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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

General Design Rules for Bimetallic Platinum(II) Complexes

A series of platinum(II) bimetallic complexes were studied to investigate the effects of ligands on both the geometric and electronic structure. Modulating the Pt-Pt distance through the bridging ligand architecture was found to dictate the nature of the lowest energy electronic transitions, localized in one-half of the molecule or delocalized across the entire molecule. By reducing the separation between the platinum atoms, the lowest energy electronic transitions will be dominated by the metal-metal-to-ligand charge transfer transition. Conversely, by increasing the distance between the platinum atoms, the lowest electronic transition will be largely localized metal-to-ligand charge transfer or ligand centered in nature. Additionally, the cyclometalating ligands were observed to have a noticeable stabilizing effect on the triplet excited states as the conjugation increased, arising from geometric reorientation and increased electron delocalization of the ligands. Furthermore, such stabilization of the triplet state energy has been shown to alter the excited state potential energy landscape as well as the excited state trajectory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1989

Electronic spectra and photophysics of platinum(II) complexes with alpha-diimine ligands - Solid-state effects. I - Monomers and ligand pi dimers

Two types of emission behavior for Pt(II) complexes containing alpha-diimine ligands have been observed in dilute solution. If the complex also has weak field ligands such as chloride, ligand field (d-d) excited states become the lowest energy excited states. If only strong field ligands are present, a diimine 3(pi-pi/asterisk/) state becomes the lowest. In none of the cases studied did metal-to-ligand charge transfer excited state lie lowest.

Miskowski, Vincent M.↗
DOE OSTI2021

Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear Pt II →Ge IV Complex

Abstract Searching for a connection between the two‐electron redox behavior of Group‐14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [( o ‐(Ph 2 P)C 6 H 4 ) 2 Ge IV Cl 2 ]Pt II Cl 2 and [( o ‐(Ph 2 P)C 6 H 4 ) 2 ClGe III ]Pt III Cl 3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [( o ‐(Ph 2 P)C 6 H 4 ) 2 ClGe III ]Pt I Cl with quantum yields of 1.7 % and 3.2 % for the Ge IV –Pt II and Ge III –Pt III isomers, respectively. Conversion of the Ge IV –Pt II isomer into the platinum germyl complex is a rare example of a light‐induced transition‐metal/main‐group‐element bond‐forming process. Finally, transient‐absorption‐spectroscopy studies carried out on the Ge III –Pt III isomer point to a ligand arene–Cl . charge‐transfer complex as an intermediate.

Karimi, Mohammadjavad↗
DOE OSTI2021

Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear Pt II →Ge IV Complex

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph 2 P)C 6 H 4 ) 2 Ge IV Cl 2 ]Pt II Cl 2 and [(o-(Ph 2 P)C 6 H 4 ) 2 ClGe III ]Pt III Cl 3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph 2 P)C 6 H 4 ) 2 ClGe III ]Pt I Cl with quantum yields of 1.7 % and 3.2 % for the Ge IV –Pt II and Ge III –Pt III isomers, respectively. Conversion of the Ge IV –Pt II isomer into the platinum germyl complex is a rare example of a light-induced transition-metal/main-group-element bond-forming process. Additionally, transient-absorption-spectroscopy studies carried out on the Ge III –Pt III isomer point to a ligand arene–Cl. charge-transfer complex as an intermediate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Multi-state Catalysts Modulated by Mechanical Force (Final Report)

