Diaqua{2,6-bis[N-(2-pyridinylmethyl)carbamoyl]phenolato-κ2 O 1,O 2}zinc(II)

In the title compound, [Zn(C20H17N4O3)2(H2O)2], the ZnII atom, lying on a twofold rotation axis, is six-coordinated in a distorted octahedral geometry by two phenolate O atoms and two carbonyl O atoms from two 2,6-bis[(pyridin-2-ylmethyl)carbamoyl]phenolate ligands and by two water molecules. A three-dimensional network is built up from an extensive array of hydrogen bonds and π–π interactions between the pyridyl rings, with a centroid–centroid distance of 3.666 (3) Å.

In the title compound, [Zn(C 20 H 17 N 4 O 3 ) 2 (H 2 O) 2 ], the Zn II atom, lying on a twofold rotation axis, is six-coordinated in a distorted octahedral geometry by two phenolate O atoms and two carbonyl O atoms from two 2,6-bis[(pyridin-2-ylmethyl)carbamoyl]phenolate ligands and by two water molecules. A three-dimensional network is built up from an extensive array of hydrogen bonds andinteractions between the pyridyl rings, with a centroid-centroid distance of 3.666 (3) Å .
Financial support from the Thailand Research Fund (MRG5080149 and RTA5080006) and the Centre of Innovation in Chemistry: Postgraduate Education and Research Program in Chemistry (PERCH-CIC) are gratefully acknowledged.
Diaqua{2,6-bis[N-(2-pyridinylmethyl)carbamoyl]phenolato-2 O 1 ,O 2 }zinc(II) C. Suksai, S. Watchasit, T. Tuntulani and C. Pakawatchai Comment Zinc complexes of common amide-containing ligands have been widely explored and have received much attention in biomimetic research . For example, the zinc complex with 6-(pivaloylamido-2-pyridylmethyl)amine ligand has been synthesized to serve as models for amide hydrolysis activity . Recently, zinc and copper complexes with a family of pyridylmethylamide ligands have been synthesized and showed that these ligands coordinate to metal ions with different coordination modes (Chaudhuri et al., 2007). It should be mentioned that zinc complexes containing aqua ligands have been used as model studies for zinc-hydrolase enzyme because of the functional unit at the active site of zinc-hydrolase enzyme is a zinc-bound water molecule, which is deprotonated at near neutral pH to generate a strongly nucleophilic Zn-OH group (Lipscomb & Sträter, 1996). Moreover, the aqua ligand bound to zinc ion is further stabilized via the formation of a hydrogen bond with a carboxylate or phenolic group from amino acid residues (Kimura, 1994). This hydrogen bond has been postulated to play a role in the activation of the coordinated aqua ligand in the catalytic pathway.
In an ongoing effort to study the interaction of zinc ion with aqua ligand, we report here the synthesis and characterization of the title compound, a new zinc complex with 2,6-bis[(pyridin-2-ylmethyl)carbamoyl]phenolate and aqua ligands. In the title compound, the Zn II atom is situated on a twofold rotation axis in a distorted octahedral coordination geometry, which is defined by two phenolate O atoms, two carbonyl O atoms and two cis water molecules (Fig. 1). The O1-Zn1-O1 i and O4-Zn1-O2 i [symmetry code: (i) -x, y, 1/2 -z] angles deviate from linearity (Table 1). These results are in accordance with the distorted octahedral geometry. It is noteworthy that each ligand behaves in a bidentate coordination fashion involving one phenolate O atom and one carbonyl O atom, while the two amide N atoms and pyridyl N atoms are free of coordination with the Zn atom. The two phenyl rings of coordinated molecules are tilted to one another with a dihedral angle of 72.3 (3)°. Remarkably, the intramolecular N3-H3A···O1 hydrogen bond forms a pseudo-six-membered ring (Fig. 1).
The water molecule is involved in an extensive intermolecular hydrogen-bonding network, as shown in Fig. 2. Atom O4 of aqua ligand acts as a hydrogen-bond donor to the uncoordinated carbonyl O3 atom and uncoordinated pyridyl N2 atom of adjacent complex molecules, respectively (Table 2). Additionally, the molecules are held together by intermolecular hydrogen bond between the uncoordinated amide N1 atom and uncoordinated pyridyl N4 atom. Not only the intermolecular hydrogen bonds, but also there are intermolecular π-π interactions in the crystal structure, which occur between the pyridyl rings containing atoms N2 and N4 of adjacent molecules, with a centroid-centroid distance of 3.666 (3) Å.
supplementary materials sup-2 Experimental Intermediate products (I), (II) (Gumbley & Stewart, 1984) and (III) (Goldsmith et al., 2002) have been synthesized in accordance with the published procedures. The methods to synthesize compounds (IV) and (V) are shown in Fig. 3.
A methanol solution (5 ml) of Zn(ClO 4 ) 2 .6H 2 O (2.22 g, 5.96 mmol) was added dropwise to a stirred solution of compound (V) (1.00 g, 2.98 mmol) in methanol (10 ml) at room temperature and the solution was stirred for 3 h. Water (10 ml) was added to the solution to precipitate a white solid. The precipitate was filtered off and washed with water to obtain the white powder of the title compound (yield 28%, 0.66 g).