Crystal structure of a new homochiral one-dimensional zincophosphate containing l-me-thio-nine.

catena-Poly[[(l-me-thio-nine-κO)zinc]-μ3-(hydrogen phosphato)-κ(3) O:O':O''], [Zn{PO3(OH)}(C5H11NO2S)] n , a new one-dimensional homochiral zincophos-phate, was hydro-thermally synthesized using l-me-thio-nine as a structure-directing agent. The compound consists of a network of ZnO4 and (HO)PO3 tetra-hedra that form ladder-like chains of edge-fused Zn2P2O4 rings propagating parallel to [100]. The chains are decorated on each side by zwitterionic l-me-thio-nine ligands, which inter-act with the inorganic framework via Zn-O coordination bonds. The structure displays inter-chain N-H⋯O and O-H⋯S hydrogen bonds.

Chemical context

In the last two decades, the blossoming of research on hybrid organic-inorganic open-framework systems has been motivated by the growing inter­est in obtaining materials that combine the functional properties of organic and inorganic components (Wang et al., 2014 ▸; Murugavel et al., 2008 ▸; Thomas, 1994 ▸). Since their discovery in 1991 (Gier & Stucky, 1991 ▸), attention on hybrid zincophosphates has arisen because of the diversity of new open-framework structures that can be obtained (Kefi et al., 2007 ▸; Fleith et al., 2002 ▸; Stojakovic et al., 2009 ▸; Mekhatria et al., 2011 ▸). Although in the majority of cases the organic mol­ecules are hydrogen-bonded to the mineral framework or trapped in the micropores of the material, they can also be directly linked to the inorganic network through coordination bonds (Mekhatria et al., 2011 ▸; Fan et al., 2005 ▸; Fan & Hanson, 2005 ▸; Zhao et al., 2008 ▸; Dong et al., 2010 ▸). In such systems and in the related class of zincophosphites, amino acids have been used as chiral structure-directing agents with only partial success. Enanti­opure histidine, for example, has been shown to template the formation of zincophosphate (Mekhatria et al., 2011 ▸; Fan et al., 2005 ▸; Zhao et al., 2008 ▸) or zincophosphite (Chen & Bu, 2006 ▸) materials. The amino acid coordinates the Zn atom via either its carboxyl­ate group (Mekhatria et al., 2011 ▸; Zhao et al., 2008 ▸), its imidazole ring (Fan et al., 2005 ▸) or both functions (Chen & Bu, 2006 ▸). However, racemization of histidine takes place during the synthesis and the reported materials are achiral. Among the rare homochiral systems so far assembled are ladder-like zincophosphites [HA·ZnHPO3] where the amino­acid [HA = l-asparagine (Gordon & Harrison, 2004 ▸) or l-tryptophan (Dong et al., 2010 ▸)] is O-bound to the inorganic framework. Using l-histidine, a zincophosphate [Zn3(H2O)(PO4)(HPO4)(HA)2(A)] was also isolated displaying ladder-like chains decorated by pendant ZnO2N2 tetra­hedra (Dong et al., 2010 ▸). In this material, the two neutral amino acid mol­ecules act as monodentate ligands through their imidazole function, while the deprotonated one chelates a Zn atom via its imidazole and amino groups.

We report herein a new zincophosphate compound, [Zn(HPO4)(l-met)] (I), containing O-bound l-me­thio­nine (l-met) and exhibiting a simple ladder-like homochiral structure. The compound was obtained as a minority phase together with hopeite [Zn3(PO4)2·4H2O; Hill & Jones, 1976 ▸] and residues of the reagents by hydro­thermal synthesis starting from zinc oxide, ortho­phospho­ric acid and l-me­thio­nine in water. A needle-like single crystal of sufficient size and quality was isolated from the product mixture and a single-crystal X-ray analysis performed at room temperature.

