Structural studies of some heterocyclic compounds.

Single crystal X-ray analysis has been used to examine the solid state structures of a selection of heterocyclic compounds which fall into three categories: 1. Triazole and imidazole compounds. The activity of fungicides is highly dependent upon the predominant conformation adopted by the molecule. The crystal and molecular structures of five compounds showing fungicidal activity and provided by I.C.I. Plant Protection have been determined. The conformations of the compounds, which contain either a 1,2,4-triazol-1-yl or imidazol-l-yl ring have been compared. The most noteworthy feature is the significant difference in the conformation adopted by triadimefon compared with the other triazole compounds studied. 2. Macrocyclic metal compoundsSingle crystal X-ray analyses of five macrocyclic complexes containing alkaline earth metal ions (calcium, strontium, and barium) have been completed. The relative sizes of the macrocyclic cavity and the metal ion play a crucial role in determining the structure adopted. Thus, in the complexes M(NCS -2(L) .nH-2 C (M = Ca, n = 0; M = Sr or Ba, n = 1) in which L is the macrocyclic ligand 3,25,21-triaza-o,9,12-trioxabicyclo(15.31)heneicosa-1(21), 2,15,17,19-pentaene; increasing size of the metal ion is accompanied by (i) a progressive displacement of the metal ion from the mean plane through the six donor atoms and (ii) an increase in the coordination number of the metal from eight (calcium) to nine ( strontium and barium).3. Phosphorus heterocyclic compoundsThe structures of three phosphorus heterocycies have beendetermined in an attempt to establish the importance of ring strain within the heterocyclic phosphonium ring systems. While the small endocyclic C-P-C angle of 94(1)° found in 5-(p-bromo--benzyl)-5-phenyl-dibenzophospholium bromide is indicative of the presence of significant ring strain within the phosphorus heterocycle, such effects appear to be of much less importance in the six- and seven-membered ring systems studied, viz: 10-(4-bromobenzyl)-10-phenylphenoxaphosphonium bromide and 5-phenyl-10,11-dihydrobenzo(b,f)phosphep.in-5-oxide.