A New Zinc(II) Thiocyanate Complex of a Pyridine-4-carbohydrazide Schiff Base: Crystal Structure and Redox Properties of a Related Copper(II) Complex
Ousmane Sall
Department of Chemistry, Cheikh Anta Diop University, Dakar, Senegal.
Moussa Faye
Department of Chemistry, Alioune Diop University, Bambey, Senegal.
Alassane Saïdou Diallo
Department of Chemistry, Alioune Diop University, Bambey, Senegal.
Abdoul Sall
Department of Chemistry, Alioune Diop University, Bambey, Senegal.
Farba Bouyagui Tamboura
Department of Chemistry, Alioune Diop University, Bambey, Senegal.
Ibrahima Elhadj Thiam
Department of Chemistry, Cheikh Anta Diop University, Dakar, Senegal.
Moussa Dieng *
Department of Chemistry, Alioune Diop University, Bambey, Senegal.
Mohamed Gaye
Department of Chemistry, Cheikh Anta Diop University, Dakar, Senegal.
*Author to whom correspondence should be addressed.
Abstract
A new zinc(II) complex, ZnCl(SCN)(H₂L)₂, derived from the Schiff base ligand N′-[(E)-(2-hydroxy)methylidene]pyridine-4-carbohydrazide (H₂L), was synthesised and structurally characterised by single-crystal X-ray diffraction. The complex crystallises in the orthorhombic space group Ama2, with unit-cell parameters a = 26.0306(2) Å, b = 16.0094(1) Å, and c = 6.840(1) Å. The asymmetric unit comprises two neutral H₂L ligands coordinated to the Zn²⁺ ion through their pyridine nitrogen atoms, one thiocyanate anion (SCN⁻) coordinated through nitrogen, one chloride anion, and one lattice water molecule. The zinc centre adopts a distorted tetrahedral geometry, with Zn–N bond lengths of 1.979(4) and 2.052(3) Å, a Zn–Cl bond length of 2.1919(12) Å, and bond angles that depart markedly from the ideal tetrahedral value (103–125°). To complement the structural study, the redox behaviour of the related copper(II) complex [Cu(H₂L)Cl·H₂O]Cl (L-4) was investigated by cyclic voltammetry in acetonitrile containing 0.1 M TEATFB, using a Pt disk working electrode (r = 2 mm), a stainless-steel wire counter electrode, and an Ag/AgCl reference electrode. Over the potential range −1.0 to +1.0 V versus SCE and at scan rates of 10–50 mV s⁻¹, the voltammograms displayed a single quasi-reversible redox couple, characterised by a sharp cathodic peak at −0.75 V and a broader anodic peak at −0.45 V versus SCE. The observation of a single redox wave indicates a uniform Cu(II) coordination environment, consistent with the structural and spectroscopic data obtained for the complex.
Keywords: Schiff base, zinc(II) complex, copper(II) complex, single-crystal X-ray diffraction, coordination chemistry