Solvent controlled nuclearity in Cu(ii) complexes linked by the CO32−ligand: synthesis, structure and magnetic properties

Abstract

Two new carbonato-bridged copper complexes with different nuclearity have been synthesized and structurally characterized through X-ray diffraction analyses: the tetranuclear complex [Cu^II₄(μ₄-CO₃)(μ-Cl)₂(dpt)₄](ClO₄)₄·3 MeOH, 2·3MeOH and the trinuclear [Cu^II₃(μ₃-CO₃)(ClO₄)₂(dpt)₃(OH₂)](ClO₄)₂·H₂O, 3·H₂O (dpt is bis(3-aminopropyl)amine). A rationalisation for the synthetic pathways that lead to the formation of tri- and tetra-nuclear complexes is described, proving that 2 is an intermediate to generate 3. For the tetranuclear complex 2·3MeOH, this report represents the first accurate and rigorous synthetic and structural description of this type of complex. For the trinuclear complex 3·H₂O, it constitutes the first example of an asymmetric trinuclear μ₃-carbonato bridged complex. Magnetic susceptibility data were fitted according to the molecular structures using the following Hamiltonians: H = −J₁₂S₁S₂ − J₁₃(S₁S₃ + S₂S₄) − J₁₄(S₁S₄ + S₂S₃) − J₃₄S₃S₄, which corresponds to a rectangular array of spins for 2·3MeOH, and H = −J(S₁S₂ + S₂S₃ + S₁S₃), which corresponds to a triangular array of spins, corrected with a J′ intertrimer coupling or ZFS parameter to fit low T data, for 3·H₂O. The best fit parameters obtained were J₁₂ = −189.9 cm⁻¹, J₃₄ = −22.2 cm⁻¹, J₁₄ = −60.0 cm⁻¹, J₁₃ = 15.0 cm⁻¹, g = 2.18 and with R = 1.2 × 10⁻⁷ for 2·3MeOH and J = 13.89 cm⁻¹, J′ = −0.07 cm⁻¹ and g = 2.1 with R = 5.3 × 10⁻⁴ for 3·H₂O.