EPR investigations on the Ni(III), Pd(III), Pt(III) and Cu(II) bis-chelates of the dithiolene parent ligand bis(cis)ethylenedithiolate

Möller, Einar; Kirmse, R.

doi:10.1016/s0020-1693(96)05480-1

Cited by 13 publications

(4 citation statements)

References 21 publications

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“…In the series of dimesitylplatinum systems, the bptz complex 1 •- exhibits a distinctly smaller g anisotropy than 4 •- . Since the large spin−orbit coupling contributions from platinum 27 are a major factor in influencing g values, 1a-m, we conclude that the metal participation at the SOMO is lower in 1 •- than in 4 •- (due to a lower lying π* orbital of bptz) and in 6 •- relative to 5 •- . Previous studies on mononuclear systems have similarly revealed that reduced diorganoplatinum(II) species exhibit a higher degree of metal contribution to the spin distribution than tetraorganoplatinum(IV) analogues. 1e,m Incidentally, the isotropic values g iso do not reflect these details; however, they indicate that the reduced (Pt IV ) 2 systems differ from the reduced (Pt II ) 2 species by the sign of the g factor deviation from the free electron value of g e = 2.0023.…”

Section: Resultsmentioning

confidence: 83%

On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds [R_kPt(μ-L)PtR_k]ⁿ,k= 2 or 4

et al. 1998

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Symmetrically dinuclear complexes between the bis-bidentate bridging ligands µ-L (µ-L ) 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) or 2,5-bis(1-phenyliminoethyl)pyrazine (bpip)) and the organoplatinum fragments PtMes 2 (Mes ) mesityl), PtMe 2 , or PtMe 4 were synthesized as deeply colored compounds. Low-energy charge-transfer transitions from metal d orbitals (Pt II ) or metal-carbon σ bond combinations (Pt IV ) to low-lying π* orbitals of the π acceptor ligands are responsible for long-wavelength absorption maxima λ max (CT) > 700 nm. UV/Vis and EPR spectroelectrochemical results for reversible reduction processes indicate the formation of [Pt IV ] 2 (µ-L •-) and [Pt II ] 2 (µ-L •-) species, however, the latter exhibit a significant metal contribution according to a Pt II /Pt I formulation. Cyclic voltammetry reveals that the remarkable system [Mes 2 Pt(µ-bptz)PtMes 2 ] n forms an enormously stabilized radical anion (n ) 1-) with ∆E 1/2 ) 1250 V and K c ) 10 21.2 and a Pt III /Pt II mixed-valent state (n ) 1+) with ∆E 1/2 ) 80 mV and K c ) 23. This small K c value is attributed to the predominantly d σ orbital character of the redox orbitals on the Pt(II) centers. Experimental SectionMaterials and Procedures. The ligands bptz 8 and bpip 9 and the platinum precursor complexes (DMSO)2PtMes2, 10 [Pt2-Me8(µ-SMe2)2], 11 and [Pt2Me4(µ-SMe2)2] 12 were obtained following literature procedures. All preparations and physical measurements were carried out in dried solvents under an argon atmosphere, using Schlenk techniques. Furthermore, the tetramethylplatinum(IV) compounds had to be prepared and studied in the absence of intense light.Bis(dimesitylplatinum) Complexes (µ-L)[PtMes2]2: 1 (L ) bptz) and 4 (L ) bpip). In a typical reaction, 295 mg (0.5 mmol) of dimesitylbis(dimethylsulfoxido)platinum(II) was suspended together with 0.25 mmol of the bridging ligand in 70 mL of toluene and heated under reflux for 5 days. The sulfoxide vibration ν(SdO) at 1130 cm -1 of the platinum precursor complex 13 had by then disappeared. At the end of the reaction, the temperature was lowered within another day to accomplish slow precipitation of the products. The solids were collected on a microporous frit and washed with diethyl ether. We thus obtained a poorly soluble blue-black powder for the bptz complex 1 in a 224 mg (81%) yield.

