EARLY-AND LATE-LANTHANIDE PYRIDINETHIOLATES - SYNTHESIS, REDOX STABILITY, AND STRUCTURE

The early and late lanthanides form stable complexes with the pyridine thiolate (2-S-NC5H4, or Spy) ligands. The Ce compound Ce(SPy)(3) is re latively insoluble in neutral organic donor solvents such as THF or py ridine but can be solubilized by the addition of [PEt4][SPy] to form t he orange homoleptic cerium thiolate [PEt4][Ce(SPy)(4)] (1). Low-tempe rature structural characterization of 1 showed that the complex is iso structural with the known Eu(III) derivative, Further oxidation of Ce( III) with dipyridyl disulfide does not occur. Molecular 1 is coloured due to a low-energy f(1)-to-d(1) promotion. As the size of the lanthan ide ion decreases, the solubility of neutral Ln(SPy)(3) appears to inc rease, Colorless [PEt4][Ln(SPy)(4)] (Ln = Ho (2), Tm (3)) can also be isolated by fractional crystallization, and the compounds are isostruc tural with the Ce and Eu derivatives. The neutral complexes of Ho and Tm are also slightly soluble in acetonitrile and dimethoxyethane and v ery soluble in pyridine. Both divalent and trivalent Yb complexes of t he pyridinethiolate ligand dissolve in and crystallize from pyridine. Divalent Yb(SPy)(2) crystallizes as the pentagonal bipyramidal molecul e (py)(3)Yb(SPy)(2) (4). One pyridine nitrogen and the four donor atom s of the two pyridinethiolate ligands are bound in equatorial position s, and two neutral pyridine ligands occupy the axial sites. The Yb(III ) compound crystallizes readily from pyridine as molecular 8-coordinat e (py)(2)Yb(SPy)(3) (5). Compounds 4 and 5 are intensely coloured; 4 h as a visible Yb(II)-to-pyridine charge transfer excitation that is vir tually identical in energy to the analogous excitation in SmI2(py)4, w hile 5 has a visible S-to-Yb charge transfer absorption. Crystal data (Mo K alpha, 153(5) K) are as follows: 1, monoclinic space group P2/n, a = 15.115(6) Angstrom, b = 16.117(4) Angstrom, c = 26.443(7) Angstro m, beta = 90.14(3)degrees, Z = 4; 4, monoclinic space group Cc, a = 10 ,588(1) Angstrom, b = 16.810(3) Angstrom, c = 14.833(5) Angstrom, beta = 109.1(2)degrees, Z = 4; 5, monoclinic space group P2(1)/n, a = 9.87 2(2) Angstrom, b = 16,293(4) Angstrom, c = 19.214(3) Angstrom, beta = 101.51(2)degrees, Z = 4.