A. W. Cordes

Symmetry breaking localisation of the unpaired electron in spiro-bis(1,9-disubstituted-phenalenyl)boron radicals

Abstract We report the crystal structure of a spiro-bis(1,9-disubstituted-phenalenyl)boron cation ( 2 + ) and by comparison with the structures of a series of radicals we conclude that the changes in bond lengths in the radicals compared to those of the corresponding cation can be qualitatively predicted by the sign of the partial bond order of the singly occupied molecular orbital (SOMO), which contains the additional electron. By use of this information, we can analyse the structures of the π-dimer radicals 1 and 2 and ascertain the location of the unpaired electron in these compounds. Where these radicals exist as paramagnetic π-dimers (high-temperature regime), the unpaired electrons reside mainly in the phenalenyl units not directly involved in the π-dimer interaction. At low temperatures, where the diamagnetic π-dimers exist, the electrons localise in the phenalenyl units directly involved in the π-dimer, but there still exists some degree of delocalisation of the electrons to the other halves of the molecules. We postulate that the increase in delocalisation of the unpaired electrons is related to the increase of the conductivity by about two orders of magnitude as the electrons spin pair.

A bimodal dithiadiazolyl diradical: crystal structure and magnetic properties of the 2,2′-dimethylbiphenylene bridged derivative

The two termini of the torsionally strained dithiadiazolyl diradical S2N2C–C6H3Me–MeC6H3–CN2S2 3 possess different solid state structural environments; the bulk magnetic susceptibility of 3 is interpreted in terms of the distinct properties of the two radical centres.

4,4'-Dimethyl-1,1'-bi(1,2,3,5-diselenadiazole)

The radical units Se 2 N 2 CMe dimerize with long Se...Se distances of 3.159(3) and 3.187(3) A to give the title compound, C 4 H 6 N 4 Se 4 . There are two crystallographically independent dimers in the unit cell. The dimers adopt a twisted conformation with parallel ring planes. One ring is rotated on the axis between ring centers by approximately 90° from the eclipsed position to give Se-Se-Se-Se torsion angles of 86.81(15) and 88.95 (17)°. Se-Se bond lengths within the radicals vary from 2.306 (3) to 2.330 (3) A.

3,7-Bis(2-thienyl)-1,5,2,4,6,8-dithiatetrazocine

The title molecule, 3,7-bis(2-thienyl)-1,5,2,4,6,8-dithiatetrazocine, C 10 H 6 N 4 S 4 , is planar within 0.069 (5) A and crystallizes in the monoclinic space group P2 1 /c. There are two centrosymmetric molecules in the cell; these are stacked such that each eight-membered C 2 N 4 S 2 ring has a thienyl ring above and below it. The mean interplanar separation is 3.55 (2) A.

Structure of 1,3-dichloro-5-phenyl-1λ4,3λ4,2,4,6-dithiatriazine

C7HsC12N3S2, Mr=266.17, triclinic, P), a=6-028(1), b=9-985(2), c=10.157 (3) /~, ct= 117.33 (2), fl= 106.73(2), y=90.31(1) °, V= 513-3(4)/~3, Z=2, D x=1.72gcm -3, 2(MoK~t)= 0.71073 A, /1 = 9.85 cm -1, F(000) = 268, T= 293 K, R = 0.032 for 1547 unique observed reflections. The SNCNS portion of the ring is planar within 0-060 (2)/~ and the third N is displaced 0.336 (2) A from this plane on the side opposite the S-bonded C1 atoms. The S-N distances range from 1.581 (1) to 1.615 (2)/~ and the N-C distances are 1.327 (2) and 1.344 (2) ./k. Experimental. Compound prepared by the reaction of chlorine gas with PhCNsS 3 obtained from the reaction of PhC(NSiMe3) with SaNaC1 a. Crystals obtained from a 50:50 mixture of dichloromethane and hexanes. Air-sensitive parallelpiped data crystal 0.20 × 0.50 × 0.46 mm sealed in a glass capillary. Density not measured. Intensities measured with an Enraf-Nonius CAD-4 diffractometer using 09-20 scans of 4 to 16 ° min -~ in 0. Unit cell determined from least-squares analysis of angle data for 20 reflections with 22 < 20 < 40 °. Analytical absorption correction based on crystal shape varied from 0.67 to 1-00. Data collected to sin0/2 of 0-59/~-~, -7<h<7, -ll_<k<ll, 0 < l <_ 12. Four standard reflections (244, 444, 325, 335) varied +2%; linear-drift correction applied. 1907 reflections measured, 1796 unique (Ri, t =0.01), 247 reflections with I < 3o(1) considered unobserved. Two reflections (101, 131) which saturated the counter with their high intensities were omitted. Solved by direct methods using MULTANll/82 (Main, Fiske, Hull, Lessinger, Germain, Declercq & Woolfson, 1982) and Fourier methods. Full-matrix least squares minimized ~.wAF 2. H atoms refined isotropically, other atoms anisotropically for a total of 147 variables. R -- 0.032, wR=0.043, S= 1.64, where non-Poisson w-2= a(I) + 0.0016F 2. Final (Zl/tT)max < 0.03, dPmax----- 0.36(2) and APmin=--0.35 (2)e/~ -3 on final dif- ference map. Atomic scattering factors and anomalous- dispersion corrections from International Tables for X-ray Crystallography (1974) and programs used those