Lanthanide-mercury amalgams react with diphenyl diselenide to form tris(benzeneselenolates) that can be isolated as the crystalline pyridine coordination complexes (pyridine)(3)Ln(SePh)(3) (Ln = Ho (1), Tm (2), Yb (3)). The structure of 2 was established by low temperature single crystal X-ray diffraction. The complex is dimeric in the solid state, with 7-coordinate metal centers connected by a pair of mu(2)-(benzeneselenolate) ligands. Thermal decomposition of the selenolates gives a variety of solid state metal selenides : 1 gives HoSe, HoSe2, and Ph(2)Se; 2 gives Tm2Se3 and Ph(2)Se; 3 gives Yb2Se3 and Ph(2)Se. Trivalent thiolates can also be prepared by this amalgam reaction. For comparison, the structure of Yb(SPh)(3)(pyridine)(3) (4) was also determined-4 is a monomeric mer-octahedral compound with inequivalent Yb-S bonds. Both 3 and 4 have an intense visible chalcogen-to-ytterbium charge transfer absorption band. Crystal data (Mo K alpha, 153(2) K) are as follows. 2 : Triclinic space group , a = 10.435(2) Angstrom, b = 12.748(2) Angstrom, c = 14.453(2) Angstrom, alpha = 69.85(2)degrees, beta = 80.71(2)degrees, and gamma = 69.03(2)degrees. 4 : Triclinic space group , a = 9.836(10) Angstrom, b = 11.304(14) Angstrom, c = 16.202(11) Angstrom, alpha = 80.70 degrees, beta = 77.91(7)degrees, and gamma = 68.34(9)degrees.