Normal coordinate analysis of 4-aminopyridine. Effect of substituent on pyridine ring in metal complexes of 4-substituted pyridines

The normal coordinate analysis has been performed for 4-aminopyridine (4-ap y) assuming C-2v molecular symmetry, A Urey-Bradley force field has been us ed. The force constants are adjusted to fit the observed frequencies for 4- apy and its deuterated species. The vibrational assignment has been made on the basis of the calculated frequencies and potential energy distributions . The calculated frequencies were in good agreement with the observed frequ encies. The substituent effect upon the M-nitrogen (ligand) (L =4-methlypyr idine, 4-ethylpyridine, 4-vinylpyridine, 4-aminopyridine and 4-cyanopyridin e) and pyridine ring frequencies has also been investigated. The frequency shifts are found to be sensitive to the substituent in the 4-position of th e pyridine ring. (C) 2001 Elsevier Science B.V. All rights reserved.