Towards the Design of Linear Homo‐Trinuclear Metal Complexes Based on a New Phenol‐Functionalised Diazamesocyclic Ligand: Structural Analysis and Magnetism

Abstract

AbstractThe formation of two novel phenoxo‐bridged linear trimetallic CuII and NiII complexes, [Cu3(μ‐L)2](CH3OH)2(ClO4)2 (1) and [Ni3(μ‐L)2(CH3OH)2](ClO4)2 (2), with a new diazamesocyclic ligand functionalised by additional phenol donor pendants (H2L = N,N′‐ bis(2‐hydroxybenzyl)‐1,4‐diazacycloheptane), has been achieved and both complexes have been characterised by IR spectroscopy, elemental analyses, conductivity measurements, thermal analyses and UV/Vis techniques. Single‐crystal X‐ray diffraction analyses revealed that both 1 and 2 have the similar phenoxo‐bridged linear trinuclear cores. For 1, two terminal and the central CuII ion are in square‐planar environments with the adjacent intramolecular Cu···Cu separation of 2.9376(9) Å. For 2, however, two terminal NiII ions are in square‐planar environments and the central NiII ion assumes an octahedral geometry by axial coordination of two methanol ligands, the adjacent intramolecular Ni···Ni distance being 3.007(3) Å. In both cases, the 1,4‐diazacycloheptane (DACH) ring adopts the normal boat configuration. The magnetic properties of complexes 1 and 2 have been investigated by variable‐temperature magnetic susceptibility measurements in the solid state. Complex 1 displays a very strong antiferromagnetic coupling interaction between the neighbouring μ‐phenoxo CuII centres with a J parameter of −314 cm−1 and the magneto‐structural correlation for such complexes is discussed in detail. For complex 2, the result indicates that both terminal NiII ions are diamagnetic and the central NiII shows typical paramagnetic behaviour. The presence of zero‐field splitting for NiII with a D parameter of 11 cm−1, being active at low temperature, is further corroborated by the magnetisation measurement at 2 K. Additionally, the interesting ESR spectra of 1 at different temperatures (from 298 K to 8 K) were investigated and interpreted. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)