cis-Diaqua­bis[(E)-4-(2-hydroxy­benzyl­idene­amino)benzoato-κ²O,O′]cadmium(II): two-dimensional layers built from strong O—H...O hydrogen bonding in the coordination sphere

In the title compound, [Cd(C₁₄H₁₀NO₃)₂(H₂O)₂], which crystallizes with Z = 4 in the space group C2c, the Cd atom is located on a twofold rotation axis and coordinated by six O atoms from two water mol­ecules and two carboxylate groups of two planar 4-(2-hydroxy­benzyl­idene­amino)­benzoate lig­ands, with a dihedral angle of 85.6 (1)° between them. Strong O—H...O hydrogen bonding in the coordination sphere, together with π–π stacking inter­actions, assemble the mol­ecules into two-dimensional layers.

S1. Comment

Schiff base metal complexes have versatile functions, for example, Schiff base titanium(IV), cobalt(II), vanadium(III, IV, V) and copper(II) complexes can act as catalysts (Huang et al., 2002; Niimi et al., 2000; Liu & Anson, 2001; Bluhm et al., 2003), Tb^III salen complexes have luminescent properties (Yang & Jones, 2005), nonlinear absorption behaviour has been investigated in Schiff base zinc(II) and copper(I) complexes (Das et al., 2006), and so on. All these properties have attracted our interest. In one recent experiment, we synthesized 4-(2-hydroxybenzylideneamino)benzoic acid and intended to complex it with metal ions via the Schiff base moiety, but instead, the title compound, (I), was obtained, with the carboxylate group coordinating to Cd.

A perspective view of compound (I), with the atom-labelling scheme, is illustrated in Fig. 1. In (I), the Cd atom is located on a twofold rotation axis and is coordinated by six O atoms from two water molecules and two carboxyl groups of two 4-(2-hydroxybenzylideneamino)benzoic acid ligands. The two Cd—O(carboxyl) bond lengths are 2.232 (4) and 2.508 (4) Å, exhibiting an obvious difference. The two water molecules are tightly coordinated to Cd, with a Cd—O(water) distance of 2.191 (4) Å. All these features are similar to those in the analogous complexes [Cd(C₇H₄NO₄)₂(H₂O)₂], [Cd(C₇H₄ClO₂)₂(H₂0)₂] and [Cd(C₉H₇O₄)₂·(H₂O)₂] (Rodesiler et al., 1985; Vásquez-Árciga et al., 2004). In the present compound, the ligand adopts a planar geometry, forming a large π conjugation system. The two coordinated planar ligands form a dihedral angle of 85.6 (1)°, leading to an arrowhead shape for (I).

A noteworthy feature of this compound is that it is the carboxylate group and not the Schiff base moiety that coordinates to Cd. The Schiff base moiety is only involved in an intramolecular hydrogen bond. To date, analogous coordination has only been reported for the crystal structures of Sn complexes (Yin et al., 2005). This situation possibly implies that the coordination ability of the Schiff base moiety in this ligand is affected by the terminal carboxylate group, or that Cd and Sn have a greater preference for coordination by the two O atoms of the carboxylate group than do other metal ions. Indeed, there are many such Cd and Sn complexes in which Cd or Sn are coordinated by both O atoms of one carboxylate group (see, for example, Charles et al., 1983; Rodesiler et al., 1985; Ng et al., 1990; Aletras et al., 1997; Gao et al., 2004; Zou et al., 2004; Paz & Klinowski, 2004; Vásquez-Árciga et al., 2004; Garbauskas et al., 1991; Tiekink, 1991; Baul & Tiekink, 1996, 1999; Baul et al., 2005; Yin et al., 2005; Parvez et al., 1997; Teoh et al., 1997).

