Studies of the Intramolecular Aromatic-ring Stacking Interactions in the Ternary Platinum(Ⅱ) Complexes

The stability constants of some ternary mixed-ligand complexes, Pt(Phen)(CA) , where Phen=1,10-phenanthroline and CA- =carboxylate, were determined by means of potentiometric pH titration in aqueous solutions(I=0.1 mol/L, KNO3; 25 ℃), and the stability of them was compared with that of the corresponding binary complexes. It was revealed that the ternary complexes containing phenylalkane carboxylates ligands(PCA-) are much more stable than those formed with formate and acetate. The results indicate that there exist the intramolecular aromatic-ring interactions between the phenanthroline ring of Phen and the phenyl moiety of ligand PCA- in the ternary mixed-ligand Pt(Phen)(PCA)- complexes. The extent of the stacking interactions, which depends on the number of methylene groups between the phenyl moieties and the coordinated phenylalkane carboxylate groups, was calculated. The best-fitted stack was obtained for the complexes with 2-phenylacetate and 3-phenylpropionate as the ligands.     

Origin of the Aggregation-Induced Phosphorescence of Platinum(II) Complexes: The Role of Metal–Metal Interactions on Emission Decay in the Crystalline State

Discerning the origins of the phosphorescent aggregation-induced emission (AIE) from Pt(II) complexes is crucial for developing the broader range of photo-functional materials. Over the past few decades, several mechanisms of phosphorescent AIE have been proposed, however, not have been directly elucidated. Herein, we describe phosphorescence and deactivation processes of four class of AIE active Pt(II) complexes in the crystalline state based on experimental and theoretical investigation. These complexes show metal-to-ligand and/or metal−metal-to-ligand charge transfer emission in crystalline state with different heat resistance against thermal emission quenching. The calculated energy profiles including the minimum energy crossing point between S₀ and T₁ states were consistent with the heat resistant properties, which provided the mechanism for AIE expression. Furthermore, we have clarified the role of metal-metal interaction in AIE by comparing two computational models.     

Tuning the Excited State of Tetradentate Pd(Ⅱ) and Pt(Ⅱ)Complexes through Benzannulated N-Heteroaromatic Ring and Central Metal

A series of tetradentate Pd(Ⅱ) and Pt(Ⅱ) complexes containing fused 5/6/6 metallocycles with phenyl N-heteroaromatic ben-zo[d]imidazole (pbiz),benzo[d]oxazole (...     

Studies of the Intramolecular Aromatic-ring Stacking Interactions in the Ternary Platinum（Ⅱ） Complexes

The stability constants of some ternary mixed-ligand complexes, Pt (Phen)(CA) , where Phen-1,10-phenanthroline and CA^-=carboxylate, were determined by means of potentiometric pH titration in aqueous solutions (I=0. 1mol/L, KNO3; 25℃), and the stability of them was compared with that of the corresponding binary complexes. It was revealed that the ternary complexes containing phenylalkane carboxylates ligands (PCA-) are much more stable than those formed with formate and acetate. The results indicate that there exist the intramolecular aromatic-ring interactions between the phenanthroline ring of Phen and the phenyl moiety of ligand PCA- in the ternary mixed-ligand Pt(Phen) (PCA)^- complexes. The extent of the stacking interactions, which depends on the number of methylene groups between the phenyl moieties and the coordinated phenylalkane carboxylate groups, was calculated. The best-fitted stack was obtained for the complexes with 2-phenylacetate and 3-phenylpropionate as the ligands.     

Variance of Solid-state Pt···Pt Interactions in Luminescent Cyclometalated Cationic Pt(Ⅱ)-isocyanide Complexes

Polymorphic structures of cyclometalated cationic Pt(Ⅱ)-isocyanide complexes(–)-1 [Pt((-)-NNC)(Dmpi)]Cl with different packing modes can be isolated before. In this paper, a series of solid-state powders with variable colors(yellow, orange and red) have been obtained from the evaporation of complex(–)-1 in different solvents. The crystallinity, thermogravimetric properties, absorption, luminescence and excited state lifetimes have been studied. In addition, intermolecular Pt···Pt interactions in the optimized configurations of different aggregates have been explored, and calculations of frontier molecular orbitals of monomer, dimer, trimer and tetramer have been carried out.     

