Sodium rubidium hydrogen citrate, NaRbHC₆H₅O₇, and sodium caesium hydrogen citrate, NaCsHC₆H₅O₇: crystal structures and DFT comparisons

The crystal structures of sodium rubidium hydrogen citrate and sodium caesium hydrogen citrate have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. In NaRbHC₆H₅O₇, the Na and Rb cation coordination spheres form triple chains along the a-axis direction, and chains of very strong O—H—O hydrogen bonds run along [111], while in NaCsHC₆H₅O₇ the Na and Cs coordination polyhedra form layers parallel to (101), and there are chains of very short and strong hydrogen bonds along [100].

Abstract

The crystal structure of sodium rubidium hydrogen citrate, NaRbHC₆H₅O₇ or [NaRb(C₆H₆O₇)]_n, has been solved and refined using laboratory powder X-ray diffraction data, and optimized using density functional techniques. This compound is isostructural to NaKHC₆H₅O₇. The Na atom is six-coordinate, with a bond-valence sum of 1.16. The Rb atom is eight-coordinate, with a bond-valence sum of 1.17. The distorted [NaO₆] octa­hedra share edges to form chains along the a-axis direction. The irregular [RbO₈] coordination polyhedra share edges with the [NaO₆] octa­hedra on either side of the chain, and share corners with other Rb atoms, resulting in triple chains along the a-axis direction. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds; the O⋯O distances are 2.426 and 2.398 Å. The Mulliken overlap populations in these hydrogen bonds are 0.140 and 0.143 electrons, which correspond to hydrogen-bond energies of about 20.3 kcal mol⁻¹. The crystal structure of sodium caesium hydrogen citrate, NaCsHC₆H₅O₇ or [NaCs(C₆H₆O₇)]_n, has also been solved and refined using laboratory powder X-ray diffraction data, and optimized using density functional techniques. The Na atom is six-coordinate, with a bond-valence sum of 1.15. The Cs atom is eight-coordinate, with a bond-valence sum of 0.97. The distorted trigonal–prismatic [NaO₆] coordination polyhedra share edges to form zigzag chains along the b-axis direction. The irregular [CsO₈] coordination polyhedra share edges with the [NaO₆] polyhedra to form layers parallel to the (101) plane, unlike the isolated chains in NaKHC₆H₅O₇ and NaRbHC₆H₅O₇. A prominent feature of the structure is the chain along [100] of very short, very strong O—H⋯O hydrogen bonds; the refined O⋯O distances are 2.398 and 2.159 Å, and the optimized distances are 2.398 and 2.347 Å. The Mulliken overlap populations in these hydrogen bonds are 0.143 and 0.133 electrons, which correspond to hydrogen-bond energies about 20.3 kcal mol⁻¹.

Chemical context  

A systematic study of the crystal structures of Group 1 (alkali metal) citrate salts has been reported in Rammohan & Kaduk (2018 ▸). The study was extended to lithium metal hydrogen citrates in Cigler & Kaduk (2018 ▸). The two title compounds (Figs. 1 ▸ and 2 ▸) are a further extension to citrates that contain more than one alkali metal cation.

Figure 1.

The asymmetric unit of NaRbHC₆H₅O₇, with the atom numbering and 50% probability spheroids.

Figure 2.

The asymmetric unit of NaCsHC₆H₅O₇, with the atom numbering and 50% probability spheroids.

Structural commentary  

Sodium rubidium hydrogen citrate is isostructural to NaKHC₆H₅O₇ (Rammohan & Kaduk, 2016 ▸). Sodium caesium hydrogen citrate has a related but different structure. The root-mean-square deviations of the non-hydrogen atoms in the refined and optimized structures are 0.116 and 0.105 Å for NaRbHC₆H₅O₇ and NaCsHC₆H₅O₇, respectively. Comparisons of the refined and optimized structures are given in Figs. 3 ▸ and 4 ▸. The excellent agreement between the structures is strong evidence that the experimental structures are correct (van de Streek & Neumann, 2014 ▸). This discussion uses the DFT-optimized structures. All of the citrate bond distances, bond angles, and torsion angles fall within the normal ranges indicated by a Mercury Mogul Geometry Check (Macrae et al., 2008 ▸). The citrate anion in both structures occurs in the trans,trans-conformation (about C2—C3 and C3—C4), which is one of the two low-energy conformations of an isolated citrate (Rammohan & Kaduk, 2018 ▸). The central carboxyl­ate group and the hy­droxy group occur in the normal planar arrangement.

Figure 3.

Comparison of the refined and optimized structures of sodium rubidium hydrogen citrate. The refined structure is in red, and the DFT-optimized structure is in blue.

Figure 4.

Comparison of the refined and optimized structures of sodium caesium hydrogen citrate. The refined structure is in red, and the DFT-optimized structure is in blue.

In the Rb compound, the citrate chelates to Na19 through the terminal carboxyl­ate oxygen O11 and the central carboxyl­ate oxygen O16. The Na⁺ cation is six-coordinate, with a bond-valence sum of 1.16. The Rb⁺ cation is eight-coordinate, with a bond-valence sum of 1.17. Both cations are thus slightly crowded.

In the Cs compound, the citrate triply chelates to Na20 through the terminal carboxyl­ate oxygen O12, the central carboxyl­ate oxygen O15, and the hydroxyl oxygen O17. The Na⁺ cation is six-coordinate, with a bond-valence sum of 1.15. The Cs⁺ cation is eight-coordinate, with a bond-valence sum of 0.97. The Rb—O and Cs—O bonds are ionic, but the Na—O bonds have slight covalent character, according to the Mulliken overlap populations.