The hydrogen-bonding interactions in (I) are listed in Table 2 and illustrated in Figs. 2 and 3. It is interesting that in (I), the main intermolecular hydrogen bonds are formed by six coordinated O atoms, where four O atoms of two carboxyl groups act as hydrogen-bond acceptors and two water molecules as hydrogen-bond donors, forming four pairs of strong hydrogen bonds with O···O distances of only 2.686 (6) and 2.786 (5) Å. Two such pairs (O1—H1B···O3) link the molecules of (I) in an arrangement along the b axis, constructing a one-dimensional penniform tape with the arrowheads pointing in the same direction and the planes of the ligands partly overlapped in a parallel fashion (Fig. 2). In spite of the fact that the centroid-to-centroid distances between corresponding six-membered rings of the parallel ligands are more than 4.412 (4) Å, the perpendicular contacts are only about 3.4 Å. As the π-electron cloud is delocalized over the whole ligand, a π–π stacking interaction thus still exists between the parallel ligands, contributing to the stabilization of the one-dimensional tapes. A further two pairs of O1—H1A···O2 hydrogen bonds join the penniform tapes in an antiparallel fashion and alternating with each other in the c axis direction, organizing the tapes into two-dimensional layers, in which the coordination spheres are tightly hydrogen-bonded as sheets (Fig. 3) in the middle.

S2. Experimental

Compound (I) was synthesized by adding an ethanol (15 ml) solution of 4-(2-hydroxybenzylideneamino)benzoic acid (0.128 g) to an aqueous solution (5 ml) of CdSO₄·8H₂O (0.381 g). The mixed solution was refluxed at 333 K for 2 h after adjusting the pH to 7 with 0.1 M NaOH, then filtered after cooling to room temperature. Yellow crystals of (I) were obtained from the filtrate at room temperature over a period of 10 d.

S3. Refinement

H atoms attached to C atoms were placed in geometrically idealized positions, with Csp²—H = 0.93 Å, and constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C). H atoms attached to O atoms were located in difference Fourier maps and their global U_iso value was refined. The constrained O—H distances are in the range 0.82–0.83 Å.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL/PC (Sheldrick, 1999); software used to prepare material for publication: SHELXTL/PC.

Figures

	Fig. 1. The structure of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. Dotted lines indicate hydrogen bonds. Unlabelled atoms are related to labelled atoms by the symmetry operator (1 − x, y, 3/2 − z). [Please check added symmetry code]
	Fig. 2. The one-dimensional penniform tape built from O—H···O hydrogen bonding (dotted lines) and π–π stacking between the planar ligands of (I). Cd atoms are cross-hatched, O atoms are hatched, N atoms have a central dot, C atoms are part shaded and H atoms are small open circles.
	Fig. 3. The two-dimensional sheet built from O—H···O hydrogen bonding (dotted lines) around the Cd coordination spheres. Cd atoms are cross-hatched, O atoms are hatched and H atoms are small open circles.

cis-Diaquabis[(E)-4-(2-hydroxybenzylideneamino)benzoato-κ²O,O']cadmium(II)

Crystal data

[Cd(C14H10NO3)2(H2O)2]	F(000) = 1272
Mr = 628.89	Dx = 1.686 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 1151 reflections
a = 40.703 (6) Å	θ = 3.1–21.2°
b = 5.0970 (8) Å	µ = 0.94 mm^−1
c = 12.2793 (18) Å	T = 298 K
β = 103.498 (3)°	Rod, yellow
V = 2477.1 (6) Å^3	0.37 × 0.08 × 0.06 mm
Z = 4

Data collection

Bruker SMART 1K CCD area-detector diffractometer	2152 independent reflections
Radiation source: fine-focus sealed tube	1817 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.050
ω scans	θmax = 25.0°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 2000)	h = −48→47
Tmin = 0.723, Tmax = 0.946	k = −5→6
5875 measured reflections	l = −7→14

