MOLECULAR PRECURSORS TO LANTHANIDE(II)-BASED SEMICONDUCTORS - SYNTHETIC PATHWAYS TOWARD THE PREPARATION OF LANTHANIDE MONOCHALCOGENIDE PRECURSORS

We describe the preparation of homoleptic complexes of divalent europium, samarium, ytterbium, and lead and tetravalent tin with selenolates and tellurolates incorporating bully aryl substituents, and the characterization of these complexes by H-1, C-13, Se-77, Pb-207, Te-125, and Yb-151 NMR spectroscopy and magnetic measurements. All derivatives Ln(QR)(2)(solv)(x) (Ln = Eu, Sm, Yb; Q = Se, Te; R mesityl, supermesityl) can be prepared by transmetalation of LnX(2)(THF)(3) (X = Br, I) with the potassium salt of the arylselenolate or -tellurolate anions. NMR studies suggest that these complexes exist as monomers in solution down to -60 degrees C. Ytterbium selenolates can also be prepared by the reaction of the divalent ytterbium amide Yb[N(TMS)(2)](2)DME(2) with organoselenols, but this route leads to some oxidation of ytterbium to ytterbium(III) and is therefore less satisfactory than the transmetalation route. Pb(SeMes)(2) (Mes = 2,4,6-trimethylphenyl) can be prepared by reaction of lead(II) acetylacetonate with mesitylselenol, and Sn(TeMes)(4) by transmetalation of SnX(2) (X = Cl, Br) with the potassium salt of mesityltellurolate; in these syntheses, no reduction of tin or lead to the zerovalent metals is seen, unlike other attempted synthetic routes to these complexes.