Crystal structure and Hirshfeld surface analysis of a Schiff base: (Z)-6-[(5-chloro-2-meth­oxy­anilino)methyl­idene]-2-hy­droxy­cyclo­hexa-2,4-dien-1-one

The title compound, C₁₄H₁₂ClNO₃, adopts the keto–enamine tautomeric form. In the crystal, mol­ecules form stacks along the [001] direction. The crystal packing is further stabilized by O—H⋯O and C—H⋯O hydrogen bonds and C—H⋯Cl and C—H⋯π contacts.

Abstract

The title compound, C₁₄H₁₂ClNO₃, is a Schiff base that exists in the keto–enamine tautomeric form and adopts a Z configuration. In the crystal, the dihedral angle between the planes of the benzene rings is 5.34 (15)°. The roughly planar geometry of the mol­ecule is stabilized by a strong intra­molecular N—H⋯O hydrogen bond. In the crystal, pairs of centrosymmetrically related mol­ecules are linked by O—H⋯O hydrogen bonds, forming R ₂ ²(10) rings. Besides this, the mol­ecules form stacks along the [001] direction with C—H⋯π and C—H⋯Cl contacts between the stacks. The inter­molecular inter­actions in the crystal were analysed using Hirshfeld surfaces. The most significant contribution to the crystal packing is from H⋯H contacts (30.8%).

Chemical context  

Schiff bases are widely used as ligands in coordination chemistry (Calligaris & Randaccio, 1987 ▸) and they are also of inter­est in various fields because of their diverse biological activity (Lozier et al., 1975 ▸; Costamagna et al., 1992 ▸). Some Schiff bases derived from salicyl­aldehyde have attracted the inter­est of chemists and physicists because they show thermo­chromism and photochromism in the solid state (Cohen et al., 1964 ▸; Hadjoudis et al., 1987 ▸). The origin of their photo- and thermochromism is related to the reversible intra­molecular proton transfer associated with a change in the electronic structure (Hadjoudis et al., 1987 ▸). The o-hy­droxy Schiff bases obtained by the condensation of o-hy­droxy­aldehydes with aniline have been extensively examined in this context. Such compounds can exist in two tautomeric forms, viz. keto–enamine (N—H⋯O) and phenol–imine (N⋯H—O) (Stewart & Lingafelter, 1959 ▸; Petek et al., 2010 ▸). We report herein the synthesis and the crystal and mol­ecular structures of the title compound, as well as an analysis of its Hirshfeld surfaces.

Structural commentary  

As shown in Fig. 1 ▸., the asymmetric unit of the title compound contains only one mol­ecule, which adopts the keto–enamine tautomeric form: the H atom is located at N1, and the lengths of the N1—C7 and C8—C9 bonds indicate their single-bond character, whereas the O2—C9 and C7—C8 bonds are double (Table 1 ▸). Overall, the bond lengths in the title structure compare well with those of other keto–enamine tautomers known from the literature (see the Database survey section). The whole mol­ecule is almost planar, with a dihedral angle of 5.34 (15)° between the benzene ring planes. The meth­oxy C14 atom deviates from the plane of the C1–C6 benzene ring by 0.038 (4) Å. The torsion angles C1—C6—N1—C7 and N1—C7—C8—C9 are 5.8 (5) and −0.6 (5)°, respectively. The planar mol­ecular conformation is stabilized by the intra­molecular N1—H2⋯O2 hydrogen bond (Table 2 ▸).

Figure 1.

The mol­ecular structure of the title compound with the displacement ellipsoids drawn at the 50% probability level. The intra­molecular N—H⋯O hydrogen bond is shown as a dashed line.

Table 1. Selected bond lengths (Å).

O2—C9	1.292 (4)	C8—C13	1.410 (5)
O3—C10	1.358 (4)	C9—C10	1.426 (4)
N1—C6	1.413 (4)	C10—C11	1.359 (5)
N1—C7	1.302 (4)	C11—C12	1.402 (5)
C7—C8	1.408 (4)	C12—C13	1.349 (4)
C8—C9	1.429 (4)

Table 2. Hydrogen-bond geometry (Å, °).

