Investigation of the Nature of Intermolecular Interactions in Tetra(thiocyanato)corrolato-Ag(III) Complexes: Agostic or Hydrogen Bonded?

Abstract

Tetra­(thiocyanato)­corrolato-Ag­(III) complexes presented here constitute a new class of metallo-corrole complexes. The spectroscopic properties of these complexes are quite unusual and interesting. For example, the absorption spectra of these β-substituted corrolato-Ag­(III) complexes are very different from those of the β-unsubstituted corrolato-Ag­(III) derivatives. Single-crystal XRD analysis of a representative tetra­(thiocyanato)­corrolato-Ag­(III) derivative reveals C–H···Ag interactions. The C–H···Ag interactions are rarely demonstrated in the crystal lattice of a discrete coordination/organometallic compound. Optimization of the hydrogen positions of the crystal structure discloses the geometrical parameters of the said interaction as a Ag···H distance of 2.597 Å and ∠C–H···Ag of 109.62°. The natural bond orbital analysis provides information about the donor–acceptor orbitals involved in the interactions and their interaction energies. It was observed that the σC–H orbital overlaps with the vacant d-orbital of Ag with an interaction energy of 17.93 kJ/mol. The filled d-orbital of Ag overlaps with the σ*C–H orbital with an interaction energy of 4.79 kJ/mol. The highlights of this work are that the H···Ag distance is outside of the distance range for the typical agostic interaction but fitted with the weak H-bond distance. However, the ∠C-H···Ag angle is within the range of the agostic interaction. Both crystallographic data and electronic structure calculations reveal that these kinds of intermolecular interactions in square-planar d8 Ag­(III) complexes are intermediate in nature. Thus, they cannot be categorically called either hydrogen bonding or agostic interaction.

NIR-emissive, singlet-oxygen-sensitizing gold tetra(thiocyano)corroles

“…FB 2,3,17,18-tetrathiocyano corroles (FB = free base) were prepared by following an earlier literature method developed by us. 33 Gold metallation was performed into the FB 2,3,17,18-tetrathiocyano corrole cavity by using gold acetate as a metal precursor in an acetonitrile and pyridine mixture at RT (RT = room temperature) in the aerial condition. 21 The composition and purity of the 2,3,17,18-tetra(thiocyano)corrolato-Au( iii ) complexes ( 1–2 ) were established by a series of analytical techniques, i.e.…”

“…44 The synthetic methodologies and full spectroscopic characterization of free base corroles: 2,3,17,18-tetra(thiocyano)-10-(4-bromophenyl)-5,15-bis(4-cyanophenyl)corrole and 2,3,17,18-tetrathiocyano-10-(4,7-dimethoxynaphthalen-1-yl)-5,15-bis(4-cyanophenyl)corrole were reported earlier by us. 33…”

“…18 Herein, we report a new class of Au corroles, 19–32 based on 2,3,17,18-tetrathiocyanocorrole ligands developed in one of our laboratories. 33 We accordingly describe two new complexes – 2,3,17,18-tetra(thiocyano)-10-(4-bromophenyl)-5,15-bis(4-cyanophenyl)corrolato-Au( iii ), 1 , and 2,3,17,18-tetrathiocyano-10-(4,7-dimethoxynaphthalen-1-yl)-5,15-bis(4-cyanophenyl)corrolato-Au( iii ), 2 (Scheme 1). Full spectroscopic characterization and one crystal structure are presented for the complexes.…”

Three-centre electron sharing indices (3c-ESIs) as a tool to differentiate among (an)agostic interactions and hydrogen bonds in transition metal complexes

“…[23][24][25] Again, caution should be taken when using these approaches, which could lead to misidentification. 11,12,[26][27][28][29] Despite the relevance of these kinds of interactions in organometallic chemistry, 4,12,[30][31][32] there is not yet a rigorous methodology capable of unambiguously identifying them.…”

“…Recently, Sahu and coworkers observed an intermolecular interaction between two tetra(thiocyanato)corrolato-Ag(III) molecules (Scheme 2d, GEGRIX) which could not be correctly assigned due to the strong discrepancies obtained from the different computational techniques used. 29 According to the authors, this behaviour denoted the dual character of the interaction (i.e., agostic and hydrogen bond). However, due to the nature of these interactions (see Scheme 1), it is not possible to have both of them in the same MÁ Á ÁH-C moiety.…”