. . "ve as comprising an optionally substituted aryl or heteroaryl group, optional substituents include halogen, especially fluorine, chlorine and bromine atoms, and nitro, cyano, amino, hydroxy, phenoxy, C.sub.1-4-alkyl, C.sub.1-4 -alkoxy, C.sub.1-4 -haloalkyl, C.sub.1-4 -haloalkenyl, C.sub.1-4 -haloalkoxy, C.sub.1-4 -haloalkylthio, C.sub.1-4 -alkylsulfonyl and halosulfanyl groups such as SF.sub.5." . . . .