title: Geometry and bond-length alternation in nonlinear optical materials. I. Standard parameters in two precursors.
abstract: 2-{3-Cyano-4-[4-(N-formylanilino)-trans-1,3-butadienyl]-5,5-dimethyl-2,5-dihydrofuran-2-ylidene}propanedinitrile, C(22)H(18)N(4)O(2), (I), and 2-{3-cyano-4-[6-(N-formylanilino)-trans,trans-1,3,5-hexatrienyl]-5,5-dimethyl-2,5-dihydrofuran-2-ylidene}propanedinitrile, C(24)H(20)N(4)O(2), (II), show the alternating single/double-bond behaviour of push-pull chromophores. In the two structures, the planar polyene chains are twisted with respect to the furanylidene ring by 18.2 (2) and 12.4 (2) degrees , respectively. Comparison with structures of related and parent molecules shows subtle but consistent bond-length variations consistent with charge-delocalized structures. Crystal cohesion is provided by various sets of hydrogen bonds, viz. C-H(methyl)...N(cyano) and bifurcated (C=C-H)(2)...O=C in (I), and C-H(methyl/phenyl)...O and C=C-H...N(cyano) in (II).
authors.affiliation: Industrial Research Limited, PO Box 31-310, Lower Hutt, New Zealand. g.gainsford@irl.cri.nz
authors.forename: Graeme J
authors.initials: GJ
authors.lastname: Gainsford
authors.forename: M Delower H
authors.initials: MD
authors.lastname: Bhuiyan
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Kay