Heterometallic Co(ii)–Ru2(ii,iii) carbonates: from discrete ionic crystals to three-dimensional network

Abstract

An investigation of the reaction conditions influence on the self-assembling of Ru₂(CO₃)₄³⁻ paddle wheel precursors and Co²⁺ ions in aqueous solution has resulted in a series of Co–Ru₂ hetero-metallic complexes with different composition and dimensionality, namely [K_1/3{Co(H₂O)₆}_4/3{Ru₂(CO₃)₄(H₂O)₂}]·2H₂O (1), [KCo(H₂O)₅Ru₂(CO₃)₄]·5H₂O (2), and [KCo(H₂O)₄Ru₂(CO₃)₄]·H₂O (3). These complexes exhibit dimensional diversity due to the various linking modes of Co²⁺ ions. X-Ray structural analysis reveals that complex 1 is composed of ionic crystals with the Ru₂(CO₃)₄³⁻ : Co(H₂O)₆²⁺ : K⁺ ratio of 3 : 4 : 1. For complex 2, one water of each Co(H₂O)₆²⁺ is substituted by one oxygen of Ru₂(CO₃)₄³⁻ forming [Co(H₂O)₅Ru₂(CO₃)₄]⁻, then the neighboring Ru₂(CO₃)₄³⁻ units are connected to each other through the remaining two carbonate oxygen atoms forming a negative square-grid layer [Co(H₂O)₅Ru₂(CO₃)₄]_nⁿ⁻. In complex 3, two water molecules of each Co(H₂O)₆²⁺ are substituted by the oxygen atoms of Ru₂(CO₃)₄³⁻ units, which are connected to each other forming the square-grid layer [Ru₂(CO₃)₄]_n³ⁿ⁻ similar to that in 2, then Co(H₂O)₄²⁺ ions bond to neighboring [Ru₂(CO₃)₄]_n³ⁿ⁻ layers in a cis mode forming the three-dimensional network [Co(H₂O)₄Ru₂(CO₃)₄]_nⁿ⁻. Complex 2 exhibits ferromagnetic coupling between Ru₂⁵⁺ and Co²⁺, and long-range ordering is observed below 5.0 K. In contrast, complex 3 with a 3-D sublattice displays spin-glass behavior with the coexistence of spin-canting with magnetic ordering at 4.7 K.