Crystal structure of 1,1'-{(pentane-1,5-di-yl)bis[(aza-niumylyl-idene)methanylyl-idene]}bis(naphthalen-2-olate).

The whole mol-ecule of the title compound, C27H26N2O2, is generated by twofold rotational symmetry, with the central C atom of the pentyl chain located on the twofold rotation axis. The compound crystallizes as a bis-zwitterion, and there are two intra-molecular N-H⋯O hydrogen bonds generating S(6) ring motifs. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, forming ribbons propagating along [001], and enclosing R 2 (2)(22) ring motifs.

Chemical context

Tetra­dentate NNOO Schiff-bases have been used extensively as supporting ligands in d-block chemistry because of their ability to stabilize metals in various oxidation states (Alaghaz et al., 2014 ▸; Kianfar et al., 2015 ▸; Mikhn class="Gene">alyova et al., 2014 ▸; Borthakur et al., 2014 ▸; Basumatary et al., 2015 ▸). For many years, particular attention has been devoted to imines because of their uses as catalysts in various organic transformations (Khorshidifard et al., 2015 ▸), and for their anti­cancer (Shiju et al., 2015 ▸), anti­fungal (Abo-Aly et al., 2015 ▸) and anti­bacterial (Salehi et al., 2015 ▸) properties. They have also been used as sensors (Bandi et al., 2013 ▸), corrosion inhibitors (Dasami et al., 2015 ▸) and optical and fluorescent probes (Shoora et al., 2015 ▸; Prabhakara et al., 2015 ▸).

The microwave-assisted synthesis method, in solvent or solvent-free, is efficient and rapid. It gives cleaner reactions, is ease to use, gives higher yields and is a more economical synthetic process for the preparation of Schiff base compounds compared to conventional methods. It has been used to enhance the yield and reduce the time of certain reactions: for example, a one-step synthesis of D-A-D chromo­phores as active materials for organic solar cells (Jeux et al., 2015 ▸), or the synthesis of a series of acyclic n class="Chemical">Schiff base–chromium(III) complexes (Kumar et al., 2015 ▸).

In a continuation of our work on Schiff base ligands, we report herein on the crystal structure of the title compound, synthesized un class="Gene">sing two methods, viz. microwave irradiation and conventional, by condensing o-hy­droxy­naphthaldehyde and 1,5-di­amino­pentane.

Structural commentary

The whole mol­ecule of the title compound, Fig. 1 ▸, is generated by twofold rotational symmetry, with the central C atom of the pentyl chain, C14, located on the twofold rotation axis. It crystallizes as a n class="Chemical">bis-zwitterion, with strong intra­molecular N—H⋯O hydrogen bonding between the imino N atom N1 (N1’), and the O atom, O1 (O1i) [d (O⋯N) = 2.5437 (17) Å; symmetry code: (i) −x, y, −z + ], forming S(6) ring motifs (Fig. 1 ▸ and Table 1 ▸). The pentyl chain has an extended conformation with the naphthalene rings inclined to one another by 89.94 (5)°.

Figure 1

The mol­ecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intra­molecular hydrogen bonds are shown as dashed lines (see Table 1 ▸). The unlabelled atoms are related to the labelled atoms by twofold rotational symmetry (atom C14 lies on the twofold axis; symmetry code: −x, y, −z + ).

Table 1

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
N1H1NO1	0.96(2)	1.72(2)	2.5437(17)	141.3(16)
C12H12AO1i	0.99	2.45	3.2871(19)	142

Symmetry code: (i) .

Supra­molecular features

In the crystal, mol­ecules are linked by pairs of C—H⋯O hydrogen bonds, forming ribbons propagating along [001] and enclon class="Gene">sing (22) ring motifs (Table 1 ▸ and Fig. 2 ▸).

Figure 2

Crystal packing of the title compound viewed along the b axis. The hydrogen bonds are shown as dashed lines (see Table 1 ▸). For clarity, only the H atoms involved in hydrogen bonding have been included.

Database survey

Recently, our group reported the crystal structures of three new Schiff bases synthesized un class="Gene">sing conventional or ultrasonic irradiation methods by reacting primary amines and o-hy­droxy­naphthaldehyde (Ouari et al., 2015a ▸,b ▸,c ▸). They too crystallize as bis-zwitterionic compounds with strong intra­molecular N—H⋯O hydrogen bonds forming S(6) ring motifs.

