Polymeric aqua(μ₄-maleato-κ⁴O)­pyridyl­nickel(II)

The title nickel coordination polymer, [Ni(C₄H₂O₄)(C₅H₅N)(H₂O)]_n, has been obtained from the reaction of NiCl₂·6H₂O with disodium maleate and pyridine in an alcohol–water solution. Single-crystal X-ray analysis revealed that each Ni atom contains an approximately octahedral coordination environment in the compound with the maleate ligand in a novel coordination mode. The molecule has mirror symmetry. O—H...O hydrogen bonds exist in the corrugated two-dimensional structure; this is further extended into a three-dimensional framework via strong non-classical C—H...O interactions between adjacent layers.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.012 Å
• R factor = 0.056
• wR factor = 0.138
• Data-to-parameter ratio = 10.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

In the past decade, polycarboxylate ligands are widely used in the preparation of coordination polymers with open framework structure because they are capable of forming one-, two-, or three-dimensional networks by bridging between metal centers in a number of different manners (Shi et al., 2000; Kepert et al., 2000; Burrows et al., 2000). Maleate is a versatile ligand, which exhibit the ability to coordinate to metal atoms in several ways (Zhang et al., 1999). Nevertheless, Ni^II or Co^II maleato complexes are rare. In order to further investigate the coordination fashion of maleate, a much larger data of this type of compound needs to be obtained. We have recently prepared some new maleate bridged Ni^II and Co^II complexes with pyridine (py) and 2,2'-bipyridine (bipy) as a second ligand. This paper reports the structure of one of them, in which maleic dianion coordinated to metal center in a quite rare coordination mode (Prout et al., 1971; Lis, 1983; Li et al., 1996), namely, [Ni(µ-maleato)(py)(H₂O)]_n, (I).

As shown in Fig. 1, each six-coordinate central Ni²⁺ ion is in an approximate octahedral coordination environment, with the two axial coordination positions occupied by O atom of the water molecule and N atom of the pyridine molecule. The Ni—O distances are in the range of 2.060 (4)–2.100 (6) Å and the Ni—N distance is 2.083 (7) Å, with the O—Ni—O(N) angles between 86.8 (2) and 90.8 (2)°. The Ni²⁺ ion is deviated from the equatorial plane about only 0.074 Å toward the axially coordinated water molecule. O atoms of the maleate dianion coordinated to Ni²⁺ in two different modes: each carboxyl group of a maleic ligand offers one O atom to chelated a Ni atom to form a seven-membered ring in a boat conformation with the C═C distance of 1.33 (1) Å; while the two remaining O atoms of the same maleate ligand bridged to the other two Ni atoms. As a result, the Ni²⁺ ions are bridged by maleic anions in a rarely tetra-dentate coordination fashion with a syn-anti coplanar conformation of the carboxyl group, forming a two- dimensional corrugated structure. Every four adjacent Ni²⁺ ions in the layer produce a bended square hole under the linkage of the maleate ligands, with the distance of 5.5 Å between every two adjacent Ni atoms. In addition, there exist two kinds of hydrogen bond interactions in the crystal: (i) intralayer hydrogen bond OW—WA···O1B; (ii) interlayer hydrogen bond C4C(pyridine)–H4AC···OW. Those weak interactions are benefit to the extra stabilization of the crystal structure.

S2. Experimental

An aqueous solution (10 ml) of NiCl₂·6H₂O (0.238 g, 1.0 mmol) was added to an alcohol–watter (1:1) solution (10 ml) containing maleic acid (0.116 g, 1.0 mmol) and sodium hydrate (0.080 g, 2.0 mmol) with stirring. After 80 min, pyridine (0.1 ml, 1.2 mmol) was added dropwise into the above reaction mixture and stirred for 30 min, then filtered. The filtrate was finally left at room temperature and single crystals adequate for X-ray diffraction studies were obtained after two weeks.

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SMART; Program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; software used to prepare material for publication: SHELXTL97.

S3. Refinement

H atoms were all located theoretically and refined as riding, except for atom HWA which was refined isotropically.

Computing details

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

Figures

	Fig. 1. A view of (I) with the atomic numbering scheme. Displacement ellipsoids at the 30% probability level. H atoms have been omitted for clarity.
	Fig. 2. Cell packing of (I), viewed down the c axis, showing the hydrogen bonds.

aqua(µ₄-maleato-κ⁴O)pyridylnickel(II)

Crystal data

Ni(C4H2O4)(C5H5N)(H2O)]	F(000) = 552
Mr = 269.88	Dx = 1.780 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 29 reflections
a = 17.9522 (13) Å	θ = 2.3–25.0°
b = 7.5712 (5) Å	µ = 1.93 mm^−1
c = 7.4092 (6) Å	T = 293 K
V = 1007.06 (13) Å^3	Block, green
Z = 4	0.22 × 0.14 × 0.10 mm

Data collection

Siemens SMART CCD diffractometer	950 independent reflections
Radiation source: fine-focus sealed tube	701 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.075
ϕ and ω scans	θmax = 25.0°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −21→12
Tmin = 0.695, Tmax = 0.824	k = −6→9
3021 measured reflections	l = −8→7

