Geometry Optimizations of the Ground and Excited Triplet State Structures of the Low-Valent Metal−Metal Bonded Isocyanide and Carbonyl Di- and Trinuclear Palladium Complexes Using Density Functional Theory

Abstract

In relation to the known complexes Pd2(CNMe)6 2+ and Pd2(CN-t-Bu)4Cl2, Pd2(tmb)2Cl2 (tmb = 2,5-dimethyl-2‘,5‘-diisocyanohexane) and Pd3(dppm)3CO2+ (dppm = ((C6H5)2P)2CH2), respectively, the ground and lowest energy triplet excited state geometries of the model compounds Pd2(CNMe)4Cl2 and Pd2(CN(CH2)4NC)2Cl2, and Pd3(PH3)6CO2+ have been optimized using density functional theory. The computations for ground state structures are in excellent agreement with the X-ray data. In the excited states, bond lengthening (due to the change in Pd−Pd bond order 0 → 1) is predicted. In the bridged species, Pd2(CN(CH2)4NC)2Cl2, the computations reveal that twisting of the dihedral angle must occur in order to account for the large change in Pd−Pd distance. Finally, the Pd−Pd bond lengthening for the Pd3(dppm)3CO2+ cluster in the 3A2 excited state is predicted to be ∼0.19 Å relative to the ground state. This value has also been confirmed by an analysis of the emission band using Heller's time-dependent theory.

Triplet Energy Transfers in Well-Defined Host–Guest Porphyrin–Carboxylate/Cluster Assemblies

“…This relatively larger Stokes shift is consistent with the large dσdσ* excited state distortion (Δ Q (Pt–Pt) = +0.18 Å, lengthening) experimentally reported for the homologue [Pt 3 2+ ] . The size of τ F (<9.4 ps) is consistent with the rather low intensity of the fluorescence.…”

“…The calculated average Pd–Pd bond distance is 2.698 Å (2.712, 2.694, and 2.687 Å; basis set 6-31g* for P, C, O, and H in MeOH solvent field) in the S 0 state, which compares favorably to the X-ray data (average 2.613 Å) . In the T 1 state, the calculated Pd–Pd bond distance increases as predicted due to the experimentally determined nature of the lowest energy excited states (S 1 and T 1 are dσdσ*) . An examination of the optimized geometries of [Pd 3 2+ ] indicates the presence of a drastic distortion of the skeleton where two P atoms are placed significantly out of the average Pd 3 plane.…”

Generation, Characterization, and Electrochemical Behavior of the Palladium–Hydride Cluster [Pd3(dppm)3(μ3‐CO)(μ3‐H)]+ (dppm=Bis(diphenylphosphinomethane)

“…[20] The representation of the HOMO and LUMO are provided in Figure 8 and a brief description of only relevant features are presented, as detailed descriptions of the frontier MOs for [Pd 3 ] 2 + and [Pt 3 ] 2 + species are reported elsewhere. [37][38][39] The HOMO exhibits weak PdÀPd bonding and antibonding Pd À H and Pd À CO interactions, which are also common for halide adducts of [Pd 3 ] 2 + . [36] The LUMO is essentially M-based, and exhibits antibonding Pd À Pd interactions.…”

“…[37][38][39] The HOMO exhibits weak PdÀPd bonding and antibonding Pd À H and Pd À CO interactions, which are also common for halide adducts of [Pd 3 ] 2 + . [36] The LUMO is essentially 956(1) ).…”

Ultrafast Electron Transfers in Organometallic Supramolecular Assemblies Built with a NIR-Fluorescent Tetrabenzoporphyrine Dye and the Unsaturated Cluster Pd3(dppm)3(CO)2+

“…The LUMO is composed of the in-plane dσ*(Pd−Pd) MO centered on the [Pd 3 2+ ] cluster. This computational result is consistent with previous DFT calculations on the free cluster 22 and the cluster assembled with a dye. 8 This MO "insertion" of a cluster-localized MO within the four π and π* levels of the porphyrin dye is relevant, as it adds the possibility of electronic transitions between the filled frontier MOs of the dyes and this LUMO, although these are expected to be forbidden due to poor MO overlaps.…”