The inorganic–organic hybrid zinc phosphite poly[(μ₃-hydrogen phosphito-κ³O:O′:O′′)(piperidin-1-ium-4-car­box­yl­ate-κO)zinc(II)]

A new inorganic–organic hybrid zinc phosphite, [Zn(HPO₃)(C₆H₁₁NO₂)]_n, has been synthesized hydro­thermally. Proton­ated piperidin-1-ium-4-carboxyl­ate (PDCA) was generated in situ by hydrolysis of the piperidine-4-carboxamide precursor. The P atom possesses a typical PO₃H pseudo-pyramidal geom­etry. The crystal structure features an unusual (3,4)-connected two-dimensional inorganic zinc–phosphite layer, with organic PDCA ligands appended to the sheets and protruding into the inter­layer region. Helical chains of opposite chirality are involved in the construction of a puckered sheet structure.

S1. Introduction

Zeolites and related crystalline microporous materials have been extensively investigated for decades due to their rich structural chemistry and wide range of applications in catalysis, separation, ion-exchange etc (Cheetham et al., 1999; Davis, 2002; Parnham & Morris, 2007; Jiang et al., 2010). Of the many known open-framework compounds, metal phosphites have recently attracted special inter­est because they show structural diversity and versatility similar to that of the phosphates. Compared with the 4-connected PO₄ unit, the presence of a 3-connected HPO₃^2- group can reduce the M—O—P connectivity and thus favours the generation of open structures with larger pore sizes. Prominent examples include a trimetallic phosphite, Zn₂Al_0.57Cr_0.10(HPO₃)₄(C₆H₁₁NH₃)₂(H₂O)₄ (Cr-NKU-24), a low density beryllium phosphite, (C₄H₁₂N)₂[Be₃(HPO₃)₄] (SCU-24), and six zinc phosphites with 24-ring channels, an aluminium-zinc bimetallic phosphite, (C₄H₉NH₃)₂[AlFZn₂(HPO₃)₄] (NTHU-5), with 26R channels, and recently reported gallium zincophosphites (the NTHU-13 family) with 28R, 40R, 48R, 56R, 64R and 72R channels (Liang et al., 2006; Lai et al., 2007; Yang et al., 2007; Li et al., 2008; Luo et al., 2011; Wang et al., 2012; Lin et al., 2013) [Please associate the references with the examples above]. Metal–phosphite frameworks are usually synthesized hydro­thermally using various organic amines as templates. In most cases, such organic moieties are protonated and serve as charge-compensating and space-filling constituents. In a few cases, organic molecules are neutral and bonded directly to the metal atoms to form inorganic–organic hybrid architectures (Rodgers & Harrison, 2000; Shi et al., 2003; Kirkpatrick & Harrison, 2004). Herein, we prepared a new hybrid open-framework zinc phosphite, nanemy poly[(µ₃-hydrogen phosphito-κ³O:O':O')(piperidin-1-ium-4-carboxyl­ate-κO)zinc(II)], (I), in which the unusual N-protonated piperidin-1-ium-4-carboxyl­ate (PDCA) was generated in situ from the piperidine-4-carboxamide precursor.

S2. Experimental

S2.1. Synthesis and crystallization

The title compound was synthesized under mild solvothermal conditions. In a typical synthesis, a mixture of Zn(CH₃COO)₂.2H₂O (1 mmol, 0.22 g), H₃PO₃ (5 mmol, 0.41 g), piperidine-4-carboxamide (3 mmol, 0.39 g), ethanol (51 mmol, 3 ml) and H₂O (56 mmol, 2 ml) was sealed in a 25 ml Teflon-lined steel autoclave and heated under autogenous pressure at 428 K for 7 d. Colourless prism-like crystals were recovered by filtration, washed with distilled water and dried in air.

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms bound to C atoms were positioned geometrically, with C—H distances of 0.97 Å, and constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C). H atoms bound to P, O and N atoms were located in a difference Fourier map and treated as riding, with U_iso(H) = 1.2U_eq(P,O,N).

S3. Results and discussion

As shown in Fig. 1, the asymmetric unit of (I) contains one Zn²⁺ ion, one [HPO₃]^2- (hydrogen phosphite) unit and one PDCA ligand. A review of the literature shows that most ligands introduced into the hybrid metal phosphites are of direct use, and mainly feature as rigid oxalate- and bi­pyridine-type molecules. By contrast, reports on in situ hydro­(solvo)thermal ligand (template) syntheses in this area are still limited. Thus, the in situ formation of the PDCA ligand in (I) is unique. The Zn1 atom is in a distorted tetra­hedral geometry formed by three O atoms from three neighboring [HPO₃]^2- groups and one O atom from the PDCA ligand. The Zn—O bond lengths range from 1.947 (2) to 1.999 (2) Å, and the O—Zn—O angles lie in the 91.47 (9)–117.82 (10)° range. Atom P1 makes three P—O—Zn linkages with adjacent Zn atoms, with the fourth vertex occupied by a terminal H atom. The P—O bond lengths are in the range of 1.515 (2)–1.528 (2) Å, and the O—P—O angles span from 110.29 (12) to 113.75 (13)°.

