catena-Poly­[[[aqua(2-methyl-4-oxo-4H-pyran-3-olato-[kappa]O³,O⁴)copper(II)]-[mu]-chloro] monohydrate]

In the title complex, {[Cu(C₆H₅O₃)Cl(H₂O)]·H₂O}_n, the Cu^II atom has a deformed square-pyramidal coordination geometry formed by two O atoms of the maltolate ligand, two bridging Cl atoms and the coordinated water O atom. The Cu atoms are bridged by Cl atoms to form a polymeric chain. The deprotonated hydroxyl and ketone O atoms of the maltolate ligand form a five-membered chelate ring with the Cu atom. Stacking interactions and hydrogen bonds exist in the crystal.

S1. Comment

Maltol (3-hydroxy-2-methyl-4H-pyran-4-one, (I), is a naturally occurring non-toxic compound. This compound has the ability to be deprotonated readily (pK_a = 8.38; Hedlund & Öhman, 1988) and can act as an anionic chelating O,O'-bidentate ligand towards a number of biologically active metal ions. The metal complexes of (I) can be solubilized in water, and many biological studies have been reported employing this compound as a ligand. For instance, the Al^III complex has been studied in relation to apoptosis (Tsubouchi et al., 2001) and Alzheimer's disease (Finnegan et al., 1986), the Fe^III complex has been used in the treatment of iron deficiency anaemia (Harvey et al., 1998), and the V^IV complex is a potent insulin mimic (Caravan et al., 1995). The efficacy of the Cu^II and Sn^II complexes in oral care formations (Creeth et al., 2000) has also been reported. A number of crystal structures of maltolate–metal complexes have been reported, viz. Al^III (Finnegan et al., 1986; Yu et al., 2002), V^IV (Caravan et al., 1995; Sun et al., 1996, 1998), Fe^III (Ahmet et al., 1988), Zn^II (Ahmed et al., 2000), Mo^IV (Lord et al., 1999), Ru^IV (Fryzuk et al., 1997), Sn^II (Barret et al., 2001) and Sn^IV (Denekamp et al., 1992; Bhattacharya et al., 1994). In this study, to obtain further evidence for the chelating mode of maltol with divalent metal ions, we have analyzed the crystal structure of the maltolate–Cu^II complex, (II).

The crystal structure of (II) is shown in Fig. 1. In this compound, the Cu atom is surrounded by five atoms in a square-pyramidal coordination geometry (Fig. 1), in which the basal plane is made up of two O atoms of the maltolate ligand, one Cl atom and one water O atom, and the Cl atom of the next complex occupies the apical position. The Cu atom is shifted about 0.15 Å from the average basal plane toward the apical Cl atom. The deprotonated hydroxyl and ketone O atoms of the ligand form a five-membered chelate ring with the Cu atom. The ketone C1—O2 bond length [1.272 (2) Å] is longer than that of free maltol [1.244 (3)–1.254 (3) Å; Burgess et al., 1996], and is shorter than the enol bond length [C2—O3 = 1.339 (2) Å] (Table 1). This indicates a distinction between Lewis acid–base interactions for the two types of O atoms. The Cl atom coordinates from the apical position more weakly to the tetracoordinate basal plane around the Cu atom, forming a square-pyramidal geometry, then the complexes related by the a glide form polymeric chain [Cl1—Cu1 = 2.2445 (6) Å, Cl1—Cu1ⁱ = 2.7546 (9) Å, Cu1—Cl1—Cu1ⁱ = 124.04 (3)° and Cl1—Cu1ⁱ—Cl1ⁱ 101.38 (2)°; symmetry code: (i) -1/2 + x, 1/2 - y, z] (Fig. 1). The two different Cu—Cl distances in the title compound are similar to those in the 5-formyluracil thioosemicarbazone–Cu^II complex [apical Cu—Cl = 2.665 (3) Å and basal Cu—Cl = 2.260 (3) Å], and the longer appical Cu—Cl bond is due to a Jahn–Teller effect (Ferrari et al., 1998). The polymeric chain and the analogous coordination sphere were observed in the crystal structure of catena-poly[bis(2-aminopyrimidine)aquacopper(II)-µ²-sulfato dihydrate] (Lumme et al., 1996).

