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Re(CO)5Cl reacts with salophenH2 to yield Re(I)2(salophenH)(CO)6Cl. A crystal structure determination has shown that this binuclear complex contains two Re(CO)3 fragments which are bridged by a chloride and a heavily constrained salophenH– anion as ligands. Under ambient conditions in solution and in the solid state, the complex displays an orange emission which originates from the lowest-energy IL/MLCT triplet. In solution, this phosphorescence is completely quenched by oxygen. [ABSTRACT FROM AUTHOR]

The salts (NnBu4)[Zn(caffeine)Cl3] and (AsPh4)[Pt(caffeine)Cl3] were prepared and their crystal structures determined by single crystal X-ray diffraction. The free ligand caffeine, as well as the complex anions [M(II)(caffeine)Cl3]− with M = Zn and Pt show an absorption spectrum with an intense band at λmax = 275 nm, which is attributed to an IL π–π* transition of the caffeine. A second band at ca. 300 nm is much weaker and largely obscured by the π–π* band. This second band is assigned to an IL n–π* transition. Both complex anions exhibit a photoluminescence (fluorescence), which originates from the n–π* state. The position of the n–π* state is recognized by the excitation band which distinctly overlaps with the fluorescence band. [ABSTRACT FROM AUTHOR]

The salts (NnBu4)[Zn(caffeine)Cl3] and (AsPh4)[Pt(caffeine)Cl3] were prepared and their crystal structures determined by single crystal X-ray diffraction. The free ligand caffeine, as well as the complex anions [M(II)(caffeine)Cl3]− with M = Zn and Pt show an absorption spectrum with an intense band at λmax = 275 nm, which is attributed to an IL π–π* transition of the caffeine. A second band at ca. 300 nm is much weaker and largely obscured by the π–π* band. This second band is assigned to an IL n–π* transition. Both complex anions exhibit a photoluminescence (fluorescence), which originates from the n–π* state. The position of the n–π* state is recognized by the excitation band which distinctly overlaps with the fluorescence band. [ABSTRACT FROM AUTHOR]

The salt [NHEt3][Re(I)(quinaldate)(CO)3Cl] was obtained by the reaction of Re(CO)5Cl with quinaldic acid and triethylamine in toluene. The crystal structure analysis of this salt revealed the presence of the complex anion [Re(quinaldate)(CO)3Cl]−, with the d6 Re(I) metal center in a pseudo-octahedral environment. The electronic spectra in absorption and emission exhibit bands which are attributed to quinaldate IL and CT transitions at comparable energies. The longest-wavelength emission originates from a Re(I) to quinaldate MLCT triplet, which can be quenched in solution by oxygen or triethylamine. [ABSTRACT FROM AUTHOR]

The salt [Rh(III)(phpy)2(dtoxa)]Cl with phpy = 2-(2-pyridyl)phenyl anion and dtoxa = dithiooxamide has been characterized by its crystal structure and its electronic spectra. Since Rh(III) is rather redox-inert, the lowest-energy excited state of the complex cation is of the IL (dtoxa) type. In the solid state as well as in solution the complex is luminescent and displays a dtoxa IL phosphorescence at λmax = 607 nm with φϕ = 10−3 and τ = 3.7 ns in CH2Cl2. [ABSTRACT FROM AUTHOR]

The complex Ag(I)(flavonolate)(PPh3)2 has been prepared and characterized including the crystal structure. This compound shows in degassed solution two emission bands, a fluorescence at λmax=505 nm and a phosphorescence at λmax=780 nm. Both emissions originate from lowest-energy flavonolate intraligand excited singlet and triplet states, respectively. In the presence of oxygen, the phosphorescence disappears and the complex becomes light-sensitive. The flavonolate ligand undergoes a photooxidation by oxygen. [ABSTRACT FROM AUTHOR]

