_si_001.pdf (980.3KB, pdf)
ao8b01355_si_002.cif (17.8KB, cif)

References

  1. Wolff J. J. Crystal Packing and Molecular Geometry. Angew. Chem., Int. Ed. 1996, 35, 2195–2197. 10.1002/anie.199621951. [DOI] [Google Scholar]
  2. Lehn J. M.Supramolecular Chemistry: Concepts and Perspectives; VCH: Weinheim, 1995; pp 1–271. [Google Scholar]
  3. Rosi N. L.; Kim J.; Eddaoudi M.; Chen B.; O’Keeffe M.; Yaghi O. M. Rod packings and metal-organic frameworks constructed from rod-shaped secondary building units. J. Am. Chem. Soc. 2005, 127, 1504–1518. 10.1021/ja045123o. [DOI] [PubMed] [Google Scholar]
  4. Steed J. W.; Atwood J. L.. Supramolecular Chemistry; John Wiley & Sons Ltd: Chichester, 2009; pp 1–745. [Google Scholar]
  5. Rao C. N.; Natarajan S.; Vaidhyanathan R. Metal carboxylates with open architectures. Angew. Chem., Int. Ed. 2004, 43, 1466–1496. 10.1002/anie.200300588. [DOI] [PubMed] [Google Scholar]
  6. Bauer E. B. Chiral-at-metal complexes and their catalytic applications in organic synthesis. Chem. Soc. Rev. 2012, 41, 3153–3167. 10.1039/c2cs15234g. [DOI] [PubMed] [Google Scholar]
  7. Xuan W.; Zhang M.; Liu Y.; Chen Z.; Cui Y. A chiral quadruple-stranded helicate cage for enantioselective recognition and separation. J. Am. Chem. Soc. 2012, 134, 6904–6907. 10.1021/ja212132r. [DOI] [PubMed] [Google Scholar]
  8. Wisser B.; Lu Y.; Janiak C. Chiral Coordination Polymers with Amino Acids. Z. Anorg. Allg. Chem. 2007, 633, 1189–1192. 10.1002/zaac.200700088. [DOI] [Google Scholar]
  9. Wisser B.; Chamayou A.-C.; Miller R.; Scherer W.; Janiak C. A chiral C3-symmetric hexanuclear triangular-prismatic copper(II) cluster derived from a highly modular dipeptidic N,N′-terephthaloyl-bis(S-aminocarboxylato) ligand. CrystEngComm 2008, 10, 461–464. 10.1039/b717207a. [DOI] [Google Scholar]
  10. Ma L.-F.; Wang L.-Y.; Wang J.-G.; Wang Y.-F.; Feng X. Two Novel Three-Dimensional Lead(II) Coordination Polymers Involving 16-Membered Rings: [Pb2(Bs-glu)2(bipy)2] and [Pb2(Bs-glu)2(phen)2]. Z. Anorg. Allg. Chem. 2006, 632, 487–490. 10.1002/zaac.200500413. [DOI] [Google Scholar]
  11. Ganguly R.; Sreenivasulu B.; Vittal J. J. Amino acid-containing reduced Schiff bases as the building blocks for metallasupramolecular structures. Coord. Chem. Rev. 2008, 252, 1027–1050. 10.1016/j.ccr.2008.01.005. [DOI] [Google Scholar]
  12. Vittal J. J. Supramolecular structural transformations involving coordination polymers in the solid state. Coord. Chem. Rev. 2007, 251, 1781–1795. 10.1016/j.ccr.2007.02.002. [DOI] [Google Scholar]
  13. Burrows A. D.; Chan C.-W.; Chowdhry M. M.; McGrady J. E.; Mingos D. M. P. Multidimensional crystal engineering of bifunctional metal complexes containing complementary triple hydrogen bonds. Chem. Soc. Rev. 1995, 24, 329–339. 10.1039/cs9952400329. [DOI] [Google Scholar]
  14. Brammer L.Perspective in Supramolecular Chemistry - Crystal Design: Structure and Function; John Wiley & Sons Ltd: Chichester, 2003; Vol. 7, pp 1–75. [Google Scholar]