The development of more efficient catalytic processes and new approaches to control catalytic activity and selectivity are central to the realization of more selective, atom economic, and energy efficient routes to value added chemicals and polymers. The reactivity and selectivity of a transition metal catalyst is intimately related to the ligand-sphere geometry and, in many cases, the ideal ligand geometry for one step of a catalytic cycle is poorly matched to the ideal ligand geometry for another, resulting in sub-optimal efficiency. Macroscopic mechanical forces are both large, potentially much larger than interatomic forces, and are directional and localized to an extent that differentiates them from other forms of energy input such as heat or light. As such, mechanical force represents a heretofore untapped approach to modulate catalyst geometry, with the potential to reversibly modulate catalyst geometry on the timescale of catalytic turnover or monomer enchainment. This project has addressed the fundamental challenges in material-to-molecule strain coupling associated with the development of a new class of mechanically responsive catalysts (mechanocatalysts) in which active organotransition metal catalysts are strategically embedded in a flexible polymer network such that application of external mechanical force (stretching or deformation) leads to modulation of catalyst geometry, and hence reactivity and selectivity. Our efforts during the tenure of this grant were directed toward the elucidation of force-reactivity relationships of elementary transformations that occur within the first coordination sphere of a transition metal complex employing stiff stilbene photoswitches tethered to a flexible bidentate phosphine ligand derived from MeOBiphep as molecular force probes which provide a range of compressive and extension forces to the coupled transition metal complex depending on the geometry of the stiff stilbene and length of the tethering chains. During the tenure of this grant, we have quantified the rate of C(sp 2 )-C(sp 2 ) reductive elimination from platinum(II) diaryl complexes containing bis(phosphine) force probe ligands as a function of mechanical force; compressive forces decreased the rate of reductive elimination whereas extension forces increased the rate relative to the strain-free MeOBiphep complex with a 3.4-fold change in rate over a ~290 pN range of restoring forces. In a similar manner, we have quantified the rate of oxidative addition of bromobenzene to low-ligated palladium(0) complexes containing force probe ligands as a function of mechanical force; compressive forces increase the rate of oxidative addition, whereas tensile forces decrease the rate with a ~6 fold change in rate across ~340 pN of force applied to the complexes. In both cases, experimental and computational analyses argue strongly against any significant force-induced perturbation of ground state geometry within the first coordination sphere of the reactant complexes. Rather, the force/rate behavior observed for these transformations across these ranges of forces is attributed to the coupling of force to the nuclear motion comprising the reaction coordinates for reductive elimination and oxidative addition. These results together inform the development of catalysts whose activity can be tuned by an external force that is adjusted within a catalytic cycle and suggest opportunities to experimentally map geometry changes associated with reactions in transition metal complexes and potential strategies for force-modulated catalysis.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2026

Photochemically Triggered Para-Hydrogen-Induced Polarization in a Diplatinum Trihydride Complex

Transition metal complexes containing platinum(II) are of substantial interest for their rich photophysics, biomedical applications, and catalytic function. Nuclear magnetic resonance (NMR) spectra of the spin-1/2 isotope, 195Pt, offer detailed insights into the molecular structures of closed-shell Pt(II) complexes, including solvent effects. However, the sensitivity of 195Pt NMR is mediocre, and its NMR spectra are typically complex. As a result, 1H NMR spectra are used as the primary characterization tool for Pt(II)-based molecules, relying on J-coupling to the 195Pt nucleus to provide structural information from the resulting satellite peaks. In efforts to significantly improve the information content from 1H NMR spectroscopy in a Pt(II)-containing molecule, we utilize [Pt2H2(μ-H)(μ-dppm)2]PF6, where dppm is bis(diphenylphosphino)methane, and leverage its established photoactivity with UV light and H2 for para-hydrogen-induced polarization (PHIP) to enhance the resultant NMR signals, revealing numerous 195Pt J-couplings. Moreover, we investigate direct solvent hyperpolarization effects, as well as the indirect effects of solvent on the various observed J-coupling constants in the Pt species, demonstrating correlations with both Lewis basicity and dielectric constant.

Brown, Emily E. [Department of Chemistry; North Ca↗
DOE OSTI2025

Data for: Climatic Imprint on Interfacially-Controlled Platinum-Palladium Resources

