INVESTIGATION OF CONJUGATED DINITRONES - DERIVATIVES OF PYRROLINE OXIDE

The molecular structure of three derivatives of bis(2-R-5,5-dimethyl-3 -oxo-1-oxide pyrrolin-1-ylidene-3), where R = CH3 (5a), C6H5 (5b), C(C H3)(3) (5c), and of the complex of 5b with copper(II) hexafluoroacetyl acetonate [Cu(hfac)(2) (5b)] was investigated by X-ray diffraction ana lysis in the framework of our studies of the possible tautomeric equil ibrium conjugated dinitrone nitroxide biradical. The pyrroline rings o f the molecules under analysis are planar (rms deviations of atoms are no more than 0.041 Angstrom), and the interplanar angles are 32.01(5) , 42.84(9), and 51.45(7)degrees for 5a, 5b, and 5c, respectively. It i s established that the bond lengths of the C(2)-C(3)=C(3a)-C(2a) fragm ent are equalized to C(2)-C(3) 1.42 and C(3)-C(3a) 1.40 Angstrom. The N-->O bond lengths of the nitrone group are within 1.250(4)-1.282(4) A ngstrom [in Cu(hfac)2 (5b)]. The geometrical data obtained do not perm it us to make an unambiguous choice between the tautomeric structures. The magnetic susceptibility measurements of the Cu(hfac)2 solid compl ex (5b) and the absence of paramagnetism in solid compounds 5 indicate that they are diamagnetic.