Structural commentary

The asymmetric unit contains one zinc cation, one hydrogenphosphate anion and one l-me­thio­nine ligand in its zwitterionic form. It is shown in Fig. 1 ▸ along with the symmetry-equivalent O atoms required to complete the coordination sphere of Zn. Such a formulation is in accordance with charge balance considerations assuming usual valences for Zn (2+), P (5+), O (2−) and H (1+). The ammonium and HPO4 2− hydrogen atoms were clearly located in Fourier difference maps. The zinc ion is tetra­hedrally coordinated by the oxygen atoms (O2, O3i and O4ii) of three different (HO)PO3 2− groups and by the carboxyl­ate oxygen (O5) of me­thio­nine, with (Zn—O)av = 1.95 Å and O—Zn—O angles in the range 103.84 (11)–115.56 (11)° (Table 1 ▸). The hydrogenphosphate group is connected to three different zinc ions through O2, O3 and O4. The corresponding P—O distances range between 1.510 (3) and 1.525 (2) Å while the terminal P1—O1 bond is much longer [1.584 (3) Å], as expected for a pendant OH group (Fan et al., 2005 ▸; Fan & Hanson, 2005 ▸). The O—P—O and Zn—O—P angles are in the ranges 103.27 (14)–114.41 (14) and 129.16 (14)–132.83 (15)°, respectively.

Figure 1

The asymmetric unit of (I), plus the O atoms required to complete the coordination sphere of Zn. Displacement ellipsoids are drawn at the 40% probability level, while H atoms are shown as spheres of arbitrary radius. [Symmetry codes: (i) x − 1, y, z; (ii) x − ,  − y, 1 − z].

Table 1

Selected bond lengths ()

Zn1O2	1.936(2)	P1O1	1.584(3)
Zn1O3i	1.940(2)	P1O2	1.510(3)
Zn1O4ii	1.968(2)	P1O3	1.525(2)
Zn1O5	1.943(3)	P1O4	1.522(2)

Symmetry codes: (i) ; (ii) .

As a consequence of the 21 axis lying parallel to [100], the alternating ZnO4 and (HO)PO3 tetrahedra form neutral ladder-like chains of edge-fused Zn2P2O4 rings that propagate parallel to the [100] direction (Fig. 2 ▸). l-Me­thio­nine mol­ecules are grafted on each side of the ladder and act as monodentate ligands rather than as a chelants (Brand et al., 2001 ▸). The geometrical parameters of the amino acid are unexceptional for zwitterionic me­thio­nine (Alagar et al., 2005 ▸). No extra framework components are present. As its most inter­esting aspect, the structure is homochiral: all me­th­io­nine ancillary ligands have the same S configuration at their C2 atoms as in the starting material (l-me­thio­nine). Such a structure is similar to that previously reported for zincophosphite chains (Dong et al., 2010 ▸; Gordon & Harrison, 2004 ▸) but is, to the best of our knowledge, unknown for zinco­phos­phates.

Figure 2

Ladder-like chains running parallel to [100] and decorated by l-me­thio­nine ligands in the structure of (I). Atoms are depicted as spheres with arbitrary radius. Color code: C gray, N blue, O red, H light gray, P purple, Zn green.

Supra­molecular features

No intra­chain hydrogen bonds are present, differing from the l-asparagine derivative described by Gordon & Harrison (2004 ▸). The ladder-like chains in (I) are assembled via a network of hydrogen-bonding inter­actions (Fig. 3 ▸ and Table 2 ▸). The ammonium group is engaged in three hydrogen bonds with a neighboring chain obtained by unitary translation along [010]. The hydrogen-bond acceptors are the HPO4 2− oxygen atoms O3 and O4 and the non-coordinating carboxyl­ate oxygen O6 of the me­thio­nine ligand. Along the [001] direction, the ladders are linked by hydrogen bonds between the pendant OH groups and the me­thio­nine sulfur atoms.

Figure 3

Crystal packing diagram for compound (I), viewed along [100]. Dashed lines represent hydrogen-bonding inter­actions (see Table 2 ▸ for details). Atoms are depicted as spheres with arbitrary radius using the same color code as in Fig. 2 ▸.

