Crystal and molecular structure and spectral properties of the dimeric alkoxo-oxygen coordinated copper(II) complex formed with 2-diethylaminoethanol and 3-hydroxobenzoic acid

Abstract

The crystal and molecular structure of [Cu 2(C 6H 14NO) 2(3-OH·C 6H 4COO) 2] has been determined by three dimensional X-ray crystallography. The complex crystallizes in the monoclinic space group P2 1/ n with a = 8.733(5), b = 21.670(19), c = 15.270(10) Å, β = 96.14(5)°, Z = 4. The structure was solved by direct methods and refined to the R values 0.057 and 0.052 using 2043 independent reflections. The C atoms of the 2-diethylaminoethanolato ligands are disordered through having one or more rotational orientations. Each Cu(II) ion has a distorted elongated square- pyramidal environment (4 + 1). Two alkoxo O atoms, a benzoato O atom and an amino N atom form the basal plane with CuO bonds of 1.885–1.935 Å and a CuN bond of 1.984(8)–2.023(6) Å, and the axial site is occupied by a phenolic O atom with a CuO distance of 2.562(6) or 2.808(6) Å. The CuCu distance in the non-centrosymmetric dimer is 2.958- (2)Å. The dimers are joined into a one-dimensional polymeric chain in the direction of the c-axis by phenolic O atoms. These form long bonds to the Cu(II) ions and strong hydrogen bonds to the uncoordinated carboxylate O atoms. The electronic spectrum in Nujol shows a broad flat band, centred at about 16000 cm −1 with a shoulder at 27000 cm −1. The broad band is attributed to d-d transitions and the shoulder to charge transfer from a p π orbital of the bridging O atom to the unfilled d orbital of the Cu(II) ion. The latter is a characteristic feature of the alkoxo-bridged structure. The IR spectrum shows the carboxylate stretching frequency ν(COO)(asym) as a broad band at 1550 cm −1, and ν(COO)(sym) as a broad band at 1390 cm −1 with a shoulder at 1375 cm −1. The known structures of copper(II) 2-dialkylaminoethanolato complexes are tabulated.