Cg1 is the centroid of the C1–C6 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C7—H7⋯Cl01i	0.93	2.88	3.737 (3)	154
C14—H14B⋯O3ii	0.96	2.59	3.295 (4)	131
O3—H3⋯O2ii	0.87 (4)	2.00 (4)	2.780 (4)	148 (4)
N1—H2⋯O2	0.97 (4)	1.82 (4)	2.598 (3)	136 (4)
C3—H3A⋯Cg1iii	0.93	2.73	3.463 (3)	136

Symmetry codes: (i) ; (ii) ; (iii) .

Supra­molecular features  

In the crystal, the mol­ecules are connected via O—H⋯O hydrogen bonds into centrosymmetric pairs with an (10) graph-set motif (Table 2 ▸, Fig. 2 ▸). Mol­ecules related by a [001] translation form stacks with an inter­planar distance of 3.420 (3) Å and a shortest inter­centroid separation of 3.6797 (17) Å. The mol­ecular packing is further stabilized by C—H⋯O, C—H⋯Cl and C—H⋯π inter­actions between the mol­ecules of the neighbouring stacks (Fig. 3 ▸). Details of all these contacts are given in Table 2 ▸.

Figure 2.

A view of the crystal packing of the title compound. Dashed lines denote the intra- and inter­molecular hydrogen bonds.

Figure 3.

The packing diagram showing the stacking, C—H⋯π and C—H⋯Cl inter­actions.

Database survey  

A search of the Cambridge Structural database (CSD, version 5.40, update November 2018; Groom et al., 2016 ▸) for the 3-[(E)-(phenyl­imino)­meth­yl]-benzene-1,2-diol fragment revealed eight hits where this fragment adopts the keto–enamine tautomeric form and 21 hits where it exists as the phenol–imine tautomer. Distinctive bond lengths (N1—C7, C7=C8, C8—C9, C9=O2) in the title structure are the same within standard uncertainties as the corresponding bond lengths in the structures of 2-hy­droxy-6-[(2-meth­oxy­phen­yl)amino­methyl­ene]cyclo­hexa-2,4-dienone (FOCCOQ; Şahin et al., 2005 ▸) and 6-[(4-chloro­phenyl­amino)­methyl­ene]-2,3-di­hydroxy­cyclo­hexa-2,4-dien-1-one (CIRTED; Karabıyık et al., 2008 ▸). In the structures of typical phenol–imine tautomers, viz., 3-[(3-bromo­phen­yl)imino­meth­yl]benzene-1,2-diol (CUCZUW; Keleşoğlu et al., 2009b ▸), 3-[(2-bromo­phen­yl)imino­meth­yl]benzene-1,2-diol (XEYSOK; Temel et al., 2007 ▸) and 3-[(4-butyl­phen­yl)imino­meth­yl]benzene-1,2-diol (XOZJUS; Keleşoğlu et al., 2009a ▸), the C9—O2 and C7—C8 bond lengths are distinctly longer, being in the ranges 1.324–1.355 Å and 1.427–1.447 Å, respectively. It is likely that the inter­molecular O—H⋯O hydrogen bond, where the keto O atom acts as an hydrogen-bond acceptor, is an important prerequisite for the tautomeric shift toward the keto–enamine form. In fact, in all eight structures of the keto–enamine tautomers, hydrogen bonds of this type are observed. However, in 16 of 21 structures of phenol–imine tautomers, such hydrogen bonds are also present. This means that there is another unknown reason for the formation of keto–enamine tautomers.

