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 (pmadH(2)) as multidentate chelating and/or bridging ligand have been synthesized and characterized. The ligand pmadH(2) has two potential bridging functional groups [μ-O and μ-(N-O)] and consequently shows several coordination modes. While a polymeric 1D Cu(II) complex [Cu(pmadH(2))(2)(NO(3))](NO(3)) (1) was obtained upon treatment of Cu(NO(3))(2)·3H(2)O with pmadH(2) at room temperature in the absence of base, a high temperature reaction in the presence of base yielded a tetranuclear Cu(II)-complex [Cu(4)(pmad)(2)(pmadH)(2)(NO(3))](NO(3))(H(2)O) (2). One of the Cu(II) 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(NO(3))(2)·3H(2)O and NiCl(2)·6H(2)O yielded a tetranuclear heterometallic Cu(II)(2)Ni(II)(2) complex [Cu(2)Ni(2)(pmad)(2)(pmadH)(2)Cl(2)]·H(2)O (3) containing both square planar (Ni(II)) and square pyramidal (Cu(II)) 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 (J(1) = +10.7 cm(-1) and J(2) = -2.7 cm(-1) with g = 2.1) leading to a resultant ferromagnetic behavior. Complex 3 shows expected antiferromagnetic interaction between two Cu(II) centers through -N-O- bridging pathway with J(1) = -3.4 cm(-1) and g = 2.08. DFT calculations have been used to corroborate the magnetic results.