Synthesis, structure and magnetic properties of 3D interpenetrating nets of M(pyrazine)[Au(CN) 2] 2 (M=Cu, Ni, Co) supported by aurophilic interactions

Abstract

New inorganic coordination polymers of the form M(pyrazine)[Au(CN) 2] 2 (M=Cu ( 1); Ni ( 2); Co ( 3)) have been prepared and the copper(II) analogue structurally characterised. The X-ray analysis revealed two 3D interpenetrating α-polonium networks consisting of 1D chains of Cu–pyrazine units connected by [Au(CN) 2] bridges. The two networks are connected via weak aurophilic interactions (AuAu: 3.4729(2) Å). Thermogravimetric analysis of all three compounds indicated the robust nature of these 3D systems, with decomposition beginning at 260 ( 1), 406 ( 2) and 360°C ( 3). The magnetic susceptibility of 1 shows a maximum in χ M at 5.0 K; these data could be fitted to the theoretical expressions for either a 1D or a 2D Heisenberg antiferromagnetic array ( J=−2.74 cm −1, g=2.32 and J=−3.45 cm −1, g=2.33, respectively). The magnetic susceptibility versus temperature data for 2 and 3 showed effects primarily associated with single-ion zero-field splitting; any weak antiferromagnetic coupling in these systems is very weak and hence was not quantified. Although the aurophilic interactions between the [Au(CN) 2] units may positively influence both the formation of an interpenetrating structure and its subsequent thermal stability, the incorporation of anionic [Au(CN) 2] units into M(pyrazine) systems does not seem to significantly increase magnetic interactions.