Poly[tetraaquadi-μ₄-malonato-barium(II)zinc(II)]

The title complex, [BaZn(C₃H₂O₄)₂(H₂O)₄]_n, is polymeric, due to the connectivity brought about by each malonate dianion bonding to two different Zn^II cations and two different Ba^II cations. The Ba^II cations, on crystallographic twofold axes, have slightly distorted square-anti­prismic coordination, with Ba—O distances ranging from 2.795 (2) to 2.848 (2) Å. The Zn^II cations, which lie on crystallographic centres of symmetry, have distorted octa­hedral coordination, with Zn—O bonds in the range 2.0364 (19)–2.3248 (18) Å. The water mol­ecules participate in extensive O—H...O hydrogen bonding. The structure comprises alternating layers along [100], with one type containing Zn^II cations and malonate dianions, while the other is primarily composed of Ba^II cations and water mol­ecules.

S1. Comment

In recent years, the rational design and synthesis of coordination polymers has been one of the most active research fields in coordination chemistry and materials science (Selby et al., 2003). There has been considerable interest in the design and synthesis of complexes with carboxylate ligands because carboxylates can give rise to different coordination modes with metal ions and increase recognition of the role of metals in biological systems (Wang et al., 2004; Maji et al., 2003). One special class of such compounds concerns coordination polymers based on assemblies of transition metal ions and α,ω-dicarboxylic acids. As one of the lower members in the α,ω-dicarboxylate family, malonate anions are of particular interest in the construction of coordination polymers with specific architectures (Rodriguez-Martin et al., 2002). The malonate ligand, with two neighbouring carboxylate groups, is a very flexible ligand. Its basic coordination mode is as a chelate via two distal carboxylate O atoms to form a six-membered ring, and the coordinating ability of the nonchelating O atoms makes the formation of polymeric networks possible (Djeghri et al., 2005). In addition, the malonate anion, with its versatile coordinating ability as a monodentate, chelated bidentate or bridging ligand, can create various patterns (Delgado et al., 2004). However, only a very limited amount of detailed structural data of heterobimetallic complexes, especially those involving alkaline earth metals, is currently available (Gil de Muro et al., 2004). Here, we report the structure of the title heterobimetallic malonate complex, (I).

The asymmetric unit in the structure of (I) comprises half a Ba^II cation, half a Zn^II cation, a complete malonate dianion defined by atoms C1–C3/O1–O4, and two independent water molecules, O5 and O6, and is shown in Fig. 1 in a symmetry-expanded view which displays the full coordination of the Ba^II and Zn^II cations. The unique M—O distances and O—M—O angles are given in Table 1.

The Ba^II cation, lying on a crystallographic twofold axis, is eight-coordinate, bonded to O atoms from four different malonate groups (O4) and four water molecules (O5 and O6). The Ba—O(water) distances are in the range 2.825 (2)–2.848 (2) Å, while the Ba—O(malonate) distances are shorter and cover the slightly narrower range of 2.795 (2)–2.807 (2) Å. These Ba—O distances are comparable with the values reported for barium malonate (Hodgson & Asplund, 1991). The Ba polyhedra may be described as slightly distorted square antiprisms. They share edges to form chains propagating in the c direction. The Ba···Ba separation within the chains [4.7101 (7) Å] is too long to imply any metal–metal bonding.

The Zn^II cations, coincident with crystallographic centres of symmetry, have octahedral coordination, with atoms O2 and O3 of two bidentate malonate anions at the equatorial sites [Zn—O 2.0364 (19) and 2.0391 (18) Å, respectively], and two O1 atoms from two other malonate anions at the apical sites [Zn—O 2.3248 (18) Å]. All of the cis O—Zn—O bond angles are close to 90° [in the range 85.47 (7)–94.53 (7)°] and, because of the site symmetry of Zn, all of the trans angles are exactly 180°. Thus, the coordination octahedra around the Zn^II ions can be visualized as being distorted due to axial elongation.

