Redetermination of poly[μ-chlorido-hepta­chlorido-μ3-l-proline-μ2-l-proline-tetra­mercury(II)]

D Kalaiselvi; R Mohan Kumar; R Jayavel

doi:10.1107/S160053680802196X

. 2008 Jul 19;64(Pt 8):m1048–m1049. doi: 10.1107/S160053680802196X

Redetermination of poly[μ-chlorido-heptachlorido-μ₃-l-proline-μ₂-l-proline-tetramercury(II)]

D Kalaiselvi ^a, R Mohan Kumar ^b, R Jayavel ^a,^*

PMCID: PMC2961966 PMID: 21203036

Abstract

The asymmetric unit of the title compound, [Hg₄Cl₈(C₅H₉NO₂)₂]_n, consists of four HgCl₂ units and two L-proline ligands in the zwitterionic form. In each HgCl₂ unit, the Hg^II ion is strongly bonded to two Cl atoms, and the Hg^II ions in two of the HgCl₂ units are chelated by O atoms of two l-proline ligands, with one strong and one weak Hg—O bond. In the crystal structure, HgCl₂ and L-proline units are linked to form an extended chain along the a axis. The chain structure is further stabilized by N—H⋯Cl hydrogen bonds, and the chains are arranged in layers parallel to the ab plane. The structure of the title compound was originally determined by Ehsan, Malik & Haider [(1996). J. Banglad. Acad. Sci. 20, 175] but no three-dimensional coordinates are available.

Related literature

For related literature, see: Janczak & Luger (1997 ▶); Jiang & Fang (1999 ▶); Kurtz & Perry (1968 ▶); Long (1995 ▶); McL Mathieson & Welsh (1952 ▶); Nockemann & Meyer (2002 ▶); Padmanabhan et al. (1995 ▶); Pandiarajan et al. (2002a ▶,b ▶); Schaffers & Keszler (1993 ▶); Subha Nandhini et al. (2001 ▶); Tedmann et al. (2004 ▶); Yukawa et al. (1982 ▶, 1983 ▶, 1985 ▶); Ehsan et al. (1996 ▶).

Experimental

Crystal data

[Hg₄Cl₈(C₅H₉NO₂)₂]
M _r = 1316.23
Triclinic,
a = 7.2742 (4) Å
b = 9.4472 (5) Å
c = 10.4767 (6) Å
α = 108.621 (3)°
β = 107.260 (2)°
γ = 97.353 (2)°
V = 631.51 (6) Å³
Z = 1
Mo Kα radiation
μ = 25.10 mm⁻¹
T = 293 (2) K
0.20 × 0.10 × 0.10 mm

Data collection

Bruker Kappa APEXII area-detector diffractometer
Absorption correction: multi-scan (Blessing, 1995 ▶) T _min = 0.082, T _max = 0.188 (expected range = 0.035–0.081)
10896 measured reflections
3956 independent reflections
3773 reflections with I > 2σ(I)
R _int = 0.044

Refinement

R[F ² > 2σ(F ²)] = 0.037
wR(F ²) = 0.111
S = 1.03
3956 reflections
255 parameters
21 restraints
H-atom parameters constrained
Δρ_max = 1.75 e Å⁻³
Δρ_min = −2.51 e Å⁻³
Absolute structure: Flack (1983 ▶), 1736 Friedel pairs
Flack parameter: 0.057 (16)

Data collection: APEX2 (Bruker, 2004 ▶); cell refinement: APEX2; data reduction: SAINT (Bruker, 2004 ▶); program(s) used to solve structure: SIR92 (Altomare et al., 1993 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2003 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053680802196X/lh2640sup1.cif

e-64-m1048-sup1.cif^{(22.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S160053680802196X/lh2640Isup2.hkl

e-64-m1048-Isup2.hkl^{(193.9KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

O4—Hg4	2.888 (10)
O4—Hg3	2.828 (11)
O2—Hg2	2.869 (13)
O1—Hg1	2.564 (11)
O1—Hg2	2.566 (12)
O3—Hg3	2.486 (13)
O3—Hg2	2.634 (12)
Cl1—Hg1	2.326 (6)
Cl2—Hg1	2.276 (6)
Cl3—Hg2	2.323 (6)
Cl4—Hg2	2.337 (6)
Cl5—Hg3	2.316 (6)
Cl6—Hg3	2.304 (6)
Cl7—Hg4	2.300 (6)
Cl8—Hg4	2.255 (7)
Hg1—Cl3ⁱ	3.009 (6)

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Symmetry code: (i) Inline graphic .

Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯Cl7ⁱ	0.90	2.63	3.282 (14)	130
N1—H1B⋯Cl6ⁱ	0.90	2.40	3.290 (16)	167
N2—H2A⋯Cl4ⁱⁱ	0.90	2.40	3.267 (15)	163
N2—H2B⋯Cl5ⁱⁱ	0.90	2.60	3.234 (15)	128

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

The authors thank Dr K. Chinnakali, Department of Physics, Anna University, Chennai, for useful discussions and suggestions.

supplementary crystallographic information

Comment

During the last few years, organic non-linear optical (NLO) crystals have attracted much interest due to their superior properties over inorganic NLO materials, such as higher susceptibility, faster response and the capability of designing components on the molecular level. However, unlike inorganic NLO crystals, they have not come into wide use, owing to drawbacks such as the difficulty of growing large size perfect single crystals and poor physicochemical stability. Under these circumstances, crystals of metal-organic materials with NLO effects have been developed which are expected not only to retain high NLO effects, but also to minimize some of the shortcomings of pure organic crystals; in other words, they have the advantages of both organic and inorganic crystals in terms of their physicochemical properties. This approach has resulted in their practical use in frequency-doubling of laser radiation (Long, 1995; Jiang & Fang, 1999). The crystal structure of L-proline monohydrate (Janczak & Luger, 1997), DL-proline monohydrate (Padmanabhan et al., 1995), L-prolinium tartrate (Subha Nandhini et al.,2001), bis (L-proline) hydrogen (1+) perchlorate (Pandiarajan et al.,2002a), bis (L-proline) hydrogen nitrate (Pandiarajan et al., 2002b), L-alanine cadmium chloride (Schaffers & Keszler, 1993), dichloro(4-hydroxy-L-proline)cadmium(II) (Yukawa et al., 1982), dichloro(L-proline)cadmium(II) hydrate (Yukawa et al., 1983), dichlorobis(L-proline)Zinc(II) (Yukawa et al., 1985) and bis-DL-prolinatocopper(II)dihydrate (McL Mathieson & Welsh, 1952) have been reported. The present study reports the crystal structure of the title salt, a complex of L-proline with mercury chloride. The second harmonic generation (SHG) effect of the crystals was measured by the powder SHG technique (Kurtz & Perry, 1968) and was found to be 2.5 times that of potassium dihydrogen phosphate crystals.

The asymmetric unit consists of four HgCl₂ units and two L-proline zwitterions (Fig.1). In each HgCl₂ units the metal atom is strongly bonded to two Cl atoms, with Hg—Cl distances in the range 2.255 (7) Å–2.337 (6) Å. These distances are comparable with those observed for ammonium mercury (II) dichloride nitrate (Nockemann & Meyer, 2002) and (2,2-bipyridine N,N'-dioxide-k₂O,O')dichloro-mercury(II) (Tedmann et al., 2004). Metal atoms in two HgCl₂ units (Hg2 and Hg3) are also chelated by carboxylate O atoms of two L-proline ligands, with one strong and one weak Hg—O bonds [Hg2—O1 2.566 (12) Å, Hg2—O2 2.869 (13) Å, Hg3—O3 2.486 (13) Å and Hg3—O4 2.828 (13) Å]. These distances are comparable with those observed for ammonium mercury (II) dichloride nitrate (Nockemann & Meyer, 2002). The two HgCl₂L units (L is L-proline) are linked via Hg2—O3 bond [Hg2—O3 2.634 (12) Å]. Of the remaining two HgCl₂units, one unit (Hg1) is bonded to atom O1 of the adjacent L-proline ligand and atom Cl3 in the adjacent unit cell [Hg1···O1 2.564 (11) Å and Hg1—Cl3(1 + x,y,z) 3.009 (7) Å], and the other unit is weakly bonded with atom O4 [Hg4—O4 2.888 (12) Å]. The geometry around metal atoms Hg1, Hg2 and Hg3 is nearly linear as a result of constraints imposed by chelation [Cl2—Hg1—Cl1 168.25 (18)°, Cl3—Hg2—Cl4 166.19 (18)° and Cl6—Hg3—Cl5 163.51 (18)°] whereas that around atom Hg4 is linear [Cl8—Hg4—Cl7 178.5 (3)°].

In the crystal structure, the HgCl₂ and L-proline units are linked to form an extended chain along the a axis (Fig.2). The chain structure is further strengthened by N—H···Cl hydrogen bonds (Table 2). The polymeric chains are arranged into layers parallel to the ab plane (Fig.3). The structure of the title compound was originally determined by Ehsan et al. (1996) but no three-dimensional coordinates are available.

Experimental

The title compound was crystallized at room temperature by slow evaporation of an aqueous solution of L-proline and mercury(II) chloride in a stoichimetric ratio of 1:2.