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Use of 2-pyrimidineamidoxime to generate polynuclear homo-/heterometallic assemblies: Synthesis, crystal structures and magnetic study with theoretical investigations on the exchange mechanism
, Rajesh Chakrabarty, Sandip Mukherjee, You Song, Partha Mukherjee Sarathi
Published in
Volume: 39
Issue: 41
Pages: 9766 - 9778
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 [$\mu$-O and $\mu$-(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{\textperiodcentered}3H2O with pmadH2 at room temperature in the absence of base, a high temperature reaction in the presence of base yielded a tetranuclear Cu II-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{\textperiodcentered}3H2O and NiCl2{\textperiodcentered}6H2O yielded a tetranuclear heterometallic CuII2NiII2 complex [Cu2Ni2(pmad)2(pmadH)2Cl 2]{\textperiodcentered}H2O (3) containing both square planar (Ni II) 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 J 1 = -3.4 cm-1 and g = 2.08. DFT calculations have been used to corroborate the magnetic results. {\textcopyright} 2010 The Royal Society of Chemistry.
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