Poly[aqua­(μ₂-4,4′-bipyridyl-κ²N:N′)(μ₂-3-phospho­natobenzene­sulfonato-κ²O:O′)copper(II)]

The title polymer, [Cu(C₆H₅O₆PS)(C₁₀H₈N₂)(H₂O)]_n, was synthesized by a hydro­thermal method. The Cu^II ion is five-coordinated by one phospho­nate O atom, one sulfonate O atom, two N atoms of the bipyridyl ligand and one water mol­ecule. The coordination geometry around the metal centre can be described as slightly distorted square-pyramidal. The Cu^II ions are connected by bidentate bridging phospho­nato-benzene­sulfonate ligands, forming one-dimensional helical chains along [010], which are further bridged by bidentate 4,4′-bipyridyl ligands, generating a two-dimensional layered crystal structure. The layered structure features an eight-membered ring including four Cu^II ions, two [O₃S–C₆H₄–PO₃H]²⁻ anions and two 4,4′-bipyridyl ligands. Hydrogen bonds involving aqua ligands, phospho­nate O and sulfonate O atoms are observed between the layers,

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.047
• wR factor = 0.105
• Data-to-parameter ratio = 12.8

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT720_ALERT_4_C Number of Unusual/Non-Standard Label(s) ........          2
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.16 Ratio

Alert level G
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K
PLAT793_ALERT_1_G Check the Absolute Configuration of P1     = ...          S
PLAT794_ALERT_5_G Check Predicted Bond Valency for Cu1         (2)       2.19

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   4 ALERT level G = General alerts; check

   4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

The chemistry of metal phosphonates has been a research field of rapid expansion in recent years, mainly due to their potential applications in the area of catalysis, ion exchange, proton conductivity, intercalation chemistry, photochemistry, and materials chemistry (Clearfield, 1998; Maeda, 2004; Mao, 2007). The strategy of attaching functional groups such as amine, hydroxyl or carboxylate groups to the phosphonic acid can lead to a number of new metal phosphonates with micro-porous or open-framework structures. However, reports on the use of sulfonate group as a functional group to build metal phosphonate open frameworks are almost unknown to date. Recently, our increasing attention has been devoted to the metal coordination chemistry of phenylphosphonic acid ligand bonded to a sulfonate group, which can adopt a variety of coordination modes and form a variety of metal cluster compounds when an ancillary ligand, such as 1,10-phenanthroline or 4,4'-bipyridyl (4,4'-bipy), is also applied (Du et al., 2006a, 2006b; Du, Li, Liu & Mao, 2007; Du, Xu, Li & Mao, 2007). As an expansion of our previous work, we have also obtained a Cu^II sulfonate-phosphonate by applying this synthetic route. Herein, we report its synthesis and crystal structure.

The structure of the title compound features a layered architecture. The asymmetric unit contains one Cu^II ion, one [O₃S—C₆H₄—PO₃H]^2- dianion, one 4,4'-bipy molecule, and one coordinated water molecule. Cu^II ion is five-coordinated with one phosphonate O atom from one [O₃S—C₆H₄—PO₃H]^2- anion, one sulfonate O atom from a symmetry related [O₃S—C₆H₄—PO₃H]^2- anion, two N atoms from two symmetry related 4,4'-bipy ligands, and one water molecule (Fig. 1). The coordination geometry around Cu can be described as a slightly distorted square-pyramid. The square plane is formed by one phosphonate O atom, two N atoms and the water molecule. The apical position is occupied by a sulfonate O atom. The Cu—O [1.964 (3)–2.234 (3) Å] and Cu—N [1.992 (3)–1.994 (3) Å] bond lengths are comparable to those reported for other Cu^II sulfonate/phosphonates complexes (Drumel et al., 1996; Zhong et al., 2005).

The phosphonate group is not completely deprotonated, as required for charge balance. The [O₃S—C₆H₄—PO₃H]^2- ligand is bidentate and bridges two Cu^II ions via one phosphonate O atom and one sulfonate O atom. These bridges result in the formation of a one-dimensional helical chain along [010] (Fig. 2). These helical chains are further connected by bidentate bridging 4,4'-bipy ligands, to form a layered architecture (Fig. 3). The layered structure features an eight-membered ring including four Cu^II ions, two [O₃S—C₆H₄—PO₃H]^2- anions and two 4,4'-bipy ligands. Between the layers, hydrogen bonds are formed, involving phosphonate O atom O2, sulfonate O atom O6 and the water molecule O1W (Fig. 4; Table 2). The O···O contacts range from 2.595 (4) to 2.701 (5) Å. Such a complex hydrogen-bond network is likely to contribute to the overall stability of the crystal structure and prevents guest molecules entering into the interstitial voids between the layers.