Hirshfeld surface analysis  

The Hirshfeld surface analysis, together with the two-dimensional fingerprint plots, is a powerful tool for the visualization and inter­pretation of inter­molecular contacts in mol­ecular crystals, since it provides a concise description of all inter­molecular inter­actions present in a crystal structure (Spackman & Jayatilaka, 2009 ▸; McKinnon et al., 2007 ▸). All surfaces and 2D fingerprint plots were generated using CrystalExplorer3.1 (Wolff et al., 2012 ▸). The mappings of d_i, d_e, d_norm, shape-index and curvedness for the title structure are shown in Fig. 4 ▸. The Hirshfeld surface of a mol­ecule in the crystal is presented in Fig. 5 ▸, with the prominent hydrogen-bonding inter­actions shown as intense red spots. The two-dimensional fingerprint plots provide information about the percentage contributions of the various inter­atomic contacts. As can be seen from these plots (Fig. 6 ▸), the most important are the H⋯H inter­actions, which contribute 30.8% to the total Hirshfeld surface. Other contributions are from O⋯C/C⋯O (1.2%), O⋯H/H⋯O (17.2%), C⋯C (7.2%), O⋯O/O⋯O (1.0%), Cl⋯H/H⋯Cl (17.8%) and C⋯H/H⋯C (21.8%). Analogous features were observed recently for some compounds of the same class (Kansız et al., 2018 ▸; Özek Yıldırım et al., 2018 ▸). The donor and acceptor centers of the hydrogen bonding are represented as blue (positive) and red (negative) regions on the Hirshfeld surface mapped over the electrostatic potential (Fig. 7 ▸). The electrostatic potential of the Cl01 atom is less negative as compared to those of atoms O2 and O3 of the hy­droxy groups, as indicated by the lighter red color.

Figure 4.

The Hirshfeld surface of the title compound mapped with (a) d_norm, (b) d_i, (c) d_e, (d) curvedness and (e) shape-index.

Figure 5.

The d _norm-mapped Hirshfeld surface showing the inter­molecular inter­actions in the title compound.

Figure 6.

Two-dimensional fingerprint plots with d_norm views of all, the H⋯H, O⋯H/H⋯O, C⋯H/H⋯C and N⋯H/H⋯N contacts in the title compound.

Figure 7.

The view of the Hirshfeld surface of the title compound plotted over the electrostatic potential energy.

Synthesis and crystallization  

The title compound was prepared by mixing solutions of 2,3-di­hydroxy­benzaldehyde (34.5 mg, 0.25 mmol) and 5-chloro-2-meth­oxy­aniline (39.4 mg, 0.25 mmol), both in 15 mL of ethanol, with subsequent stirring for 5 h under reflux. Single crystals were obtained by slow evaporation of an ethanol solution (yield 65%; m.p. 442–444 K).

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. The C-bound H atoms were geometrically positioned with C—H distances of 0.93–0.96 Å and refined as riding, with U _iso(H) = 1.2U _eq(C) or U _iso(H) = 1.5U _eq(C) for methyl H atoms. The O- and N-bound H atoms were located in a difference map and freely refined.

Table 3. Experimental details.

Crystal data
Chemical formula	C14H12ClNO3
M r	277.70
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	296
a, b, c (Å)	14.7251 (9), 14.4444 (9), 6.1698 (4)
β (°)	98.241 (5)
V (Å3)	1298.74 (14)
Z	4
Radiation type	Mo Kα
μ (mm−1)	0.30
Crystal size (mm)	0.23 × 0.16 × 0.09
Data collection
Diffractometer	Stoe IPDS 2
Absorption correction	Integration (X-RED32; Stoe & Cie, 2002 ▸)
T min, T max	0.948, 0.979
No. of measured, independent and observed [I > 2σ(I)] reflections	13658, 2491, 1120
R int	0.115
(sin θ/λ)max (Å−1)	0.617
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.057, 0.100, 0.90
No. of reflections	2491
No. of parameters	181
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	0.16, −0.24

Computer programs: X-AREA and X-RED (Stoe & Cie, 2002 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL2014 (Sheldrick, 2015b ▸), ORTEP-3 for Windows and WinGX (Farrugia, 2012 ▸) and PLATON (Spek, 2009 ▸).

