Syntheses, structures and magnetic properties of two copper(II) tricyanomethanide complexes with 2,2′-bipyrimidine as bridging ligands

Two copper(II) tricyanomethanide (tcm) complexes with 2,2′-bipyrimidine (bpym) as co-ligands Cu₄(bpym)₅(tcm)₈ · 2H₂O (1) and [Cu₂(bpym)₂(tcm)₄ · H₂O]_n (2) have been synthesized, and structurally and magnetically characterized. Compound 1 displays a tetranuclear structure, in which each middle copper(II) atom is coordinated by two bridging bpym molecules and two terminal tcm ligands to form a tetragonal bipyramidal geometry, while each side copper(II) atom is surrounded by one bridging bpym, one terminal bpym, one terminal bonded tcm and one terminal weakly coordinated tcm ligands to give a square bipyramidal geometry. In 1 the four neighbouring copper(II) atoms are joined to each other by the bpym molecules, which leads to the formation of a tetranuclear structure. Compound 2 features an infinite chain structure, in which two slightly different chains exist. In each chain the copper(II) atom is bonded to two bridging bpym molecules and two terminal tcm ligands to form a tetragonal bipyramidal geometry, the adjacent copper(II) atoms are linked each other by the bpym ligands to define an infinite chain structure. In 2 the distances between two neighbouring copper(II) atoms in one chain are different. Moreover these distances in one chain are also different from those of the other chain. Magnetic susceptibility measurements for the two complexes in the temperature range 2-300 K reveal the occurrence of significant antiferromagnetic interactions for 1 (J₁ = -20.42 cm^-1, J₂ = -5.29 cm^-1 and g = 2.22) and 2 (T > 50 K, θ = -20.00 K, C = 0.86 cm³ mol^-1 K), respectively.