Magnetic Frustration and Spin Disorder in Isostructural M(μ-OH2)2[Au(CN)2]2 (M = Mn, Fe, Co) Coordination Polymers Containing Double Aqua-Bridged Chains: SQUID and μSR Studies

A series of isostructural M(μ-OH2)2[Au(CN)2]2 (M = Co, Fe, and Mn) coordination polymers was synthesized from the reaction of M(II) with [nBu4N][Au(CN)2]. The basic structural motif for these polymers is analogous to that of previously reported Cu(II)- and Ni(II)-containing polymers and contains repeating double aqua bridges between metal centers that yield a chain structure with pendant [Au(CN)2]− units. The aqueous reaction with Fe(III) yields Fe(μ-OH2)(μ-OH)[Au(CN)2]2, which has a similar structure. The magnetic properties of these polymers were investigated by a combination of SQUID magnetometry and zero-field muon spin relaxation. The double aqua bridges were found to mediate ferromagnetic interactions along the chains in the Co(II)-containing polymer, whereas intrachain antiferromagnetic interactions are present in the Fe(II)-, Fe(III)-, and Mn(II)-containing polymers. Weak magnetic interchain interactions mediated through hydrogen bonds, involving the bridging water molecules and the pendant cyanid...