Poly[tetra­aqua­di-μ₃-malonato-calcium(II)­zinc(II)]

The title complex, [CaZn(C₃H₂O₄)₂(H₂O)₄]_n, is a two-dimensional polymer and consists of CaO₈ and ZnO₆ polyhedra linked together by malonate ligands. The Ca^II cation, lying on a twofold axis, is coordinated by two water mol­ecules and six malonate O atoms. The Zn^II cation, which lies on an inversion center in an octa­hedral environment, is coordinated by four malonate O atoms in an equatorial arrangement and two water mol­ecules in axial positions. The Zn—O and Ca—O bond lengths are in the ranges 2.0445 (12)–2.1346 (16) and 2.3831 (13)–2.6630 (13) Å, respectively. The structure comprises alternating layers along the [101] plane, the shortest Zn...Zn distance being 6.8172 (8) Å. The whole three-dimensional structure is maintained and stabilized by the presence of hydrogen bonds.

S1. Comment

There has been considerable interest in the design and synthesis of transition metal complexes with carboxylate ligands in coordination chemistry, owing to the fact that such complexes have potential application in molecular-based magnets, catalysis, supramolecular chemistry and biological systems (Li et al., 2002; Shi et al., 2000; Devereux et al., 2000). Because of the significant flexibility of dicarboxylate ligands, the malonate dianion may act as monodentate, chelated bidentate and tridentate bridging ligands to form various one-, two- and three-dimensional structures (Ray & Hathaway, 1982; Saadeh et al., 1993; Xue et al., 2003; Delgado et al., 2004). Zn^II complexes with the malonate (mal) ligand have potential applications in modified metalloenzymes and in precursor systems for Zn-containing ceramic materials, and several structures of Zn^II complexes with malonate ligands have been reported (Zhang et al., 2003; Lin et al., 2003; Burrows et al., 2000; Delgado et al., 2003; Fu et al., 2006). However, to the best of our knowledge, there are a few structural data on hetero-bimetallic Zn^II malonate complexes, especially those involving alkaline-earth metals (Guo & Guo, 2006). We report here the synthesis and crystal structure of the title complex, [CaZn(mal)₂(H₂O)₄)], (I), one such hetero-bimetallic malonate–Zn^II complex.

The molecular structure of (I), shown in Fig 1, can be described as a two-dimensional network of metal ions, which are linked by the malonate ligand (Fig. 2). Two of the coordination water molecules are linked to the Ca^II ions and the other two to the transition metal ions. The Zn^II ion lies on an inversion centre and is octahedrally coordinated by six O atoms from two malonate groups (atoms O1 and O3) and two water molecules (atoms O2). The Zn—O bonds lengths are slightly different (Table 1), and the Zn—O_mal bonds are somewhat longer than those in [BaZn(mal)₂(H₂O)₄)] (Guo & Guo, 2006). The Ca^II ion, which lies on a twofold axis, is six-coordinated by two O atoms (O6) from two water molecules and six O atoms (O3, O4 and O5) from four malonate ligands, forming an irregular polyhedron. The Ca—O bonds lengths are significantly different (Table 1), and the Ca—O_mal bond lengths are comparable to the corresponding ones found in the [CaMn(mal)₂(H₂O)₄)] and [CaNi(mal)₂(H₂O)₄)]·2H₂O complexes (Gil de Muro et al., 2000). Each malonate ligand adopts three coordination modes to connect with metal cations. As shown in Fig. 1, one carboxyl group adopts a bidentate 1,2-chelating and a monodentate bridging mode (through O3 and O4) and the other carboxyl group adopts a monodentate bridging mode (through O1 and O5). Furthermore, the two carboxyl groups adpot the bidentate 1,3-chelating mode (through O1 and O3). The resulting chelate ring exhibits an envelope conformation in which only the methylene group is significantly shifted from the ring plane [by 0.369 (2) Å]. The O—C—O angle for the monodentate carboxylate group is 123.19 (15)°, slightly larger than 120.54 (15)° for the chelating one. Atoms O3 link the Zn and Ca ions [Zn1—O3—Ca1 = 141.43 (6)°], forming perpendicular planes to the [101] direction, with the shortest Zn···Zn distance 6.8172 (8) Å and the shortest Ca···Ca 7.0582 (9) Å. The coordinated water molecules are linked to carboxylate atoms O1, O4 and O5 through hydrogen bonds, and the whole three-dimensional package in this structure is maintained and stabilized by the presence of hydrogen bonds (Fig. 3). The characteristics of the hydrogen-bond network are given in Table 2.

