Synthesis, crystal structure and spectrothermal characterization of zinc(II) salicylato complex with 2,2′-azobispyridine, [Zn(Hsal)2(H2O)(abpy)]·H2O

doi:10.1016/j.dyepig.2006.06.035

Dyes and Pigments

Volume 75, Issue 3, 2007, Pages 521-525

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Abstract

The novel aqua(azobispyridine)bis(salicylato)zinc(II) monohydrate complex (1) was synthesized and characterized by means of elemental analysis, IR and UV-vis spectroscopy, thermal analysis and X-ray diffraction techniques. The crystal structure analysis indicates that the mononuclear 1 shows an s-cis/E/s-cis configured azobispyridine ligand, with the distortion from square pyramidal toward trigonal bipyramidal Zn(II) ion coordinated to one pyridyl and one azo N atom together with two carboxylate oxygen atoms and one aqua ligand. The crystal packing involves both hydrogen-bonding and π–π interactions. The title complex undergoes a thermochromic phase transition at ca. 189 °C, changing from 1 (brown complex) to 2 (purple complex) and the thermal decomposition of 1 proceeds in four stages.

Introduction

Salicylic acid and metal salicylates have been used for many years as anti-inflammatory, antipyretic and analgesic drugs in medicine [1], [2], [3]. In aqueous solutions, the acid affords hydrogensalicylate (Hsal⁻) and salicylate (sal²⁻) ions. The Hsal⁻ anion can bind to metals as unidentate carboxylate, bidentate chelating (employing one carboxylate oxygen and hydroxyl oxygen atoms) or bidentate bridging carboxylate ligand. The studies of the material chemistry of the azoaromatic compounds have attracted increasing attention because of their unique combination of geometrical and electronic structures [4], [5], [6], [7]. The 2,2′-azobispyridine (abpy), derived from the 2,2′-bipyridine through the insertion of the azo (diazene) group between the two pyridyl moieties is known to form an unusual complex [8]. The abpy ligand has several different coordination modes involving five-membered chelate ring formation (N double bond N–C–N–M), as shown in Scheme 1. When one 2-pyridyl ring remains uncoordinated, because of the repulsion effects between azo N-atom lone pairs and ortho-CH or pyridyl N-atom lone pairs, a singly chelating complex can form, as in IIa or IIb. The abpy ligand rings can also involve in π–π and π–ring interactions, forming extended networks of supramolecular architectures [9], [10]. These types of interactions have attracted particular attention especially in fields such as developing new functional materials, crystal engineering, molecular recognition and self-assembly of organometallic compounds [11], [12]. The aim of this work was to prepare a new mixed-ligand salicylato complex of Zn(II) with 2,2′-azobispyridine and undertake its crystal structure and spectrothermal analysis.

Section snippets

Synthesis of 1

Sodium salicylate (1.11 g, 6.96 mmol) was dissolved in water (50 ml) and added to the 50 ml of hot water solution of ZnSO₄·7H₂O (1.0 g, 3.48 mmol). The mixture was stirred at 323 K for 3 h and then cooled to room temperature. The crystals formed were filtered off and washed with water and acetone, and dried in a vacuum. Abpy was prepared following the method of Rivarola et al. [13]. A solution of abpy (0.11 g, 0.61 mmol) in acetonitrile (20 ml), was added dropwise with stirring to a solution of [Zn(Hsal)₂

Description of the crystal structure

The asymmetric unit of the complex consists of one 1 unit. One of the o-hydroxyphenyl groups is disordered over two positions, with occupancies of 0.6 for A group and 0.4 for B group (Fig. 1). The Zn(II) ion is coordinated by two salicylate oxygen atoms [Zn1–O2 = 1.9682 (19) Å, Zn1–O5 = 2.007 (2) Å], two abpy nitrogen atoms [Zn1–N1 = 2.081 (2) Å; Zn1–N3 = 2.301 (2) Å], and an aqua ligand [Zn1–O1 = 2.044 (2) Å]. These bond distances are found to be similar to those of related Zn(II) complexes [17], [18]. All

Supplementary data

Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as the supplementary publication no. CCDC 275406. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336033 or e-mail: [email protected]).

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Synthesis, crystal structure and spectrothermal characterization of zinc(II) salicylato complex with 2,2′-azobispyridine, [Zn(Hsal)2(H2O)(abpy)]·H2O

Abstract

Introduction

Section snippets

Synthesis of 1

Description of the crystal structure

Supplementary data

Inorg Chem Commun

Inorg Chim Acta

J Organomet Chem

J Organomet Chem

Inorg Chem Commun

J Mol Struct

Inorg Chim Acta

Inorg Chim Acta

J Mol Struct

Acta Crystallogr

J Chem Soc Dalton Trans

Dalton Trans

Synthesis, crystal structure and spectrothermal characterization of zinc(II) salicylato complex with 2,2′-azobispyridine, [Zn(Hsal)₂(H₂O)(abpy)]·H₂O