scholarly journals Square-Planar Heteroleptic Complexes of α-Diimine-NiII-Catecholate Type: Intramolecular Ligand-to-Ligand Charge Transfer

Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4622
Author(s):  
Kira I. Pashanova ◽  
Vladlena O. Bitkina ◽  
Ilya A. Yakushev ◽  
Maxim V. Arsenyev ◽  
Alexandr V. Piskunov
Keyword(s):  
Charge Transfer ◽  
Molecular Design ◽  
Crystal Packing ◽  
Molecular Geometry ◽  
Lamellar Crystal ◽  
Heteroleptic Complexes ◽  
Redox Active ◽  
Ligand Charge Transfer ◽  
Square Planar ◽  
Electron Reduction

Two heteroleptic NiII complexes combined the redox-active catecholate and 2,2′- bipyridine ligand platforms were synthesized to observe a photoinduced intramolecular ligand-to-ligand charge transfer (LL’CT, HOMOcatecholate → LUMOα-diimine). A molecular design of compound [NiII(3,6-Cat)(bipy)]∙CH3CN (1) on the base of bulky 3,6-di-tert-butyl-o-benzoquinone (3,6-DTBQ) was an annelation of the ligand with an electron donor glycol fragment, producing derivative [NiII(3,6-Catgly)(bipy)]∙CH2Cl2 (2), in order to influence the energy of LL’CT transition. A substantial longwave shift of the absorption peak was observed in the UV-Vis-NIR spectra of 2 compared with those in 1. In addition, the studied NiII derivatives demonstrated a pronounced negative solvatochromism, which was established using a broad set of solvents. The molecular geometry of both compounds can be ascribed as an insignificantly distorted square-planar type, and the π–π intermolecular stacking of the neighboring α-diimines is realized in a crystal packing. There is a lamellar crystal structure for complex 1, whereas the perpendicular T-motifs with the inter-stacks attractive π–π interactions form the packing of complex 2. The redox-active nature of ligand systems was clearly shown through the electrochemical study: a quasi-reversible one-electron reduction of 2,2′-bipyridine and two reversible successive one-electron oxidative conversations (“catecholate dianion—o-benzosemiquinonato radical anion—neutral o-benzoquinone”) were detected.

Metal to ligand charge-transfer spectra of some square-planar complexes of rhodium(I) and iridium(I)

1977 ◽  
Vol 16 (8) ◽  
pp. 1950-1955 ◽  
Author(s):  
Gregory L. Geoffroy ◽  
Huseyin. Isci ◽  
James. Litrenti ◽  
W. Roy. Mason
Keyword(s):  
Charge Transfer ◽  
Ligand Charge Transfer ◽  
Square Planar ◽  
Square Planar Complexes

Luminescence of a New Ru(II) Polypyridine Complex Controlled by a Redox-Responsive Protonable Anthra[1,10]phenanthrolinequinone

2005 ◽  
Vol 70 (11) ◽  
pp. 1891-1908 ◽  
Author(s):  
František Hartl ◽  
Sandrine Vernier ◽  
Peter Belser
Keyword(s):  
Charge Transfer ◽  
Quantum Yield ◽  
Emission Intensity ◽  
Luminescence Quenching ◽  
Luminescence Quantum Yield ◽  
Ligand Charge Transfer ◽  
Redox Responsive ◽  
Electron Reduction ◽  
Mlct State

Redox-controlled luminescence quenching is presented for a new Ru(II)-bipyridine complex [Ru(bpy)2(1)]2+ where ligand 1 is an anthra[1,10]phenanthrolinequinone. The complex emits from a short-lived metal-to-ligand charge transfer, 3MLCT state (τ = 5.5 ns in deaerated acetonitrile) with a low luminescence quantum yield (5 × 10-4). The emission intensity becomes significantly enhanced when the switchable anthraquinone unit is reduced to corresponding hydroquinone. On the contrary, chemical one-electron reduction of the anthraquinone moiety to semiquinone in aprotic tetrahydrofuran results in total quenching of the emission.

