containing 1 2 or 3 heteroatoms selected from n o se or s wherein each u03c0 b and u03c0 c is independently optionally substituted with one or more ring substituents as defined herein suitably each u03c0 b is a 6 membered aryl ring in another embodiment when taken in combination each u03c0 b and r independently forms a moiety u03c0 bc selected from moieties u03c0 bc1 u03c0 bc2 u03c0 bc3 and u03c0 bc4 are directly bonded to 1 or 2 boron atoms via either or both nitrogen atoms respectively moieties u03c0 bc1 u03c0 bc2 u03c0 bc3 and u03c0 bc4 are directly bonded to 1 or 2 u03c0 a moieties via either or both c and moieties u03c0 bc1 u03c0 bc2 u03c0 bc3 and u03c0 bc4 are each independently optionally substituted with one or more ring substituents as defined herein it will be understood that for u03c0 bc moieties having two n atoms either or both of the n atoms may form a dative bond to boron it will be further understood that where the u03c0 bc moieties are linked by c to only one u03c0 a moiety such u03c0 bc moieties may i be substituted at the other c by any ring substituent defined herein or ii be linked at the other c to another moiety of formulae i to v in any manner described herein suitably when taken in combination each u03c0 b and u03c0 c independently forms a moiety u03c0 bc selected from wherein moieties u03c0 bc1 u03c0 bc2 and u03c0 bc4 are each independently optionally substituted with one or more ring substituents as defined herein more suitably when taken in combination each u03c0 b and u03c0 c independently.