  15. Beatty A. M. Hydrogen bonded networks of coordination complexes. CrystEngComm 2001, 3, 243. 10.1039/b109127c. [DOI] [Google Scholar]
  16. Aakeröy C. B.; Beatty A. M. Aust. J. Chem. 2001, 54, 409–421. 10.1071/CH01133. [DOI] [Google Scholar]
  17. Desiraju G. R. Hydrogen bonds and other intermolecular interactions in organometallic crystals. J. Chem. Soc., Dalton Trans. 2000, 21, 3745–3751. 10.1039/b003285i. [DOI] [Google Scholar]
  18. Subramanian S.; Zaworotko M. J. Exploitation of the hydrogen bond: recent developments in the context of crystal engineering. Coord. Chem. Rev. 1994, 137, 357–401. 10.1016/0010-8545(94)03008-E. [DOI] [Google Scholar]
  19. Alam M. A.; Nethaji M.; Ray M. Structural Characterization of an Enantiopure Hydroxo-Bridged Binuclear Iron(III) Complex with Empty One-Dimensional Helical Channels. Inorg. Chem. 2005, 44, 1302–1308. 10.1021/ic049145n. [DOI] [PubMed] [Google Scholar]
  20. Alam M. A.; Koner R. R.; Das A.; Nethaji M.; Ray M. Rationalizing the Effects of Amino Acid Side Chain, Pyridine, and Imidazole on the Assembly and Reversible Disassembly of a Octanuclear Cu(II) Complex. Cryst. Growth Des. 2007, 7, 1818–1824. 10.1021/cg070250s. [DOI] [Google Scholar]
  21. Sahoo S. C.; Dubey M.; Alam M. A.; Ray M. Effect of metal coordination and intra-molecular H-bond on the acidity of phenolic proton in a set of structurally characterized octahedral Ni(II) complexes of l-histidine derivative. Inorg. Chim. Acta 2010, 363, 3055–3060. 10.1016/j.ica.2010.03.051. [DOI] [Google Scholar]
  22. Sahoo S. C.; Ray M. Three Point Chiral Recognition and Resolution of Amino Alcohols Through Well-Defined Interaction Inside a Metallocavity. Chem. - Eur. J. 2010, 16, 5004–5007. 10.1002/chem.201000078. [DOI] [PubMed] [Google Scholar]
  23. Alam M. A.; Nethaji M.; Ray M. Synthesis of a Self-Assembled Molecular Capsule that Traps Pyridine Molecules by a Combination of Hydrogen Bonding and Copper(II) Coordination. Angew. Chem., Int. Ed. 2003, 42, 1940–1942. 10.1002/anie.200250591. [DOI] [PubMed] [Google Scholar]
  24. Yang X.; Ranford J. D.; Vittal J. J. Isomerism in 1D Coordination Polymers of Cu(II) Complexes of N-(2-Hydroxybenzyl)-l-valine: Influence of Solvent and Coordination Sphere on the Conformation. Cryst. Growth Des. 2004, 4, 781–788. 10.1021/cg0499717. [DOI] [Google Scholar]
  25. Liu K.; Cruzan J. D.; Saykally R. J. Water Clusters. Science 1996, 271, 929–933. 10.1126/science.271.5251.929. [DOI] [Google Scholar]
  26. Ugalde J. M.; Alkorta I.; Elguero J. Water Clusters: Towards an Understanding Based on First Principles of Their Static and Dynamic Properties. Angew. Chem., Int. Ed. 2000, 39, 717–721. . [DOI] [PubMed] [Google Scholar]
  27. Dias S. S. P.; André V.; Kłak J.; Duarte M. T.; Kirillov A. M. Topological Diversity of Supramolecular Networks Constructed from Copper(II) Aminoalcohol Blocks and 2,6-Naphthalenedicarboxylate Linkers: Self-Assembly Synthesis, Structural Features, and Magnetic Properties. Cryst. Growth Des. 2014, 14, 3398–3407. 10.1021/cg500716d. [DOI] [Google Scholar]
