Equilibrium, Kinetic and MechanisticStudies of Formation of Cis- mono (AA)bis (oxalato) Chromate (III) Complex (where AA is glycine, alanine and histidine)In Monderately Aqueous Acidic Solution

Equilrium, kinetic and mechanistic studies for the coordination of some amino acids AA; glycine, alanine, and histidine, to Cr (III) center of trans [Cr(ox)2(H20)2]~ {TI} complex in monderately acidic range of pH=4.8-6.7 (ju =0.4M NaN03) are reported. The equilibrium constants at 25°C were found, logKequ.=4.951,5.206and5.128for glycine, alanine, and histidine, ligation reactions respectively. The substitution reaction is kinetically involve two parallel complex reactions, each includes iheree different consecutive steps of different species of Cr(III). The reactant Ti, branches through hyrolysis into, doubly charged anion, conjugated base of trans[Cr(ox)2(H20)OH]^-2 which interacts with (AAH) to from outer-sphere complex, that is followed by interchange reaction of one molecule H2 0 with one end of AA ion from an active intermediate species of trans- [Cr(ox)2(AA)OH]^-3 which changes to final product ; cis- [Cr(ox)2(AA)r.While the remaining part of reactant interacts also with zwitter ion (AAH) on other side to form another outer-sphere complex which also undergoes interchange reaction of one molecule H2O with A A ion to give two active intermediates species, trans and cis-[Cr(ox)2(AA)H20] , which later convert to the same product; cis- [Cr(ox)2(AA)]2 The interchange rate constant of trans- [Cr(ox)2(AA)OH]^3- formation relatively appears much larger than (Delta H*=8.8kcal/mol) that of cis[Cr(ox)2( AA)H20]^2- formation ( Delta H*=14.0Kcal/mol), while the latter rate constant is nearly (formation ( Delta H*=14.0Kcal/mol), while the latter rate constant is nearly (5-10) time larger than that of trans-[Cr(ox)2(AA)H20]2^- formatio