Table 2

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
O1HO1S1iii	0.81(1)	2.37(1)	3.177(3)	175(5)
N1H1AO4iv	0.89	2.07	2.820(3)	141
N1H1BO6v	0.89	1.99	2.785(4)	149
N1H1CO3vi	0.89	2.05	2.931(4)	172

Symmetry codes: (iii) ; (iv) ; (v) ; (vi) .

Synthesis and crystallization

The reaction mixture, with a molar composition of 2:1:1:180 for ZnO:P2O5:l-me­thio­nine:H2O, was prepared by mixing zinc oxide (Merck, 99%) with an appropriate amount of distilled water. Proper amounts of ortho­phospho­ric acid (Biochem, 98%) and l-me­thio­nine (Merck, 99%) were then added, under stirring. After heating at 373 K for 3 days, the solid obtained was recovered, washed with distilled water and dried at 333 K overnight. The solid product, consisting of small shiny crystals, turned out to be multiphasic, with hopeite and (I) as major components. Qualitative and qu­anti­tative phase analyses by powder XRD and Rietveld refinement gave (wt%): 80±1% of hopeite, 7.0±0.5% of (I), 2±0.2% of l-me­thio­nine, 1±0.2% of zinc oxide and 10±1% of an amorphous phase. Such a composition is in reasonable agreement with the C, H, N, S content of the bulk phase determined by combustion analysis. Analysis calculated (wt%) for the composition resulting from Rietveld refinement (neglecting the amorphous phase): C, 2.16 (13); H, 1.83 (3); N, 0.50 (3); S, 1.15 (7). Found: C, 2.5; H, 1.9; N, 0.6; S, 2.4. The occurrence of hopeite and (I) as main phases was confirmed by scanning electron microscopy and semi-qu­anti­tative EDS analysis. So far, we have been unable to isolate the new compound in pure form, and attempts to crystallize it in fluoride medium remained unsuccessful.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. C-bound H atoms were added in calculated positions with C—H = 0.98, 0.97, 0.96 Å for tertiary, secondary and methyl hydrogen atoms, respectively (the CH3 group was subjected to torsion-angle refinement). Isotropic displacement parameters for C—H hydrogen atoms were constrained to those of the parent atom, with U iso(H) = 1.5U eq(C) for methyl and U iso(H) = 1.2U eq(C) for the remaining hydrogen atoms. In a subsequent ΔF map, four electron-density residuals were clearly located close to the nitro­gen atom and to the non-bridging phosphate oxygen atom and refined as the ammonium and hydrogenphosphate H atoms, respectively. The ammonium group was constrained to have an idealized geometry with N—H = 0.89 Å and was subjected to torsion-angle refinement with a common U iso value for its H atoms. Note that when the occupancy factor of N-bound hydrogen atoms was decreased to 2/3, to model a rotationally disordered amino group, their U iso refined to an unphysically low value. The hydroxyl hydrogen atom was refined freely, but the O—H distance was restrained to 0.82 (1) Å. The Flack parameter for the complete structural model was x = 0.054 (16) by a classical fit to all intensities (Flack, 1983 ▸) and 0.063 (10) from 841 selected quotients (Parsons et al., 2013 ▸). The final refinement was then carried out as a two-component inversion twin, resulting in a 0.055 (16) fraction of the inverted component.

Table 3

Experimental details

Crystal data
Chemical formula	[Zn(HPO4)(C5H11NO2S)]
M r	310.56
Crystal system, space group	Orthorhombic, P212121
Temperature (K)	298
a, b, c ()	5.2210(2), 9.1889(4), 22.1559(10)
V (3)	1062.93(8)
Z	4
Radiation type	Mo K
(mm1)	2.67
Crystal size (mm)	0.33 0.07 0.01
Data collection
Diffractometer	BrukerNonius X8 APEX four-circle
Absorption correction	Multi-scan (SADABS; Bruker, 2008 ▸)
T min, T max	0.804, 0.974
No. of measured, independent and observed [I > 2(I)] reflections	7417, 2699, 2334
R int	0.029
(sin /)max (1)	0.682
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.026, 0.056, 1.00
No. of reflections	2699
No. of parameters	144
No. of restraints	1
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
max, min (e 3)	0.39, 0.36
Absolute structure	Refined as an inversion twin
Absolute structure parameter	0.055(16)

