Bis(4-methylanilinium) and bis(4-iodoanilinium) pentamolybdates from laboratory X-ray powder data and total energy minimization

Abstract

The crystal structures of poly[bis(4-methylanilinium) [tetra-μ3-oxido-hexa-μ2-oxido-hexaoxidopentamolybdenum(VI)]], {(C7H10N)2[Mo5O16]}n, (I), and poly[bis(4-iodoanilinium) [tetra-μ3-oxido-hexa-μ2-oxido-hexaoxidopentamolybdenum(VI)]], {(C6H7IN)2[Mo5O16]}n, (II), were determined from laboratory X-ray powder diffraction data using the direct-space parallel-tempering approach and refined by total energy minimization in the solid state. Both compounds adopt layered structures, in which layers of the inorganic {[Mo5O16]2−}npolyanion alternate with layers of the organoammonium cations parallel to the (100) plane. The asymmetric units contain three Mo atoms (one situated on a twofold axis, Wyckoff position 4e), eight O atoms and one organic cation. Despite the fact that the structure determinations are based on powder diffraction data, due to the total energy minimization approach applied the Mo—O bond lengths can formally be assigned to one of the three groups, reflecting different types of O-atom placement within the polyanion. The cations form relatively strong N—H...O hydrogen bonds, anchoring one end of the organic molecules to both terminal and shared O atoms. The interactions involving the opposite end of the benzene rings are much weaker and include C—H...O and C—H...π bonds in (I) and an I...O halogen bond in (II). Mutual rotation of the benzene rings in both structures leads to the formation of a C—H...H—C dihydrogen bond, with H-atom separations of 1.95 Å in (I) and 2.12 Å in (II). Differential scanning calorimetry measurements show that the interactions between the inorganic and organic layers are stronger in (I) than in (II).