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) = 0.137	H-atom parameters constrained
S = 1.14	w = 1/[σ^2(Fo^2) + (0.0725P)^2] where P = (Fo^2 + 2Fc^2)/3
2152 reflections	(Δ/σ)max < 0.001
177 parameters	Δρmax = 0.98 e Å^−3
0 restraints	Δρmin = −0.86 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
Cd1	0.5000	−0.90020 (11)	0.7500	0.0262 (2)
O1	0.48036 (12)	−1.1990 (8)	0.6233 (3)	0.0416 (11)
O2	0.52837 (10)	−0.7167 (8)	0.6059 (3)	0.0355 (10)
O3	0.54295 (10)	−0.6166 (7)	0.7845 (3)	0.0284 (9)
O4	0.66066 (14)	0.4579 (11)	0.4512 (4)	0.0603 (15)
H4A	0.6495	0.3362	0.4697	0.090*
C1	0.54599 (14)	−0.5835 (11)	0.6837 (5)	0.0255 (13)
C2	0.56943 (14)	−0.3749 (10)	0.6629 (5)	0.0245 (12)
C3	0.57139 (17)	−0.3043 (13)	0.5556 (5)	0.0362 (15)
H3	0.5578	−0.3900	0.4945	0.043*
C4	0.59277 (16)	−0.1118 (12)	0.5378 (5)	0.0335 (14)
H4	0.5933	−0.0664	0.4649	0.040*
C5	0.61374 (14)	0.0170 (12)	0.6266 (5)	0.0249 (13)
C6	0.61306 (16)	−0.0570 (13)	0.7341 (5)	0.0362 (16)
H6	0.6275	0.0231	0.7949	0.043*
C7	0.59095 (15)	−0.2504 (12)	0.7518 (5)	0.0325 (15)
H7	0.5906	−0.2972	0.8247	0.039*
C8	0.65359 (15)	0.3584 (11)	0.6730 (5)	0.0295 (14)
H8	0.6521	0.3388	0.7470	0.035*
C9	0.67626 (15)	0.5548 (11)	0.6473 (5)	0.0303 (14)
C10	0.67906 (16)	0.5987 (13)	0.5364 (5)	0.0367 (15)
C11	0.70082 (19)	0.7869 (16)	0.5143 (6)	0.0525 (19)
H11	0.7028	0.8133	0.4412	0.063*
C12	0.71974 (18)	0.9373 (13)	0.6003 (7)	0.052 (2)
H12	0.7340	1.0666	0.5842	0.062*
C13	0.71760 (17)	0.8974 (13)	0.7100 (6)	0.0431 (17)
H13	0.7308	0.9956	0.7679	0.052*
C14	0.69576 (16)	0.7108 (13)	0.7316 (5)	0.0389 (16)
H14	0.6938	0.6871	0.8050	0.047*
N1	0.63558 (12)	0.2109 (10)	0.5985 (4)	0.0289 (11)
H1A	0.4803	−1.2056	0.5563	0.035*
H1B	0.4671	−1.3064	0.6383	0.035*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.0359 (4)	0.0172 (3)	0.0266 (4)	0.000	0.0094 (3)	0.000
O1	0.076 (3)	0.029 (2)	0.023 (2)	−0.017 (2)	0.018 (2)	−0.0040 (18)
O2	0.050 (3)	0.032 (2)	0.025 (2)	−0.012 (2)	0.0094 (19)	−0.0064 (19)
O3	0.041 (2)	0.026 (2)	0.021 (2)	−0.0036 (19)	0.0133 (17)	0.0037 (17)
O4	0.078 (4)	0.077 (4)	0.031 (3)	−0.038 (3)	0.021 (3)	−0.005 (3)
C1	0.033 (3)	0.020 (3)	0.025 (3)	0.009 (3)	0.009 (3)	−0.002 (2)
C2	0.031 (3)	0.018 (3)	0.026 (3)	0.003 (3)	0.010 (2)	0.002 (2)
C3	0.056 (4)	0.033 (3)	0.016 (3)	−0.016 (3)	0.002 (3)	−0.003 (3)
C4	0.050 (4)	0.036 (4)	0.016 (3)	−0.006 (3)	0.011 (3)	0.005 (3)
C5	0.029 (3)	0.026 (3)	0.022 (3)	0.002 (3)	0.010 (2)	0.000 (2)
C6	0.038 (4)	0.049 (4)	0.022 (3)	−0.015 (3)	0.007 (3)	−0.002 (3)
C7	0.044 (4)	0.039 (4)	0.015 (3)	−0.009 (3)	0.007 (3)	0.001 (3)
C8	0.034 (3)	0.028 (4)	0.030 (3)	0.004 (3)	0.013 (3)	0.004 (3)
C9	0.032 (3)	0.023 (4)	0.036 (4)	0.003 (3)	0.010 (3)	0.001 (3)
C10	0.036 (3)	0.045 (4)	0.031 (4)	−0.006 (3)	0.012 (3)	0.004 (3)
C11	0.063 (5)	0.056 (5)	0.041 (4)	−0.016 (4)	0.018 (4)	0.007 (4)
C12	0.048 (4)	0.036 (5)	0.071 (6)	−0.014 (3)	0.015 (4)	0.009 (4)
C13	0.039 (4)	0.043 (4)	0.047 (4)	−0.005 (3)	0.011 (3)	0.000 (3)
C14	0.041 (4)	0.036 (4)	0.037 (4)	−0.002 (3)	0.003 (3)	0.003 (3)
N1	0.033 (3)	0.031 (3)	0.025 (3)	−0.004 (2)	0.011 (2)	0.000 (2)

