Poly[aqua-[mu]₃-2,2-dimethyl­malonato-zinc(II)]

The title complex, [Zn(C₅H₆O₄)(H₂O)]_n, has a two-dimensional layer structure. The Zn atoms, in a geometry that is closer to trigonal bipyramidal than square pyramidal, are coordinated by two O atoms of a bidentate dimethyl­malonate ligand, two O atoms of monodentate dimethylmalonate ligands and one O atom from the aqua ligand. The crystal structure is characterized by the intra­layer motif of a hydrogen-bonded network. Neighboring layers are linked together to build up a three-dimensional network via van der Waals forces.

S1. Comment

From a coordination standpoint, malonate is a versatile ligand, displaying a variety of bonding modes. For example, mono-deprotonation of malonic acid can lead to complexes containing the coordinated HOOCCH₂CO₂ (malH) anion. This anion is known to bond to metals simultaneously via chelating bidentate and monodentate carboxylate groups, e.g. in [Cu(malH)₂] (Delgado, Sanchiz et al., 2004). Deprotonation of the parent acid generates the [CH₂(CO₂)₂]^2- (mal²⁻) dianion, which can be found coordinating to metals both through two distal carboxylate O atoms to form a six-membered ring and through non-chelating O atoms to build up bridged compounds, as in {[Co(H₂O)₂][Co(mal)₂(H₂O)₂]}_n (Delgado, Hernandez-Molina et al., 2004). In heterobimetallic malonate complexes involving transition and alkaline-earth metals, malonate dianions have also been used to construct coordination polymers by acting as chelating bidentate ligands or as simple bridges between metal centers. Consequently, many heteronuclear malonate complexes have been synthesized and structurally characterized (Djeghri et al., 2005, 2006; Gil de Muro et al., 1998, 2000, 2004; Guo & Cao, 2006; Guo & Guo, 2006; Fu et al., 2006).

Although many complexes that use malonate as a ligand have been synthesized, up to now only a few complexes that use dimethylmalonate as a ligand are known to us (Zhang et al., 2002). Five-coordinated complexes of the metal ions are not common, and these are mainly complexes involving copper, malonate and other ligands (Sieroń, 2004; Xiong et al., 2001). For the complexes of Zn and the malonate ligand, five-coordinated complexes are rarely reported. In the course of our study of heterobimetallic malonate complexes involving zinc and alkaline-earth metals, using dimethylmalonic acid, we expected a structure similar or isotypic to that of [BaZn(C₃H₂O₄)₂(H₂O)₄]_n (Guo & Guo, 2006), but interestingly, a completely different crystal structure was obtained, the title novel five-coordinated dimethylmalonate–zinc complex, (I), and we report its crystal structure here.

The asymmetric unit in the structure of (I) comprises one Zn atom, one complete dimethylmalonate dianion and one water molecule. The structure is shown in Fig. 1 in a symmetry-expanded view, which displays the full coordination of the Zn atom. Selected geometric parameters are given in Table 1.

The Zn atoms are five-coordinated by two chelating O atoms (atoms O1 and O3) of the dimethylmalonate dianion, one O atom from the water molecule (O5) and two O atoms (O2ⁱ and O4ⁱⁱ; see Table 1 for symmetry code) in a monodentate fashion from two symmetry-related dimethylmalonate anions. The Zn atom deviates 0.0120 (3) Å from the least-squares plane defined by atoms O5, O2ⁱ and O3 atoms; all of the cis O—Zn—O bond angles (see Table 1) are close to 90° [in the range 86.23 (7)–97.86 (7)°; Table 1], the trans angle O4ⁱⁱ—Zn1—O1 is 168.74 (7)°, and the structure index τ, indicating the relative amount of trigonality (τ = 0 for a square pyramid and τ = 1 for a trigonal bipyramid; Addison et al., 1984), is 0.58, and thus the coordination geometry of Zn is closer to distorted trigonal–bipyramidal than to square–pyramidal.