S2. Experimental

ZnO (0.81 g, 1 mmol) and Ca(OH)₂ (0.0714 g, 1 mmol) were added slowly to an aqueous solution (20 ml) of malonic acid (0.312 g, 3 mmol), and the reaction mixture was stirred continuously at 328 K. After 2 h, the reaction mixture was cooled to room temperature and filtered. Colorless single crystals were obtained from the filtrate after several months.

S3. Refinement

All the water H atoms were located in a difference Fourier map and their positional parameters were refined with O—H distances restrained to 0.833</span>(13)–0.865<span style=" font-weight:600;">(12) Å [please give initial restraint rather than the final values]; the U_iso(H) values were set at 1.5U_eq(O)???. The remaining H atoms were positioned geometrically and allowed to ride on their parent atoms, with C—H bond lengths of 0.97 Å [U_iso(H) = 1.5U_eq(C)].

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART; data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997) or SHELXTL (Bruker, 1997)??; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of (I), showing displacement ellipsoids at the 30% probability level. [Symmetry codes: (a) x, −1 + y, z; (b) x, 1 + y, z; (c) −x, y, 1/2 − z; (d) 1/2 − x, 3/2 − y, 1 − z; (f) 1/2 + x, 3/2 − y, 1/2 + z.]
	Fig. 2. The polymeric chains of (I), viewed along the b axis.
	Fig. 3. The hydrogen-bond interactions in (I), viewed along the b axis, with hydrogen bonds shown as dashed lines.

Poly[tetraaquadi-µ₃-malonato-calcium(II)zinc(II)]

Crystal data

[CaZn(C3H2O4)2(H2O)4]	F(000) = 776
Mr = 381.61	Dx = 2.103 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C2yc	Cell parameters from 2498 reflections
a = 13.9736 (17) Å	θ = 2.9–28.3°
b = 7.5445 (9) Å	µ = 2.53 mm^−1
c = 13.1729 (15) Å	T = 292 K
β = 119.788 (2)°	Prism, colorless
V = 1205.2 (2) Å^3	0.30 × 0.30 × 0.20 mm
Z = 4

Data collection

Bruker SMART CCD area-detector diffractometer	1368 independent reflections
Radiation source: fine-focus sealed tube	1302 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.017
ϕ and ω scans	θmax = 27.5°, θmin = 3.2°
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −17→17
Tmin = 0.518, Tmax = 0.632	k = −5→9
3428 measured reflections	l = −16→16

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) = 0.060	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0338P)^2 + 0.8399P] where P = (Fo^2 + 2Fc^2)/3
1368 reflections	(Δ/σ)max < 0.001
105 parameters	Δρmax = 0.33 e Å^−3
11 restraints	Δρmin = −0.40 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
C1	0.12671 (13)	0.6719 (2)	0.24436 (14)	0.0183 (3)
C2	0.15715 (13)	0.0046 (2)	0.29495 (14)	0.0186 (3)
C3	0.16243 (15)	−0.1483 (2)	0.22378 (14)	0.0223 (3)
H3A	0.2378	−0.1584	0.2394	0.033*
H3B	0.1168	−0.1191	0.1416	0.033*
O1	0.19797 (11)	0.98730 (16)	0.40460 (10)	0.0270 (3)
O2	0.39111 (13)	0.7362 (2)	0.47783 (13)	0.0358 (4)
H2A	0.4468 (17)	0.795 (3)	0.5226 (19)	0.054*
H2B	0.393 (2)	0.712 (4)	0.4163 (16)	0.054*
O3	0.15766 (11)	0.61574 (16)	0.34670 (10)	0.0259 (3)
O4	0.06660 (11)	0.57927 (17)	0.15758 (11)	0.0297 (3)
O5	0.11516 (11)	0.14530 (16)	0.24176 (11)	0.0265 (3)
O6	−0.10368 (12)	0.28096 (19)	0.04880 (12)	0.0284 (3)
H6A	−0.1431 (17)	0.187 (2)	0.0385 (16)	0.043*
H6B	−0.1527 (16)	0.352 (2)	−0.0005 (18)	0.043*
Ca1	0.0000	0.37120 (6)	0.2500	0.01798 (12)
Zn1	0.2500	0.7500	0.5000	0.02086 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0200 (7)	0.0160 (7)	0.0200 (8)	0.0019 (6)	0.0108 (6)	0.0007 (6)
C2	0.0197 (7)	0.0171 (7)	0.0198 (8)	−0.0006 (6)	0.0105 (6)	0.0012 (6)
C3	0.0335 (9)	0.0168 (8)	0.0197 (8)	−0.0014 (7)	0.0156 (7)	0.0002 (6)
O1	0.0422 (7)	0.0186 (6)	0.0166 (6)	0.0044 (5)	0.0120 (5)	0.0017 (5)
O2	0.0291 (7)	0.0546 (10)	0.0253 (8)	−0.0071 (6)	0.0146 (6)	−0.0102 (6)
O3	0.0374 (7)	0.0199 (6)	0.0180 (6)	−0.0055 (5)	0.0120 (5)	0.0004 (5)
O4	0.0369 (7)	0.0254 (6)	0.0189 (6)	−0.0090 (6)	0.0079 (6)	−0.0021 (5)
O5	0.0372 (7)	0.0207 (6)	0.0244 (6)	0.0096 (5)	0.0173 (6)	0.0069 (5)
O6	0.0350 (7)	0.0260 (6)	0.0205 (7)	−0.0033 (6)	0.0108 (6)	0.0001 (5)
Ca1	0.0224 (2)	0.0151 (2)	0.0169 (2)	0.000	0.01013 (19)	0.000
Zn1	0.02814 (17)	0.01706 (16)	0.01446 (16)	0.00036 (10)	0.00837 (13)	0.00127 (9)

