Synthesis, crystal structure and physico-chemical studies of neodymium and erbium methoxides containing thienyl substituents

Two novel mononuclear neodymium alkoxides [Nd{OC(C14H11S2)}3(thf)3]·thf (9) and [Nd{OC(C16H13S)}3(thf)3]·thf (10) have been prepared by the reaction between Nd[N(SiMe3)2]3and the tertiary alcohols HO-C(C14H11S2) (3) and HO-C(C16H13S) (4). The geometry around the neodymium metal is almost octahedral with a facial ligand arrangement similar to [Nd{OC(C8H5S2)3}3(thf)3]·4thf (5), [Nd{OC(C4H3S)3}3(thf)3]·thf (7) and Er[OC(C4H3S)3]3(thf)3(8) (X-ray diffraction on single crystals). The cyclic voltammograms of a series of neodymium and erbium alkoxides indicate that the electrochemical properties are essentially dominated by the organic ligands. In comparison to the carbinols HO-C(C8H5S2)3(1), HO-C(C4H3S)3(2), HO-C(C14H11S2) (3) or HO-C(C16H13S) (4), the oxidation peak potentials of the thienyl units for the neodymium alkoxides [Nd{OC(C8H5S2)3}3(thf)3]·4thf (5), [Nd{OC(C4H3S)3}3(thf)3]·thf (7), [Nd{OC(C14H11S2)}3(thf)3]·thf (9) and [Nd{OC(C16H13S)}3(thf)3]·thf (10) are marginally shifted towards higher values by 0.03-0.10 V, whereas for Er[OC(C8H5S2)3]3(thf) (6) and Er[OC(C4H3S)3]3(thf)3(8) a decrease of these potentials is noticed. Repetitive cyclic voltammetry does not generate polymeric films for7-10, as found for the free organic ligands2-4. Contrarily, the mononuclear precursors [Nd{OC(C8H5S2)3}3(thf)3]·4thf (5) and Er[OC(C8H5S2)3]3(thf) (6) are electro-oxidized and electro-active polymer films are obtained and characterized. To investigate the positions of the excited states of the ligands, emission spectra of the carbinols1-4have been recorded. The luminescence studies of the neodymium alkoxides reveal an energy transfer from the ligand to the metal centre with a remarkable Nd emission efficiency upon ligand excitation in the case of5.