Six-Nuclear Complexes of Platinum(II) and Palladium(II) with Mercamine and β-Mercaptoethanol

The platinum(II) and palladium(II) complexes [Pt₆(SCH₂CH₂NH₂)₈]Cl₄ and [Pd₆(SCH₂CH₂OH)₈ Cl₄· 5H₂O with mercamine and β-mercaptoethanol, respectively, were synthesized. It was found on the basis of the comparison of IR and X-ray electron spectra of the ligands and complexes, and also of the data of X-ray diffraction analysis that the bidentate coordination of ligands through sulfur and nitrogen atoms is realized in the platinum(II) complex. In the palladium(II) complex β-mercaptoethanol is coordinated in a mixed-mode type. In both complexes sulfur atoms of the ligands occupy a bridging position.     

Synthesis, Structure and Noncovalent Interactions of Palladium(II) Complexes with N-Benzoyl-β-phenylalaninate Dianion and Aromatic Diimine

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σ-Silane Platinum(II) Complexes as Intermediates in C−Si Bond-Coupling Processes

Platinum complexes [Pt(NHC′)(NHC)][BAr^F] (in which NHC′ denotes a cyclometalated N-heterocyclic carbene ligand, NHC) react with primary silanes RSiH₃ to afford the cyclometalated platinum(II) silyl complexes [Pt(NHC-SiHR′)(NHC)][BAr^F] through a process that involves the formation of C−Si and Pt−Si bonds with concomitant extrusion of H₂. Low-temperature NMR studies indicate that the process proceeds through initial formation of the σ-SiH complexes [Pt(NHC′)(NHC)(HSiH₂R)][BAr^F], which are stable at temperatures below −10 °C. At higher temperatures, activation of one Si−H bond followed by a C−Si coupling reaction generates an agostic SiH platinum hydride derivative [Pt(H)(NHC′-SiH₂R)(NHC)][BAr^F], which undergoes a second Si−H bond activation to afford the final products. Computational modeling of the reaction mechanism indicates that the stereochemistry of the silyl/hydride ligands after the first Si−H bond cleavage dictates the nature of the products, favoring the formation of a C−Si bond over a C−H bond, in contrast to previous results obtained for tertiary silanes. Furthermore, the process involves a trans-to-cis isomerization of the NHC ligand before the second Si−H bond cleavage.     

Intense Red-Blue Luminescence Based on Superfine Control of Metal–Metal Interactions for Self-Assembled Platinum(II) Complexes

A series of assembled Pt^II complexes comprising N-heterocyclic carbene and cyanide ligands was constructed using different substituent groups, [Pt(CN)₂(R-impy)] (R-impyH⁺=1-alkyl-3-(2-pyridyl)-1H-imidazolium, R=Me ( Pt-Me ), Et ( Pt-Et ), ⁱPr ( Pt- ⁱ Pr ), and ^tBu ( Pt- ^t Bu )). All the complexes exhibited highly efficient photoluminescence with an emission quantum yield of 0.51–0.81 in the solid state at room temperature, originating from the triplet metal-metal-to-ligand charge transfer (³MMLCT) state. Their emission colors cover the entire visible region from red for Pt-Me to blue for Pt- ^t Bu . Importantly, Pt- ^t Bu is the first example that exhibits blue ³MMLCT emission. The ³MMLCT emission was proved and characterized based on the temperature dependences of the crystal structures and emission properties. The wide-range color tuning of luminescence using the ³MMLCT emission presents a new strategy of superfine control of the emission color.     

