Add time:08/23/2019         Source:sciencedirect.com

The preparation of stable Lewis base adducts of CuL (H2L=Schiff base derived from the condensation of o-hydroxypropiophenone (OHP) and salicylhydrazide (SHZ)) is described. The N-donors bipy and bipyam ligands (bipy=2,2′-bipyridyl; bipyam=2,2′-bipyridylamine) give the complexes [Cu(OHP-SHZ)(bipy)] (I) and [Cu(OHP-SHZ)(bipyam)]H2O (II) which have been characterized by physical and spectroscopic techniques. Crystals of I are orthorhombic, space group Pcab, with a=10.221(3), b=12.643(3), c=35.448(3) Å, V=4581(2) Å3 and Z=8. The structure of complex I is shown to comprise discrete monomeric [Cu(OHP-SHZ)(bipy)] molecules in which the Cu(II) atom environment exhibits a highly distorted five-coordinated geometry. Crystals of II are monoclinic, space group C2/c, with a=24.804(3), b=13.231(3), c=14.739(3) Å, β=99.57(2)°, V=4770(2) Å3 and Z=8. The structure of this complex consists of discrete entities associated into H-bonded binuclear units via the lattice water molecules. The coordination sphere around the copper center is nearly square pyramidal. The transition from a six-membered chelated ring to a five-membered one results in a less distorted coordination polyhedron around the Cu(II) ion. In both complexes the OHP-SHZ ligand occupies three of the coordination sites through the same (ONO) donor atoms while the remaining positions are occupied by the pyridine N atoms. EPR spectra provide evidence of the existence of very weak magnetic exchange coupling in the complex [Cu(OHP-SHZ)(bipyam)]H2O (II). Thermogravimetric and differential scanning calorimetric studies of complex I show that this complex loses the bipy molecule through an endothermic process with ΔH=81.75 kJ mol−1. The best kinetic parameter values corresponding to the process involving the loss of the bipy molecule were found on the basis of the agreement between non-isothermal and isothermal methods and are given by the Abou-Shaaban–Simonelli equation in isothermal conditions. The better representation of the reaction mechanism is the phase-boundary, spherical symmetry reaction.

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