2,8,9-Tris(2-methylpropyl)-2,5,8,9-tetraaza-1λ5-phosphatricyclo[3.3.3.01,5]undecan-5-ium chloride dihydrate

The asymmetric unit of the title hydrated salt, C18H40N4P+·Cl−·2H2O, consists of two ionic molecules and four water molecules. The molecular geometry around the pentacoordinate P atom is trigonal–bipyramidal, with a H atom and an apical N atom in axial positions and three N atoms with isobutyl substituents in equatorial positions. The Cl− ions and water molecules are connected via O—H⋯Cl hydrogen bonds, forming chains along [100]. The ethylene bridging groups are disordered with refined site-occupancy ratios of 0.578 (9):0.422 (9).

Unlike proazaphosphatranes, their protonated phosphonium salts known as azaphosphatranes with the five-membered tricyclic frameworks exist as solid states. Even though a lot of azaphosphatranes have appeared in the literature, only few examples of their solid state structures have been reported (Kingston et al., 2005;Liu et al., 1999;Liu et al., 2000;Mohan et al., 1996;Thirupathi et al., 2003;Wroblewski et al., 1995). In addition, the similar structure of the title complex (I) with four chloroform molecules in the monoclinic unit was reported in the literature; however, no crystallographic data and parameters were provided (Kisanga et al., 2001). Herein, we report the X-ray structure of the title complex (I).
The title compound (I) could be isolated in more than 90% yield via the reaction of (i-BuNHCH 2 CH 2 ) 3 N with ClP(NMe 2 ) 2 , prepared in situ in acetonitrile by the slow addition of 1 equivalent of PCl 3 to 2 equivalents of P(NMe 2 ) 3 . In (I) (Fig. 1), the nearly ideal trigonal bipyramidal geometry around the phosphorus atom is confirmed by the sum of the N eq -P-N eq angle of 358.8 ° and the average N eq -P-N ax angle value of 86.3 °. The axial transannular P-N distance of 1.973 (2) Å and the average equatorial P-N bond distance of 1.664 (3) Å are in the range of typical values determined on azaphosphatranes derivatives (Kingston et al., 2005;Liu et al., 1999;Liu et al., 2000;Mohan et al., 1996;Thirupathi et al., 2003;Wroblewski et al., 1995).

Experimental
The title compound (I) could be isolated in more than 90% yield via the reaction of (i-BuNHCH 2 CH 2 ) 3 N with ClP(NMe 2 ) 2 , prepared in situ in acetonitrile by the slow addition of 1 equivalent of PCl 3 to 2 equivalents of P(NMe 2 ) 3 .
The crystal was obtained by slow evaporation of solvent in refrigerator.

Refinement
H atoms attached to C atoms were positioned geometrically and refined using a riding model, with C-H = 0.93-0.97 Å and with U iso (H) = 1.2 (1.5 for methyl groups) times U eq (C). The water H atoms were found in difference Fourier maps and refined freely.
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.