inorganic compounds Hexagonal ammonium zinc phosphate, (NH 4 )ZnPO 4,at10K

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1 inorganic compounds Acta Crystallographica Section C Crystal Structure Communications ISSN Hexagonal ammonium zinc phosphate, (NH 4 )ZnPO 4,at10K William T. A. Harrison, a * Alexandre N. Sobolev b and Mark L. F. Phillips c a Department of Chemistry, University of Aberdeen, Aberdeen AB24 3UE, Scotland, b Department of Chemistry, University of Western Australia, Nedlands, WA 6907, Australia, and c Hayward Boulevard, Hayward, CA 94542, USA Correspondence w.harrison@abdn.ac.uk Received 18 January 2001 Accepted 13 February 2001 The title compound, (NH 4 )ZnPO 4 ±HEX, is built up from a three-dimensional network of ZnO 4 and PO 4 tetrahedra [d av (ZnÐO) = (7) A Ê and d av (PÐO) = (7) A Ê ], fused together via ZnÐOÐP links [ av = (4) ]. An undisordered linear ZnÐOÐP bond occurs (all three atoms lie on a threefold axis). Extra-framework NH 4 + cations, which interact with the [ZnPO 4 ] framework by hydrogen bonds, complete the crystal structure. Comment MZnPO 4 phases (M is a univalent cation) built up from a three-dimensional framework of vertex-sharing ZnO 4 and PO 4 tetrahedra are of interest for their physical properties (Blum et al., 1986), their phase transition behaviour (Kahlenberg, 1998; Hammond et al., 1998), and their structural relationship to polymorphs of silica and aluminosilicate zeolites (Harrison, 2000). Here, we describe the lowtemperature (10 K) structure of the hexagonal form (Averbuch-Pouchot & Durif, 1968) of ammonium zinc phosphate, (NH 4 )ZnPO 4. We have named this phase (NH 4 )ZnPO 4 ±HEX in order to distinguish it from monoclinic (NH 4 )ZnPO 4 ±ABW (Bu et al., 1997). There are 12 framework (two Zn, two P and eight O) and eight extra-framework (two N and six H) atoms in this structure. The geometrical parameters for the ZnO 4 and PO 4 tetrahedra [d av (ZnÐO) = (7) A Ê and d av (PÐO) = (7) A Ê ] are typical (Bu et al., 1997). The linkage of these moieties by ZnÐOÐP bonds results in a strictly alternating array of Zn and P tetrahedral nodes, with an average ZnÐOÐP bond angle of (4), excluding the linear Zn2ÐO6ÐP2 bond. The framework structure of (NH 4 )ZnPO 4 ±HEX is built up from in nite sheets of tetrahedral six-rings arrayed normal to [0001] (Fig. 2). Topologically, this linkage pattern of Zn and P atoms via O-atom bridges may be described as layers of simple 6 3 hexagonal nets (Hyde & O'Keeffe, 1996). The fourth ZnÐ O or PÐO vertex points approximately either up (U) or down (D) with respect to the [0001] direction. Using the up/down classi cation (Liebau, 1985), two types of six-ring may be identi ed as UDUDUD and UUUDDD. In this structure, there are three UUUDDD rings for every UDUDUD ring in any [0001] sheet. The extra-framework ammonium cations occupy the [0001] channels and interact with the [ZnPO 4 ] framework by NÐ HO hydrogen bonds (Table 2). N1 occupies the UUUDDD channels and makes four NÐHO hydrogen bonds to framework oxygen species. N2 occupies the UDUDUD channels and makes three equivalent hydrogen bonds as N2Ð H22O1. The N2ÐH21 moiety, which occupies the threefold axis does not participate in any hydrogen bond; all these bonds point the same way in this polar crystal structure. Framework atoms O1±O5 act as hydrogen-bond acceptors, with