Metal pyrazolate polymers. Part 1. Synthesis, structure, and magnetic properties of the [Cu(pz)2]x polymer

Abstract

A novel and reliable method for the synthesis of polybis(μ-pyrazolato-N,N′)copper(II), [Cu(pz)₂]_x(where pz = N₂C₃H₃), is presented. Single crystals of the polymer suitable for X-ray study have been grown under carefully controlled conditions. Crystals of polybis(μ-pyrazolato-N,N′)copper(II) are orthorhombic, a = 7.917(1), b = 11.491(2), c = 7.778(1) Å, Z = 4, space group Ibam. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.029 and R_w = 0.038 for 507 reflections with I ≥ 3σ(I). The crystal structure consists of infinite double-bridged polymeric chains. The Cu atom has a D₂ distorted tetrahedral coordination geometry with Cu—N = 1.957(2) Å and N—Cu—N = 94.3(1)–139.5(1)°. Magnetic susceptibility studies (4.2 to 299 K) on this material reveal very strong antiferromagnetic exchange between copper(II) centres in the extended linear chains. The magnetic data have been successfully analyzed according to the isotropic Heisenberg model for linear chains with −J = 78 cm⁻¹ and g = 2.12. Keywords: crystal structure, copper(II) pyrazolate chain polymer, antiferromagnetic exchange.