The binuclear complex Re(I)2(μ-4,4′-bipyridine)(8-quinolinolato)2(CO)6 has been prepared and characterized including the crystal structure. This complex shows, dependent on the conditions, three emissions, which originate from the quinolinolate IL excited state (fluorescence and phosphorescence) and from a Re(I) to 4,4′-bipyridine MLCT state (phosphorescence). [ABSTRACT FROM AUTHOR]

Baltic amber shows a greenish photoluminescence upon UV illumination. When amber is dissolved in organic solvents such as ethanol, an emission spectrum is observed, which resembles that of pyrene. At higher concentrations, pyrene undergoes an aggregation, which shifts the emission to longer wavelength. In solid amber, an analogous aggregation apparently takes place. Depending on the size of the solid amber particles, a bluish (λmax = 450 nm) to greenish (λmax = 480 nm) luminescence appears. [ABSTRACT FROM AUTHOR]

Pyridoxal (vitamin B 6 aldehyde) thiosemicarbazone (B 6 TSC) is deprotonated to its anion (B 6 TSC – H + ) in basic solution at pH = 9. It shows an intense green fluorescence with λ max = 500 nm and a quantum yield of unity. Zn(II)(B 6 TSC – H + )(acetate) displays an blue-green intraligand (B 6 TSC) fluorescence of moderate intensity. The complex cation [Pt(II)(B 6 TSC)Cl] + is isolated as tetraphenylborate. In basic solution (pH = 9) this cation is deprotonated to the neutral complex [Pt(II)(B 6 TSC – H + )Cl] which exhibits the same green intraligand fluorescence as the free anion (B 6 TSC – H + ) − . However, in the platinum complex this emission is much less intense. It is reduced to φ = 10 − 2 . [ABSTRACT FROM AUTHOR]

The complex (IPr)Cu(I)Cl with IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene shows a luminescence in the UV (λ max = 375 nm) in solution and in the solid state (λ max = 347 nm). This emission is suggested to originate from a MLCT triplet. [ABSTRACT FROM AUTHOR]

The electronic spectra of the complexes M(III)(oxinate) 3 with M = Fe, Ru, Os and oxinate = 8-quinolinolate are dominated by oxinate to M(III) LMCT transitions. Nevertheless, these complexes are also characterized by a fluorescence at higher energies, which originates from the oxinate ligands. This green luminescence appears in solution as well as in the solid state under ambient conditions. The electronic coupling between the IL and the LMCT states is apparently not strong enough to lead to a complete quenching of the oxinate IL fluorescence. [ABSTRACT FROM AUTHOR]

The complex Cu(I)(PPh 3 ) 2 (oxinate) with oxine = 8-quinolinole is luminescent under ambient conditions. In the solid state it shows an emission which originates from the lowest-energy oxinate ILCT state. It consists of a fluorescence and a phosphorescence. In solution saturated with argon, a single broad emission band appears which seems to be composed of a more intense fluorescence and a much weaker phosphorescence at longer wavelength. If this solution is saturated with air, the complete emission band becomes less intense. This is quite surprising, since the oxinate ILCT fluorescence of other oxinate complexes is not quenched by oxygen. It is conceivable that the fluorescence largely consists of a delayed fluorescence. When the emitting triplet is depopulated by a thermally activated transition to the fluorescent singlet, both emissions, the delayed fluorescence and the phosphorescence, may undergo a luminescence quenching. For a simple comparison, the photoluminescence of Ag(PPh 3 ) 2 (oxinate) was also briefly examined. The absorption and emission spectra of this silver complex in solution at r.t. resemble those of the copper complex. [ABSTRACT FROM AUTHOR]

In basic solution the complex Re(I) [bipy(OH)2] (CO)3Cl with bipy(OH)2 = 3,3'-dihydroxy-2,2'-bipyridine is deprotonated at one of the phenolic OH substituents. Upon irradiation of the anion {Re[bipy(OH)(O)] (CO)3Cl}- the yellow solution becomes reddish brown. It is suggested that the photolysis is associated with an isomerization at the chelate from N,N to N,O coordination. [ABSTRACT FROM AUTHOR]