Supplementary Material

CCDC reference: 1886956

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

C14H12ClNO3	F(000) = 576
Mr = 277.70	Dx = 1.420 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 14.7251 (9) Å	Cell parameters from 8086 reflections
b = 14.4444 (9) Å	θ = 1.4–27.1°
c = 6.1698 (4) Å	µ = 0.30 mm−1
β = 98.241 (5)°	T = 296 K
V = 1298.74 (14) Å3	Irregular specimen, red
Z = 4	0.23 × 0.16 × 0.09 mm

Data collection

Stoe IPDS 2 diffractometer	2491 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	1120 reflections with I > 2σ(I)
Detector resolution: 6.67 pixels mm-1	Rint = 0.115
rotation method scans	θmax = 26.0°, θmin = 2.0°
Absorption correction: integration (X-RED32; Stoe & Cie, 2002)	h = −18→18
Tmin = 0.948, Tmax = 0.979	k = −17→17
13658 measured reflections	l = −7→7

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.057	Hydrogen site location: mixed
wR(F2) = 0.100	H atoms treated by a mixture of independent and constrained refinement
S = 0.90	w = 1/[σ2(Fo2) + (0.0293P)2] where P = (Fo2 + 2Fc2)/3
2491 reflections	(Δ/σ)max < 0.001
181 parameters	Δρmax = 0.16 e Å−3
0 restraints	Δρmin = −0.24 e Å−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

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

	x	y	z	Uiso*/Ueq
Cl01	0.49115 (8)	0.36774 (9)	−0.2476 (2)	0.1172 (6)
O1	0.11503 (15)	0.37573 (16)	−0.0556 (4)	0.0611 (6)
O2	0.10563 (15)	0.50349 (16)	0.4247 (4)	0.0601 (7)
O3	0.0461 (2)	0.5981 (2)	0.7618 (4)	0.0782 (9)
N1	0.2392 (2)	0.46609 (18)	0.2056 (5)	0.0497 (8)
C1	0.3568 (2)	0.4173 (2)	−0.0160 (6)	0.0608 (10)
H1A	0.4026	0.4475	0.0774	0.073*
C2	0.3782 (2)	0.3706 (2)	−0.1958 (6)	0.0606 (10)
C3	0.3124 (2)	0.3262 (2)	−0.3362 (6)	0.0583 (10)
H3A	0.3277	0.2961	−0.4592	0.070*
C4	0.2231 (2)	0.3264 (2)	−0.2937 (6)	0.0540 (9)
H4	0.1780	0.2953	−0.3869	0.065*
C5	0.2002 (2)	0.3725 (2)	−0.1142 (5)	0.0459 (8)
C6	0.2675 (2)	0.4193 (2)	0.0256 (5)	0.0454 (8)
C7	0.2902 (2)	0.5189 (2)	0.3445 (6)	0.0546 (9)
H7	0.3515	0.5266	0.3277	0.066*
