The syntheses, structures, and electronic and resonance-Raman spectroscopy of halogen-bridged platinum(II,IV) chain complexes involving equatorially co-ordinated terdentate amines: X- ray crystal structure of [PtII(Me-dien)I][PtIV(Me-dien)I3]I2, and spectroscopy of [PtII(dien)(NO2)][PtIV(dien)(NO2)Br2]Br2

Abstract

Three chain platinum(II,IV) complexes of the type [PtL₃X][PtL₃XY₂]Z₂(L₃= terdentate ligand, X = halogen or NO₂^–, Y = halogen, Z = monoanion) have been synthesised. Two of these have been studied in detail, one by X-ray and the other by spectroscopic methods. The first, [Pt(Me-dien)I]-[Pt(Me-dien)I₃]I₂(Me-dien =N-methyldiethylenetriamine), has been found to crystallize in the monoclinic space group P2₁/n, with a= 19.830(8), b= 12.220(5), c= 11.079(6)Å, β= 96.49(4)°, and Z= 4. Refinement on 1 543 independent reflections led to a final R value of 0.043. The Pt–I chain distances are 2.679(3) and 2.691(3)Å(Pt^IV) and 3.443(3) and 3.560(3)Å(Pt^II) the chain deviating substantially at iodine and platinum(II) from linearity [Pt^IV–I–Pt^II= 150.5(1) and 149.1(1)°; I–Pt^II-I = 162.8(1)°], but not at platinum(IV)[I–Pt^IV–I = 179.4(1)°]. The second complex studied in detail, [Pt(dien)(NO₂)][Pt(dien)(NO₂) Br₂] Br₂(dien = diethylenetriamine), was found to yield a very intense resonance-Raman spectrum, the principal observed progression being v₁ν₁, where ν₁(181.5 cm^–1) is the symmetric stretching mode of the chain, ν_sym(Br–Pt^IV–Br). Analysis of these data yields ω₁ and x₁₁ values of 181.9 and –0.2 cm^–1, respectively. Further, much weaker, progressions of the sorts v₁ν₁+ν_sym(NO₂)(to v₁= 5) and v₁ν₁+δ_sym(NO₂)(to v₁= 4) were also detected. The results add substantially to the few previously known data on halogenbridged mixed-valence chain complexes of platinum in which each unit carries a single positive charge.