Dinuclear lanthanoid(III) dithiocarbamato complexes bridged by (E)-N-benzylidenepicolinohydrazonate: Syntheses, crystal structures and spectroscopic properties

(E)-N-Benzylidenepicolinohydrazide (Hbphz) was used to synthesize a series of hydrazonato-bridged homodinuclear Ln^III₂ dithiocarbamato (RR′dtc⁻) complexes of the form [{Ln(RR′ dtc)₂}₂(µ-bphz)₂] {Ln = La, Pr, Nd, Sm or Eu; RR′ = dimethyl-(Me₂) or pyrrolidine-(pyr)}. X-ray crystallographic studies revealed that these complexes possessed a common head-to-tail type dinuclear structural motif in which two hydrazonato ligands bridged two Ln^III centers in the μ − 1 κ²N(py),O:2 κ²O,N(imine) mode and two RR′dtc ligands coordinated to each Ln^III center. Interestingly, while the Sm^III and Eu^III complexes crystallized as simple 8:8-coordinate dinuclear molecules, the lighter Ln^III (i.e. La^III, Pr^III and Nd^III) complexes afforded in some cases 9:9-coordinate molecules, where the ninth coordination site was occupied by a solvent ethanol or methanol molecule. Even for the lighter Ln^III complexes, the complexes were solved in dichloromethane or chloroform as the 8:8-coordinate dimer, as revealed by ¹H NMR spectroscopy. In the UV–visible absorption and magnetic circular dichroism (MCD) spectra of the complexes, similar spectral patterns for ligand-centered and Laporte forbidden f–f transitions were observed. The MCD spectral studies demonstrated the characteristic magneto-optical behavior of the complexes.