Crystal structure of caesium tetramethyldithioimidodiphosphinate

A supramolecular two-dimensional polymer structure of caesium tetramethyldithioimidodiphosphinate is reported.

In the title crystal, the salt [CsMe 2 P(S)NP(S)Me 2 ] is self-assembled as an undulating supramolecular two-dimensional polymeric structure, poly[( 4tetramethyldithioimidodiphosphinato)caesium], [Cs(C 4 H 12 NP 2 S 2 )] n , which is parallel to the bc plane. The Cs cations are hexacoordinated, being chelated by two thioimidophosphinate groups and two sulfur atoms from neighboring ligands. The anions are linked to the Cs cations by CsÁ Á ÁS and CsÁ Á ÁN electrostatic interactions.

Supramolecular features
In the crystal, the salt [CsMe 2 P(S)NP(S)Me 2 ] (I) is selfassembled as an undulating supramolecular 2D polymeric structure, which is parallel to the bc plane ( Figs. 2 and 3). The Cs cations are hexacoordinated and linked to four different anions by CsÁ Á ÁS and CsÁ Á ÁN electrostatic interactions (Fig. 4). Analysis of this CsS 4 N 2 polyhedron with the SHAPE 2.1 program (Llunell et al., 2013) gave CShM values of 9.50434 and 8.43874 for a regular octahedron and a trigonal prism,

Figure 2
A view along the c axis, showing the undulating two-dimensional polymer structure. Hydrogen atoms were omitted for clarity.

Figure 3
A view along the a axis of the supramolecular two-dimensional polymer structure parallel to the bc plane. Hydrogen atoms were omitted for clarity.

Figure 1
The asymmetric unit of the title compound (I), showing the atom-labeling scheme.

Figure 4
A view of the hexacoordination of the caesium cation. Atoms with the suffix A, B or C are at the symmetry positions A: 1 À x, 1 À y, 1 À z; B: 1 À x, 1 2 + y, 1 respectively, meaning that the coordination environment of the cesium atom is highly irregular. These polyhedra interconnect either by sharing vertices or an edge. The CsÁ Á ÁS ionic bond distances vary from 3.4377 (3) to 3.4726 (3) Å , which are close to the value of 3.51Å predicted from the ionic radii (Shannon, 1976). Regarding the N-Cs bond distances, two different distances were determined. One of them is 3.2054 (9) Å , which is close to the value of 3.13 Å predicted from the ionic radii, and the other is 3.651 Å , which is less than the value of 4.4 Å predicted from the van der Waals radii (Batsanov, 2001). Furthermore, five methyl groups are located in a close vicinity of the Cs + cation with the CsÁ Á ÁH distance shorter than 4 Å , but only the shortest Cs1Á Á ÁH2C(1 -x, 1 -y, 1 -z) distance of 3.269 Å is similar to those observed in [LiCs(HMDS) 2 ] 1 and can be labeled as an agostic interaction (Ojeda-Amador et al., 2016). The cyclic motifs Cs 2 S 2 , Cs 2 N 2 , Cs 2 N 2 P 2 S 2 in this arrangement possess crystallographic inversion symmetry.

Synthesis and crystallization
Cs[Me 2 P(S)] 2 N (I) was obtained by the reaction of [Me 2 P(S)NHP(S)(Me 2 )] with Cs 2 CO 3 , according to a method previously described (Schmidpeter & Ebeling, 1968) and isolated solvent-free. The salt Cs[Me 2 P(S)] 2 N was recrystallized by slow evaporation from methanol. The spectroscopic data of the received sample (vide infra) coincided with the published ones and are therefore not reported; however, they can be consulted in the above-mentioned reference.

Crystal data
[Cs(C 4 H 12 NP 2 S 2 )] M r = 333.12 Monoclinic, P2 1 /c a = 11.0320 (2)  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.