Compounds of the invention are of the formula (I); wherein: is a double bond and X is C; or is a single bond and X is N, CH or CQR1; and wherein: n is 1 to 10; R is H or QR1; each R′ is independently selected from H and QR1; each Q is independently selected from a bond, CO, NH, S, SO, SO2 or O; each R1 is independently selected from C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, substituted or unsubstituted aryl or heteroaryl, acyl, C1-C10 cycloalkyl, halogen, C1-C10 alkylaryl or C1-C10 heterocycloalkyl; L is a nitrogen-containing heteroaryl; and W is a zinc-chelating residue; or a pharmaceutically acceptable salt thereof. The compounds are useful in therapy.