The third crystal structure containing the hydroxo-bridged cis-diammineplatinum(II) dimer has been determined for a perchlorate salt of the complex, [Pt(2)(NH(3))(4)(micro-OH)(2)](ClO(4))(2). However, the dinuclear cations in the nitrate and the carbonate salts, [Pt(2)(NH(3))(4)(micro-OH)(2)](NO(3))(2) [Faggiani, Lippert, Lock & Rosenberg (1977). J. Am. Chem. Soc. 99, 777-781] and [Pt(2)(NH(3))(4)(micro-OH)(2)](CO(3)).H(2)O [Lippert, Lock, Rosenberg & Zvagulis (1978). Inorg. Chem. 17, 2971-2975], were reported to possess a nearly planar geometry. The cation in the title perchlorate salt has been found to possess an exceptional bent form in which two Pt coordination planes within the dimer are tilted at an angle of 151.7 (1) degrees to one another. The diplatinum entity has a syn orientation with regard to the conformation of two hydroxo bridges, in part due to the one-dimensional hydrogen-bonding network achieved in the crystal structure. DFT MO investigations have also been carried out to reveal that the planar-bent selection could be induced by the anti-syn selection at the H(hydroxo) atoms. Comparison has also been made between the geometrical features of the three salts from the viewpoint of the orientation of H(hydroxo) atoms.