Issue 41, 2020

Au3-to-Ag3 coordinate-covalent bonding and other supramolecular interactions with covalent bonding strength

Abstract

An efficient strategy for designing charge-transfer complexes using coinage metal cyclic trinuclear complexes (CTCs) is described herein. Due to opposite quadrupolar electrostatic contributions from metal ions and ligand substituents, [Au(μ-Pz-(i-C3H7)2)]3·[Ag(μ-Tz-(n-C3F7)2)]3 (Pz = pyrazolate, Tz = triazolate) has been obtained and its structure verified by single crystal X-ray diffraction – representing the 1st crystallographically-verified Image ID:d0sc02520h-t1.gif stacked adduct of monovalent coinage metal CTCs. Abundant supramolecular interactions with aggregate covalent bonding strength arise from a combination of M–M′ (Au → Ag), metal–π, π–π interactions and hydrogen bonding in this charge-transfer complex, according to density functional theory analyses, yielding a computed binding energy of 66 kcal mol−1 between the two trimer moieties – a large value for intermolecular interactions between adjacent d10 centres (nearly doubling the value for a recently-claimed Au(I) → Cu(I) polar-covalent bond: Proc. Natl. Acad. Sci. U.S.A., 2017, 114, E5042) – which becomes 87 kcal mol−1 with benzene stacking. Surprisingly, DFT analysis suggests that: (a) some other literature precedents should have attained a stacked Image ID:d0sc02520h-t2.gif product akin to the one herein, with similar or even higher binding energy; and (b) a high overall intertrimer bonding energy by inferior electrostatic assistance, underscoring genuine orbital overlap between M and M′ frontier molecular orbitals in such polar-covalent M–M′ bonds in this family of molecules. The Au → Ag bonding is reminiscent of classical Werner-type coordinate-covalent bonds such as H3N: → Ag in [Ag(NH3)2]+, as demonstrated herein quantitatively. Solid-state and molecular modeling illustrate electron flow from the π-basic gold trimer to the π-acidic silver trimer with augmented contributions from ligand-to-ligand’ (LL′CT) and metal-to-ligand (MLCT) charge transfer.

Graphical abstract: Au3-to-Ag3 coordinate-covalent bonding and other supramolecular interactions with covalent bonding strength

Supplementary files

Article information

Article type
Edge Article
Submitted
03 May 2020
Accepted
10 Sep 2020
First published
11 Sep 2020
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2020,11, 11179-11188

Au3-to-Ag3 coordinate-covalent bonding and other supramolecular interactions with covalent bonding strength

Z. Lu, B. Chilukuri, C. Yang, A. M. Rawashdeh, R. K. Arvapally, S. M. Tekarli, X. Wang, C. T. Cardenas, T. R. Cundari and M. A. Omary, Chem. Sci., 2020, 11, 11179 DOI: 10.1039/D0SC02520H

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