The synthesis, characterization, and X-ray crystal structure of the yellow dimorph, [Pt(terpy)Cl]Cl(.)2H(2)O, are reported. The yellow acicular crystals are monoclinic: space group P2(1)/n, a = 6.908(3) Angstrom, b = 17.06700(11) Angstrom, c = 13.8390(10) Angstrom, beta = 98.607(4)degrees, and D-calc =2.204 Mg m(-3) for Z = 4. The cation consists of platinum coordinated to tridentate terpyridine ligand and to chloride ion. The coordination geometry is essentially square-planar with distortions arising from the constraints of the terpyridine ligand. Bond distances are within the acceptable limits of predicted values. The cations stack in a head-to-tail orientation with an intermolecular Pt-Pt distance of 3.39 Angstrom.