INVESTIGATIONS ON UV-ABSORPTION SPECTRA OF SOME PYRIDINE ADDITION COMPOUNDS

UV-absorption spectra of the pyridine addition compounds PyHCl, BF3 · py, BCl3 · py, BBr3 · py, AlCl3 · py, AlBr3 · py, SiF4 · 2py, SiCl4 · 2py, SiHCl3 · 2py, SiBr4 · 2py, GeCl4 · 2py, and PCl5 · py were measured. The shift of the long-wave π-π*-pyridine band could be explained by a simple Hückel calculation, using either a positive or a negative hN for the pyridine molecule. The charge distribution, resulting from calculation with negative hN agrees with those obtained by an ab-initio-calculation of McLean for HCN [7] and by a LCAO-calculation, including σ- and π-electrons, for pyridine of Veillard and Berthier [8]. The Lewis acids, forming addition compounds with pyridine, are arranged according to increasing acceptor strength using the results of the Hückel-calculations. © 1968 Springer-Verlag.