Template or ligand? Different structural behaviours of aromatic amines in combination with zincophosphite networks

The solution-mediated syntheses and crystal structures of catena-poly[bis(2-amino-3-hydroxypyridinium) [zinc-di-μ-phosphonato] dihydrate], (I), and poly[(benzene-1,2-diamine)(μ5-phosphonato)zinc], [Zn(HPO3)(C6H8N2)]n, (II) are described. The extended structure of (I) features [010] anionic chains of vertex-sharing ZnO4 tetrahedra and HPO3 pseudopyramids while that of of (II) features a direct Zn—N bond to the neutral 1,2-diaminobenzene species as part of ZnO3N tetrahedra as well as HPO3 pseudopyramids.


Chemical context
Organically templated zinc phosphites (ZnPOs) are a wellestablished family of organic/inorganic open frameworks (e.g. Harrison et al., 2001;Dong et al., 2015;Huang et al., 2017). The stated motivations for studying these phases include their potential applications in catalysis, separation and as 'functional materials' (Wang et al., 2003). Important features of their crystal structures include the nature of the polyhedral building units [ZnO 4 , ZnO 3 (H 2 O), ZnO 3 N, HPO 3 ] and their connectivity, which defines the Zn:P ratio; for example, ZnO 4 and HPO 3 units sharing all their vertices as Zn-O-P bonds will lead to an anionic [Zn 3 (HPO 3 ) 4 ] n 2nÀ framework (a 3:4 Zn:P ratio), the charge of which must be balanced by the organic templating cation (e.g. Katinaitė & Harrison, 2017). If, however, one of the P-O vertices is 'terminal' (a formal P O double bond that does not link to zinc), then a [Zn(HPO 3 ) 2 ] n 2nÀ stoichiometry (1:2 Zn:P ratio) arises (e.g. Halime et al., 2011). A combination of HPO 3 (all vertices bonding) and HPO 3 (one terminal vertex) units leads to a [Zn 2 (HPO 3 ) 3 ] n 2nÀ framework (2:3 Zn:P ratio) (Lin et al., 2004a). Another important structural feature of these phases is the 'dual character' of the organic species: most commonly it is a protonated organic amine, which interacts with the ZnPO ISSN 2056-9890 framework via N-HÁ Á ÁO hydrogen bonds (e.g. Harrison & McNamee, 2010). However, direct Zn-N bonds are also possible (e.g. Fan et al., 2005), in which case the (unprotonated) organic species could be said to be acting as a ligand, although its steric bulk means that it does exert a 'templating effect' on the extended structure. This has an important effect on the zinc-to-phosphorus ratio; for example, a combination of ZnO 3 N and HPO 3 (all vertices bonding) units leads to a neutral [Zn(HPO 3 )] n (1:1 Zn:P ratio) network (e.g. Lin et al., 2004b). The complex structure of {(C 4 H 12 N 2 )[Zn 5 (HPO 3 ) 6 -(C 4 H 10 N 2 )]} n (Harrison, 2006) is notable for featuring the same organic species acting as a protonated template and a ligand in the same structure.

