Synthesis, luminescence, and electrochemical studies of a new series of octanuclear ruthenium(ii) complexes of tolylterpyridine appended calixresorcarenes

Abstract

A new series of octanuclear Ru(II) complexes of tolylterpyridine appended calixresorcarenes [{Ru(ttpy)}₈(L1)](PF₆)₁₆ (4), [{Ru(ttpy)}₈(L2)](PF₆)₁₆ (5), and [{Ru(ttpy)}₈(L3)](PF₆)₁₆ (6) [L1 = 2,8,14,20-tetraethyl-4,6,10,12,16,18,22,24-octa(4′-p-benzyloxy-(2,2′:6′,2′′-terpyridinyl))calix[4]resorcarene; L2 = 2,8,14,20-tetraphenyl-4,6,10,12,16,18,22,24-octa(4′-p-benzyloxy-(2,2′:6′,2′′-terpyridinyl))calix[4]resorcarene; and L3 = 2,8,14,20-tetra-p-tolyl-4,6,10,12,16,18,22,24-octa(4′-p-benzyloxy-(2,2′:6′,2′′-terpyridinyl))calix[4]resorcarene] have been synthesized and characterized. The tetraethyl-, tetraphenyl-, and tetra-p-tolylcalixresorcarenes (1), (2), and (3), respectively, are characterized by single crystal X-ray diffraction: (1) a = 13.5771(4) Å, b = 7.9566(3) Å, c = 18.3912(6) Å, α = γ = 90°, β = 103.146(2)°, V = 1934.69(11) ų, Z = 2, monoclinic, P2/n; (2) a = 11.9710(8) Å, b = 12.7057(9) Å, c = 13.8570(9) Å, α = 94.731(2)°, β = 108.558(2)°, γ = 106.657(2)°, V = 1878.9(2) ų, Z = 1, triclinic, P; and (3) a = 26.076(3) Å, b = 20.056(2) Å, c = 16.0193(19) Å, α = γ = 90°, β = 116.056(3)°, V = 7526.3(14) ų, Z = 4, monoclinic, C2/c, respectively. The octanuclear complexes 4–6 are nonluminescent at 298 K, but exhibit ³MLCT luminescence at 654, 649, and 646 nm, respectively, at 77 K in acetonitrile. In the solid state at 298 K they exhibit ³MLCT luminescence at 658, 658, and 665 nm, respectively. The complexes exhibit a monoexponential decay profile in acetonitrile and in the solid state at 298 K. The redox active hosts 4–6 containing eight [Ru(ttpy)₂]²⁺ moieties undergo quasireversible one-electron oxidation at 1.25, 1.26, and 1.25 V versus Ag/Ag⁺, respectively, in acetonitrile. The study demonstrates the versatility of the octanucleating calixresorcarene based ligands L1, L2, and L3 in forming octanuclear Ru(II) complexes.