only O6 not involved in these guest-framework interactions. (NH 4 )ZnPO 4 ±HEX is isostructural with (NH 4 )CoPO 4 (Feng et al., 1997) and -AgZnPO 4 (Hammond et al., 1998). As noted recently (Hammond et al., 1998; Harrison, 2000), the (NH 4 )ZnPO 4 ±HEX structure is not isostructural with hexagonal nepheline types, such as -(Na 3/4 K 1/4 )AlGeO 4 Figure 1 Fragment of the (NH 4 )ZnPO 4 ±HEX structure (50% displacement ellipsoids). [Symmetry codes: (i) 1 x + y, 1 x, z; (ii) 1 y, x y, z; (iii) 1 + x y, x, z; (iv) y, 1 x + y, z; (v) x + y, x, z; (vi) y, x y, z.] Figure 2 Polyhedral view down [0001] of (NH 4 )ZnPO 4 ±HEX, with selected tetrahedra labelled to show a UDUDUD six-ring centred at x =0, y = 1, and a UUUDDD six-ring at x = 1 2, y = 1. The N1 ammonium cations occupy the UUUDDD channels and the N2 ammonium cations occupy the UDUDUD channels. 508 # 2001 International Union of Crystallography Printed in Great Britain ± all rights reserved Acta Cryst. (2001). C57, 508±509

2 inorganic compounds (Hammond & Barbier, 1998), which have the same space group and similar lattice parameters to (NH 4 )ZnPO 4 ±HEX. The nepheline types contain just one topologically distinct sixring (type UDUDUD), as adopted by the tridymite form of SiO 2. A notable feature of the (NH 4 )ZnPO 4 ±HEX structure is the symmetry constrained linear Zn2ÐO6ÐP2 bond. At 10 K, there is negligible anisotropy in the thermal motion of O6, which has a ratio of longest-to-shortest ellipsoid axes, U3/U1, of 3.11, compared to an average of 2.53 for the other ve O atoms. Conversely, in -AgZnPO 4 (Hammond et al., 1998), the equivalent linear ZnÐOÐP bond is disordered over three equivalent positions about the threefold axis [resulting ZnÐ OÐP bond angle = (4) ]. It was suggested that AgÐO bonding may play a role in promoting this situation, whereas for (NH 4 )ZnPO 4 ±HEX, the linear ZnÐO6ÐP bond is the only one not involved in interactions with the ammonium cation. Experimental A mixture of N 2 H 4 (2.35 g, 73 mmol), zinc acetate (2.20 g, 10 mmol), 85% H 3 PO 4 (4.6 g, 40 mmol) and water (9.08 g, 500 mmol) was placed in a plastic bottle (initial ph = 6.5) and heated to 343 K for 14 d. Numerous bicapped hexagonal rods (maximum size 1 mm) of the title compound were recovered by vacuum ltration and drying in air. Elemental analyses (found: N 7.85, 2.22%; calculated: 7.86, H 2.24%) were consistent with the crystal structure. Crystal data (NH 4 )ZnPO 4 M r = Hexagonal, P6 3 a = (2) A Ê c = (2) A Ê V = (3) A Ê 3 Z =8 D x = Mg m 3 Data collection Huber diffractometer /2 scans Absorption correction: analytical (ABSORB; Hall et al., 1995) T min = 0.824, T max = measured re ections 3049 independent re ections 3026 re ections with I > 2(I) Re nement Re nement on F 2 R[F 2 >2(F 2 )] = wr(f 2 ) = S = re ections 109 parameters All H-atom parameters re ned w = 1/[ 2 (F 2 o ) + (0.013P) P] where P =(F 2 o +2F 2 c )/3 Mo K radiation Cell parameters from 20 re ections = 13.3±13.7 = 5.95 mm 1 T = 10 (2) K Hexagonal prism, colourless mm R int = max = 37.6 h =0! 18 k = 18! 15 l = 14! 