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Acta Cryst. (2009). E65, o722-o723    [ doi:10.1107/S1600536809008137 ]

A second tricilinc polymorph of 6,6'-diethoxy-2,2'-[propane-1,2-diylbis(nitrilomethylidyne)]diphenol

H.-K. Fun, R. Kia, H. Kargar and A. Jamshidvand

Abstract top

The title Schiff base compound, C21H26N2O4, is a second triclinic polymorph of a previously reported room-temperature structure [Jia (2009). Acta Cryst. E65, o646]. Strong intramolecular O-H...N hydrogen bonds generate S(6) ring motifs. Intermolecular C-H...O interactions link neighbouring molecules into dimers with an R22(16) ring motif. The mean planes of the two benzene rings are almost perpendicular to each other, making a dihedral angle of 88.24 (5)°. An interesting feature of the crystal structure is the intermolecular short C...O [3.1878 (13) Å] contact which is shorter than the sum of the van der Waals radii of the relevant atoms. The crystal structure is further stabilized by intermolecular C-H...[pi] and [pi]-[pi] interactions [centroid-centroid distance = 3.7414 (6) Å]. The structure has a stereogenic centre but the space group is centrosymmetric, so the molecule exists as a racemate.

Comment top

Schiff bases are one of the most prevalent mixed-donor ligands in the field of coordination chemistry. They play an important role in the development of coordination chemistry related to catalysis and enzymatic reactions, magnetism, and supramolecular architectures (Calligaris & Randaccio, 1987). Structures of Schiff bases derived from substituted benzaldehydes and closely related to the title compound have been reported earlier (Li et al., 2005; Bomfim et al., 2005; Glidewell et al., 2006; Sun et al., 2004; Fun et al., 2008).

The molecule of the title compound (Fig. 1), is a potentially tetradentate Schiff base ligand. The bond lengths (Allen et al., 1987) and angles are comparable to the earlier room-temperature polymorph which was published previously (Jia, 2009). Strong intramolecular O—H···N hydrogen bonds generate S(6) ring motifs (Bernstein et al., 1995). Intermolecular C—H···O interactions link neighbouring molecules into dimers with a R22(16) ring motif (Bernstein et al., 1995). The mean planes of the two benzene rings are almost perpendicular to each other making a dihedral angle of 88.24 (5)°. The interesting feature of the crystal structure is the short C18···O2 [3.1878 (13) Å, symmetry code: 1 - x, 1 - y, 1 - z] contact which is shorter than the sum of the van der Waals radii of the relevant atoms. The crystal structure, is further stabilizd by intermolecular C—H···π and π-π interactions [centroid to centroid distance of 3.7414 (6) Å]. The structure has a stereogenic centre but the space group is centrosymmetric, so the molecule exists as racemate.

Related literature top

For hydrogen-bond motifs, see: Bernstein et al. (1995). For information on Schiff base ligands, complexes and their applications, see: Calligaris & Randaccio (1987). For the other polymorph, see: Jia, (2009). For related structures, see: Li et al. (2005); Bomfim et al. (2005); Glidewell et al. (2005, 2006); Sun et al. (2004); Fun et al. (2008). For bond-length data, see: Allen et al. (1987). For stability of the temperature controller used for data collection, see: Cosier & Glazer (1986). Cg1 and Cg2 are the centroids of the C1–C6 and C11–C16 benzene rings, respectively.

Experimental top

The synthetic method has been described earlier (Fun et al., 2008), except that 3-ethoxy salicylaldehyde and 2-methyl-2,3-propanediamine were used as starting materials. Single crystals suitable for X-ray diffraction were obtained by evaporation of an ethanol solution at room temperature.