Ultralong C-C bonds in hexaphenylethane derivatives

2008 ◽  
Vol 80 (3) ◽  
pp. 547-553 ◽  
Author(s):  
Takanori Suzuki ◽  
Takashi Takeda ◽  
Hidetoshi Kawai ◽  
Kenshu Fujiwara
Keyword(s):  
Bond Length ◽  
Molecular Design ◽  
Crystal Packing ◽  
Detailed Examination ◽  
Steric Repulsion ◽  
Wide Range ◽  
Rational Molecular Design ◽  
Electron Reduction ◽  
Highly Strained ◽  
Crystal Packing Force

The longer C-C bond than the standard (1.54 Å) is so weakened that it is cleaved easily, as found in the parent hexaphenylethane (HPE). However, the compounds with an ultralong C-C bond (1.75 Å) can be isolated as stable solids when the bond-dissociated species does not undergo any reactions other than bond reformation. This is the central point in designing the highly strained HPEs, which were obtained by two-electron reduction of the corresponding dications. Steric repulsion of "front strain" is the major factor to expand the central C-C bond of HPEs. During the detailed examination of the ultralong C-C bond, the authors discovered the intriguing phenomenon of "expandability": the C-C bond length can be altered over a wide range by applying only a small amount of energy (1 kcal mol-1) supplied by crystal packing force. This observation indicates that the much longer C-C bond than the shortest nonbonded contact (1.80 Å) will be realized under the rational molecular design concept.

scholarly journals The Effect of N-Heterocyclic Carbene Units on the Absorption Spectra of Fe(II) Complexes: A Challenge for Theory

2020 ◽  
Author(s):  
Olga S. Bokareva ◽  
Omar Baig ◽  
Mohamed Al-Marri ◽  
Oliver Kühn ◽  
Leticia Gonzalez
Keyword(s):  
Charge Transfer ◽  
Absorption Spectra ◽  
Excited States ◽  
Partial Charge Transfer ◽  
Polypyridyl Ligands ◽  
Electronic Excited States ◽  
Heteroleptic Complexes ◽  
Ligand Charge Transfer ◽  
Exact Exchange ◽  
Triplet Excited States

<div>The absorption spectra of five Fe(II) homoleptic and heteroleptic complexes containing strong sigma-donating N-heterocyclic carbene (NHC) and polypyridyl ligands have been theoretically characterized using a tuned range-separation functional.</div><div>From a benchmark comparison of the obtained results against other functionals and a multiconfigurational reference, it is concluded that none of the methods is completely satisfactory to describe the absorption spectra.</div><div>Using a compromised choice of 20\% exact exchange, the electronic excited states underlying the absorption spectra are analyzed.</div><div>The low-lying energy band of all the compounds shows predominant metal-to-ligand charge transfer (MLCT) character while the triplet excited states have metal-centered (MC) nature, which becomes more pronounced with increasing the number of NHC-donor groups. Excited MC states with partial charge transfer to the NHC-donor groups are higher in energy than comparable states without these contributions. The presence of the low-lying MC states prevents the formation of long-lived MLCT states.</div>

scholarly journals The Effect of N-Heterocyclic Carbene Units on the Absorption Spectra of Fe(II) Complexes: A Challenge for Theory

2020 ◽  
Author(s):  
Olga S. Bokareva ◽  
Omar Baig ◽  
Mohamed Al-Marri ◽  
Oliver Kühn ◽  
Leticia Gonzalez
Keyword(s):  
Charge Transfer ◽  
Absorption Spectra ◽  
Excited States ◽  
Partial Charge Transfer ◽  
Polypyridyl Ligands ◽  
Electronic Excited States ◽  
Heteroleptic Complexes ◽  
Ligand Charge Transfer ◽  
Exact Exchange ◽  
Triplet Excited States