Geometric parameters (Å, º)

C1—O4	1.243 (2)	O2—H2B	0.844 (13)
C1—O3	1.267 (2)	O3—Zn1	2.0445 (12)
C1—C3^i	1.516 (2)	O3—Ca1	2.6630 (13)
C2—O5	1.246 (2)	O4—Ca1	2.4368 (13)
C2—O1^ii	1.269 (2)	O5—Ca1	2.3831 (13)
C2—C3	1.511 (2)	O6—Ca1	2.4024 (14)
C3—H3A	0.9700	O6—H6A	0.868 (12)
C3—H3B	0.9700	O6—H6B	0.856 (13)
O1—Zn1	2.0989 (12)	Ca1—C1^iii	2.9012 (17)
O2—Zn1	2.1346 (16)	Zn1—O3^iv	2.0445 (12)
O2—H2A	0.834 (13)
O4—C1—O3	120.54 (15)	O4^iii—Ca1—O4	99.79 (7)
O4—C1—C3^i	118.07 (14)	O5^iii—Ca1—O3	152.94 (4)
O3—C1—C3^i	121.39 (14)	O5—Ca1—O3	95.76 (5)
O5—C2—O1^ii	123.19 (15)	O6^iii—Ca1—O3	76.49 (5)
O5—C2—C3	117.12 (14)	O6—Ca1—O3	128.77 (4)
O1^ii—C2—C3	119.65 (14)	O4^iii—Ca1—O3	75.24 (5)
C2—C3—C1^ii	116.77 (14)	O4—Ca1—O3	50.37 (4)
C2—C3—H3A	108.1	O5^iii—Ca1—O3^iii	95.76 (5)
C1^ii—C3—H3A	108.1	O5—Ca1—O3^iii	152.94 (4)
C2—C3—H3B	108.1	O6^iii—Ca1—O3^iii	128.77 (4)
C1^ii—C3—H3B	108.1	O6—Ca1—O3^iii	76.49 (5)
H3A—C3—H3B	107.3	O4^iii—Ca1—O3^iii	50.37 (4)
C2^i—O1—Zn1	126.55 (11)	O4—Ca1—O3^iii	75.24 (5)
Zn1—O2—H2A	118.5 (18)	O3—Ca1—O3^iii	92.29 (6)
Zn1—O2—H2B	127.8 (19)	O5^iii—Ca1—C1^iii	97.10 (5)
H2A—O2—H2B	109 (2)	O5—Ca1—C1^iii	174.17 (5)
C1—O3—Zn1	126.86 (11)	O6^iii—Ca1—C1^iii	103.56 (5)
C1—O3—Ca1	87.63 (10)	O6—Ca1—C1^iii	102.04 (5)
Zn1—O3—Ca1	141.43 (6)	O4^iii—Ca1—C1^iii	25.06 (4)
C1—O4—Ca1	98.85 (10)	O4—Ca1—C1^iii	84.17 (5)
C2—O5—Ca1	136.34 (11)	O3—Ca1—C1^iii	79.42 (5)
Ca1—O6—H6A	113.1 (12)	O3^iii—Ca1—C1^iii	25.86 (4)
Ca1—O6—H6B	118.5 (16)	O3^iv—Zn1—O3	180.0
H6A—O6—H6B	100.7 (18)	O3^iv—Zn1—O1^iv	88.30 (5)
O5^iii—Ca1—O5	88.69 (7)	O3—Zn1—O1^iv	91.70 (5)
O5^iii—Ca1—O6^iii	78.34 (5)	O3^iv—Zn1—O1	91.70 (5)
O5—Ca1—O6^iii	78.28 (5)	O3—Zn1—O1	88.30 (5)
O5^iii—Ca1—O6	78.28 (5)	O1^iv—Zn1—O1	180.00 (7)
O5—Ca1—O6	78.34 (5)	O3^iv—Zn1—O2^iv	90.76 (6)
O6^iii—Ca1—O6	147.07 (7)	O3—Zn1—O2^iv	89.24 (6)
O5^iii—Ca1—O4^iii	90.22 (5)	O1^iv—Zn1—O2^iv	91.63 (6)
O5—Ca1—O4^iii	156.57 (4)	O1—Zn1—O2^iv	88.37 (6)
O6^iii—Ca1—O4^iii	78.58 (5)	O3^iv—Zn1—O2	89.24 (6)
