A discrete Cu cluster and a 3D MnII-CuII framework based on assembly of Mn2Cu4 clusters: synthesis, structure and magnetic properties.

Abstract

The synthesis, single-crystal structure characterization and detailed magnetic study of a homometallic hexanuclear CuII cluster [Cu6(μ3-OH)2(ppk)6(H2O)2(NO3)4] (1) and a three-dimensional (3D) compound [{MnCu2(dpkO2H)2(dpkO2)N3}·(NO3)·H2O]n (2) (ppk = phenyl-2-pyridyl ketoxime; dpk = di-2-pyridyl ketone) consisting of heterometallic MnII-CuII hexanuclear cores as secondary building units are reported in this paper. In compound 1, two symmetry-related Cu3 triangles consisting of a hydroxido-bridged trinuclear unit, [Cu3(μ3-OH)(ppk)3(H2O)(NO3)]+, are assembled through nitrate bridging giving rise to the homometallic Cu6 cluster. Compound 2 contains heterometallic {MnCu} cores, which are further connected to each other through an azido bridging ligand in all the crystallographic directions, resulting in a 3D metal-organic framework. Construction of such a heterometallic 3D framework from {MnCu} units is until now, unknown. Magnetic studies of both 1 and 2 were performed in detail and both compounds show dominant antiferromagnetic interaction in the respective clusters. Compound 1 reveals significant spin frustration and anti-symmetric exchange interaction in the trinuclear cores, with a significantly high value of Jav (-655 cm-1). Furthermore, compound 2 exhibits a dominant antiferromagnetic interaction, which is also supported by an extensive magneto-structural correlation which considers the different magnetic pathways.