Structural, spectroscopic and potentiometric investigation on the coordination properties of 4-NO 2-hippuric acid towards Cu(II) in binary and ternary systems

Abstract

The solid state and aqueous solution study on the binary and ternary system copper(II)-4-NO 2-hippuric acid is reported. The binary complex separated in the solid state is [Cu(4-NO 2-hip) 2(H 2O) 2] 2·4H 2O and the crystal structure has been determined. The compound is monoclinic, space group P2 1/ a, with cell dimensions a =7.289(3), b=44.25(1), c=7.344(7) Å, β = 102.05(6)°, Z = 2, R = 0.055 and R′= 0.053. The structure consists of dimeric penta-coordinated [Cu(4-NO 2-hip) 2(H 2O) 2] 2 units and lattice water molecules. The copper atom is coordinated by two 4-NO 2-hip anions acting as carboxylate ligands and two water molecules. One 4-NO 2-hip anion acts as monodentate ligand and the second acts as monodentate bridging ligand through one carboxylic oxygen which is an equatorial ligand for one copper atom and is the apical ligand for the second copper atom. In the ternary system with 2,2′-bipyridine (bpy) we separated mono-amine and bis-amine species, in that with 1,10-phenanthroline (ophen) only the mono-amine species was obtained. For the compound [Cu(bpy) 2(4-NO 2-hip)]·NO 3·H 2O the crystal and molecular structure was determined. The crystal is triclinic, space group P 1 , with cell dimensions: a = 10.162(2), b = 10.953(5), c = 13.651(2) Å, α=96.76(3), β=100.40(1), γ=96.19(3)°, Z=2, R=0.043 and R′=0.048. The copper atom is coordinated by the two bpy molecules and by the 4-NO 2-hip anion which acts as an asymmetrically bidentate ligand through the carboxyl group. The Cu-O(1) bond distance is normal, while the Cu-O(2) one is significantly longer (2.646(3) Å), so the geometry can be represented as (4+1+1*). On the basis of the ESR spectrum the copper(II) ground state is established as d x 2−y 2 . In solution the prevailing species are [CuL 2] in the binary, system, [CuAL 2] and [CuAL(OH)] in the ternary system.