Geometric parameters (Å, º)

Cd1—O1	2.191 (4)	C6—C7	1.386 (8)
Cd1—O3	2.232 (4)	C6—H6	0.9300
Cd1—O2	2.508 (4)	C7—H7	0.9300
Cd1—C1^i	2.736 (6)	C8—N1	1.275 (7)
O1—H1A	0.82	C8—C9	1.446 (8)
O1—H1B	0.82	C8—H8	0.9300
O2—C1	1.252 (7)	C9—C14	1.397 (9)
O3—C1	1.284 (7)	C9—C10	1.411 (8)
O4—H4A	0.83	C10—O4	1.343 (8)
C1—C2	1.489 (8)	C10—C11	1.375 (9)
C2—C7	1.383 (8)	C11—C12	1.384 (10)
C2—C3	1.386 (8)	C11—H11	0.9300
C3—C4	1.362 (8)	C12—C13	1.385 (10)
C3—H3	0.9300	C12—H12	0.9300
C4—C5	1.384 (8)	C13—C14	1.370 (9)
C4—H4	0.9300	C13—H13	0.9300
C5—C6	1.378 (8)	C14—H14	0.9300
C5—N1	1.425 (8)
O1—Cd1—O1^i	91.9 (2)	C4—C5—N1	116.3 (5)
O1—Cd1—O3	136.46 (15)	C5—C6—C7	120.2 (6)
O1—Cd1—O3^i	100.12 (16)	C5—C6—H6	119.9
O3—Cd1—O3^i	99.3 (2)	C7—C6—H6	119.9
O1—Cd1—O2^i	127.49 (16)	C2—C7—C6	121.2 (5)
O3—Cd1—O2^i	95.38 (14)	C2—C7—H7	119.4
O1—Cd1—O2	84.83 (14)	C6—C7—H7	119.4
O3—Cd1—O2	54.77 (13)	N1—C8—C9	122.7 (6)
O2^i—Cd1—O2	136.2 (2)	N1—C8—H8	118.6
Cd1—O1—H1A	130.9	C9—C8—H8	118.6
Cd1—O1—H1B	117.0	C14—C9—C10	117.8 (6)
H1A—O1—H1B	110.4	C14—C9—C8	120.9 (6)
C1—O2—Cd1	86.6 (3)	C10—C9—C8	121.4 (5)
C1—O3—Cd1	98.6 (3)	O4—C10—C11	119.1 (6)
O2—C1—O3	119.8 (5)	O4—C10—C9	120.8 (5)
O2—C1—C2	122.2 (5)	C11—C10—C9	120.1 (6)
O3—C1—C2	117.9 (5)	C10—C11—C12	120.4 (7)
O2—C1—Cd1	66.2 (3)	C10—C11—H11	119.8
O3—C1—Cd1	53.8 (3)	C12—C11—H11	119.8
C2—C1—Cd1	169.1 (4)	C11—C12—C13	120.7 (6)
C7—C2—C3	117.6 (5)	C11—C12—H12	119.7
C7—C2—C1	120.4 (5)	C13—C12—H12	119.7
C3—C2—C1	121.9 (5)	C14—C13—C12	118.8 (6)
C4—C3—C2	121.3 (5)	C14—C13—H13	120.6
C4—C3—H3	119.3	C12—C13—H13	120.6
C2—C3—H3	119.3	C13—C14—C9	122.3 (6)
C3—C4—C5	121.0 (5)	C13—C14—H14	118.9
C3—C4—H4	119.5	C9—C14—H14	118.9
C5—C4—H4	119.5	C10—O4—H4A	115.2
C6—C5—C4	118.6 (6)	C8—N1—C5	121.4 (5)
C6—C5—N1	125.1 (5)
O1—Cd1—O2—C1	−165.5 (3)	C1^i—Cd1—C1—C2	28 (2)
