Structure of a Pt(II)-Pt(IY) Mixed-Valence Linear Chain Complex: Bis (1,2-diaminopropane )platinum(II)bis (1,2-diaminepropane ) - dibromoplatinum(IV)tetraperchlorate

Abstract

<jats:p>[Pt(C<jats:sub>3</jats:sub>H<jats:sub>10</jats:sub>N<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>][Pt(C<jats:sub>3</jats:sub>H<jats:sub>10</jats:sub>N<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>Br<jats:sub>2</jats:sub>](ClO<jats:sub>4</jats:sub>)<jats:sub>4</jats:sub> crystallizes as flat orthorhombic needles with cell dimensions: a = 7.74(1); b = 11.14(2); c = 19.42(3) Å, Z = 1. Since rotation photo­graphs showed diffuse patterns corresponding to odd values of k without any Bragg reflections, the subcell for which b = 5.57(1) Å was adopted for the structural analysis; it has systematic absences consistent with space groups Pc 2 a and Pcma; the structure was refined in both space groups by least squares and difference Fourier syntheses to R = 0.062 in Pc 2a and R = 0.064 in Pcma. A final decision between the two space groups proved to be impossible within the scope of the experiment. An analysis of the “diffuse” layers reveals that the bridging bromines vibrate in a one-dimensional collective mode within a lattice of “uniform”, fixed platinum cations. </jats:p>

Two crystalline modifications of dibromobis(1,2-diaminoethane)platinum(IV) bis(1,2-diaminoethane)platinum(II) tetrakis(perchlorate), [PtBr2(C2H8N2)2][Pt(C2H8N2)2](ClO4)4

“…In particular, no hint of the occurrence of super-reflections was found down to 11 K. These experimental findings suggest that the diffusions in the k-odd layers are caused by a thermally activated movement of the Br-ions along the chain direction. This anisotropic motion may be described as a 'phonon-like' mode (Cannas, Marongiu, Martin & Keller, 1983;Cannas, Marongiu, Keller, Mfiller & Martin, 1984), as 'mobile valence-alternation domain walls' (Ichinose, 1984), or by similiar dynamic models. In any case: a Br--disordered 'time-averaged' picture of the excited states of the crystal is obtained from the X-ray data at room temperature.…”

“…Diffuse patterns, which make the choice of an unambiguous space group more difficult (Beauchamp, Layek & Theophanides, 1982), twinning (Cannas, Marongiu, Keller, Miiller & Martin, 1984) and chiral building blocks (Cannas, Marongiu, Martin & Keller, 1983) are among the difficulties recently discussed in detail. Some of the discrepancies could be resolved by observing the temperature dependence of the 'diffuse patterns' down to 4 K (Cannas, Marongiu, Martin & Keller, 1983;Cannas, Marongiu, Keller, Mfiller & Martin, 1984). On the basis of these data it was proposed that an anisotropic, thermally activated, 'phonon-like' lattice mode-mainly including the chain halides -is responsible for the diffuse patterns.…”

Mixed-valence linear-chain complexes: X-ray structural characterization of a PdII/PdIVBr2 chain and of three mixed-metal chains, [NiPt(en)4Cl2]4+, [PdPt(pn)4Cl2]4+ and [NiPt(pn)4Cl2]4+, all as perchlorate salts

“…For complexes (3) and (4), which also form an isostructural pair, there is again a space-group problem. Matsumoto et al (1978) determined the structure of the analogous Pt"/Pt ~v chloride and assumed the space group P22~2 v Cannas et al (1983) determined the structure of the analogous bromide and found systematic absences consistent with space groups Pba2 or Pbam, but were unable to distinguish between the two. Our results agree with those of Cannas et al (1983) in that the presence of a and b glides is confirmed.…”

“…Matsumoto et al (1978) determined the structure of the analogous Pt"/Pt ~v chloride and assumed the space group P22~2 v Cannas et al (1983) determined the structure of the analogous bromide and found systematic absences consistent with space groups Pba2 or Pbam, but were unable to distinguish between the two. Our results agree with those of Cannas et al (1983) in that the presence of a and b glides is confirmed. Refinement of the structure of complex (3) in Pba2, which requires the metal atom to occupy a site of symmetry 2 and thus restricts the relative conformations of the two pn ligands to be the same, gave a final R value of 0.026.…”

“…Extensive spectroscopic, structural and conductivity studies of complexes with empirical formulae Pt(LL) 2-X(C104) 2 have shown them to be mixed-valence linear-chain semiconductors of the type [Pt(LL)2I-[Pt(LL)2X2](C104) 4, where LL=l,2-ethanediamine (en) or 1,2-propanediamine (pn) and X = CI, Br, or I (Matsumoto, Yamashita, Ueda & Kida, 1978;Cannas, Marongiu, Martin & Keller, 1983;Clark, 1984). These complexes consist of linear chains of nearly planar Pt(LL)2 units which are bridged asymmetrically in the chain direction by halide ions.…”