A discrete Cu-6(II) cluster and a 3D Mn-II-Cu-II 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 Cu-II cluster [Cu-6(mu(3)-OH)(2)(ppk())6(H2O)2(NO3)(4)] (1) and a three-dimensional (3D) compound [{MnCu2(dpkO(2)H)(2)(dpkO(2))N-3}center dot(NO3)center dot H2O](n) (2) (ppk = phenyl-2-pyridyl ketoxime; dpk = di-2-pyridyl ketone) consisting of heterometallic Mn-II-Cu-II hexanuclear cores as secondary building units are reported in this paper. In compound 1, two symmetry-related Cu-3 triangles consisting of a hydroxido-bridged trinuclear unit, [Cu-3(mu(3)-OH)(ppk)(3)(H2O)(NO3)](+), are assembled through nitrate bridging giving rise to the homometallic Cu-6 cluster. Compound 2 contains heterometallic {(Mn2Cu4II)-Cu-II} 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 {(Mn2Cu4II)-Cu-II} 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