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

Date Published: July 01, 2011

Publisher: International Union of Crystallography

Author(s): M. Tabatabaee, M. R. Fotuhiardakani, Alan J. Lough.


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).

Partial Text

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 ▶).




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