A new refinement of monoclinic tetracyanoethylene (TCNE) from X-ray and neutron data

Abstract

The monoclinic phase of TCNE (C6N4) was submitted to a new X-ray and neutron diffraction analysis. Contrary to the results reported by Bekoe and Trueblood (1960) we found a slight disorder, such that 3.8 -5 % of the molecules are rotated about 90 degrees in the molecular plane around their center of gravity. The final i?-values are 0.035 for the X-rayand 0.033 for the neutron-data. The resulting X -N-map showed clearly resolved peaks, whose hights correspond well with theoretical calculations.

Theoretical Study of the Electronic Excited States of Tetracyanoethylene and Its Radical Anion

“…[25] In this sense, it is worth recalling that the accurate determination of such bond distances is particularly difficult, since this parameter turns out to be very sensitive to the theoretical approach used in the calculations, [4,33] and also to the experimental technique employed for its determination. [23][24][25][34][35][36] Regarding bond angles, the computed values and the experimental data are in agreement within one degree. The CÀCN segment is predicted to deviate slightly from linearity, in line with previous theoretical results [4,10,26,33] and with the conclusions obtained through X-ray and neutron diffraction measurements.…”

“…The CÀCN segment is predicted to deviate slightly from linearity, in line with previous theoretical results [4,10,26,33] and with the conclusions obtained through X-ray and neutron diffraction measurements. [22,23,35] Addition of an electron to TCNE yields significant changes in the geometry (cf. Table 2).…”

Polymorphism in the [(TTF)2(TCNE)2] Charge-Transfer Complex

“…The nodal properties of the LUMO orbital (b2g symmetry in point group D2h ) of neutral TCNE give a 7r-bonding character to the C-CN bond and an antibonding character to C = C and C-=N bonds. Consistent with this view, the present value of the C=C bond of 1.397 À is higher than that found for cubic [ 1.344(3 ) Â] [24] and monoclinic [1.348(2) À] [25] neutral TCNE, indicating a partial negative charge on TCNE.…”

A systematic pairwise comparison of geometric parameters obtained by X-ray and neutron diffraction

“…Suitable data for ethylene derivatives are still limited [Table l(a)], but all ten X, N pairs show consistent and highly significant X-shortening of the C--C bond. This is readily interpreted (Becker, Coppens & Ross, 1973;Druck & Guth, 1982) as movement of each C (by -0.005 A,) towards the bonding density feature of the double bond. In C-C=C substructures such a movement of the central C along the C--C vector might be expected to lengthen C-C(X) by up to 0.002A,.…”