In the crystal structure of (II), there are O—H···O hydrogen-bond interactions between solvate water molecules and the deprotonated O atoms of the maltolate ligands, and between solvate water and the copper-coordinated water molecules (Table 2). Also, stacking interactions exist between neighboring pyran rings [O1···C1ⁱⁱ 3.493 (3) Å, C2···C4ⁱⁱ 3.506 (3) Å and C3···C5ⁱⁱ 3.515 (4) Å; symmetry code: (ii) -x, -y, 1 - z].

The title compound is composed of maltolate and metal in a 1:1 ratio. This is the first observation of a 1:1 metal complex of maltol, although 2:1 and 3:1 maltolate–metal complexes, with Zn^II (2:1), Sn^II (2:1), Fe^III (3:1) and Al^III (3:1), have been reported. In all the metal complexes of maltol reported, the bidentate maltolate ligand forms a five-membered chelate ring.

S2. Experimental

Maltol and CuCl₂·2H₂O were dissolved in a 50% ethanol–water mixture in a 4:1 molar ratio. Green plate-shaped crystals of (II) were obtained by slow evaporation at room temperature.

S3. Refinement

The H atoms of the ligand molecule were allowed for as riding atoms. Those of water molecules were located from difference Fourier maps and their coordinates refined with fixed isotropic vibration parameters.

Computing details

Data collection: MSC/AFC Diffractometer Control (Molecular Structure Corporation, 1992); cell refinement: MSC/AFC Diffractometer Control; data reduction: TEXSAN (Molecular Structure Corporation, 2000); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP II (Johnson, 1976); software used to prepare material for publication: TEXSAN.

Figures

Fig. 1. ORTEPII (Johnson, 1976) drawing of the title compound with the atomic numbering scheme. Ellipsoids for non-H atoms are shown at the 50% probability level.

(II)

Crystal data

[Cu(C6H5O3)Cl(H2O)]·H2O	F(000) = 524
Mr = 260.13	Dx = 1.920 Mg m^−3
Monoclinic, P21/a	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: -P 2yab	Cell parameters from 22 reflections
a = 7.163 (2) Å	θ = 14.6–15.0°
b = 18.604 (2) Å	µ = 2.71 mm^−1
c = 7.357 (2) Å	T = 296 K
β = 113.38 (2)°	Plate, green
V = 899.9 (4) Å^3	0.40 × 0.20 × 0.10 mm
Z = 4

Data collection

Rigaku AFC-5R diffractometer	Rint = 0.009
ω–2θ scans	θmax = 27.5°, θmin = 3.0°
Absorption correction: ψ scan (North et al., 1968)	h = 0→9
Tmin = 0.527, Tmax = 0.763	k = 0→24
2302 measured reflections	l = −9→8
2069 independent reflections	3 standard reflections every 150 reflections
1778 reflections with I > 2σ(I)	intensity decay: 0.5%

Refinement

Refinement on F^2	w = 1/[σ^2(Fo^2) + (0.027P)^2 + 0.3833P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.021	(Δ/σ)max = 0.001
wR(F^2) = 0.058	Δρmax = 0.34 e Å^−3
S = 1.07	Δρmin = −0.28 e Å^−3
2069 reflections	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
132 parameters	Extinction coefficient: 0.0047 (8)
H atoms treated by a mixture of independent and constrained refinement

Special details

Refinement. Refinement using reflections with F² > -10.0 σ(F²). The weighted R-factor (wR) and goodness of fit (S) are based on F². R-factor (gt) are based on F. The threshold expression of F² > 2.0 σ(F²) is used only for calculating R-factor (gt).

