Layer structural bimetallic metamagnets obtained from the aggregation of Ru2(CO3)43− and Co2+ in existence of halogen

Abstract

An investigation of halogen (Cl⁻ and Br⁻) influence on the self-assembling Ru₂(CO₃)₄³⁻ paddle-wheel precursors and Co²⁺ ions in aqueous solution has resulted in two novel layer structural bimetallic carbonate complexes, [{Co(H₂O)₄}₂Ru₂(CO₃)₄(H₂O)Cl]_n·7.5nH₂O (1), and [{Co(H₂O)₄}₂Ru₂(CO₃)₄(H₂O)₂]_n·[{Co(H₂O)₄}₂Ru₂(CO₃)₄Br₂]_n·10.5nH₂O (2). X-ray structural analysis reveals that complexes 1 and 2 contain similar square-grid layer structures, in which each Co(H₂O)₄²⁺ bonds to two Ru₂(CO₃)₄³⁻ units in a trans manner forming square-grid layer [{Co(H₂O)₄}₂Ru₂(CO₃)₄]_nⁿ⁺, and X⁻ (Cl⁻ and Br⁻) ions influence the packing diagram between neighboring layers. For complex 1, two axial positions of each Ru₂(CO₃)₄³⁻ paddlewheel are terminated by H₂O and Cl⁻, respectively, forming a neutral layer [{Co(H₂O)₄}₂Ru₂(CO₃)₄(H₂O)Cl]_n. Meanwhile in complex 2, the axial positions of each Ru₂(CO₃)₄³⁻ in the layer [{Co(H₂O)₄}₂Ru₂(CO₃)₄]_nⁿ⁺ are terminated by two H₂O or two Br⁻, forming two oppositely charge layers packing alternatively, namely, the positive layer [{Co(H₂O)₄}₂Ru₂(CO₃)₄(H₂O)₂]_nⁿ⁺ and negative layer [{Co(H₂O)₄}₂Ru₂(CO₃)₄Br₂]_nⁿ⁻. These two complexes are metamagnets, showing magnetic ordering T_c = 5.1 K, T_N = 2.6 K for 1, and T_c = 2.7 K, T_N = 2.3 K for 2, and the metamagnetism transition fields are ~1.2 kOe and ~0.5 kOe K for 1 and 2, respectively.