In analogy to peroxide, disulfide is an oxidant as well as a reductant. Accordingly, as a ligand of a reducing metal center, low-energy MLCT transitions can occur, while with oxidizing metals low-energy LMCT transitions should be observed. Such MLCT and LMCT excitations are expected to induce redox reactions. The complexes [CpFe(II)(CO) 2 ] 2 μ-S 2 (Cp C 5 H 5 ) and {[Fe(III)(CN) 5 ] 2 μ-S 2 } 6 − are suitable examples to explore this behavior. [ABSTRACT FROM AUTHOR]

Riboflavin reacts with Pt(C 6 H 5 CN) 2 Cl 2 in acetic acid to yield insoluble [Pt(riboflavin) 4 ]Cl 2 . This brown compound shows a bright yellow-orange photoluminescence with λ max = 635 nm. This emission is suggested to originate from the lowest-energy IL (riboflavin) triplet. This assignment is based on the comparison to the photoluminescence of solid riboflavin which exhibits a fluorescence as well as a phosphorescence, again under ambient conditions. [ABSTRACT FROM AUTHOR]

The complex Pt(II)(PPh 3 ) 2 (C 6 O 6 ) was prepared by the reaction of Ag 2 C 6 O 6 with cis-Pt(PPh 3 ) 2 Cl 2 in acetonitrile. Pt(PPh 3 ) 2 (C 6 O 6 ) is characterized by a lowest-energy IL (rhodizonate) excited state. The complex shows an IL fluorescence, but is also photoactive. The photolysis leads to the conversion of rhodizonate to croconate in the coordinated state: Pt(II)(PPh 3 ) 2 (C 6 O 6 ) → Pt(II)(PPh 3 ) 2 (C 5 O 5 ) + CO. [ABSTRACT FROM AUTHOR]

The Lewis base–Lewis acid adducts with the Lewis bases pyrazine, triphenyphosphine, neocuproine (2,9-dimethyl-1,10-phenanthroline), cuproine (2,2′-diquinolyl) and triphenylborane as Lewis acid were prepared. Their electronic spectra are characterized by low-energy electronic transitions which are attributed to phenyl (BPh 3 ) to Lewis base, ligand to ligand charge transfer (LLCT) transitions. These Lewis base-BPh 3 complexes display a distinct blue to green fluorescence in solution which originates from the lowest-energy LLCT singlets. [ABSTRACT FROM AUTHOR]

The complex Fe(II)(binap)Cl 2 with binap = 2,2′-bis(diphenylphosphino)-1,1′-binaphtyl shows an intraligand phosphorescence in the solid state under ambient conditions. Surprisingly, low-energy LF (ligand field) excited states do not quench this emission. Tetrahedral Fe(II) complexes are d 6 high-spin complexes with a quintet ground state and a quintet state as the only LF excited state. However, this excited quintet is so low in energy that it may not be able to interfere with the observed phosphorescence. This apparently applies to Fe(binap)Cl 2 which shows its LF absorption at λ max = 3100 nm and IL phosphorescence at λ max = 505 nm. It is anticipated that the present report will stimulate more studies of this subject. [ABSTRACT FROM AUTHOR]

Complexes of the type [Rh II 2 (CO 3 ) 4 (H 2 O)L] n − with L = N-methylpyrazinium + and 1-heptyl-4-(4-pyridinyl)pyridinium + cations display intense long-wavelength (Rh(II) to L) MLCT absorptions. With L = H 2 O, MLCT absorptions are not identified, but the photoreactivity of the complex in aqueous solution supports the assumption that (Rh(II) to CO 3 2 − ) MLCT excited states are accessible. Upon irradiation with white light, Rh(II) is photooxidized while carbonate is reduced to CO. The efficiency of this photolysis is very low. However, the occurrence of this photoredox reaction is, nevertheless, of general interest with regard to the photochemical reduction of CO 2 . [ABSTRACT FROM AUTHOR]

