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Summar38 h single-crystal X-ray diffraction study of benzenes,ls with an integration ratio of 4:3. No other The apparent spectral equivalence p-MeC,H,-(N,S)-C,H,Me-p' has shown that the 4,sgroup has the bis-imino-sulphur structure -N = S = N-. peaks are observed. SEVERAL symmetrical Ar-(N,S) -Ax compounds have been prepared1-* and structures such as azothioarene (I), bisarylimino-sulphur (11) and 2,S-diaryl-l,Z,S-thiodiazirine (I1 I) have been suggested .lA7 ,9@Chemical evidence, partial assignment of the i.r. spectra2pp dipole moment measurements,10 and n.m.r. data11 did not allow the structure of the -(N2S)-group to be assigned unambiguously, geometric isomerism also being possible.The n.m.r. spectrum of the p,p '-ditolyl derivativeB consists of a single peak at 6 2.30 p.p.m. (CH,) (6 values from Me,Si, in CCI,) and a symmetrical resonance group centred at 6 7-18 p.p.m., which resembles an A2B2 system of p-disubstituted

The crystal structure of 1, 3-trans-bis(4-chlorophenyl)-2,4-trans-di(4-pyridyl)cyclobutane, C26H20CI2N2, has been determined from 1765 three-dimensional intensities, collected with an automated Philips PW 1100 four-circle single-crystal diffractometer and refined to R = 0.058. Cell constants are a = 16.307 (8), b = 13.907 (2), c = 9.666 (3) A,/3 ---94.47 (5) °, z = 4; the space group is P21/n. The cyclobutane ring has a puckered conformation, and the two dihedral angles are 19.1 and 19.2 °. The structure determined shows that the dimerization process is a head-to-tail reaction.

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The structure of 1-thiocarbamoylimidazolidine-2-thione, C4H7N382, has been determined from X-ray three-dimensional diffraction data. The crystals are monoclinic, space group P21/c, a= 4.958 + 0.003, b= 10.092+0.005, c= 13"841 +0"006/~, ,O= 103.0+0.2 °, Z=4. The structure has been determined by Patterson and direct methods and refined by full-matrix least squares (R= 0.057). The molecule is nearly planar, with an intramolecular N-H. • • S hydrogen bond of 2.998/~. Bond lengths and resonance in the dithiobiuret moiety are discussed. Two pairs of intermolecular N-H... S hydrogen bonds of 3.409 and 3.449/~ bring molecules together across centres of symmetry and give rise to infinite chains which are superimposed on each other, by the a-axis repeat, at a perpendicular distance of 3.506/~.

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