Co-ordination compounds on the surface of laponite: tri-2-pyridylamine complexes
Abstract
Freshly prepared [Co(tripyam)2](ClO4)2(tripyam = tri-2-pyridylamine) contains some low-spin isomer (2E ground state)‘frozen’ into the solid; this reverts to the 4T form over 3 months. Ion exchange of orange [Co(tripyam)2]2+ from aqueous solution onto laponite gives a pink clay, the exchanged cation being [Co(tripyam)2(H2O2)]2+ with bidentate pyridylamine ligands. Isomeric [Cu(tripyam)2](ClO4)2(tridentate ligands) and [Cu(tripyam)2(ClO4)2](bidentate ligands) are absorbed onto laponite as [Cu(tripyam)2(H2O)2]2+ with bidentate ligands; however, the copper clay is thermochromic undergoing a reversible change from green to blue at 100 °C. The temperature of the colour change may be increased by employing copper(II) complexes of substituted tri-2-pyridylamines. The thermochromism is a function of the variable denticity of the ligands.
Orange [Co(tripyam)2]2+(terdentate ligands) may be exchanged using a novel microwave method which accelerates the ion-exchange reaction, but not the aquation reaction; however, over 1 year the sorbed complex aquates to [Co(tripyam)2(H2O)2]2+. Although low-spin [Fe(tripyam)2]2+(terdentate ligands) is stable on laponite, in general the clay surface has greater affinity for the bis(bidentate) complex species.
Cyclic voltammetric studies of acetonitrile solutions show an order of ease of oxidation of cobalt(II) Complexes: [Co(bipy)3]2+ > [Co(6-dmdpa)2]2+ > [Co(tripyam)2]2+ where bipy = 2, 2′-bipyridyl and 6-dmdpa =(6-methyl-2-pyridyl)-di-(2-pyridyl)amine. Clay(laponite)-modified platinum electrodes dipped into acetonitrile solutions of [Co(bipy)3]3+ or [Co(tripyam)2]2+ give very similar E1/2 values to those obtained for the free complexes in acetonitrile solution. However, electrodes prepared from laponite pre-exchanged with pink [Co(tripyam)2(H2O)2]2+or [Co(bipy)3]3+ were rigorously electro-inactive.
Please wait while we load your content...