14 3 standard re ections every 97 re ections intensity decay: none (/) max = max = 0.38 e A Ê 3 min = 0.58 e A Ê 3 Extinction correction: SHELXL97 (Sheldrick, 1997) Extinction coef cient: (5) Absolute structure: Flack (1983) Flack parameter: (5) All H atoms were located from difference maps and their atomic coordinates and isotropic displacement factors were freely re ned. Table 1 Selected geometric parameters (A Ê, ). Zn1ÐO (7) Zn1ÐO (8) Zn1ÐO (7) Zn1ÐO (7) Zn2ÐO (12) Zn2ÐO5 i (7) Zn2ÐO5 ii (7) Zn2ÐO (7) P1 v ÐO1ÐZn (4) P1ÐO2ÐZn (4) P1 vi ÐO3ÐZn (4) Data collection: local routines; cell re nement: local routines; data reduction: local routines; program(s) used to solve structure: SHELXS86 (Sheldrick, 1985); program(s) used to re ne structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and ATOMS (Shape Software, 1999); software used to prepare material for publication: SHELXL97. Supplementary data for this paper are available from the IUCr electronic archives (Reference: GD1138). Services for accessing these data are described at the back of the journal. References P1ÐO (7) P1ÐO3 iii (7) P1ÐO1 iv (7) P1ÐO (7) P2ÐO (13) P2ÐO4 i (7) P2ÐO (7) P2ÐO4 ii (7) P2ÐO4ÐZn (4) P1ÐO5ÐZn (4) P2ÐO6ÐZn Symmetry codes: (i) 1 x y; 1 x; z; (ii) 1 y; x y; z; (iii) 1 x y; x; z 1 2 ; (iv) y; 1 x y; z 1 2 ; (v) 1 x y; x; 1 2 z; (vi) y; 1 x y; 1 2 z. Table 2 Hydrogen-bonding geometry (A Ê, ). DÐHA DÐH HA DA DÐHA N1ÐH11O5 i 0.83 (3) 1.97 (2) (13) 165 (2) N1ÐH12O4 ii 0.84 (3) 1.98 (3) (14) 169 (3) N1ÐH13O2 iii (17) (17) (12) (19) N1ÐH14O3 iv 0.89 (2) 1.90 (2) (14) 166 (2) N2ÐH22O1 iii 0.85 (2) 2.10 (2) (15) (17) Symmetry codes: (i) x y; x; 1 2 z; (ii) 1 x; 1 y; z 1 2 ; (iii) x y; 1 x; z; (iv) x y; x; z 1 2. Averbuch-Pouchot, M. T. & Durif, A. (1968). Mater. Res. Bull. 3, 719±722. Blum, D., Durif, A. & Averbuch-Pouchot, M. T. (1986). Ferroelectrics, 69, 283± 292. Bu, X., Feng, P., Gier, T. E. & Stucky, G. D. (1997). Zeolites, 19, 200±208. Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. Feng, P., Bu, X., Tolbert, S. H. & Stucky, G. D. (1997). J. Am. Chem. Soc. 119, 2497±2504. Flack, H. D. (1983). Acta Cryst. A39, 876±881. Hall, S. R., King, G. D. S. & Stewart, J. M. (1995). Xtal3.4 User's Manual. University of Western Australia, Australia. Hammond, R., Barbier, J. & Gallardo, C. (1998). J. Solid State Chem. 141, 177± 185. Hammond, R. P. & Barbier, J. (1998). Acta Cryst. B54, 211±220. Harrison, W. T. A. (2000). Z. Kristallogr. 215, 288±292. Hyde, B. G. & O'Keeffe, M. (1996). In Crystal Structures: Patterns and Symmetry. Washington: Mineralogical Society of America. Kahlenberg, V. (1998). Z. Kristallogr. 213, 13±18. Liebau, F. (1985). In Structural Chemistry of Silicates. New York: Springer- Verlag. Shape Software (1999). ATOMS. Shape Software Inc., 521 Hidden Valley Road, Kingsport, TN 37663, USA. Sheldrick, G. M. (1985). SHELXS86. University of GoÈttingen, Germany. Sheldrick, G. M. (1997). SHELXL97. University of GoÈttingen, Germany. Acta Cryst. (2001). C57, 508±509 William T. A. Harrison et al. (NH 4 )ZnPO 4 509

3 supporting information [doi: /s ] Hexagonal ammonium zinc phosphate, (NH 4 )ZnPO 4, at 10 K William T. A. Harrison, Alexandre N. Sobolev and Mark L. F. Phillips Computing details Data collection: local routines; cell refinement: local routines; data reduction: local routines; program(s) used to solve structure: SHELXS86 (Sheldrick, 1986); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and ATOMS (Shape Software Inc., 1999); software used to prepare material for publication: SHELXL97. (I) Crystal data (NH 4 ) (ZnPO 4 ) M r = Hexagonal, P6 3 Hall symbol: P 6c a = (2) Å c = (2) Å