Refinement top

H atoms of the hydroxy groups were positioned by a freely rotating O—H bond and constrained with a fixed distance of 0.84 Å. The rest of the hydrogen atoms were positioned geometrically and refined using a riding model with C—H = 0.95–1.00 Å and Uiso(H) = 1.2 or 1.5 Ueq(C). A rotating-group model was applied for the methyl groups.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound with atom labels and 50% probability ellipsoids for non-H atoms. Dashed lines indicate intramolecular O—H···N hydrogen bonds.
[Figure 2] Fig. 2. The crystal structure of the title compound, viewed down the b-axis, showing dimer formation by R22(16) ring motif.
6,6'-diethoxy-2,2'-[propane-1,2-diylbis(nitrilomethylidyne)]diphenol top
Crystal data top
C21H26N2O4Z = 2
Mr = 370.44F(000) = 396
Triclinic, P1Dx = 1.277 Mg m−3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 8.9729 (2) ÅCell parameters from 9912 reflections
b = 10.7008 (4) Åθ = 2.5–33.9°
c = 11.3633 (2) ŵ = 0.09 mm−1
α = 107.432 (1)°T = 100 K
β = 108.487 (1)°Block, yellow
γ = 95.979 (1)°0.56 × 0.27 × 0.25 mm
V = 963.03 (5) Å3
Data collection top
Bruker SMART APEXII CCD area-detector
diffractometer		5527 independent reflections
Radiation source: fine-focus sealed tube4721 reflections with I > 2σ(I)
graphiteRint = 0.026
φ and ω scansθmax = 30.0°, θmin = 2.0°
Absorption correction: multi-scan
(SADABS; Bruker, 2005)		h = −12→12
Tmin = 0.952, Tmax = 0.978k = −15→15
19581 measured reflectionsl = −15→15
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.045Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.136H-atom parameters constrained
S = 1.05 w = 1/[σ2(Fo2) + (0.0795P)2 + 0.2658P]
where P = (Fo2 + 2Fc2)/3
5527 reflections(Δ/σ)max = 0.001
249 parametersΔρmax = 0.53 e Å−3
0 restraintsΔρmin = −0.23 e Å−3
Crystal data top
C21H26N2O4γ = 95.979 (1)°
Mr = 370.44V = 963.03 (5) Å3
Triclinic, P1Z = 2
a = 8.9729 (2) ÅMo Kα radiation
b = 10.7008 (4) ŵ = 0.09 mm−1
c = 11.3633 (2) ÅT = 100 K
α = 107.432 (1)°0.56 × 0.27 × 0.25 mm
β = 108.487 (1)°
Data collection top
Bruker SMART APEXII CCD area-detector
diffractometer		5527 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2005)		4721 reflections with I > 2σ(I)
Tmin = 0.952, Tmax = 0.978Rint = 0.026
19581 measured reflectionsθmax = 30.0°
Refinement top
R[F2 > 2σ(F2)] = 0.045H-atom parameters constrained
wR(F2) = 0.136Δρmax = 0.53 e Å−3
S = 1.05Δρmin = −0.23 e Å−3
5527 reflectionsAbsolute structure: ?
249 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.

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.