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Section: Resultsmentioning

confidence: 83%

On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds [R_kPt(μ-L)PtR_k]ⁿ,k= 2 or 4

et al. 1998

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“…The g av value indicates that the unpaired electron is located mainly on the ligand, because similar g values were found for Ni(II)− and Pd(II)−phenoxyl radical species (vide supra). However, the observed large g -anisotropy can arise from large orbital contributions by strong spin−orbit coupling by the Pt atom …”

Section: Resultsmentioning

confidence: 99%

Syntheses and Electronic Structures of One-Electron-Oxidized Group 10 Metal(II)−(Disalicylidene)diamine Complexes (Metal = Ni, Pd, Pt)

et al. 2007

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Group 10 metal(II) complexes of H2tbu-salen (H2tbu-salen = N,N'-bis(3',5'-di-tert-butylsalicylidene)ethylenediamine) and H2tbu-salcn (H2tbu-salcn = N,N'-bis(3',5'-di-tert-butylsalicylidene)-1,2-cyclohexanediamine) containing two 2,4-di(tert-butyl)phenol moieties, [Ni(tbu-salen)] (1a), [Ni(tbu-salcn)] (1b), [Pd(tbu-salen)] (2a), [Pd(tbu-salcn)] (2b), and [Pt(tbu-salen)] (3), were prepared and structurally characterized by X-ray diffraction, and the electronic structures of their one-electron-oxidized species were established by spectroscopic and electrochemical methods. All the complexes have a mononuclear structure with two phenolate oxygens coordinated in a very similar square-planar geometry. These complexes exhibited similar absorption spectra in CH2Cl2, indicating that they all have a similar structure in solution. Cyclic voltammograms of the complexes showed a quasi-reversible redox wave at E1/2 = 0.82-1.05 V (vs Ag/AgCl), corresponding to formation of the relatively stable one-electron-oxidized species. The electrochemically oxidized or Ce(IV)-oxidized species of 1a, 2a, and 3 displayed a first-order decay with a half-life of 83, 20, and 148 min at -20 degrees C, respectively. Ni(II) complexes 1a and 1b were converted to the phenoxyl radicals upon one-electron oxidation in CH2Cl2 above -80 degrees C and to the Ni(III)-phenolate species below -120 degrees C. The temperature-dependent conversion was reversible with the Ni(III)-phenolate ground state and was found to be a valence tautomerism governed by the solvent. One-electron-oxidized 1b was isolated as [Ni(tbu-salcn)]NO3 (4) having the Ni(II)-phenoxyl radical ground state. One-electron-oxidized species of the Pd(II) complexes 2a and 2b were different from those of the Ni(II) complexes, the Pd(II)-phenoxyl radical species being the ground state in CH2Cl2 in the range 5-300 K. The one-electron-oxidized form of 2b, [Pd(tbu-salcn)]NO3 (5), which was isolated as a dark green powder, was found to be a Pd(II)-phenoxyl radical complex. On the other hand, the ESR spectrum of the one-electron-oxidized species of Pt(II) complex 3 exhibited a temperature-independent large g anisotropy in CH2Cl2 below -80 degrees C, while its resonance Raman spectrum at -60 degrees C displayed nu8a of the phenoxyl radical band at 1600 cm-1. These results indicated that the ground state of the Pt(II)-phenoxyl radical species has a large distribution of the radical electron spin at the Pt center. One-electron oxidation of 3 gave [Pt(tbu-salen)]NO3 (6) as a solid, where the oxidation state of the Pt center was determined to be ca. +2.5 from the XPS and XANES measurements.

