Synthesis, characterization, and magnetic properties of new complexes based on self-assembled homotrinuclear units CuII–CuII–CuII

Abstract

Three new supramolecular entities of Cu^II have been synthesized and characterized: [Cu₂(H₂O)₂(tmen)₂(μ-Cu(H₂O)(pba))](PF₆)₂ (1), [{Cu₂(H₂O)(tmen)₂(μ-Cu(pba))}(μ-SeCN)]_n(ClO₄)_n·2nH₂O (2) and [{Cu₂(H₂O)(tmen)₂(μ-Cu(pba))}(μ-SeCN)]_n(PF₆)_n·2nH₂O (3), where pba = 1,3-propanediylbis(oxamato) and tmen = N,N,N′N′-tetramethylethylenediamine. The crystal structures of 1 and 2 were solved. Complex 1 is the precursor of 3; complex 2 is derived from the ClO₄⁻ analogue of 1. The two complexes have a central core in common: a trinuclear Cu^II complex with the two terminal Cu^II ions blocked by N,N,N′N′-tetramethylethylenediamine and with the same environment in the Cu^II central atom. In the case of complex 1, the structure is a double chain of trinuclear entities linked by hydrogen bonds owing to coordinated water molecules. In the case of complex 2, the selenocyanate ligands produce intermolecular linkages giving a one-dimensional system. The counter anions PF₆⁻ and ClO₄⁻ do not participate directly in the formation of the supramolecular entities. For complex 3 we propose a one-dimensional structure such as found for complex 2. The magnetic properties of the three complexes were studied by susceptibility measurements vs. temperature; a fit was made by the irreducible tensor formalism (ITO). The values obtained were: J₁ = −342.1 cm⁻¹, J₂ = 0.61 cm⁻¹ for 1, J₁ = −282.2 cm⁻¹, J₂ = 2.6 cm⁻¹ for 2 and J₁ = −245.4 cm⁻¹, J₂ = 1.3 cm⁻¹ for 3.