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C24H40B2O36Zn, monoclinic, P121/c1 (no. 14), a = 10.8691(2) Å, b = 9.6525(2) Å, c = 17.9549(3) Å, * = 103.587(1)°, V = 1831.0 Å, Z = 2, Rgt(F) = 0.029, wRref(F ) = 0.088, T = 173 K. Source of material The title compound was prepared by the reaction of boric and citric acids with zinc carbonate at molar ratio 1 : 2 : 0.5 as described previously [1]. The crystals suitable for X-ray analysis were obtained by slowly evaporation of the reaction solution in repeated syntheses. Colourless single crystals of the title complex appeared in one months. The crystals were filtered off and dried in air. Discussion The crystal structure of the title compound is composed of a complex cation [Zn(H2O)6], two bis(citrato)borat anions [(C6H6O7)2B] and two crystallization water molecules. Zn(II) lies on an inversion centre and is coordinated by six water molecules which forms a slightly distorted octahedral complex cation, Zn(II) is not coordinated by oxygen atoms of the complex anion. In complex cation the average bond length of Zn—O is 2.099 Å (bond lengths in the range of 2.086(1) 2.110(1) Å). The univalent spiran-type bis(citrato)borate anion [(C6H6O7)2B] is formed by bidentate coordination of the boron atom to two citric acid molecules and has a pseudo C2 symmetry. The difference between the two connected functional groups is responsible for the nonequivalence of the B—O bonds and the distortion of the BO4 tetrahedron. The bonds B—O(carb., hydr.) (with average length 1.497 ± 0.016 Å) are longer than the B—O(hydr.) bonds (with average length 1.458 ± 0.005 Å). Conformation of four terminal carboxyl groups in the complex anion is different: three carboxyl groups adopt a sin-periplanar conformation, carboxyl group H9–O9–C5–O10 reveals anti-periplanar conformation. The B atom is common for the two five-membered heterocycles. The carbonyl oxygen atoms O5 and O6 are coplanar (0.007(1) Å and 0.002(1) Å ) with the C3–O1–B–O2–C6 and C9–O3–B–O4–C12 planes of the ring. The two boron chelate rings are planar (with accurracy of 0.053(2) Å and 0.0023(2) Å, respectively), the dihedral angle between them being 88.65(4)°. The basic element of the crystal structure occurs to be linear centrosymmetrical macrocomplexes formed by the hexaaquazinc(II) cation, two univalent spiran-type complex anions and two coordination water molecules. The 12 hydrogen bonds and electrostatic interaction between the cation and anions lead to the moieties into macrocomplex structure. Other three independent hydrogen bonds interlink the macrocomplexes to a stable three-dimensional structure. Z. Kristallogr. NCS 224 (2009) 627-628 / DOI 10.1524/ncrs.2009.0276 627 © by Oldenbourg Wissenschaftsverlag, München Crystal: colorless prism, size 0.11 × 0.24 × 0.36 mm Wavelength: Mo K+ radiation (0.71073 Å) .: 8.02 cm−1 Diffractometer, scan mode: Bruker-Nonius Kappa CCD, #/% 2,max: 55° N(hkl)measured, N(hkl)unique: 6897, 4185 Criterion for Iobs, N(hkl)gt: Iobs > 2 )(Iobs), 3683 N(param)refined: 366 Programs: SHELXS-97 [2], SHELXL-97 [3], ORTEP-III [4] Table 1. Data collection and handling. H(11) 4e 0.329(3) 0.469(3) 0.003(2) 0.063(9) H(9) 4e 1.034(3) −0.109(3) 0.096(2) 0.053(8) H(13) 4e 0.812(3) 0.154(3) 0.418(2) 0.054(8) H(7) 4e 1.126(3) 0.631(3) 0.270(2) 0.051(8) H(10A) 4e 0.569(2) 0.191(2) 0.273(1) 0.023(5) H(10B) 4e 0.553(2) 0.335(3) 0.313(1) 0.041(6) H(4A) 4e 1.098(2) 0.150(2) 0.094(1) 0.027(5) H(4B) 4e 1.065(2) 0.105(2) 0.172(1) 0.035(6) H(8A) 4e 0.418(2) 0.418(2) 0.197(1) 0.023(5) H(8B) 4e 0.434(2) 0.279(3) 0.155(1) 0.030(6) H(2A) 4e 1.162(2) 0.328(2) 0.206(1) 0.029(5) H(2B) 4e 1.146(2) 0.390(2) 0.122(1) 0.026(5) H(2WA) 4e 0.652(3) −0.064(3) 0.126(1) 0.042(7) H(2WB) 4e 0.630(2) 0.071(3) 0.136(1) 0.036(6) H(3WA) 4e 0.284(3) 0.046(3) 0.014(2) 0.055(8) H(3WB) 4e 0.329(4) 0.183(5) 0.011(2) 0.08(1) H(1WA) 4e 0.547(2) 0.269(3) −0.035(1) 0.032(6) H(1WB) 4e 0.641(3) 0.211(3) 0.013(2) 0.056(8) H(4WA) 4e 0.742(4) 0.705(4) 0.139(2) 0.09(1) H(4WB) 4e 0.835(4) 0.772(4) 0.119(2) 0.08(1) Table 2. Atomic coordinates and displacement parameters (in Å). Atom Site x y z Uiso

Crystal structure of hexaaquazinc(II) bis(citrato)borate dihydrate, [Zn(H 2 O) 6 ][(C 6 H 6 O 7 ) 2 B] 2 · 2H 2 O