Poly[[diaqua­bis([mu]₂-1-oxo-2,6,7-trioxa-1-phosphabicyclo­[2.2.2]octane-4-carboxyl­ato)copper(II)] dihydrate]

The asymmetric unit of the title complex, {[Cu(C₅H₆O₆P)₂(H₂O)₂]·2H₂O}_n, consists of half a Cu atom, one complete 1-oxo-2,6,7-trioxa-1-phosphabicyclo­[2.2.2]octane-4-carboxyl­ate anion ligand and two non-equivalent water mol­ecules. The Cu atom lies on a crystallographic inversion centre and has an elongated axially distorted octa­hedral environment. A two-dimensional layer structure parallel to (100) is formed as a result of the connectivity brought about by each anion bonding to two different Cu atoms via a carboxylate O atom and a bridging O atom of a C-O-P group. The water mol­ecules participate in extensive O-H...O hydrogen bonding. Neighbouring layers are linked together by inter­molecular hydrogen-bonding inter­actions. The crystal structure is characterized by intra- and inter­layer motifs of a hydrogen-bonded network. This study demonstrates the usefulness of carboxylates with caged phosphate esters in crystal engineering.

S1. Comment

Compounds that contain caged phosphate esters can serve as host–guest systems and have been studied in the context of hydrogen-bond patterns. For example, in O=P(OCH₂)₃CCH₂OH (Guo & Zang, 2007), the O atom of the P=O group links with the H atom of the alcohol group to form hydrogen-bonded one-dimensional spiral molecular chains; in C₁₂H₉N₂⁺·OP(OCH₂)₃CCOO^-·OP(OCH₂)₃CCOOH·H₂O (Wang et al., 2007), there is a hydrogen-bonding interaction of the O atom of the P=O group of the neutral caged phosphate ester with the H atom of the monoprotonated 1,10-phenanthroline molecule. On the other hand, from a coordination standpoint, the use of a carboxylate that contains a caged phosphate ester, such as OP(OCH₂)₃CCOO^-, is of interest as a ligand in generating metal-organic coordination polymers of different dimensionalities, because it may act in monodentate, bidentate and combined modes of coordination via its carboxylate group and the P═O group of the caged phosphate ester and lead to a great variety of structures. However, the literature data show that for metal–phosphate ester systems, especially for complexes involving Cu, only a few complexes have been reported to date (Taylor & Waugh, 1977; Shi et al., 2001; Morize et al., 2003). Complexes of Cu and carboxylate anions with caged phosphate ester complexes are rarely reported. When we use 1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-carboxylate as ligand, interestingly, a novel six-coordinated Cu complex, (I), was obtained. Not only the carboxylate group but also, unexpectedly, the C—O—P group coordinates to the metal; in addition, a novel hydrogen-bond pattern is formed by a phosphoryl O atom of the caged phosphate ester and an H atom of a water molecule. We describe here the structure of the two-dimensional metal-caged phosphate ester framework, parallel to (100), with strong O—H···O intra- and interlayer hydrogen-bonding, leading to three-dimensional supramolecular networks.

The asymmetric unit in the structure of (I) comprises half a Cu atom, one complete 1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-carboxylate ligand and two non-equivalent water molecules, and is shown in Fig. 1 in a symmetry-expanded view, which displays the full coordination of the Cu atom. Selected geometric parameters are given in Table 1.

The Cu atom, lying on a crystallographic centre of symmetry, is octahedrally coordinated, with two O6 atoms and two water molecules in a planar arrangement and two O4 atoms forming the opposing apices of the octahedron. All of the cis O—Cu—O bond angles are close to 90° [in the range 87.02 (7)–92.98 (7)°] and, because of the site symmetry of Cu, all of the trans angles are exactly 180°. Thus, the coordination octahedron of the Cu atoms can be visualized as having an elongated axial distortion.

