Ab initio investigation of the geometrical behavior in solution and electronic structure of the anion complexes [bis(1,3-dithiole-2-thione-4,5-dithiolate)M], for M = Bi(III), Sb(III), and Zn(II).

CONTEXT: 1,3-Dithiole-2-thione-4,5-dithiolate (dmit) ligands are known for their conductive and optical properties. Dmit compounds have been assessed for use in sensor devices, information storage, spintronics, and optical material applications. Associations with various metallic centers endow dmit complexes with magnetic, optical, conductive, and antioxidant properties. Optical doping can facilitate the fabrication of magnetic conductor materials from ground-state nonmagnetic cations. While most studied complexes involve transition-metal centers due to their diverse chemistry, compounds with representative elements are less explored in the literature. This study investigated the structural and electronic properties of bisdmit complexes with representative Bi(III), Sb(III), and Zn(II) cations. AIMD calculations revealed two new geometries for Bi(III) and Zn(II) complexes, diverging from the isolated geometry typically used in quantum chemical calculations. The coordination of acetonitrile molecules to the cationic centers of the complexes resulted in unstable structures, while the dimerization of the complexes was stable. SA-CASSCF/NEVPT2 calculations were applied to the structures of the isolated complexes and stable dimers, confirming the multireference character of the electronic structure of the three systems and the multiconfigurational character of the Bi(III) complex. The electronic spectra simulated by the STEOM-DLPNO-CCSD calculations accurately reproduced the experimental UV‒Vis spectra indicating the participation of the isolated Bi(III) dmit complex and its dimeric form in solution. METHODOLOGY: AIMD calculations of the dmit salts were conducted using the GFN2-xTB method with 60 explicit acetonitrile molecules as the solvent at 300 K for a total simulation time of 50.0 ps, with printing intervals of 0.5 fs. The final geometries were optimized employing the PBEh-3c compound method, incorporating implicit conductor-like polarizable continuum model (CPCM) solvation for acetonitrile. Local energy decomposition (LED) analysis at the DLPNO-CCSD(T)/Def2-TZVP level of theory was utilized to investigate the stability of the complex geometries identified by AIMD. The electronic structures of the complexes were assessed using the SA-CASSCF/NEVPT2/Def2-TZVP method to confirm the multiconfigurational and multireference nature of their electronic structures. Electronic spectra were analyzed using the STEOM-DLPNO-CCSD/Def2-TZVP method, with CPCM used to simulate an acetonitrile medium.

Electronic analysis of n-propyl xanthate complexes with group 12 metals: a theoretical-experimental study.

CONTEXT: Xanthates are organic compounds of great interest in coordination chemistry due to their different basic sites, which allow them to form complexes with different coordination modes and geometries. These compounds are relevant in the environment and act as heavy metal collectors in aqueous environments. In this theoretical-experimental work, electronic spectroscopy studies of n-propyl xanthate complexes with group 12 metals were performed. This study verified structural differences in these systems, depending on the environment in which they are inserted. In addition, structural differences were observed when the solid was changed to an n-hexane solution. Thus, it was observed that the complexes assume a mononuclear structure in solution, while they present a polymeric form in the solid phase. The electronic spectra obtained through TD-DFT calculations were compared to those of the previously synthesized complexes. In the final theoretical analysis, the main orbitals involved in these transitions were assigned using population analysis calculations. The synthesis of the complexes was confirmed through infrared (MID and FAR), UV‒Vis, Raman, and NMR-1H spectroscopic analyses. METHODS: The structures of the mononuclear and polymeric complexes were optimized in vacuum and n-hexane. Under vacuum, DFT levels M06L/6-311 + + G** + LANL2TZ and M06L/def2-TZVP were used for the mononuclear complexes, and M06L/LANL2DZ + LANL2 were used for the polymer complexes. For the calculations of the mononuclear complexes in n-hexane, the same level of theory was used for the solid state. TD-DFT calculations for 300 excited states were performed with the same levels of theory and used the optimized structures of the complexes. Furthermore, population analysis was carried out on all the systems studied. Gaussian 09 software was used for the structure optimization, TD-DFT, and population analysis calculations. GaussSum software was used to evaluate the molecular orbitals and electronic spectra.