  28. Demadis K. D.; Panera A.; Anagnostou Z.; Varouhas D.; Kirillov A. M.; Císařová I. Disruption of “Coordination Polymer” Architecture in Cu2+ Bis-Phosphonates and Carboxyphosphonates by Use of 2,2′-Bipyridine as Auxiliary Ligand: Structural Variability and Topological Analysis. Cryst. Growth Des. 2013, 13, 4480–4489. 10.1021/cg4009625. [DOI] [Google Scholar]
  29. Kirillova M. V.; Kirillov A. M.; Guedes da Silva M. F. C.; Kopylovich M. N.; Fraústo da Silva J. J. R.; Pombeiro A. J. L. 3D hydrogen bonded metal-organic frameworks constructed from [M(H2O)6][M′(dipicolinate)2]·mH2O (M/M′ = Zn/Ni or Ni/Ni). Identification of intercalated acyclic (H2O)6/(H2O)10 clusters. Inorg. Chim. Acta 2008, 361, 1728–1737. 10.1016/j.ica.2006.12.016. [DOI] [Google Scholar]
  30. Das M. C.; Bharadwaj P. K. Molecular Ice with Hybrid Water–Bromide Network around a Cryptand with a Bromide Ion Included in the Cavity to Form a Host-within-a-Host-Like Structure. Eur. J. Inorg. Chem. 2007, 2007, 1229–1232. 10.1002/ejic.200601082. [DOI] [Google Scholar]
  31. Keutsch F. N.; Saykally R. J. Water clusters: Untangling the mysteries of the liquid, one molecule at a time. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 10533–10540. 10.1073/pnas.191266498. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Suzuki M.; Tanaka S. Molecular and cellular regulation of water homeostasis in anuran amphibians by aquaporins. Comp. Biochem. Physiol., Part A: Mol. Integr. Physiol. 2009, 153, 231–241. 10.1016/j.cbpa.2009.02.035. [DOI] [PubMed] [Google Scholar]
  33. Wikström M. Proton translocation by bacteriorhodopsin and heme-copper oxidases. Curr. Opin. Struct. Biol. 1998, 8, 480–488. 10.1016/S0959-440X(98)80127-9. [DOI] [PubMed] [Google Scholar]
  34. Okamura M. Y.; Paddock M. L.; Graige M. S.; Feher G. Proton and electron transfer in bacterial reaction centers. Biochim. Biophys. Acta, Bioenerg. 2000, 1458, 148–163. 10.1016/S0005-2728(00)00065-7. [DOI] [PubMed] [Google Scholar]
  35. Zaslavsky D.; Gennis R. B. Proton pumping by cytochrome oxidase: progress, problems and postulates. Biochim. Biophys. Acta, Bioenerg. 2000, 1458, 164–179. 10.1016/S0005-2728(00)00066-9. [DOI] [PubMed] [Google Scholar]
  36. Weinhold F. Quantum cluster equilibrium theory of liquids: General theory and computer implementation. J. Chem. Phys. 1998, 109, 367–372. 10.1063/1.476573. [DOI] [Google Scholar]
  37. Weinhold F. Quantum cluster equilibrium theory of liquids: Illustrative application to water. J. Chem. Phys. 1998, 109, 373–384. 10.1063/1.476574. [DOI] [Google Scholar]
  38. Gregory J. K.; Clary D. C. Structure of Water Clusters. The Contribution of Many-Body Forces, Monomer Relaxation, and Vibrational Zero-Point Energy. J. Phys. Chem. 1996, 100, 18014–18022. 10.1021/jp9616019. [DOI] [Google Scholar]
  39. Buck U.; Ettischer I.; Melzer M.; Buch V.; Sadlej J. Structure and Spectra of Three-Dimensional (H2O)n Clusters, n = 8,9,10. Phys. Rev. Lett. 1998, 80, 2578–2581. 10.1103/PhysRevLett.80.2578. [DOI] [Google Scholar]