Related literature

For related literature about the metal phosphonates chemistry, see: Clearfield (1998); Maeda (2004); Mao (2007). A related chemistry using two bridging ligands has been developed: Du et al. (2006a, 2006b); Du, Li, Liu & Mao (2007); Du, Xu, Li & Mao (2007). For complexes structurally related to the title compound, see: Drumel et al. (1996); Zhong et al. (2005).

S2. Experimental

A mixture of Cu(OAc)₂ (65 mg, 0.36 mmol), 3-phosphono-benzenesulfonic acid (86 mg, 0.36 mmol) and 4,4'-bipy (50 mg, 0.32 mmol) in 10 ml distilled water with an initial pH value of ca. 3.5, was put into a Parr Teflon-lined autoclave (23 ml) and heated at 413 K for 4 days. Blue brick-shaped crystals of the title polymer were collected in a ca. 12% yield based on Cu. Analysis calculated for C₁₆H₁₅O₇N₂P₁S₁Cu₁: C 40.55, H 3.19, N 5.91%; found: C 40.64, H 3.30, N 5.82%.

S3. Refinement

H atoms bonded to C atoms were positioned geometrically and included in the refinement using a riding-model approximation, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(carrier C). Water H atoms were located in a difference map and refined with O—H and H···H distances restrained to 0.85 (1) and 1.39 (1) Å, respectively, and U_iso(H) = 1.5U_eq(O1W). H atom of protonated HPO₃ group was positioned geometrically (O—H = 0.82 Å) and included in the refinement in the riding-model approximation, with U_iso(H) = 1.5U_eq(O2).

Computing details

Data collection: SMART (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2004) and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Bruker, 2004).

Figures

	Fig. 1. A view of the structure of the title compound, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity. Atoms labeled with the suffixes A, B and C are generated by symmetry codes (-x, 1/2 + y, 1/2 - z), (-1 + x, 1/2 - y, -1/2 + z) and (-x, -1/2 + y, 1/2 - z), respectively.
	Fig. 2. A one-dimensional helical chain of Cu^II sulfonate-phosphonate in the title compound. Cu and C atoms are drawn as green and black circles, respectively. The CPO3 and CSO3 groups are shaded in pink and yellow, respectively. H atoms have been omitted for clarity.
	Fig. 3. View of the layer structure of the title compound down [001]. The CuO3N2 polyhedra, CPO3 and CSO3 groups are shaded in green, pink and yellow, respectively. C atoms are drawn as black circles and H atoms have been omitted for clarity.
	Fig. 4. View of the three-dimensional supramolecular structure of the title compound down [010]. The CuO3N2 polyhedra, CPO3 and CSO3 groups are shaded in green, pink and yellow, respectively. C atoms are drawn as black circles and H atoms have been omitted for clarity. Hydrogen bonds are represented by dashed lines.

Poly[aqua(µ₂-4,4'-bipyridyl-κ²N:N')(µ₂-3-πhosphonatobenzenesulfonato-κ²O:O')copper(II)]

Crystal data

[Cu(C6H5O6PS)(C10H8N2)(H2O)]	F(000) = 964
Mr = 473.87	Dx = 1.790 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3426 reflections
a = 10.9824 (2) Å	θ = 2.3–25.7°
b = 11.2924 (3) Å	µ = 1.50 mm^−1
c = 15.1189 (3) Å	T = 293 K
β = 110.331 (1)°	Brick, blue
V = 1758.20 (7) Å^3	0.30 × 0.25 × 0.20 mm
Z = 4

Data collection

Bruker SMART APEXII CCD diffractometer	3351 independent reflections
Radiation source: fine-focus sealed tube	2413 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.052
narrow frame method scans	θmax = 25.7°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −13→12
Tmin = 0.645, Tmax = 0.741	k = −13→10
9468 measured reflections	l = −18→18

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)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.106	H atoms treated by a mixture of independent and constrained refinement
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0375P)^2 + 2.653P] where P = (Fo^2 + 2Fc^2)/3
3351 reflections	(Δ/σ)max < 0.001
261 parameters	Δρmax = 0.82 e Å^−3
0 restraints	Δρmin = −0.52 e Å^−3

