Chromium Acetylide Complex Based Ferrimagnet and Weak Ferromagnet

The crystal structures and magnetic properties of new molecule-based magnets, [CrCyclam(CC−3-thiophene)2][Ni(mdt)2] (1) and [CrCyclam(CC−Ph)2][Ni(mdt)2](H2O) (2) (Cyclam = 1,4,8,11-tetraazacyclotetradecane, mdt = 1,3-dithiole-4,5-dithiolate), are reported. The crystal structures of both compounds are characterized by ferrimagnetic chains of alternately stacked [CrCyclam(CC−R)]+ cations and [Ni(mdt)2]− anions with intrachain exchange interactions of 2J = −6.1 K in 1 and −5.7 K in 2 (H = −2J ∑i Si·Si+1). The material 1 exhibits ferrimagnetic transition at 2.3 K owing to weak interchain antiferromagnetic interactions between cations and anions. In the case of 2, cations in adjacent ferrimagnetic chains are bridged by a water molecule, resulting in an interchain antiferromagnetic coupling. Despite a centrosymmetry of a whole crystal of 2, one bridging water molecule occupies only one of the two centrosymmetric sites and breaks a local centrosymmetry between adjacent cations. The interchain antiferromagnetic interaction and Dzyaloshinsky−Moriya interaction originated from the local symmetry breakdown of 2 bring a weak-ferromagnetic transition at 3.7 K with a coercive force of less than 0.8 mT, followed by the second magnetic phase transition at 2.9 K. Below this temperature, the coercive force rapidly increases from 1 to 11.8 mT as the temperature decreases from 2.9 to 1.8 K, while the remanent magnetization monotonically increases from 0.008 μB at 3.6 K to 0.12 μB at 1.8 K.