Structural, spectral and magnetic investigations of various types of compounds and their isomers isolated from the system copper(II)–C(CN)3––pyrazole

Abstract

From the system Cu^II–C(CN)₃^––Hpz (Hpz = pyrazole) the following compounds were isolated: [Cu{C(CN)₃}(Hpz)₄][C(CN)₃]1, [Cu{C(CN)₃}₂(Hpz)₃]2, α-[Cu{C(CN)₃}₂(Hpz)₂]3, β-[Cu{C(CN)₃}₂(Hpz)₂]4 and [Cu{Hpz·C(CN)₃}₂]5. They were studied by the use of spectroscopic and cryomagnetic methods. The structures of 1 and 2 were refined to R values of 0.0369 and 0.0374 for 1346 and 2066 independent reflections respectively. Compound 1 crystallises in space group P2₁/c, with a= 9.568(4), b= 16.692(7), c= 14.957(9)Å, β= 94.05(4)° and Z= 4; 2 crystallises in space group P, with a= 7.607(4), b= 8.942(6), c= 16.027(10)Å, α= 95.95(6), β= 90.83(5), γ= 106.88(5)° and Z= 2. Both compounds show elongated pseudo-octahedral copper environments, with the Hpz molecules in the equatorial plane. In 1 one C(CN)₃ group bridges the Cu^II atoms in axial positions while the second group is anionic. Compound 2 contains mono- as well as bi-dentate bridging C(CN)₃ groups; the latter join the basic structure units into binuclear species. Weak ferromagnetic coupling operates between the copper(II) centres inside the dimers. Physical measurements show that compounds 3 and 4 display rhombic octahedral arrangements around Cu^II in which all C(CN)₃ groups are bridging. The α and β compounds are distortion isomers. Compound 5, a coligand isomer with respect to 3 and 4, contains new anionic chelate ligands, HNC(pz)CH(CN)₂^–, formed by nucleophilic addition. In all these three compounds polymeric chains are present in which and between which there is magnetic interaction.