Effect of Structural Motif on Magnetic Properties in Molybdenum Chlorides of Mo5+ Ions: Ferromagnetism from Mo2Cl10 Dimers and Antiferromagnetism from Isolated MoCl6- Anions.

The evolution of magnetic properties in molybdenum chloride systems caused by structural motif changes was investigated by magnetic property measurements and DFT calculations. In ξ-MoCl5, characterized by the presence of molybdenum dimers, the formation of ferromagnetic (FM) order is observed at T1 = 12.4 K and its additional transformation at T2 = 2.6 K. The influence of the electronic structure on the FM state was studied by substituting Nb5+ and Re5+ for Mo5+. Replacing half the Mo5+(4d1) cations with Re5+(5d2) leads to the formation of a ferrimagnetically ordered state below TNRe1 = 3.8 K and its additional transformation below TNRe2 = 2.6 K in Re0.5Mo0.5Cl5. In contrast, introducing Nb5+(4d0) suppresses a long-range order formation in Nb0.5Mo0.5Cl5. The PCl4MoCl6 compound containing isolated MoCl6- octahedral anions exhibits transition to a long-range ferrimagnetic order below TNPCl4 = 4.2 K.