title: 1-Methyl-1-azonia-3,5-diaza-7-phosphatricyclo-[3.3.1.1]decane tetra-fluoro-borate.
abstract: The title compound, C(7)H(15)N(3)P(+)·BF(4) (-) or [PTA-Me][BF(4)], is the N-methyl-ated derivative of the well known water-soluble amino-phosphine 1,3,5-triaza-7-phosphaadamantane (PTA). The asymmetric unit consists of a cage-like cation [PTA-Me](+) and a disordered tetra-fluoro-borate anion; two F atoms are disordered equally over two sites. A network of weak inter-molecular C-H⋯F hydrogen bonds results in a three-dimensional supra-molecular assembly.
authors.forename: Piotr
authors.initials: P
authors.lastname: Smoleński
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Kirillov
authors.forename: M Fátima C
authors.initials: MF
authors.lastname: Guedes da Silva
authors.forename: Armando J L
authors.initials: AJ
authors.lastname: Pombeiro