In the present structure, the variability of the malonate ligand can be clearly seen (Fig. 1). The whole dimethylmalonate molecule chelates the Zn atom to form a six-membered ring. The resulting six-membered chelate ring (Zn1/O1/C1–C3/O3) has a boat conformation, with atoms Zn1 and C2 lying 0.4166 (4) and 0.6295 (8) Å, respectively, out of the O1/C1/C3/O3 mean plane. Atom O2 of the O1/C1/O2 carboxylate group adopts a monodentate mode to connect to Znⁱ (see Fig. 1 for symmetry codes); thus, the two Zn atoms are linked together via atoms O1, C1 and O2. This results in a Zn1···Zn1ⁱ distance of 5.098 (8) Å. Similarly, atom O4 of the O3/C3/O4 carboxylate group coordinates to Znⁱⁱ with a Zn1···Zn1ⁱⁱ distance of 5.001 (1) Å. Two Zn atoms are linked together via these carboxylate groups acting in monodentate mode, forming a 12-membered ring. Four Zn atoms are associated into a 16-membered ring via carboxylate groups acting in chelating and monodentate fashions. Each Zn atom is connected to four other Zn atoms through biscarboxylate bridges in the bc plane, resulting in planes perpendicular to the [100] direction. A complete two-dimensional polymeric layer is formed in the direction of the bc plane (Fig. 2).

The Zn—O_water bond and the Zn—O_{dimethylmalonate} bonds (see Table 1) are somewhat shorter than those in the six-coordinated complex [CaZn(mal)₂(H₂O)₄]_n (Fu et al., 2006), and are comparable with the values reported for five-coordinated zinc complex involving carboxylate and containing other ligands (Erxleben, 2001). The O—C—O angles for two carboxylate groups are almost the same (O1—C1—O2 122.3 (2) and O4—C3—O3 122.8 (2)°, respectively). The two C—O bond distances (O1—C1 and O2—C1) of the carboxylate group of O1/C1/O2 are 1.246 (3) and 1.266 (3) Å, respectively, while the two C—O bond distances (O4—C3 and O3—C3) of the carboxylate group of O3/C3/O4 are 1.271 (3) and 1.244 (3) Å, respectively. This indicates that the mesomeric effect for the carboxylate group of O1/C1/O2 is larger than that of the carboxylate group of O3/C3/O4.

The crystal structure owes its formation to a strong intermolecular hydrogen bond (Brown, 1976) between atom O3ⁱⁱ and atom H5E of the water molecule. Hydrogen bonding also plays an important role in the stabilization of the extended two-dimensional network structure (Table 2). The structure consists of alternating layers in the [100] direction. The neighbouring layers are linked together to build up a three-dimensional network mainly by van der Waals forces.

S2. Experimental

The title complex was prepared under continuous stirring with successive addition of dimethylmalonic acid (0.53 g, 4 mmol), Na₂CO₃ (0.22 g, 2 mmol), Zn(NO₃)₂·6H₂O (0.49 g, 2 mmol) and barium nitrate (0.52 g 2 mmol) to distilled water (30 ml) at room temperature. After filtration, slow evaporation over a period of three week at room temperature provided colorless plate-like crystals of (I).

S3. Refinement

The H atoms of the water molecule were found in difference Fourier maps. However, during refinement, they were fixed at O–H distances of 0.85 Å and their U_iso(H) values were set at 1.2U_eq(O). The H atoms of methyl groups were treated as riding, with C–H = 0.96 Å and U_iso(H) = 1.5U_eq(C).

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Bruker, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the structure of (I), showing the atom-numbering scheme and coordination of the Zn atom; displacement ellipsoids are drawn at the 30% probability level. [Symmetry codes: (i) −x + 1, y + 1/2, −z + 1/2; (ii) x, −y + 5/2, z − 1/2.]
	Fig. 2. Packing diagram of (I), showing the two-dimensional polymeric layer in the direction of the bc plane, viewed down the a axis.

