The role of transition metal atoms as hydrogen bond acceptors: a neutron diffraction study of [NPrn4]2[PtCl4]·cis-[PtCl2(NH2Me)2] at 20 K

Abstract

Single-crystal neutron diffraction has allowed accurate characterisation of N–H ⋯ Pt and N–H ⋯ Cl interactions linking the two square-planar platinum(II) units which comprise the dianion of [NPrⁿ₄]₂[PtCl₄]·cis-[PtCl₂(NH₂Me)₂]1: Pt ⋯ H 2.262(11)Å, N–H ⋯ Pt 167.1(9)°; Cl ⋯ H 2.318(12)Å, N–H ⋯ Cl 151.0(12)°. An extensive network of C–H ⋯ Cl hydrogen bonding between the cation and anion species is also revealed, and provides valuable information on what is one of the least well characterised types of hydrogen bond. A weak C–H ⋯ Pt interaction between one cation unit and the anion is also observed. In the light of this and particularly the stronger intra-anion N–H ⋯ Pt interaction, a new type of three-centre four-electon hydrogen bridge, involving a transition-metal atom, is proposed. Further supporting evidence is drawn from a re-evaluation of spectroscopic data for similar interactions previously reported. This type of interaction is contrasted with the more well known three-centre two-electron M–H⇀M, C–H⇀M, Si–H⇀M and B–H⇀M interactions and compared with conventional four-electron hydrogen bonds. Compound 1 is triclinic, space group P(no.2), Z= 2, with a= 10.680(4), b= 11.926(2), c= 15.350(15)Å, α= 93.88(4), β= 100.57(5) and γ= 96.58(4)° at 20 K. Final R(F²)= 0.124, S= 1.136 for 5244 F² values (F₀² > 0.0).