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

Abstract (E)-N-Benzylidenepicolinohydrazide (Hbphz) was used to synthesize a series of hydrazonato-bridged homodinuclear LnIII2 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 LnIII centers in the μ − 1 κ2N(py),O:2 κ2O,N(imine) mode and two RR′dtc ligands coordinated to each LnIII center. Interestingly, while the SmIII and EuIII complexes crystallized as simple 8:8-coordinate dinuclear molecules, the lighter LnIII (i.e. LaIII, PrIII and NdIII) 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 LnIII 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.