Schwingungs-und Elektronenspektren der bindungsisomeren Hexakis(thiocyanato(N)-thiocyanato(S))-osmate(III) und (IV) / Vibrational and Electronic Spectra of Bond-Isomeric Hexakis(thiocyanato(N)-thiocyanato(S))osmates(III) and (IV)

Abstract

<jats:title>Abstract</jats:title><jats:p>Well-resolved IR and Raman spectra of the two sets of all 10 isomeric complexes [Os(NCS)<jats:sub>n</jats:sub>(SCN)<jats:sub>6-n</jats:sub>]<jats:sup>3-/2-</jats:sup>, n = 0-6, have been recorded. For both series, ν<jats:sub>CS(N)</jats:sub> &gt; ν<jats:sub>CS(S)</jats:sub> and δ<jats:sub>NCS</jats:sub> &gt; δ<jats:sub>SCN</jats:sub>; for the Os(III) complexes, v<jats:sub>CN(N)</jats:sub> ~ v<jats:sub>CN(S)</jats:sub> and v<jats:sub>OsN</jats:sub> ≥ v<jats:sub>OsS</jats:sub> while for the Os(IV) compounds, v<jats:sub>CN(N)</jats:sub> &lt; v<jats:sub>CN(S)</jats:sub> and v<jats:sub>OsN</jats:sub> ~ v<jats:sub>OsS</jats:sub>. The vibrational spectra of the n = 0 and n = 6 members of both sets are assigned according to D<jats:sub>3d</jats:sub> and O<jats:sub>h</jats:sub> point symmetry, respectively. For the mixed linkage isomers the band pattern is strongly influenced by pseudo-octahedral coupling wherever frequencies of N- and S-bonded groups coincide. The metal-ligand stretching region is therefore assigned according rather to pseudo-O<jats:sub>h</jats:sub>, pseudo-D<jats:sub>3d</jats:sub> and pseudo-D<jats:sub>4h</jats:sub> symmetry than to D<jats:sub>4h</jats:sub>, C<jats:sub>4v</jats:sub>, C<jats:sub>3v</jats:sub> and C<jats:sub>2v </jats:sub>microsymmetry. The charge-transfer spectra of both series are similar, showing a parallel hypsochromic shift with increasing n value. Upon oxidation, a bathochromic shift of the CT bands by an average of 5400 cm<jats:sup>-1</jats:sup> is observed, and the intensity increases by a factor 2-2.5. Weak absorptions in the near infrared region are assigned to intraconfigurational transitions. </jats:p>

Preparation and Spectroscopic Investigations of Mixed Octahedral Complexes and Clusters

“…On tempering of TBA or PPN salts of pure compounds as well as of mixtures of those systems, stepwise rearrangements occur, which result in an increasing amount of complexes with increased numbers of N-bonded thiocyanate ligands. Thus, the respective terminal members of the series are accessible; namely, for Ru n = 5 (TBA salt), n = 6 (PPN salt); Rh n = 4; Os n = 6; and for Ir n = 5. − Clearly, it is important to temper below the melting point, not only to limit decomposition, which can occur at elevated temperatures, but also because mixtures of [M(NCS) n (SCN) 6 - n ] 3- with lower values of n are rearranged or thiocyanate bridged dinuclear complexes are formed during melting…”

“…Suitable techniques for ionic species are ionophoresis as a basic analytical tool 277,278 and DEAE ion exchange column chromatography for larger scale preparations of pure compounds. Through this, the series, [M(NCS) n (SCN) 6 - n ] 3- , M = Ru, n = 1−5; ,,, Rh, n = 0−4; , Os, n = 0−6; − ,, Ir, n = 0−5, have been separated into the individual linkage isomers, or in some cases, into highly enriched stereoisomers. ,,, …”

“…This is true with regard to both the bonding mode of the ambidentate ligand, as well as any systematic trends pertaining to the number n in [M(NCS) n (SCN) 6 - n ] z - systems. Nevertheless, if separation into pure individual species is accomplished, as in the case of the series, [M(NCS) n (SCN) 6 - n ] 3- , M = Ru, n = 1−5; ,,, Rh, n = 0−4; , Os, n = 0−6; − ,, and Ir, n = 0−5, a definitive and consistent characterization by vibrational (IR and Raman) and electronic spectroscopy is possible. For the two series, [Os(NCS) n (SCN) 6 - n ] 3-/2- , n = 0−6, the electrochemical reversibility of all 20 different individual complex ions has been studied by cyclic voltammetry .…”

“…For example, a high-voltage paper ionopherogram of the reaction products of K 3 [RhCl 6 ] with aqueous KSCN, obtained in 1 h, may be more informative than the X-ray structure of K 3 [Rh(SCN) 6 ], since the single crystal measured may be the primary component of the precipitate only because it forms crystals more easily than other species. Another astonishing example of this type of confusion can be found on the X-ray photoelectron spectroscopy of [Os(SCN) 6 ] 3- , in which a 6-fold S-coordinated complex is postulated, although the cited reaction of K 2 [OsCl 6 ] with aqueous KSCN does not yield this species, not even in trace amounts. , …”

Inorganic Metal Thiocyanates

“…139,140 There are no reports of the synthesis of binary Os(NCS)x or Ir(NCS)x though both are likely to be stable in the +3 oxidation state as implied by the existence of molecular [M(NCS) 6 ] 3anions 141,142 I note that Os(NCS) 3 is likely to be the best candidate for a magnetic ReO 3 -structured metal thiocyanate as it has the most extensive linkage isomerism with thiocyanate of any paramagnetic metal. 143 Pd(NCS) 2 , Pt(NCS) 2 and Au(NCS) have all been reported and chemical elemental analysis suggests they are pure phase compounds. Pd(NCS) 2 and Pt(NCS) 2 are reported from the thermal decomposition of M(NCS) 2 (NH 3 ) 2 .…”