O6—Ca1—O4^iii	124.27 (5)	O3—Zn1—O2	90.76 (6)
O5^iii—Ca1—O4	156.57 (4)	O1^iv—Zn1—O2	88.37 (6)
O5—Ca1—O4	90.22 (5)	O1—Zn1—O2	91.63 (6)
O6^iii—Ca1—O4	124.27 (5)	O2^iv—Zn1—O2	180.0
O6—Ca1—O4	78.58 (5)
O5—C2—C3—C1^ii	−134.05 (16)	C1—O3—Ca1—O5	94.38 (10)
O1^ii—C2—C3—C1^ii	48.3 (2)	Zn1—O3—Ca1—O5	−109.96 (10)
O4—C1—O3—Zn1	−176.98 (12)	C1—O3—Ca1—O6^iii	170.84 (10)
C3^i—C1—O3—Zn1	3.7 (2)	Zn1—O3—Ca1—O6^iii	−33.50 (10)
O4—C1—O3—Ca1	−15.71 (16)	C1—O3—Ca1—O6	14.73 (12)
C3^i—C1—O3—Ca1	164.99 (15)	Zn1—O3—Ca1—O6	170.39 (9)
O3—C1—O4—Ca1	17.41 (17)	C1—O3—Ca1—O4^iii	−107.63 (10)
C3^i—C1—O4—Ca1	−163.26 (13)	Zn1—O3—Ca1—O4^iii	48.03 (10)
O1^ii—C2—O5—Ca1	−40.0 (3)	C1—O3—Ca1—O4	8.89 (9)
C3—C2—O5—Ca1	142.36 (13)	Zn1—O3—Ca1—O4	164.55 (13)
C2—O5—Ca1—O5^iii	−46.16 (15)	C1—O3—Ca1—O3^iii	−59.75 (9)
C2—O5—Ca1—O6^iii	32.20 (16)	Zn1—O3—Ca1—O3^iii	95.91 (10)
C2—O5—Ca1—O6	−124.46 (17)	C1—O3—Ca1—C1^iii	−82.29 (11)
C2—O5—Ca1—O4^iii	41.4 (2)	Zn1—O3—Ca1—C1^iii	73.37 (10)
C2—O5—Ca1—O4	157.25 (16)	C1—O3—Zn1—O1^iv	−157.36 (14)
C2—O5—Ca1—O3	107.09 (16)	Ca1—O3—Zn1—O1^iv	53.62 (10)
C2—O5—Ca1—O3^iii	−146.29 (15)	C1—O3—Zn1—O1	22.64 (14)
C1—O4—Ca1—O5^iii	166.32 (12)	Ca1—O3—Zn1—O1	−126.38 (10)
C1—O4—Ca1—O5	−106.46 (11)	C1—O3—Zn1—O2^iv	111.03 (15)
C1—O4—Ca1—O6^iii	−30.54 (12)	Ca1—O3—Zn1—O2^iv	−37.99 (10)
C1—O4—Ca1—O6	175.48 (11)	C1—O3—Zn1—O2	−68.97 (15)
C1—O4—Ca1—O4^iii	52.25 (9)	Ca1—O3—Zn1—O2	142.01 (10)
C1—O4—Ca1—O3	−9.16 (9)	C2^i—O1—Zn1—O3^iv	161.58 (14)
C1—O4—Ca1—O3^iii	96.62 (11)	C2^i—O1—Zn1—O3	−18.42 (14)
C1—O4—Ca1—C1^iii	71.92 (12)	C2^i—O1—Zn1—O2^iv	−107.70 (14)
C1—O3—Ca1—O5^iii	−167.16 (11)	C2^i—O1—Zn1—O2	72.30 (14)
Zn1—O3—Ca1—O5^iii	−11.51 (17)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O6—H6A···O1^v	0.87 (1)	2.00 (2)	2.7973 (19)	153 (2)
O6—H6B···O1^vi	0.86 (1)	2.19 (2)	3.019 (2)	163 (2)
O2—H2B···O5^vii	0.84 (1)	2.09 (1)	2.931 (2)	175 (3)
O2—H2A···O4^viii	0.83 (1)	1.98 (1)	2.791 (2)	166 (3)

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