Trinuclear Complex Compounds of Iron(III) with Some α-Amino Acids: Synthesis and Physicochemical Studies

Six new compounds of general formula [Fe(3)O(A)(6)(H(2)O)(3)]NO(3) center dot nH(2)O, where A = Gly(-), n = 3 (I); A = Ala(-), n = 4 (II); A = Val(-), n = 2 (III); A = Met(-), n = O (IV); A = Leu(-), n = 1 (V); and A = Trp(-), n = 5 (VI), are synthesized by substituting the acetate radicals in (mu(3)-oxo) hexakis(mu-acetato-O,O')-triaquotriiron(III) nitrate with anions of various alpha-amino acids. The Mossbauer parameters of the complexes (T = 300 K, delta(Na+) = 0.63-0.64 mm/s, Delta E(Q) = 0.62-0.76 mm/s; and T = 80 K, delta(Na+) = 0.71-0.74 mm/s, Delta E(Q) = 0.73-0.82 mm/s) are indicative of the presence of the iron(III) ions in high-spin state. The temperature dependence (300-102 K) of magnetic susceptibility of I-VI satisfactorily fits the Heisenberg-Dirac-van Vleck model for the three iron ions (S(1) = S(2) = S(3) = 5/2) occupying vertices of the isosceles triangle (C(2v) symmetry) and coupled to one another through the exchange interaction with parameters (cm(-1)): J(1) = -37.36 and J(2) = -51.42 (I); J(1) = -16.18 and J(2) = -28.42 (II); J(1) = -17.74 and J(2) = -36.45 (III); J(1) = -16.51 and J(2) = -33.93 (IV); J(1) = -12.97 and J(2) = -27.11 (V); and J(1) = -27.08 and J(2) = -39.27 (VI). The thermal analysis data suggest the low thermal stability of the compounds (T(onset) = 30-60 degrees C with following stepwise decomposition).