Crystal Structure of Zinc(II) Complex of a Pyridine Containing Self-Assembling System
The self-assembling system ligand LH2, [pyda·H2] 2+ [pydc] 2-, (pyda = 2,6-pyridinediamine; pydc·H2 = 2,6pyridinedicarboxylic acid), that has been recently synthesized in our laboratory is a novel self-assembling system which arises from both ion pairing and hydrgen bonding simultaneously. 1 The anionic form of pydc·H2 is a rigid tridentate ligand, which is capable of forming many stable complexes with divalent transition metals.    The [Ag(pydc)(pydc·H2)]·H2O, 2 [Ni(pydc·H)2]·3H2O, 3
... nd [Cu(pydc·H)2]·3H2O, 4 complexes are some examples in this regard. Using the thermal analysis and high temperature reflectance spectroscopy, Ascenzo et al. found out that the reaction between ZnCO3 and pydc·H2 in 1:2 mole ratio, resulted in the formation of [Zn(pydc·H)2]·2H2O complex. 5 Literature survey on this complex showed that no Xray crystal data has been reported to date. Here, we wish to report the synthesis and X-ray crystal data of an ionic Zn(II) complex which resulted from the reaction between LH2 and ZnCl2 in water. The Zn(II) ionic complex includes dianionic and monoanionic forms of pydc·H2 simultaneously and one pyridinum cation, as counter ion, that causes hydrogen bondings. The resulting ionic Zn(II) complex would assemble into layers by hydrogen-bonds (O-H···O -) and ( + N-H···O -). Preparation: To a solution of ZnCl2 (0.124 g , 0.9 mmol) in water (20 cm 3 ) was added a solution of LH2 (0.5 g, 1.8 mmol) 1 in water (150 cm 3 ) and the resulting light yellow solution was stirred for 15 min. After two days, light yellow crystals were obtained (Scheme 1). The crystals were collected, washed with fresh distilled water and dried. The pure light yellow block- The X-ray data were collected by graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The crystal and experimental data are listed in Table 1 . The structure was solved by direct methods using SHELXS-97. 6 The non-hydrogen atoms were refined anisotropically by the full matrix least-square method. The hydrogen atoms were obtained from a difference Fourier map and some of the hydrogen atoms were included in the ideal position with fixed isotropic U values equal to 1.2 times that of the atom they are attached to. The final atomic coordinates of the non-hydrogen are listed in Table 2 . The selected bond distances and angles are given in Table 3 . The molecular structure of the title compound is shown in Fig. 1 together with the atom-labeling scheme. The central metal ion is coordinated by four oxygen atoms (O1, O3, O5, O7) and two nitrogen atoms (N1, N2). The two O1-Zn-O3 and O7-Zn-O5 angles are 152.65˚ and 151.09˚, respectively. This shows that the four carboxylate groups of 219 Formula: C19H21N6O11Zn Formula weight = 560.78 Crystal system: triclinic Space group: P1 Z = 2 a = 6.9482(10)Å = 102.603(2)b = 10.4796 (15)Å = 93.925(2)c = 16.678(2)Å = 104.354(2)V = 1138.4(3)Å 3 DX = 1.636 g/cm 3 Absorption coefficient = 1.50 mm -1 F(0 0 0) = 576 Crystal dimensions (mm): 0.25 × 0.1 × 0.1 R = 0.0401 Rw = 0.0857 range for data collection: 2.07 to 28.73G oodness-of-fit = 1.043 Largest diff. Peak and hole: 0.393 and -0.507 eÅ -3 No. of reflections used = 5153 No. of parameters = 346 Measurement: Bruker SMART Program system: SHELXS-97, SHELXL-97, Bruker SHELXTL Structure determination: direct method Refinement: full-matrix least-squares of F 2 Table 1 Crystal and experimental data θ α β γ Scheme 1 The synthetic method for [pydc·H][Zn(pydc)(pydc·H)]· 3H2O complex. two [pydc] 2and [pydc·H]anions are oriented in a flattened tetrahedral arrangement around the Zn(II) atom. The dianionic [pydc] 2unit and monoanionic [pydc·H]unit are almost perpendicular to each other (i.e., O3-Zn-N2-C9 tortion angle is -97.7˚, N2-Zn-O3 and N2-Zn-O1 angles are 101.37˚ and 105.10˚, respectively). The geometry of the zinc atom is distorted octahedral. The molecular structure consists of monomeric units [pyda·H][Zn(pydc)(pydc·H)]·3H2O in which the two [pydc] 2and [pydc·H]moieties act as tridentat ligands. The protonated position in the cationic counter ion is the pyridine nitrogen atom, while the two protons in the ligand LH2 are located at the two -NH2 nitrogen positions. The intermolecular forces which exist between anionic and cationic units in the Zn(II) complex consist of both H-bonding and ion-pairing. Three uncoordinated water molecules increase the number of H-bonding in the crystal lattice. The data found in this work for the unit [pyda·H] + are quite similar to the previous data reported for the [pyda·H2] moiety. 1 The metal-ligand bond distances of the title compound are consistent with those found in K2Zn[NH(CH2CO2)] (Zn-N = 2.16 Å; Zn-O = 2.03 Å, 2.12 Å). 7 In [pyda·H][Zn(pydc)(pydc·H)]·3H2O the Zn-N distance is 2.023 Å, and the average of Zn-O distances is 2.196 Å. The N1-Zn-N2 angle (axial) is 165.24˚, which shows a significant deviation from linearity. The Zn atom is positioned at the inversion center of the molecule. The structure is stongly stabilized by a complicated network of hydrogen bonds. Hydrogen coordinates, isotropic displacement parameters, bond angles, bond lengths and torsional angles are available as supplementary materials.