Poly[aqua-µ₃-2,2-dimethylmalonato-zinc(II)]

Crystal data

[Zn(C5H6O4)(H2O)]	F(000) = 432
Mr = 213.48	Dx = 2.048 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 2430 reflections
a = 8.7030 (15) Å	θ = 2.4–26.4°
b = 8.5986 (15) Å	µ = 3.52 mm^−1
c = 9.4773 (16) Å	T = 294 K
β = 102.532 (3)°	Plate, colorless
V = 692.3 (2) Å^3	0.16 × 0.14 × 0.08 mm
Z = 4

Data collection

Bruker SMART CCD area-detector diffractometer	1226 independent reflections
Radiation source: fine-focus sealed tube	1095 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
ϕ and ω scans	θmax = 25.0°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −7→10
Tmin = 0.585, Tmax = 0.762	k = −10→10
3431 measured reflections	l = −11→9

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)] = 0.022	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.059	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0351P)^2 + 0.2489P] where P = (Fo^2 + 2Fc^2)/3
1226 reflections	(Δ/σ)max < 0.001
102 parameters	Δρmax = 0.35 e Å^−3
0 restraints	Δρmin = −0.34 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	0.36802 (3)	1.15706 (3)	0.14054 (3)	0.01770 (12)
O1	0.4384 (2)	0.94483 (19)	0.23933 (18)	0.0242 (4)
O2	0.41908 (19)	0.73675 (17)	0.36938 (17)	0.0215 (4)
O3	0.2773 (2)	1.20331 (19)	0.31001 (17)	0.0240 (4)
O4	0.2543 (2)	1.15105 (17)	0.53252 (18)	0.0225 (4)
C1	0.3724 (3)	0.8702 (3)	0.3221 (2)	0.0161 (5)
C2	0.2260 (3)	0.9367 (2)	0.3679 (2)	0.0174 (5)
C3	0.2563 (3)	1.1090 (3)	0.4073 (2)	0.0163 (5)
C4	0.0842 (3)	0.9267 (3)	0.2373 (3)	0.0295 (6)
H4A	0.0620	0.8197	0.2123	0.044*
H4B	0.1092	0.9805	0.1563	0.044*
H4C	−0.0063	0.9739	0.2622	0.044*
C5	0.1885 (4)	0.8473 (3)	0.4951 (3)	0.0307 (7)
H5A	0.2777	0.8508	0.5750	0.046*
H5B	0.1649	0.7411	0.4674	0.046*
H5C	0.0993	0.8937	0.5230	0.046*
O5	0.2936 (2)	1.03312 (19)	−0.04362 (17)	0.0245 (4)
H5D	0.3321	0.9459	−0.0605	0.029*
H5E	0.2885	1.1026	−0.1080	0.029*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.02421 (19)	0.01388 (18)	0.01636 (18)	−0.00081 (10)	0.00736 (12)	0.00131 (10)
O1	0.0276 (10)	0.0201 (9)	0.0282 (9)	0.0061 (7)	0.0133 (8)	0.0078 (7)
O2	0.0248 (9)	0.0132 (8)	0.0283 (9)	0.0052 (7)	0.0098 (8)	0.0047 (7)
O3	0.0442 (11)	0.0134 (8)	0.0183 (8)	0.0001 (8)	0.0157 (8)	0.0009 (7)
O4	0.0347 (11)	0.0175 (9)	0.0168 (9)	−0.0053 (7)	0.0086 (8)	−0.0031 (6)
C1	0.0170 (12)	0.0150 (11)	0.0150 (11)	−0.0008 (9)	0.0007 (10)	−0.0028 (9)
C2	0.0196 (12)	0.0129 (11)	0.0209 (12)	0.0003 (9)	0.0070 (10)	0.0003 (9)
C3	0.0186 (12)	0.0141 (11)	0.0172 (12)	0.0012 (9)	0.0059 (10)	0.0000 (9)
C4	0.0210 (14)	0.0328 (15)	0.0337 (15)	−0.0019 (11)	0.0038 (12)	−0.0123 (12)
C5	0.0462 (18)	0.0152 (13)	0.0390 (17)	0.0024 (11)	0.0276 (15)	0.0036 (11)
O5	0.0388 (11)	0.0128 (8)	0.0218 (9)	0.0021 (7)	0.0059 (8)	0.0003 (7)

Geometric parameters (Å, º)

