Structure and Properties of a Biradical Containing Acetylene and Phenylene Groups in the Bridge

X-band EPR spectroscopy and X-ray analysis (XRA) were used to study structure and dynamics of the intramolecular electron spin exchange in nitroxide biradical B1, in which radical rings are linked by two acethylene groups (-C equivalent to C-) and two para-phenylene groups -(C6H4-) as well as of the corresponding radical R1. The existence of two (cys- and trans-) conformers with different values of the exchange integral of the biradical and conformational transitions between them have been revealed. The energetically most stable geometry of biradical B1 has been calculated using DFT method with its good agreement with the X-ray data.