Structure of 1,5-bis(dimethylamino)-1,5-diphenylpentadienylium perchlorate and modelling of pentadienylium salts (cyanine dyes)

C₂₁H₂₅N₂⁺.ClO₄⁻ (orange crystals), M_r = 404.9, orthorhombic; P2₁2₁2₁, a = 7.810 (2), b = 15.007 (3), c = 18.326 (3) Å, V = 2147.8 (7) ų. Graphite-monochromated Mo Kα source at room temperature; λ = 0.71069 Å, μ = 0.22 mm⁻¹, Z = 4; F(000) = 856, D_x = 1.25 g cm⁻³, R = 0.057 for 1392 independent data. As for the unsubstituted pentamethinium dyes, the chain lies in an all-trans planar configuration. Molecular modelling calculations reproduce the X-ray structure with good accuracy, even in the case of more crowded pentadienylium cations, i.e. 1,5-bis(dimethylamino)-1,3,5-triphenylpentadienylium perchlorate.

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