Rapid and Accurate Prediction of the Axial Magnetic Anisotropy in Cobalt(II) Complexes Using a Machine-Learning Approach.

Estimating the magnetic anisotropy for single-ion magnets is complex due to its multireference nature. This study demonstrates that deep neural networks (DNNs) can provide accurate axial magnetic anisotropy (D) values, closely matching the complete-active-space self-consistent-field (CASSCF) quality using density functional theory (DFT) data. We curated an 86-parameter database (UFF1) with electronic data from over 33000 cobalt(II) compounds. The DNN achieved an R2 of 0.906 and a mean absolute error of 18.1 cm-1 in comparison to reference CASSCF D values. Remarkably, it is 11 times more accurate than DFT methods and 7700 times faster. This approach hints at DNNs predicting the anisotropy in larger molecules, even when trained on smaller ligands.

Theoretical studies of Zn2+ complexes with alkyl xanthate ligands: a thermochemical, electronic energy decomposition, and natural bond orbital analysis.

CONTEXT: Xanthates are organic compounds that present great interest for coordination chemistry, because they can bond in different ways to the metal ion. Thus, these compounds have several applications, being best known for their environmental application. In fact, xanthates are recognized for their application as heavy metal collector agents in aqueous environments. In view of this application, this study is aimed at showing the thermochemical and electronic parameters obtained for the reactions of substitution water molecules in the aqua zinc complexes, by xanthate ligands (n-propyl, n-butyl, and n-pentyl xanthates). In addition to their environmental application, xanthates have shown biological properties, such as anti-bacterial and anti-cancer. In recent years, xanthates have also been used in the technological area, where it participates as a precursor of sulfides for the manufacture of thin films. Our results showed complexes with distorted octahedral geometries and with negative values of enthalpy and Gibbs free energy, indicating exothermic and spontaneous processes. For all the complexes, it was observed that Zn2+ complexes have both an ionic and covalent character. However, the monosubstituted complexes showed a predominance of the ionic character. In addition, high donor-acceptor interaction energies were obtained, indicating a good superposition between the s and p orbitals involved in the Zn-S bond. METHODS: This work consists in theoretical studies of Zn2+ complexes with alkyl xanthate ligands, with different structures, where optimization and normal modes calculations were performed at different DFT levels: M06L, M06-2X, wB97XD, and B3LYP/6-311++G**+LANL2TZ, with Gaussian09 program. The process of substitution of two aqua by two xanthate ligands was analyzed in stages, forming cationic and neutral complexes, in the first and second stages, respectively. In addition, electronic energy decomposition (EDA) and natural bond orbital (NBO) analysis were performed at level M06L/6-311++G**+LANL2TZ with Gamess program.

Field-induced single-ion magnets exhibiting tri-axial anisotropy in a 1D Co(II) coordination polymer with a rigid ligand 4,4'-(buta-1,3-diyne-1,4-diyl)dibenzoate.

Herein a 1D Co(II) coordination polymer of formula [Co(η1-L1)(η2-L1)(py)2(H2O)]n (CoCP) has been synthesised using the rigid H2L1 proligand, containing a long spacer bearing two triple bonds. Single-crystal X-ray diffraction showed that Co(II) adopts a distorted octahedral geometry. The state-averaged complete active self-consistent field (SA-CASSCF) calculation showed that the ground state of CoCP is a high spin quartet with a highly multiconfigurational character of its electronic structure. Due to the large intra- and intermolecular distances between the spin carriers, the magnetic interactions are negligible and the zero-field splitting (ZFS) effects of cobalt(II) ions are predominant. This behavior was confirmed by direct current (DC) magnetic measurements and theoretical calculations using the broken-symmetry approach. Quantum chemical calculations indicate that CoCP has a negative axial component possessing mixed tri-axial anisotropy. The DC magnetic susceptibility data were fitted with a Griffith-Figgis Hamiltonian and the obtained parameters are in good agreement with those simulated by the ab initio calculation. Alternating current (AC) magnetic measurements showed a field induced slow magnetic relaxation in CoCP, which is attributed to the hyperfine interaction effects.