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

	x	y	z	Uiso*/Ueq
Cl1	0.15307 (8)	0.29022 (3)	0.79480 (7)	0.0319 (1)
Cu1	0.29255 (4)	0.18032 (1)	0.83113 (3)	0.02541 (9)
O1	0.1738 (2)	−0.01327 (8)	0.3219 (2)	0.0350 (3)
O2	0.3677 (2)	0.07854 (7)	0.8616 (2)	0.0333 (3)
O3	0.1566 (2)	0.15755 (7)	0.5507 (2)	0.0272 (3)
O4W	0.4171 (2)	0.18564 (8)	1.1217 (2)	0.0321 (3)
O5W	0.7954 (2)	0.23087 (9)	1.3565 (2)	0.0337 (3)
C1	0.3117 (3)	0.0479 (1)	0.6938 (3)	0.0256 (4)
C2	0.1949 (3)	0.0891 (1)	0.5207 (3)	0.0241 (4)
C3	0.1290 (3)	0.0572 (1)	0.3388 (3)	0.0290 (4)
C4	0.2865 (3)	−0.0518 (1)	0.4834 (3)	0.0355 (5)
C5	0.3568 (3)	−0.0246 (1)	0.6671 (3)	0.0323 (4)
C6	0.0068 (4)	0.0906 (1)	0.1453 (3)	0.0401 (5)
H4	0.3168	−0.0993	0.4667	0.0426*
H4WA	0.369 (4)	0.212 (1)	1.175 (4)	0.0385*
H4WB	0.534 (3)	0.197 (1)	1.170 (4)	0.0385*
H5	0.4339	−0.0528	0.7754	0.0388*
H5WA	0.774 (4)	0.257 (1)	1.428 (4)	0.0404*
H5WB	0.895 (3)	0.209 (1)	1.420 (4)	0.0404*
H6A	0.0750	0.0843	0.0573	0.0481*
H6B	−0.0093	0.1410	0.1635	0.0481*
H6C	−0.1245	0.0681	0.0895	0.0481*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0350 (3)	0.0259 (2)	0.0323 (3)	0.0043 (2)	0.0107 (2)	−0.0013 (2)
Cu1	0.0315 (1)	0.0223 (1)	0.0179 (1)	0.00096 (9)	0.0049 (1)	−0.00092 (8)
O1	0.0450 (9)	0.0291 (7)	0.0298 (8)	−0.0012 (7)	0.0137 (7)	−0.0091 (6)
O2	0.0474 (8)	0.0248 (7)	0.0204 (7)	0.0026 (6)	0.0057 (6)	0.0014 (5)
O3	0.0329 (7)	0.0226 (6)	0.0194 (6)	0.0030 (6)	0.0033 (5)	−0.0014 (5)
O4W	0.0339 (8)	0.0368 (8)	0.0212 (7)	0.0003 (7)	0.0062 (6)	−0.0046 (6)
O5W	0.0308 (8)	0.0438 (9)	0.0219 (7)	0.0024 (7)	0.0055 (6)	−0.0027 (6)
C1	0.0278 (9)	0.0231 (9)	0.0247 (9)	−0.0012 (7)	0.0091 (8)	0.0013 (7)
C2	0.0250 (9)	0.0230 (9)	0.0225 (9)	0.0002 (7)	0.0073 (7)	0.0006 (7)
C3	0.032 (1)	0.0275 (10)	0.0256 (9)	−0.0019 (8)	0.0094 (8)	−0.0039 (8)
C4	0.045 (1)	0.0219 (9)	0.042 (1)	0.0033 (9)	0.020 (1)	−0.0017 (8)
C5	0.038 (1)	0.0235 (9)	0.033 (1)	0.0033 (8)	0.0114 (9)	0.0035 (8)
C6	0.049 (1)	0.043 (1)	0.0208 (9)	0.000 (1)	0.0067 (9)	−0.0029 (9)

Geometric parameters (Å, º)

