A refinement of the structure of calcium hexaantipyrine perchlorate and a comparative study of some metal hexaantipyrine perchlorates

Abstract

Calcium hexa-antipyrine perchlorate, Ca(C₁₁H₁₂ON₂)₆(CIO₄) ₂, is isomorphous with the corresponding magnesium and lead compounds and crystallizes in trigonal space group P3̅ with one formula unit in an elementary cell of dimensions a = 14.33 and c = 9.78 Å. The structure was refined by structure-factor least-squares method to an R value of 0.118 to 1131 observed refexions. The structural features of magnesium, calcium and lead hexa-antipyrine perchlorates are compared. The coordination of antipyrine oxygen atoms around the metal ion is octahedral in all three cases; thie octahedron becomes clongated along the 3̅ axis as the size of the metal ion increases. The nature of metal-oxygen bonds is discussed on the basis of the known electronegativivity coefficients of the relavant atoms and the observed metal-oxygen distances. In the antipyrine molecule, both the phenyl and the pyrazolone rings are planar and are inclined with respect to each other by angles varying from 62 to 68 °. An attempt has been made to explain the observed bond lengths in the pyrazolone ring in terms of the major canonical structures proposed.