The complexes [Re I (L–L)(CO) 3 Cl] with L–L = lumazine and folic acid were prepared and their electronic spectra were measured. The free ligands L–L, as well as both complexes, show an emission which is attributed to the fluorescence of L–L. This luminescence is apparently facilitated by excited state proton transfer. [ABSTRACT FROM AUTHOR]

Abstract: The setting of gypsum plaster can be monitored by luminescence rigidochromism. The progress of the setting process which is accompanied by hardening is indicated by a blue shift of the phosphorescence of a suitable water soluble rhenium complex. This rigidity increase of the plaster/water mixture takes place in two phases. In the beginning the rigidity increase is rather large while in the second much longer phase it is relatively small. The addition of a plasticizer (or retarder) keeps the rigidity smaller in the beginning, but only slightly affects the final rigidity of the set plaster. [Copyright &y& Elsevier]

Abstract: Coordination compounds, which simultaneously contain a reducing and an oxidizing ligand are frequently characterized by low-energy LLCT transitions. In suitable cases, CT interactions between such donors and acceptors may also occur in purely organic molecules. In particular, certain zwitterions have been known for many decades to display CT bands in their absorption spectra. In the present review the close relationship between such zwitterions and metal complexes with low-energies LLCT transitions is illustrated by suitable examples. Moreover, in some cases the zwitterions themselves serve as ligands. The CT properties of these zwitterions are preserved but modified by coordination. Some examples of ILCT transitions of this type are discussed in the second part of our report. [Copyright &y& Elsevier]

Abstract: Generally, metal-centered ff states dominate the discussion of the excited state properties of lanthanide complexes. In particular, the luminescence properties of Eu(III) and Tb(III) compounds have been studied in great detail for many decades. However, other types of excited states such as MC fd, MLCT, LMCT, MMCT and IL are also of interest. In this context, we have recently examined the excited state behavior of selected Ce(III), Ce(IV), Eu(II) and Gd(III) complexes which are luminescent and/or photoreactive. [Copyright &y& Elsevier]

Abstract: Peroxide is a reductant as well as an oxidant. It follows that O2 2− as a ligand can serve as CT donor, but also as CT acceptor. In combination with oxidizing and reducing metals low-energy ligand-to-metal (LMCT) and metal-to-ligand (MLCT) transitions, respectively, occur. Photoredox reactions originating from such LMCT and MLCT excited states are well known. In the case of diperoxo complexes M(O2)2, peroxide intraligand transitions play an important role. IL excitation is followed by interligand charge transfer (LLCT) within the (O2 2−)2 moiety. As a result, a photodismutation to 2O2− and O2 takes place. Accordingly, IL excitation of MeReVII(O2)2O leads to the formation of MeReVIIO3 and O2. [Copyright &y& Elsevier]

Abstract: Excited state properties of coordination compounds have been studied for many years. Surprisingly, rather little is known about excited states, which are based on intramolecular interligand interactions. There are two types of these interligand excited states. In homoleptic complexes, such as Mg(C5H5)2, ligand–ligand interaction creates new low-energy interligand states, which are comparable to intermolecular excimers of aromatic molecules. In heteroleptic complexes of the type (C7H7)M(C5H5), low-energy ligand-to-ligand charge transfer (LLCT) excited states are available. Various organometallic compounds, which are characterized by such interligand excited states, are discussed in this account. [Copyright &y& Elsevier]

Abstract: The electronic spectrum of the diperoxo complex MeReVII(O2)2O shows a peroxide IL (intraligand) absorption at λ max ∼260nm in addition to the well-known peroxide to Re(VII) LMCT band at λ max =358nm. Upon IL excitation, the diperoxo group undergoes a dismutation. Accordingly, MeRe(O2)2O photolyzes to MeReVIIO3 and O2. LMCT excitation at λ irr =405nm is assumed to generate the radical pair in the primary photochemical step. Back electron transfer and reaction with water leads finally to the monoperoxo complex MeReVII(O2)O2 and H2O2. [Copyright &y& Elsevier]

