<p>A new family of oligonuclear cyano compounds incorporatingtransition (Pt) and main group (Tl) metals bound with anon-buttressed Pt-Tl bond was synthesised in aqueous solution.The metal-metal linkage is formed in the reaction betweenplatinum and thallium in their stable oxidation forms, Pt(II)and Tl(III), or<i>vice versa</i>: Pt(IV) and Tl(I). Four binuclear complexeswith a general composition [(CN)<sub>5</sub>Pt-Tl(CN)<sub>n</sub>(aq)]<sup>n-</sup>(n = 0-3) and a trinuclear species [(NC)<sub>5</sub>Pt-Tl-Pt(CN)<sub>5</sub>]<sup>3-</sup>were identified and structurally characterised insolution by multinuclear NMR, EXAFS and vibrationalspectroscopy. In aqueous solution the complexes exist inequilibrium. The distribution between the species can bealtered by varying the molar ratio Pt/Tl, cyanide concentrationand pH. Stability constants of the compounds weredetermined.</p><p>A new compound (NC)<sub>5</sub>PtTl was also prepared in solid and its crystalstructure solved by a combination of X-ray powder diffractionand EXAFS. Altogether the values of<sup>195</sup>Pt-<sup>205</sup>Tl spin-spin coupling constants (25-71 kHz),interatomic Pt-Tl distances (2.598-2.638 Å), and vibrationstretching frequencies v (Pt-Tl) (159-164 cm<sup>-1</sup>) are fully indicative of a direct and unsupportedPt-Tl bond. The calculated values of Pt-Tl force constants(1.56-1.74 N· cm<sup>-1</sup>) are characteristic for single metal-metal bond.The oxidation status in the compounds can be viewed asintermediate between II and IV for platinum, and between I andIII for thallium, as reflected by the chemical shifts of<sup>195</sup>Pt and<sup>205</sup>Tl nuclei, C≡ N stretching frequencies andelectron binding energies.</p><p>The compounds are capable to undergo a photoinducedtwo-electron transfer between the coupled hetero-metal ions.Upon irradiation into the metal-to-metal charge transferabsorption band, effective photoredox reaction takes place. Itresults in scission of the Pt-Tl bond and formation of variouscomplexes of oxidised platinum (Pt(III, IV)) and reducedthallium (Tl(I)). The values of photodecomposition quantumyields were determined from a stationary photolysis study ofthe heterometallic complexes. Nanosecond laser flash photolysisof the heteronuclear Pt-Tl cyano compounds was performed in thetimescale range 1· 10<sup>-6</sup>- 5· 10<sup>-2</sup>s and several intermediate species were detectedand characterised by optical spectroscopy.</p><p>The heteronuclear Pt-Tl cyano compounds can be furthermodified in terms of their stability, solubility, and lightabsorption characteristics. It has been found that the platinumpentacyano unit of the [(NC)<sub>5</sub>Pt-Tl(CN)<sub>n</sub>(aq)]<sup>n-</sup>species is inert towards the tested ligands,whereas the thallium "part" of the complexes can be tunedsignificantly. A number of complexes [(NC)<sub>5</sub>Pt-Tl(L)<sub>m</sub>]<sup>x-</sup>(L-ligand) were prepared and characterised insolution. Compounds [(NC)<sub>5</sub>Pt-Tl(nta)(H<sub>2</sub>O)]<sup>3-</sup>, [(NC)<sub>5</sub>Pt-Tl(bipy)(DMSO)<sub>3</sub>], and [(NC)<sub>5</sub>Pt-Tl(bipy)<sub>2</sub>]have been prepared in solid and their structuresdetermined by single-crystal X-ray diffraction.</p><p><b>Keywords:</b>thallium, platinum, cyanide, metal-metal bond,non-buttressed, heterobimetallic, photoinduced, electrontransfer, redox reaction, NMR, chemical shift, spin-spincoupling constant, Raman, EXAFS, X-ray diffraction,equilibrium, oxidation state, oxidative addition,photolysis</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:kth-3174 |
| Date | January 2001 |
| Creators | Maliarik, Mikhail |
| Publisher | KTH, Chemistry, Stockholm : Kemi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Trita-OOK, ; 1063 |
Page generated in 0.0025 seconds