Structure of 3-(2-benzimidazolyl)-7-(diethylamino)coumarin

Abstract

C20H19N302, M r = 33339, triclinic, P1, a = 10.350(7), b=12990(5), c=6753(3) A, a= 100.89(4), /3 = 10623(4), 3'=9884(5) °, V 8352 (8) A 3, Z = 2, O m = 1345, Dx = 1325 g cm- , A(Mo Ka) = 0.71069 A, /x = 0.817 cm-1, F(000) = 352, T=296K. Final R value is 0.071 for 1626 observed reflections. The coumarin and benz- imidazole ring systems are planar. Intramolecular hydrogen bonds of N--H...O type exist. The crystal structure is stabilized by van der Waals forces. anisotropic thermal parameters for non-H and iso- tropic for H atoms, final R = 0.071, wR = 0-067, S = 1.65, w = l'9825/(~r2(tFo() 000004Fo2). The R value is high due to poor crystal quality, (A/O')max = 0.014, final difference map featureless with max. and min. peak heights 0.35 and -0.27 e/~-3; no correc- tion for secondary extinction, atomic scattering fac- tors for all atoms as in SHELX76 (Sheldrick, 1976), geometrical calculations using PARST (Nardelli, 1983). Introduction. Some aminocoumarin derivatives, in weakly polar solvents and under laser excitation, give an anomalous band due to the TICT (twisted intra- molecular charge transfer) state. Solute-solvent interactions aid the stability of this state (Masi- lamani, Sastikumar, Natarajan & Natarajan, 1987). The title compound (also called coumarin 7) is found to give laser action at 525 nm in the vapour phase (Logunov, Startsev & Stoilov, 1981), and in a mix- ture of water and N,N-dipropylacetamide (Tuccio, Drexhage & Reynolds, 1973). The possibility of occurrence and stability of the TICT state for the title compound is discussed on a structural basis.