Synthesis and crystallization

Method 1: Microwave synthesis

2-Hy­droxy-1-naphthaldehyde (0.344g, 2 mmol), mixed and ground in a mortar, was placed in a reaction flask, and then 1,5-di­amino­pentane (0.109 g, 1 mmol) in 2 ml of methanol was added. The reaction mixture was then irradiated in a microwave oven for 1 min at 600 W. Upon completion, based on TLC ann class="Gene">alysis (silica gel, CH2Cl2/MeOH, 9.5/0.5, v/v), the product was washed with methanol (3 × 3 ml) and diethyl ether (3 × 3 ml) and filtered. Yellow crystals of the title compound, suitable for X-ray diffraction analysis, were obtained after two days by slow evaporation of a solution in DMSO/MeOH (yield: 95%, m.p.: 438–440 K). Elemental analysis calculated for C27H26N2O2: C, 80.00; H, 6.38; N,6.82%; found: C, 80.42; H, 6.63; N, 6.56%.

Method 2: Conventional synthesis

The title Schiff base was prepared by condensation between 1,5-di­amino­pentane (51 mg, 0.5 mmol) and 2-hy­droxy-1-naphthaldehyde (172 mg, 1 mmol) in n class="Chemical">methanol (10 ml). The mixture was refluxed and stirred under a nitro­gen atmosphere for 3 h. The precipitate obtained was filtered, washed with methanol and diethyl ether and dried in vacuum overnight. Yellow single crystals of the title compound were obtained by slow evaporation of a solution in methanol (yield 71%; m.p.: 438–440 K).

As expected, the yield using method 1 (95%) is significantly greater than that un class="Gene">sing method 2 (71%).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. The iminium H atom was located from a difference Fourier map and freely refined. C-bound n class="Disease">H atoms were included in calculated positions and treated as riding atoms: C—H = 0.95 − 0.99 Å with U iso(H) = 1.2U eq(C). Atom C14 lies on the twofold rotation axis and the H atoms were placed using instruction HFIX 23 (Sheldrick, 2015 ▸); the occupancy of the methyl­ene H atoms were fixed automatically at 0.5.

Table 2

Experimental details

Crystal data
Chemical formula	C27H26N2O2
M r	410.50
Crystal system, space group	Monoclinic, P2/c
Temperature (K)	173
a, b, c ()	20.9080(13), 4.7429(2), 10.6810(6)
()	96.419(3)
V (3)	1052.54(10)
Z	2
Radiation type	Mo K
(mm1)	0.08
Crystal size (mm)	0.45 0.20 0.10
Data collection
Diffractometer	Nonius KappaCCD
Absorption correction	Multi-scan (MULSCAN in PLATON; Spek, 2009 ▸)
T min, T max	0.792, 1.000
No. of measured, independent and observed [I > 2(I)] reflections	5781, 1958, 1402
R int	0.049
(sin /)max (1)	0.606
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.049, 0.120, 1.08
No. of reflections	1958
No. of parameters	146
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
max, min (e 3)	0.16, 0.14

Computer programs: COLLECT (Nonius, 1998 ▸), DENZO and SCALEPACK (Otwinowski Minor, 1997 ▸), SHELXS2014 (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸), Mercury (Macrae et al., 2008 ▸) and PLATON (Spek, 2009 ▸).

Crystal structure: contains datablock(s) I, Global. DOI: 10.1107/S2056989015014437/su5181sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015014437/su5181Isup2.hkl

CCDC reference: 1416064

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

C27H26N2O2	F(000) = 436
Mr = 410.50	Dx = 1.295 Mg m−3
Monoclinic, P2/c	Mo Kα radiation, λ = 0.71073 Å
a = 20.9080 (13) Å	Cell parameters from 7575 reflections
b = 4.7429 (2) Å	θ = 1.0–27.5°
c = 10.6810 (6) Å	µ = 0.08 mm−1
β = 96.419 (3)°	T = 173 K
V = 1052.54 (10) Å3	Plate, yellow
Z = 2	0.45 × 0.20 × 0.10 mm

Nonius KappaCCD diffractometer	1402 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.049
phi and ω scans	θmax = 25.5°, θmin = 2.9°
Absorption correction: multi-scan (MULSCAN in PLATON; Spek, 2009)	h = −25→23
Tmin = 0.792, Tmax = 1.000	k = −5→5
5781 measured reflections	l = −12→8
1958 independent reflections

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.049	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.120	w = 1/[σ2(Fo2) + (0.0549P)2 + 0.0593P] where P = (Fo2 + 2Fc2)/3
S = 1.08	(Δ/σ)max < 0.001
1958 reflections	Δρmax = 0.16 e Å−3
146 parameters	Δρmin = −0.14 e Å−3
0 restraints	Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.033 (7)

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.

