Heterometallic chalcogenolate compounds containing both lanthanide (Ln) and group 12 metals (M) represent an extremely broad molecular class, having the general formula LnM(EPh)(x)(L)(y), where L is a neutral donor ligand. In this paper we show how M, L, and the ratio Ln:M can be varied to give bi-, tetra-, penta-, and hexametallic chalcogenolates. The compounds [(py)(3)Eu(mu(2)-SePh)(2)(mu(3)-SePh)Hg(SePh)](2) (1), (THF)(4)Eu(mu(2)-SePh)(3)ZnSePh (2), [Sm(THF)(7)][Zn-4(mu(2)-SePh)(6)(SePh)(4)] (3), and [Yb(THF)(6)][Hg-5(mu(2)-SePh)(8)(SePh)(4)]. 2THF (4) have been prepared, and their structures have been established by low temperature single crystal X-ray diffraction. The synthesis and structural characterization of the heterometallic chalcogenolate [(py)(2)Sm(SePh)(mu-SePh)(3)Na(py)(2)](2) (5) is also described in order to compare the relative effects of the alkali and group 12 metals on heterometallic structure and electronic properties. From the crystal structures it is clear that the group 12 ion polarizes Se electron density away from the Ln ion, weakening the Ln-Se bond, and increasing the Ln-Se bond length. UV-visible data support the structural interpretations, with Ln(II) metal-to-pyridine charge transfer and lanthanide(III) selenolate to metal charge transfer absorption energies, both indicating that the group 12 metal withdraws electron density from the lanthanide ion. Unambiguous assignment of heterometallic solution structure is impossible, because the molecules are fluctional, and the er, from spectroscopic measurements, and from the isolation of 1 in 90% yield, it is clear that the compounds do maintain some form of heterometallic structure in donor solvents as basic as pyridine.