Synthesis and structural characterisation of cis- and trans-[(hppH)2PtCl2] [(hppH)3PtCl]+Cl- and some new salts of the [hppH2]+ cation (hppH=1,3,4,6,7,8-Hexahydro-2H-pyrimido[1,2-α]pyrimidine):: The importance of hydrogen bonding

The reaction between the guanidine derivative hppH (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-alpha]pyrimidine) and K(2)ptCl(4) in H2O affords the salt [hppH(2)](2)[ptCl(4)], which reacts further with Li(hpp) in thf to give cis-[(hppH)(2)PtCl2]. The corresponding trans isomer is obtained from the reaction between [(dmso)(2)PtCl2] and hppH. hppH easily replaces another chlorido ligand to give [(hppH)(3)ptCl]Cl-+(-). [hppH(2)]Cl is formed as a hygroscopic side-product in the synthesis of [(hppH)(2)PtCl2] and takes up 1 equiv. of H2O to give [hppH(2)]Cl center dot H2O. We report the crystal structures of cis- and trans- [(hppH)(2)PtCl2], [(hppH)(3)PtCl]Cl-+(-) and some salts of the [hppH(2)](+) cation, namely [hppH(2)](2)[PtCl4] and the Pt-free salts [hppH(2)][BPh4], [hppH(2)]Cl and [hppH(2)]Cl center dot H2O, which have an increasing degree of directed intermolecular hydrogen contacts. The crystal structure of [hppH(2)]Cl center dot H2O features helical chains of Cl-center dot H2O connected via [hppH(2)](+) cations. The effects of hydrogen bonding on the structures of these compounds in the solid state are discussed. Finally, quantum chemical calculations provide further insight into the structures and properties of some of these compounds. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).