Synthesis, luminescence, and electrochemical studies of tetra- and octanuclear ruthenium(ii) complexes of tolylterpyridine appended calixarenes

Abstract

Tetra- and octanuclear Ru(II) complexes of tolylterpyridine appended calixarenes, [{Ru(ttpy)}₄(L¹)](PF₆)₈ (3) and [{Ru(ttpy)}₈(L²)](PF₆)₁₆ (4) [L¹ = 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra(4′-p-benzyloxy-(2,2′:6′,2′′-terpyridinyl))calix[4]arene; L² = 5,11,17,23,29,35,41,47-octa-tert-butyl-49,50,51,52,53,54,55,56-octa(4′-p-benzyloxy-(2,2′:6′,2′′-terpyridinyl))calix[8]arene; and ttpy = 4′-(p-tolyl)-2,2′:6′,2′′-terpyridine] have been synthesized and characterized. 5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetrahydroxycalix[4]arene (1) was characterized using single crystal X-ray diffraction, whereas 5,11,17,23,29,35,41,47-octa-tert-butyl-49,50,51,52,53,54,55,56-octahydroxycalix[8]arene (2) was characterized using NMR and mass spectrometry. The tetra- and octanuclear complexes 3 and 4 are nonluminescent at 298 K, but exhibit ³MLCT emission at 650 nm at 77 K in acetonitrile. In the solid state at 298 K they exhibit ³MLCT emission at 663 and 666 nm, respectively. The polynuclear complexes 3 and 4 containing four and eight [Ru(ttpy)₂]²⁺ moieties undergo one-electron oxidation at 1.27 and 1.25 V versus Ag/Ag⁺, respectively, in acetonitrile. This study demonstrates the versatility of the tolylterpyridine appended calix[4]arene and calix[8]arene in forming polynuclear Ru(II) complexes.