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Electronic absorption and emission spectra of [M25(MPA)18]− (M = Au, Ag; MPA = SCH2CH2COOH) clusters have been recorded for energies below 5 eV at the time-dependent density functional theory (TDDFT) level using B3LYP and TPSSh functionals and compared to the calculated ones using the computationally inexpensive simplified TDDFT (sTDDFT) approach. The results show a qualitative agreement between the TDDFT and sTDDFT approaches used here, which were also in line with the experimental and theoretical spectra previously reported. However, the sTDDFT calculations were several orders of magnitude faster than those obtained by TDDFT. Our results support that sTDDFT provides an excellent balance between accuracy and low computational cost, becoming a suitable approach for studying the absorption and emission spectra of noble-metal clusters of sizes that would be unaffordable by the traditional TDDFT methods. The main peaks of the experimental absorption spectrum of [Au25(MPA)18]− have been previously assigned, whereas [Ag25(MPA)18]− has not been synthesised. However, its absorption spectrum resulted in having similar features to the experimental spectrum of [Ag25(GSH)18]− (GSH = glutathione), used to validate our results. The emission spectra, which to date have not been reported either from experimental or theoretical means, were simulated by using the molecular structure of the first excited triplet state (T1). The emission spectra were obtained by comparing them to those of [M25(GSH)18]− since no experimental luminescence spectra have been reported for [M25(MPA)18]−. The calculations suggest that [Ag25(SR)18]− (SR = thiolate) clusters have a weak luminescence band in the NIR region. Finally, solvent shifts were found to be minor, whereas the absorption bands seem to be significantly redshifted in solid-state materials. [ABSTRACT FROM AUTHOR]

Fluoroacetate is a toxic compound whose environmental accumulation may represent an important contamination problem, its elimination is therefore a challenging issue. Fluoroacetate dehalogenase catalyzes its degradation through a two step process initiated by an SN2 reaction in which the aspartate residue performs a nucleophilic attack on the carbon bonded to the fluorine; the second step is hydrolysis that releases the product as glycolate. In this paper, we present a study based on density functional theory calculations of the SN2 initiation reaction modeled through the interaction between the substrate and the propionate anion as the nucleophile. Results are analyzed within the framework of the reaction force and using the reaction electronic flux to identify and characterize the electronic activity that drives the reaction. Our results reveal that the selective protonation of the substrate catalyzes the reaction by decreasing the resistance of the structural and electronic reorganization needed to reach the transition state. Finally, the reaction energy is modulated by the degree of stabilization of the fluoride anion formed after the SN2 reaction. In this way, a site-induced partial protonation acts as a chemical switch in a key process that determines the output of the reaction. [ABSTRACT FROM AUTHOR]

The understanding of closed-shell interactions has become of tremendous relevance in the ever-growing field of supramolecular chemistry. Here, we present a theoretical study in which we characterised the intermolecular interactions between gold-based building blocks, namely ([Au(NH3)2]NO3)n (n = 1,2,4,8) and ([Au(NCH)2][AuCl4])n (n = 1,2). Due to the complex nature of these interactions, several methods were used such as the MP2, CCSD(T), PBE-D3, B3LYP-D3, and CAM-B3LYP-D3 (DFT-D3) levels. In all models were found closed-shell contacts among the gold atoms, interactions that resulted in being consistent with the presence of a high ionic contribution and a dispersion-type interaction. The absorption spectra of these models were calculated by the single excitation time-dependent-DFT (TD-DFT) method and CC2 levels, being the aurophilic interactions mainly responsible for the bands in both types of models. The theoretical models agree with the experimental results. [ABSTRACT FROM AUTHOR]

The electronic structure, spectroscopic properties, and solid state chemistry of monomer and dimers of [AuPh(CNPh)] complex were studied at post-Hartree-Fock (MP2, SCS-MP2, and CC2) and density functional theory levels. The absorption spectra of these complexes were calculated using single excitation time-dependent (TD) methods at DFT, CC2, and SCS-CC2 levels. The influences of the bulk are accounted for at the PBE-D3 level, incorporating dispersion effects. The calculated values agree with the experimental range, where absorption and emission energies reproduce experimental trends with large Stokes shifts. The aurophilic interaction is identified as a key factor influencing the spectroscopic and structural properties of these complexes. The intermetallic interactions were found as the main factor responsible for MMCT electronic transitions in the models studied., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