<div>The absorption spectra of five Fe(II) homoleptic and heteroleptic complexes containing strong sigma-donating N-heterocyclic carbene (NHC) and polypyridyl ligands have been theoretically characterized using a tuned range-separation functional.</div><div>From a benchmark comparison of the obtained results against other functionals and a multiconfigurational reference, it is concluded that none of the methods is completely satisfactory to describe the absorption spectra.</div><div>Using a compromised choice of 20\% exact exchange, the electronic excited states underlying the absorption spectra are analyzed.</div><div>The low-lying energy band of all the compounds shows predominant metal-to-ligand charge transfer (MLCT) character while the triplet excited states have metal-centered (MC) nature, which becomes more pronounced with increasing the number of NHC-donor groups. Excited MC states with partial charge transfer to the NHC-donor groups are higher in energy than comparable states without these contributions. The presence of the low-lying MC states prevents the formation of long-lived MLCT states.</div>

Synthesis and Photochemical Properties of Re(I) Tricarbonyl Complexes Bound to Thione and Thiazole-2-ylidene Ligands

2020 ◽  
Author(s):  
Matthew Stout ◽  
Brian Skelton ◽  
Alexandre N. Sobolev ◽  
Paolo Raiteri ◽  
Massimiliano Massi ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Excited States ◽  
Ligand Exchange ◽  
Ligand Substitution ◽  
Bidentate Ligand ◽  
The Other ◽  
Ligand Exchange Reaction ◽  
Multiple Products ◽  
Ligand Charge Transfer ◽  
Photochemical Properties

<p>Three Re(I) tricarbonyl complexes, with general formulation Re(N^L)(CO)<sub>3</sub>X (where N^L is a bidentate ligand containing a pyridine functionalized in the position 2 with a thione or a thiazol-2-ylidene group and X is either chloro or bromo) were synthesized and their reactivity explored in terms of solvent-dependent ligand substitution, both in the ground and excited states. When dissolved in acetonitrile, the complexes bound to the thione ligand underwent ligand exchange with the solvent resulting in the formation of Re(NCMe)<sub>2</sub>(CO)<sub>3</sub>X. The exchange was found to be reversible, and the starting complex was reformed upon removal of the solvent. On the other hand, the complexes appeared inert in dichloromethane or acetone. Conversely, the complex bound to the thiazole-2-ylidene ligand did not display any ligand exchange reaction in the dark, but underwent photoactivated ligand substitution when excited to its lowest metal-to-ligand charge transfer manifold. Photolysis of this complex in acetonitrile generated multiple products, including Re(I) tricarbonyl and dicarbonyl solvato-complexes as well as free thiazole-2-ylidene ligand.</p>

Disazo (Bishydrazone) pigments based on acetoacetanilides

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Robert Christie ◽  
Adrian Abel
Keyword(s):  
Crystal Packing ◽  
Molecular Geometry ◽  
Coupling Reactions ◽  
Dominant Group ◽  
Color Strength ◽  
Decomposition Products ◽  
Organic Pigments ◽  
Yellow Pigments ◽  
Structure Investigations ◽  
Coupling Components

Abstract Disazoacetoacetanilide pigments, more commonly known as diarylide yellows, are the most important group of yellow classical organic pigments. They were commercialized in the early 20th century many years after the introduction of the structurally related monazoacetoacetanilides (Hansa yellows). The molecules adopt the bis-ketohydrazone tautomeric form. X-ray single crystal structure investigations have provided an insight into the influence of the molecular geometry and crystal packing arrangements in the solid state on the properties of the pigments in application. The synthesis of diarylide pigments is relatively straightforward, the conditions essentially following those used for the corresponding monoazo pigments, so that the products are economically priced. In the case of these disazo pigments, suitable aromatic amines (1 mol) are bis-diazotized and the resulting bis-diazonium salts reacted with acetoacetanilide coupling components (2 mol), the two azo coupling reactions occurring at the same time. They are by far the dominant group of yellow pigments used in printing inks, well-suited for most standard process yellow inks. They were formerly important in the coloration of plastics but are no longer recommended for polymers processed above 200 °C, under which conditions toxic decomposition products are formed. Diarylide yellow pigments are characterized by high color strength, good to excellent solvent fastness, and good chemical stability, although they generally show inferior lightfastness.

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