Chlorine and temperature directed self-assembly of Mg–Ru2(ii,iii) carbonates and particle size dependent magnetic properties

Abstract

A series of heterometallic magnesium diruthenium(II,III) carbonates, namely K{Mg(H₂O)₆}₂[Ru₂(CO₃)₄Cl₂]·4H₂O (1), K₂[{Mg(H₂O)₄}₂Ru₂(CO₃)₄(H₂O)Cl]Cl₂·2H₂O (2), K[Mg(H₂O)₅Ru₂(CO₃)₄]·5H₂O (3) and K[Mg(H₂O)₄Ru₂(CO₃)₄]·H₂O (4), were synthesized from the reaction of Ru₂(CO₃)₄³⁻ and Mg²⁺ in aqueous solution. Compound 1 is composed of ionic crystals with the Ru₂(CO₃)₄Cl₂⁵⁻ : Mg(H₂O)₆²⁺ : K⁺ ratio of 1 : 2 : 1. Compound 2 consists of two dimensional layer structures, in which each octahedral environment Mg(H₂O)₄²⁺ bonds to two [Ru₂(CO₃)₄(H₂O)Cl]⁴⁻ units in a cis manner forming a neutral square-grid layer {Mg(H₂O)₄Ru₂(CO₃)₄(H₂O)Cl}_n. For compound 3, one water molecule of each Mg(H₂O)₆²⁺ is substituted by an oxygen atom of Ru₂(CO₃)₄³⁻ forming [Mg(H₂O)₅Ru₂(CO₃)₄]⁻, and then the neighboring Ru₂ dimers are linked together by the rest of the two oxygen atoms of carbonates to form a layer structure {Mg(H₂O)₅Ru₂(CO₃)₄}_nⁿ⁻. In compound 4, the neighboring squared-grid layers {Ru₂(CO₃)₄}_n³ⁿ⁻, similar to those in compound 3, are linked by each octahedral environment Mg(H₂O)₄²⁺ in a cis manner forming the three-dimensional network {Mg(H₂O)₄Ru₂(CO₃)₄}_nⁿ⁻. Compound 3 shows ferromagnetic coupling between Ru₂ dimers, and a long-range ordering is observed below 3.8 K. Compound 4 displays a magnetic ordering below 3.5 K, and a systematic study of the size-dependent magnetic properties of compound 4 reveals that the coercivity of 4 has been improved with reduced sample particle size from the micrometer to the nanometer scale.