Photochemistry of Coordination Compounds. XIII. Photochemical Behavior and Electronic Spectra of Some d⁸ Glycinato Complexes

Abstract

The photochemical behavior of tr~ns-Ni(gly)~.2H~O, trans-Pd(gly)z, and cisand trans-Pt(gly)z has been studied. Ni( gly)~.2HzO, trans-Pd(gly)z, and trens-Pt(gly)e are not appreciably photosensitive to excitation in d-d bands. Pd(g1y)z and trans-Pt(g1y)z are decomposed as a consequence of the excitation in electron-transfer bands.when excited in d-d bands changes into the trans isomer. mp and 0.13 =k 0.01 a t 313 mp. tion of a tetrahedral intermediate. chemical data. transtrans-cis-Pt( gly)z The quantum yields of this photoreaction are 0.12 f 0.01 a t 254 For this photoisomerization an intramolecular mechanism is suggested involving the forma-The ultraviolet spectra of cis-and trans-Pt(g1y)z are discussed on the basis of the photo-Vol. 4 , No. 9, Sepember 1965 PHOTOCHEMISTRY OF COBALT(III)-AMINO ACID COMPLEXES 1247 the cis + trans photoisomerization of Pt(gly)n, in order to explain the lack of the inverse photochemical process, it might be thought that one of the steps of the inverse isomerization is improbable for energetic rea-sons. Such critical steps may be either the passage from the trans triplet excited state to the tetrahedral intermediate state or the passage from the tetrahedral state to the cis triplet excited state.The photochemical behavior of the following complexes has been studied: or-tris( glycinato)cobalt ( 111), p-tris( g1ycinato)- ( 111)3--, and p-tris(g1utamato)cobalt(II1)3-. The solutions of these complexes are very photosensitive (quantum yields 0.16-0.33) to light of 254 and 313 mp wave length, which corresponds to electron-transfer bands, whereas they are only slightly photosensitive t o excitation in d-d bands. Irradiation a t 254 mp leads to the decomposition of the complexes, with production of Co(HzO)sZf ions, amino acids, and amino acid oxidation products. The photochemical behavior of the complexes does not substantially depend on the type of coordinated amino acid or on the geometrical configuration of the complexes. The quantum yield a t 254 mp increases slightly with temperature and is practically independent of the H' concentration of the solution. The nature of the excited states is correlated with their chemical behavior. A mechanism is proposed which interprets the photochemical decomposition as results from excitation a t an electron-transfer band. cobalt(III), a-tris(alaninato)cobalt(III), or-tris(valinato)cobalt(III), or-tris(glutamato)cobalt

Preparation and Characterization of Self-Assembled Polymer−Metal Complex Micelle from cis-Dichlorodiammineplatinum(II) and Poly(ethylene glycol)−Poly(α,β-aspartic acid) Block Copolymer in an Aqueous Medium

“…One is due to the ligand exchange reaction of the Pt(II) complex from chloride or aqua to carboxylate in the PEG−P(Asp) block copolymer. An increase in absorbance at about 250 nm is attributed to the shift of the d−d band in Pt(II), which is hidden by the electron-transfer band (peak maximum <240 nm), based on a change in the crystal field stabilization energy due to ligand substitution in Pt(II) complexes . Actually, it was reported that the ligand substitution reaction between carboxylate and chloride in Pt(II) complex was estimated by the difference in spectrophotometric absorbance based on the d−d band in Pt(II) .…”

Photolysis of methylcobalamin

“…Transition-metal complexes may possess absorption bands of four limiting types, depending on whether the electronic transition (1) is localised on the metal (d-d' transition), (2) is localised on the ligand (e.g., x-x* as in the corrinoids), (3) involves the movement of charge between the metal and ligand (charge-transfer spectra), or (4) where the relevant orbitals in the ground and excited states involve both ligand and metal (e.g., Mn04-). Almost all work on the photochemistry of metal complexes concerns transitions of types (1) and (3) ; see, e.g., the recent reviews by Balzani et aZ., 17 Wehry,l* and Adamson.lg The cobalt (111) corrinoids provide examples of type (2). The only other examples of this type so far established are the iron@) p o r p h y r i n ~.…”

Photochemistry of coordination compounds. XVI. Hexabromoplatinate(IV) and hexaiodoplatinate(IV) ions

“…21•22 Apparatus.-Radiation of 254, 313, and 365 µ wras obtained using the irradiation equipment previously reported. 23 Narrow Photochemistry of Hexahaloplatinate (IV) Ions 355 spectral bands centered at 433 and 530 µ were isolated from a Philips Attralux Spot 150-w incandescent lamp by means of Schott and Gen. interference double filters (Tmnx, 50 and 45%; half-width, 20 and 11 µ, respectively). To reduce heating in the filters 5 ml of CuS04 (4%, w/v) in 0.1 N H2S04 solution was situated facing the lamp.…”