Polymorphic form IV of olanzapine

2-Methyl-4-(4-methylpiperazin-1-yl)-10H-thieno[2,3-b][1,5]-benzodiazepine, C17H20N4S, commonly known as olanzapine, is a psychotropic agent that belongs to the thienobenzodiazepine class of drugs. A new polymorph form IV was obtained upon attempted cocrystallization with nicotinamide in a 1:1 ratio from an ethyl acetate solution. Two butterfly-like molecules form centrosymmetric dimers stabilized by weak C-H center dot center dot center dot pi interactions between the 4-methylpiperazin-1-yl fragment and the benzene/thiophene aromatic system. Form IV consists of a herringbone arrangement of dimers, whereas the previously reported form II has parallel dimers. Both crystal structures are sustained by an N-H center dot center dot center dot N hydrogen bond.