Structural commentary
Compound (I) features unusual disorder of the zincophosphite component of the structure, in a 0.7962 (13):0.2038 (13) ratio for the major and minor components, respectively. The major component features two zinc atoms (Zn1 and Zn2), four phosphorus atoms (P1-P4) and 12 oxygen atoms (O1-O12), the latter being parts of pseudo-pyramidal HPO 3 2À hydrogenphosphite anions (Fig. 1). Both zinc ions adopt typical tetrahedral coordination geometries to four nearby O atoms (which all bridge to an adjacent P atom) with mean Zn-O separations of 1.939 and 1.937 Å for Zn1 and Zn2, respectively. The ranges of O-Zn-O bond angles for Zn1 [101.6 (3)-126.2 (3)] and Zn2 [102.1 (3)-125.8 (3) ] seem to indicate a high degree of distortion from a regular tetrahedral geometry for these polyhedra, but these data should be approached with caution because of the disorder of the ZnPO framework (vide infra). The P atoms in (I) all display their expected tetrahedral geometries to three O atoms (two of which bridge to Zn atoms and one is 'terminal', hence the 1:2 Zn:P stoichiometry) and one H atom. As usual (Harrison, 2011) the H atom attached to the P atom does not show any propensity to form hydrogen bonds. The mean P-O separation for the terminal vertices (1.510 Å ) is slightly shorter than the corresponding value for the bridging O atoms (1.538 Å ), although there is some overlap of individual values. The O-P-O bond angles in (I) are clustered in the narrow range of 111.0 (4)-113.8 (4) (mean = 112.5 ) and are comparable to those in related structures (e.g. Dong et al., 2015). For the oxygen atoms (O1-O12) associated with the major disorder component, the mean Zn-O-P angle is 129.6 ( Table 1); four of these O atoms (O3, O6, O9 and O12) are parts of the terminal P O vertices. The geometrical data for the minor disorder component of the chain (atoms Zn11, Zn12, P11-P14, O21-O28) are broadly similar to those of the major component, although their precision is about four to five times lower.

Figure 1
The asymmetric unit of (I) showing the major disorder component only and expanded to show the complete zinc coordination polyhedra (50% displacement ellipsoids). Symmetry codes: (i) x, y À 1, z; (ii) x, y + 1, z.
of 0.0146 Å 2 for the major-disorder O atoms. This may indicate that there are actually separate, adjacent, sites for the major and minor components for these O atoms but they cannot be resolved from the present data. The polyhedral connectivity in (I) leads to [010] infinite anionic four-ring [Zn(HPO 3 ) 2 ] n 2nÀ chains of strictly alternating vertex-sharing ZnO 4 and HPO 3 groups with only translational symmetry building up the chains. Fig. 2 shows a fragment of a chain including both disorder components in which it may be seen that one can be superimposed on the other by means of a simple translation of approximately b/2. Each disorder component of the chain has four crystallographically unique water molecules of crystallization associated with it (O1w-O4w and O11w-O14w for the major and minor disorder components, respectively) and all of them form two O-HÁ Á ÁO hydrogen bonds to their adjacent chains.

Figure 3
Detail of (I) showing the hydrogen-bonding interactions of the N1 cation with the major disorder component of the ZnPO chain.  View of a fragment of a [010] zincophosphite chain in (I) showing the major (red bonds) and minor (blue bonds) disorder components with selected atoms labelled. Note that O1, O4, O7 and O10 are common to both components.
components of the chain, respectively. A view down [010] of the packing for (I) (Fig. 5) shows the anionic chains interspersed by the organic cations, which themselves form wavy (001) sheets.
The structure of (II) consists of ZnO 3 N tetrahedra and HPO 3 pseudo pyramids as well as neutral 1,2-diaminobenzene molecules (Table 3, Fig. 6). The Zn-N bond, which is notably longer than the Zn-O vertices (mean = 1.935 Å ) arises from a direct bond to the organic species, which could be said to be acting as a ligand rather than a (protonated) templating agent. The Zn-and P-centred polyhedra are linked by O atoms (mean Zn-O-P angle = 133.0 ) and there are no terminal O atoms. This '3+3' bonding mode naturally leads to the 1:1 Zn:P stoichiometry in (II).
The extended structure of (II) contains (010)  The unit-cell packing in (I) viewed down [010] with H atoms omitted for clarity. Table 3 Selected geometric parameters (Å , ) for (II).

Figure 6
Fragment of the structure of (II) with hydrogen bonds indicated by double-dashed lines (50% displacement ellipsoids). Symmetry codes: (i)

Figure 7
A six-ring window in (II) constructed from ZnO 3 N and HPO 3 building units. Symmetry codes:

Table 4
Hydrogen-bond geometry (Å , ) for (II). (4) 3.400 (3) 132 (3) very contorted six-ring windows (Fig. 7). The pendant organic molecules protrude either side of the sheets (Fig. 8). The structure of (II) is consolidated by N-HÁ Á ÁO hydrogen bonds, which are absolutely typical in this family of phases (Huang et al., 2017) and less common N-HÁ Á Á interactions ( Table 4). All of these bonds are intra-sheet interactions and no directional inter-sheet interactions beyond normal van der Waals contacts could be identified, the shortest of these being H3Á Á ÁH4 (2.67 Å ).

