Compounds of formula (I) and salts are provided: wherein R4 is fluoro, R5 is selected from hydrogen, halogen, cyano, C1-6alkyl, C1-6alkyl substituted with one or more fluorine atoms, C1-6alkoxy, and C1-6alkoxy substituted with one or more fluorine atoms; and R6 is selected from halogen, cyano, C1-6alkyl, C1-6alkyl substituted with one or more fluorine atoms, C3-6cycloalkyl, C3-6cycloalkyl substituted with one or more fluorine atoms, C1-6alkoxy and C1-6alkoxy substituted with one or more fluorine atoms, and Q is hydrogen or C1-6alkyl. The compounds are expected to be useful for therapy, for example in the treatment of psychotic disorders and cognitive impairment.