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Publication costs assisted by the Katholieke Universiteit LeuvenTwo crystal structures of dehydrated NH4-exchanged chabazite crystals were studied by use of single-crystal X-ray diffraction methods after dehydration at 320 "C, and at 600 "C following a steaming period. No significant differences are observed between the two structures; there is no preference of the protons for a single oxygen species nor any indication of A1 removal from the framework after steaming. A strong correlation between T-0-T bond angles and T-0 distances in adjacent tetrahedra shows an identical slope with that of dehydrated H mordenite. The framework oxygens, all pointing either to the hexagonal prisms or to the centers of the framework eight-rings, prohibit the free vibration of OH bonds in the large cavity. This explains the 30 cm-' decrease of the HF bands as compared to the value predicted from the framework composition.

A series of carbonyl derivatives of 5‐imino‐Δ3‐1,2,4‐thiadiazolines has been prepared and shown by X‐ray analysis of a selected example to have a trithiapentalene‐like structure. When diphenylketene was used as acylating reagent, the primary product (14), obtained at room temperature, rearranged on heating in a polar solvent into a Δ2‐thiazolin‐4‐one (15). The structure of 15 has been confirmed by X‐ray analysis, and shown to be a zwitterion. Rearranged products (i.e., 16 and 20‐22) were also obtained when 3 was reacted with dimethyl acetylenedicarboxylate or methanesulfonyl chloride, whereas tosyl chloride gave normal tosylated derivatives (17‐19). The latter have also a nearly linear N‐S…O arrangement, but the interaction between S and O is weak.