Paramagnetic intermediates in the thermal reactions of benzo[2,1-b ;-3,4-b']dithiophen-4,5-dione with some metal(III) compounds of the heavier Group VB elements

The paramagnetic adducts resulting from the thermal reaction between benzo[2,1-6;3,4-b']dithiophen-4,5-dione and some organometallic derivatives of arsenic, antimony, and bismuth have been investigated by e.s.r. spectroscopy, From the e.s.r. data two alternative structural situations can be envisaged for these radicals, which in principle can be depicted either as species containing a four-co-ordinated metal atom (I) , or as the average of a rapid equilibrium between two equivalent three-co-ordinate tautomers (la and b).