[Fe(bpym)(CN)_4]~-:A New Building Block for Designing Single-Chain Magnets

摘要

We herein present the preparation,crystal structure,magnetic properties,and theoretical study of new heterobimetallic chains of formula {[Fe~(III)(bpym)(CN_4)]_2M~(II)(H_2O)_2} centre dot 6H_2O [bpym = 2,2'-bipyrimidine;M = Zn (2),Co (3),Cu (4),and Mn (5)] which are obtained by using the building block PPh_4[Fe(bpym)-(CN)_4] centre dot H_2O (1) (PPh_4+ = tetraphenylphosphonium) as a ligand toward the fully solvated M~(II) ions.The structure of complex 1 contains mononuclear [Fe(bpym)(CN)_4]~- anions.Compounds 2-5 are isostructural 4,2-ribbonlike bimetallic chains where the [Fe(bpym)(CN)_4]~- unit acts as a bis-monodenate ligand through two of its four cyanide ligands toward the M atom.Water hexamer clusters (4) and regular alternating fused six- and four-membered water rings with two dangling water molecules (2,3,and 5) are trapped between the cyanide-bridged 4,2-ribbonlike chains.1 and 2 behave as magnetically isolated low-spin iron(lll) centers.3 behaves as a single-chain magnet (SCM) with intrachain ferromagnetic coupling,slow magnetic relaxation,hysteresis effects,and frequency-dependent ac signals at T < 7 K).As expected for a thermally activated process,the nucleation field (H_n) in 3 increases with decreasing T and increasing v.Below 1.0 K,H_n becomes temperature independent but remains strongly sweep rate dependent.In this temperature range,the reversal of the magnetization may be induced by a quantum nucleation of a domain wall that then propagates due to the applied field.4 and 5 are ferro- and ferrimagnetic chains respectively,with metamagnetic-like behavior (4).DFT-type calculations and QMC methodology provided a good understanding of the magnetic properties of 3-5.