The Bravais–Friedel–Donnay–Harker (Bravais, 1866 ▸; Friedel, 1907 ▸; Donnay & Harker, 1937 ▸) method suggests that we might expect a platy morphology for NaRbHC₆H₅O₇, with {001} as the principal faces, and an elongated morphology for NaCsHC₆H₅O₇, with {010} as the long axis. Fourth-order spherical harmonic preferred orientation models were included in the refinements; the texture indices were 1.050 and 1.011, indicating that preferred orientation was slight for the rotated flat-plate specimen of NaRbHC₆H₅O₇, but not significant in this rotated capillary specimen of NaCsHC₆H₅O₇. Examination of the products under an optical microscope indicated that the morphologies were not especially anisotropic.

Supra­molecular features  

In the crystal structure of NaRbHC₆H₅O₇ (Fig. 5 ▸), distorted [NaO₆] octa­hedra share edges to form chains along the a-axis direction. The irregular [RbO₈] coordination polyhedra share edges with the [NaO₆] octa­hedra on either side of the chain, resulting in triple chains along the a-axis direction. The most prominent feature of the structure is the chain along [111] of very short, very strong O—H⋯O hydrogen bonds (Table 1 ▸); the refined O⋯O distances are 2.180 (9) and 2.234 (20) Å, and the optimized distances are 2.426 and 2.398 Å. The Mulliken overlap populations in these hydrogen bonds are 0.140 and 0.143 electrons, which correspond to hydrogen-bond energies about 20.6 kcal mol⁻¹, according to the correlation in Rammohan & Kaduk (2018 ▸). H18 forms bifurcated hydrogen bonds: one is intra­molecular to O15, and the other is inter­molecular to O11.

Figure 5.

Crystal structure of NaRbHC₆H₅O₇, viewed down the a axis.

Table 1. Hydrogen-bond geometry for [NaRb(C₆H₆O₇)].

D—H⋯A	D—H(Å)	H⋯A(Å)	D⋯A(Å)	D—H⋯A(°)	Mulliken overlap(electrons)	H-bond energy(kcal mol−1)
O13—H22⋯O13i	1.199	1.199	2.398	180.0	0.143	20.7
O11—H21⋯O11ii	1.213	1.213	2.426	180.0	0.140	20.5
O17—H18⋯O15	0.979	1.873	2.575	126.2	0.059	13.3
O17—H18⋯O11iii	0.979	2.507	3.180	125.8	0.016	6.9
C2—H8⋯O14iv	1.094	2.478	3.541	163.7	0.018

Symmetry codes: (i) 2 − x, 2 − y, 2 − z; (ii) 1 − x, 1 − y, 1 − z; (iii) 1 + x, y, z; (iv) x − 1, y, z.

In the crystal structure of NaCsHC₆H₅O₇ (Fig. 6 ▸), distorted trigonal–prismatic [NaO₆] share edges to form zigzig chains along the b-axis direction. The irregular [CsO₈] coordination polyhedra share edges with the [NaO₆] polyhedra to form layers parallel to the (101) plane, unlike the isolated chains in NaKHC₆H₅O₇ and NaRbHC₆H₅O₇. A prominent feature of the structure is the chain along [100] of very short, and very strong O—H⋯O hydrogen bonds (Table 2 ▸); the refined O11⋯O11 and O14⋯O14 distances are 2.398 and 2.159 Å, and the optimized distances are 2.398 and 2.347 Å. The Mulliken overlap populations in these hydrogen bonds are 0.143 and 0.133 electrons, which correspond to hydrogen-bond energies about 20.3 kcal mol⁻¹. H18 forms an intra­molecular hydrogen bond to O13, one of the terminal carboxyl­ate oxygen atoms.

Figure 6.

Crystal structure of NaCsHC₆H₅O₇, viewed down the b axis.

Table 2. Hydrogen-bond geometry for [NaCs(C₆H₆O₇)].

D—H⋯A	D—H(Å)	H⋯A(Å)	D⋯A(Å)	D—H⋯A(°)	Mulliken overlap(electrons)	H-bond energy(kcal mol−1)
O14—H22⋯O14i	1.200	1.200	2.347	156.1	0.133	19.9
O11—H21⋯O11ii	1.203	1.203	2.398	170.6	0.143	20.7
O17—H18⋯O13111	0.976	1.941	2.779	142.4	0.046	11.7

Symmetry codes: (i) − − x, − + y,  − z; (ii) −x, y, −z; (iii)  + x, − − y, − + z.

Database survey  

Details of the comprehensive literature search for citrate structures are presented in Rammohan & Kaduk (2018 ▸). After manually locating the peaks in the pattern of NaRbHC₆H₅O₇, the pattern was indexed using Jade9.8 (MDI, 2017 ▸). A reduced-cell search in the Cambridge Structural Database (CSD Version 5.39, update of November 2018; Groom et al., 2016 ▸) yielded 39 hits, among which was NaKHC₆H₅O₇ (Rammohan & Kaduk, 2016 ▸).

After manually locating the peaks in the pattern of NaCsHC₆H₅O₇, the pattern was indexed on a C-centered monoclinic cell using Jade9.8 (MDI, 2017 ▸). A reduced-cell search in the CSD yielded no hits. The cell was converted to I-centered, to yield a β angle closer to 90°.

Synthesis and crystallization  

Stoichiometric qu­anti­ties of Na₂CO₃ and Rb₂CO₃ were added to a solution of 10.0 mmol citric acid monohydrate in 10 mL water. After the fizzing subsided, the clear solution was dried in an oven at 403 K to yield the white solid NaRbHC₆H₅O₇.

2.0236 g (10.0 mmol) of H₃C₆H₅O₇(H₂O) were dissolved in 10 mL of deionized water. 0.5318 g of Na₂CO₃ (1.0 mmol Na, Sigma–Aldrich) and 1.6911 g of Cs₂CO₃ (10.0 mmol of Ca, Sigma–Aldrich) were added to the citric acid solution slowly with stirring. The resulting clear colorless solution was evaporated to dryness in a 403 K oven to yield NaCsHC₆H₅O₇.