Database survey
So far as we are aware, no zincophosphites with either of the organic species described here have been reported previously. It may be noted that the C 6 H 7 N 2 O + cation in (I) has been reported as a counter-ion with simple, discrete MCl 4 2À anions where M = Co (Koval'chukova et al., 2008) and Cu (Halvorson et al., 1990) and with polymeric two-dimensional copper/ bromide networks (Place et al., 1998). A structure containing Zn-N bonds related to (II) featuring the isomeric 1,4-diaminobenzene species has been described (Kirkpatrick & Harrison, 2004). In this compound, the diamine bonds to zinc atoms from both its N atoms and acts as a 'pillar' linking ZnPO sheets into a three-dimensional framework. A survey of of the Cambridge Structural Database (Groom et al., 2016: updated to April 2018) for zinc phosphite frameworks with a directly bonded ligand/template (i.e. those containing a N-Zn-O-P-H fragment) revealed 21 matches.

Synthesis and crystallization
Compound (I) was prepared from 1.00 g ZnO, 2.00 g H 3 PO 3 and 1.35 g 2-amino-3-hydroxypyridine. These components were added to a PTFE bottle containing 20 ml of water and shaken well, to result in an off-white slurry. The bottle was sealed and placed in an oven at 353 K for 48 h and then removed to cool to room temperature. Product recovery by vacuum filtration yielded a mass of pale-brown laths of (I).
To prepare (II), 1.00 g zinc acetate, 0.74 g H 3 PO 3 , 0.99 g 1,2-diaminobenzene and 20 ml of water were placed in a PTFE bottle and shaken well, to result in a brown slurry. The bottle was sealed and placed in an oven at 353 K for 48 h and then removed to cool to room temperature. Product recovery by vacuum filtration yielded a few colourless blocks of (II) accompanied by unidentified dark-brown sludge.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. The structure of (I) proved to be difficult to solve and refine. The systematic absences pointed to space group P2 1 /n but no chemically reasonable models could be established in this centrosymmetric space group. Lower symmetry space groups were then tried and a plausible model in Pn was developed, as the complex nature of the disorder of the chain became apparent. In the early stages of the refinement, site occupancies were freely varied to establish which atoms belonged to which disorder component; the occupancies for O1, O4, O7 and O10 barely varied from unity and were fixed as fully occupied. When the disorder model was becoming clear, constrained refinements of site occupancies for the major and minor disorder components (including their associated water molecules of crystallization) led to refined values of 0.7962 (13):0.2038 (13). The structure of (II) was solved and refined without difficulty.
For (I), the H atoms associated with the P atoms were located in difference maps, relocated to idealized positions (P-H = 1.32 Å ) and refined as riding atoms. The N-and Obound H atoms of the cations were located in difference maps and refined as riding atoms in their as-found relative positions. Most of the water H atoms were located in difference maps and refined in a similar fashion; the remainder were placed geometrically to form reasonable hydrogen bonds and refined as riding atoms. The C-bound H atoms were placed geometrically (C-H = 0.95 Å ) and refined as riding atoms. In every case, the constraint U iso (H) = 1.2U eq (carrier) was applied. The crystal of (I) chosen for data collection was found to be an inversion twin in a 0.56 (2):0.44 (2) domain ratio.

catena-Poly[bis(2-amino-3-hydroxypyridinium) [zinc-di-µ-phosphonato] dihydrate] (I)
Crystal data (C 5  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.   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.71 e Å −3 Δρ min = −0.27 e Å −3 Absolute structure: Flack (1983) parameter Absolute structure parameter: 0.016 (14) sup-12 Acta Cryst. (2018). E74, 1411-1416 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.  (14) 0.0028 (9) −0.0015 (10) 0.0001 (11)