  40. Gruenloh C. J. Infrared Spectrum of a Molecular Ice Cube: The S4 and D2d Water Octamers in Benzene-(Water)8. Science 1997, 276, 1678–1681. 10.1126/science.276.5319.1678. [DOI] [Google Scholar]
  41. Blanton W. B.; Gordon-Wylie S. W.; Clark G. R.; Jordan K. D.; Wood J. T.; Geiser U.; Collins T. J. Synthesis and Crystallographic Characterization of an Octameric Water Complex, (H2O)8. J. Am. Chem. Soc. 1999, 121, 3551–3552. 10.1021/ja982100z. [DOI] [Google Scholar]
  42. Doedens R. J.; Yohannes E.; Khan M. I. Novel water clusters in the crystalline state: structures of a symmetrical, cyclic hexamer and an ‘opened-cube’ octamer. Chem. Commun. 2002, 1, 62–63. 10.1039/b108866a. [DOI] [PubMed] [Google Scholar]
  43. Sun Y.-q.; Zhang J.; Ju Z.-f.; Yang G.-Y. A uudd Cyclic Water Tetramer and an Opened Octameric Water Cluster in the Charge-Transfer Salts of the Bipyridinium Cation. Aust. J. Chem. 2005, 58, 572–577. 10.1071/CH05110. [DOI] [Google Scholar]
  44. Wang Y.; Okamura T.-A.; Sun W.-Y.; Ueyama N. Large (H2O)56(OH)6 and (H2O)20 Clusters inside a Nanometer-Sized M6L8 Cage Constructed by Five-Coordinated Copper(II) and Flexible Carboxamide-Containing Tripodal Ligand. Cryst. Growth Des. 2008, 8, 802–804. 10.1021/cg701242z. [DOI] [Google Scholar]
  45. Yuan G.; Zhu C.; Liu Y.; Fang Y.; Cui Y. Water clusters induced assembly of chiral organic microstructures showing reversible phase transformations and luminescence switching. Chem. Commun. 2010, 46, 2307–2309. 10.1039/b923259a. [DOI] [PubMed] [Google Scholar]
  46. Luo G.-G.; Xiong H.-B.; Sun D.; Wu D.-L.; Huang R.-B.; Dai J.-C. A Discrete Spirocyclic (H2O)9 Cluster and 1D Novel Water Chain with Tetrameric and Octameric Clusters in Cationic Hosts. Cryst. Growth Des. 2011, 11, 1948–1956. 10.1021/cg200111j. [DOI] [Google Scholar]
  47. Ma B.-Q.; Sun H.-L.; Gao S. Observation of an octameric water cluster containing a book-shaped hexamer in a 4f–3d complex. Chem. Commun. 2005, 2336–2338. 10.1039/b501161b. [DOI] [PubMed] [Google Scholar]
  48. Hao H.-J.; Sun D.; Liu F.-J.; Huang R.-B.; Zheng L.-S. Discrete Octamer Water Cluster and 1D T5(2) Water Tape Trapped in Two Luminescent Zn(II)/1,2-Bis(imidazol-1′-yl)ethane/Dicarboxylate Hosts: From 2D (4,4) Net to 3D 5-Fold Interpenetrated Diamond Network. Cryst. Growth Des. 2011, 11, 5475–5482. 10.1021/cg201067q. [DOI] [Google Scholar]
  49. Hazra A.; Kanoo P.; Mohapatra S.; Mostafa G.; Maji T. K. A flexible supramolecular host with a crowned chair octameric water cluster and highly selective adsorption properties. CrystEngComm 2010, 12, 2775–2780. 10.1039/b924511a. [DOI] [Google Scholar]
  50. Ghosh S. K.; Bharadwaj P. K. Octameric Water Clusters of Staircase Structure Present in a Metal-Organic Framework Built from Helical Lanthanide Coordination Polymers. Eur. J. Inorg. Chem. 2005, 2005, 4886–4889. 10.1002/ejic.200500735. [DOI] [Google Scholar]
