The crystal structure of (C2H9N2)2[Zn3(HPO3)4], a three-dimensional zincophosphite framework containing 16-membered rings templated by the unsymmetrical dimethyl hydrazinium cation

The title open framework contains 16-ring pores templated by pairs of side-by-side unsymmetrical dimethyl hydrazinium cations.


Chemical context
Organically templated zinc phosphites are now a well-established family of open frameworks (e.g.: Phillips et al., 2002;Luo et al., 2010;Wang et al., 2011;Dong et al., 2015;Huang et al., 2017). As part of our occasional studies in this area (Harrison & McNamee, 2010), we now describe the synthesis and structure of the title compound, (I), which represents the first example of a protonated unsymmetrical dimethyl hydrazine (C 2 H 8 N 2 or UDMH is the neutral molecule and C 2 H 9 N 2 + is the cation) acting as a templating agent for an inorganic open framework. So far as we are aware, the only crystal structures containing C 2 H 9 N 2 + that have been reported previously are molecular salts with different simple counterions (Katinaitė & Harrison, 2016, and references therein).

Structural commentary
The asymmetric unit of (I) comprises two zinc cations (Zn1 with site symmetry 2 and Zn2 on a general position), two HPO 3 2À hydrogen phosphite groups and one C 2 H 9 N 2 + cation ISSN 2056-9890 ( Fig. 1). Both zinc ions adopt their usual tetrahedral coordination geometries (  (Dong et al., 2015). P1 deviates from its pyramid of attached O atoms by 0.418 (4) and the equivalent deviation for P2 is 0.420 (3) Å .
The structure of (I) is completed by the charge-balancing C 2 H 9 N 2 + cation, which is protonated at the central (methylated) N2 atom, as is most commonly seen for this species (Katinaitė & Harrison, 2016). The C-N and N-N bond lengths are indistinguishable and N2 deviates from the plane of N1, C1 and C2 by 0.434 (8) Å .
In the extended framework structure of (I), the zinc-and phosphorus-centred building units strictly alternate: every O atom forms a Zn-O-P bridge (mean angle = 131.4 ), thus there are no 'dangling' Zn-OH 2 , P O or P-OH bonds as found in some zincophosphite frameworks (Shi et al., 2004;Liu et al., 2008), which is fully consistent with the 3:4 Zn:P stoichiometry of the anionic [Zn 3 (HPO 3 ) 4 ] 2À component of the structure (Harrison & McNamee, 2010). In addition, there are no Zn-N bonds (direct metal-to-template links) in (I); compare Kirkpatrick & Harrison (2004), Lin et al. (2004) and Harrison (2006).
The polyhedral connectivity in (I) can be broken down as follows: the Zn2, P1 and P2 polyhedra form four-ring (i.e.: a loop of two Zn atoms and two P atoms) chains, with the zinc  Table 1 Selected geometric parameters (Å , ).

Figure 2
Fragment of (I) showing a 16-ring channel occupied side-by-side by two C 2 H 9 N 2 + template cations.

Figure 3
The unit-cell packing in (I) viewed approximately along [110] with the framework represented topologically (i.e. as Zn-P links).

Figure 1
The asymmetric unit of (I) expanded to show the zinc coordination polyhedra (50% displacement ellipsoids). For symmetry codes, see  (Bennett & Marcus, 1988). When the template is included in the calculation, PLATON indicates no free space, suggesting that the template is a 'snug fit' within the inorganic framework of (I).
In the extended structure, large 16-ring pores (Figs. 2 and 3) are apparent in the framework, which alternately propagate in [110] and [110] with respect to the c-axis direction. Measured atom-to-atom, the 16-ring has a dimension of $5.7 Â 14.6 Å . Pairs of template cations lie roughly in the plane of the 16rings and interact with framework oxygen atoms by way of N-HÁ Á ÁO hydrogen bonds (Table 2). It is notable that the HÁ Á ÁO separation for the charge-assisted N2 + -H3NÁ Á ÁO3 bond is much shorter than the HÁ Á ÁO separations for the terminal N1H 2 grouping. Within the asymmetric unit, an R 2 2 (7) loop is apparent (Fig. 1). Possible weak C-HÁ Á ÁO interactions (Table 2) consolidate the structure.

Synthesis and crystallization
Caution! UDMH is toxic, potentially carcinogenic and may form explosive mixtures with oxidizing agents: all appropriate safety precautions should be taken when handling it. Zinc oxide (1.63 g), phosphorus acid (1.64 g) and 20 ml of a 1.0 M aqueous UDMH solution were mixed in a 1:1:1 molar ratio in a sealed PTFE bottle and heated to 353 K for 24 h and then cooled to room temperature over a few hours. Product recovery by vacuum filtration yielded some colourless blocks of (I) accompanied by an unidentified white powder.

1,1-Dimethylhydrazinium tetraphoshonoatotrizincate(II)
Crystal data Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.011 (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. Refinement. Refined as a 2-component twin with components rotated about (001) (2)