Also evident in Fig. 1 is the variability of the coordination modes of the malonate dianion, with monodentate (O1), bidentate chelating (O2 and O3) and bridging (O4) bonding modes all present. The chelate rings around the Zn^II cations have an envelope conformation, with the methylene groups (C2) displaced by 0.561 (3) Å from the plane defined by the other atoms in the ring.

The structure as a whole consists of two distinct types of layer, both parallel to (100) and stacked alternately in the a direction. The first of these (Fig. 2) is composed entirely of Zn^II cations and malonate dianions and occurs at x = 0 and 1/2. In this case, complete two-dimensional connectivity is achieved by means of O1—C1—O2 bridges between neighbouring Zn coordination octahedra. The O4 atoms, which bridge between Ba^II cations in neighbouring layers of the other type, project from the layer surfaces. Within the type 1 layers, the Zn···Zn separations are 5.822 (1) Å, while between them they are 6.843 (1) Å. It is within these layers that the weak C2—H2A···O2 and C2—H2B···O3 hydrogen bonds (Table 2) apppear (dashed lines in Fig. 2, although acceptor O2 is partially obscured by C3).

The other type of layer, type 2, alternating with the first and centred on x = 1/4 and 3/4, primarily contains the Ba^II cations and the water molecules (Fig. 2). Two forms of connectivity occur within the type 2 layers. Firstly, atoms O4 on the surfaces of the type 1 layers create chains of edge-sharing Ba polyhedra propagating in the c direction and, at the same time, link the two types of layer and complete the three-dimensional connectivity of the structure. The interlayer connectivity is further enhanced by O5—H5A···O2 and O6—H6A···O1 hydrogen bonds (Table 2). The remaining hydrogen bonds given in Table 2 occur entirely within the type 2 layers. Those of the form O5—H5B···O6 reinforce the connectivity of the chains of edge-sharing polyhedra, while those of the form O6—H6B···O5 interconnect neighbouring chains and complete the connectivity within the type 2 layers.

S2. Experimental

The title complex was prepared under continuous stirring with successive addition of malonic acid (0.43 g, 4 mmol), zinc chloride (0.28 g, 2 mmol) and Ba(OH)₂·8H₂O (0.63 g, 2 mmol) to distilled water (40 ml) at room temperature. After filtration, slow evaporation over a period of a week at room temperature provided colourless plate-like crystals of (I).

S3. Refinement

The H atoms of the water molecule were found in difference Fourier maps and were fixed during refinement at an O—H distance of 0.85 Å, with U_iso(H) = 1.2U_eq(O). The H atoms of C—H groups were positioned geometrically and were treated using a riding model, with C—H = 0.97 Å and U_iso(H) = 1.2U_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 and ATOMS (Dowty, 1998); software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. The coordination of the metal ions in (I). Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes (i) -x + 1, -y + 1, -z + 1; (ii) x, -y + 1/2, z + 1/2; (iii) -x + 1, y + 1/2, -z + 1/2; (iv) -x + 1/2, y, z + 1/2; (v) -x + 1/2, -y + 1/2, z.] Fig. 2. Revised caption to be supplied with revised Figure.

Poly[tetraaqua-µ₃-malonato-malonatobarium(II)zinc(II)]

Crystal data

[BaZn(C3H2O4)2(H2O)4]	F(000) = 920
Mr = 478.87	Dx = 2.595 Mg m^−3
Orthorhombic, Pccn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ab 2ac	Cell parameters from 3082 reflections
a = 19.014 (3) Å	θ = 3.2–26.3°
b = 6.8434 (10) Å	µ = 5.21 mm^−1
c = 9.4203 (14) Å	T = 294 K
V = 1225.8 (3) Å^3	Plate, colourless
Z = 4	0.20 × 0.20 × 0.08 mm

Data collection

Bruker SMART CCD area-detector diffractometer	1262 independent reflections
Radiation source: sealed tube	1042 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
φ and ω scans	θmax = 26.4°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −23→19
Tmin = 0.370, Tmax = 0.662	k = −8→8
6308 measured reflections	l = −7→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)] = 0.019	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.046	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.023P)^2 + 0.24P] where P = (Fo^2 + 2Fc^2)/3
1262 reflections	(Δ/σ)max = 0.001
93 parameters	Δρmax = 0.41 e Å^−3
0 restraints	Δρmin = −0.56 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.