Spin-frustration with two quasi-degenerated spin states of a copper(II) heptanuclear complex obtained from an amino acid ligand.

The Cu(ii) heptanuclear complex (Cu7atac) was synthesised using the hydrated amino acid ligand 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (Hatac·H2O). Single crystal X-ray diffraction analysis revealed a µ3-hydroxo bridged Cu(ii) heptanuclear complex, consisting of two triangular subunits and one Cu(ii) ion as a bridge with the formula [Cu7(atac)6(µ3-OH)2(NO3)2(H2O)10](NO3)4. The magnetic behaviour of this discrete 0D complex shows strong antiferromagnetic couplings between Cu(ii) mediated by N,N bonding and an anti-anti modes of the carboxylate anion of the ligand atac-. The magnetic data were fitted considering a 3J model. To support the model used to fit the magnetic data of the Cu7atac complex, theoretical calculation methods (complete active space self-consistent field, CASSCF, density functional theory (DFT) using the UKS TPSS/Def2-TZVP//Def2-SVP level and periodic boundary conditions (PBC) using PBE/DZVP-MOLOPT-GTH) were performed to obtain the spin states, spin density map and J couplings. The theoretical results suggest that Cu7atac is a spin-frustrated complex in the ground state, in which the doublet spin state co-exists with the quartet spin state.

Vibrational spectroscopic and Hirshfeld surface analysis of carvedilol crystal forms.

The drug carvedilol, used to treat cardiovascular conditions, is known to exist in distinct crystalline forms. Polymorphs II and III and the hydrate are characterized by variations in their molecular packing and conformation. This study deals with the spectroscopic (supported by quantum chemistry calculations) characterization of carvedilol structures. Band assignments were performed considering the isolated molecules and periodic calculations. We discuss the correlation between the vibrational modes and the intermolecular forces in the crystalline structures. Towards a better understanding of the intermolecular interactions, Hirshfeld surface was used. Besides band shifts related to stretching vibrations of N-H and O-H groups, differences between other modes have shown the possibility of using infrared spectroscopy to distinguish the crystal forms; technique routinely used in quality control of pharmaceutics. According to the spectroscopic analysis, the N-H groups participate in stronger bonds in the polymorph III, which contributes to its greater stability. With Hirshfeld surface we concluded that the bond with the nitrogen of the aliphatic chain participating as hydrogen acceptor in polymorph II is responsible for the pointy peaks in the fingerprint plot. This can explain why polymorph II shows lower dissolution in acid medium, as described in a previous work of our group.

Molecular structure, natural bond analysis, vibrational and electronic spectra, surface enhanced Raman scattering and Mulliken atomic charges of the normal modes of [Mn(DDTC)2] complex.

Theoretical and experimental bands have been assigned for the Fourier Transform Infrared and Raman spectra of the bis(diethyldithiocarbamate)Mn(II) complex, [Mn(DDTC)2]. The calculations have been based on the DFT/B3LYP method, second derivative spectra and band deconvolution analysis. The UV-vis experimental spectra were measured in acetonitrile solution, and the calculated electronic spectrum was obtained using the TD/B3LYP method with 6-311G(d, p) basis set for all atoms. Charge transfer bands and those d-d spin forbidden were assigned in the UV-vis spectrum. The natural bond orbital analysis was carried out using the DFT/B3LYP method and the Mn(II) hybridization leading to the planar geometry of the framework was discussed. Surface enhanced Raman scattering (SERS) was also performed. Mulliken charges of the normal modes were obtained and related to the SERS enhanced bands.

Synthesis, crystal structures and magnetic behaviour of four coordination compounds constructed with a phosphinic amide-TEMPO radical and [M(hfac)2] (M = Cu(II), Co(II) and Mn(II)).

