UNEXPECTED ASSEMBLY OF A (MU-OXO)(MU-FORMATO)DIIRON(III) COMPLEX FROMAN AEROBIC METHANOLIC SOLUTION OF FE(III) AND THE TPA LIGAND

Crystals of a (mu-oxo)(mu-formato)diiron(III) complex [Fe-2(mu-O)(TPA) (2)(O2CH)](ClO4)(3) (1) formed from a methanolic solution of Fe(ClO4)( 3) and the tetradentate tripodal ligand tris(2-pyridylmethyl)amine (TP A) in methanol when left standing for days under aerobic conditions, d espite the fact that no formate ion had been added to the solution. Co mplex 1 was found to have UV-Vis and H-1 NMR properties very similar t o those of [Fe-2(mu-O)(TPA)(2)(O2CCH3)](ClO4)(3) (2), and its formula weight was corroborated by fast atom bombardment mass spectrometry. Co mplex 1 crystallized in the monoclinic space group P2(1) (No. 4) with a = 11.693(3), b = 10.414(4), c = 18.144(6) Angstrom, and beta = 93.98 (3)degrees. The structure was determined at -84 degrees C from 4464 ou t of a total of 6753 reflections with R = 0.058 and R-w = 0.068. The c rystal structure confirmed the presence of a (mu-oxo)(mu-carboxylato)d iiron(III) unit with distinct iron sites as found for 2. The formate b ridge was shown to derive from the aerobic oxidation of methanol; 1 wa s not formed in the absence of air, and 2 was formed from the reaction carried out in ethanol solvent. Manometric measurements showed that t he amount of dioxygen consumed was approximately stoichiometric to the combined amounts of for-mate found in 1 (80%) and formaldehyde (20%) found in the reaction mixture. (C) 1998 Elsevier Science S.A, All righ ts reserved.