Palladium(II) and Platinum(II) Complexes of N-Phenyl- and N-Ethyl-N′-pyrimidin-2-ylthiourea

Palladium(II) and platinum(II) complexes of N-ethyl-N′-pyrimidin-2-ylthiourea(HL¹) and N-phenyl-N′-pyrimidin-2-ylthiourea (HL²) have been prepared, and the complexes [M(HL)Cl₂], [Pt(L)₂], [Pd(HL¹)₂]Cl₂, and [Pd(L²)₂] (where M = Pd^II or Pt^II) were characterized. The spectroscopic data are consistent with coordination of thioureas as neutral or monoanionic ligands to Pd^II and Pt^II through S and a pyrimidine-N. The IR spectra show shifts of CS and pyrimidine ring stretch bands to lower and higher frequencies, respectively. The ¹H NMR spectra differentiate between H(4′) and H(6′) resonances and indicate downfield shifts for all protons of pyrimidine [H(4′), H(5′), and H(6′)], two resonances for two N?H protons for complexes containing the neutral ligand (HL), and only one N?H proton chemical shift for complexes containing the monoanion (L). ¹³C NMR chemical shifts of pyrimidine carbons are correlated with the type of bonding between Pd^II or Pt^II and pyrimidine-N. The magnetic susceptibilities suggest a diamagnetic planar structure for all complexes.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

One-and Two-photon Excited Fluorescence of Zinc(II),Cadmium(II)Complexes Containing Phenothiazine Ligand

In fluorescence imaging, two-photon excitation (TPE) has developed as an important alternative to traditional one-photon excitation (OPE) in fluorescence microscopy and spectroscopy1,2. The intrinsic advantages of the two-photon excitation include reduced background fluorescence from fluorophores outside the focal volume, decreased photobleaching, inherent optical sectioning capability, and lower photodamage of sensitive biological sample3. But, all the reported materials, which exhibit a …     

Photochemical Behavior of Platinum(II) and Palladium(II) Complexes of 4,4′-Dimethyl-2,2′-Bipyridine

Several mixed-ligand complexes of formula [MX 2 (MBPY)] {where M is Pd(II) or Pt(II); X is Cl m , I m , N 3 m or NO 2 m and MBPY is 4,4'-dimethyl-2,2'-bipyridine} have been prepared. The UV-Vis spectra of these complexes were found to show a low-lying MLCT band and on irradiation at the MLCT band these complexes sensitize the oxidation of 2,2,6,6-tetramethyl-4-piperidinol (XH) in N , N -dimethylformamide (DMF) to 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinoloxy free radical (XO). This photo-oxidation reaction involves singlet molecular oxygen ( 1 O 2 ) as an intermediate and its presence was confirmed by quenching studies using bis(diethyldithiocarbamato)nickel(II) [Ni(DDTC) 2 ], a well-known 1 O 2 quencher. The ability of the complexes to photosensitize the above photo-oxidation reaction follows the order: [Pt ( N 3 ) 2 ( MBPY ) ] ( 2 ) ～ [Pt ( NO 2 ) 2 ( MBPY ) ] ( 3 ) > [PtCl 2 ( MBPY ) ] ( 4 ) > [PtI 2 ( MBPY ) ] ( 1 ) > [Pd ( NO 2 ) 2 ( MBPY ) ] ( 7 ) ～ [Pd ( N 3 ) 2 ( MBPY ) ] ( 6 ) > [PdCl 2 ( MBPY ) ] ( 8 ) > [PdI 2 ( MBPY ) ] ( 5 ), which reflects the nature of the metal ion and the nature of the ligands present in the complexes.     

Through-Space Spin Coupling in a Silver(II) Porphyrin Dimer upon Stepwise Oxidations: AgII⋅⋅⋅AgII,AgII⋅⋅⋅AgIII,and AgIII⋅⋅⋅AgIII Metallophilic Interactions