Data package for manuscript "Climatic Imprint on Interfacially-Controlled Platinum-Palladium Resources" by Emily G. Wright, Ivey Wang, Yihang Fang, Elaine D. Flynn, and Jeffrey G. Catalano. This dataset contains adsorption results from experiments designed to investigate the effect of chloride on Pd(II) adsorption to goethite and Pt(II) adsorption to hematite and goethite, including lab experiments, X-ray absorption fine structure spectroscopy, and models of retention within a laterite. See the associated manuscript for full methods information. The file "Wright2025_PtAds_data.csv" contains the target starting Pt concentration (uM), final aqueous Pt and associated error (in uM), calculated adsorbed Pt and associated error (in umol/m2), target and measured aqueous chloride (mM), target aqueous nitrate (mM), final pH, and mineral concentration/loading (g/L). Associated mineral-free controls (mineral loading = 0 g/L) are included; the aqueous Pd error was not calculated and chloride was not measured in every sample. These data appear in Figures 1, S3, S4, S5, S20, and S22 in the associated manuscript. The file "Wright2025_PdAds_data.csv" contains the target starting Pd concentration (uM), final aqueous Pd and associated error (in uM), calculated adsorbed Pd and associated error (in umol/m2), target and measured aqueous chloride (mM), and mineral concentration/loading (g/L). Associated mineral-free controls (mineral loading = 0 g/L) are included; the aqueous Pd error was not calculated and chloride was not measured in every sample. These data appear in Figures 1, S3, S4, S5, and S20 in the associated manuscript. The file "Wright2025_MineralBatches_data.csv" contains the mineral identity and BET specific surface area (m2/g) for every mineral batch synthesized and used in experiments. The annealing time used is listed for hydrothermally annealed goethite. These data appear in Table S2 in the associated manuscript. The file "Wright2025_XRD_data.csv" contains the XRD patterns for every mineral batch synthesized as the counts as a function of two theta (in degrees). See "Wright2025_MineralBatches_data.csv" for more details on specific mineral batches. These data appear in Figure S2 in the associated manuscript. The file "Wright 2025_ZetaPotential_data.csv" contains the measured zeta potentials for samples of goethite (batch G2) at pH 4 the presence of varying amounts of sodium chloride. These data appear in Table S3 in the associated manuscript. The file "Wright2025_XAFSSamples_data.csv" contains the specific mineral batch, measured final aqueous Pd or Pt (uM), measured final aqueous chloride (mM), and estimated adsorbed Pd or Pt (umol/m2) of all XAFS samples. These data appear in Tables S4, S7, S8, and S10 in the associated manuscript. The files "Wright2025_PdXAFS_data.csv" and "Wright2025_PtXAFS_data.csv" contain the normalized spectra of Pd and Pt, respectively, adsorbed to minerals at varying chloride concentrations. See "Wright2025_XAFSSamples_data.csv" for a guide to sample names. Note that "05" in a sample name is equivalent to "0.5". These data appear in Figures 2, S6, S7, S8, S12, S13, and S14 in the associated manuscript. The file "Wright2025_LateriteProfileProfileModelParameters_data.csv" include the ratio of hematite to hematite and goethite in two synthetic, modeled profiles, as well as the modeled surface areas of goethite and hematite as a function of relative depth within the modeled weathering zone. These data were used, in conjunction with equations presented in the paper, to calculate the theoretical concentrations of Pd and Pt (and the resulting Pt/Pd ratio) within the profiles. These data appear in Figure 3 in the associated manuscript. The file "Wright2025_Imagery_data.zip" is a zipped folder containing the TEM and STEM images appear in Figures S18 and S19. Individual files are labeled as either STEM (Fig. S18) or TEM (Fig. S19) with a letter representing the part of the multipart figure.

58 GEOSCIENCES↗
DOE OSTI2023

Metal-assisted delayed fluorescent emitters employing pyrido-pyrrolo-acridine and analogues

Metal-assisted delayed fluorescent (MADF) emitters including cyclic tetradentate platinum (II) and palladium (II) complexes employing 8H-pyrido[3′,2′:4,5]-pyrrolo[3,2,1-de]acridine and its analogues. These complexes provide improved color purity and enhanced operational stability and are suitable for luminescent labels, emitters for organic light emitting diodes (OLEDs), and lighting applications.

Li, Jian↗
DOE OSTI2023

Dinuclear Ligand-to-Ligand Charge Transfer Complexes

The synthesis and characterization of dinuclear ligand-to-ligand charge transfer complexes are described. Each complex is comprised of square-planar platinum(II) coordinated to a 3-tert-butyl-orthocatecholate donor and a 4,4’-di-tert-butyl-2,2’-bipyridine acceptor. Both complexes exhibit donor x acceptor ligand-to-ligand charge transfer (LL’CT) bands in the visible spectrum. The platinum complexes are covalently attached at the catecholate 5-position to either a meta- or para-phenylene bridge fragment. Both cyclic voltammetry and electronic absorption spectroscopy exhibit features characteristic of intramolecular interaction between the platinum centres. The LL’CT excited state lifetimes are ~twofold longer than the mononuclear parent complex. Here, the properties of these complexes are discussed and compared to similar complexes in the literature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Aromatic heterobicycle-fused porphyrins: impact on aromaticity and excited state electron transfer leading to long-lived charge separation

