title: Unprecedented dinuclear Robson type macrocyclic complexes having two +iii metal ions in two compartments and the role of the diimino moiety on the stability of metal ion oxidation states.
abstract: The work in this investigation deals with the syntheses, characterization, crystal structures and catechol oxidase activity of four diphenoxo-bridged Co(III)Co(III) compounds of composition [Co(III)Co(III)L(Me-pn)(N3)4]·6H2O (), [Co(III)Co(III)L(Me-pn)(N3)4]·4H2O (), [Co(III)Co(III)L(Et-pn)(N3)4]·3.5H2O () and [Co(III)Co(III)L(Et-pn)(N3)4]·CH3CN·2.5H2O (), and two diphenoxo-bridged Co(III)Co(II) compounds of composition [Co(III)Co(II)L(Me-Me2pn)(N3)3]·2H2O () and [Co(III)Co(II)L(Et-Me2pn)(N3)3]·H2O (). In these compounds, H2L(Me-pn), H2L(Et-pn), H2L(Me-Me2pn) and H2L(Et-Me2pn) are four Robson type tetraiminodiphenolate macrocyclic ligands, in which the superscript Me and Et indicate that the dialdehyde components are 4-methyl-2,6-diformyl-phenol and 4-ethyl-2,6-diformyl-phenol, respectively, while pn and Me2pn indicate that the diamine components are 1,3-diaminopropane and 2,2-dimethyl-1,3-diaminopropane, respectively. The Co(III)Co(III) compounds are further characterized by (1)H NMR spectra. Compounds and are prepared following a metal-templated synthesis, while compounds and are prepared by direct synthesis, which includes using a pre-isolated macrocycle, [H4L(Me-pn)](ClO4)2/[H4L(Et-pn)](ClO4)2, as a reactant. On changing the diamine component of the corresponding macrocycle from 1,3-diaminopropane to 2,2-dimethyl-1,3-diaminopropane, but otherwise following the similar reaction procedure (both direct and template), the Co(III)Co(II) compounds [Co(III)Co(II)L(Me-Me2pn)(N3)3]·2H2O (), [Co(III)Co(II)L(Et-Me2pn)(N3)3]·H2O (), [Co(III)Co(II)L(Me-Me2pn)(N3)3]·0.5MeCN·0.27H2O (; Inorg. Chim. Acta, 2014, 412, 38) and [Co(III)Co(II)L(Et-Me2pn)(N3)3]·MeCN (; Dalton Trans., 2013, 42, 4561) are formed, rather than Co(III)Co(III) compounds. Like compounds and , all the compounds show catechol oxidase activity (substrate: 3,5-di-tert-butyl catechol). The kinetic parameters for , and have been determined. Their Kcat values are, respectively, 212.6, 188.0 and 191.3 h(-1). ESI-MS (positive) spectra of some representative cases (with and without the substrate) have been recorded and the positive species have been assigned well. Unprecedented and surprising aspects of the composition/structure and properties of the complexes in this investigation have been discussed.
authors.affiliation: Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata 700 009, India. sm_cu_chem@yahoo.co.in.
authors.forename: Leena
authors.initials: L
authors.lastname: Mandal
authors.forename: Sasankasekhar
authors.initials: S
authors.lastname: Mohanta