Each tetra­hedral [HPO₃]^2- group is alternately linked to three neighbouring tetra­hedral ZnO₄ groups to form a two-dimensional wave-like (ZnHPO₃)_n layer with unique eight- and 16-membered rings (Fig. 2). The Zn···Zn distances in the eight-membered ring is 4.3712 (5) Å, while the separation of the inversion related Zn atoms [at (x, y, z) and (-x+1, -y, -z+1)] in the 16-membered ring is 7.6703 (5) Å. Inter­estingly, two types of helices with opposite chirality are involved in the construction of the inorganic layer. One-dimensional infinite helical chains of opposite chirality, co-existing in the structure consisting of –Zn1—O1—P1—O2– and –Zn1—O2ⁱ—P1ⁱ—O1ⁱ– chains [symmetry code: (i) -x+1, y-1/2, -z+1/2] couple with each other by sharing the common O3 atoms to generate the zinc–phosphite layer. The central axis of each helical chain is a twofold screw axis along the crystallographic b axis. It is worth noting that similar layer structures made up of chains of opposite chirality are particularly rare in microporous materials. One typical example is (C₅H₆N₂)Zn(HPO₃), which also crystallized in the space group P2₁/c and an aromatic cyclic amine (pyridin-2-amine) was introduced (Jiang et al., 2003). The monoprotonated zwitterionic PDCA ligand in (I), adopting a monodentate coordination mode, is bonded to the tetra­hedral Zn centre and protrude away from the inorganic layers as pendent groups. Fig. 3 shows the packing of the layers along the [100] direction. The cyclic hydro­phobic rings of the PDCA ligands protrude toward the inter­layer region. Strong hydrogen bonds exist between the –NH₂ groups of the piperidine rings and the bridging phosphite O2 and carboxyl­ate O5 atoms within the layer [N···O = 2.787 (4)–2.837 (4) Å], which inter­connect adjacent zinc–phosphite sheets into a three-dimensional supra­molecular framework.

Related literature

For related literature, see: Cheetham et al. (1999); Davis (2002); Jiang et al. (2003, 2010); Kirkpatrick & Harrison (2004); Lai et al. (2007); Li et al. (2008); Liang et al. (2006); Lin et al. (2013); Luo et al. (2011); Parnham & Morris (2007); Rodgers & Harrison (2000); Shi et al. (2003); Wang et al. (2012); Yang et al. (2007).

Computing details

Data collection: APEX2 (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. See Table 2 for symmetry codes.
	Fig. 2. A view of the two-dimensional zinc phosphite layer in the bc plane. [Symmetry codes: (v) -x+1, -y+1, -z+1; (vi) -x+1, -y, -z+1.]
	Fig. 3. The packing of the wave-like layers of (I) along the [100] direction.

Poly[(µ₃-hydrogen phosphito-κ³O:O':O')(piperidin-1-ium-4-carboxylate-κO)zinc(II)]

Crystal data

[Zn(HPO3)(C6H11NO2)]	F(000) = 560
Mr = 274.51	Dx = 1.858 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 9838 reflections
a = 10.2729 (3) Å	θ = 3.0–27.5°
b = 9.8483 (5) Å	µ = 2.66 mm^−1
c = 10.6510 (3) Å	T = 295 K
β = 114.368 (4)°	Prism, colourless
V = 981.57 (6) Å^3	0.18 × 0.16 × 0.12 mm
Z = 4

Data collection

Bruker APEXII area-detector diffractometer	2245 independent reflections
Radiation source: fine-focus sealed tube	1948 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.086
φ and ω scans	θmax = 27.5°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −13→13
Tmin = 0.646, Tmax = 0.741	k = −12→12
9838 measured reflections	l = −13→13

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.099	H-atom parameters constrained
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0324P)^2 + 0.3072P] where P = (Fo^2 + 2Fc^2)/3
2245 reflections	(Δ/σ)max = 0.001
127 parameters	Δρmax = 0.51 e Å^−3
0 restraints	Δρmin = −0.83 e Å^−3

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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² 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 (Ų)

	x	y	z	Uiso*/Ueq
Zn1	0.59984 (4)	0.09765 (3)	0.20238 (3)	0.02282 (15)
P1	0.56544 (9)	0.32106 (8)	0.40558 (8)	0.0219 (2)
H1	0.6920	0.3352	0.4630	0.026*
O1	0.5465 (2)	0.1791 (2)	0.3426 (2)	0.0275 (5)
O2	0.5000 (3)	0.4281 (2)	0.2952 (2)	0.0381 (6)
O3	0.5101 (2)	0.3250 (2)	0.5181 (2)	0.0305 (5)
O4	0.8064 (2)	0.0573 (3)	0.2548 (2)	0.0388 (6)
O5	0.8103 (3)	0.2806 (3)	0.2693 (3)	0.0553 (8)
C1	1.2002 (4)	0.1373 (4)	0.1882 (4)	0.0416 (9)
H1A	1.2093	0.1101	0.1047	0.050*
H1B	1.2357	0.2295	0.2100	0.050*
C2	1.2730 (4)	0.0739 (4)	0.4343 (4)	0.0375 (9)
H2A	1.3127	0.1626	0.4687	0.045*
H2B	1.3264	0.0068	0.5030	0.045*
C3	1.1170 (4)	0.0700 (4)	0.4119 (3)	0.0329 (8)
H3A	1.1093	0.0941	0.4969	0.039*
H3B	1.0800	−0.0213	0.3869	0.039*
C4	1.0443 (4)	0.1332 (4)	0.1641 (4)	0.0394 (9)
H4A	1.0060	0.0432	0.1334	0.047*
H4B	0.9906	0.1975	0.0924	0.047*
C5	1.0278 (3)	0.1687 (4)	0.2979 (3)	0.0318 (8)
H5	1.0662	0.2603	0.3261	0.038*
C6	0.8708 (4)	0.1703 (4)	0.2727 (3)	0.0334 (8)
N1	1.2879 (3)	0.0454 (3)	0.3033 (3)	0.0373 (7)
H1C	1.3804	0.0539	0.3183	0.045*
H1D	1.2617	−0.0411	0.2780	0.045*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0280 (2)	0.0227 (2)	0.0242 (2)	0.00042 (15)	0.01722 (18)	0.00089 (13)
P1	0.0270 (4)	0.0213 (4)	0.0231 (4)	−0.0013 (3)	0.0161 (3)	−0.0020 (3)
O1	0.0382 (13)	0.0209 (12)	0.0334 (11)	−0.0017 (10)	0.0248 (10)	−0.0041 (9)
O2	0.0621 (18)	0.0270 (13)	0.0383 (13)	0.0166 (12)	0.0338 (13)	0.0090 (10)
O3	0.0410 (14)	0.0325 (13)	0.0275 (11)	−0.0077 (11)	0.0237 (10)	−0.0069 (9)
O4	0.0264 (13)	0.0436 (16)	0.0504 (15)	0.0007 (12)	0.0200 (12)	0.0056 (12)
O5	0.0499 (17)	0.0443 (18)	0.086 (2)	0.0152 (14)	0.0422 (16)	0.0042 (15)
C1	0.036 (2)	0.059 (3)	0.039 (2)	0.0049 (19)	0.0246 (17)	0.0136 (18)
C2	0.033 (2)	0.043 (2)	0.040 (2)	0.0021 (17)	0.0179 (17)	0.0096 (16)
C3	0.0321 (19)	0.041 (2)	0.0294 (17)	0.0012 (16)	0.0163 (15)	0.0056 (15)
C4	0.0278 (19)	0.059 (3)	0.0343 (18)	0.0037 (18)	0.0158 (16)	0.0089 (17)
C5	0.0275 (18)	0.033 (2)	0.0391 (18)	0.0020 (15)	0.0184 (15)	0.0013 (15)
C6	0.0283 (18)	0.045 (2)	0.0323 (17)	0.0080 (17)	0.0178 (15)	0.0064 (15)
N1	0.0297 (16)	0.0384 (18)	0.0529 (18)	0.0018 (14)	0.0262 (15)	0.0051 (14)

Geometric parameters (Å, º)