Metallophilic interactions between closed-shell metal ions are becoming a popular tool for a variety of applications related to high-end materials. Heavier d⁸ transition-metal ions are also considered to have a closed shell and can be involved in such interactions. There is no systematic investigation so far to estimate the structure and energy characteristics of metallophilic interactions in Ag^II/Ag^II (d⁹/d⁹), Ag^III/Ag^III (d⁸/d⁸), and mixed-valent Ag^II/Ag^III (d⁹/d⁸) complexes, which have been demonstrated in the present study. Both interporphyrinic and intermetallic interactions were investigated on stepwise oxidation by using a rigid ethene-bridged cis silver(II) porphyrin dimer and the results compared with those for highly flexible ethane-bridged analogues. By controlling the nature of chemical oxidants and their stoichiometry, both 1e and 2e oxidations were done stepwise to generate Ag^II/Ag^III mixed-valent and Ag^III/Ag^III porphyrin dimers, respectively. Unlike all other ethene-bridged metalloporphyrin dimers reported earlier, in which 2e oxidation stabilizes only the trans form, such an oxidation of silver(II) porphyrin dimer stabilizes only the cis form because of the metallophilic interaction. Besides silver(II) ⋅⋅⋅ silver(II) interactions in cis silver(II) porphyrin dimer, stepwise oxidations also enabled us to achieve various hitherto-unknown silver(II) ⋅⋅⋅ silver(III) and silver(III) ⋅⋅⋅ silver(III) interactions, which thereby allow significant modulation of their structure and properties. The strength of Ag ⋅⋅⋅ Ag interaction follows the order Ag^II/Ag^II (d⁹/d⁹)<Ag^II/Ag^III (d⁹/d⁸)<Ag^III/Ag^III (d⁸/d⁸). Single-crystal XRD, X-ray photoelectron spectroscopy (XPS), ¹H NMR and EPR spectroscopy, and variable-temperature magnetic investigations revealed various oxidation states of silver and metallophilic interactions, which are also well supported by computational analysis.     

Emissive or Nonemissive? A Theoretical Analysis of the Phosphorescence Efficiencies of Cyclometalated Platinum(II) Complexes

We herein report a theoretical analysis based on a density functional theory/time‐dependent density functional theory (DFT/TDDFT) approach to understand the different phosphorescence efficiencies of a family of cyclometalated platinum(II) complexes: [Pt(NCN)Cl] ( 1 ; NCN=1,3‐bis(2‐pyridyl)phenyl^?), [Pt(CNN)Cl] ( 2 ; CNN=6‐phenyl‐2,2′‐bipyridyl^?), [Pt(CNC)(CNPh)] ( 3 ; CNC=2,6‐diphenylpyridyl^2?), [Pt(R‐CNN)Cl] ( 4 ; R‐CNN=3‐(6′‐(2′′‐naphthyl)‐2′‐pyridyl)isoquinolinyl^?), and [Pt(R‐CNC)(CNPh)] ( 5 ; R‐CNC=2,6‐bis(2′‐naphthyl)pyridyl^2?). By considering both the spin–orbit coupling (SOC) and the electronic structures of these complexes at their respective optimized singlet ground (S₀) and first triplet ( ) excited states, we were able to rationalize the experimental findings that 1) 1 is a strong emitter while its isomer 2 is only weakly emissive in CH₂Cl₂ solution at room temperature; 2) although the cyclometalated ligand of 3 has a higher ligand‐field strength than that of 1 , 3 is nonemissive in CH₂Cl₂ solution at 298 K; and 3) extension of π conjugation at the lateral aryl rings of the cyclometalated ligands of 2 and 3 to give 4 and 5 , respectively, leads to increased emission quantum yields under the same conditions. We found that Jahn–Teller and pseudo‐Jahn–Teller effects are operative in complexes 2 and 3 , respectively, on going from the optimized S₀ ground state to the optimized excited state, and thus lead to large excited‐state structural distortions and hence fast nonradiative decay. Furthermore, a strong‐field ligand may push the two different occupied d orbitals so far apart that the SOC effect is small and the radiative decay rate is slow. This work is an example of electronic‐structure‐driven tuning of the phosphorescence efficiency, and the DFT/TDDFT approach is demonstrated to be a versatile tool for the design of phosphorescent materials with target characteristics.     