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

- 3.1849 (156) x + 6.5309 (19) y - 2.3300 (75) z = 0.4070 (85)

* 0.1010 (0.0010) Zn1 * -0.0257 (0.0015) O2 * -0.1932 (0.0016) O3 * -0.0316 (0.0014) C1 * 0.1495 (0.0014) C3 0.5614 (0.0033) C2

Rms deviation of fitted atoms = 0.1196

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ba1	0.2500	0.2500	0.52818 (2)	0.01638 (9)
Zn1	0.5000	0.5000	0.5000	0.01937 (12)
O1	0.54011 (10)	0.2908 (3)	0.0985 (2)	0.0197 (5)
O2	0.54437 (9)	0.4342 (3)	0.3092 (2)	0.0196 (5)
O3	0.40616 (9)	0.3862 (3)	0.4356 (2)	0.0189 (4)
O4	0.32197 (10)	0.3454 (3)	0.2774 (2)	0.0258 (5)
O5	0.30956 (10)	0.5905 (3)	0.6479 (2)	0.0250 (5)
H5B	0.2910	0.6093	0.7286	0.037*
H5A	0.3535	0.5680	0.6479	0.037*
O6	0.31906 (10)	−0.1026 (3)	0.4483 (2)	0.0262 (5)
H6A	0.3598	−0.1248	0.4144	0.039*
H6B	0.3037	−0.1871	0.5071	0.039*
C1	0.51063 (14)	0.3776 (4)	0.1993 (3)	0.0148 (6)
C2	0.43322 (13)	0.4256 (4)	0.1853 (3)	0.0150 (6)
H2A	0.4295	0.5640	0.1643	0.018*
H2B	0.4155	0.3560	0.1030	0.018*
C3	0.38439 (14)	0.3825 (4)	0.3079 (3)	0.0158 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ba1	0.01577 (14)	0.02050 (13)	0.01286 (13)	0.00297 (11)	0.000	0.000
Zn1	0.0121 (2)	0.0321 (3)	0.0138 (2)	−0.0028 (2)	−0.00031 (19)	−0.0055 (2)
O1	0.0170 (10)	0.0264 (11)	0.0158 (11)	−0.0002 (8)	0.0039 (8)	−0.0065 (8)
O2	0.0113 (10)	0.0313 (12)	0.0161 (11)	−0.0002 (8)	0.0000 (8)	−0.0062 (9)
O3	0.0152 (10)	0.0280 (11)	0.0136 (10)	−0.0049 (9)	−0.0013 (9)	0.0007 (9)
O4	0.0126 (10)	0.0461 (14)	0.0187 (11)	−0.0096 (10)	−0.0007 (9)	0.0006 (11)
O5	0.0167 (10)	0.0325 (12)	0.0257 (12)	0.0018 (9)	0.0010 (9)	0.0016 (10)
O6	0.0196 (11)	0.0285 (12)	0.0304 (13)	0.0027 (10)	0.0049 (10)	0.0053 (10)
C1	0.0168 (14)	0.0125 (12)	0.0152 (15)	−0.0027 (12)	0.0008 (12)	0.0032 (11)
C2	0.0131 (14)	0.0186 (14)	0.0135 (15)	−0.0015 (11)	−0.0005 (11)	0.0000 (11)
C3	0.0151 (14)	0.0136 (13)	0.0187 (16)	−0.0008 (12)	0.0003 (11)	0.0019 (12)

Geometric parameters (Å, º)

