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 FeO 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 FeOFe 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.
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