Computer programs: APEX2 and SAINT (Bruker, 2008 ▸), SIR92 (Altomare et al., 1993 ▸), SHELXL2014 (Sheldrick, 2015 ▸) and ORTEP-3 for Windows and WinGX (Farrugia, 2012 ▸).

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S2056989015011561/wm5165sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015011561/wm5165Isup2.hkl

Supporting information file. DOI: 10.1107/S2056989015011561/wm5165Isup3.pdf

CCDC reference: 1012270

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Zn(HPO4)(C5H11NO2S)]	Dx = 1.941 Mg m−3
Mr = 310.56	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P212121	Cell parameters from 2621 reflections
a = 5.2210 (2) Å	θ = 2.4–28.2°
b = 9.1889 (4) Å	µ = 2.67 mm−1
c = 22.1559 (10) Å	T = 298 K
V = 1062.93 (8) Å3	Needle, colourless
Z = 4	0.33 × 0.07 × 0.01 mm
F(000) = 632

Bruker–Nonius X8 APEX four-circle diffractometer	2699 independent reflections
Radiation source: fine-focus sealed tube	2334 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
Detector resolution: 66 pixels mm-1	θmax = 29.0°, θmin = 2.4°
phi and ω scans	h = −6→6
Absorption correction: multi-scan (SADABS; Bruker, 2008)	k = −8→12
Tmin = 0.804, Tmax = 0.974	l = −28→30
7417 measured reflections

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.026	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.056	w = 1/[σ2(Fo2) + (0.0227P)2] where P = (Fo2 + 2Fc2)/3
S = 1.00	(Δ/σ)max = 0.001
2699 reflections	Δρmax = 0.39 e Å−3
144 parameters	Δρmin = −0.36 e Å−3
1 restraint	Absolute structure: Refined as an inversion twin
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.055 (16)

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. After all nonhydrogen atoms were located and refined anisotropically, the model converged to wR(F2) = 0.0877 with a Flack parameter (determined by classical fit to all intensities) x = 0.044 (17) (Flack, 1983); for the inverted structure, the same parameters were 0.1288 and 0.94 (3), respectively. The absolute structure was then well defined and corresponded to an L configuration for the methionine ligand. C-bound hydrogen atoms were added in calculated positions with C—H = 0.98, 0.97, 0.96 Å for tertiary, secondary and methyl H atoms, respectively (the CH3 group was subject to torsion angle refinement using AFIX 137 instruction). Isotropic displacement parameters for C—H H atoms were constrained to those of the parent atom, with Uiso(H) = 1.5Ueq(C) for methyl and Uiso(H) = 1.2Ueq(C) for the remaining H atoms. In a subsequent ΔF map, four electron density residuals were clearly located close to the nitrogen atom and to the nonbridging phosphate oxygen and refined as the ammonium and hydrogenphosphate H atoms, respectively. The ammonium group was constrained to have an idealized geometry with N—H = 0.89 Å and was subject to torsion angle refinement with a common Uiso value for its H atoms. Note that when the occupancy factor of N-bound H atoms was decreased to 2/3, to model a rotationally disordered amino group, their Uiso refined to an unphysically low value. The hydroxyl hydrogen was refined freely, but the O—H distance was restrained to 0.82 (1) Å. The Flack parameter for the complete structural model was x = 0.054 (16) by classical fit to all intensities (Flack, 1983) and 0.063 (10) from 841 selected quotients (Parsons et al., 2013). Final refinement was carried out as a 2-component inversion twin, resulting in a 0.055 (16) fraction of inverted component.

