Investigation of conjugated dinitrones — derivatives of pyrroline oxide

The molecular structure of three derivatives ofbis(2- R- 5,5- dimethyl- 3- oxo- 1- oxide pyrrolin- 1- ylidene- 3),where R =CH3 (@#@5a@#@), C6H5 (@#@5b@#@), C(CH3)3 (@#@5c@#@), and of the complex of5bwith copper(II)hexafluoroacetylacetonate [Cu(hfac)2 (@#@5b@#@)] was investigated by X- ray diffraction analysis in the framework of our studies of the possible tautomeric equilibrium conjugated dinitrone ↔ nitroxide biradical. The pyrroline rings of the molecules under analysis are planar (rms deviations of atoms are no more than 0.041 å), and the interplanar angles are 32.01(5), 42.84(9), and 51.45(7)‡ for5a,5b,and5c,respectively. It is established that the bond lengths of the C(2)- C(3) =C(3a)- C(2a) fragment are equalized to C(2)- C(3) 1.42 and C(3)- C(3a) 1.40 å. The N→O bond lengths of the nitrone group are within 1.250(4)- 1.282(4) å) [in Cu(hfac)2 (5b)]. The geometrical data obtained do not permit us to make an unambiguous choice between the tautomeric structures. The magnetic susceptibility measurements of the Cu(hfac)2 solid complex (5b) and the absence of paramagnetism in solid compounds 5 indicate that they are diamagnetic.