(Dimethylphosphoryl)methanaminium chloride

The crystal structure of the title salt, C3H11NOP+·Cl−, is primarily built from centrosymmetric dimers of two cations, connected head-to-tail by two charge-supported strong N—H⋯O hydrogen bonds, with a graph-set descriptor R 2 2(10). The chloride counter-anions connect these dimeric cationic units into chains along the a-axis direction.

The crystal structure of the title salt, C 3 H 11 NOP + ÁCl À , is primarily built from centrosymmetric dimers of two cations, connected head-to-tail by two charge-supported strong N-HÁ Á ÁO hydrogen bonds, with a graph-set descriptor R 2 2 (10). The chloride counter-anions connect these dimeric cationic units into chains along the a-axis direction.
Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2011); software used to prepare material for publication: publCIF (Westrip, 2010). (Dimethylphosphinyl)methanamine (dpma) can easily be obtained by a two-step synthesis (Varbanov et al., 1987). To date only a limited number of structurally characterized dpma containing compounds are reported. On the one hand the structures of some transition metal complexes have been reported: Zn, Ni and Pd, (Borisov et al., 1994); Cu, (Kochel, 2009). On the other hand the solid state structure of the dpma molecule itself has been determined (Kochel, 2009). A recent search in the Cambridge Crystallographic Data Base showed, that there is no structural report on the N-protonated (dimethylphosphoryl)methanaminium (dpmaH) so far, whereas the salt of the N-methylated derivative (Kaukorat et al., 1997) and also more sophisticated substituated compounds are known (Zagraniarsky et al., 2008). Alkyldiphosphinates have been used as tectons (for the term tecton, see: Brunet et al., 1997;Resnati & Metrangolo, 2007) to construct hydrogen bonded frameworks (Glidewell et al., 2000) and also amino phosphinic anions are known to construct hydrogen bonded one-dimensional, two-dimensional and three-dimensional supramolecular architectures (Chen et al., 2010). The structure determination on the title compound is part of our continuing interest on the hydrogen bonding of methylphosphinic acids and its derivatives (Reiss & Engel, 2008) and its capability as tectons for the crystal engineering of new structural motifs and yet unknown species (Meyer et al., 2010).
The synthesis of the title compound dpmaHCl succeeded by the reaction of dpma with concentrated hydrochloric acid.
Hence, the cationic dpmaH features the hydrogen bond donor group NH 3 + at the one end and the hydrogen bond accepting group -P=O at the other end, this tecton should be able to form a variety of connections among themselves and to various counter anions. In the title structure two dpmaH cations are connected by strong -NH + ···O=P-hydrogen bonds (Tab. 1) head to tail to form cyclic dimers ( Fig. 1; first level graph-set descriptor: R 2 2 (10); Etter et al., 1990;Bernstein et al., 1995;Grell et al., 2002). These dimers are located on centres of inversion in the triclinic space group P1. All bond lengths and angles in the dpmaH cation are in the typical range. Each dicationic cyclic dimer forms hydrogen bonds to four neighbouring chloride anions. These chloride anions form hydrogen bonds to the next dimeric unit giving an onedimensional chain structure along [100]. The second level graph-set descriptor of this backbone-connection is C 1 2 (4) (Fig.  2). Two dpmaH cations of neighbouring dimers and the two chloride anions located between them form a complex hydrogen bonded eighteen-membered ring motif (third level graph-set descriptor: R 4 6 (18); Fig. 2) around a center of inversion ( Fig. 2 & 3). The bond lengths of the two crystallographic independent, charge supported NH + ···Clhydrogen bonds are nearly identical and in the typical range for the combination of aminium groups connected to chloride anions (Farrugia et al., 2001;Kovács & Varga, 2006;Reiss & Bajorat, 2008). A constructor-graph (Grell et al., 2002) of exactly that part of the title structure shown in Fig. 2 is shown in Fig. 3. In this schematic diagram cations and anions are replaced by dots. Each hydrogen bond is represented by an arrow from the donor to the acceptor.

Experimental
In a typical reaction 0.5 g (4.67 mmol) dpma was dissolved in 3 ml of concentrated hydrochloric acid (30-32%). The mixture was heated for a few minutes to give a clear, colourless solution. On slow cooling to room temperature colourless platelets grow from the mother liquor. The title compound is hygroscopic and storage at ambient conditions liquefies the crystalline material within a few minutes.
To check the purity of the synthesized material, powder diffraction data of a representative part of the bulk phase were collected at ambient temperature on a Stoe Stadi P diffractometer equipped with a PositionSensitiveDetector (flat sample, transmission, Cu Kα1). A profile fit (Solovyov, 2004) on the powder diffraction data based on the structure model obtained from the single-crystal experiment proved the identity of the title structure with the bulk sample (Fig. 4).

Refinement
Methyl H-atoms were identified in difference syntheses, idealized and refined using rigid groups allowed to rotate about the P-C bond (AFIX 137 option of the SHELXL97 program). The coordinates of all other H-atoms were refined freely with individual U Iso values.