Di-μ-chlorido-bis{[2-({[2-(2-pyridyl)ethyl](2-pyridylmethyl)amino}methyl)phenol]zinc(II)} bis(perchlorate) dihydrate

The title compound, [Zn2Cl2(C20H21N3O)2](ClO4)2·2H2O, consists of a dinuclear ZnII cationic complex, two disordered perchlorate anions and two water molecules as solvate. The [Zn2(μ-Cl)2(HL)2]2+ cation [HL is 2-({[2-(2-pyridyl)ethyl](2-pyridylmethyl)amino}methyl)phenol] has a centrosymmetric structure with the ZnII ions in a distorted octahedral environment surrounded by an N3OCl2 donor set. HL acts as a tetradentate ligand through three N atoms from one amine group and two pyridyl arms and one O atom from the phenolic arm. The three N-donor sites of the HL ligand are arranged in meridional fashion, with the pyridine rings coordinated in trans positions with respect to each other. Consequently, the amine and phenol groups are trans to the asymmetric di-μ-chlorido exogenous bridges. A polymeric chain is formed along [010] by C(12)R 4 2(8) intermolecular hydrogen bonding. The perchlorate anion is disordered and was modelled by two sites in a 0.345 (18):0.655 (18) ratio. Water–perchlorate O—H⋯O interactions form cyclic structures, while phenol–water O—H⋯O interactions generate an infinite chain. In addition, weak intermolecular C—H⋯π(Ph) interactions between pyridine donor and phenol acceptor groups of neighboring cations build a two-dimensional polymeric structure parallel to (110).

The title compound, [Zn 2 Cl 2 (C 20 H 21 N 3 O) 2 ](ClO 4 ) 2 Á2H 2 O, consists of a dinuclear Zn II cationic complex, two disordered perchlorate anions and two water molecules as solvate. The [Zn 2 (-Cl) 2 (HL) 2 ] 2+ cation ethyl](2pyridylmethyl)amino}methyl)phenol] has a centrosymmetric structure with the Zn II ions in a distorted octahedral environment surrounded by an N 3 OCl 2 donor set. HL acts as a tetradentate ligand through three N atoms from one amine group and two pyridyl arms and one O atom from the phenolic arm. The three N-donor sites of the HL ligand are arranged in meridional fashion, with the pyridine rings coordinated in trans positions with respect to each other. Consequently, the amine and phenol groups are trans to the asymmetric di--chlorido exogenous bridges. A polymeric chain is formed along [010] by C(12)R 4 2 (8) intermolecular hydrogen bonding. The perchlorate anion is disordered and was modelled by two sites in a 0.345 (18):0.655 (18) ratio. Water-perchlorate O-HÁ Á ÁO interactions form cyclic structures, while phenol-water O-HÁ Á ÁO interactions generate an infinite chain. In addition, weak intermolecular C-HÁ Á Á(Ph) interactions between pyridine donor and phenol acceptor groups of neighboring cations build a two-dimensional polymeric structure parallel to (110).

Comment
Zinc is found in an all known forms of life as a trace element. It plays important roles in biological systems and its divalent ion is present in the active sites of several classes of metalloenzymes (Parkin, 2004). The design of artificial nucleases has recently received considerable interest due to their potential applications in catalysis, molecular biology and drug development (Mitić et al., 2006;Morrow & Iranzo, 2004;Rajski & Williams, 1998). Intense efforts have been devoted to the improvement of mimetic models for nucleases and peptidases through mono and polynuclear complexes (Boseggia et al., 2004;Mancin & Tecillia, 2007;Mitić et al., 2006). Recent studies have demonstrated that zinc complexes show anti-inflammatory and anti-tumoral activity (Beraldo & Gambino, 2004;Singla & Wadhwa, 1995;Zhou et al., 2003).
The cation of (I) is a dinuclear Zn II complex showing centrosymmentric molecular structure with local symmetry C i . Zinc(II) ions are in distorted octahedral environment surrounded by N 3 O donor set of the HL ligand (HL is (2-pyridylethyl)(2-pyridylmethyl)(2-hydroxybenzyl)amine) and two Clas exogenous bridges (Fig. 1). HL ligand acts as a typical four-chelating ligand and it is coordinated to the metal center through its three nitrogen atoms of the amine group and two pyridinic arms and one oxygen atom from protonated phenolic arm. The three N-donor sites of the HL ligand are arranged in meridional fashion, where pyridine rings are coordinated in trans positions with respect to each other. Consequently, the amine and phenol groups are trans to the asymmetric bis(µ-chloro) bridges.
Bond lengths around metal center are in the expected range and comparable to other zinc(II) complexes with N 2 O donor set (Ojida et al., 2006;Trösch & Vahrenkamp, 1998;Gross & Vahrenkamp, 2005). The long distance Zn-O phenol is typical for the coordination of protonated phenol group. The asymmetric bridge is due to the fact that two different groups with different trans effect are in trans positions to the chloro bridge. The distance Zn-Cl is shorter when amine group is trans to the bridge, whereas this distance is longer when phenol group is trans to µ-Cl. The cis angles are ranging from 77.69 (14)°t o 100.55 (9)°, being the more closed angle restricted by a five-membered chelate ring formed by 2-methylpyridine arm.
The three-dimensional packing of (I) is governed by an extensive and interesting hydrogen bonding network (Fig. 2).
Water molecules of crystallization and perchlorate anions form a cyclic structures by O1W-H···O interactions with a graph set of R 4 2 (8). These rings link the dinuclear cations through O10-H···O1W interactions between phenol and water groups building infinite one-dimensional chains along [010] direction with C(12) graph set. In addition, weak C-H···π(phenol) intermolecular interactions between pyridine (donor) and phenol (acceptor) groups of neighboring molecules also contribute to the stabilization of the crystalline structure aggregating the linear chains in two-dimensional polymer parallel to (110) plane. The calculated distance H35···centroid phenol is 3.136 Å and the angle C35-H35-Centroid is 147.55°. Finally, the molecules of (I) are stacked viewing along [100] in perpendicular projection of the linear chains.
supplementary materials sup-2 Experimental HL ligand has been prepared according to the procedure described by Yan & Que (1988). To a solution of HL (0.239 g, 0.78 mmol) in methanol (10 ml) was dropped 10 ml of the suspension containing 0.291 g of Zn(ClO) 4 .6H 2 O (0.78 mmol) in methanol. The mixture was stirred for 15 minutes at room temperature. After one hour on standing, a white precipitate was formed and it was filtered off and dried under vacuum (yield 0.63 g, 74%). The white powder was recrystallized in ethanol affording colorless crystals.

Refinement
H atoms were placed at their idealized positions with distances of 0.97 and 0.93 Å for CH 2 and CH Ar , respectively. U iso of the H atoms were fixed at 1.2 times of the U eq of the preceding atom. Hydrogen atoms of the phenol and water of crystallization were found from Fourier difference map and treated with riding model and its U iso were also fixed at 1.2 times U eq of the parent O atom. Perchlorate anion is disordered with two alternative positions for all oxygen atoms. The occupancy for disordered atoms of 0.655 (18) and 0.345 (18) were refined. Although disordered O atoms and some carbon atoms show abnormal adp, all non-hydrogen atoms were refined anisotropically with positive definite thermal tensor. Further, the final indices wR 2 decreased more than 33% (from about 0.18 to 0.1211) after anisotropic refinement of the disordered atoms. Fig. 1. The molecular structure of (I) with partial labeling scheme. Hydrogen atoms were omitted for clarity. Displacement ellipsoids are shown at the 30% probability level. Symmetry code: -x+1, -y+1, -z+1.