Ag(III)···Ag(III) Argentophilic Interaction in a Cofacial Corrole Dyad

Face-to-Face Gold Porphyrins

The interaction of square-planar metal complexes through space is of fundamental interest and relevant for the potential cooperative catalysis of two metal complex sites. In order to elucidate gold/gold, gold/porphyrin, and porphyrin/porphyrin interactions in the formal oxidation states +III and +II (after reduction) and in the excited triplet state after light excitation, a Pacman bis(gold(III)) complex [Au2(DPD)][PF6]2 with square-planar face-to-face gold(porphyrin) moieties has been prepared and characterized. Absorption and luminescence spectroscopy, cyclic voltammetry, and EPR spectroscopy on [Au2(DPD)]n+ and a mononuclear reference are complemented by DFT and TDDFT calculations.

A homoleptic AgIII complex stabilized by succinimidate ligands

Herein, the first example of a homoleptic AgIII complex stabilized by a monodentate N-donor ligand is presented. Na2[S2O8] oxidizes the linear AgI complex, Na[Ag(succ)2] (1Na), to form a square planar argentate(iii) ion, [Ag(succ)4]-, which crystallizes with a polymeric chain-structure, M[Ag(succ)4] (2M), when treated with alkali metal sulfate M2SO4 (M = K, Rb, Cs). A mixed-valent Robin-Day class I system, [(H2O)Ag][Ag(succ)4] (2Ag), forms in the absence of K+/Rb+/Cs+ ion. Diamagnetic 2Cs displays a succinimide C[double bond, length as m-dash]O stretching frequency at higher energy than does the isoelectronic PdII complex, [(H2O)Na]2[Pd(succ)4] (3Na). Moreover, 2Cs displays UV-vis absorptions that are more intense and occur at lower energy than those in 3Na. The electron-deficient nature of 2Cs is further evident from its ability to oxidize water to O2. From 109Ag magic-angle spinning NMR studies, a highly deshielded AgIII environment in 2Cs (2080 ppm) relative to the AgI starting material 1Na (492 ppm) is observed.

Where are the Excess Electrons in Subvalent Compounds? The Case of Ag7Pt2O7

Subvalent compounds raise the question of where those valence electrons not belonging to chemical bonds are. In the limiting case of Ag7Pt2O7, there is just one-electron excess in the chemical formula requiring the presence of Ag atoms with oxidation states below +1, assuming conventional Pt4+ and O2- ions. Such a situation challenges the understanding of the semiconducting and diamagnetic behavior observed in this oxide. Previous explanations that localize pairwise the electron excess in tetrahedral Ag4 interstices do not suffice in this case, since there are six silver tetrahedral voids and only an excess of nine electrons in the unit cell. Here, we provide an alternative explanation for the subvalent nature of this compound by combining interatomic distances, electron density-based descriptors, and orbital energetic analysis criteria. As a result, Ag atoms that do not participate in their valence electron are revealed. We identify excess electrons located in isolated subvalent silver clusters with electron-deficient multicenter bonds resembling pieces of metallic bonding in fcc-Ag and Ag7Pt2 alloy. Our analysis of the electronic band structure also supports the multicenter bonding picture. This combined approach from the real and reciprocal spaces reconciles existing discrepancies and is key to understanding the new chemistry of silver subvalent compounds.

Magnetic Circular Dichroism of Porphyrinoid Silver Complexes: Evidence of the Electronic Structure Inversion upon Protonation of the N-Confused Core

We report a systematic investigation of a series of Ag(II) and Ag(III) complexes of porphyrins and their analogues using UV-vis magnetic circular dichroism (MCD) spectroscopies and theoretical calculations. Ag(II) and Ag(III) octaethyl- and tetraarylporphyrins show the usual sign sequence in the Q-band region (i.e., negative to positive intensities with increasing energy) of their MCD spectra, indicative of the ΔHOMO > ΔLUMO relationship (ΔHOMO is the energy difference between Michl's a and s orbitals, and ΔLUMO is the energy difference between Michl's -a and -s pair of MOs). In contrast, Ag(II) complexes of β,β'-pyrrole-modified porphyrins (with an effective chlorin-type π-system) and Ag(III) corroles have sign reverse features in the MCD spectra of their Q-band region (ΔHOMO < ΔLUMO relationships). The Ag(III) complex of N-confused porphyrin shows the ΔHOMO > ΔLUMO relationship in the neutral state and the ΔHOMO < ΔLUMO relationship in the protonated form.