New alkynyl complexes [Pt2M4 {C equivalent to C(3-OMe)C6H4}(8)] (M = Ag 1, Cu 2) have been synthesized and their structures and properties compared to those of related [Pt2M4(C equivalent to CPh)(8)] compounds. For the Pt-Ag derivatives, the X-ray structures of the discrete yellow solvate monomer, [Pt2Ag4 {C equivalent to C(3-OMe) C6H4} 8](.)2THF ([1(.)2THF]), and the dark garnet unsolvated polymeric form, [Pt2Ag4 {C equivalent to C(3-OMe)C6H4}(8)](infinity) ([1](infinity)), are presented. The yellow form ([1(.)2THF]) exhibits a distorted octahedral geometry of the metal centers with the platinum atoms mutually trans and the four silver atoms in the equatorial plane. Pairs of Ag atoms are weakly bridged by THF molecules [mu-(Ag2O)-O-...(THF)]. The garnet form ([ 1]) has an unprecedented infinite stacked chain of octahedral clusters linked by short (PtPt)-Pt-... bonds (3.1458(8) angstrom). In both forms, different types of weak C-(HO)-O-... (OMe) hydrogen bonds are observed. For comparative purposes, we have also provided the crystal structures of the yellow monomer form, [Pt2Ag4( C equivalent to CPh)(8)](CHCl3)-C-., and the red dimer form, [Pt2Ag4(CtCPh)(8)](2) (Pt-Pt 3.221(2) angstrom). These clusters display intense photoluminescence in both solution and the solid state, at room temperature and 77 K. The emission observed for the yellow form [1(.)2THF] in the solid state is assigned to a (MLM)-M-3'CT [Pt(d)/pi(C equivalent to CR)-> Pt(p(z))/Ag(sp)/pi*(C equivalent to CR)] state modified by (PtAg)-Ag-..., Ag... Ag, and Ag-...(THF) contacts. However, in the garnet form [ 1] and in 2, the emissions are related to the axial Pt-Pt bonds and are assigned as phosphorescence from a metal-metal-to-ligand charge-transfer ((MMLCT)-M-3) excited state ([1](infinity)), or an admixture of a metal-metal (Pt-Pt) centered (3)(d sigma*p(z)sigma) and (MMLCT)-M-3 excited state ( 2). For 1, a remarkable quenching and a shift to higher energies in the emission is observed on changing from CH2Cl2 to THF, and for both 1 and 2, the emission spectra at 77 K varies with the concentration, showing their tendency to stack even in glass.