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 > 2sigma(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 (Å2) top
xyzUiso*/Ueq
O10.45973 (9)0.68396 (7)1.04387 (8)0.02067 (16)
H10.39960.60740.99890.031*
O20.23678 (10)0.61221 (7)0.56112 (7)0.02165 (17)
H20.21990.56170.60180.032*
O30.60593 (9)0.93704 (7)1.19014 (7)0.02040 (16)
O40.30071 (10)0.74269 (7)0.41348 (7)0.02157 (17)
N10.20357 (10)0.51029 (9)0.87252 (9)0.01932 (18)
N20.22170 (11)0.39204 (9)0.61688 (9)0.01981 (18)
C10.37342 (12)0.77863 (10)1.03131 (9)0.01695 (19)
C20.45003 (12)0.91483 (10)1.10727 (10)0.01745 (19)
C30.36454 (13)1.01381 (10)1.09335 (10)0.0202 (2)
H3A0.41651.10551.14210.024*
C40.20267 (13)0.98033 (11)1.00838 (11)0.0230 (2)
H4A0.14561.04921.00030.028*
C50.12610 (12)0.84751 (11)0.93638 (11)0.0218 (2)
H5A0.01580.82490.88010.026*
C60.21104 (12)0.74568 (10)0.94623 (10)0.01782 (19)
C70.13033 (12)0.60568 (10)0.86605 (10)0.0193 (2)
H7A0.02110.58520.80790.023*
C80.11726 (12)0.37212 (10)0.78846 (10)0.0197 (2)
H8A0.00550.37120.73250.024*
C90.20882 (13)0.31383 (10)0.70025 (10)0.0209 (2)
H9A0.31820.31270.75640.025*
H9B0.15250.22000.64320.025*
C100.25539 (12)0.33633 (10)0.51501 (10)0.0195 (2)
H10A0.26240.24480.49360.023*
C110.28343 (12)0.40753 (10)0.43059 (10)0.01798 (19)
C120.32606 (13)0.34087 (11)0.32285 (10)0.0224 (2)
H12A0.33190.24920.30410.027*
C130.35938 (13)0.40746 (11)0.24449 (10)0.0236 (2)
H13A0.38810.36170.17210.028*
C140.35108 (12)0.54260 (11)0.27131 (10)0.0211 (2)
H14A0.37320.58800.21650.025*
C150.31054 (12)0.61053 (10)0.37785 (10)0.01799 (19)
C160.27562 (11)0.54322 (10)0.45865 (9)0.01716 (19)
C170.11095 (14)0.29050 (11)0.87711 (11)0.0251 (2)
H17A0.05830.33210.93760.038*
H17B0.22070.28840.92860.038*
H17C0.04970.19870.82200.038*
C180.68435 (13)1.07531 (10)1.27022 (10)0.0207 (2)
H18A0.62841.11291.33060.025*
H18B0.68181.12951.21290.025*
C190.85652 (13)1.07880 (11)1.34933 (11)0.0250 (2)
H19A0.91171.17141.40710.038*
H19B0.91191.04461.28870.038*
H19C0.85761.02261.40360.038*
C200.32265 (13)0.81235 (11)0.32824 (11)0.0228 (2)
H20A0.24820.76260.23570.027*
H20B0.43450.82130.33050.027*
C210.28754 (16)0.94927 (12)0.37877 (13)0.0284 (2)
H21A0.30391.00110.32420.043*
H21B0.36020.99650.47100.043*
H21C0.17570.93900.37390.043*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0213 (3)0.0161 (3)0.0204 (4)0.0042 (3)0.0039 (3)0.0045 (3)
O20.0338 (4)0.0181 (3)0.0173 (3)0.0072 (3)0.0154 (3)0.0053 (3)
O30.0215 (3)0.0164 (3)0.0181 (3)0.0023 (3)0.0042 (3)0.0027 (3)
O40.0309 (4)0.0184 (3)0.0173 (3)0.0041 (3)0.0113 (3)0.0066 (3)
N10.0206 (4)0.0199 (4)0.0153 (4)0.0007 (3)0.0065 (3)0.0044 (3)
N20.0234 (4)0.0187 (4)0.0165 (4)0.0036 (3)0.0070 (3)0.0059 (3)
C10.0202 (4)0.0180 (4)0.0139 (4)0.0042 (3)0.0082 (3)0.0053 (3)
C20.0204 (4)0.0183 (4)0.0145 (4)0.0037 (3)0.0085 (3)0.0049 (3)
C30.0257 (5)0.0191 (4)0.0187 (5)0.0064 (4)0.0124 (4)0.0055 (4)
C40.0251 (5)0.0247 (5)0.0240 (5)0.0110 (4)0.0132 (4)0.0090 (4)