Abstract: The electronic spectra of solid MgCp2 (Cp=cyclopentadienyl) show features which indicate the presence of intramolecular interligand interactions. The fluorescence of MgCp2 (λmax=363 nm) undergoes a considerable Stokes shift which is apparently caused by a bonding attraction between both Cp rings in the excited state. An additional phosphorescence of the (Cp−)2 fragment (λmax=535 nm) appears at 77 K. [Copyright &y& Elsevier]

The lead(II) β-diketonates Pb(acac)2, Pb(hfac)2, Pb(tta)2, Pb(dbm)2 and Pb(dpm)2 with acac = acetylacetonate, hfac = hexafluoroacetylacetonate, tta = thenoyltrifluoroacetonate, dbm = dibenzoylmethanate and dpm = dipivaloylmethanate show an intraligand (IL) phosphorescence in low temperature glasses. With the exception of Pb(dpm)2 this emission appears also at room temperature (r.t.) for the solid compounds while in solution this phosphorescence is rather weak. [Copyright &y& Elsevier]

The gadolinium(III) chelates Gd(dtpaH2), Gd(hfac)3, Gd(tta)3 and Gd(qu)3 with dtpa=1,1,4,7,7-diethylenetriaminepentaacetate, hfac=hexafluoroacetylacetonate, tta=thenoyltrifluoroacetonate and qu=8-quinolinolate (or oxinate) show a phosphorescence under ambient conditions. While the UV emission of Gd(dtpaH2) at λmax=312 nm comes from a metal-centered ff state, the bluish (λmax=462 nm), green (λmax=505 nm) and red (λmax=650 nm) luminescence of Gd(hfac)3, Gd(tta)3 and Gd(qu)3, respectively, originates from the lowest-energy intraligand triplets. [Copyright &y& Elsevier]

The complex [(η-C5Me5)RhIII(η-C7H7)]3+ is characterized by a C5Me5- → C7H7+ ligand-to-ligand charge transfer transition which appears at λmax=340 nm in absorption and 596 nm in emission. [Copyright &y& Elsevier]

Excited state properties of organometallic compounds have been studied for many years. Owing to strong covalent bonding, molecular orbitals of organometallics are frequently delocalized. Accordingly, the usual classification of electronic transitions in coordination compounds (e.g. metal-centered and charge transfer) may not always be appropriate. Nevertheless, in suitable cases various important organic ligands can function as CT donors (e.g. cyclopentadienyl anions, allyl anions, carbenes) and CT acceptors (e.g. acetylenes, carbenes, arenes, cyclohexadienyl cations, cycloheptatrienyl cations). Accordingly, organometallic complexes with these ligands are frequently characterized by CT absorptions. CT excitation can lead to an emission or photoreaction. This behavior is illustrated by selected examples which have been recently studied in our laboratory. [Copyright &y& Elsevier]

The N-heterocyclic carbene 1,3-di-t-butylimidazol-2-ylidene (dbiy) can function as charge transfer (CT) donor and acceptor if it is coordinated to oxidizing and reducing metals, respectively. The complex TiIVCl4(dbiy)2 shows a ligand-to-metal CT absorption at 450 nm whereas Ni0(CO)2(dbiy)2 is characterized by a metal-to-ligand charge transfer absorption at λmax=365 nm. While TiIVCl4(dbiy)2 is not luminescent, Ni0(CO)2(dbiy)2 displays a room temperature emission at λmax=510 nm which is assumed to originate from the lowest-energy MLCT triplet. [Copyright &y& Elsevier]

The organometallic compound GdCp3 (Cp=cyclopentadienyl) in ether solution shows a green luminescence (λmax=523 nm, φ=0.2). It is suggested that this emission originates from a triplet of the Cp33− moiety. [Copyright &y& Elsevier]

The emission spectrum of Zn(DIQ)2 with DIQ=5,7-diiodo-8-quinolinolate consists of an intraligand (IL) fluorescence at λmax=550 nm and a rather weak IL phosphorescence at λmax=804 nm. While the appearance of the phosphorescence under ambient conditions is certainly caused by the heavy atom effect of the iodine substituents their influence is smaller than might be expected. [Copyright &y& Elsevier]

