Spontaneous symmetry breaking in the formation of a dinuclear gadolinium semiquinonato complex: Synthesis, high-field EPR studies, and magnetic properties

The synthesis and characterisation of an asymmetric dinuclear gadolinium(II I) semiquinonato complex, namely [Gd-2(HBPz(3))(2)(dtbsq)(4)]. CHCl3 (1: HB Pz(3) = hydrotris(pyrazolyl)borate, dtbsq = 3,5-di-tert-butyl-o-semiquinone ), is reported. The crystal structure of 1 was determined at room temperatu re. It crystallises in the triclinic system P (1) over bar, with a=16.735(5 ) Angstrom, b = 17.705(5) Angstrom, c = 19.553(5) Angstrom, alpha = 99.680( 5)degrees, beta = 109.960(5)degrees, gamma = 107.350(5)degrees, Z=2 and R=9 .96. The structure of 1 consists of a dinuclear asymmetric unit in which th e two gadolinium(III) ions have coordination numbers of eight and nine. Thr ee of the dioxolene molecules act as asymmetric bridging ligands, while the fourth molecule behaves as a bidentate ligand towards a single metal ion. The magnetic properties of 1 were investigated by means of susceptibility m easurements and high-field electron paramagnetic resonance (HF-EPR) spectro scopy. They revealed an S=0 ground spin stale with excited states of higher spin very close in energy and a small negative zero-field splitting with a transverse anisotropy term for a S=7 state.