BOND LENGTH BOND ORDER RELATIONS AND CALCULATED GEOMETRIES FOR SOME BENZENOID AROMATICS, INCLUDING PHENANTHRIDINE - STRUCTURES OF 5,6-DIMETHYLPHENANTHRIDINIUM TRIFLATE, ',O'',O''',O''''](PICRATE-KAPPA(2)-O,O')POTASSIUM, AND ,16-DIAZA-18-CROWN-6-KAPPA(4)-O,O',O'',O''']SODIUM IODIDE DICHLOROMETHANE SOLVATE

The crystal structures of the title compounds are studied in order to investigate the role of novel fluoroionophores in complexation of sodi um and potassium. In the potassium complex seven coordination, includi ng the picrate ligand, is encountered. An additional coordination site is via the phenanthridine nitrogen at 3.252 (2) Angstrom (second coor dination). The complex is of C-1 symmetry and the aza-18-crown-6 macro cylic ring exhibits a crown-type conformation. The 7,16-diaza-18-crown -6 macrocycle accommodates a six-coordinate sodium with two additional ligands, via nitrogen from phenanthridine units. The complex cation s hows a crystallographic twofold symmetry. The macrocycle is not of the crown-type conformation. In both complexes the alkali metals are shif ted out of the cavity centres towards a picrate ligand in henanthridin ylmethyl)-aza-18-crown-6-(KO)-O-5,O',O '',O''',O''''](picrate-(KO)-O-2 ,O')-potassium and the phenanthridine units in -phenanthridinyl-KN-met hyl)-7,16-diaza-18-crown-6- (KO)-O-4,O',O '',O''']sodium iodide dichlo romethane solvate. Semi-empirical and molecular mechanics calculations based on various force fields were used for the optimization of phena nthridine geometry. The values obtained are compared with experimental data. Valence bond calculations of bond lengths in some benzenoid aro matic systems (C-C bonds in benzenoid hydrocarbons, azabenzenoid hydro carbons and picrate-like systems; C-N bonds in the azabenzenoids; C-O bonds in the picrate-like systems), as well as some analogous Huckel m olecular orbital calculations (C-C bonds in the benzenoid hydrocarbons and the azabenzenoids), were found to agree with the observed values (average differences up to 0.015 Angstrom). These approaches can be us ed by means of bond length-bond order relations for prediction of bond lengths in the phenanthridine units as well as in the picrate.