Properties and single-crystal X-ray structure of Bis[3,3″-bis(4-methylphenyl)-2,2′:6′,2″-terpyridine]iron(II) hexafluorophosphate–acetonitrile–diisopropyl ether (1/1.5/1)

Abstract

Absorption and electrochemical properties are reported for the iron(II) complex of the unusually substituted ligand 3,3″-bis(4-methylphenyl)-2,2′:6′,2″-terpyridine, along with the structure determination of the complex by single-crystal X-ray crystallography. Crystal data for C₆₇H_64.5F₁₂FeN_7.5OP₂, M 1336.6: triclinic, a 12.768(3), b 15.789(4), c 17.160(4) Å, α 85.553(6), β 77.756(6), γ 66.754(5)˚, V 3106.1(12) ų, space group P 1, Z 2, ρ 1.43 g cm^–3, µ 0.30 mm^-1 for &lgr; 0.6849 Å, R 0.091 for 4456 observed (I > 2σ(I) ) reflections, wR₂ 0.241, Δρ1.68 e Å^–3. The structural analysis reveals that, as observed in analogous bisterpyridineiron(II) complexes, the ligands adopt the preferred meridional binding motif. As a result, the ‘pulling-in’ of the outer pyridine rings forces each pair of 3,3″ substituted tolyl groups to diverge, resulting in an average distance between the tolyl methyl groups of c. 11.6 Å. The cyclic voltammetery of the complex in MeCN displays upon oxidative scanning a reversible one-electron wave (E˚ = + 0.99 V v. s.c.e.) and three one-electron waves under reducing conditions (E₁˚ = –1.27 V, E₂˚ = –1.51 V, E₃˚ = –1.96 V v. s.c.e.). The electronic spectrum in acetonitrile contained an MLCT band centred at 571 nm, with a molar absorption coefficient of 18210 M^–1 cm^–1. When compared to similar phenyl-substituted terpyridine ligand iron(II) complexes this is a relatively low value and is assigned to reduced electronic delocalization throughout the terpyridine backbone.