Use of 2-pyrimidineamidoxime to generate polynuclear homo-/heterometallic assemblies: synthesis, crystal structures and magnetic study with theoretical investigations on the exchange mechanism

Abstract

Three new transition metal complexes using 2-pyrimidineamidoxime (pmadH2) as multidentate chelating and/or bridging ligand have been synthesized and characterized. The ligand pmadH2 has two potential bridging functional groups [μ-O and μ-(N–O)] and consequently shows several coordination modes. While a polymeric 1D CuII complex [Cu(pmadH2)2(NO3)](NO3) (1) was obtained upon treatment of Cu(NO3)2·3H2O with pmadH2 at room temperature in the absence of base, a high temperature reaction in the presence of base yielded a tetranuclear CuII-complex [Cu4(pmad)2(pmadH)2(NO3)](NO3)(H2O) (2). One of the CuII centers is in a square pyramidal environment while the other three are in a square planar geometry. Reaction of the same ligand with an equimolar mixture of both Cu(NO3)2·3H2O and NiCl2·6H2O yielded a tetranuclear heterometallic CuII2NiII2 complex [Cu2Ni2(pmad)2(pmadH)2Cl2]·H2O (3) containing both square planar (NiII) and square pyramidal (CuII) metal centers. Complexes 1–3 represent the first examples of polynuclear metal complexes of 2-pyrimidineamidoxime. The analysis of variable temperature magnetic susceptibility data of 2 reveals that both ferromagnetic and antiferromagnetic interactions exist in this complex (J1 = +10.7 cm−1 and J2 = −2.7 cm−1 with g = 2.1) leading to a resultant ferromagnetic behavior. Complex 3 shows expected antiferromagnetic interaction between two CuII centers through –N–O– bridging pathway with J1 = −3.4 cm−1 and g = 2.08. DFT calculations have been used to corroborate the magnetic results.