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

	x	y	z	Uiso*/Ueq
Cu1	−0.25750 (5)	0.30566 (5)	0.18344 (3)	0.02307 (16)
P1	−0.12583 (11)	0.29056 (10)	0.03360 (7)	0.0269 (3)
S1	0.33196 (10)	0.04087 (10)	0.19138 (8)	0.0301 (3)
N1	−0.0778 (3)	0.2833 (3)	0.2746 (2)	0.0218 (8)
N2	0.5660 (3)	0.2033 (3)	0.5851 (2)	0.0266 (8)
C1	0.0481 (4)	0.2855 (4)	0.0959 (3)	0.0250 (10)
C2	0.1169 (4)	0.1801 (4)	0.1125 (3)	0.0260 (10)
H2A	0.0747	0.1098	0.0877	0.031*
C3	0.2487 (4)	0.1789 (4)	0.1661 (3)	0.0229 (9)
C4	0.3123 (4)	0.2822 (4)	0.2027 (3)	0.0310 (11)
H4A	0.3997	0.2807	0.2400	0.037*
C5	0.2458 (5)	0.3879 (4)	0.1837 (4)	0.0413 (12)
H5A	0.2893	0.4582	0.2070	0.050*
C6	0.1144 (4)	0.3905 (4)	0.1301 (3)	0.0362 (11)
H6A	0.0705	0.4624	0.1170	0.043*
C7	−0.0052 (4)	0.3733 (4)	0.3224 (3)	0.0309 (10)
H7A	−0.0419	0.4484	0.3162	0.037*
C8	0.1217 (4)	0.3587 (4)	0.3804 (3)	0.0332 (11)
H8A	0.1693	0.4237	0.4118	0.040*
C14	0.4058 (4)	0.3201 (4)	0.4718 (3)	0.0390 (12)
H11A	0.3841	0.3917	0.4398	0.047*
C13	0.5286 (4)	0.3021 (5)	0.5364 (3)	0.0416 (12)
H12A	0.5887	0.3631	0.5463	0.050*
C12	0.4804 (4)	0.1147 (4)	0.5676 (3)	0.0319 (11)
H13A	0.5055	0.0437	0.6000	0.038*
C11	0.3556 (4)	0.1246 (4)	0.5027 (3)	0.0305 (10)
H14A	0.2994	0.0603	0.4913	0.037*
C10	0.3146 (4)	0.2293 (4)	0.4552 (3)	0.0243 (10)
C9	0.1792 (4)	0.2478 (4)	0.3922 (3)	0.0234 (9)
C15	0.1028 (4)	0.1546 (4)	0.3436 (3)	0.0258 (10)
H17A	0.1362	0.0781	0.3496	0.031*
C16	−0.0228 (4)	0.1768 (4)	0.2864 (3)	0.0277 (10)
H18A	−0.0725	0.1135	0.2539	0.033*
O1	−0.1830 (3)	0.3664 (3)	0.09164 (19)	0.0294 (7)
O2	−0.1690 (3)	0.1599 (3)	0.0405 (2)	0.0424 (9)
H2B	−0.2074	0.1342	−0.0126	0.064*
O3	−0.1557 (3)	0.3310 (3)	−0.0648 (2)	0.0389 (8)
O4	0.2841 (3)	−0.0182 (3)	0.2586 (2)	0.0396 (8)
O5	0.4693 (3)	0.0663 (3)	0.2314 (3)	0.0547 (10)
O6	0.2960 (4)	−0.0212 (3)	0.1014 (2)	0.0618 (11)
O1W	−0.3168 (3)	0.2021 (4)	0.2649 (2)	0.0486 (10)
H1WB	−0.273 (5)	0.185 (5)	0.324 (4)	0.054 (17)*