In the present work we describe the synthesis, crystal structures and magnetic properties of four coordination compounds obtained by assembling a new phosphinic amide containing the TEMPO moiety, 1-piperidinyloxy-4-[(diphenylphosphinyl)amino]-2,2,6,6-tetramethyl radical (dppnTEMPO), with [M(hfac)2] building blocks (M = Cu(II), Co(II), Mn(II)). The crystal structures of the coordination compounds revealed the usefulness of the functionalized radical to provide discrete or extended architectures. In the copper compound () the ligand is coordinated through the oxygen atom of the NP[double bond, length as m-dash]O linkage to the metal, which exists in a square pyramidal or octahedral geometry. For the cobalt and manganese complexes (), both the phosphinic amide and the nitroxide oxygen atoms are involved in the coordination to the metal leading to one dimensional systems. In the cobalt complex () an interesting spin topology in the zig-zag chain was obtained due to the oxygen atom of the phosphinic amide group being µ2 coordinated to two cobalt(ii) ions. The magnetic behaviour of the coordination compounds shows overall antiferromagnetic interactions involving the metal ion and the organic radical. DFT calculations were performed in order to assign the main path for the magnetic interactions.

Molecular structure, natural bond analysis, vibrational, and electronic spectra of aspartateguanidoacetatenickel(II), [Ni(Asp)(GAA)]·H2O: DFT quantum mechanical calculations.

The aspartateguanidoacetatenickel (II) complex, [Ni(Asp)(GAA)], was synthesized and structural analysis was performed by means of the experimental methods: determination of the C, H, N and O contents, thermogravimetry, infrared and Raman spectroscopy. DFT:B3LYP/6-311G(d, p) calculations have been performed giving optimized structure and harmonic vibrational wavenumbers. Second derivative of the FT-infrared, FT-Raman and Surface Raman Enhanced Scattering (SERS) spectra, and band deconvolution analysis were also performed. Features of the FT-infrared, FT-Raman and SERS confirmed theoretical structure prediction. Full assignment of the vibrational spectrum was also supported by a carefully analysis of the distorted geometries generated by the normal modes. The Natural Bond Orbital analysis (NBO) was also carried out as a way to study the Ni (II) hybridization leading to the pseudo planar geometry of the framework, and the extension of the atomic N and O hybrid orbital of the different amino acids in the bond formation. Bands of charge transfer and d-d transitions were assigned in the UV-Vis spectrum.

Vibrational and electronic spectroscopy of neutral antimony coordination compounds of the 1,3-dithiole-2-thione-4,5-dithiolate (dmit).

The S 1s X-ray absorption near edge structure (XANES) and X-ray photoelectron spectra (XPS) of the neutral complexes [SbL(dmit)] (L = Br or I; dmit =1,3-dithiole-2-thione-4,5-dithiolate) have been measured using tunable synchrotron radiation. The valence shell electronic excitation by ultraviolet-visible (UV-vis) spectroscopy and the infrared vibrational spectra are presented and analyzed. The UV-vis results lead to an assignment of bands at 400 nm as π(Sm) → π*(C═S), where S(m) is the thiolate sulfur. The corresponding S 1s → π*(C═S) transition was identified at 2468.3 eV. Ab initio calculations, within the improved virtual orbital (IVO) method, carried out with the GSCF3 program, were applied to establish a complete and accurate spectral assignment. It has been the first attempt to apply such methodology for dmit coordination compounds, and very consistent results were obtained.

cis-Bis{(E)-2-[(2-fluoro-phen-yl)imino-meth-yl]phenolato-κ(2) N,O}bis-(pyridine-κN)nickel(II).

The structure of the title compound, [Ni(C13H9FNO)2(C5H5N)2], consists of an Ni(II) atom on a crystallographic center of symmetry, octa-hedrally bonded through both the N and O atoms to two 2-[(2-fluoro-phen-yl)imino-meth-yl]phenolate (L) ligands, as well as two pyridine ligands. The F atoms of L are disordered over two positions related by a 180° rotation of the fluoro-phenyl group around its external C-N bond.

An experimental and theoretical study of the electronic spectra of tetraethylammonium [bis(1,3-dithiole-2-thione-4,5-dithiolato)M(III)] and tetraethylammonium [bis(1,3-dithiole-2-one-4,5-dithiolato)M(III)] (M = Sb or Bi).

