The Charge Transfer Spectra of d8 Transition Metal Halide Complexes and the 1849 Å Photolysis of Aqueous PtCl₄²⁻

Abstract

The ultraviolet spectra of the d8 complexes PtX,2-, AuX,-, and Pd2X62-(X = C1-or Rr-) are reported. The assignments are based on a standard ordering of molecular orbital energy levels and on the trends in the band frequencies a s related to the different metals a n d ligands. In addition to the low intensity d-d bands, two distinct high intensity regions are identified, an initial set of charge transfer ligand to metal bands followed by a sequence of essentially d -> p bands. The 1849 A irradiation of aqueous PtCIaZ-results in a redox reaction via photoelectron formation with 4e,,-= 0.25 & 0.02. The primary photolytic act is interpreted as initial excitation of the d -+ p transition 'A,, -> 'E,,(3) (esn* -> ozun*).--- Introduction Following an earlier study of the y-radiolysis of aqueous ~t C 1 2 -(1) some preliminary experiments were carried out to determine the effects of U.V. light on the same system. In addition t o photohydrolysis anticipated from the work of Balzani and Carassiti (2), N, evolution was observed when aqueous PtC142--N,0 solutions were illuminated with 1849 A light. The formation of N,, exclusive of that part emanating from direct photodissociation of N,O, is suggestive of photoelectron formation.Although only a limited number of transition metal complexes have been reported as sources for the photolytic production of hydrated electrons it is possible to identify three common features, these being that the ion used (i) be relatively inert towards cap-, (ii) forms a stable complex of the same stolchiometry and one equivalent higher in oxidation state, and (iii) that the exciting radiation is in the charge transfer region (3). Since PtC1,' -is obviously lacking in the first two characteristics it seemed in prospect that a unifying feature might be revealed in the charge transfer spectrum of PtCI2-. Thus, the present study was prompted both by an inherent interest in the previously uninvestigated spectral region effected by 1849 A light and by the expectation that the resultant data might provide a reasonable basis for rationalizing the short wavelength photochemistry of PtC12-.While there is considerable spectral data available on the low intensity d-d bands (4), only two charge transfer bands appearing as moderately intense overlapping bands centered at about 45 000 cm-' have been reported for PtC14'-. The origin of the two bands have been variously interpreted a s arising from the transitions 'Als -+ 'Azu (bZun + blgo*) and ' A ! , -t 'Eu(l) (eun -, b,,o*) (5, 6) to the combinat~on 'A,,. -, 'A,, + '~~ ( 1 ) for the first band with the h~g h frequency band being due to either 'A!,j 'EU(2) ('euo + bl,o*) or a 5d -t 6p transition (7,8). Neglecting the high energy 3a1,0* orbital, it can be easily shown, using the molecular orbital energy diagram given in Fig. 1, that there are eight fully allowed transitions anticipated for the U.V. spectrum of PtC1,'-.Since only two bands have thus far been reported, the region beyond 45 000 cm-' promised t o be rich in spectral data.In this study an attempt has...

Enhancing Galvanic Replacement in Plasmonic Hollow Nanoparticles: Understanding the Role of the Speciation of Metal Ion Precursors

“…The absorption bands in the near‐infrared and visible regions are typically weak and associated with transitions located on the metal atom (e. g., d‐d transitions), while the ultraviolet bands are more intense and related to charge transfer (CT) transitions (i. e., ligand to metal, LMCT, or metal to ligand, MLCT). For square planar metal halide complexes such as (M=metal and L=halide), two strong absorption bands are anticipated from LMCT involving transitions p σ →d x2‐y2 and, at lower energy, p π →d x2‐y2 and these bands can be used to monitor hydrolysis as their intensity and energy change over time due to ligand exchange. The absorption spectrum of dilute (5× M) in 1 M HCl (to avoid hydrolysis) shown in Figure a displays two absorption bands (315 and 226 nm) corresponding to charge transfer transitions .…”