Zn1—O3	1.9776 (16)	C2—C3	1.537 (3)
Zn1—O2^i	1.9967 (17)	C2—C4	1.549 (3)
Zn1—O5	2.0276 (16)	C4—H4A	0.9600
Zn1—O4^ii	2.0761 (16)	C4—H4B	0.9600
Zn1—O1	2.0815 (16)	C4—H4C	0.9600
O1—C1	1.246 (3)	C5—H5A	0.9600
O2—C1	1.266 (3)	C5—H5B	0.9600
O3—C3	1.271 (3)	C5—H5C	0.9600
O4—C3	1.244 (3)	O5—H5D	0.8503
C1—C2	1.543 (3)	O5—H5E	0.8481
C2—C5	1.523 (3)
O3—Zn1—O2^i	120.48 (7)	C3—C2—C4	108.22 (19)
O3—Zn1—O5	134.07 (8)	C1—C2—C4	108.50 (19)
O2^i—Zn1—O5	105.44 (7)	O4—C3—O3	122.8 (2)
O3—Zn1—O1	86.63 (7)	O4—C3—C2	118.3 (2)
O2^i—Zn1—O1	97.86 (7)	O3—C3—C2	118.88 (19)
O2^i—Zn1—O4^ii	92.98 (7)	C2—C4—H4A	109.5
O3—Zn1—O4^ii	90.52 (7)	C2—C4—H4B	109.5
O5—Zn1—O4^ii	87.95 (7)	H4A—C4—H4B	109.5
O5—Zn1—O1	86.23 (7)	C2—C4—H4C	109.5
O4^ii—Zn1—O1	168.74 (7)	H4A—C4—H4C	109.5
C1—O1—Zn1	127.18 (15)	H4B—C4—H4C	109.5
C1—O2—Zn1^iii	121.59 (15)	C2—C5—H5A	109.5
C3—O3—Zn1	127.36 (15)	C2—C5—H5B	109.5
C3—O4—Zn1^iv	126.67 (15)	H5A—C5—H5B	109.5
O1—C1—O2	122.3 (2)	C2—C5—H5C	109.5
O1—C1—C2	120.5 (2)	H5A—C5—H5C	109.5
O2—C1—C2	117.2 (2)	H5B—C5—H5C	109.5
C5—C2—C3	110.45 (19)	Zn1—O5—H5D	124.0
C5—C2—C1	111.6 (2)	Zn1—O5—H5E	101.9
C3—C2—C1	108.48 (18)	H5D—O5—H5E	116.6
C5—C2—C4	109.6 (2)
O3—Zn1—O1—C1	29.59 (19)	O1—C1—C2—C3	−44.4 (3)
O2^i—Zn1—O1—C1	149.91 (19)	O2—C1—C2—C3	137.1 (2)
O5—Zn1—O1—C1	−105.0 (2)	O1—C1—C2—C4	72.9 (3)
O4^ii—Zn1—O1—C1	−46.0 (4)	O2—C1—C2—C4	−105.6 (2)
O2^i—Zn1—O3—C3	−109.3 (2)	Zn1^iv—O4—C3—O3	−27.1 (3)
O5—Zn1—O3—C3	69.3 (2)	Zn1^iv—O4—C3—C2	155.24 (16)
O4^ii—Zn1—O3—C3	156.9 (2)	Zn1—O3—C3—O4	152.96 (19)
O1—Zn1—O3—C3	−12.2 (2)	Zn1—O3—C3—C2	−29.4 (3)
Zn1—O1—C1—O2	175.34 (15)	C5—C2—C3—O4	3.2 (3)
Zn1—O1—C1—C2	−3.1 (3)	C1—C2—C3—O4	−119.4 (2)
Zn1^iii—O2—C1—O1	16.3 (3)	C4—C2—C3—O4	123.1 (2)
Zn1^iii—O2—C1—C2	−165.24 (15)	C5—C2—C3—O3	−174.6 (2)
O1—C1—C2—C5	−166.3 (2)	C1—C2—C3—O3	62.9 (3)
O2—C1—C2—C5	15.2 (3)	C4—C2—C3—O3	−54.6 (3)

Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) x, −y+5/2, z−1/2; (iii) −x+1, y−1/2, −z+1/2; (iv) x, −y+5/2, z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5E···O3^ii	0.85	1.83	2.645 (2)	159
O5—H5D···O2^v	0.85	1.92	2.765 (2)	170

Symmetry codes: (ii) x, −y+5/2, z−1/2; (v) x, −y+3/2, z−1/2.