Coordination geometries and crystal structures of cadmium(II) complexes with a new amino alcohol (NN′O) ligand

Abstract

The new ligand 2-(2-(2-hydroxyethylamino)ethylamino)cyclohexanol, (HEAC), was prepared under microwave conditions through ring opening of cyclohexene oxide with 2-(2-amino-ethylamino)ethanol. Its cadmium(II) complexes [Cd2(HEAC)2(μ-Cl)2Cl2] (1) and [Cd(HEAC)2][CdI4] (2) were identified by elemental analysis, FT-IR, Raman, 1H NMR spectroscopies, and single-crystal X-ray diffraction. HEAC formed 1 : 1 M : L complexes with cadmium chloride and cadmium iodide. Complex 1 crystallized as a dimer with two asymmetrically bound bridging Cl− and a terminally coordinated Cl− on each metal. The geometry around the cadmiums in 1 with four five-membered chelate rings and four Cl− ligands is distorted octahedral for each Cd(II). The cyclohexanol OH of each ligand forms intramolecular hydrogen bonds. In 2, the coordination numbers for cadmium in [Cd(HEAC)2]2+ and [CdI4]2− moieties are six and four, respectively. In [Cd(HEAC)2]2+ each ligand coordinates through two N- and one O-donors, leading to a distorted octahedral geometry. The geometry of [CdI4]2− in 2 is slightly distorted tetrahedral. The protonation equilibrium constants of the two secondary amino groups in HEAC, determined by pH-potentiometry, were 6.26 and 9.26, respectively, at 25°C. Stability constants for this ligand with Ni(II), Cu(II), and Zn(II) (1 : 1 M : L), determined by glass-electrode potentiometry, were 7.13, 10.50, and 5.42, respectively.