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

• Published in: Inorganic chemistry 2009-01, Vol.48 (1), p.55-67
• Main Authors: Lefebvre, Julie, Tyagi, Pooja, Trudel, Simon, Pacradouni, Vighen, Kaiser, Christina, Sonier, Jeff E, Leznoff, Daniel B
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic801094m

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 [ n Bu4N][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 cyanide groups, are also present. In zero field, the interchain interactions yield a phase transition to a disordered spin-frozen magnetic state below 2−5 K for every polymer. However, the degree of spin disorder varies considerably, depending on the metal center.