The 1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-carboxylate ligand contains both a carboxylate group and a bicyclic OP(OCH₂)₃C cage. The P1—O1 distance is the shortest of all four P—O bonds. These P—O distances are comparable to the values reported for another cage compound (Guo & Zang, 2007). The configuration around the P atom is distorted tetrahedral. As expected, atom O6 of the carboxylate group of the ligand adopts a monodentate mode to connect with the Cu atom. The Cu—O_water bond and the Cu—O_carboxylate bond (see Table 1) are shorter than those in the diaqua-dimethanol-bis(N-tosylvalinto-O)copper(II) six-coordinated complex (Battaglia et al., 1987) and in the catena-[bis(µ₂-pentane-1,5-dioate-O)tetraamminediaquadi-χopper(II) tetrahydrate] five-coordinated complex (Devereux et al., 1999). This means that the coordinated interaction for the carboxyl O atom and water molecules with the metal is stronger. Interestingly, the phosphoryl atom O1 of the caged phosphate ester does not coordinate to the Cu atom, but atom O4 of the P—O—C group in the bicyclic OP(OCH₂)₃C cage adopts an unexpected bridging bonding mode to another Cu atom. The Cu—O_phosphate distance [2.7045 (19) Å] is longer than that of the coordinated bonds with an ether O atom bonding to a Cu atom in the poly[aquadi -µ3-oxydiacetatodicopper(II)] complex (Guo, 2008) and with a carboxylate group bridging to the metal in the catena-poly[[bis(benzimidazole) (salicylato-κO)copper(II)]-µ-salicylato-O,O':O''] complex (Li et al., 2005). This coordinated bond is a weak interaction because its distance is comparable to the values reported for copper complexes involving carboxylate and other weak ligands, such as the perchlorate anion (Burčák et al., 2005) and the nitrate ligand (Choi et al., 2006). To the best of our knowledge, the present structure is the first structurally characterized copper(II) complex having both a carboxylate group and a caged phosphate ester as ligands. In this complex, each Cu atom is bonded to four ligands, while each ligand connects with other two Cu atoms. These result in four Cu atoms being interconnected into a 24-membered ring and complete a two-dimensional layer connectivity of the structure parallel to the bc plane (Fig. 2).

Connectivity is further enhanced by hydrogen-bonding interactions. The molecular interaction of the phosphoryl O1 atom and noncoordinated water molecule O8 creates a novel hydrogen-bond pattern. Within the bc plane along the crystallographic c direction (Fig. 2), O7—H7B···O8 and O8—H8B···O1^v hydrogen-bonding interactions (symmetry codes as in Table 2) are responsible for the formation of a 24-membered hydrogen-bonded R₄⁴(24) ring graph set (Bernstein et al.,1995), which links two ligands with two Cu atoms together. Atom H7A is involved in an intermolecular O7—H7A···O5ⁱ hydrogen bond and a six-membered hydrogen-bonded R₁¹(6) ring graph set via strong intermolecular hydrogen bonding (Brown, 1976).

In addition, the noncoordinated O5 atom and atom H8A of water molecule O8 in the present structure engage in other distinct hydrogen-bonding interactions (see Table 2), which, together, are responsible for the conformation of the polymer. The structure consists of alternating layers in the [100] direction. Within the ac plane along the crystallographic a direction (Fig. 3), weak O8—H8A···O5^iv hydrogen-bonding interactions not only link two ligands from neighbouring layers together and build up a 20-membered hydrogen-bonded R₄⁴(20) ring graph set, but also join two coordinated O7 water molecules from neighbouring layers together and form a 12-membered hydrogen-bonded R₆⁴(12) ring graph set.

Related literature

For related literature, see: Battaglia et al. (1987); Bernstein et al. (1995); Brown (1976); Burčák et al. (2005); Choi et al. (2006); Devereux et al. (1999); Guo (2008); Guo & Zang (2007); Li et al. (2005); Morize et al. (2003); Shi et al. (2001); Taylor & Waugh (1977); Wang et al. (2007).