H1WA	−0.397 (6)	0.170 (5)	0.251 (4)	0.063 (18)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0101 (2)	0.0324 (3)	0.0205 (3)	−0.0011 (2)	−0.00244 (19)	0.0020 (2)
P1	0.0194 (6)	0.0349 (7)	0.0226 (6)	0.0000 (5)	0.0025 (5)	0.0020 (5)
S1	0.0210 (6)	0.0277 (6)	0.0382 (6)	−0.0018 (4)	0.0059 (5)	0.0023 (5)
N1	0.0148 (17)	0.033 (2)	0.0160 (16)	−0.0025 (15)	0.0030 (14)	0.0025 (15)
N2	0.0147 (18)	0.033 (2)	0.0252 (18)	0.0031 (16)	−0.0021 (15)	−0.0043 (17)
C1	0.022 (2)	0.030 (3)	0.023 (2)	−0.0005 (18)	0.0080 (18)	0.0015 (18)
C2	0.021 (2)	0.025 (2)	0.029 (2)	−0.0062 (18)	0.0053 (18)	0.0022 (19)
C3	0.020 (2)	0.027 (2)	0.021 (2)	−0.0010 (18)	0.0071 (17)	0.0046 (18)
C4	0.015 (2)	0.039 (3)	0.037 (3)	−0.0042 (19)	0.0058 (19)	−0.004 (2)
C5	0.028 (3)	0.029 (3)	0.062 (3)	−0.008 (2)	0.010 (2)	−0.013 (2)
C6	0.027 (3)	0.030 (3)	0.049 (3)	0.002 (2)	0.011 (2)	0.001 (2)
C7	0.020 (2)	0.029 (3)	0.036 (3)	0.0048 (19)	0.0006 (19)	−0.002 (2)
C8	0.017 (2)	0.036 (3)	0.037 (3)	−0.0040 (19)	−0.004 (2)	−0.005 (2)
C14	0.021 (2)	0.036 (3)	0.047 (3)	−0.002 (2)	−0.004 (2)	0.012 (2)
C13	0.019 (2)	0.045 (3)	0.050 (3)	−0.006 (2)	−0.003 (2)	0.004 (3)
C12	0.022 (2)	0.035 (3)	0.029 (2)	0.006 (2)	−0.0031 (19)	0.002 (2)
C11	0.020 (2)	0.033 (3)	0.030 (2)	−0.0035 (19)	−0.0018 (19)	−0.003 (2)
C10	0.014 (2)	0.032 (3)	0.021 (2)	0.0032 (17)	−0.0010 (17)	−0.0025 (18)
C9	0.014 (2)	0.033 (2)	0.020 (2)	0.0025 (18)	0.0029 (17)	0.0034 (19)
C15	0.021 (2)	0.024 (2)	0.024 (2)	0.0040 (17)	−0.0022 (18)	0.0002 (18)
C16	0.022 (2)	0.032 (3)	0.023 (2)	−0.0041 (19)	0.0001 (18)	−0.0043 (19)
O1	0.0221 (16)	0.0367 (18)	0.0262 (16)	0.0022 (13)	0.0045 (13)	0.0057 (13)
O2	0.0341 (19)	0.037 (2)	0.046 (2)	−0.0052 (15)	0.0014 (16)	0.0017 (15)
O3	0.038 (2)	0.053 (2)	0.0217 (16)	−0.0008 (16)	0.0048 (14)	0.0050 (14)
O4	0.0273 (18)	0.043 (2)	0.048 (2)	0.0022 (15)	0.0118 (15)	0.0174 (16)
O5	0.0181 (18)	0.044 (2)	0.095 (3)	−0.0030 (15)	0.0114 (19)	0.012 (2)
O6	0.094 (3)	0.039 (2)	0.042 (2)	0.009 (2)	0.012 (2)	−0.0112 (18)
O1W	0.0240 (19)	0.075 (3)	0.035 (2)	−0.0198 (18)	−0.0045 (16)	0.021 (2)

