Iridium thioether chemistry: the synthesis and structures of [IrL2][PF6]3 and [IrHL2][PF6]2(L = 1,4,7-trithiacyclononane)
Abstract
Reaction of [{IrCl(C8H14)2}2] with 4 molar equivalents of 1,4,7-trithiacyclononane (L) in water–methanol (2 : 1, v/v) in the presence of HBF4 affords the iridium(III) hydrido complex [IrHL2]2+. The complex [IrHL2][PF6]2·2MeNO2 crystallises in the monoclinic space group Cc, a= 19.456 0(17), b= 8.152 5(9), c= 21.935(3)Å, β= 117.008(7)°, and Z= 4. The single-crystal X-ray structure of the complex shows one L ligand bound facially to IrIII, Ir–S(1)(trans to H) 2.476(5), Ir–S(4) 2.298(5), Ir–S(7) 2.321(5)Å, with the second L bound as a bidentate ligand through only two S donors, Ir–S(11) 2.344(5), Ir–S(41) 2.319(5)Å; the dangling donor S(71) lies 4.329(6)Å from the iridium centre. The sixth co-ordination site is taken up by a hydride, Ir–H 1.58(6)Å. Treatment of [IrHL2][PF6]2 with aqueous HNO3 affords the homoleptic thioether complex [IrL2]3+. The complex [IrL2][PF6]3·5MeNO2 crystallises in the monoclinic space group C2/c, a= 8.581 7(13), b= 21.338(4), c= 23.482(7)Å, β= 90.94(2)°, and Z= 4. The single-crystal X-ray structure of the complex confirms homoleptic hexathia co-ordination at a centrosymmetric, octahedral iridium(III) centre, Ir–S(1) 2.342(3), Ir–S(4) 2.341(3), Ir–S(7) 2.338(3)Å. The redox properties of [IrL2]3+ are discussed and compared to those of the rhodium(III) analogue [RhL2]3+. Spectroelectrochemical measurements using a u. v. –visible optically transparent electrode system confirm the isosbestic and reversible interconversion of [RhL2]3+, [RhL2]2+, and [RhL2]+.