An official website of the United States government
Molecules undergo a structural change to minimize the energy of excited states generated via external stimuli such as light. This is particularly problematic for Cu(I) coordination complexes which are an intriguing alternative to the rare and expensive transition metal containing complexes (e.g., Pt, Ir, Ru, etc.) but suffer from short excited state lifetimes due to D2d to D2 distortion and solvent coordination. Here we investigate strategic surface binding as an approach to hinder this distortion and increase the excited state lifetime of Cu(I) polypyridyl complexes. Using transient absorption spectroscopy, we observe a more than 20-fold increase in excited state lifetime, relative to solution, for a Cu(I) complex that can coordinate to the ZrO2 via both carboxylated ligands. In contrast, the Cu(I) complex that coordinates via only one ligand has a less pronounced enhancement upon surface binding and exhibits greater sensitivity to coordinating solvents. A combination of ATR-IR and polarized visible ATR measurements as well as theoretical calculations suggest that the increased lifetime is due to surface binding which decreases the degrees of freedom for molecular distortion (e.g., D2d to D2), with the doubly bound complex exhibiting the most pronounced enhancement.
more »
« less
This content will become publicly available on September 16, 2026
A systematic study of naphthyridine-derived ligands for well-defined silver(I) dimers
Dinuclear silver(I) complexes have recently gained attention for potential applications in visible light photochemistry. Our group has demonstrated that strong visible light absorption can occur in silver(I) dimers featuring redox-active naphthyridine diimine (NDI) ligands, resulting from a combination of close silver–silver interactions and low-lying ligand π* orbitals. A shortcoming of this previous work is that the sliver-NDI complexes displayed fluxional behavior due to rapid ligand exchange in solution; the ability to produce silver(I) dimers with targeted properties that maintain well-defined structures in solution remains an unmet challenge. Here, we describe the synthesis and characterization of a series of silver(I) dimers with naphthyridine-derived ligands, in which the ligand scaffold is systematically varied in order to determine structure/property relationships. We find that truncation of the NDI framework into an asymmetric “L-shaped” design results in a family of ligands that reliably produce structurally analogous silver(I) dimers. Ligands that maintain the π-conjugation of the iminopyridine motif consistently give silver(I) dimers with visible light absorption due to metal–metal to ligand charge transfer (MMLCT) transitions, and introduction of anionic (X-type) sites further increases stability in solution.
more »
« less
- Award ID(s):
- 1956197
- PAR ID:
- 10655293
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Dalton Transactions
- Volume:
- 54
- Issue:
- 36
- ISSN:
- 1477-9226
- Page Range / eLocation ID:
- 13651 to 13657
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The copper(I), silver(I), and gold(I) metals bind π‐ligands by σ‐bonding and π‐back bonding interactions. These interactions were investigated using bidentate ancillary ligands with electron donating and withdrawing substituents. The π‐ligands span from ethylene to larger terminal and internal alkenes and alkynes. Results of X‐ray crystallography, NMR, and IR spectroscopy and gas phase experiments show that the binding energies increase in the order Agmore » « less
-
null (Ed.)A series of cerium( iv ) mixed-ligand guanidinate–amide complexes, {[(Me 3 Si) 2 NC(N i Pr) 2 ] x Ce IV [N(SiMe 3 ) 2 ] 3−x } + ( x = 0–3), was prepared by chemical oxidation of the corresponding cerium( iii ) complexes, where x = 1 and 2 represent novel complexes. The Ce( iv ) complexes exhibited a range of intense colors, including red, black, cyan, and green. Notably, increasing the number of the guanidinate ligands from zero to three resulted in significant redshift of the absorption bands from 503 nm (2.48 eV) to 785 nm (1.58 eV) in THF. X-ray absorption near edge structure (XANES) spectra indicated increasing f occupancy ( n f ) with more guanidinate ligands, and revealed the multiconfigurational ground states for all Ce( iv ) complexes. Cyclic voltammetry experiments demonstrated less stabilization of the Ce( iv ) oxidation state with more guanidinate ligands. Moreover, the Ce( iv ) tris(guanidinate) complex exhibited temperature independent paramagnetism (TIP) arising from the small energy gap between the ground- and excited states with considerable magnetic moments. Computational analysis suggested that the origin of the low energy absorption bands was a charge transfer between guanidinate π orbitals that were close in energy to the unoccupied Ce 4f orbitals. However, the incorporation of sterically hindered guanidinate ligands inhibited optimal overlaps between Ce 5d and ligand N 2p orbitals. As a result, there was an overall decrease of ligand-to-metal donation and a less stabilized Ce( iv ) oxidation state, while at the same time, more of the donated electron density ended up in the 4f shell. The results indicate that incorporating guanidinate ligands into Ce( iv ) complexes gives rise to intense charge transfer bands and noteworthy electronic structures, providing insights into the stabilization of tetravalent lanthanide oxidation states.more » « less
-
The tripyrrin-1,14-dione biopyrrin, which shares the scaffold of several naturally occurring heme metabolites, is a redox-active platform for metal coordination. We report the synthesis of square planar platinum( ii ) tripyrrindiones, in which the biopyrrin binds as a tridentate radical and the fourth coordination position is occupied by either aqua or tert -butyl isocyanide ligands. These complexes are stable through chromatographic purification and exposure to air. Electron paramagnetic resonance (EPR) data and density functional theory (DFT) analysis confirm that the spin density is located predominantly on the tripyrrindione ligand. Pancake bonding in solution between the Pt( ii ) tripyrrindione radicals leads to the formation of diamagnetic π dimers at low temperatures. The identity of the monodentate ligand ( i.e. , aqua vs . isocyanide) affects both the thermodynamic parameters of dimerization and the tripyrrindione-based redox processes in these complexes. Isolation and structural characterization of the oxidized complexes revealed stacking of the diamagnetic tripyrrindiones in the solid state as well as a metallophilic Pt( ii )−Pt( ii ) contact in the case of the aqua complex. Overall, the properties of Pt( ii ) tripyrrindiones, including redox potentials and intermolecular interactions in solution and in the solid state, are modulated through easily accessible changes in the redox state of the biopyrrin ligand or the nature of the monodentate ligand.more » « less
-
Abstract Primary phosphido complexes of aluminum(III) are rare, particularly those that are not supported by interactions with Lewis bases or stabilizing cations. Here we report two new examples of unsupported primary phosphido complexes of Al(III). The ancillary ligand on Al is a pincer ligand, diiminopyridine (denoted as I2P). Solid‐state structures show distorted tetrahedral geometry about Al and single bond character in the Al−P bond. Near infra‐red spectra display low energy absorption bands near 1050 nm that are consistent with pincer ligand – Al charge transfer transitions and metalloaromatic character in the “(I2P2−)Al” fragment of the molecules. The phosphido ligands lie out of the I2P ligand plane by up to 15° and this is consistent with our previous reports where π‐donor halide ligands occupy the fourth coordination site on Al.more » « less