Ba1—O4	2.807 (2)	O4—C3	1.247 (3)
Ba1—O4^i	2.795 (2)	O5—H5B	0.85
Ba1—O5	2.825 (2)	O5—H5A	0.85
Ba1—O6	2.848 (2)	O6—H6A	0.85
Zn1—O1^ii	2.3248 (18)	O6—H6B	0.85
Zn1—O2	2.0364 (19)	C1—C2	1.514 (4)
Zn1—O3	2.0391 (18)	C2—C3	1.511 (4)
O1—C1	1.252 (3)	C2—H2A	0.97
O2—C1	1.277 (3)	C2—H2B	0.97
O3—C3	1.272 (3)
O1^ii—Zn1—O2	88.44 (7)	O5^iv—Ba1—O6^iv	128.26 (6)
O2—Zn1—O3	90.88 (8)	O5^iv—Ba1—O6	65.91 (6)
O1^ii—Zn1—O3	85.47 (7)	O4^iv—Ba1—O6	78.77 (6)
O4^i—Ba1—O4^iii	65.72 (8)	C1—O1—Zn1^v	124.18 (17)
O4^iv—Ba1—O4	65.38 (8)	C1—O2—Zn1	125.03 (17)
O4^i—Ba1—O4	121.51 (7)	C3—O3—Zn1	124.99 (18)
O4^iii—Ba1—O4	153.04 (10)	Zn1—O3—Ba1	146.49 (9)
O4^i—Ba1—O5	70.19 (6)	C3—O4—Ba1^vi	135.00 (19)
O4^iii—Ba1—O5	70.62 (6)	C3—O4—Ba1	108.49 (18)
O4—Ba1—O5	87.07 (6)	Ba1^vi—O4—Ba1	114.45 (7)
O4—Ba1—O5^iv	136.32 (7)	Ba1—O5—H5B	108.4
O4—Ba1—O6	75.52 (6)	Ba1—O5—H5A	104.2
O4^i—Ba1—O6	78.36 (6)	H5B—O5—H5A	115.9
O4—Ba1—O6^iv	78.77 (6)	Ba1—O6—H6A	132.0
O4^iii—Ba1—O6	130.22 (6)	Ba1—O6—H6B	104.2
O5—Ba1—O6^iv	65.91 (6)	H6A—O6—H6B	115.7
O5—Ba1—O6	128.26 (6)	O1—C1—O2	122.2 (3)
O5—Ba1—O5^iv	132.94 (8)	O1—C1—C2	118.1 (2)
O6^iv—Ba1—O6	149.35 (9)	O2—C1—C2	119.6 (2)
O4^i—Ba1—O4^iv	153.04 (10)	C3—C2—C1	119.2 (2)
O4^iii—Ba1—O4^iv	121.51 (7)	C3—C2—H2A	107.5
O4^iv—Ba1—O5	136.32 (7)	C1—C2—H2A	107.5
O4^i—Ba1—O5^iv	70.62 (6)	C3—C2—H2B	107.5
O4^iii—Ba1—O5^iv	70.19 (6)	C1—C2—H2B	107.5
O4^iv—Ba1—O5^iv	87.07 (6)	H2A—C2—H2B	107.0
O4^i—Ba1—O6^iv	130.22 (6)	O4—C3—O3	122.1 (3)
O4^iii—Ba1—O6^iv	78.36 (6)	O4—C3—C2	116.6 (2)
O4^iv—Ba1—O6^iv	75.52 (6)	O3—C3—C2	121.3 (2)
C2—C3—O3—Zn1	13.0 (4)	O2—C1—C2—C3	−49.6 (4)
C1—C2—C3—O4	−151.0 (3)	O1—C1—C2—C3	133.7 (3)
C1—C2—C3—O3	29.7 (4)	Zn1—O2—C1—C2	22.8 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5A···O2^vii	0.85	1.98	2.812 (3)	165
O5—H5B···O6^i	0.85	2.14	2.836 (3)	140
O6—H6A···O1^v	0.85	1.99	2.810 (3)	161
O6—H6B···O5^viii	0.85	2.02	2.825 (3)	157
C2—H2A···O2^ii	0.97	2.59	3.506 (3)	157
C2—H2B···O3^ix	0.97	2.29	3.217 (3)	159

Symmetry codes: (i) x, −y+1/2, z+1/2; (ii) −x+1, y+1/2, −z+1/2; (v) −x+1, y−1/2, −z+1/2; (vii) −x+1, −y+1, −z+1; (viii) x, y−1, z; (ix) x, −y+1/2, z−1/2.