Refinement  

The initial structural model for NaRbHC₆H₅O₇ was taken from Rammohan & Kaduk (2016 ▸), replacing the K by Rb and changing the lattice parameters to the observed values. Pseudovoigt profile coefficients were as parameterized in Thompson et al. (1987 ▸) and the asymmetry correction of Finger et al. (1994 ▸) was applied as well as the microstrain broadening description by Stephens (1999 ▸). The hydrogen atoms were included in fixed positions, which were re-calculated during the course of the refinement. Crystal data, data collection and structure refinement (Fig. 7 ▸) details are summarized in Table 3 ▸. The U _iso of C2, C3, and C4 were constrained to be equal, and those of H7, H8, H9, and H10 were constrained to be 1.3 × that of these carbon atoms. The U _iso of C1, C5, C6, and the oxygen atoms were constrained to be equal, and that of H18 was constrained to be 1.3 × this value. The U _iso of H21 and H22 were fixed.

Figure 7.

Rietveld plot for NaRbHC₆H₅O₇. The red crosses represent the observed data points, and the green line is the calculated pattern. The magenta curve is the difference pattern, plotted at the same scale as the other patterns. The vertical scale has been multiplied by a factor of 10 for 2θ > 46.0°. The row of black tick marks indicates the reflection positions for this phase.

Table 3. Experimental details.

	[NaRb(C6H6O7)]	[NaCs(C6H6O7)]
Crystal data
M r	298.57	346.00
Crystal system, space group	Triclinic, P	Monoclinic, I2
Temperature (K)	300	300
a, b, c (Å)	5.9864 (2), 8.4104 (3), 10.2903 (3)	10.8913 (5), 5.5168 (2), 17.7908 (8)
α, β, γ (°)	74.798 (3), 76.756 (3), 72.878 (2)	90, 97.014 (4), 90
V (Å3)	471.28 (3)	1060.96 (6)
Z	2	4
Radiation type	Kα1, Kα2, λ = 1.540593, 1.544451 Å	Kα1, Kα2, λ = 0.709319, 0.713609 Å
μ (mm−1)	–	2.09
Specimen shape, size (mm)	Flat sheet, 24 × 24	Cylinder, 12 × 0.3
Data collection
Diffractometer	Bruker D2 Phaser	PANalytical Empyrean
Specimen mounting	Standard holder	Glass capillary
Data collection mode	Reflection	Transmission
Scan method	Step	Step
2θ values (°)	2θmin = 5.001 2θmax = 100.007 2θstep = 0.020	2θmin = 1.011 2θmax = 49.991 2θstep = 0.017
Refinement
R factors and goodness of fit	R p = 0.028, R wp = 0.038, R exp = 0.022, R(F 2) = 0.13613, χ2 = 3.028	R p = 0.045, R wp = 0.059, R exp = 0.026, R(F 2) = 0.08622, χ2 = 5.570
No. of parameters	84	80
No. of restraints	29	29
H-atom treatment	Only H-atom displacement parameters refined	Only H-atom displacement parameters refined

The same symmetry and lattice parameters were used for the DFT calculations as for each powder diffraction study. Computer programs: DIFFRAC.Measurement (Bruker, 2009 ▸), FOX (Favre-Nicolin & Černý, 2002 ▸), GSAS (Larson & Von Dreele, 2004 ▸), Mercury (Macrae et al., 2008 ▸), DIAMOND (Crystal Impact, 2015 ▸) and publCIF (Westrip, 2010 ▸).

Analysis of the systematic absences in the pattern of NaCsHC₆H₅O₇ suggested the space groups I2, Im, or I2/m. The volume of the unit cell corresponded to Z = 4. Space group I2 was selected, and confirmed by successful solution and refinement of the structure. The structure was solved with FOX (Favre-Nicolin & Černý, 2002 ▸). The maximum sin θ/λ used for structure solution was 0.55 Å, and a citrate, Cs, Na, and O (water mol­ecule) were used as fragments. The solution with the lowest cost factor has the Cs, Na, and O on top of each other, but the Cs was eight-coordinate and all six carboxyl­ate oxygen atoms were coordinated to the Cs atom. The structure was examined for voids using Materials Studio (Dassault Systemes, 2017 ▸). One void at approximately 0.375,0.600,0.379 had acceptable coordination to O atoms, and was assigned as Na20. Another void was assigned as O21, but this moved too close to the citrate anion on refinement and was discarded. Active hydrogen atoms were placed by analysis of hydrogen-bonding inter­actions. The refinement strategy (Fig. 8 ▸) was similar to that used for the Rb compound. Cs19 was refined anisotropically.

Figure 8.

Rietveld plot for NaCsHC₆H₅O₇. The red crosses represent the observed data points, and the green line is the calculated pattern. The magenta curve is the difference pattern, plotted at the same scale as the other patterns. The vertical scale has been multiplied by a factor of 10 for 2θ > 28.8°. The row of black tick marks indicates the reflection positions for this phase.

Density functional geometry optimizations (fixed experimental unit cells) were carried out using CRYSTAL14 (Dovesi et al., 2014 ▸). The basis sets for the H, C, and O atoms were those of Gatti et al. (1994 ▸), the basis sets for Na was that of Dovesi et al. (1991 ▸), and the basis sets for Rb and Cs were those of Sophia et al. (2014 ▸). The calculations were run on eight 2.1 GHz Xeon cores (each with 6 GB RAM) of a 304-core Dell Linux cluster at Illinois Institute of Technology, using 8 k-points and the B3LYP functional, and took 10.8 and 7.5 h.