Unusual Changes of C−H Bond Lengths in Chiral Zinc Complexes Induced by Noncovalent Interactions

In order to better understand the effect of non-covalent weak interactions on molecules, we have explored a variety of weak interactions, such as improper H-bonding (HB), tetrel bonds (TBs) and halogen bonds, in fluorinated chiral zinc complexes. High resolution neutron diffraction studies revealed a methylene carbon-hydrogen bond elongation and shortening due to TB and improper HB interactions, respectively. To show the accumulative effects of multiple weak interactions on the C−H bond, three types of tetrel bonds have been carefully examined. We have also shown how C−H bond elongation can be easily offset by forming an improper HB with the H atom from this C−H bond. Non-covalent interaction and electrostatic potential analysis investigations have been used to affirm the nature of the interactions based on density functional theory (DFT) and other related calculations.     

A vibrational study of the metal—olefin bond in norbornadiene complexes of Rh(I), Pd(II) and Pt(II)

Vibrational assignments of the complexes [RhClC₇H₈]₂, PtCl₂C₇H₈, and PdCl₂C₇H₈ have been undertaken. A reinvestigation of the norbornadiene spectrum was necessary and a new set of assignments is given. The shift in energy of bands I and II and the out-of-plane olefinic CH wagging modes, as well as the relative energies of the bands associated with the metal—olefin motions are consistent with the total metal—norbornadiene interaction following the order Rh>Pt>Pd and the extent of the π component being ordered as Rh⋍Pt>Pd.     

Excited Donor–Acceptor Complexes in the Polymerization of Vinyl Monomers

Butyl methacrylate was found to affect the composition of radical intermediates formed in the photoreduction of benzophenone with triethylamine. In the presence of the monomer, the yield of free radicals decreased and the yield of complexes of the geminate radical pair increased. This was explained by the formation of excited ternary complexes resulted from the interaction of the excited triplet state of benzophenone with the ground-state complex of butyl methacrylate and triethylamine. The substituent effect in benzophenone on the stability of the radical complex was studied. The reaction rate constant for the decay of the radical complex was correlated with the Hammett ⁰ _c constant that determines the mesomeric effect of the substituent.     

Excited State Mixed-Valence Complexes: From the Special Pair to the Creutz–Taube Ion and Beyond

Compounds and complexes with mixed-valence electronic ground states, such as the Creutz–Taube ion, have proven to be excellent vehicles through which to study intramolecular electron-transfer processes. In a recent contribution by Cadranel and co-workers, time-resolved pump-probe spectroscopy reveals photo-induced metal-to-bridge charge transfer within the homovalent analogue of the Creutz–Taube ion, [{(NH₃)₅Ru}(μ-pz){Ru(NH₃)₅}]⁴⁺, giving rise to two closely lying excited states with mixed-valence character, one with a shorter lifetime (τ=136 ps) and weakly-coupled (Robin-Day Class II) character, the other a longer-lived (τ=2.8 ns) configurational isomer with more delocalized electronic structure. Electron transfer reactions from the longer-lived species demonstrate analogies with the photo-induced reactions of the photosynthetic special pair, suggesting this state as a reference system for excited state mixed-valency, and a framework from which to explore photocatalytic reactions.     

Ionic Platinum(II)–Imidobis(diphenylthiophosphinato) Complexes: Preparation,Structure, and Thermal Behavior

The PPh₂P(S)NHP(S)PPh₂ (dppaS₂) ligand reacts with the starting complexes PtCl₂(L-L) (L-L = Ph₂PCH₂PPh₂), (dppm), Ph₂PCH₂CH₂PPh₂ (dppe), Ph₂PCH₂CH₂CH₂PPh₂ (dppp), and NaClO₄·H₂O. Final products are monomeric complexes, and their formulas are [Pt(L-L)(dppaS₂-H)] [(L-L = dppm(1), dppe(2), dppp(3)]. All of these have been characterized by ¹H, ¹³C^,31{P¹H} NMR, FTIR, and elemental analysis. These complexes were also examined by TGA, DTA, and DSC analysis. Complexes 2 and 3 were crystallographically characterized.