1-Methyl-1-azonia-3,5-diaza-7-phospha­tricyclo­[3.3.1.1]decane 7-oxide triiodide

The title compound, C(7)H(15)N(3)OP(+)·I(3) (-), is a derivative of the well known water-soluble amino-phosphine 1,3,5-triaza-7-phosphaadamantane (PTA). The crystal structure is composed of a cage-like 1-methyl-1-azonia-3,5-diaza-7-phospha-tricyclo-[3.3.1.1]decane 7-oxide cation and a triiodide anion. The N-methyl-ation of the PTA cage results in a slight elongation of the corresponding C-N bonds, while the oxidation of the P atom leads to a slight shortening of the C-P bonds in comparison with those of PTA. In general, most of the bonding parameters are comparable with those reported for related compounds bearing the PTA core. Two inter-molecular C-H⋯O hydrogen bonds between methyl-ene groups and the P=O group are responsible for the linkage of neighbouring cations into linear one-dimensional hydrogen-bonded chains.