Physical and chemical properties of squarate complexes. II. Mössbauer spectroscopy and magnetic susceptibility studies of several dimeric and trimeric iron(III) complexes containing the squarate dianion

Abstract

Products obtained by the reaction of certain bases with μ-dihydroxo-bis[squaratodiaquoiron(III) dihydrate, [Fe(C 4O 4)(H 2O) 2(OH)] 2·2H 2O, I, have been isolated and studied by the complementary methods of 57Fe Mössbauer spectroscopy and magnetic susceptibility. Reaction of I with pyridine or substituted pyridine bases gives materials with formula [Fe(C 4O 4)(L) 2(OH)] 2·2H 2O where L = pyridine, 4-methylpyridine, or 3-methylpyridine. The Fe 2(OH) 2 bridging unit is maintained in these complexes as evidenced by their variable-temperature magnetic susceptibility behavior. The data are very well described with a HDVV S 1= S 2 = 5 2 dimer model where J ≅−8 cm −1 and g = 2.00. Dimethylsulfoxide (DMSO) reacts with I to give a μ 3-oxo complex containing coordinated DMSO, [Fe 3O(C 4O 4) 3(DMSO) 3(H 2O) 3](OH). Magnetic susceptibility data for this complex are analyzed with a HDVV S 1 = S 2 = 5 2 trimer model by assuming equivalent spin sites. Results of this analysis give J = −39 cm −1 and g = 2.00. The proposed trimeric structure of this complex is also inferred from the presence of a strong infrared absorption near 550 cm −1 assigned to the FeO stretching mode, V asym(Fe 3O). Reaction of I with KOH in ethanol yields a material whose magnetic susceptibility versus temperature behavior is indicative of a S 1 = S 2 = 5 2 dimer with J = 96 cm −1 and g = 2.00. Presence of a strong infrared absorption at 820 and 750 cm −1, assigned to the FeOFe stretching mode,v asym(Fe 2O) is additional evidence for the proposed μ-oxo structure for this complex, [Fe(C 4O 4)(H 2O) 2] 2O. Mössbauer spectral parameters for these ferric squarate complexes are consistent with proposed structures.