Redetermination of 6,6′-dimeth­oxy-2,2′-[hexane-1,6-diylbis(nitrilo­dimethyl­idyne)]diphenol

M Tabatabaee; M R Fotuhiardakani; Alan J Lough

doi:10.1107/S1600536811020599

. 2011 Jun 4;67(Pt 7):o1579–o1580. doi: 10.1107/S1600536811020599

Redetermination of 6,6′-dimethoxy-2,2′-[hexane-1,6-diylbis(nitrilodimethylidyne)]diphenol

M Tabatabaee ^a,^*, M R Fotuhiardakani ^a, Alan J Lough ^b

PMCID: PMC3151875 PMID: 21836990

Abstract

The title compound, C₂₂H₂₈N₂O₄, contains two independent centrosymmetric molecules (A and B). In the previous structure determination [Xia et al. (2007 ▶). Acta Cryst. E63, o259] both A and B were modelled as neutral molecules with the H atoms of the the O—H groups included in calculated positions. In this redetermination, the transferrable H atoms were located in difference maps and freely refined, indicating that one molecule (A) crystallizes in the neutral (nonzwitterionic) form and the other in the zwitterionic form, namely 6,6′-dimethoxy-2,2′-[hexane-1,6-diylbis(nitrilodimethylidyne)]diphenol–6,6′-dimethoxy-2,2′-[hexane-1,6-diylbis(nitriliodimethylidyne)]diphenolate (1/1). This finding is supported by significant differences in the C—O(H) (A) and C—O⁻ (B) bond lengths. In the crystal, the zwitterionic molecules (B) are involved in intermolecular N—H⋯O hydrogen bonds forming one-dimensional chains along [001]. Each independent molecule forms an intramolecular O—H⋯N (A) or N—H⋯O (B) hydrogen bond. In molecule B, one of the –CH₂– groups is disordered over two sets of sites with refined occupancies of 0.659 (8) and 0.341 (8).

Related literature

For background to Schiff bases as ligands, see: Ray et al. (2008 ▶); Tabatabaee et al. (2006 ▶). For the previous crystal structure of the title compound, see: Xia et al. (2007 ▶).

Experimental

Crystal data

C₂₂H₂₈N₂O₄
M _r = 384.46
Monoclinic,
a = 21.2660 (4) Å
b = 8.4296 (3) Å
c = 11.1215 (9) Å
β = 92.3440 (17)°
V = 1992.02 (18) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 150 K
0.32 × 0.24 × 0.18 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: multi-scan (SORTAV; Blessing, 1995 ▶) T _min = 0.871, T _max = 0.990
9462 measured reflections
3462 independent reflections
1976 reflections with I > 2σ(I)
R _int = 0.042

Refinement

R[F ² > 2σ(F ²)] = 0.075
wR(F ²) = 0.247
S = 1.05
3462 reflections
268 parameters
6 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.35 e Å⁻³
Δρ_min = −0.39 e Å⁻³

Data collection: COLLECT (Nonius, 2002 ▶); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997 ▶); data reduction: DENZO–SMN; program(s) used to solve structure: SIR92 (Altomare et al., 1994 ▶); program(s) used to refine structure: SHELXTL (Sheldrick, 2008 ▶); molecular graphics: PLATON (Spek, 2009 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536811020599/hb5887sup1.cif

e-67-o1579-sup1.cif^{(20.3KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811020599/hb5887Isup2.hkl

e-67-o1579-Isup2.hkl^{(169.8KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1A—H1O⋯N1A	1.05 (5)	1.64 (5)	2.575 (4)	146 (4)
N1B—H2O⋯O1B	0.98 (5)	1.87 (5)	2.655 (4)	136 (4)
N1B—H2O⋯O1Bⁱ	0.98 (5)	2.31 (5)	2.976 (4)	125 (4)

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Symmetry code: (i) Inline graphic .

Acknowledgments

This research was supported by the Yazd Branch, Islamic Azad University, Yazd, Iran. AJL thanks NSERC Canada for funding.

supplementary crystallographic information

Comment

Schiff base ligands of salicylaldehyde and diamine can act as tetradentate ligands and provide suitable coordination modes for transition metal ions (Ray et al. 2008). As part of our studies on Schiff bases and their complexes (Tabatabaee et al., 2006) we have re-determined the crystal structure of the title compound, (I).

The title compound contains two centrosymmetric independent molecules [A and B] (see Figs. 1 and 2). In the original crystal structure determination (Xia et al., 2007) the H atoms of the the N—H groups were included in calculated positions. In the current determination we refined the positional and isotropic displacement parameters of these H atoms which shows that one independent molecule [B], crystallizes in the zwitterionic form. This finding is supported by the significant differnces in the distances of the C6A—O1A and C6B—O1B bonds. The zwitterionic molecules [B] are involved in intermolecular N—H···O hydrogen bonds forming one-dimensional chains along [001] (see Fig. 3). Each independent molecule forms an intramolecular O—H···N (A) or N—H···O (B) hydrogen bond. In molecule B one of the –CH₂– groups is disordeered over two sets of sites (Fig. 2) with refined occupancies 0.659 (8) and 0.341 (8). In one of the independent molecules in the original determination (Xia et al., 2007) the anisotropic displacement ellipsoids of the C atoms in the hexyl chain are significantly larger than in the other.

Experimental

All purchased chemicals were of reagent grade and used without further purification. A solution of hexamethylenediamine (1.162 g, 10 mmol) in EtOH (30 ml) was treated with 2-hydroxy-3-methoxybezaldehyde (3.043 g, 20 mmol) and the resulting mixture was acidified with 37% hydrochloric acid (10 drops). The reaction mixture was refluxed for 6 h. The progress of the reaction was monitored by TLC using hexane/ethylacetate (1/2) as eluent. After completion of reaction, the solid residue was filtered and washed with cold ethanol (10 ml). The filtrate was dissolved in CH₃OH and kept at 277 K. Orange blocks of (I) were obtained after a few days (yield 82%).