SYNTHESIS, CHARACTERIZATION AND THERMAL STUDIES OF BIS(2-AMINOETHYL)METHYLAMINE(MEDIEN) COMPLEXES OF CADMIUM(II) - SINGLE-CRYSTAL STRUCTUREOF CD(MEDIEN)I-2

[Cd(medien)(m)]X-2. nH(2)O [where medien is bis(2-aminoethyl)methylami ne, m=2 and n=0 when X is Cl- (1), Br- (2), I- (3), NCS- (4) and NO3- (5); m=1 and n=0 when X is Cl- (1a), Br- (2a) and I- (3a); m=2 and n=3 when X is 0.5SO(4)(2-) (6) and 0.5SeO(4)(2-) (7); m=1 and n=1 when X is 0.5SO(4)(2-) (6a) and 0.5SeO(4)(2-) (7a)] have been synthesized fro m solution and investigated thermally in the solid slate. Cd(medien)X- 2 [X=Cl- (1b), Br- (2b), I- (3a), 0.5SO(4)(2-) (6c) and 0.5SeO(4)(2-) (7c)] have been synthesized in the solid slate pyrolytically from thei r corresponding parent bis complexes. Upon heating, Cd(medien)Cl-2 (1a ) and Cd(medien)Br-2 (2a) undergo an endothermic irreversible phase tr ansition [185-200 degrees C, Delta H = 6.5 kJ mol(-1) for Cd(medien)Cl -2; 190-210 degrees C, Delta H= 6.7 kJ mol(-1) for Cd(medien)Br-2]. [C d(medien)(2)](NCS)(2) shows two reversible phase transitions in the te mperature ranges 94-102 and 155-162 degrees C, having Delta H values o f 6.3 and 6.8 kJ mol(-1), respectively. [Cd(medien)(2)](NO3)(2) also s hows a reversible endothermic phase transition on heating (166-177 deg rees C, Delta H = 31.4 kJ mol(-1); 137-127 degrees C, Delta H = -29.0 kJ mol(-1)). The transitions are assumed to be due to the conformation al changes in the triamine chelate rings. A comparison of the thermal stabilities of bis(2-aminoethyl) amine (dien) and bis(2-aminoethyl)met hylamine(medien) complexes of cadmium(II) shows that T-i (the initial temperature of decomposition) decreases on methyl substitution on the secondary amine nitrogen atom of bis(2-aminoethyl)amine. All the bis t riamine complexes are proposed to exist in s-fac octahedral geometry. The single-crystal structure of Cd (medien)I-2 reveals that the coordi nation of cadmium is five-fold. Two nitrogen atoms of the ligand, toge ther with one of the two iodine atoms, constitute the basal plane of a distorted trigonal bipyramid. Another nitrogen atom of the ligand and the second iodine atom at apical positions are located at a distance of -.086(6) and 3.190(1) Angstrom, respectively, from the basal plane.