A new synthetic method to fuse benzo[4,5]imidazo[2,1-a]isoindole to the porphyrin periphery at the β,β-positions has been developed, and its impact on the aromaticity and electronic structures is investigated. Reactivity investigation of the fused benzoimidazo-isoindole component reveals fluorescence quenching of a zinc porphyrin (AMIm-2) upon treatment with a Brønsted acid. The reaction of the zinc porphyrin (AMIm-2) with methyl iodide initiated a new organic transformation, resulting in the ring-opening of isoindole with the formation of an aldehyde and dimethylation of the benzoimidazo component. The fused benzoimidazo-isoindole component acted as a good ligand to bind platinum(II), forming novel homobimetallic and heterobimetallic porphyrin complexes. The fusion of benzoimidazo-isoindole on the porphyrin ring resulted in bathochromically shifted absorptions and emissions, reflecting the extended conjugation of the porphyrin π-system. Time-resolved emission and transient absorption spectroscopy revealed stable excited state species of the benzoimidazo-isoindole fused porphyrins. Zinc porphyrin AMIm-2 promoted excited state electron transfer upon coordinating with an electron acceptor, C60, generating a long-lived charge-separated state, in the order of 37.4 μs. The formation of the exceptionally long-lived charge-separated state is attributed to the involvement of both singlet and triplet excited states of AMIm-2, which is rarely reported in porphyrins.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Complexes of Platinum Group Metals with a Conformationally Locked Scorpionate in a Metal–Organic Framework: An Unusually Close Apical Interaction of Palladium(II)

Here, we report synthetic strategies for installing platinum group metals (PGMs: Pd, Rh, Ir, and Pt) on a scorpionate-derived linker (TpmC*) within a metal–organic framework (MOF), both by room-temperature postsynthetic metalation and by direct solvothermal synthesis, with a wide range of metal loadings relevant for fundamental studies and catalysis. In-depth studies for the palladium adduct Pd(II)@Zr-TpmC* by density-functional-theory-assisted extended X-ray absorption fine structure spectroscopy reveals that the rigid MOF lattice enforces a close Pd(II)–N apical interaction between the bidentate palladium complex and the third uncoordinated pyrazole arm of the TpmC* ligand (Pd–N apical = 2.501 ± 0.067 Å), an interaction that is wholly avoided in molecular palladium scorpionates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

N-heterocyclic carbene platinum-butadiyne Click/iClick complexes. Towards blue-violet phosphorescence

By employing two different methods, namely, Click and iClick, a series of four trans-NHC-Pt(II) triazole-acetylide complexes containing benzyl (3a), methylnaphthalene (3b), methylanthracene (3c), and phenyl (3d) substituents at the terminal triazole ring were synthesized and characterized. The traditional click approach involves first synthesizing a triazole-acetylene and then attaching to the Pt ion. In the iClick approach, the triazole is formed via cycloaddition by combining a trans-platinum butadiyne with the corresponding organic azide. The complexes were interrogated to determine the effects of conjugation and ligand substituent on their photophysical properties. Complex 3a exhibits a photoluminescence lifetime of 4.3 μs at 77 K. Ascribed to emission from conformers differing due to the torsion of the aryl acetylide ligands, employing different excitation wavelengths results in different emission spectra. Complex 3a emits in the violet region with CIE coordinates of (0.159, 0.021) under 290 nm excitation and shifts to CIE coordinates of (0.161, 0.019) under 320 nm excitation. Finally, complex 3d, having a photoluminescence lifetime of 13.1 μs at room temperature, emits in the sky-blue region with CIE coordinates of (0.237, 0.355).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ultrafast branching in intersystem crossing dynamics revealed by coherent vibrational wavepacket motions in a bimetallic Pt($\mathrm{II}$) complex