V = (3) Å 3 Z = 8 F(000) = 704 Data collection Huber diffractometer Radiation source: fine-focus sealed tube Graphite monochromator θ/2θ scans Absorption correction: analytical (ABSORB; Hall et al., 1995) T min = 0.824, T max = measured reflections Refinement Refinement on F 2 Least-squares matrix: full R[F 2 > 2σ(F 2 )] = wr(f 2 ) = S = reflections 109 parameters 1 restraint Primary atom site location: structure-invariant direct methods D x = Mg m 3 Melting point: decomposes before melting K Mo Kα radiation, λ = Å Cell parameters from 20 reflections θ = µ = 5.95 mm 1 T = 10 K Hexagonal prism, colourless mm 3049 independent reflections 3026 reflections with I > 2σ(I) R int = θ max = 37.6, θ min = 3.2 h = 0 18 k = l = standard reflections every 97 reflections intensity decay: none Secondary atom site location: difference Fourier map Hydrogen site location: difference Fourier map H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o2 ) + (0.013P) P] where P = (F o 2 + 2F c2 )/3 (Δ/σ) max = Δρ max = 0.38 e Å 3 Δρ min = 0.58 e Å 3 sup-1

4 Extinction correction: SHELXL, Fc * =kfc[ xfc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: (5) Absolute structure: Flack H D (1983), Acta Cryst. A39, Absolute structure parameter: (5) 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. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 ) x y z U iso */U eq N (8) (8) (10) (10) N (16) (18) Zn (9) (9) (11) (2) Zn (2) (3) P (2) (2) (3) (4) P (5) (6) O (7) (7) (7) (10) O (7) (7) (7) (9) O (7) (7) (8) (9) O (7) (7) (8) (9) O (7) (7) (8) (9) O (13) (19) H (3) (2) (3) (5)* H (3) (2) (3) (5)* H (18) (18) (2) (3)* H (2) (2) (3) (5)* H (4) (9)* H (2) (2) (2) (5)* Atomic displacement parameters (Å 2 ) U 11 U 22 U 33 U 12 U 13 U 23 N (2) (2) (3) (2) (2) (2) N (3) (3) (4) (13) Zn (4) (4) (4) (3) (3) (3) Zn (4) (4) (6) (2) P (7) (8) (9) (6) (6) (6) P (8) (8) (15) (4) O (2) (2) (2) (18) (16) (17) O (2) (2) (2) (19) (17) (16) O (2) (2) (2) (18) (2) (19) O (2) (2) (2) (19) (18) (18) sup-2

5 O (2) (2) (2) (19) (19) (18) O (3) (3) (4) (14) Geometric parameters (Å, º) N1 H (2) Zn2 O5 i (7) N1 H (2) Zn2 O5 ii (7) N1 H (17) Zn2 O (7) N1 H (2) P1 O (7) N2 H (4) P1 O3 iii (7) N2 H (2) P1 O1 iv (7) Zn1 O (7) P1 O (7) Zn1 O (8) P2 O (13) Zn1 O (7) P2 O4 i (7) Zn1 O (7) P2 O (7) Zn2 O (12) P2 O4 ii (7) H11 N1 H (2) O2 P1 O3 iii (4) H11 N1 H (2) O2 P1 O1 iv (4) H12 N1 H (18) O3 iii P1 O1 iv (4) H11 N1 H (19) O2 P1 O (4) H12 N1 H (2) O3 iii P1 O (4) H13 N1 H (18) O1 iv P1 O (4) H21 N2 H (13) O6 P2 O4 i (3) O4 Zn1 O (3) O6 P2 O (3) O4 Zn1 O (3) O4 i P2 O (3) O1 Zn1 O (3) O6 P2 O4 ii (3) O4 Zn1 O (3) O4 i P2 O4 ii (3) O1 Zn1 O (3) O4 P2 O4 ii (3) O2 Zn1 O (3) P1 v O1 Zn (4) O6 Zn2 O5 i (2) P1 O2 Zn (4) O6 Zn2 O5 ii (2) P1 vi O3 Zn (4) O5 i Zn2 O5 ii (2) P2 O4 Zn (4) O6 Zn2 O (2) P1 O5 Zn (4) O5 i Zn2 O (2) P2 O6 Zn O5 ii Zn2 O (2) Symmetry codes: (i) x+y+1, x+1, z; (ii) y+1, x y, z; (iii) x y+1, x, z 1/2; (iv) y, x+y+1, z 1/2; (v) x y+1, x, z+1/2; (vi) y, x+y+1, z+1/2. Hydrogen-bond geometry (Å, º) D H A D H H A D A D H A N1 H11 O5 vii 0.83 (3) 1.97 (2) (13) 165 (2) N1 H12 O4 viii 0.84 (3) 1.98 (3) (14) 169 (3) N1 H13 O2 ix (17) (17) (12) (19) N1 H14 O3 x 0.89 (2) 1.90 (2) (14) 166 (2) N2 H22 O1 ix 0.85 (2) 2.10 (2) (15) (17) Symmetry codes: (vii) x y, x, z+1/2; (viii) x+1, y+1, z 1/2; (ix) x+y, x+1, z; (x) x y, x, z 1/2. sup-3