One dimensional inorganic oxovanadium polymers functionalized with manganese(II) complexes: Structural and magnetic characterization

Two organo-inorganic hybrid manganese(II) vanadates [Mn(phen) ₂(VO₃)₂]_∞ (1) and [{Mn(bipy)(VO₃)₂}{VO₂(bipy)}(VO ₃)(V₂O₆)]_∞ (2) were synthesized hydrothermally. Compound 1 is a chain consisting in VO₃ units propagating along the b axis, decorated with {Mn(phen)₂} ⁺² subunits. Compound 2 is a ladder like structure propagating along the a axis, consisting of two helical chains connected by the heterobinuclear {Mn(bipy)VO₄ (2,2′-bipy)} moieties, generating a double helical structure. Magnetization measurements reveal that dominant antiferromagnetic interactions are mediated between the manganese(II) centers for both structures through oxovanadate bridges. Magnetic data of compound 1 were fitted with the analytical expression for a regular chain model, estimating a J value of -0.30 cm^-1. The DAVE code was use to fit experimental data and calculate the values of the super exchange constants for 2, assuming four different exchange pathways, J₁₂ = -0.17 cm^-1; J₂₃ = -0.12 cm^-1; J₁₃ = -0.08 cm^-1; J₂₄ = -0.05 cm^-1. DFT calculations on a tetranuclear fragment of 2, using diamagnetic substitutions, gave super exchange values of J₁₂ = -17.5 cm^-1 and J₂₃ = -8.5 cm^-1, corroborating the antiferromagnetic nature of the interactions as observed experimentally.