S2. Experimental

A 20 ml aqueous solution of anhydrous sodium carbonate (0.37 g, 3.5 mmol) and 1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-carboxylic acid (0.78 g, 4.0 mmol) was added dropwise into a solution of cupric nitrate (0.49 g, 2 mmol) in 20 ml of distillated water under stirring at room temperature for 20 min. After filtration, slow evaporation of the filtrate over a period of two weeks at room temperature provided the crystals of (I).

S3. Refinement

All water H atoms were found in difference Fourier maps and were fixed during refinement at O—H distances of 0.85 Å, with U_iso(H) = 1.2U_eq(O). The H atoms of CH groups were treated as riding [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 (Bruker, 1997); program(s) used to solve structure: SHELXTL (Version 6.12; Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Version 6.12; Sheldrick, 2008); molecular graphics: SHELXTL (Version 6.12; Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Version 6.12; Sheldrick, 2008).

Figures

	Fig. 1. A view of the structure of (I), showing the numbering scheme and Cu coordination octahedra; displacement ellipsoids are drawn at the 30% probability level. [Symmetry codes: (i) -x + 1, -y + 1, -z + 1; (ii) -x + 1, y + 1/2, -z + 3/2; (iii) x, -y + 1/2, z - 1/2.]
	Fig. 2. The packing, showing the connectivity of a two-dimensional layer and the hydrogen-bonding interactions (as dashed lines) of the structure parallel to bc plane, viewed down the a axis.
	Fig. 3. The packing, viewed down the b axis, showing the hydrogen-bonding interactions as dashed lines in the direction of the ac plane.

Poly[[diaquabis(µ₂-1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-carboxylato)copper(II)] dihydrate]

Crystal data

[Cu(C5H6O6P)2(H2O)2]·2H2O	F(000) = 534
Mr = 521.74	Dx = 1.892 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3022 reflections
a = 8.340 (3) Å	θ = 2.8–26.3°
b = 8.863 (3) Å	µ = 1.45 mm^−1
c = 12.565 (4) Å	T = 294 K
β = 99.575 (5)°	Prism, blue
V = 915.8 (5) Å^3	0.20 × 0.16 × 0.12 mm
Z = 2

Data collection

Bruker SMART CCD area-detector diffractometer	1618 independent reflections
Radiation source: fine-focus sealed tube	1462 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
ϕ and ω scans	θmax = 25.0°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −6→9
Tmin = 0.756, Tmax = 0.842	k = −10→10
4612 measured reflections	l = −14→13

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.027	H-atom parameters constrained
wR(F^2) = 0.075	w = 1/[σ^2(Fo^2) + (0.0379P)^2 + 0.5822P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max = 0.001
1618 reflections	Δρmax = 0.36 e Å^−3
134 parameters	Δρmin = −0.36 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0199 (17)

