On, off and intermediate coordination of a bridgehead triarylamine donor in tripodal complexes: Towards the tuning of coordinative bond distance

Abstract

A series of first row transition metal complexes of the tripodal ligand 2,2′,2″/-nitrilotribenzoic acid H3L has been prepared and characterised by X-ray crystallography: Mononuclear [M(L)]- species [Cu(H2O)4]3[Cu(L)(H2O)] 6·25H2O (2), [Co-(H2O) 6][Co(L)(H2O)]·8H2O (4), [Zn(H 2O)6] [Zn(L)(H2O)]·8H2O (5) and a neutral [M(L)] complex [FeIII(L)(H2O) 3]·5H2O (8) are formed as well as dimeric [M(L)]22- species (HNEt3)2[Cu(L)] 2·2CH3CN (1), (HNEt3) 3[Ni(L)]2(ClO4)·H2O (3), (HNEt3)2[FeII(L)]2·2CH 3CN (6) and (HNEt3)2[FeIII2(L)2(μ-O)] (7). The complexes display a unique variation in the M-N distance (2.09 Å for CuII to 3.29 Å for FeIII) to the bridgehead triphenylamine donor and are classified into compounds with "On", "Off" and "Intermediate" N-coordination. The trigonal-bipyramidal coordination polyhedron changes towards tetrahedral in the intermediate and octahedral in the Off-state. The M-N distance of individual complexes is reversibly tuned by external chemical input such as changes of metal ion oxidation state (FeII/FeIII) or variation of the axial coligand as a consequence of solvent or pH variation. Possible reasons for the exceptional tolerance of the M-N bond to distance variations are discussed under consideration of gas phase DFT calculations of [Zn(L)]-.