C50.0199 (4)0.0271 (5)0.0209 (5)0.0080 (4)0.0096 (4)0.0087 (4)
C60.0191 (4)0.0202 (4)0.0153 (4)0.0039 (3)0.0084 (3)0.0057 (3)
C70.0190 (4)0.0231 (5)0.0150 (4)0.0018 (3)0.0070 (3)0.0058 (4)
C80.0195 (4)0.0194 (4)0.0169 (4)0.0010 (3)0.0047 (3)0.0050 (4)
C90.0264 (5)0.0188 (4)0.0178 (4)0.0055 (4)0.0078 (4)0.0070 (4)
C100.0226 (4)0.0166 (4)0.0164 (4)0.0043 (3)0.0055 (4)0.0038 (3)
C110.0194 (4)0.0181 (4)0.0140 (4)0.0041 (3)0.0052 (3)0.0033 (3)
C120.0276 (5)0.0212 (5)0.0169 (4)0.0079 (4)0.0088 (4)0.0033 (4)
C130.0272 (5)0.0277 (5)0.0155 (4)0.0083 (4)0.0103 (4)0.0037 (4)
C140.0218 (5)0.0262 (5)0.0152 (4)0.0041 (4)0.0075 (4)0.0066 (4)
C150.0184 (4)0.0188 (4)0.0146 (4)0.0026 (3)0.0052 (3)0.0043 (3)
C160.0185 (4)0.0185 (4)0.0125 (4)0.0036 (3)0.0059 (3)0.0029 (3)
C170.0282 (5)0.0245 (5)0.0222 (5)0.0000 (4)0.0093 (4)0.0096 (4)
C180.0247 (5)0.0160 (4)0.0181 (4)0.0019 (3)0.0081 (4)0.0021 (3)
C190.0253 (5)0.0213 (5)0.0222 (5)0.0020 (4)0.0049 (4)0.0042 (4)
C200.0276 (5)0.0240 (5)0.0205 (5)0.0041 (4)0.0116 (4)0.0105 (4)
C210.0377 (6)0.0249 (5)0.0295 (6)0.0082 (4)0.0168 (5)0.0140 (4)
Geometric parameters (Å, °) top
O1—C11.3514 (12)C9—H9B0.9900
O1—H10.8400C10—C111.4542 (15)
O2—C161.3484 (11)C10—H10A0.9500
O2—H20.8400C11—C161.4046 (13)
O3—C21.3643 (12)C11—C121.4087 (14)
O3—C181.4432 (12)C12—C131.3765 (16)
O4—C151.3701 (12)C12—H12A0.9500
O4—C201.4338 (13)C13—C141.4008 (15)
N1—C71.2780 (14)C13—H13A0.9500
N1—C81.4644 (13)C14—C151.3905 (14)
N2—C101.2777 (13)C14—H14A0.9500
N2—C91.4614 (14)C15—C161.4112 (14)
C1—C61.4062 (13)C17—H17A0.9800
C1—C21.4153 (13)C17—H17B0.9800
C2—C31.3885 (14)C17—H17C0.9800
C3—C41.4018 (15)C18—C191.5110 (15)
C3—H3A0.9500C18—H18A0.9900
C4—C51.3802 (15)C18—H18B0.9900
C4—H4A0.9500C19—H19A0.9800
C5—C61.4046 (14)C19—H19B0.9800
C5—H5A0.9500C19—H19C0.9800
C6—C71.4617 (14)C20—C211.5107 (16)
C7—H7A0.9500C20—H20A0.9900
C8—C91.5242 (15)C20—H20B0.9900
C8—C171.5277 (15)C21—H21A0.9800
C8—H8A1.0000C21—H21B0.9800
C9—H9A0.9900C21—H21C0.9800
C1—O1—H1109.5C13—C12—C11120.54 (9)
C16—O2—H2109.5C13—C12—H12A119.7
C2—O3—C18116.03 (8)C11—C12—H12A119.7
C15—O4—C20116.95 (8)C12—C13—C14120.13 (9)
C7—N1—C8118.97 (9)C12—C13—H13A119.9
C10—N2—C9117.69 (9)C14—C13—H13A119.9
O1—C1—C6122.09 (9)C15—C14—C13120.23 (10)
O1—C1—C2118.39 (8)C15—C14—H14A119.9
C6—C1—C2119.52 (9)C13—C14—H14A119.9
O3—C2—C3125.27 (9)O4—C15—C14124.90 (9)
O3—C2—C1115.48 (9)O4—C15—C16114.95 (8)
C3—C2—C1119.25 (9)C14—C15—C16120.15 (9)
C2—C3—C4120.94 (9)O2—C16—C11122.22 (9)
C2—C3—H3A119.5O2—C16—C15118.56 (9)
C4—C3—H3A119.5C11—C16—C15119.22 (9)
C5—C4—C3120.10 (10)C8—C17—H17A109.5
C5—C4—H4A119.9C8—C17—H17B109.5
C3—C4—H4A119.9H17A—C17—H17B109.5
C4—C5—C6120.06 (10)C8—C17—H17C109.5
C4—C5—H5A120.0H17A—C17—H17C109.5
C6—C5—H5A120.0H17B—C17—H17C109.5
C5—C6—C1120.10 (9)O3—C18—C19107.74 (8)
C5—C6—C7119.59 (9)O3—C18—H18A110.2
C1—C6—C7120.30 (9)C19—C18—H18A110.2
N1—C7—C6121.39 (9)O3—C18—H18B110.2