[PtCl6]2− is known to be photoreduced by UV light to [PtCl4]2− in chloroform, but at irradiation wavelengths of 254 nm or lower the reverse reaction, photooxidation of [PtCl4]2− to [PtCl6]2−, occurs. This is a solvent-initiated process, proceeding through absorption of light by CHCl3 and subsequent bond homolysis. The quantum yield, based on the light absorbed by CHCl3, is 0.20. Tetrachloroplatinate(II) and hexachloroplatinate(IV) may be cycled back and forth several times by changing the irradiation wavelength. [Copyright &y& Elsevier]

The complex [bipy(OH)2]Re(I)(CO)3Cl with bipy(OH)2=3,3′-dihydroxy-2,2′-bipyridine has been prepared and characterized by elemental analysis, ESI MS and UV–Vis spectroscopy. The complex shows a yellow emission at λmax=582 nm which originates from the lowest-energy bipy(OH)2 intraligand (IL) triplet. The compound undergoes a reversible deprotonation to [(bipyO2)Re(I)(CO)3Cl]2− which is not luminescent under ambient conditions. [Copyright &y& Elsevier]

The solid compound Cu2(CF3SO3)2(C6H6) shows an intense emission at λmax=518 nm (φ∼10−2, τ=0.5 μs) which is suggested to originate from a CuI to benzene metal-to-ligand charge transfer (MLCT) triplet. The spin-allowed MLCT transition gives rise to an excitation maximum at λ=318 nm which appears also as long-wavelength band at λmax=315 nm in the absorption spectrum of the complex in solution. [Copyright &y& Elsevier]

Phosphine ligands determine the excited state properties of a variety of coordination compounds. Phosphines not only influence metal-centered excited states, but participate directly in charge transfer transitions owing to their electron donating and accepting ability. Moreover, intraligand excited states are accessible if the phosphine carries suitable substituents. This diversity is illustrated by selected examples. The excited state behavior is discussed on the basis of spectral (absorption and emission) and photochemical properties of appropriate phosphine complexes. [Copyright &y& Elsevier]

Ionic transition metal complexes are well known to participate in optical outer-sphere charge transfer (OSCT) of ion pairs which consist of oxidizing cations and reducing anions. Frequently, simple anions such as iodide or oxalate have been used as electron donors. Unfortunately, many important anions such as H−, C6H5−, S2− and O22− are not suitable owing to their strong nucleophilicity. However, this nucleophilicity can be attenuated if these anions are replaced by appropriate derivatives including BH3CN− as hydridic, B(C6H5)4− as carbanionic, PO3S3− as sulfidic and BO3− as peroxidic donors. A variety of ion pairs which contain such anions and cationic transition metal complexes or organic cations are characterized by OSCT absorptions in their electronic spectra. Many ion pairs of this type are photoactive upon OSCT excitation. [Copyright &y& Elsevier]

The complex (phanephos)ReI(CO)3Cl with phanephos=4,12-bis(diphenylphosphino)-[2.2]-paracyclophane is characterized by a lowest-energy intraligand (IL) excited state of the 2,2-paracyclophane moiety. This IL transition appears at λmax=340 nm in absorption and at 383 (fluorescence) and 480 nm (phosphorescence, at r.t.) in emission. [Copyright &y& Elsevier]

The complex (quinap)ReI(CO)3Cl, with quinap =1-(2-diphenylphosphino-1-naphthyl)isoquinoline, shows a luminescence at λmax=582 nm with φ=0.12 and τ=1.4 μs in solution (e.g., CH2Cl2) at r.t. It is suggested that this emission originates from a ReI to quinap metal-to-ligand charge transfer triplet. [Copyright &y& Elsevier]

The complex (PPh3)2CuBH4 and 9,10-phenanthrenequinone form a weak adduct in CH2Cl2 which dissociates into its components in DMSO. The adduct is characterized by (PPh3)2CuBH4→phenanthrenequinone outer sphere charge transfer (OSCT) absorptions at λmax=707 and 514 nm. The coordinated BH4− ligand reduces the quinone to hydroquinone thermally and photochemically by OSCT excitation with φ=0.05 at λirr=700 nm. [Copyright &y& Elsevier]