Supplementary Material

CCDC references: 1890745, 1890746, 1890747, 1890748

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Poly[(µ-hydrogen citrato)rubidiumsodium] (KADU1716_publ). Crystal data

[NaRb(C6H6O7)]	V = 471.28 (3) Å3
Mr = 298.57	Z = 2
Triclinic, P1	Dx = 2.104 Mg m−3
Hall symbol: -P 1	Kα1, Kα2 radiation, λ = 1.540593, 1.544451 Å
a = 5.9864 (2) Å	T = 300 K
b = 8.4104 (3) Å	Particle morphology: powder
c = 10.2903 (3) Å	white
α = 74.798 (3)°	flat_sheet, 24 × 24 mm
β = 76.756 (3)°	Specimen preparation: Prepared at 403 K
γ = 72.878 (2)°

Poly[(µ-hydrogen citrato)rubidiumsodium] (KADU1716_publ). Data collection

Bruker D2 Phaser diffractometer	Data collection mode: reflection
Radiation source: selaed X-ray tube	Scan method: step
Specimen mounting: standard holder	2θmin = 5.001°, 2θmax = 100.007°, 2θstep = 0.020°

Poly[(µ-hydrogen citrato)rubidiumsodium] (KADU1716_publ). Refinement

Least-squares matrix: full	84 parameters
Rp = 0.028	29 restraints
Rwp = 0.038	2 constraints
Rexp = 0.022	Only H-atom displacement parameters refined
R(F2) = 0.13613	Weighting scheme based on measured s.u.'s
4701 data points	(Δ/σ)max = 0.03
Profile function: CW Profile function number 4 with 27 terms Pseudovoigt profile coefficients as parameterized in P. Thompson, D.E. Cox & J.B. Hastings (1987). J. Appl. Cryst.,20,79-83. Asymmetry correction of L.W. Finger, D.E. Cox & A. P. Jephcoat (1994). J. Appl. Cryst.,27,892-900. Microstrain broadening by P.W. Stephens, (1999). J. Appl. Cryst.,32,281-289. #1(GU) = 2.580 #2(GV) = 0.000 #3(GW) = 1.999 #4(GP) = 0.000 #5(LX) = 4.181 #6(ptec) = 1.74 #7(trns) = 4.34 #8(shft) = -2.5167 #9(sfec) = 0.00 #10(S/L) = 0.0235 #11(H/L) = 0.0200 #12(eta) = 0.0000 Peak tails are ignored where the intensity is below 0.0050 times the peak Aniso. broadening axis 0.0 0.0 1.0	Background function: GSAS Background function number 1 with 10 terms. Shifted Chebyshev function of 1st kind 1: 1751.95 2: -322.287 3: 62.9433 4: -1.65870 5: 15.3537 6: -30.8122 7: 27.0452 8: -10.7829 9: 5.15006 10: -0.147912

Poly[(µ-hydrogen citrato)rubidiumsodium] (KADU1716_publ). Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.592 (2)	0.5051 (13)	0.6742 (10)	0.021 (2)*
C2	0.556 (2)	0.5974 (17)	0.7878 (10)	0.003 (6)*
C3	0.7655 (17)	0.6762 (10)	0.7701 (7)	0.003 (6)*
C4	0.744 (2)	0.7373 (16)	0.9020 (8)	0.003 (6)*
C5	0.905 (3)	0.851 (3)	0.8880 (9)	0.021 (2)*
C6	0.7512 (17)	0.8313 (11)	0.6487 (8)	0.021 (2)*
H7	0.54367	0.50387	0.89029	0.004 (7)*
H8	0.38434	0.70246	0.78480	0.004 (7)*
H9	0.79156	0.62260	0.98785	0.004 (7)*
H10	0.55240	0.80973	0.93127	0.004 (7)*
O11	0.507 (2)	0.5851 (14)	0.5670 (8)	0.021 (2)*
O12	0.657 (3)	0.3441 (14)	0.6967 (12)	0.021 (2)*
O13	0.898 (3)	0.9131 (19)	0.9900 (15)	0.021 (2)*
O14	1.045 (2)	0.8875 (18)	0.7771 (10)	0.021 (2)*
O15	0.914 (3)	0.8275 (16)	0.5451 (11)	0.021 (2)*
O16	0.5597 (18)	0.9458 (15)	0.6434 (12)	0.021 (2)*
O17	0.983 (2)	0.5533 (13)	0.7469 (11)	0.021 (2)*
H18	1.06896	0.61913	0.65793	0.027 (3)*
Na19	0.2740 (17)	0.8715 (12)	0.5586 (9)	0.038 (5)*
Rb20	0.1828 (6)	0.2215 (5)	0.7148 (3)	0.060 (2)*
H21	0.5	0.5	0.5	0.03*
H22	1.0	1.0	1.0	0.03*

Poly[(µ-hydrogen citrato)rubidiumsodium] (KADU1716_publ). Geometric parameters (Å, º)

