Redetermination of the crystal structure of tetrammineplatinum(II) dichloride - A microporous hydrogen-bonded 3D network exhibiting a temperature-dependent order-disorder phase transition

The title compound [Pt(NH3)(4)]Cl-2 (1), prepared by reaction of (NH4)(2)[PtCl4] with an excess of NH3 in aqueous solution, was crystallized from water and its structure redetermined by single-crystal X-ray diffraction at four different temperatures in the range from 273 K down to 100 K. 1 is composed of square-planar [Pt(NH3)(4)](2+) complex cations and Cl- anions and crystallizes in the tetragonal crystal system. Remarkably, the solid state structure is porous (approx. 18% of the crystal volume is void space) and features one-dimensional open channels of a diameter of similar to 3-4 angstrom. Unexpectedly, these channels are free of solvent molecules, although the crystals were obtained from aqueous solutions. N-H center dot center dot center dot Cl hydrogen bonding interactions between the square-planar [Pt(NH3)(4)](2+) dications and the Cl- counter ions result in a three-dimensional hydrogen bonding network that stabilizes the porous solid state structure. The hydrogen atoms of the ammonia ligands and their corresponding N-H center dot center dot center dot Cl hydrogen bonds are localized at low temperature (space group I4/mmm) but disorder dynamically above 173 K (space group P4/mmm). The order-disorder transition is accompanied by significant changes in the Pt-Pt stacking distances and a fourfold reduction of the unit cell volume.