Copper(I)-catalysed reactions of cis-PtCl₂(L)₂ (L = Pet₃, L₂= dppe, dppp) with buta-1,3-diyne have given the corresponding diynyl complexes, cis-Pt(C≡CC≡CH)2(L)2 (L = Pet₃ 1, L₂= dppe 2, dppp 3) whose solid-state structures have been determined from single crystal X-ray diffraction studies. Theoretical calculations were carried out to probe the electronic structure of these diynyl complexes. Complex 2 reacts with Co₂(CO)₈ to give a bis-adduct 5 and with Ru₃(µ-dppm)(CO)₁₀ to give a mono-adduct 6; in both, the least hindered C≡C triple bond(s) is(are) coordinated. Lithiation (LiBut) of 2 gives a dilithio derivative, which has been converted to dimethyl 7 or mono-SiMe₃ 8 or -Au(PPh₃) 9 complexes. Cu(I) and Ag(I) (MI) adducts ( tweezer complexes) have been obtained from reactions of 2 with MISCN or [MI(NCMe)₄]⁺. An ES mass spectrometric study of the interactions of 2 with Group 1 cations and with Tl⁺ is also described; comparative experiments with {W(CO)₃Cp}₂(µ-C₈), in which the four C≡C triple bonds do not have a tweezer conformation, have also been carried out. The degree of association is determined by the competitive solvation of the Group 1 cation. Coupling of the buta-1,3-diynyl complexes with Pt(OTf)₂(L )₂ gives homo- or mixed-ligand molecular squares cyclo-{(L)₂Pt(µ-C CC C)₂Pt(L )₂}₂ (L, L = Pet₃, L₂, L ₂= dppe, dppp; not all combinations), of which the molecular structure of cyclo-{Pt(µ-C CC C)(dppe)}₄ 17 is described (as solvates containing dmso). The molecular squares form adducts with substituted ammonium triflates [NH₂R₂][OTf] (R = Et, Pri, Cy; NH₂R₂= dbuH) and with Group 11 cations [MI(NCMe)]⁺.