C1—C2	1.5091 (17)	O14—Rb20iv	3.028 (14)
C1—O11	1.261 (3)	O15—C6	1.269 (3)
C1—O12	1.267 (3)	O15—Na19ii	2.332 (16)
C2—C1	1.5091 (17)	O15—Na19v	2.504 (13)
C2—C3	1.5403 (17)	O15—Rb20i	3.013 (16)
C3—C2	1.5403 (17)	O16—C3	2.429 (6)
C3—C4	1.5392 (17)	O16—C6	1.263 (3)
C3—C6	1.5486 (17)	O16—O15	2.193 (8)
C3—O17	1.419 (3)	O16—O16v	3.04 (2)
C4—C3	1.5392 (17)	O16—Na19	2.382 (17)
C4—C5	1.5111 (17)	O16—Na19v	2.439 (13)
C5—C4	1.5111 (17)	O16—Rb20vi	2.839 (11)
C5—O13	1.275 (3)	O17—C3	1.419 (3)
C5—O14	1.274 (3)	O17—Rb20ii	2.769 (10)
C6—C3	1.5486 (17)	Na19—O11	2.393 (16)
C6—O15	1.269 (3)	Na19—O12i	3.453 (14)
C6—O16	1.263 (3)	Na19—O14vii	2.366 (13)
O11—C1	1.261 (3)	Na19—O15vii	2.332 (16)
O11—Na19	2.393 (16)	Na19—O15v	2.504 (13)
O11—Rb20i	3.366 (12)	Na19—O16	2.382 (17)
O12—C1	1.267 (3)	Na19—O16v	2.439 (13)
O12—C2	2.411 (8)	Rb20—O11i	3.366 (12)
O12—Rb20	3.246 (14)	Rb20—O12vii	3.044 (13)
O12—Rb20ii	3.044 (13)	Rb20—O12	3.246 (14)
O13—C5	1.275 (3)	Rb20—O13iii	2.931 (16)
O13—Rb20iii	2.931 (16)	Rb20—O14viii	3.028 (14)
O13—H22	1.117 (10)	Rb20—O15i	3.013 (16)
O14—C4	2.433 (14)	Rb20—O16ix	2.839 (11)
O14—C5	1.274 (3)	Rb20—O17vii	2.769 (10)
O14—Na19ii	2.366 (13)
C2—C1—O11	118.7 (8)	O11—Na19—O15v	158.0 (5)
C2—C1—O12	120.3 (6)	O11—Na19—O16	92.2 (5)
O11—C1—O12	119.1 (7)	O11—Na19—O16v	108.6 (6)
C1—C2—C3	109.8 (5)	O14vii—Na19—O15vii	75.6 (5)
C2—C3—C4	107.2 (4)	O14vii—Na19—O15v	93.6 (5)
C2—C3—C6	110.0 (4)	O14vii—Na19—O16	84.7 (5)
C2—C3—O17	110.1 (5)	O14vii—Na19—O16v	140.0 (6)
C4—C3—C6	108.9 (5)	O15vii—Na19—O15v	82.9 (6)
C4—C3—O17	110.8 (5)	O15vii—Na19—O16	159.9 (7)
C6—C3—O17	109.9 (4)	O15vii—Na19—O16v	114.6 (6)
C3—C4—C5	113.0 (7)	O15v—Na19—O16	94.3 (7)
C4—C5—O13	118.6 (6)	O15v—Na19—O16v	52.7 (2)
C4—C5—O14	121.5 (11)	O16—Na19—O16v	78.1 (5)
O13—C5—O14	119.9 (8)	O11i—Rb20—O12vii	109.5 (3)
C3—C6—O15	119.6 (5)	O11i—Rb20—O12	53.0 (3)
C3—C6—O16	119.2 (5)	O11i—Rb20—O13iii	151.0 (3)
O15—C6—O16	120.1 (6)	O11i—Rb20—O14viii	130.8 (3)
C1—O11—Na19	118.5 (9)	O11i—Rb20—O15i	67.2 (3)
C1—O11—Rb20i	123.9 (10)	O11i—Rb20—O16ix	77.9 (3)
Na19—O11—Rb20i	81.1 (4)	O11i—Rb20—O17vii	82.2 (3)
C1—O12—Rb20	105.2 (8)	O12vii—Rb20—O12	144.3 (4)
C1—O12—Rb20ii	110.5 (10)	O12vii—Rb20—O13iii	93.8 (4)
Rb20—O12—Rb20ii	144.3 (4)	O12vii—Rb20—O14viii	78.6 (3)
C5—O13—Rb20iii	132.3 (10)	O12vii—Rb20—O15i	68.6 (3)
C5—O14—Na19ii	160.1 (13)	O12vii—Rb20—O16ix	135.6 (4)
C5—O14—Rb20iv	118.0 (12)	O12vii—Rb20—O17vii	66.2 (4)
Na19ii—O14—Rb20iv	81.6 (5)	O12—Rb20—O13iii	98.0 (3)
C6—O15—Na19ii	118.8 (12)	O12—Rb20—O14viii	137.1 (3)
C6—O15—Na19v	90.6 (6)	O12—Rb20—O15i	117.4 (3)
C6—O15—Rb20i	119.3 (11)	O12—Rb20—O16ix	76.0 (3)
Na19ii—O15—Na19v	97.1 (6)	O12—Rb20—O17vii	79.7 (3)
Na19ii—O15—Rb20i	121.9 (4)	O13iii—Rb20—O14viii	69.3 (3)
Na19v—O15—Rb20i	79.8 (4)	O13iii—Rb20—O15i	140.0 (3)
C6—O16—Na19	112.9 (12)	O13iii—Rb20—O16ix	97.6 (4)
C6—O16—Na19v	93.8 (6)	O13iii—Rb20—O17vii	92.2 (4)
C6—O16—Rb20vi	158.9 (12)	O14viii—Rb20—O15i	72.0 (3)
Na19—O16—Na19v	101.9 (5)	O14viii—Rb20—O16ix	66.0 (4)
Na19—O16—Rb20vi	85.5 (4)	O14viii—Rb20—O17vii	139.1 (4)
Na19v—O16—Rb20vi	92.3 (4)	O15i—Rb20—O16ix	75.4 (4)
O11—Na19—O14vii	107.9 (5)	O15i—Rb20—O17vii	110.9 (4)
O11—Na19—O15vii	97.9 (6)	O16ix—Rb20—O17vii	154.8 (3)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x+1, y, z; (iii) −x+1, −y+1, −z+2; (iv) x+1, y+1, z; (v) −x+1, −y+2, −z+1; (vi) x, y+1, z; (vii) x−1, y, z; (viii) x−1, y−1, z; (ix) x, y−1, z.

