Reaction of tetrameric trimethylplatinum(IV) iodide with an excess of 3-substituted pyridines in chloroform afforded mononuclear complexes, [PtMe₃L₂I] (L = 3-CNpy, 3-Brpy, 3-MeOpy, 3-Mepy and 3-Etpy). The complexes were characterized by ¹H NMR, CHN analysis and X-ray single crystal structure analysis. The mononuclear complexes undergo reaction with trimethylplatinum(IV) iodide in chloroform to form the corresponding dinuclear forms (both syn and anti). A comparison of both the mononuclear and dinuclear forms in solution for a particular pyridine substituent has been studied in detail with the help of ¹H NMR spectroscopy, ably supported by DFT computational studies. The investigation further shows the influence of the pyridine substituent on controlling the mode of the reaction. The crystal structures of two dinuclear complexes, syn-[PtMe₃(3-CNpy)I]₂ and anti-[PtMe₃(3-Brpy)I]₂, have also been described here.