Synthesis, crystal structures and magnetism of planar and roof-shaped hydroxo-bridged dinuclear copper(II) compounds with di-2-pyridylamine as a ligand

Abstract

The compounds [Cu(dpyam)(OH)Br] 2(H 2O) 4 ( 1), [Cu(dpyam)(OH)(CF 3SO 3)] 2 ( 2) and [Cu 2(dpyam) 2(OH) 2(OH 2)]Br 2(H 2O) 2 ( 3) have been synthesized and their crystal structures determined by X-ray crystallographic methods. Compound 1 crystallises in the triclinic system, space group P 1 ̄ . The lattice constants are a=8.892(1), b=9.346(1), c=9.358(1) Å, α=112.2(1), β=108.3(1), γ=95.8(2)° with Z=1 and R 1=0.0292. Compound 2 crystallises in the triclinic system, space group P 1 ̄ . The lattice constants are a=8.1616(5), b=9.4156(6), c=10.2921(6) Å, α=72.58(2), β=72.48(4), γ=73.19(2)° with Z=1 and R 1=0.0595. Crystals of 3 are orthorhombic with space group Cmc2 1. The lattice constants are a=15.979(1), b=8.550(1), c=18.237(1) Å with Z=4 and R=0.0623. Compound 1 contains a dinuclear [Br(dpyam)Cu(OH) 2Cu(dpyam)Br] unit with a dihedral angle between the CuO 2 planes of 179.9°. Each copper atom is in a square-pyramidal coordination environment; the basal plane consists of two bridging hydroxo groups and two dpyam ligands coordinated through their nitrogen atom. The fifth axial coordination site of each copper(II) ion is occupied by a Br atom, at a weak semi-coordination distance of 2.803(2) and 2.804(2) Å. For compound 2, the coordination geometry around each copper(II) ion is distorted elongated octahedral, CuN 2O 4. The equatorial positions are occupied by the two nitrogen atoms of dpyam and the two oxygen atoms of the bridging hydroxo groups, where the apical positions are occupied by oxygen atoms from both triflate groups. In the dinuclear units of compound 3 the triply-bridged Cu(II) ions show a distorted square pyramidal coordination. The fifth apical ligand is a longer bonded bridging water molecule for 3, at distances of 2.220(2) Å, which joins the basal CuN 2O 2 planes in a roof-shaped configuration (dihedral angle 135.8 o). The CuCu distances are 2.993(2), 2.964(2) and 2.849(2) Å for compounds 1, 2 and 3, respectively. The magnetic susceptibility measurements revealed a ferromagnetic interaction between the Cu(II) atoms for compound 2, with a singlet–triplet energy gap ( J) around 83 cm −1. Compound 1 has an antiferromagnetic interaction with a J of −48.6 cm −1, whereas compound 3 is very weakly antiferromagnetic with J=−0.6 cm −1.