The role of substituents in the molecular and crystal structure of 1-(adamantane-1-carbonyl)-3-(mono)- and 3,3-(di) substituted thioureas

Three novel 1-(adamantane-1-carbonyl) thioureas were synthesized by the reaction of adamantyl isothiocyante with corresponding amines and fully characterized by spectroscopy methods. Two isomeric species, i.e. 1-(adamantane-1-carbonyl)-3-(3-nitrophenyl)thiourea (1) and 1-(adamantane-1-carbonyl)-3-(4-nitrophenyl)thiourea (2), are structurally characterized and a third related compound, namely 1-(adamantane-1-carbonyl)-3,3-(methyl-phenyl)thiourea (3) has been also included for assessing the role of the nitrogen substitution on the structural properties. As determined by X-ray analysis, compounds 1 and 2 exhibit the S conformation with the CO and CS double bonds in a pseudo-antiperiplanar orientation, whereas the U form is found for compound 3. These conformational features are mainly dictated by the substitution degree on the thiourea core and the ability of forming an intra-molecular NH⋯OC hydrogen bond for mono-substituted analogues 1 and 2. These dissimilar interactions affect the vibrational properties, which have been determined by infrared and Raman spectroscopies and quantum chemical calculations at the B3LYP/6-311++G** level of approximation.