  51. Yang G.-P.; Wang Y.-Y.; Liu P.; Fu A.-Y.; Zhang Y.-N.; Jin J.-C.; Shi Q.-Z. Formation of Three New Silver(I) Coordination Polymers Involving 1,2-Phenylenediacetic Acid via the Modulation of Dipyridyl-Containing Ligands. Cryst. Growth Des. 2010, 10, 1443–1450. 10.1021/cg901545k. [DOI] [Google Scholar]
  52. Atwood J. L.; Barbour L. J.; Ness T. J.; Raston C. L.; Raston P. L. A Well-Resolved Ice-like (H2O)8 Cluster in an Organic Supramolecular Complex. J. Am. Chem. Soc. 2001, 123, 7192–7193. 10.1021/ja015757k. [DOI] [PubMed] [Google Scholar]
  53. Khullar S.; Mandal S. K. Supramolecular Assemblies of Dimanganese Subunits and Water Clusters Organized by Strong Hydrogen Bonding Interactions: Single Crystal to Single Crystal Transformation by Thermal De-/Rehydration Processes. Cryst. Growth Des. 2012, 12, 5329–5337. 10.1021/cg300937f. [DOI] [Google Scholar]
  54. Khullar S.; Mandal S. K. Structural diversity of the encapsulated water clusters in the 3D supramolecular assemblies: a cyclic quasi-planar hexamer of water constructed through strong hydrogen bonding interactions. CrystEngComm 2013, 15, 6652–6662. 10.1039/c3ce40882e. [DOI] [Google Scholar]
  55. Ludwig R. Water: From Clusters to the Bulk. Angew. Chem., Int. Ed. 2001, 40, 1808–1827. . [DOI] [PubMed] [Google Scholar]
  56. Ghosh S. K.; Bharadwaj P. K. A Dodecameric Water Cluster Built around a Cyclic Quasiplanar Hexameric Core in an Organic Supramolecular Complex of a Cryptand. Angew. Chem., Int. Ed. 2004, 43, 3577–3580. 10.1002/anie.200454002. [DOI] [PubMed] [Google Scholar]
  57. Mascal M.; Infantes L.; Chisholm J. Water Oligomers in Crystal Hydrates—What’s News and What Isn’t?. Angew. Chem., Int. Ed. 2006, 45, 32–36. 10.1002/anie.200501839. [DOI] [PubMed] [Google Scholar]
  58. Infantes L.; Motherwell S. Water clusters in organic molecular crystals. CrystEngComm 2002, 4, 454–461. 10.1039/b204934a. [DOI] [Google Scholar]
  59. Tsai C. J.; Jordan K. D. Monte Carlo simulation of (H2O)8: Evidence for a low-energy S4 structure and characterization of the solid ↔ liquid transition. J. Chem. Phys. 1991, 95, 3850–3853. 10.1063/1.460788. [DOI] [Google Scholar]
  60. Ball P.H2O: A Biography of Water; Weidenfled and Novolson: London, 1999; pp 1–387. [Google Scholar]
  61. Nakamoto K.Infrared Spectra of Inorganic and Coordination Compounds Part B, 6th ed.; John Wiley & Sons: New York, 2009; pp 1–424. [Google Scholar]
  62. Dunn T. M.The Visible and Ultraviolet Spectra of Complex Compounds in Modern Coordination Chemistry; Interscience: New York, 1960; pp 1–266. [Google Scholar]
  63. Nakanishi K.; Berova N.; Woody R. W.. Circular Dichroism: Principles and Applications; VCH: New York, 1994; pp 1–576. [Google Scholar]
  64. Spek A. L. PLATON. Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, 65, 148–155. 10.1107/S090744490804362X. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao8b01355_si_001.pdf (980.3KB, pdf)
ao8b01355_si_002.cif (17.8KB, cif)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES