Poly[μ₂-4-amino­benzoato-aqua-μ₂-nitrato-zinc]

In the title compound, [Zn(C₇H₆NO₂)(NO₃)(H₂O)]_n, the Zn atom is coordinated by two nitrate ions, one aqua mol­ecule and two 4-amino­benzoate ions in a distorted octa­hedral geometry. The structure of the compound exhibits a two-dimensional layer, which is formed by the inter­connection of [Zn(C₇H₆NO₂)(H₂O)]_n chains via μ₂-nitrate bridges or by the inter­connection of [Zn(NO₃)(H₂O)]_n chains via μ₂-4-amino­benzoate bridges.

S1. Comment

Metal–organic framework materials have made rapid progress in recent years because this class of materials may have interesting physicochemical properties and potential applications such as adsorption, ion exchange and shape-selective catalysis, and as non-linear optical and magnetic materials. A number of rigid or flexible bridging ligands have been employed to construct metal–organic materials, including one-, two- or three-dimensional frameworks. Generally, the construction of frameworks can be achieved using either covalent bonds or weaker intermolecular forces, e.g. hydrogen bonds, aryl–aryl interactions etc.

As a bifunctional organic ligand, 4-aminobenzoic acid (4-abaH) has been reported in coordination chemistry because of the richness of its coordination modes. Firstly, 4-abaH can act as a carboxylic acid synthon and also as a good monodentate ligand through the amine group (Le Fur & Masse, 1996; Chen & Chen, 2002). Secondly, deprotonated 4-aminobenzoic acid can act as a monodentate ligand through a carboxylate O atom (Sundberg et al., 1998; Chandrasekhar et al., 1988; Amiraslanov et al., 1979), chelating and/or bridging ligands through its amide and/or carboxylate groups (Zheng et al., 2001; Rzaezynska & Belskii, 1994; Hauptmann et al., 2000). Finally, 4-abaH may be protonated to form organic cation templating agents (Wang et al., 2002). Recently, a compound containing mixed 4-aminobenzoate and another nitrogen-donor ligand has been synthesized in our group (Zhang & Lu, 2005). As a part of our continuing investigation of this type of compound, we report here the synthesis and characterization of the title complex, (I).

As shown in Fig. 1, the Zn atom of (I) is coordinated by two chelating carboxylate O atoms from one 4-aminobenzoate ion, two bridging nitrate O atoms, an N atom from the other 4-aminobenzoate ion and one coordinated water molecule in a distorted octahedral geometry. The two nitrate O atoms [O4 and O5ⁱⁱ; symmetry code: (ii) 1/2 + x, 1/2 - y, 1/2 + z] are at the apical positions [Zn—O = 2.124 (2) and 2.333 (2) Å, and O—Zn—O = 165.97 (8)°], while the two carboxylate O atoms [O1ⁱ and O2ⁱ; symmetry code: (i) -1/2 + x, 1/2 - y, 1/2 + z], the N atom (N1), and the water O atom (O3) define the equatorial plane (mean deviation 0.224 Å). Zn is raised above the equatorial plane by 0.284 Å towards the apical atom, O4.

The 4-aminobenzoate ligand adopts a chelating/bridging coordination mode (Wang et al., 2002), linking two neighbouring Zn coordination centres to form a one-dimensional chain, [Zn(H₂O)(C₇H₆NO₂)]_n, with a Zn—N—C bond angle of 115.9 (2)° and a Zn···Zn separation of 9.40 (2) Å. Similarly, the nitrate ion acts as a µ₂-bridge (Huang et al., 2004; Ling et al., 2004), linking two neighbouring metal centres to form another one-dimensional chain, [Zn(NO₃)(H₂O)]_n, with Zn—O—N bond angles of 112.5 (2) and 124.9 (2)° and a Zn···Zn separation of 5.74 (3) Å. Thus, compound (I) exhibits a two-dimensional layer-like structure (Fig. 2), which is formed by the interconnection of neighbouring [Zn(H₂O)(C₇H₆NO₂)]_n chains via µ₂-NO₃^- bridges or by that of neighbouring [Zn(NO₃)(H₂O)]_n chains via µ₂-4-aminobenzoate bridges. The two-dimensional layer consists of rectangular grids with dimensions of 9.40 (2) × 5.74 (3) Å, based on the Zn···Zn distances.

It is noteworthy that there is hydrogen bonding in the title compound. One weak interaction occurs between the layers in (I). The water ligand forms hydrogen bonds with the carboxylate O atoms of the 4-aminobenzoate, with O—H···O distances of 2.720 (3) and 2.721 (3) Å (Table 2). Such hydrogen bonding-interactions consolidate the structural architecture and further extend the two-dimensional layers into a three-dimensional framework.

Related literature

For related literature, see: Amiraslanov et al. (1979); Chandrasekhar et al. (1988); Chen & Chen (2002); Hauptmann et al. (2000); Huang et al. (2004); Le Fur & Masse (1996); Ling et al. (2004); Rzaezynska & Belskii (1994); Sundberg et al. (1998); Wang et al. (2002); Zhang & Lu (2005); Zheng et al. (2001).

S2. Experimental

An ethanol solution (8 ml) of 2,2'-bipyridine (1.2 mmol) and 4-aminobenzoic acid (1.6 mmol) was added slowly to an aqueous solution (10 ml) of Zn(NO₃)₂·6H₂O (1 mmol) with continuous stirring. After half an hour, the reaction mixture was allowed to stand at room temperature undisturbed for two weeks, resulting in colourless crystals of (I) (yield 71%). Analysis, calculated for C₇H₈N₂O₆Zn: C 29.86, H 2.86, N 9.95%; found: C 29.81, H 2.71, N 9.89%.

S3. Refinement

The H atoms of the coordinated water molecule were located in a difference Fourier map and refined isotropically. The remaining H atoms were constrained to an ideal geometry, with N—H = 0.90 and C—H = 0.93 Å, and with U_iso(H) = 1.2U_eq(C,N). [Please check added text]

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SAINT (Siemens, 1994); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Siemens, 1994); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A locally expanded unit of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) -1/2 + x, 1/2 - y, 1/2 + z; (ii) 1/2 + x, 1/2 - y, 1/2 + z].
	Fig. 2. The two-dimensional structure of (I). All H atoms have been omitted for clarity.

Poly[µ₂-4-aminobenzoato-aqua-µ₂-nitrato-zinc]

Crystal data

[Zn(C7H6NO2)(NO3)(H2O)]	F(000) = 568
Mr = 281.52	Dx = 1.900 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 2033 reflections
a = 10.6087 (16) Å	θ = 3.1–27.5°
b = 9.4342 (10) Å	µ = 2.51 mm^−1
c = 11.1367 (19) Å	T = 293 K
β = 118.000 (6)°	Prism, colourless
V = 984.1 (2) Å^3	0.20 × 0.16 × 0.08 mm
Z = 4

Data collection

Siemens SMART CCD area-detector diffractometer	2256 independent reflections
Radiation source: fine-focus sealed tube	1864 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.044
ω scans	θmax = 27.5°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −13→13
Tmin = 0.760, Tmax = 1.000	k = −12→12
7449 measured reflections	l = −14→11

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) = 0.092	H atoms treated by a mixture of independent and constrained refinement
S = 1.11	w = 1/[σ^2(Fo^2) + (0.0384P)^2 + 0.3274P] where P = (Fo^2 + 2Fc^2)/3
2256 reflections	(Δ/σ)max < 0.001
153 parameters	Δρmax = 0.59 e Å^−3
0 restraints	Δρmin = −0.43 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	0.65364 (4)	0.31488 (4)	0.60597 (4)	0.02357 (13)
N1	0.7853 (3)	0.1528 (3)	0.6138 (3)	0.0242 (6)
H1A	0.8548	0.1442	0.7002	0.029*
H1B	0.7345	0.0718	0.5918	0.029*
N2	0.4198 (3)	0.1554 (3)	0.4055 (3)	0.0265 (6)
C1	1.0579 (3)	0.2065 (3)	0.2796 (3)	0.0224 (7)
C2	0.9809 (3)	0.1954 (3)	0.3620 (3)	0.0238 (7)
C3	1.0246 (4)	0.2765 (4)	0.4775 (4)	0.0358 (9)
H3A	1.0980	0.3416	0.5001	0.043*
C4	0.9610 (4)	0.2626 (4)	0.5607 (4)	0.0347 (9)
H4	0.9922	0.3174	0.6389	0.042*
C5	0.8513 (3)	0.1673 (3)	0.5268 (3)	0.0230 (7)
C6	0.8038 (4)	0.0875 (4)	0.4093 (4)	0.0307 (8)
H6	0.7276	0.0253	0.3848	0.037*
C7	0.8698 (4)	0.1003 (3)	0.3285 (3)	0.0293 (8)
H7	0.8394	0.0447	0.2508	0.035*
O1	1.1493 (2)	0.2996 (2)	0.3035 (2)	0.0280 (5)
O2	1.0290 (2)	0.1165 (2)	0.1837 (2)	0.0253 (5)
O3	0.6962 (3)	0.4876 (2)	0.5259 (3)	0.0274 (5)
H3C	0.752 (6)	0.549 (5)	0.580 (5)	0.081 (18)*
H3B	0.626 (4)	0.524 (4)	0.460 (4)	0.031 (11)*
O4	0.4943 (2)	0.2617 (2)	0.4067 (2)	0.0312 (5)
O5	0.3488 (3)	0.0910 (2)	0.2962 (2)	0.0320 (5)
O6	0.4198 (3)	0.1176 (3)	0.5109 (3)	0.0419 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0249 (2)	0.0260 (2)	0.0228 (2)	0.00055 (16)	0.01374 (18)	−0.00098 (16)
N1	0.0281 (15)	0.0263 (14)	0.0233 (15)	−0.0005 (11)	0.0164 (13)	0.0019 (11)
N2	0.0234 (15)	0.0264 (15)	0.0236 (15)	−0.0010 (12)	0.0058 (12)	−0.0025 (12)
C1	0.0226 (17)	0.0261 (16)	0.0192 (16)	0.0051 (13)	0.0104 (14)	0.0045 (13)
C2	0.0262 (17)	0.0256 (16)	0.0229 (17)	−0.0006 (13)	0.0143 (15)	−0.0008 (13)
C3	0.038 (2)	0.041 (2)	0.037 (2)	−0.0182 (17)	0.0255 (19)	−0.0181 (17)
C4	0.042 (2)	0.041 (2)	0.031 (2)	−0.0125 (17)	0.0256 (19)	−0.0170 (16)
C5	0.0264 (17)	0.0240 (16)	0.0241 (17)	0.0033 (13)	0.0165 (15)	0.0015 (13)
C6	0.0303 (19)	0.0366 (19)	0.032 (2)	−0.0105 (15)	0.0198 (17)	−0.0094 (15)
C7	0.0327 (19)	0.0347 (19)	0.0250 (18)	−0.0079 (15)	0.0174 (16)	−0.0103 (15)
O1	0.0293 (13)	0.0281 (12)	0.0318 (14)	−0.0055 (10)	0.0188 (12)	−0.0011 (10)
O2	0.0274 (13)	0.0297 (12)	0.0208 (12)	−0.0036 (10)	0.0129 (11)	−0.0052 (10)
O3	0.0267 (14)	0.0265 (13)	0.0244 (14)	−0.0006 (11)	0.0082 (12)	0.0035 (11)
O4	0.0269 (13)	0.0337 (13)	0.0263 (13)	−0.0103 (11)	0.0071 (11)	−0.0011 (11)
O5	0.0344 (14)	0.0243 (12)	0.0234 (12)	−0.0001 (10)	0.0020 (11)	−0.0049 (10)
O6	0.0577 (19)	0.0393 (14)	0.0269 (14)	−0.0105 (13)	0.0185 (14)	−0.0005 (12)

Geometric parameters (Å, º)