C8	0.2572 (2)	0.5648 (2)	0.5188 (5)	0.0495 (9)
C9	0.1632 (2)	0.5551 (2)	0.5481 (5)	0.0483 (9)
C10	0.1348 (3)	0.6045 (2)	0.7269 (6)	0.0577 (9)
C11	0.1941 (3)	0.6591 (2)	0.8593 (6)	0.0669 (11)
H11	0.1733	0.6919	0.9723	0.080*
C12	0.2862 (3)	0.6667 (2)	0.8274 (6)	0.0680 (11)
H12	0.3262	0.7037	0.9205	0.082*
C13	0.3171 (3)	0.6206 (2)	0.6623 (6)	0.0619 (10)
H13	0.3784	0.6257	0.6430	0.074*
C14	0.0424 (2)	0.3301 (3)	−0.1933 (6)	0.0698 (11)
H00F	0.0378	0.3546	−0.3392	0.105*
H14B	−0.0144	0.3402	−0.1375	0.105*
H14C	0.0548	0.2649	−0.1959	0.105*
H3	0.016 (3)	0.555 (3)	0.685 (8)	0.104 (18)*
H2	0.175 (3)	0.461 (3)	0.226 (8)	0.130 (17)*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Cl01	0.0754 (8)	0.1458 (11)	0.1426 (12)	−0.0326 (7)	0.0573 (8)	−0.0628 (9)
O1	0.0504 (14)	0.0746 (16)	0.0578 (16)	−0.0021 (13)	0.0062 (12)	−0.0180 (13)
O2	0.0581 (15)	0.0667 (16)	0.0544 (17)	−0.0025 (13)	0.0051 (13)	−0.0148 (12)
O3	0.077 (2)	0.087 (2)	0.074 (2)	0.0025 (16)	0.0234 (17)	−0.0277 (16)
N1	0.0535 (19)	0.0501 (19)	0.047 (2)	−0.0040 (14)	0.0114 (17)	−0.0032 (14)
C1	0.063 (3)	0.060 (2)	0.061 (3)	−0.0134 (17)	0.014 (2)	−0.0135 (18)
C2	0.061 (2)	0.057 (2)	0.068 (3)	−0.011 (2)	0.025 (2)	−0.010 (2)
C3	0.073 (3)	0.050 (2)	0.056 (3)	0.001 (2)	0.019 (2)	−0.0059 (19)
C4	0.060 (3)	0.048 (2)	0.053 (2)	−0.0013 (17)	0.005 (2)	−0.0097 (17)
C5	0.051 (2)	0.043 (2)	0.044 (2)	0.0025 (17)	0.0085 (18)	0.0000 (17)
C6	0.055 (2)	0.041 (2)	0.041 (2)	−0.0018 (16)	0.0093 (19)	−0.0023 (15)
C7	0.059 (2)	0.052 (2)	0.053 (2)	−0.0125 (18)	0.010 (2)	−0.0031 (19)
C8	0.063 (2)	0.042 (2)	0.043 (2)	−0.0008 (16)	0.0073 (19)	−0.0044 (16)
C9	0.067 (2)	0.0347 (19)	0.042 (2)	0.0064 (17)	0.004 (2)	−0.0009 (16)
C10	0.072 (3)	0.050 (2)	0.052 (2)	0.007 (2)	0.011 (2)	−0.0005 (19)
C11	0.093 (3)	0.056 (3)	0.053 (3)	0.007 (2)	0.015 (2)	−0.0073 (19)
C12	0.088 (3)	0.058 (2)	0.055 (3)	−0.011 (2)	0.000 (2)	−0.015 (2)
C13	0.074 (2)	0.054 (2)	0.057 (3)	−0.010 (2)	0.008 (2)	−0.0087 (19)
C14	0.053 (2)	0.095 (3)	0.060 (3)	−0.002 (2)	0.002 (2)	−0.010 (2)

