Seven Clues to Ligand Noninnocence: The Metallocorrole Paradigm

• DOI: 10.1021/acs.accounts.9b00115
• Publication Date: 2019-06-21T17:04:55Z
• Authors: Sumit Ganguly; Abhik Ghosh
• Keywords: 01 natural sciences; 0104 chemical sciences

ConspectusNoninnocent ligands do not allow an unambiguous definition of the oxidation state a coordinated atom. When coordinated, also cannot be adequately represented by classic Lewis structure. A noninnocent system thus harbors oxidizing (holes) or reducing equivalents (electrons) that are delocalized over both ligand and To certain degree, is true all complexes, but phenomenon arguably most conspicuous in complexes involving with extended π-systems. The electronic structures such systems have often been mischaracterized, thereby muddying chemical literature to detriment students newcomers field.In recent years, we investigated several metallocorrole families, which turned out noninnocent. Our goal here, however, present systematic account different classes metallocorroles, rather focus on seven major tools (in nod A. G. Cairns-Smith's Seven Clues Origin Life) led us recognize behavior subsequently characterize depth. (1) optical probe: For series meso-triarylcorrole derivatives para substituents X, Soret maxima typically exquisitely sensitive nature red-shifting increasing electron-donating character group. No substituent sensitivity observed for innocent triarylcorrole derivatives. (2) Quantum chemistry: Spin-unrestricted density functional theory calculations permit simple quick visualization noninnocence terms spin profile. Even S = 0 complex, broken-symmetry method affords profile that, its fictitious notwithstanding, helps visualize intramolecular couplings. (3) NMR EPR spectroscopy: In principle, these two techniques afford experimental probes density. (4) Structure/X-ray crystallography. Ligand metallocorroles reflected small distinct skeletal bond length alternations around bipyrrole part macrocycle. addition, Cu some Ag corroles, manifests itself via strong saddling (5) Vibrational spectroscopy. Unsurprisingly, aforementioned translate structure-sensitive vibrational marker bands. (6) Electrochemistry. Noninnocent exhibit characteristically high reduction potentials, caution should exercised turning logic around. potential does necessarily signify metallocorrole; high-valent metal centers undergo metal-centered at quite potentials. (7) X-ray absorption spectroscopy (XAS). By focusing given element, central atom coordination near-edge (XANES) can provide uniquely detailed local information states, field strength, degree centrosymmetry. clear-cut distinctions between come from K-edge XANES Mn Fe corroles.For researchers faced new, potentially system, take-home message employ good majority (i.e., least four) above methods arrive reliable conclusion vis-à-vis noninnocence.