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“…Some minerals and zeolites doped with Pd III 23 as well as MCl-doped lattices (M = Na, K) are known. There are several molecular compounds having tridentate macrocyclic ligands such as 1,4,7-triazacyclononane, nido -borane, or other ligands. − Most of the reported EPR spectra for these compounds have relatively broad bands with little anisotropy and g values close to the free electron value. With few exceptions, the reported g values range from 2.123 to 2.005, and in most cases g ⊥ is very close to g || and often larger than g || in agreement with axially elongated octahedral geometry. , The only Pd III coordination compound in which the 105 Pd hyperfine structure is resolved in an EPR spectrum is [Pd(1,4,7-trithiacyclononane) 2 ] 3+ .…”

Section: Resultsmentioning

confidence: 99%

A Fractional Bond Order of 1/2 in Pd₂⁵⁺−Formamidinate Species; The Value of Very High-Field EPR Spectra

et al. 2007

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Reaction of Pd(2)(DAniF)(4), 1, (DAniF = di-p-anisylformamidinate) with 1 equiv of AgPF(6) in CH(2)Cl(2) at or below -10 degrees C produces the paramagnetic species [Pd(2)(DAniF)4]PF(6), 1-PF(6), that has been studied by X-ray crystallography, UV-vis spectroscopy, electrochemistry, and multifrequency (9.5, 34.5, 110, and 220 GHz) EPR spectroscopy. Upon oxidation of the precursor, the Pd-Pd distance decreases by 0.052 Angstrom from 2.6486(8) to 2.597(1) Angstrom. The EPR spectra show broad signals with line widths of about 1000 G. The spectra collected at high field show a large spread of g tensor components ( approximately 0.03), but these are masked at lower frequencies (9.5 and 34.5 GHz). A reinvestigation using high-field EPR of the p-tolyl analogue, which is the only other structurally characterized Pd(2)(5+) species (Cotton, F. A.; Matusz, M.; Poli, R.; Feng, X. J. Am. Chem. Soc. 1988, 110, 1144), shows that this species, which had been reported to give an isotropic 9.5 GHz EPR spectrum, also gives anisotropic 110 and 220 GHz EPR spectra with a similarly large spread of g tensor components consistent with the unpaired electron residing in a metal-based MO. The results of these studies and calculations using density functional theory are consistent with the oxidation being metal-based, resulting in an uncommon Pd(2)(5+) species with a Pd-Pd bond order of 1/2.

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EPR investigations on the Ni(III), Pd(III), Pt(III) and Cu(II) bis-chelates of the dithiolene parent ligand bis(cis)ethylenedithiolate

Cited by 13 publications

References 21 publications

On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds [R_kPt(μ-L)PtR_k]ⁿ,k= 2 or 4

On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds [R_kPt(μ-L)PtR_k]ⁿ,k= 2 or 4

Syntheses and Electronic Structures of One-Electron-Oxidized Group 10 Metal(II)−(Disalicylidene)diamine Complexes (Metal = Ni, Pd, Pt)

A Fractional Bond Order of 1/2 in Pd₂⁵⁺−Formamidinate Species; The Value of Very High-Field EPR Spectra

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EPR investigations on the Ni(III), Pd(III), Pt(III) and Cu(II) bis-chelates of the dithiolene parent ligand bis(cis)ethylenedithiolate

Cited by 13 publications

References 21 publications

On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds [RkPt(μ-L)PtRk]n,k= 2 or 4

On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds [RkPt(μ-L)PtRk]n,k= 2 or 4

Syntheses and Electronic Structures of One-Electron-Oxidized Group 10 Metal(II)−(Disalicylidene)diamine Complexes (Metal = Ni, Pd, Pt)

A Fractional Bond Order of 1/2 in Pd25+−Formamidinate Species; The Value of Very High-Field EPR Spectra

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On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds [R_kPt(μ-L)PtR_k]ⁿ,k= 2 or 4

On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds [R_kPt(μ-L)PtR_k]ⁿ,k= 2 or 4

A Fractional Bond Order of 1/2 in Pd₂⁵⁺−Formamidinate Species; The Value of Very High-Field EPR Spectra