Mono- and bidentate imidates of five-coordinate nickel(ii) with macrocyclic ligands: spectroscopic and photophysical properties

Abstract

The hydroxo-complexes [Ni(2)(mcN(3))(2)(mu-OH)](2)(PF(6))(2)] [mcN(3) = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene (Me(3)-mcN(3)) or 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene (Me(4)-mcN(3))] react with imides (Him) in 1 : 2 (succinimide, glutarimide, saccharine and 1,8-naphthalimide) or 1 : 1 (pyromellitic diimide) molar ratio, leading to the formation of the imidate complexes: [Ni(mcN(3))(H(2)O)(Im)](+) (Im = succi, gluti, sac), [Ni(mcN(3))(naphthi)](+) and [Ni(mcN(3))(H(2)O)](2)(mu-pyrdi)](2+). The single crystal structures of [Ni(Me(3)-mcN(3))(H(2)O)(sac)](PF(6)) (3a) and [Ni(Me(4)-mcN(3))(H(2)O)(sac)](sac) (3b) show that, in 3a, sac exhibits a N-monodentate coordination mode, while in 3b the coordination is through oxygen. X-Ray structure of [Ni(Me(4)-mcN(3))(naphthi)](PF(6)) (4b) shows N,O-bonded 1,8-naphthalimidate ligand. The VT (1)H NMR study, carried out on this complex, suggests that the rotation around the Ni-N bond is hindered by ca. 11.6 kcal mol(-1). These species exhibit blue luminescence which arises from a mixed MLCT and LC excited state, and these properties may be useful for structural predictions in the solid state of complexes for which crystal structures have not been established.