Geometric parameters (Å, º)

Cu1—O1	1.964 (3)	C5—H5A	0.9300
Cu1—O1W	1.966 (3)	C6—H6A	0.9300
Cu1—N1	1.992 (3)	C7—C8	1.374 (6)
Cu1—N2^i	1.994 (3)	C7—H7A	0.9300
Cu1—O4^ii	2.234 (3)	C8—C9	1.386 (6)
P1—O3	1.480 (3)	C8—H8A	0.9300
P1—O1	1.510 (3)	C14—C13	1.378 (6)
P1—O2	1.564 (3)	C14—C10	1.394 (6)
P1—C1	1.813 (4)	C14—H11A	0.9300
S1—O5	1.446 (3)	C13—H12A	0.9300
S1—O4	1.457 (3)	C12—C11	1.385 (5)
S1—O6	1.458 (4)	C12—H13A	0.9300
S1—C3	1.780 (4)	C11—C10	1.375 (6)
N1—C16	1.329 (5)	C11—H14A	0.9300
N1—C7	1.338 (5)	C10—C9	1.476 (5)
N2—C13	1.321 (6)	C9—C15	1.387 (6)
N2—C12	1.335 (6)	C15—C16	1.372 (5)
N2—Cu1^iii	1.994 (3)	C15—H17A	0.9300
C1—C2	1.385 (6)	C16—H18A	0.9300
C1—C6	1.393 (6)	O2—O6^iv	2.631 (5)
C2—C3	1.392 (6)	O2—H2B	0.8200
C2—H2A	0.9300	O4—Cu1^v	2.234 (3)
C3—C4	1.373 (6)	O1W—O3^vi	2.595 (4)
C4—C5	1.377 (6)	O1W—O5^vii	2.701 (5)
C4—H4A	0.9300	O1W—H1WB	0.87 (5)
C5—C6	1.389 (6)	O1W—H1WA	0.90 (6)
O1—Cu1—O1W	163.85 (15)	C5—C6—H6A	119.9
O1—Cu1—N1	88.69 (12)	C1—C6—H6A	119.9
O1W—Cu1—N1	87.45 (14)	N1—C7—C8	122.4 (4)
O1—Cu1—N2^i	91.53 (13)	N1—C7—H7A	118.8
O1W—Cu1—N2^i	89.36 (14)	C8—C7—H7A	118.8
N1—Cu1—N2^i	169.20 (15)	C7—C8—C9	120.4 (4)
O1—Cu1—O4^ii	96.31 (12)	C7—C8—H8A	119.8
O1W—Cu1—O4^ii	99.62 (15)	C9—C8—H8A	119.8
N1—Cu1—O4^ii	94.27 (12)	C13—C14—C10	119.0 (4)
N2^i—Cu1—O4^ii	96.43 (13)	C13—C14—H11A	120.5
O3—P1—O1	114.69 (18)	C10—C14—H11A	120.5
O3—P1—O2	113.07 (19)	N2—C13—C14	123.9 (4)
O1—P1—O2	107.39 (18)	N2—C13—H12A	118.1
O3—P1—C1	110.94 (18)	C14—C13—H12A	118.1
O1—P1—C1	106.94 (17)	N2—C12—C11	122.3 (4)
O2—P1—C1	102.99 (19)	N2—C12—H13A	118.8
O5—S1—O4	112.1 (2)	C11—C12—H13A	118.8
O5—S1—O6	113.0 (2)	C10—C11—C12	120.2 (4)
O4—S1—O6	112.6 (2)	C10—C11—H14A	119.9
O5—S1—C3	107.4 (2)	C12—C11—H14A	119.9
O4—S1—C3	105.49 (19)	C11—C10—C14	117.0 (4)
O6—S1—C3	105.6 (2)	C11—C10—C9	122.2 (4)
C16—N1—C7	117.2 (3)	C14—C10—C9	120.8 (4)
C16—N1—Cu1	120.2 (3)	C8—C9—C15	116.9 (4)
C7—N1—Cu1	122.6 (3)	C8—C9—C10	121.5 (4)
C13—N2—C12	117.5 (4)	C15—C9—C10	121.5 (4)
C13—N2—Cu1^iii	119.4 (3)	C16—C15—C9	119.0 (4)
C12—N2—Cu1^iii	123.0 (3)	C16—C15—H17A	120.5
C2—C1—C6	118.8 (4)	C9—C15—H17A	120.5
C2—C1—P1	122.1 (3)	N1—C16—C15	124.1 (4)
C6—C1—P1	119.1 (3)	N1—C16—H18A	118.0
C1—C2—C3	120.4 (4)	C15—C16—H18A	118.0
C1—C2—H2A	119.8	P1—O1—Cu1	124.93 (18)
C3—C2—H2A	119.8	P1—O2—O6^iv	126.43 (19)
C4—C3—C2	120.4 (4)	P1—O2—H2B	109.5
C4—C3—S1	120.4 (3)	S1—O4—Cu1^v	144.0 (2)
C2—C3—S1	119.1 (3)	Cu1—O1W—O3^vi	116.55 (17)
C3—C4—C5	119.6 (4)	Cu1—O1W—O5^vii	132.54 (18)
C3—C4—H4A	120.2	O3^vi—O1W—O5^vii	110.66 (16)
C5—C4—H4A	120.2	Cu1—O1W—H1WB	126 (3)
C4—C5—C6	120.5 (4)	O5^vii—O1W—H1WB	101 (3)
C4—C5—H5A	119.7	Cu1—O1W—H1WA	127 (3)
C6—C5—H5A	119.7	O3^vi—O1W—H1WA	117 (3)
C5—C6—C1	120.1 (4)	H1WB—O1W—H1WA	107 (5)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1WB···O3^vi	0.87 (5)	1.74 (6)	2.595 (4)	166 (5)
O1W—H1WA···O5^vii	0.90 (6)	1.82 (6)	2.701 (5)	163 (5)
O2—H2B···O6^iv	0.82	1.86	2.631 (5)	156

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