Syntheses and characterization of novel binuclear chromium (III) complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam)

Abstract

The syntheses and characterization of novel binuclear chromium (III) complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) are described. The complex [(cyclam)Cr(OH)] 2Cl 4 · 7H 2O ( 1) crystallizes in the monoclinic space group C2/ c with four binuclear formula units in a cell of dimensions a = 17.403 (2), b = 16.803 (3), c = 12.708 (2) Å, and β = 100.83 (1)°. The cation in 1 consists of di-μ-hydroxodichromium (III) units. The bridging OH groups lie on a twofold axis, which relates one end of the dimer to the other and gives rise to a rigorously planar Cr 2O 2 bridging unit. The Cr⋯Cr separation is 3.122 (1) Å and the average bridging Cr–O–Cr angle is 104.6 (4)°. The complex [(cyclam)Cr(SO 4)] 2 (ClO 4) · H 2O ( 5) crystallizes in the monoclinic space group P2 1/ c with two binuclear formula units in a cell of dimensions a = 9.516 (2), b = 13.263 (3), c = 14.870 (3) Å, and β = 104.08 (3)°. This cation consists of bis-μ-sulfato-di-chromium (III) units, in which the two chromium centers are bridged by two bridging sulfate groups leading to an eight-membered {Cr–O–S–O} 2 bridging framework. Both dimers exhibit antiferromagnetic interactions, with J = 27.7 cm −1 for complex 1 and J = 4.7 cm −1 for complex 5. The EPR spectrum of the complex 1 has been simulated, demonstrating that the spectrum almost entirely originates from the quintet state, while a few lines can be attributed as triplet and septet transitions.