Synthesis, crystal structure determination and physical characterization of two new hybrid inorganic–organic salts associating the organic anion ABTS 2− and its radical anion ABTS [rad]− to the transition metal cations Fe 3+ or Cu 2+: Fe 2O(ABTS) 2(H 2O) 16 and Cu(ABTS) 2·(H 2O) 8

Abstract

Synthesis, crystal structure of two new ABTS (2,2-azinobis-3-ethyl benzothiazoline-6-sulfonate) hybrid organic–inorganic salts containing Fe 3+ or Cu 2+ cations is described. Electrochemical oxidation of the diammonium salt (ABTS)(NH 4) 2·2H 2O in presence of FeSO 4·7H 2O or CuSO 4·5H 2O in aqueous solutions yields to black single crystals of Fe 2O(ABTS) 2(H 2O) 16 and Cu(ABTS) 2·(H 2O) 8. Due to the low thermal stability of three water molecules intercalated in the network, crystal structures were solved at 200 K using a STOE IPDS diffractometer. Cell parameters are: a=8.5635(7) A ̊ , b=8.69236(6) A ̊ , c=20.336(2) A ̊ , α=84.69(1)°, β=82.10(1)°, γ=81.767(9)°, space group P-1 for the iron complex and a=15.691(3) A ̊ , b=14.474(3) A ̊ , c=21.552(4) A ̊ , β=94.60(3)°, space group P2 1/c for the copper complex. Transition metal cations are in an octahedral coordination with a different condensation, corner-sharing octahedra Fe 2O 11 dimmers or CuO 6 octahedra. Taking in account these structural results, the chemical formula must be written: [Fe 2O(H 2O) 10][ABTS] 2·6H 2O and [Cu(H 2O) 5][ABTS] 2·3H 2O. The crystalline networks are also different; the iron complex salt presents a bidimensional character and the copper one can be considered as a one-dimensional network. Values obtained from bond valence calculations correspond to iron Fe 3+ and copper Cu 2+. A Mossbauer study shows that iron is in a high spin 3 + oxidation state without any magnetic ordering even at 4 K (isomer shift δ=0.62 mm s −1 and quadrupole splitting Δ E=1.64 mm s −1).