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
Cu1	0.5000	0.5000	0.5000	0.02466 (16)
P1	0.74022 (8)	0.37178 (7)	1.03132 (4)	0.02875 (19)
C1	0.8863 (3)	0.3594 (3)	0.87055 (17)	0.0315 (6)
H1A	0.8988	0.2645	0.8343	0.038*
H1B	0.9723	0.4269	0.8570	0.038*
C2	0.5874 (3)	0.3187 (3)	0.84313 (17)	0.0309 (5)
H2A	0.4820	0.3651	0.8200	0.037*
H2B	0.5937	0.2285	0.8003	0.037*
C3	0.7021 (3)	0.5742 (3)	0.88720 (18)	0.0331 (6)
H3A	0.7900	0.6430	0.8799	0.040*
H3B	0.6001	0.6224	0.8573	0.040*
C4	0.7218 (3)	0.4282 (3)	0.82625 (16)	0.0235 (5)
C5	0.7106 (3)	0.4700 (3)	0.70708 (18)	0.0254 (5)
O1	0.7486 (2)	0.3444 (2)	1.14563 (13)	0.0426 (5)
O2	0.8993 (2)	0.3337 (2)	0.98678 (12)	0.0364 (4)
O3	0.7042 (3)	0.5394 (2)	1.00047 (13)	0.0382 (5)
O4	0.6059 (2)	0.27860 (19)	0.95780 (12)	0.0323 (4)
O5	0.8369 (2)	0.5021 (2)	0.67386 (14)	0.0426 (5)
O6	0.5689 (2)	0.47317 (19)	0.65413 (12)	0.0292 (4)
O7	0.2969 (2)	0.4141 (2)	0.51900 (12)	0.0351 (4)
H7A	0.2296	0.4327	0.4617	0.042*
H7B	0.2604	0.4274	0.5780	0.042*
O8	0.1691 (2)	0.4371 (3)	0.69488 (15)	0.0498 (5)
H8A	0.0659	0.4371	0.6830	0.060*
H8B	0.1944	0.5032	0.7438	0.060*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0238 (2)	0.0364 (3)	0.0137 (2)	0.00071 (16)	0.00256 (15)	0.00346 (15)
P1	0.0359 (4)	0.0342 (4)	0.0155 (3)	−0.0065 (3)	0.0024 (2)	0.0007 (2)
C1	0.0295 (13)	0.0466 (15)	0.0179 (11)	0.0017 (11)	0.0023 (9)	0.0032 (10)
C2	0.0324 (13)	0.0432 (14)	0.0157 (10)	−0.0080 (11)	0.0004 (9)	0.0018 (10)
C3	0.0493 (15)	0.0317 (13)	0.0183 (11)	0.0007 (12)	0.0057 (10)	0.0020 (10)
C4	0.0245 (11)	0.0301 (12)	0.0152 (10)	−0.0010 (9)	0.0017 (9)	0.0003 (9)
C5	0.0281 (13)	0.0310 (12)	0.0169 (11)	0.0006 (9)	0.0026 (9)	0.0014 (9)
O1	0.0600 (12)	0.0503 (11)	0.0170 (8)	−0.0117 (9)	0.0047 (8)	0.0035 (8)
O2	0.0308 (10)	0.0568 (12)	0.0197 (8)	0.0010 (8)	−0.0015 (7)	0.0086 (8)
O3	0.0641 (13)	0.0333 (10)	0.0185 (8)	0.0003 (9)	0.0109 (8)	−0.0021 (7)
O4	0.0376 (10)	0.0421 (10)	0.0168 (7)	−0.0121 (8)	0.0029 (7)	0.0047 (7)
O5	0.0294 (10)	0.0756 (14)	0.0223 (9)	−0.0096 (9)	0.0029 (8)	0.0129 (8)
O6	0.0265 (9)	0.0447 (10)	0.0159 (8)	0.0020 (7)	0.0022 (7)	0.0038 (7)
O7	0.0312 (9)	0.0552 (12)	0.0189 (8)	−0.0059 (8)	0.0044 (7)	0.0066 (7)
O8	0.0357 (10)	0.0814 (15)	0.0347 (10)	−0.0020 (10)	0.0127 (8)	−0.0136 (10)

Geometric parameters (Å, º)