	x	y	z	Uiso*/Ueq
Zn1	0.50773 (8)	0.10750 (4)	0.55705 (2)	0.01929 (10)
P1	1.01002 (19)	0.29242 (8)	0.57930 (3)	0.01729 (16)
S1	0.3692 (2)	−0.35340 (15)	0.77437 (5)	0.0446 (3)
O1	0.9167 (5)	0.3698 (3)	0.63929 (12)	0.0322 (6)
HO1	0.848 (8)	0.309 (4)	0.6596 (19)	0.056 (16)*
O2	0.8659 (4)	0.1515 (3)	0.57061 (11)	0.0253 (5)
O3	1.2977 (4)	0.2677 (3)	0.58537 (11)	0.0226 (5)
O4	0.9594 (4)	0.4063 (3)	0.53087 (10)	0.0236 (5)
O5	0.3925 (5)	−0.0803 (3)	0.58683 (12)	0.0320 (6)
O6	0.7309 (5)	−0.1965 (3)	0.54837 (13)	0.0347 (7)
N1	0.4865 (6)	−0.4489 (3)	0.54404 (11)	0.0213 (5)
H1A	0.6565	−0.4529	0.5467	0.040 (7)*
H1B	0.4419	−0.4252	0.5065	0.040 (7)*
H1C	0.4207	−0.5354	0.5533	0.040 (7)*
C1	0.5183 (7)	−0.1933 (3)	0.57187 (13)	0.0218 (6)
C2	0.3873 (6)	−0.3376 (4)	0.58669 (15)	0.0220 (7)
H2	0.2019	−0.3274	0.5812	0.026*
C3	0.4427 (7)	−0.3861 (4)	0.65115 (14)	0.0284 (8)
H3A	0.3895	−0.4866	0.6560	0.034*
H3B	0.6258	−0.3814	0.6583	0.034*
C4	0.3057 (8)	−0.2928 (5)	0.69771 (17)	0.0368 (9)
H4A	0.1227	−0.2962	0.6902	0.044*
H4B	0.3610	−0.1925	0.6934	0.044*
C5	0.1420 (9)	−0.4984 (6)	0.7819 (2)	0.0594 (13)
H5A	0.1428	−0.5333	0.8228	0.089*
H5B	0.1875	−0.5764	0.7551	0.089*
H5C	−0.0259	−0.4634	0.7719	0.089*

	U11	U22	U33	U12	U13	U23
Zn1	0.01776 (17)	0.01329 (16)	0.02682 (17)	−0.0009 (2)	−0.0005 (2)	0.00083 (13)
P1	0.0160 (4)	0.0145 (4)	0.0214 (3)	0.0000 (5)	0.0011 (4)	−0.0014 (3)
S1	0.0541 (7)	0.0502 (8)	0.0295 (5)	−0.0040 (6)	0.0060 (5)	−0.0076 (5)
O1	0.0388 (16)	0.0272 (16)	0.0306 (13)	0.0009 (11)	0.0122 (11)	−0.0057 (11)
O2	0.0157 (11)	0.0208 (13)	0.0395 (14)	−0.0035 (10)	−0.0027 (10)	−0.0015 (11)
O3	0.0156 (11)	0.0180 (13)	0.0343 (13)	0.0017 (10)	−0.0031 (10)	−0.0025 (10)
O4	0.0252 (14)	0.0208 (12)	0.0248 (10)	0.0049 (12)	0.0017 (9)	0.0036 (9)
O5	0.0373 (14)	0.0133 (13)	0.0456 (15)	−0.0019 (11)	0.0130 (12)	0.0017 (11)
O6	0.0283 (14)	0.0252 (16)	0.0505 (17)	−0.0063 (12)	0.0121 (12)	0.0004 (13)
N1	0.0229 (14)	0.0147 (12)	0.0264 (13)	−0.0005 (16)	−0.0011 (15)	−0.0007 (9)
C1	0.0261 (17)	0.0162 (15)	0.0232 (14)	−0.0036 (19)	−0.0021 (17)	0.0029 (10)
C2	0.0202 (16)	0.0148 (17)	0.0309 (18)	−0.0001 (14)	0.0037 (14)	−0.0037 (14)
C3	0.035 (2)	0.0196 (18)	0.0306 (16)	0.0021 (15)	0.0038 (14)	0.0012 (14)
C4	0.050 (2)	0.029 (2)	0.032 (2)	0.0037 (19)	0.0103 (19)	0.0007 (17)
C5	0.082 (3)	0.052 (3)	0.045 (3)	−0.019 (3)	0.002 (3)	0.007 (2)