Retinoic acid (vitamin A acid) in acetonitrile shows a very weak fluorescence which originates from the lowest-energy ππ* singlet of the polyene chain. In the presence of several metal salts, Hg(acetate) 2 , Ag(CF 3 COO) and ZnCl 2 , this fluorescence undergoes a slight spectral shift and becomes much more intense. The reason is not quite clear, but different effects may cause this fluorescence enhancement, e.g. energy increase of the non-emissive nπ* state by coordination at the carboxylic group, metal–olefin coordination and an increase of rigidity by organized structures. [ABSTRACT FROM AUTHOR]

The complex cations [Pt 0 (C 3 Ph 3 )(PPh 3 ) 2 ] + and [Pt 0 (C 3 Ph 3 )(tripod)] + with tripod = CH 3 C(CH 2 PPh 2 ) 3 contain the smallest Hückel aromat C 3 R 3 + (with n = 0) as ligand. Since this cation is a CT acceptor, the complexes are characterized by low-energy (Pt 0 to C 3 Ph 3 + ) MLCT states. The complexes show a photoluminescence which originates from the lowest MLCT triplet. [ABSTRACT FROM AUTHOR]

Complexes of Pd(II), Rh(I) and Ir(I) with p-quinone ligands are characterized by metal or ligand (iodide,azide) to quinone CT transitions. CT excitation yields hydroquinones as reduction products. [ABSTRACT FROM AUTHOR]

Reports on the photoredox reactivity of antimony porphyrin complexes. Two-electron reduction of molecular oxygen; Disproportionate reactions; Electronic structure model.

Investigates the photoredox behavior of chloromercurate(II) complexes in acetonitrile. Elucidation of the effects of the number of coordinated ligands on photoactivity; Determination of reaction mechanism for the photochemical reactions; Ligand-to-metal charge transfer transition observed in the ultraviolet spectra of mercuric chloride and its tri and tetrachloro species in acetonitrile.

Abstract: Osmocene is intrinsically photoactive. It photolyzes in n-hexane by a reductive elimination leading to the generation of metallic osmium. Moreover, both cyclopentadienyl anions as ligands in osmocene are oxidatively eliminated. Surprisingly, they are liberated as benzene and cyclobutadiene which is trapped by diphenyl acetylene. As a result of this trapping o-terphenyl is formed. It is suggested that in the LF excited state both cyclopentadienyl ligands undergo a bending in agreement with the previous conclusions. The close approach of both ligands facilitates a CH group transfer between them. The subsequent decay generates elemental osmium, benzene and cyclobutadiene as photolysis products. [Copyright &y& Elsevier]

Abstract: The mercarbides C(HgX)4 with X− =Cl− and acetate− which are characterized by a tetrahedral (C4−Hg2+ 4)4+ core fragment show two absorptions in the UV spectral region at λmax =234nm and 270nm. They are attributed to (C4− →Hg2+) LMCT transitions. LMCT excitation of C(HgX)4 in solution leads to a photoredox decomposition according to: C(HgX)4 +2 H2O→CO2 +4 Hg0 +4 HX. [Copyright &y& Elsevier]

Abstract: When [PtIV(NH3)5Cl]3+ is deprotonated the complex [PtIV(NH3)4(NH2)Cl]2+ is formed. Upon NH2 − →PtIV LMCT excitation (λ irr >250nm) a reductive elimination takes place: [PtIV(NH3)4(NH2)Cl]2+ →[PtII(NH3)3Cl]+ +N2H4 +H+. Since Pt(II) ammine complexes can be reoxidized to Pt(IV) by H2O2 it is suggested that in a cyclic process the overall reaction could proceed according to the equation: 2 NH3 +H2O2 →N2H4 +2 H2O. [Copyright &y& Elsevier]