Cu1—O7^i	1.9080 (17)	C2—C4	1.524 (3)
Cu1—O7	1.9080 (17)	C2—H2A	0.9700
Cu1—O6	1.9409 (16)	C2—H2B	0.9700
Cu1—O6^i	1.9409 (16)	C3—O3	1.453 (3)
Cu1—O4^ii	2.7045 (19)	C3—C4	1.526 (3)
Cu1—O4^iii	2.7045 (19)	C3—H3A	0.9700
P1—O1	1.4469 (17)	C3—H3B	0.9700
P1—O3	1.5521 (19)	C4—C5	1.530 (3)
P1—O2	1.5602 (18)	C5—O5	1.230 (3)
P1—O4	1.5640 (17)	C5—O6	1.256 (3)
C1—O2	1.464 (3)	O7—H7A	0.8518
C1—C4	1.520 (3)	O7—H7B	0.8547
C1—H1A	0.9700	O8—H8A	0.8486
C1—H1B	0.9700	O8—H8B	0.8501
C2—O4	1.467 (3)
O7^i—Cu1—O7	180.0	H2A—C2—H2B	108.3
O7^i—Cu1—O6	92.98 (7)	O3—C3—C4	109.10 (19)
O7—Cu1—O6	87.02 (7)	O3—C3—H3A	109.9
O7^i—Cu1—O6^i	87.02 (7)	C4—C3—H3A	109.9
O7—Cu1—O6^i	92.98 (7)	O3—C3—H3B	109.9
O6—Cu1—O6^i	180.0	C4—C3—H3B	109.9
O6—Cu1—O4^ii	91.81 (6)	H3A—C3—H3B	108.3
O7—Cu1—O4^ii	89.19 (6)	C1—C4—C2	109.5 (2)
O1—P1—O3	112.57 (10)	C1—C4—C3	108.81 (19)
O1—P1—O2	114.60 (11)	C2—C4—C3	109.09 (19)
O3—P1—O2	104.97 (10)	C1—C4—C5	111.09 (18)
O1—P1—O4	114.16 (10)	C2—C4—C5	111.34 (18)
O3—P1—O4	105.54 (11)	C3—C4—C5	106.97 (19)
O2—P1—O4	104.02 (10)	O5—C5—O6	126.8 (2)
O2—C1—C4	109.88 (18)	O5—C5—C4	118.2 (2)
O2—C1—H1A	109.7	O6—C5—C4	115.00 (19)
C4—C1—H1A	109.7	C1—O2—P1	113.45 (14)
O2—C1—H1B	109.7	C3—O3—P1	114.68 (15)
C4—C1—H1B	109.7	C2—O4—P1	113.58 (14)
H1A—C1—H1B	108.2	C5—O6—Cu1	128.87 (15)
O4—C2—C4	109.36 (17)	Cu1—O7—H7A	106.9
O4—C2—H2A	109.8	Cu1—O7—H7B	120.3
C4—C2—H2A	109.8	H7A—O7—H7B	115.2
O4—C2—H2B	109.8	H8A—O8—H8B	104.5
C4—C2—H2B	109.8
O2—C1—C4—C2	−61.9 (2)	O1—P1—O2—C1	178.77 (16)
O2—C1—C4—C3	57.2 (3)	O3—P1—O2—C1	−57.22 (18)
O2—C1—C4—C5	174.70 (19)	O4—P1—O2—C1	53.43 (18)
O4—C2—C4—C1	55.1 (2)	C4—C3—O3—P1	5.1 (3)
O4—C2—C4—C3	−63.8 (2)	O1—P1—O3—C3	177.26 (18)
O4—C2—C4—C5	178.36 (18)	O2—P1—O3—C3	52.0 (2)
O3—C3—C4—C1	−62.6 (2)	O4—P1—O3—C3	−57.6 (2)
O3—C3—C4—C2	56.8 (3)	C4—C2—O4—P1	7.2 (2)
O3—C3—C4—C5	177.35 (19)	O1—P1—O4—C2	174.05 (16)
C1—C4—C5—O5	−28.2 (3)	O3—P1—O4—C2	49.90 (18)
C2—C4—C5—O5	−150.5 (2)	O2—P1—O4—C2	−60.34 (18)
C3—C4—C5—O5	90.5 (3)	O5—C5—O6—Cu1	9.7 (4)
C1—C4—C5—O6	154.5 (2)	C4—C5—O6—Cu1	−173.14 (15)
C2—C4—C5—O6	32.2 (3)	O7^i—Cu1—O6—C5	−19.3 (2)
C3—C4—C5—O6	−86.9 (2)	O7—Cu1—O6—C5	160.7 (2)
C4—C1—O2—P1	4.2 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O7—H7A···O5^i	0.85	1.80	2.602 (2)	157
O7—H7B···O8	0.85	1.77	2.616 (2)	173
O8—H8A···O5^iv	0.85	1.98	2.799 (3)	162
O8—H8B···O1^v	0.85	1.94	2.789 (3)	179

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