Zn1—O2	1.936 (2)	S1—C4	1.818 (4)
Zn1—O3i	1.940 (2)	S1—C5	1.792 (5)
Zn1—O4ii	1.968 (2)	O1—HO1	0.807 (13)
Zn1—O5	1.943 (3)	N1—H1A	0.8900
P1—O1	1.584 (3)	N1—H1B	0.8900
P1—O2	1.510 (3)	N1—H1C	0.8900
P1—O3	1.525 (2)	C2—H2	0.9800
P1—O4	1.522 (2)	C3—H3A	0.9700
O5—C1	1.272 (4)	C3—H3B	0.9700
O6—C1	1.226 (4)	C4—H4A	0.9700
C1—C2	1.528 (4)	C4—H4B	0.9700
N1—C2	1.486 (4)	C5—H5A	0.9600
C2—C3	1.524 (5)	C5—H5B	0.9600
C3—C4	1.521 (5)	C5—H5C	0.9600
O2—Zn1—O3i	109.71 (10)	O5—C1—C2	114.9 (3)
O2—Zn1—O5	115.56 (11)	N1—C2—C3	109.2 (3)
O3i—Zn1—O5	112.91 (11)	N1—C2—C1	107.8 (3)
O2—Zn1—O4ii	106.90 (10)	C3—C2—C1	111.7 (3)
O3i—Zn1—O4ii	107.25 (10)	N1—C2—H2	109.4
O5—Zn1—O4ii	103.84 (11)	C3—C2—H2	109.4
O2—P1—O4	114.41 (14)	C1—C2—H2	109.4
O2—P1—O3	111.98 (14)	C4—C3—C2	112.4 (3)
O4—P1—O3	109.60 (14)	C4—C3—H3A	109.1
O2—P1—O1	109.81 (15)	C2—C3—H3A	109.1
O4—P1—O1	103.27 (14)	C4—C3—H3B	109.1
O3—P1—O1	107.20 (14)	C2—C3—H3B	109.1
C5—S1—C4	101.2 (2)	H3A—C3—H3B	107.9
P1—O1—HO1	107 (4)	C3—C4—S1	112.0 (3)
P1—O2—Zn1	132.83 (15)	C3—C4—H4A	109.2
P1—O3—Zn1iii	129.87 (15)	S1—C4—H4A	109.2
P1—O4—Zn1iv	129.16 (14)	C3—C4—H4B	109.2
C1—O5—Zn1	118.4 (2)	S1—C4—H4B	109.2
C2—N1—H1A	109.5	H4A—C4—H4B	107.9
C2—N1—H1B	109.5	S1—C5—H5A	109.5
H1A—N1—H1B	109.5	S1—C5—H5B	109.5
C2—N1—H1C	109.5	H5A—C5—H5B	109.5
H1A—N1—H1C	109.5	S1—C5—H5C	109.5
H1B—N1—H1C	109.5	H5A—C5—H5C	109.5
O6—C1—O5	126.7 (3)	H5B—C5—H5C	109.5
O6—C1—C2	118.4 (3)

D—H···A	D—H	H···A	D···A	D—H···A
O1—HO1···S1v	0.81 (1)	2.37 (1)	3.177 (3)	175 (5)
N1—H1A···O4vi	0.89	2.07	2.820 (3)	141
N1—H1B···O6vii	0.89	1.99	2.785 (4)	149
N1—H1C···O3viii	0.89	2.05	2.931 (4)	172