Redox state switching of transition metals by deprotonation of the tridentate ligand 2,6-bis(imidazol-2-yl)pyridineElectronic supplementary information (ESI) available: Fig. S1: ORTEP view of the [Mn(1)2]2+ solvated complex. Fig. S2: ORTEP view of the [Mn(1)2]2+ non-solvated complex. Fig. S3: ORTEP view of the [Co(1 ? 2H)2]? complex. See http://www.rsc.org/suppdata/dt/b3/b313440g/

The chemistry of the ligand 1, 2,6-bis(imidazol-2-yl)pyridine with manganese, cobalt, nickel and ruthenium has been investigated. The ligand binds as a meridional tridentate ligand as shown by the crystal structures of [Mn(1)2](CF3SO3)2 x Et2O and [Ru(1)2](PF6)2 x 2CH3CN x H2O. The coordinated ligand is deprotonated in mildly basic solution, and this leads to a drop in the metal M(III)/M(II) reduction potential for cobalt and ruthenium of roughly 1.3 V. The crystal structure of Na2(PPN)[Co(1 - 2H)2]2(OH) x MeOH x 2H2O confirms the deprotonation and shows sodium to bind to the deprotonated nitrogen atoms. No stabilisation of the M(III) oxidation state was observed for nickel and manganese.