(kadu1716_DFT). Crystal data

C6H6NaO7Rb	α = 74.7995°
Mr = 298.57	β = 76.7573°
Triclinic, P1	γ = 72.8749°
a = 5.9859 Å	V = 471.23 Å3
b = 8.4102 Å	Z = 2
c = 10.2904 Å

(kadu1716_DFT). Data collection

h = →	l = →
k = →

(kadu1716_DFT). Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.58312	0.48855	0.68564	0.01800*
C2	0.57651	0.57925	0.79638	0.00600*
C3	0.76841	0.67872	0.76846	0.00600*
C4	0.73694	0.75315	0.89436	0.00600*
C5	0.90081	0.86416	0.88638	0.01800*
C6	0.74570	0.82427	0.63974	0.01800*
H7	0.60167	0.48235	0.88975	0.00700*
H8	0.40172	0.66683	0.81269	0.00700*
H9	0.76305	0.64923	0.98397	0.00700*
H10	0.55518	0.83019	0.91496	0.00700*
O11	0.50420	0.58854	0.57498	0.01800*
O12	0.65090	0.33239	0.70086	0.01800*
O13	0.87388	0.91272	0.99960	0.01800*
O14	1.04257	0.90330	0.78197	0.01800*
O15	0.91969	0.81409	0.54210	0.01800*
O16	0.56046	0.94323	0.63928	0.01800*
O17	0.99694	0.56509	0.74766	0.01800*
H18	1.06896	0.61913	0.65793	0.02340*
Na19	0.25929	0.87959	0.56024	0.02900*
Rb20	0.19358	0.22247	0.71319	0.05030*
H21	0.50000	0.50000	0.50000	0.03000*
H22	1.00000	1.00000	1.00000	0.03000*

(kadu1716_DFT). Bond lengths (Å)

C1—C2	1.516	C4—H10	1.095
C1—O11	1.318	C5—O13	1.294
C1—O12	1.233	C5—O14	1.243
C2—C3	1.546	C6—O15	1.271
C2—H7	1.092	C6—O16	1.256
C2—H8	1.094	O11—H21	1.213
C3—C4	1.533	O13—H22	1.199
C3—C6	1.551	O17—H18	0.979
C3—O17	1.426	H21—O11i	1.213
C4—C5	1.517	H22—O13ii	1.199
C4—H9	1.096

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+2, −y+2, −z+2.

(kadu1716_DFT). Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O13—H22···O13	1.199	1.199	2.398	180.0
O11—H21···O11	1.213	1.213	2.426	180.0
O17—H18···O15	0.979	1.873	2.575	126.2
O17—H18···O11	0.979	2.507	3.180	125.8
C2—H8···O14	1.094	2.478	3.541	163.7

Poly[(µ-hydrogen citrato)caesiumsodium] (ACIG017_publ). Crystal data

[CsNa(C6H6O7)]	Z = 4
Mr = 346.00	Dx = 2.166 Mg m−3
Monoclinic, I2	Kα1, Kα2 radiation, λ = 0.709319, 0.713609 Å
Hall symbol: I 2y	µ = 2.09 mm−1
a = 10.8913 (5) Å	T = 300 K
b = 5.5168 (2) Å	Particle morphology: powder
c = 17.7908 (8) Å	white
β = 97.014 (4)°	cylinder, 12 × 0.3 mm
V = 1060.96 (6) Å3	Specimen preparation: Prepared at 403 K

Poly[(µ-hydrogen citrato)caesiumsodium] (ACIG017_publ). Data collection

PANalytical Empyrean diffractometer	Data collection mode: transmission
Radiation source: sealed X-ray tube	Scan method: step
Specimen mounting: glass capillary	2θmin = 1.011°, 2θmax = 49.991°, 2θstep = 0.017°

Poly[(µ-hydrogen citrato)caesiumsodium] (ACIG017_publ). Refinement

Least-squares matrix: full	80 parameters
Rp = 0.045	29 restraints
Rwp = 0.059	2 constraints
Rexp = 0.026	Only H-atom displacement parameters refined
R(F2) = 0.08622	Weighting scheme based on measured s.u.'s
2932 data points	(Δ/σ)max = 0.06
Profile function: CW Profile function number 4 with 21 terms Pseudovoigt profile coefficients as parameterized in P. Thompson, D.E. Cox & J.B. Hastings (1987). J. Appl. Cryst.,20,79-83. Asymmetry correction of L.W. Finger, D.E. Cox & A. P. Jephcoat (1994). J. Appl. Cryst.,27,892-900. Microstrain broadening by P.W. Stephens, (1999). J. Appl. Cryst.,32,281-289. #1(GU) = 53.860 #2(GV) = 0.000 #3(GW) = 0.786 #4(GP) = 0.000 #5(LX) = 1.886 #6(ptec) = 0.00 #7(trns) = 0.00 #8(shft) = 0.0000 #9(sfec) = 0.00 #10(S/L) = 0.0151 #11(H/L) = 0.0173 #12(eta) = 0.5113 #13(S400 ) = 1.1E-01 #14(S040 ) = 4.6E-01 #15(S004 ) = 6.1E-03 #16(S220 ) = 2.3E-01 #17(S202 ) = 3.5E-02 #18(S022 ) = 7.8E-02 #19(S301 ) = 8.2E-02 #20(S103 ) = -1.3E-02 #21(S121 ) = 7.3E-02 Peak tails are ignored where the intensity is below 0.0050 times the peak Aniso. broadening axis 0.0 0.0 1.0	Background function: GSAS Background function number 1 with 3 terms. Shifted Chebyshev function of 1st kind 1: 711.736 2: 51.3623 3: -153.142

