A discrete Cu^II6 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 [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-OH)(ppk)₃(H₂O)(NO₃)]⁺, are assembled through nitrate bridging giving rise to the homometallic Cu₆ cluster. Compound 2 contains heterometallic {Mn^II2Cu^II4} 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 {Mn^II2Cu^II4} 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 J_av(−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.