Zn1—O1	1.9623 (19)	C1—H1B	0.9700
Zn1—O2^i	1.965 (2)	C2—N1	1.492 (4)
Zn1—O3^ii	1.947 (2)	C2—C3	1.521 (5)
Zn1—O4	1.999 (2)	C2—H2A	0.9700
P1—O1	1.528 (2)	C2—H2B	0.9700
P1—O2	1.515 (2)	C3—C5	1.529 (5)
P1—O3	1.524 (2)	C3—H3A	0.9700
P1—H1	1.1950	C3—H3B	0.9700
O2—Zn1^iii	1.965 (2)	C4—C5	1.544 (4)
O3—Zn1^iv	1.947 (2)	C4—H4A	0.9700
O4—C6	1.268 (4)	C4—H4B	0.9700
O5—C6	1.245 (4)	C5—C6	1.522 (4)
C1—N1	1.490 (4)	C5—H5	0.9800
C1—C4	1.514 (5)	N1—H1C	0.9000
C1—H1A	0.9700	N1—H1D	0.9000
O3^ii—Zn1—O1	116.28 (9)	C2—C3—C5	110.9 (3)
O3^ii—Zn1—O2^i	108.26 (10)	C2—C3—H3A	109.5
O1—Zn1—O2^i	91.47 (9)	C5—C3—H3A	109.5
O3^ii—Zn1—O4	111.45 (9)	C2—C3—H3B	109.5
O1—Zn1—O4	117.82 (10)	C5—C3—H3B	109.5
O2^i—Zn1—O4	109.10 (11)	H3A—C3—H3B	108.1
O2—P1—O3	113.75 (13)	C1—C4—C5	110.4 (3)
O2—P1—O1	111.16 (13)	C1—C4—H4A	109.6
O3—P1—O1	110.29 (12)	C5—C4—H4A	109.6
O2—P1—H1	110.9	C1—C4—H4B	109.6
O3—P1—H1	105.9	C5—C4—H4B	109.6
O1—P1—H1	104.3	H4A—C4—H4B	108.1
P1—O1—Zn1	133.06 (13)	C6—C5—C3	113.0 (3)
P1—O2—Zn1^iii	130.39 (14)	C6—C5—C4	110.6 (3)
P1—O3—Zn1^iv	128.88 (14)	C3—C5—C4	109.3 (3)
C6—O4—Zn1	107.2 (2)	C6—C5—H5	107.9
N1—C1—C4	111.2 (3)	C3—C5—H5	107.9
N1—C1—H1A	109.4	C4—C5—H5	107.9
C4—C1—H1A	109.4	O5—C6—O4	122.6 (3)
N1—C1—H1B	109.4	O5—C6—C5	119.6 (3)
C4—C1—H1B	109.4	O4—C6—C5	117.8 (3)
H1A—C1—H1B	108.0	C1—N1—C2	113.2 (3)
N1—C2—C3	110.9 (3)	C1—N1—H1C	108.9
N1—C2—H2A	109.5	C2—N1—H1C	108.9
C3—C2—H2A	109.5	C1—N1—H1D	108.9
N1—C2—H2B	109.5	C2—N1—H1D	108.9
C3—C2—H2B	109.5	H1C—N1—H1D	107.7
H2A—C2—H2B	108.0
O2—P1—O1—Zn1	56.2 (2)	N1—C1—C4—C5	56.1 (4)
O3—P1—O1—Zn1	−176.67 (16)	C2—C3—C5—C6	−179.2 (3)
O3^ii—Zn1—O1—P1	−63.1 (2)	C2—C3—C5—C4	57.2 (4)
O2^i—Zn1—O1—P1	−174.33 (19)	C1—C4—C5—C6	177.7 (3)
O4—Zn1—O1—P1	73.1 (2)	C1—C4—C5—C3	−57.3 (4)
O3—P1—O2—Zn1^iii	19.0 (3)	Zn1—O4—C6—O5	6.1 (4)
O1—P1—O2—Zn1^iii	144.26 (18)	Zn1—O4—C6—C5	−173.3 (2)
O2—P1—O3—Zn1^iv	−100.6 (2)	C3—C5—C6—O5	129.9 (3)
O1—P1—O3—Zn1^iv	133.71 (16)	C4—C5—C6—O5	−107.3 (4)
O3^ii—Zn1—O4—C6	70.4 (2)	C3—C5—C6—O4	−50.7 (4)
O1—Zn1—O4—C6	−67.8 (2)	C4—C5—C6—O4	72.2 (4)
O2^i—Zn1—O4—C6	−170.15 (19)	C4—C1—N1—C2	−55.3 (4)
N1—C2—C3—C5	−55.8 (4)	C3—C2—N1—C1	54.8 (4)

Symmetry codes: (i) −x+1, y−1/2, −z+1/2; (ii) x, −y+1/2, z−1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) x, −y+1/2, z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1C···O1^v	0.90	2.03	2.837 (4)	148
N1—H1D···O5^vi	0.90	1.89	2.787 (4)	174

Symmetry codes: (v) x+1, y, z; (vi) −x+2, y−1/2, −z+1/2.