Poly[(µ-hydrogen citrato)caesiumsodium] (ACIG017_publ). Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.5180 (19)	0.183 (7)	0.3879 (6)	0.027 (3)*
C2	0.5919 (14)	0.118 (3)	0.3242 (6)	0.002 (7)*
C3	0.5465 (10)	0.234 (2)	0.2470 (5)	0.002 (7)*
C4	0.6279 (14)	0.138 (3)	0.1886 (6)	0.002 (7)*
C5	0.588 (2)	0.249 (3)	0.1120 (6)	0.027 (3)*
C6	0.4103 (11)	0.162 (3)	0.2216 (9)	0.027 (3)*
H7	0.58724	−0.0875	0.31719	0.003 (9)*
H8	0.69162	0.17452	0.33886	0.003 (9)*
H9	0.61841	−0.06615	0.18447	0.003 (9)*
H10	0.72772	0.19018	0.20703	0.003 (9)*
O11	0.5625 (17)	0.129 (4)	0.4554 (6)	0.027 (3)*
O12	0.4121 (17)	0.285 (4)	0.3756 (9)	0.027 (3)*
O13	0.601 (3)	0.476 (3)	0.1023 (8)	0.027 (3)*
O14	0.5515 (19)	0.112 (3)	0.0558 (7)	0.027 (3)*
O15	0.3392 (15)	0.319 (3)	0.1871 (10)	0.027 (3)*
O16	0.3821 (15)	−0.062 (3)	0.2172 (12)	0.027 (3)*
O17	0.5558 (14)	0.490 (2)	0.2509 (8)	0.027 (3)*
H18	0.54799	0.56496	0.20157	0.036 (4)*
Cs19	0.3269 (3)	0.70766	0.05362 (15)	0.04276
Na20	0.3483 (18)	0.742 (6)	0.2891 (9)	0.124 (8)*
H21	0.5	0.102	0.5	0.05*
H22	0.5	0.124	0.0	0.05*

Poly[(µ-hydrogen citrato)caesiumsodium] (ACIG017_publ). Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Cs19	0.039 (3)	0.038 (3)	0.051 (3)	0.006 (5)	0.006 (2)	−0.007 (5)

Poly[(µ-hydrogen citrato)caesiumsodium] (ACIG017_publ). Geometric parameters (Å, º)

C1—C2	1.512 (2)	O14—Cs19iv	3.341 (19)
C1—O11	1.274 (7)	O15—C6	1.272 (7)
C1—O12	1.278 (7)	O15—Cs19	3.189 (17)
C2—C1	1.512 (2)	O15—Na20	2.95 (3)
C2—C3	1.540 (2)	O15—Na20i	2.18 (2)
C3—C2	1.540 (2)	O16—C6	1.272 (7)
C3—C4	1.540 (2)	O16—Cs19iii	3.17 (2)
C3—C6	1.548 (2)	O16—Na20iii	1.75 (3)
C3—O17	1.419 (7)	O16—Na20i	3.01 (3)
C4—C3	1.540 (2)	O17—C3	1.419 (7)
C4—C5	1.509 (2)	O17—Na20	2.81 (3)
C5—C4	1.509 (2)	Cs19—O11v	3.211 (17)
C5—O13	1.272 (7)	Cs19—O12vi	3.057 (15)
C5—O14	1.275 (7)	Cs19—O13	3.27 (3)
C6—C3	1.548 (2)	Cs19—O13ii	3.236 (17)
C6—O15	1.272 (7)	Cs19—O14vii	3.309 (17)
C6—O16	1.272 (7)	Cs19—O14viii	3.341 (19)
O11—C1	1.274 (7)	Cs19—O15	3.189 (17)
O12—C1	1.278 (7)	Cs19—O16vii	3.17 (2)
O12—Cs19i	3.057 (15)	Cs19—H18	3.435 (3)
O12—Na20	2.99 (4)	Na20—O12	2.99 (4)
O13—C5	1.272 (7)	Na20—O15	2.95 (3)
O13—Cs19	3.27 (3)	Na20—O15vi	2.18 (2)
O13—Cs19ii	3.236 (17)	Na20—O16vii	1.75 (3)
O14—C5	1.275 (7)	Na20—O16vi	3.01 (3)
O14—O14ii	2.16 (3)	Na20—O17	2.81 (3)
O14—Cs19iii	3.309 (17)
C2—C1—O11	118.3 (5)	C3—O17—H18	112.6 (12)
C2—C1—O12	121.9 (7)	O11v—Cs19—O12vi	59.4 (3)
O11—C1—O12	119.8 (6)	O11v—Cs19—O13	145.2 (5)
C1—C2—C3	115.3 (5)	O11v—Cs19—O13ii	76.9 (5)
C2—C3—C4	108.1 (6)	O11v—Cs19—O14vii	135.3 (5)
C2—C3—C6	110.2 (6)	O11v—Cs19—O14viii	99.6 (4)
C2—C3—O17	110.9 (6)	O11v—Cs19—O15	105.5 (4)
C4—C3—C6	108.9 (6)	O11v—Cs19—O16vii	127.7 (5)
C4—C3—O17	109.3 (6)	O12vi—Cs19—O13	137.9 (6)
C6—C3—O17	109.4 (6)	O12vi—Cs19—O13ii	135.7 (6)
C3—C4—C5	110.0 (6)	O12vi—Cs19—O14vii	124.5 (5)
C4—C5—O13	119.6 (8)	O12vi—Cs19—O14viii	124.4 (5)
C4—C5—O14	119.7 (6)	O12vi—Cs19—O15	75.3 (5)
O13—C5—O14	120.4 (7)	O12vi—Cs19—O16vii	68.9 (5)
C3—C6—O15	118.0 (6)	O13—Cs19—O13ii	76.3 (5)
C3—C6—O16	118.9 (7)	O13—Cs19—O14vii	67.1 (4)
O15—C6—O16	120.4 (6)	O13—Cs19—O14viii	90.1 (5)
C1—O11—Cs19ix	134 (2)	O13—Cs19—O15	65.5 (4)
C1—O12—Cs19i	131.6 (15)	O13—Cs19—O16vii	81.3 (4)
C5—O13—Cs19	107.5 (19)	O13ii—Cs19—O14vii	91.2 (5)
C5—O13—Cs19ii	123.3 (10)	O13ii—Cs19—O14viii	67.1 (3)
Cs19—O13—Cs19ii	85.8 (4)	O13ii—Cs19—O15	112.4 (5)
C5—O14—Cs19iii	124.4 (14)	O13ii—Cs19—O16vii	155.3 (6)
C5—O14—Cs19iv	138.3 (18)	O14vii—Cs19—O14viii	37.9 (4)
Cs19iii—O14—Cs19iv	83.5 (4)	O14vii—Cs19—O15	118.7 (4)
C6—O15—Cs19	141.8 (14)	O14vii—Cs19—O16vii	70.2 (4)
C6—O15—Na20i	107.7 (14)	O14viii—Cs19—O15	154.1 (4)
Cs19—O15—Na20i	108.7 (8)	O14viii—Cs19—O16vii	102.9 (4)
C6—O16—Cs19iii	117.6 (13)	O15—Cs19—O16vii	66.3 (3)
C6—O16—Na20iii	129 (2)	O15vi—Na20—O16vii	107.9 (15)
Cs19iii—O16—Na20iii	113.1 (11)

