Assembling Magnetic Blocks: A Strategy to Control the Nuclearity and Magnetic Properties of Polynuclear Complexes

Abstract

Synthetic strategies dealing with the polymerization of either di-μ-hydroxocopper(II) complexes or 2,2′-bipyrimidine (bpym)-containing first row transition metal ions allow the preparation of polynuclear compounds whose structures and magnetic properties are presented here. The influence of structural and chemical parameters on the magnitude of the singlet-triplet energy gap (J) in di-μ-hydroxocopper(II) complexes [LCu(OH)2CuL]2+ with L = 2,2′-bipyridine (bpy) and bpym is analyzed and discussed. Special attention is devoted to nature of the counterion which allows the preparation of hydroxo-bridge copper(II) cubane and double cubane type complexes where all the intramolecular magnetic interactions are ferromagnetic. The case of the compound [Cu2(bpy)2(OH)2(CF3SO3)2] where two dimers with different values of the angle at the hydroxo bridge (θ) coexist in the unit cell is aborded here. The polymerization of the [Cu2(bpym)2(OH)2]2+ dinuclear units through bis(chelating) bpym leads to novel copper(II) chains exhibiting regular alternating ferromagnetic (through the hydroxo bridge) and antiferromagnetic (through bpym) exchange couplings within the chain. The possibility of tuning the value of J in polynuclear complexes through bis(chelating) type ligands by playing on the electronegativity of the peripheral donor atoms is analyzed and discussed. The structural changes caused by the Jahn-Teller effect in bpym-bridged copper(II) complexes appears as a potential strategy to achieve ferromagnetic coupling between copper(II) ions. Finally, the use of bis(chelating) ligands such as oxalate and bpym and transition metal ions for designing new honeycomb layered materials of formula M2(bpym)(ox)2 · nH2O (M = divalent first-row transition metal ions) is presented and their magnetic behaviour analyzed by classical Heisenberg models.