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.14942 (5)	0.8929 (2)	−0.10611 (10)	0.0508 (4)
N1	0.13436 (6)	0.5012 (3)	0.05060 (12)	0.0436 (4)
H1N	0.1201 (8)	0.643 (4)	−0.0110 (19)	0.080 (6)*
C1	0.21054 (7)	0.8695 (3)	−0.07692 (14)	0.0412 (4)
C2	0.25371 (8)	1.0411 (3)	−0.13960 (15)	0.0497 (5)
H2	0.2364	1.1708	−0.2022	0.060*
C3	0.31790 (9)	1.0235 (3)	−0.11224 (17)	0.0546 (5)
H3	0.3446	1.1413	−0.1562	0.065*
C4	0.34731 (8)	0.8329 (3)	−0.01900 (15)	0.0469 (4)
C5	0.41450 (8)	0.8204 (4)	0.00866 (18)	0.0612 (5)
H5	0.4407	0.9383	−0.0362	0.073*
C6	0.44291 (8)	0.6423 (4)	0.09873 (19)	0.0632 (5)
H6	0.4884	0.6365	0.1169	0.076*
C7	0.40413 (8)	0.4698 (4)	0.16322 (18)	0.0589 (5)
H7	0.4235	0.3446	0.2258	0.071*
C8	0.33846 (7)	0.4769 (3)	0.13821 (16)	0.0508 (5)
H8	0.3132	0.3566	0.1841	0.061*
C9	0.30745 (7)	0.6580 (3)	0.04622 (14)	0.0403 (4)
C10	0.23834 (7)	0.6743 (3)	0.01610 (13)	0.0377 (4)
C11	0.19669 (7)	0.4956 (3)	0.07450 (14)	0.0405 (4)
H11	0.2152	0.3635	0.1348	0.049*
C12	0.09067 (7)	0.3217 (3)	0.11165 (15)	0.0440 (4)
H12A	0.1159	0.1903	0.1699	0.053*
H12B	0.0644	0.2083	0.0472	0.053*
C13	0.04669 (7)	0.4962 (3)	0.18441 (15)	0.0454 (4)
H13A	0.0219	0.6281	0.1257	0.054*
H13B	0.0733	0.6100	0.2482	0.054*
C14	0.0000	0.3185 (4)	0.2500	0.0449 (6)
H14A	−0.0247	0.1956	0.1871	0.054*	0.5
H14B	0.0247	0.1955	0.3129	0.054*	0.5

	U11	U22	U33	U12	U13	U23
O1	0.0484 (7)	0.0583 (7)	0.0443 (7)	0.0043 (5)	−0.0014 (5)	0.0039 (5)
N1	0.0412 (8)	0.0500 (8)	0.0395 (8)	0.0013 (6)	0.0038 (6)	0.0011 (6)
C1	0.0460 (9)	0.0454 (9)	0.0314 (8)	0.0001 (7)	0.0015 (7)	−0.0083 (7)
C2	0.0615 (12)	0.0473 (9)	0.0399 (10)	−0.0025 (8)	0.0040 (8)	0.0025 (7)
C3	0.0581 (11)	0.0563 (10)	0.0504 (11)	−0.0114 (8)	0.0112 (9)	0.0009 (8)
C4	0.0462 (10)	0.0501 (10)	0.0442 (10)	−0.0049 (8)	0.0049 (7)	−0.0107 (8)
C5	0.0470 (11)	0.0745 (12)	0.0629 (12)	−0.0127 (9)	0.0096 (9)	−0.0054 (10)
C6	0.0395 (10)	0.0817 (13)	0.0674 (13)	−0.0006 (9)	0.0010 (9)	−0.0129 (11)
C7	0.0472 (10)	0.0683 (12)	0.0587 (12)	0.0052 (9)	−0.0051 (9)	−0.0027 (9)
C8	0.0434 (10)	0.0578 (10)	0.0501 (11)	0.0005 (8)	0.0008 (8)	−0.0002 (8)
C9	0.0416 (9)	0.0435 (9)	0.0356 (9)	−0.0006 (7)	0.0042 (7)	−0.0103 (7)
C10	0.0402 (8)	0.0405 (8)	0.0322 (8)	−0.0008 (7)	0.0038 (7)	−0.0059 (6)
C11	0.0407 (9)	0.0446 (9)	0.0352 (9)	0.0049 (7)	−0.0002 (7)	−0.0047 (7)
C12	0.0405 (9)	0.0463 (9)	0.0450 (10)	−0.0027 (7)	0.0035 (7)	−0.0002 (7)
C13	0.0415 (9)	0.0479 (9)	0.0467 (10)	−0.0006 (7)	0.0049 (7)	0.0007 (7)
C14	0.0375 (12)	0.0466 (12)	0.0502 (14)	0.000	0.0023 (10)	0.000