Zn1—O2^i	1.998 (2)	C1—C2	1.492 (4)
Zn1—O3	2.009 (2)	C2—C3	1.376 (5)
Zn1—N1	2.045 (3)	C2—C7	1.386 (4)
Zn1—O4	2.124 (2)	C3—C4	1.384 (4)
Zn1—O5^ii	2.333 (2)	C3—H3A	0.9300
Zn1—O1^i	2.470 (2)	C4—C5	1.376 (5)
N1—C5	1.445 (4)	C4—H4	0.93
N1—H1A	0.90	C5—C6	1.384 (4)
N1—H1B	0.90	C6—C7	1.380 (4)
N2—O6	1.227 (3)	C6—H6	0.93
N2—O5	1.248 (3)	C7—H7	0.93
N2—O4	1.274 (3)	O3—H3B	0.83 (4)
C1—O1	1.240 (4)	O3—H3C	0.85 (5)
C1—O2	1.284 (4)
O2^i—Zn1—O3	105.20 (9)	O1—C1—Zn1^iii	70.95 (17)
O2^i—Zn1—N1	143.27 (9)	O2—C1—Zn1^iii	49.40 (14)
O3—Zn1—N1	109.52 (10)	C2—C1—Zn1^iii	167.9 (2)
O2^i—Zn1—O4	99.50 (9)	C3—C2—C7	118.8 (3)
O3—Zn1—O4	87.83 (10)	C3—C2—C1	119.7 (3)
N1—Zn1—O4	93.47 (10)	C7—C2—C1	121.4 (3)
O2^i—Zn1—O5^ii	88.22 (9)	C2—C3—C4	121.1 (3)
O3—Zn1—O5^ii	78.81 (10)	C2—C3—H3A	119.4
N1—Zn1—O5^ii	87.07 (10)	C4—C3—H3A	119.4
O4—Zn1—O5^ii	165.97 (8)	C5—C4—C3	119.5 (3)
O2^i—Zn1—O1^i	57.52 (8)	C5—C4—H4	120.2
O3—Zn1—O1^i	148.46 (9)	C3—C4—H4	120.2
N1—Zn1—O1^i	86.17 (8)	C4—C5—C6	120.1 (3)
O4—Zn1—O1^i	119.26 (8)	C4—C5—N1	119.4 (3)
O5^ii—Zn1—O1^i	74.77 (8)	C6—C5—N1	120.5 (3)
O2^i—Zn1—C1^i	29.20 (9)	C7—C6—C5	119.8 (3)
O3—Zn1—C1^i	130.26 (10)	C7—C6—H6	120.1
N1—Zn1—C1^i	114.26 (10)	C5—C6—H6	120.1
O4—Zn1—C1^i	111.38 (10)	C6—C7—C2	120.6 (3)
O5^ii—Zn1—C1^i	80.95 (9)	C6—C7—H7	119.7
O1^i—Zn1—C1^i	28.33 (8)	C2—C7—H7	119.7
C5—N1—Zn1	115.95 (19)	C1—O1—Zn1^iii	80.72 (18)
C5—N1—H1A	108.3	C1—O2—Zn1^iii	101.40 (18)
Zn1—N1—H1A	108.3	Zn1—O3—O2^iv	116.97 (12)
C5—N1—H1B	108.3	Zn1—O3—O1^v	118.41 (12)
Zn1—N1—H1B	108.3	O2^iv—O3—O1^v	105.54 (10)
H1A—N1—H1B	107.4	Zn1—O3—H3C	118 (3)
O6—N2—O5	121.4 (3)	O2^iv—O3—H3C	110 (3)
O6—N2—O4	119.9 (3)	Zn1—O3—H3B	115 (3)
O5—N2—O4	118.7 (3)	O1^v—O3—H3B	108 (3)
O1—C1—O2	120.3 (3)	H3C—O3—H3B	113 (4)
O1—C1—C2	121.1 (3)	N2—O4—Zn1	112.46 (18)
O2—C1—C2	118.6 (3)	N2—O5—Zn1^vi	124.93 (19)

Symmetry codes: (i) x−1/2, −y+1/2, z+1/2; (ii) x+1/2, −y+1/2, z+1/2; (iii) x+1/2, −y+1/2, z−1/2; (iv) −x+3/2, y+1/2, −z+1/2; (v) −x+2, −y+1, −z+1; (vi) x−1/2, −y+1/2, z−1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3B···O2^iv	0.83 (4)	1.89 (4)	2.720 (3)	177 (4)
O3—H3C···O1^v	0.85 (5)	1.88 (5)	2.721 (3)	171 (5)

Symmetry codes: (iv) −x+3/2, y+1/2, −z+1/2; (v) −x+2, −y+1, −z+1.