N1—C7—H7A119.3C19—C18—H18B110.2
C6—C7—H7A119.3H18A—C18—H18B108.5
N1—C8—C9108.28 (8)C18—C19—H19A109.5
N1—C8—C17108.78 (8)C18—C19—H19B109.5
C9—C8—C17109.96 (9)H19A—C19—H19B109.5
N1—C8—H8A109.9C18—C19—H19C109.5
C9—C8—H8A109.9H19A—C19—H19C109.5
C17—C8—H8A109.9H19B—C19—H19C109.5
N2—C9—C8111.50 (8)O4—C20—C21106.98 (9)
N2—C9—H9A109.3O4—C20—H20A110.3
C8—C9—H9A109.3C21—C20—H20A110.3
N2—C9—H9B109.3O4—C20—H20B110.3
C8—C9—H9B109.3C21—C20—H20B110.3
H9A—C9—H9B108.0H20A—C20—H20B108.6
N2—C10—C11122.60 (9)C20—C21—H21A109.5
N2—C10—H10A118.7C20—C21—H21B109.5
C11—C10—H10A118.7H21A—C21—H21B109.5
C16—C11—C12119.72 (10)C20—C21—H21C109.5
C16—C11—C10120.87 (9)H21A—C21—H21C109.5
C12—C11—C10119.35 (9)H21B—C21—H21C109.5
C18—O3—C2—C31.11 (15)C17—C8—C9—N2−178.20 (8)
C18—O3—C2—C1−178.73 (8)C9—N2—C10—C11−175.17 (9)
O1—C1—C2—O3−1.69 (13)N2—C10—C11—C160.46 (15)
C6—C1—C2—O3177.98 (9)N2—C10—C11—C12177.59 (10)
O1—C1—C2—C3178.45 (9)C16—C11—C12—C13−0.30 (15)
C6—C1—C2—C3−1.88 (15)C10—C11—C12—C13−177.47 (9)
O3—C2—C3—C4−177.92 (10)C11—C12—C13—C14−0.02 (16)
C1—C2—C3—C41.92 (15)C12—C13—C14—C150.56 (16)
C2—C3—C4—C5−0.39 (17)C20—O4—C15—C144.75 (14)
C3—C4—C5—C6−1.17 (16)C20—O4—C15—C16−175.21 (8)
C4—C5—C6—C11.18 (16)C13—C14—C15—O4179.28 (9)
C4—C5—C6—C7−177.88 (9)C13—C14—C15—C16−0.76 (15)
O1—C1—C6—C5−179.99 (9)C12—C11—C16—O2−179.44 (9)
C2—C1—C6—C50.35 (15)C10—C11—C16—O2−2.33 (15)
O1—C1—C6—C7−0.94 (15)C12—C11—C16—C150.10 (14)
C2—C1—C6—C7179.41 (9)C10—C11—C16—C15177.22 (9)
C8—N1—C7—C6−179.15 (9)O4—C15—C16—O2−0.05 (13)
C5—C6—C7—N1−179.86 (10)C14—C15—C16—O2179.99 (9)
C1—C6—C7—N11.08 (15)O4—C15—C16—C11−179.61 (8)
C7—N1—C8—C9121.02 (10)C14—C15—C16—C110.43 (14)
C7—N1—C8—C17−119.50 (10)C2—O3—C18—C19−177.40 (9)
C10—N2—C9—C8−161.52 (9)C15—O4—C20—C21173.58 (9)
N1—C8—C9—N2−59.47 (11)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O1—H1···N10.841.832.5752 (13)146
O2—H2···N20.841.882.6178 (13)147
C9—H9A···O1i0.992.493.4293 (14)159
C18—H18b···Cg1ii0.99002.98003.8340 (12)142.00
C7—H7A···Cg2iii0.962.723.5554 (12)176
Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) −x, −y+1, −z+1; (iii) −x+1, −y+2, −z+2.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O1—H1···N10.841.832.5752 (13)146
O2—H2···N20.841.882.6178 (13)147
C9—H9A···O1i0.992.493.4293 (14)159
C18—H18b···Cg1ii0.99002.98003.8340 (12)142.00
C7—H7A···Cg2iii0.962.723.5554 (12)176
Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) −x, −y+1, −z+1; (iii) −x+1, −y+2, −z+2.
Acknowledgements top

HKF and RK thank the Malaysian Government and Universiti Sains Malaysia for the Science Fund grant No. 305/PFIZIK/613312. RK thanks Universiti Sains Malaysia for a post-doctoral research fellowship. HK and AJ thank PNU for partial financial support. HKF also thanks Universiti Sains Malaysia for the Research University Golden Goose grant No. 1001/PFIZIK/ 811012.

references
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