Symmetry codes: (i) −x+1/2, y−1/2, −z+1/2; (ii) −x+1, y, −z; (iii) x, y−1, z; (iv) −x+1, y−1, −z; (v) x−1/2, y+1/2, z−1/2; (vi) −x+1/2, y+1/2, −z+1/2; (vii) x, y+1, z; (viii) −x+1, y+1, −z; (ix) x+1/2, y−1/2, z+1/2.

(acig017_DFT). Crystal data

C6H6CsNaO7	c = 17.7909 Å
Mr = 346.0	β = 97.0160°
Monoclinic, I2	V = 1060.98 Å3
a = 10.8918 Å	Z = 4
b = 5.5166 Å

(acig017_DFT). Data collection

DFT calculation	k = →
h = →	l = →

(acig017_DFT). Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.01539	−0.29133	−0.11491	0.02190*
C2	0.08720	−0.37073	−0.17866	0.00770*
C3	0.04485	−0.25744	−0.25560	0.00770*
C4	−0.36770	0.15585	0.18731	0.00770*
C5	−0.40727	0.26100	0.10948	0.02190*
C6	−0.09031	−0.33701	−0.28568	0.02190*
H7	0.07745	0.43212	−0.18341	0.01000*
H8	0.18550	−0.33438	−0.16183	0.01000*
H9	−0.36925	−0.04136	0.18368	0.01000*
H10	−0.27329	0.21290	0.20759	0.01000*
O11	0.06648	−0.36068	−0.04898	0.02190*
O12	−0.08435	−0.17967	−0.12642	0.02190*
O13	−0.41832	0.48425	0.09987	0.02190*
O14	−0.43234	0.10103	0.05664	0.02190*
O15	0.33500	0.32450	0.18636	0.02190*
O16	0.38339	−0.05889	0.21767	0.02190*
O17	0.05257	−0.00031	−0.24718	0.02190*
H18	0.04799	0.06496	−0.29843	0.02800*
Cs19	0.31925	−0.29064	0.05016	0.04080*
Na20	−0.15569	0.10811	−0.21537	0.10800*
H21	0.00000	−0.34288	0.00000	0.05000*
H22	0.00000	−0.35387	0.50000	0.05000*

(acig017_DFT). Bond lengths (Å)

C1—C2	1.519	O15—Na20xii	2.339
C1—O11	1.293	O16—C6xii	1.260
C1—O12	1.244	O16—Cs19	3.240
C2—C3	1.524	O16—Na20xiii	2.258
C2—H7i	1.095	O16—Na20vii	2.641
C2—H8	1.095	O17—H18	0.976
C3—C4ii	1.551	O17—Na20	2.477
C3—C6	1.566	Cs19—Cs19vi	5.517
C3—O17	1.428	Cs19—Cs19i	5.517
C4—C3iii	1.551	Cs19—O15i	3.210
C4—C5	1.515	Cs19—O12vii	3.100
C4—H9	1.090	Cs19—O13xiv	3.143
C4—H10	1.094	Cs19—O14xv	3.453
C5—O13	1.247	Cs19—O14vii	3.220
C5—O14	1.294	Cs19—O13xvi	3.246
C6—O15iv	1.267	Cs19—Cs19xvii	4.517
C6—O16iv	1.260	Cs19—Na20xiii	4.184
C6—Na20v	2.785	Cs19—Na20vii	4.234
H7—C2vi	1.095	Na20—O15vii	2.398
O11—Cs19	3.107	Na20—C6xviii	2.785
O11—H21	1.203	Na20—Na20xviii	3.568
O12—Cs19vii	3.100	Na20—Na20v	3.568
O12—Na20	2.308	Na20—O16xi	2.258
O13—Cs19viii	3.143	Na20—O15iv	2.339
O13—Cs19ix	3.246	Na20—O16vii	2.641
O14—Cs19x	3.453	Na20—Cs19xi	4.184
O14—Cs19vii	3.220	Na20—Cs19vii	4.234
O14—H22xi	1.200	H21—O11vii	1.203
O15—C6xii	1.267	H22—O14xix	1.200
O15—Cs19vi	3.210	H22—O14xiii	1.200
O15—Na20vii	2.398

Symmetry codes: (i) x, y−1, z; (ii) x+1/2, y−1/2, z−1/2; (iii) x−1/2, y+1/2, z+1/2; (iv) x−1/2, y−1/2, z−1/2; (v) −x−1/2, y−1/2, −z−1/2; (vi) x, y+1, z; (vii) −x, y, −z; (viii) x−1, y+1, z; (ix) −x, y+1, −z; (x) x−1, y, z; (xi) x−1/2, y+1/2, z−1/2; (xii) x+1/2, y+1/2, z+1/2; (xiii) x+1/2, y−1/2, z+1/2; (xiv) x+1, y−1, z; (xv) x+1, y, z; (xvi) −x, y−1, −z; (xvii) −x+1, y, −z; (xviii) −x−1/2, y+1/2, −z−1/2; (xix) −x−1/2, y−1/2, −z+1/2.

(acig017_DFT). Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O14—H22···O14	1.200	1.200	2.347	156.1
O11—H21···O11	1.203	1.203	2.398	170.6
O17—H18···O13	0.976	1.941	2.779	142.4