Co-ordination chemistry of higher oxidation states. Part 27. Synthesis, properties, and electrochemistry of some cis-tetrahalogenoiridium(IV) complexes: crystal structure of [Ir(phen)Cl4]

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Abstract
The iridium(IV) complexes cis-[Ir(L–L)Cl4][L–L = MeSCH2CH2SMe, MeSeCH2CH2SeMe, 2,2′-bipyridyl (bipy), or 1,10-phenanthroline (phen)] have been prepared by Cl2 or HNO3 oxidation of the corresponding IrIII anions [Ir(L–L)Cl4]–. Dark green cis-[Ir(L–L)Br4](L–L = bipy or phen) and cis-[Ir(py)2X4](X = Cl or Br) are also described. Iridium(III) complexes [Ir{RTe(CH2)3TeR}Cl4]–(R = Me or Ph), [{Ir[Me2Sb(CH2)3SbMe2]Cl3}n], trans-[Ir(L–L)2Cl2]+[L–L = Ph2PCH2CH2PPh2(dppe), Me2PCH2CH2PMe2(dmpe), or o-C6H4(AsMe2)2], cis-[Ir(phen)2Cl2]+, and some rhodium(III) analogues, [Rh(L–L)Cl4]–(L–L = MeSCH2CH2SMe, MeSeCH2CH2SeMe, or bipy) and trans-[Rh(dppe)2Cl2][Rh(dppe)Cl4], are described, but cannot be oxidised to the MIV state. Complexes have been characterised by i.r., u.v.–visible, n.m.r. (31P, 77Se, and 125Te) spectroscopy, and, for the complex [Ir(phen)Cl4], by X-ray diffraction. Crystals of [Ir(phen)Cl4] are monoclinic, space group P21/c with a= 7.410(8), b= 19.256(4), c= 10.477(4)Å, β= 109.39(6)°, Z= 4, and R= 0.034 for 2 052 reflections. The iridium is six-co-ordinate, Ir–N = 2.042(9), Ir–Cl = 2.298(3)–2.311(3)Å. The u.v.–visible spectra of the iridium(IV) complexes are interpreted in terms of ligand-to-metal charge-transfer transitions and compared with the analogous trans-[IrL2X4]. Electrochemical studies show that for most of the [Ir(L–L)X4]––[Ir(L–L)X4] couples the electron transfer reaction is close to reversible, with formal potentials for the oxidation occurring at more positive values than for the trans-[IrL2X4]––[IrL2X4] analogues. The rhodium(III) anions show completely irreversible oxidation reactions.

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