O1—C1	1.2858 (17)	C7—C8	1.369 (2)
N1—C11	1.2999 (19)	C7—H7	0.9500
N1—C12	1.4551 (19)	C8—C9	1.408 (2)
N1—H1N	0.96 (2)	C8—H8	0.9500
C1—C10	1.433 (2)	C9—C10	1.447 (2)
C1—C2	1.435 (2)	C10—C11	1.410 (2)
C2—C3	1.344 (2)	C11—H11	0.9500
C2—H2	0.9500	C12—C13	1.515 (2)
C3—C4	1.432 (2)	C12—H12A	0.9900
C3—H3	0.9500	C12—H12B	0.9900
C4—C5	1.404 (2)	C13—C14	1.5191 (18)
C4—C9	1.413 (2)	C13—H13A	0.9900
C5—C6	1.365 (3)	C13—H13B	0.9900
C5—H5	0.9500	C14—C13i	1.5190 (18)
C6—C7	1.388 (3)	C14—H14A	0.9900
C6—H6	0.9500	C14—H14B	0.9900
C11—N1—C12	124.46 (14)	C8—C9—C4	116.82 (14)
C11—N1—H1N	112.0 (11)	C8—C9—C10	123.95 (14)
C12—N1—H1N	123.5 (11)	C4—C9—C10	119.23 (14)
O1—C1—C10	122.62 (14)	C11—C10—C1	118.19 (14)
O1—C1—C2	119.85 (14)	C11—C10—C9	121.36 (14)
C10—C1—C2	117.52 (14)	C1—C10—C9	120.43 (13)
C3—C2—C1	121.89 (16)	N1—C11—C10	123.79 (14)
C3—C2—H2	119.1	N1—C11—H11	118.1
C1—C2—H2	119.1	C10—C11—H11	118.1
C2—C3—C4	122.09 (16)	N1—C12—C13	110.97 (12)
C2—C3—H3	119.0	N1—C12—H12A	109.4
C4—C3—H3	119.0	C13—C12—H12A	109.4
C5—C4—C9	120.18 (16)	N1—C12—H12B	109.4
C5—C4—C3	120.99 (16)	C13—C12—H12B	109.4
C9—C4—C3	118.83 (15)	H12A—C12—H12B	108.0
C6—C5—C4	121.37 (17)	C12—C13—C14	113.06 (12)
C6—C5—H5	119.3	C12—C13—H13A	109.0
C4—C5—H5	119.3	C14—C13—H13A	109.0
C5—C6—C7	118.82 (17)	C12—C13—H13B	109.0
C5—C6—H6	120.6	C14—C13—H13B	109.0
C7—C6—H6	120.6	H13A—C13—H13B	107.8
C8—C7—C6	121.16 (18)	C13i—C14—C13	112.58 (17)
C8—C7—H7	119.4	C13i—C14—H14A	109.1
C6—C7—H7	119.4	C13—C14—H14A	109.1
C7—C8—C9	121.65 (16)	C13i—C14—H14B	109.1
C7—C8—H8	119.2	C13—C14—H14B	109.1
C9—C8—H8	119.2	H14A—C14—H14B	107.8
O1—C1—C2—C3	−179.92 (15)	C3—C4—C9—C10	0.6 (2)
C10—C1—C2—C3	−0.6 (2)	O1—C1—C10—C11	2.0 (2)
C1—C2—C3—C4	0.0 (3)	C2—C1—C10—C11	−177.25 (12)
C2—C3—C4—C5	−179.42 (16)	O1—C1—C10—C9	−179.47 (13)
C2—C3—C4—C9	0.0 (2)	C2—C1—C10—C9	1.2 (2)
C9—C4—C5—C6	−0.4 (3)	C8—C9—C10—C11	−3.1 (2)
C3—C4—C5—C6	179.02 (17)	C4—C9—C10—C11	177.16 (13)
C4—C5—C6—C7	0.4 (3)	C8—C9—C10—C1	178.51 (14)
C5—C6—C7—C8	−0.3 (3)	C4—C9—C10—C1	−1.3 (2)
C6—C7—C8—C9	0.2 (3)	C12—N1—C11—C10	−178.86 (13)
C7—C8—C9—C4	−0.2 (2)	C1—C10—C11—N1	−1.3 (2)
C7—C8—C9—C10	−179.94 (15)	C9—C10—C11—N1	−179.82 (13)
C5—C4—C9—C8	0.3 (2)	C11—N1—C12—C13	117.93 (15)
C3—C4—C9—C8	−179.15 (13)	N1—C12—C13—C14	179.96 (11)
C5—C4—C9—C10	−179.95 (14)	C12—C13—C14—C13i	−176.30 (15)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···O1	0.96 (2)	1.72 (2)	2.5437 (17)	141.3 (16)
C12—H12A···O1ii	0.99	2.45	3.2871 (19)	142