Synthesis and characterization of the mixed-valent complex ion di-μ-oxobis( 1,4,8,11-tetraazacyclotetradecane)dimanganese(III, IV), [(cyclam)MnO] 23+

Abstract

The synthesis and characterization of several salts of the mixed-valence binuclear cation [(cyclam)MnO] 2 3+, where cyclam is 1,4,8,11-tetraazacyclotetradecane, are reported. The bromide salt, [(cyclam)MnO] 2Br 3·4H 2O, crystallizes in the monoclinic space group P2 1/ n with two molecules in a cell of dimensions a = 9.903(3), b = 11.565(3), c = 14.927(4) Å, β = 107.87(2)° at −100 °C. Consequently, the two manganese centers are crystallographically equivalent. An analysis of the anisotropic displacement parameters ( U ij ), coupled with evidence from other experiments, demonstrates a static disorder in the crystals between chemically inequivalent Mn(III) and Mn(IV) sites. The structure has been refined to a weighted R factor of 0.0378 based on 2368 independent intensities. The manganese-manganese separation in the dimer is 2.731(2) Å. The dithionate salt crystallizes in the monoclinic space group P2 1/ a with four molecules in a cell of dimensions a = 15.216(3), b = 11.716(4), c = 18.745(6) Å, β = 92.49(2)° at −100 °C. The complex crystallizes with two independent centrosymmetric dimers in the cell, but again this is due to a static disorder in the crystals. Disorder about one of the dithionate ions fits a model in which some of the dithionate ion has been converted to thiosulfate. The Mn-Mn separations are 2.729(5) and 2.738(5) Å. The EPR spectrum of the complex at 4 K shows the sixteen line pattern commonly observed in di-μ-oxodimanganese(III,IV) complexes. The magnetic susceptibility of the complex demonstrates that the complex has a doublet ground state, exhibiting antiferromagnetic coupling with 2 J = −237 cm −1.