O1^i—Cd1—O2—C1	−77.1 (4)	O2—C1—C2—C7	−173.4 (5)
O3—Cd1—O2—C1	−2.7 (3)	O3—C1—C2—C7	9.8 (8)
O3^i—Cd1—O2—C1	94.8 (3)	Cd1—C1—C2—C7	48 (2)
O2^i—Cd1—O2—C1	52.4 (3)	O2—C1—C2—C3	4.4 (9)
C1^i—Cd1—O2—C1	76.4 (4)	O3—C1—C2—C3	−172.3 (5)
O1—Cd1—O3—C1	28.1 (4)	Cd1—C1—C2—C3	−134.4 (19)
O1^i—Cd1—O3—C1	131.8 (3)	C7—C2—C3—C4	−2.5 (9)
O3^i—Cd1—O3—C1	−87.4 (3)	C1—C2—C3—C4	179.5 (6)
O2^i—Cd1—O3—C1	−142.5 (3)	C2—C3—C4—C5	1.1 (10)
O2—Cd1—O3—C1	2.7 (3)	C3—C4—C5—C6	1.3 (9)
C1^i—Cd1—O3—C1	−115.2 (3)	C3—C4—C5—N1	178.7 (6)
Cd1—O2—C1—O3	4.5 (5)	C4—C5—C6—C7	−2.1 (9)
Cd1—O2—C1—C2	−172.2 (5)	N1—C5—C6—C7	−179.3 (6)
Cd1—O3—C1—O2	−5.1 (6)	C3—C2—C7—C6	1.6 (9)
Cd1—O3—C1—C2	171.7 (4)	C1—C2—C7—C6	179.6 (5)
O1—Cd1—C1—O2	15.5 (4)	C5—C6—C7—C2	0.7 (10)
O1^i—Cd1—C1—O2	119.4 (3)	N1—C8—C9—C14	−179.4 (6)
O3—Cd1—C1—O2	175.2 (5)	N1—C8—C9—C10	1.6 (9)
O3^i—Cd1—C1—O2	−88.2 (3)	C14—C9—C10—O4	−179.1 (6)
O2^i—Cd1—C1—O2	−142.1 (3)	C8—C9—C10—O4	−0.1 (9)
C1^i—Cd1—C1—O2	−114.3 (3)	C14—C9—C10—C11	1.0 (9)
O1—Cd1—C1—O3	−159.7 (3)	C8—C9—C10—C11	180.0 (6)
O1^i—Cd1—C1—O3	−55.7 (3)	O4—C10—C11—C12	179.1 (7)
O3^i—Cd1—C1—O3	96.6 (3)	C9—C10—C11—C12	−1.0 (11)
O2^i—Cd1—C1—O3	42.7 (3)	C10—C11—C12—C13	1.3 (12)
O2—Cd1—C1—O3	−175.2 (5)	C11—C12—C13—C14	−1.7 (11)
C1^i—Cd1—C1—O3	70.5 (3)	C12—C13—C14—C9	1.7 (10)
O1—Cd1—C1—C2	158 (2)	C10—C9—C14—C13	−1.4 (9)
O1^i—Cd1—C1—C2	−98 (2)	C8—C9—C14—C13	179.6 (6)
O3—Cd1—C1—C2	−42.3 (19)	C9—C8—N1—C5	179.3 (5)
O3^i—Cd1—C1—C2	54 (2)	C6—C5—N1—C8	−9.5 (9)
O2^i—Cd1—C1—C2	0 (2)	C4—C5—N1—C8	173.3 (6)
O2—Cd1—C1—C2	143 (2)

Symmetry code: (i) −x+1, y, −z+3/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1B···O3^ii	0.82	1.94	2.686 (6)	152
O1—H1A···O2^iii	0.82	1.98	2.786 (5)	167
O4—H4A···N1	0.83	1.91	2.601 (6)	140

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