Metal complexes of dmit and related ligands, such as dmio, have been studied extensively over the last few decades: [dmit](2-) = bis(1,3-dithiole-2-thione-4,5-dithiolato); [dmio](2-) = bis(1,3-dithiole-2-one-4,5-dithiolato). While much effort has been placed on determining structural properties, very few vigorous spectroscopic studies of these metal complexes have been undertaken. The spectroscopic features of the infrared, Raman and UV-vis spectra, previously reported, have largely been used to characterize compounds. In particular, many details of the electronic structure are still to be revealed. We now report a detailed analysis of the UV-vis spectra of the [M(dmit)](-1) and [M(dmio)](-1) anions, where M = Sb(III) or Bi(III). Experimental spectra were deconvoluted and analysed by several theoretical methodologies, including ab initio CI, TD and CISD calculations. The results led to the assignments of several MLCT/LMCT bands, occurring between 390 and 300 nm, and the confirmation of metal orbital contributions to the HOMO-LUMO boundary.

Rearrangement, nucleophilic substitution, and halogen switch reactions of alkyl halides over NaY Zeolite: formation of the bicyclobutonium cation inside the zeolite cavity.

Rearrangement and nucleophilic substitution of cyclopropylcarbinyl bromide over NaY and NaY impregnated with NaCl was observed at room temperature. The first-order kinetics are consistent with ionization to the bicyclobutonium cation, followed by internal return of the bromide anion or nucleophilic attack by impregnated NaCl to form cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl chlorides. The product distribution analysis revealed that neither a purely kinetic distribution, similar to what is found in solution, nor the thermodynamic ratio, which favors the allylcarbinyl halide, was observed. Calculations showed that bicyclobutonium and cyclopropylcarbinyl carbocations are minimal over the zeolite structure, and stabilized by hydrogen bonding with the framework structure. A new process of nucleophilic substitution is reported, namely halogen switch, involving alkyl chlorides and bromides of different structures. The reaction occurs inside the zeolite pores, due to the confinement effects and is an additional proof of carbocation formation on zeolites. The results support the idea that zeolites act as solid solvents, permitting ionization and solvation of ionic species.

An experimental and theoretical vibrational spectroscopic study of [AsPh(4)](2)[Sn(dmit)(3)] x Me(2)CO.

As shown previously by X-ray structure determinations, [tris(1,3-dithiole-2-thione-4,5-dithiolato)stannate(IV)](2-) salts, [Q](2)[Sn(dmit)(3)], contain isolated cations and dianions. While the tin centres generally having octahedral geometries, the overall shapes of the dianions of these complexes in the solid state can differ with conformations varying from T, Y to asymmetrical arrangements. We now report, as a follow up to our earlier study on the Y-shaped complex, [NEt(4)](2)[Sn(dmit)(3)], an experimental and theoretical study of the vibrational spectra of solid solvated {[AsPh(4)](2)[Sn(dmit)(3)] x Me(2)CO}, in which the dianion has a T-shaped conformation. The infrared and Raman spectra, recorded from 4000 to 150 cm(-1), have been analysed by different ab initio calculations based on restricted Hartree-Fock (RHF) and density functional theory (DFT-Beck3LYP). The calculations were carried out on isolated dianions and cations with the 6-31G and 6-31G(d) basis sets and effective core potentials of Steven, Bash and Krauss (SBK). Fundamentals, overtones and combinations have been assigned. Generally, the Y- and T-shaped dianions exhibit similar infrared/Raman spectra, apart from differences in the C=C and the symmetrical M-S stretching frequencies: such differences can be used diagnostically to distinguish the overall shape of the tris(chelated)metallate dianion.

Bis(tetra-n-butylammonium) and bis(tetraphenylphosphonium) salts of tris(2-oxo-1,3-dithiole-4,5-dithiolato)stannate(IV), both at 120 K.

The title compounds, (C16H36N)2[Sn(C3OS4)3], (I), and (C24H20P)2[Sn(C3OS4)3], (II), are examples of complex salts of the general form [Q]2[Sn(dmio)3], where Q is nBu4N+ or Ph4P+ and dmio is the 2-oxo-1,3-dithiole-4,5-dithiolate dianion. Features of both structures are the slightly distorted octahedral coordination of tin in the propeller-shaped dianions and the absence of any significant inter-anion contacts. The structure of (I) is particularly notable because all of the dianions in the sample crystal have the same propeller configuration, which is very unusual in this type of structure.