Studies on the Nature and Strength of Pt . . .H(-N) Interactions. The Crystal Structures of Chloro[N-(2-aminoethyl)-N-(2-ammonioethyl)ethane-1,2-diamine]platinum(II) Chloride and Dichloro[4,7-diaza-1-azoniacyclononane]platinum(II) Tetrachlor

Abstract

Two complexes, namely, chloro[N-(2-aminoethyl)-N-(2-ammonioethyl)ethane-1,2-diamine]platinum(II) chloride {[PtCl(tren+H)]Cl₂} and dichloro[4,7-diaza-1-azoniacyclononane]platinum(II) tetrachloroplatinate(II)–water (1/2) {[PtCl₂(tacn+H)]₂[PtCl₄]·2H₂O}, have been prepared and structurally characterized by single-crystal X-ray diffractometry as part of a study of the nature and strength of Pt···H(–N) interactions. Crystals of [PtCl(tren+H)]Cl₂ are monoclinic, space group P2₁/c, a 8.293(2), b 14.396(6), c 11.305(3) Å, β 107.34(2)º, Z 4, and the structure has been refined to a residual of 0.042 based on 1631 reflections. Crystals of [PtCl₂(tacn+H)]₂[PtCl₄]·2H₂O are monoclinic, space group P2₁/a, a 12.834(4), b 8.206(4), c 13.116(8) Å, β 93.01(4)˚, Z 2, and the structure has been refined to a residual of 0.035 based on 1974 reflections. In [PtCl(tren+H)]²⁺, the protonated amine forms hydrogen bonds with chloride anions and no close contacts with the metal ion. In [PtCl₂(tacn+H)]⁺, a short intramolecular contact is observed between the metal and the protonated amine and the results of molecular mechanics modelling are consistent with there being a Pt···H hydrogen bond. Molecular mechanics modelling of [PtCl(tren+H)]²⁺ and [PtCl₂(dien+H)]⁺ shows that the protonated amines could readily form close contacts with the metal. It is concluded that there is evidence for the formation of Pt···H(–N) hydrogen bonds but these bonds are very weak, being similar or lower in energy than Cl···H(–NPt) hydrogen bonds.