Bond length–bond order relations and calculated geometries for some benzenoid aromatics, including phenanthridine. Structures of 5,6-dimethylphenanthridinium triflate, [N-(6-phenanthridinylmethyl)-aza-18-crown-6-κ5 O,O',O'',O''',O''''](picrate-κ2-O,O')potassium, and [N,N'-bis(6-phenanthridinyl-κN-methyl)-7,16-diaza-18-crown-6-κ4 O,O',O'',O''']sodium iodide dichloromethane solvate

Abstract

The crystal structures of the title compounds are studied in order to investigate the role of novel fluoroionophores in complexation of sodium and potassium. In the potassium complex seven coordination, including the picrate ligand, is encountered. An additional coordination site is via the phenanthridine nitrogen at 3.252 (2) Å (second coordination). The complex is of C 1 symmetry and the aza-18-crown-6 macrocylic 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 shows a crystallographic twofold symmetry. The macrocycle is not of the crown-type conformation. In both complexes the alkali metals are shifted out of the cavity centres towards a picrate ligand in [N-(6-phenanthridinylmethyl)-aza-18-crown-6-κ5 O,O′,O′′,O′′′,O′′′′](picrate-κ2 O,O′)potassium and the phenanthridine units in [N,N′-bis-(6-phenanthridinyl-κN-methyl)-7,16-diaza-18-crown-6-κ4 O,O′,O′′,O′′′]sodium iodide dichloromethane solvate. Semi-empirical and molecular mechanics calculations based on various force fields were used for the optimization of phenanthridine geometry. The values obtained are compared with experimental data. Valence bond calculations of bond lengths in some benzenoid aromatic systems (C—C bonds in benzenoid hydrocarbons, azabenzenoid hydrocarbons and picrate-like systems; C—N bonds in the azabenzenoids; C—O bonds in the picrate-like systems), as well as some analogous Hückel molecular 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 Å). These approaches can be used by means of bond length-bond order relations for prediction of bond lengths in the phenanthridine units as well as in the picrate.