We present an exhaustive exploration of the driving forces dominating the interaction between gold atoms in the trans-(AuX) 2 , where X is a halogen ligand. This work provides insights into the nature of the gold-gold contact in the trans-(AuX) 2 . The geometries and energies were calculated at the MP2, CCSD(T), and DFT-D3(BJ) (B3LYP, PBE, and TPSS) levels of theory. The results show a short Au-Au distance, typical of a covalent bond, but with a weak interaction energy associated with noncovalent interactions. It is established that the physical contributions from polarization and the electronic correlation forces are the most relevant at the post-Hartree-Fock level of theory. Also, the electrostatic term is attractive but with low contribution. Finally, the Wiberg indices and NBO analysis exposed a small covalent character between the gold atoms, revealing that this contribution is insufficient to explain the stability of the dimers. It is concluded that a sum of contributions makes it possible to establish an attraction between the gold atoms in the dimers studied beyond a classical aurophilic interaction.

Electronic absorption and emission spectra of [M 25 (MPA) 18 ] - (M = Au, Ag; MPA = SCH 2 CH 2 COOH) clusters have been recorded for energies below 5 eV at the time-dependent density functional theory (TDDFT) level using B3LYP and TPSSh functionals and compared to the calculated ones using the computationally inexpensive simplified TDDFT (sTDDFT) approach. The results show a qualitative agreement between the TDDFT and sTDDFT approaches used here, which were also in line with the experimental and theoretical spectra previously reported. However, the sTDDFT calculations were several orders of magnitude faster than those obtained by TDDFT. Our results support that sTDDFT provides an excellent balance between accuracy and low computational cost, becoming a suitable approach for studying the absorption and emission spectra of noble-metal clusters of sizes that would be unaffordable by the traditional TDDFT methods. The main peaks of the experimental absorption spectrum of [Au 25 (MPA) 18 ] - have been previously assigned, whereas [Ag 25 (MPA) 18 ] - has not been synthesised. However, its absorption spectrum resulted in having similar features to the experimental spectrum of [Ag 25 (GSH) 18 ] - (GSH = glutathione), used to validate our results. The emission spectra, which to date have not been reported either from experimental or theoretical means, were simulated by using the molecular structure of the first excited triplet state (T 1 ). The emission spectra were obtained by comparing them to those of [M 25 (GSH) 18 ] - since no experimental luminescence spectra have been reported for [M 25 (MPA) 18 ] - . The calculations suggest that [Ag 25 (SR) 18 ] - (SR = thiolate) clusters have a weak luminescence band in the NIR region. Finally, solvent shifts were found to be minor, whereas the absorption bands seem to be significantly redshifted in solid-state materials.

The electronic structure and spectroscopic properties of [AuCl(CNR)] and [AuCl(CO)] (R = -H, -CH 3 , -Cy) complexes with d 10 -d 10 type interactions were studied at the post-Hartree-Fock (MP2, SCS-MP2, CCSD(T)) and density functional theory levels. It was found that the nature of the intermetal interactions is consistent with the presence of an electrostatic (dipole-dipole) contribution and a dispersion-type interaction. The absorption spectra of these complexes were calculated using the single excitation time-dependent (TD) method at the DFT and SCS-CC2 levels. The calculated values are in agreement with the experimental range, where the absorption and emission energies reproduce the experimental trends, with large Stokes shifts. According to this, intermetallic interactions were found to be mainly responsible for the metal-metal charge transfer (MMCT) electronic transitions among the models studied., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The uses of the sulfur-gold bond in the design of new molecular clusters have gained increasing attention in recent years. Their size and shape are diverse providing a wide variety of optical and electronic properties. Here we present a computational study of the absorption and emission properties of a small [Au(dithioacetate)] 4 cluster as a model for these systems. The electronic structure of the Au 4 S 8 core of this cluster permits rationalization of the source of the optical properties and how these are connected with that specific structural scaffold. Due to the complex nature of the aurophilic intramolecular interactions taking place in this system, several methods were used, such as the MP2, SCS-MP2, PBE-D3, and TPSS-D3 levels; both in gas and solvent phases. The absorption spectra of the cluster were calculated by the single excitation time-dependent-DFT (TD-DFT) method, CC2, SCS-CC2, and ADC(2) levels. The ab initio correlated calculations and previously reported experimental data have been used to assess the performance of our calculations. Moreover, the emission T 1 -S o transition was calculated, where the SCS-CC2 level showed an excellent agreement with the experimental results. The core Au 4 S 8 was identified as mainly responsible for the absorption and emission transitions according to the theoretical model., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)