Ultrafast excited-state processes of transition metal complexes (TMCs) are governed by complicated interplays between electronic and nuclear dynamics, which demand a detailed understanding to achieve optimal functionalities of photoactive TMC-based materials for many applications. Here, in this work, we investigated a cyclometalated platinum(II) dimer known to undergo a Pt-Pt bond contraction in metal-metal-to-ligand-charge-transfer (MMLCT) excited state using femtosecond broadband transient absorption (fs-BBTA) spectroscopy in combination with geometry optimization and normal mode calculations. Using sub-20 fs pump and broadband probe pulses in fs-BBTA spectroscopy, we are able to correlate coherent vibrational wavepacket (CVWP) evolution with stimulated emission (SE) dynamics of the 1 MMLCT state. The results demonstrated that the 145 cm -1 CVWP motions with the damping times of ~ 0.9 ps and ~ 2 ps originate from coherent Pt-Pt stretching vibrations in the singlet and triplet MMLCT states, respectively. On the basis of excited-state potential energy surface calculations in our previous work, we rationalized that the CVWP transfer from Franck-Condon (FC) state to the 3 MMLCT state was mediated by a triplet ligand-centered ( 3 LC) intermediate state through two step intersystem crossing (ISC) on a time scale shorter than a period of the Pt-Pt stretching wavepacket motions. Moreover, it was found that the CVWP motion with 110 cm-1 frequency decays with the damping time of ~ 0.2 ps, well matching the time constant of 0.253 ps corresponding to a redshift in the SE feature at early time. This observation indicates that the Pt-Pt bond contraction changes the stretching frequency from 110 to 145 cm -1 and stabilize the 1 MMLCT state relative to the 3 LC state with the ~ 0.2 ps time scale. Thus, the ultrafast ISC from the 1 MMLCT to the 3 LC states occurs before the Pt-Pt bond shortening. The findings herein provide insight into understanding the impact of Pt-Pt bond contraction on ultrafast branching of the 1 MMLCT population into the direct ( 1 MMLCT → 3 MMLCT) and indirect ISC pathways ( 1 MMLCT → 3 LC → 3 MMLCT) in the Pt(II) dimer. These results revealed intricate excited state electronic and nuclear motions that could steer the reaction pathways with levels of details that have not achieved before

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ligand-Structure-Dependent Coherent Vibrational Wavepacket Dynamics in Pyrazolate-Bridged Pt(II) Dimers

Bimetallic transition metal complexes have gained increasing attention because of their versatile functions in solar energy conversion and photonics applications arising from inter-metal electronic coupling. In bimetallic platinum (Pt) complexes, electronic communication between the Pt-centered and ligand-centered moieties have been shown to be critical for defining their excited-state dynamic trajectories undergoing either localized ligand centered (LC)/metal-to-ligand-charge-transfer (MLCT) transitions or delocalized metal-metal-to-ligand-charge-transfer (MMLCT) transitions. The branching of the excited-state intersystem crossing (ISC) trajectories are modulated through structural factors that alter the relative energies of the different states. In this study, we investigated the correlation of the structural factors influencing the excited state trajectories. Using femtosecond broadband transient absorption (fs-BBTA) spectroscopy, ultrafast dynamics in the excited state of two select Pt(II) dimers have been mapped out using their coherent vibrational wavepacket signatures in corresponding transient absorption spectra. To examine how the ligand moieties of the Pt(II) dimers influence excited-state dynamics and the coherent vibrational wavepacket behavior, here we carried out comparative studies on two pyrazolate-bridged Pt(II) dimers of the general formula [Pt( t Bu 2 Pz)(N^C)] 2 ( t Bu 2 Pz = 3,5-di-tert-butylpyrazole); N^C = 7,8-benzoquinoline (bzq, 1) or 1-phenylisoquinoline (piq, 2)). We found that photoexcitation into the low energy absorption bands of 1 and 2 respectively induce the formation of 1 MMLCT states from which ultrafast ISC proceeds, resulting in stimulated emission quenching and decoherence of the vibrational wavepacket motions. The results obtained in this study suggest that both energetics and the structural rigidity of the aromatic cyclometalating ligands in 1 and 2 can significantly influence dynamics along the excited state trajectory characterized by dephasing of the coherent oscillations. The collective results provide direct evidence of how ligand structure alters electronic dynamics along excited state trajectories associated with ISC processes, providing insight into using ligand design to steer photochemical processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