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)] = 0.056	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.138	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0554P)^2 + 5.62P] where P = (Fo^2 + 2Fc^2)/3
950 reflections	(Δ/σ)max < 0.001
89 parameters	Δρmax = 0.49 e Å^−3
0 restraints	Δρmin = −0.67 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
Ni	0.21377 (6)	0.2500	0.76154 (14)	0.0199 (4)
OW	0.2997 (3)	0.2500	0.5693 (8)	0.0251 (15)
N	0.1227 (4)	0.2500	0.9358 (9)	0.0241 (17)
C1	0.1293 (5)	0.2500	1.1162 (12)	0.030 (2)
H1A	0.1769	0.2500	1.1657	0.036*
C5	0.0530 (5)	0.2500	0.8700 (13)	0.033 (2)
H5A	0.0467	0.2500	0.7454	0.039*
C3	−0.0014 (6)	0.2500	1.1621 (14)	0.043 (3)
H3A	−0.0428	0.2500	1.2376	0.052*
C2	0.0691 (5)	0.2500	1.2323 (13)	0.034 (2)
H2A	0.0764	0.2500	1.3565	0.041*
C4	−0.0099 (6)	0.2500	0.9770 (14)	0.044 (3)
H4A	−0.0571	0.2500	0.9253	0.053*
HWA	0.289 (4)	0.332 (9)	0.503 (9)	0.06 (3)*
O2	0.3425 (2)	0.5621 (6)	1.1137 (6)	0.0285 (10)
C6	0.3246 (3)	0.4544 (8)	0.9931 (8)	0.0192 (13)
C7	0.3873 (3)	0.3375 (8)	0.9326 (7)	0.0229 (13)
H7A	0.4302	0.3931	0.8912	0.028*
O1	0.2609 (2)	0.4447 (6)	0.9216 (6)	0.0274 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni	0.0159 (6)	0.0217 (5)	0.0220 (6)	0.000	0.0001 (5)	0.000
OW	0.020 (3)	0.031 (4)	0.024 (3)	0.000	0.001 (3)	0.000
N	0.026 (4)	0.022 (4)	0.024 (4)	0.000	0.005 (3)	0.000
C1	0.025 (5)	0.043 (6)	0.022 (5)	0.000	−0.007 (4)	0.000
C5	0.022 (5)	0.053 (6)	0.022 (5)	0.000	−0.004 (4)	0.000
C3	0.035 (6)	0.056 (7)	0.038 (6)	0.000	0.014 (5)	0.000
C2	0.043 (5)	0.039 (5)	0.021 (5)	0.000	−0.006 (5)	0.000
C4	0.024 (5)	0.073 (8)	0.035 (6)	0.000	0.001 (5)	0.000
O2	0.024 (2)	0.028 (2)	0.034 (2)	0.003 (2)	−0.0040 (19)	−0.011 (2)
C6	0.019 (3)	0.017 (3)	0.021 (3)	−0.006 (2)	0.001 (3)	−0.001 (3)
C7	0.017 (3)	0.028 (3)	0.024 (3)	−0.006 (3)	0.006 (2)	0.001 (3)
O1	0.019 (2)	0.024 (2)	0.039 (3)	0.0002 (19)	−0.0032 (19)	−0.012 (2)

Geometric parameters (Å, º)

Ni—O2^i	2.060 (4)	C5—H5A	0.9300
Ni—O2^ii	2.060 (4)	C3—C2	1.369 (14)
Ni—O1	2.072 (4)	C3—C4	1.380 (14)
Ni—O1^iii	2.072 (4)	C3—H3A	0.9300
Ni—N	2.083 (7)	C2—H2A	0.9300
Ni—OW	2.100 (6)	C4—H4A	0.9300
OW—HWA	0.82 (7)	O2—C6	1.252 (7)
N—C1	1.342 (11)	O2—Ni^iv	2.060 (4)
N—C5	1.344 (11)	C6—O1	1.263 (6)
C1—C2	1.381 (13)	C6—C7	1.500 (8)
C1—H1A	0.9300	C7—C7^iii	1.325 (12)
C5—C4	1.379 (13)	C7—H7A	0.9300
O2^i—Ni—O2^ii	87.3 (2)	C2—C1—H1A	118.2
O2^i—Ni—O1	174.60 (16)	N—C5—C4	123.7 (9)
O2^ii—Ni—O1	90.78 (17)	N—C5—H5A	118.2
O2^i—Ni—O1^iii	90.78 (17)	C4—C5—H5A	118.2
O2^ii—Ni—O1^iii	174.60 (16)	C2—C3—C4	118.6 (10)
O1—Ni—O1^iii	90.7 (2)	C2—C3—H3A	120.7
O2^i—Ni—N	86.83 (19)	C4—C3—H3A	120.7
O2^ii—Ni—N	86.83 (19)	C3—C2—C1	119.1 (9)
O1—Ni—N	88.02 (18)	C3—C2—H2A	120.4
O1^iii—Ni—N	88.02 (18)	C1—C2—H2A	120.4
O2^i—Ni—OW	89.99 (17)	C5—C4—C3	118.8 (10)
O2^ii—Ni—OW	89.99 (17)	C5—C4—H4A	120.6
O1—Ni—OW	95.06 (17)	C3—C4—H4A	120.6
O1^iii—Ni—OW	95.06 (17)	C6—O2—Ni^iv	134.7 (4)
N—Ni—OW	175.6 (3)	O2—C6—O1	124.7 (5)
Ni—OW—HWA	103 (5)	O2—C6—C7	113.9 (5)
C1—N—C5	116.3 (8)	O1—C6—C7	121.3 (5)
C1—N—Ni	123.3 (6)	C7^iii—C7—C6	126.1 (3)
C5—N—Ni	120.4 (6)	C7^iii—C7—H7A	116.9
N—C1—C2	123.5 (9)	C6—C7—H7A	116.9
N—C1—H1A	118.2	C6—O1—Ni	130.6 (4)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
OW—HWA···O1^ii	0.82 (7)	2.01 (7)	2.780 (5)	159 (?)
C4—H4A···OW^v	0.93	2.57	3.435 (12)	155

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