Cl1—Cu1	2.2445 (6)	O5W—H5WB	0.79 (2)
Cl1—Cu1^i	2.7546 (9)	C1—C2	1.437 (2)
Cu1—O2	1.957 (1)	C1—C5	1.418 (3)
Cu1—O3	1.947 (1)	C2—C3	1.365 (3)
Cu1—O4W	1.965 (1)	C3—C6	1.480 (3)
O1—C3	1.367 (3)	C4—C5	1.340 (3)
O1—C4	1.348 (2)	C4—H4	0.930
O2—C1	1.272 (2)	C5—H5	0.930
O3—C2	1.339 (2)	C6—H6A	0.960
O4W—H4WA	0.786 (19)	C6—H6B	0.960
O4W—H4WB	0.798 (19)	C6—H6C	0.960
O5W—H5WA	0.772 (19)
Cl1···O2^i	3.343 (2)	O3···O5W^ii	2.768 (2)
Cl1···O5W^ii	3.409 (1)	O3···O5W^viii	2.910 (2)
Cl1···O3^i	3.428 (2)	O4W···O5W^i	2.711 (3)
Cl1···O4W^i	3.474 (2)	O4W···C5^vii	3.467 (3)
Cl1···C6^iii	3.578 (2)	O4W···C6^ix	3.492 (3)
O1···C5^iv	3.405 (3)	C2···C4^vi	3.506 (3)
O1···C6^v	3.467 (3)	C3···C5^vi	3.515 (4)
O1···C1^vi	3.493 (3)	C4···C5^iv	3.467 (4)
O1···C2^vi	3.569 (3)	C4···C4^iv	3.541 (5)
O2···C5^vii	3.390 (2)
Cl1—Cu1—O2	169.82 (6)	C2—C1—C5	118.0 (2)
Cl1—Cu1—O3	93.45 (4)	O3—C2—C1	116.5 (2)
Cl1—Cu1—O4W	94.13 (5)	O3—C2—C3	124.1 (2)
Cu1—Cl1—Cu1^i	124.04 (3)	C1—C2—C3	119.3 (2)
Cl1^x—Cu1—Cl1	101.38 (2)	O1—C3—C2	120.3 (2)
O2—Cu1—Cl1^x	88.72 (6)	O1—C3—C6	112.6 (2)
O2—Cu1—O3	84.84 (5)	C2—C3—C6	127.1 (2)
O2—Cu1—O4W	86.49 (6)	O1—C4—C5	122.8 (2)
O3—Cu1—Cl1^x	91.98 (5)	O1—C4—H4	118.6
O3—Cu1—O4W	169.75 (6)	C5—C4—H4	118.6
C3—O1—C4	120.6 (2)	C1—C5—C4	118.9 (2)
Cu1—O2—C1	110.9 (1)	C1—C5—H5	120.5
Cu1—O3—C2	109.4 (1)	C4—C5—H5	120.5
Cu1—O4W—H4WA	118 (2)	C3—C6—H6A	109.5
Cu1—O4W—H4WB	116.2 (19)	C3—C6—H6B	109.5
H4WA—O4W—H4WB	102 (3)	C3—C6—H6C	109.5
H5WA—O5W—H5WB	107 (3)	H6A—C6—H6B	109.5
O2—C1—C2	118.0 (2)	H6A—C6—H6C	109.5
O2—C1—C5	124.0 (2)	H6B—C6—H6C	109.5
Cl1—Cu1—O2—C1	85.9 (3)	O3—Cu1—O2—C1	5.2 (2)
Cl1—Cu1—O3—C2	−174.6 (1)	O3—C2—C1—C5	−179.4 (2)
Cu1—O2—C1—C2	−4.6 (3)	O3—C2—C3—C6	0.2 (4)
Cu1—O2—C1—C5	175.5 (2)	O4W—Cu1—O2—C1	179.7 (2)
Cu1—O3—C2—C1	3.5 (2)	O4W—Cu1—O3—C2	−36.9 (5)
Cu1—O3—C2—C3	−177.1 (2)	C1—C2—C3—C6	179.6 (2)
O1—C3—C2—O3	−179.4 (2)	C2—C1—C5—C4	−1.1 (4)
O1—C3—C2—C1	0.0 (3)	C2—C3—O1—C4	−1.3 (3)
O1—C4—C5—C1	−0.2 (4)	C3—O1—C4—C5	1.4 (4)
O2—Cu1—O3—C2	−4.6 (1)	C3—C2—C1—C5	1.2 (3)
O2—C1—C2—O3	0.8 (3)	C4—O1—C3—C6	179.1 (2)
O2—C1—C2—C3	−178.7 (2)	C4—O1—C3—C6	179.1 (2)
O2—C1—C5—C4	178.7 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4W—H4WA···O5W^i	0.79 (3)	1.94 (2)	2.711 (2)	168 (3)
O4W—H4WB···O5W	0.80 (2)	1.94 (2)	2.706 (2)	162 (2)
O5W—H5WA···O3^iii	0.77 (3)	2.16 (2)	2.910 (2)	164 (3)
O5W—H5WB···O3^xi	0.79 (2)	1.98 (2)	2.768 (2)	172 (3)

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