Geometric parameters (Å, º)

Cl01—C2	1.739 (3)	C4—H4	0.9300
O1—C5	1.354 (3)	C5—C6	1.393 (4)
O1—C14	1.429 (4)	C7—C8	1.408 (4)
O2—C9	1.292 (4)	C7—H7	0.9300
O3—C10	1.358 (4)	C8—C9	1.429 (4)
O3—H3	0.87 (4)	C8—C13	1.410 (5)
N1—C6	1.413 (4)	C9—C10	1.426 (4)
N1—C7	1.302 (4)	C10—C11	1.359 (5)
N1—H2	0.97 (4)	C11—C12	1.402 (5)
C1—C2	1.372 (4)	C11—H11	0.9300
C1—C6	1.376 (4)	C12—C13	1.349 (4)
C1—H1A	0.9300	C12—H12	0.9300
C2—C3	1.363 (5)	C13—H13	0.9300
C3—C4	1.379 (4)	C14—H00F	0.9600
C3—H3A	0.9300	C14—H14B	0.9600
C4—C5	1.375 (4)	C14—H14C	0.9600
C5—O1—C14	117.9 (3)	C8—C7—H7	118.3
C10—O3—H3	113 (3)	C7—C8—C13	119.7 (3)
C7—N1—C6	126.1 (3)	C7—C8—C9	119.8 (3)
C7—N1—H2	116 (3)	C13—C8—C9	120.4 (3)
C6—N1—H2	118 (3)	O2—C9—C10	120.3 (3)
C2—C1—C6	119.8 (3)	O2—C9—C8	123.2 (3)
C2—C1—H1A	120.1	C10—C9—C8	116.5 (3)
C6—C1—H1A	120.1	O3—C10—C11	119.6 (3)
C3—C2—C1	121.4 (3)	O3—C10—C9	118.9 (4)
C3—C2—Cl01	118.9 (3)	C11—C10—C9	121.4 (3)
C1—C2—Cl01	119.7 (3)	C10—C11—C12	120.8 (3)
C2—C3—C4	119.2 (3)	C10—C11—H11	119.6
C2—C3—H3A	120.4	C12—C11—H11	119.6
C4—C3—H3A	120.4	C13—C12—C11	120.3 (4)
C5—C4—C3	120.4 (3)	C13—C12—H12	119.8
C5—C4—H4	119.8	C11—C12—H12	119.8
C3—C4—H4	119.8	C12—C13—C8	120.5 (3)
O1—C5—C4	125.1 (3)	C12—C13—H13	119.7
O1—C5—C6	115.0 (3)	C8—C13—H13	119.7
C4—C5—C6	119.9 (3)	O1—C14—H00F	109.5
C1—C6—C5	119.3 (3)	O1—C14—H14B	109.5
C1—C6—N1	123.7 (3)	H00F—C14—H14B	109.5
C5—C6—N1	117.0 (3)	O1—C14—H14C	109.5
N1—C7—C8	123.3 (3)	H00F—C14—H14C	109.5
N1—C7—H7	118.3	H14B—C14—H14C	109.5
C6—C1—C2—C3	0.3 (6)	C6—N1—C7—C8	179.0 (3)
C6—C1—C2—Cl01	−179.7 (3)	N1—C7—C8—C13	179.9 (3)
C1—C2—C3—C4	−1.5 (6)	N1—C7—C8—C9	−0.6 (5)
Cl01—C2—C3—C4	178.6 (3)	C7—C8—C9—O2	2.0 (5)
C2—C3—C4—C5	1.3 (5)	C13—C8—C9—O2	−178.5 (3)
C14—O1—C5—C4	−1.8 (5)	C7—C8—C9—C10	−179.3 (3)
C14—O1—C5—C6	179.2 (3)	C13—C8—C9—C10	0.1 (5)
C3—C4—C5—O1	−178.8 (3)	O2—C9—C10—O3	−1.5 (5)
C3—C4—C5—C6	0.1 (5)	C8—C9—C10—O3	179.8 (3)
C2—C1—C6—C5	1.0 (5)	O2—C9—C10—C11	179.8 (3)
C2—C1—C6—N1	−179.5 (3)	C8—C9—C10—C11	1.2 (5)
O1—C5—C6—C1	177.8 (3)	O3—C10—C11—C12	179.7 (3)
C4—C5—C6—C1	−1.2 (5)	C9—C10—C11—C12	−1.7 (6)
O1—C5—C6—N1	−1.7 (4)	C10—C11—C12—C13	0.9 (6)
C4—C5—C6—N1	179.3 (3)	C11—C12—C13—C8	0.4 (6)
C7—N1—C6—C1	5.8 (5)	C7—C8—C13—C12	178.6 (3)
C7—N1—C6—C5	−174.7 (3)	C9—C8—C13—C12	−0.9 (5)

Hydrogen-bond geometry (Å, º)

Cg1 is the centroid of the C1–C6 ring.

D—H···A	D—H	H···A	D···A	D—H···A
C7—H7···Cl01i	0.93	2.88	3.737 (3)	154
C14—H14B···O3ii	0.96	2.59	3.295 (4)	131
O3—H3···O2ii	0.87 (4)	2.00 (4)	2.780 (4)	148 (4)
N1—H2···O2	0.97 (4)	1.82 (4)	2.598 (3)	136 (4)
C3—H3A···Cg1iii	0.93	2.73	3.463 (3)	136

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