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Copper corroles are known for their unique multiconfigurational electronic structures in the ground state, which arise from the transfer of electrons from the π orbitals of the corrole to the d orbital of copper. While density functional theory (DFT) provides reasonably good molecular geometries, the determination of the ground spin state and the associated energetics is heavily influenced by functional choice, particularly the percentage of Hartree-Fock exchange. Using extended multireference perturbation theory methods (XMS-CASPT2), functional choice can be eliminated. The molecular geometries and electronic structures of both the unsubstituted and meso-triphenyl copper corroles were investigated. A minimal active space was employed for structural characterization, while larger active spaces are required to examine the electronic structure. The XMS-CASPT2 investigations conclusively identify the ground electronic state as a multiconfigurational singlet (S0) with three dominant electronic configurations, in its lowest energy and characteristic saddled structure. In contrast, the planar geometry corresponds to the triplet state (T0), which is approximately 5 kcal/mol higher in energy compared to the S0 state for both the bare and substituted copper corroles. Notably, the planarity of the T0 geometry is reduced in the substituted corrole compared to the unsubstituted one. By analyzing the potential energy surface (PES) between the S0 and T0 geometries using XMS-CASPT2, the multiconfigurational electronic structure is shown to transition towards a single electron configuration as the saddling angle decreases (i.e., as one approaches the planar geometry). Despite the ability of the functionals to reproduce the minimum energy structures, only the TPSSh-D3 PES is reasonably close to the XMS-CASPT2 surface. Significant deviations along the PES are observed with other functionals.

We report the computational investigation of the molecular geometries of a pair of manganese(III) spin crossover complexes. For the high-spin geometry, the density functionals significantly overestimate the Mn−Namine bond distances, although the geometry for the intermediate-spin is well-described. Comparisons with several wavefunction-based methods demonstrate that this error is due to the limited ability of density functional theory (DFT) to recover dispersion beyond a certain extent. Among the methods employed for geometry optimization, Møller-Plesset perturbation theory (MP2) appropriately describes the high-spin geometry, but results in a slightly reduced Mn−O distance in both the spin-states. On the other hand, complete active space second-order perturbation theory (CASPT2) results in a good description of the geometry for the intermediate spin state, but also sufficiently recovers dispersion performing well for the high-spin state. Despite the fact that the electronic structure of both spin states is dominated by one electron configuration, CASPT2 offers a balanced approach leading to molecular geometries with much better accuracy than MP2 and DFT. A scan along the Mn−Namine bond demonstrates that coupled cluster methods (i.e., DLPNO-CCSD(T)) also yield bond distances in agreement with experiment, while multiconfiguration pair density functional theory (MC-PDFT) is unable to recover dispersion well enough, analogous to single reference DFT.

A series of organometallic complexes [Cl(dppe)2 Ru-C≡C-(3-R-C4 H2 S)-C≡C-Ru(dppe)2 Cl] (3-R-C4 H2 S=3-substituted thienyl moiety; R=-H, -C2 H5 , -C3 H7 , -C4 H9 , -C6 H13 , -OMe, -CN in 5 a-5 g respectively) have been synthesized by systematic variation of 3-substituents at the thienylethynyl bridging unit. The diruthenum(II) wire-like complexes (5 a-5 g) have been achieved by the reaction of thienylethynyl bridging units, HC≡C-(3-R-C4 H2 S)-C≡CH (4 a-4 g) with cis-[Ru(dppe)2 Cl2 ]. The wire-like diruthenium(II) complexes undergo two consecutive electrochemical oxidation processes in the potential range of 0.0 - 0.8 V. Interestingly, the wave separation between the two redox waves is greatly influenced by the substituents at the 3-position of the thienylethynyl. Thus, the substitution on 3-position of the thienylethynyl bridging unit plays a pivotal role for tuning the electronic properties. To understand the electronic behavior, density functional theory (DFT) calculations of the selected diruthenium wire-like complexes (5 a-5 e) with different alkyl appendages are performed. The theoretical data demonstrate that incorporation of alkyl groups to the thienylethynyl entity leaves unsymmetrical spin densities, thus affecting the electronic properties. The voltammetric features of the other two Ru(II) alkynyl complexes 5 f and 5 g (with -OMe and -CN group respectively) show an apparent dependence on the electronic properties. The electronic properties in the redox conjugate, (5 a+ ) with Kc of 3.9×106 are further examined by UV-Vis-NIR and FTIR studies, showing optical responses in NIR region along with changes in "-Ru-C≡C-" vibrational stretching frequency. The origin of the observed electronic transition has been assigned based on time-dependent DFT (TDDFT) calculations.

Using fully internally contracted (FIC)-CASPT2 analytical gradients, geometry optimizations of spin-crossover complexes are reported. This approach is tested on a series of Fe(II) complexes with different sizes, ranging from 13 to 61 atoms. A combination of active space and basis set choices are employed to investigate their role in determining reliable molecular geometries. The reported strategy demonstrates that a wave function-based level of theory can be used to optimize the geometries of metal complexes in reasonable times and enables one to treat the molecular geometry and electronic structure of the complexes using the same level of theory. For a series of smaller Fe(II) SCO complexes, strong field ligands in the LS state result in geometries with the largest differences between DFT and CASPT2; however, good agreement overall is observed between DFT and CASPT2. For the larger complexes, moderate sized basis sets yield geometries that compare well with DFT and available experimental data. We recommend using the (10e,12o) active space since convergence to a minimum structure was more efficient than with truncated active spaces (e.g., (6e,5o)) despite having similar Fe–ligand bond distances.

2,4-Dienones undergo visible-light-promoted, photocatalyst-free dimerization in neat conditions to provide cyclohexene derivatives stereoselectively through cascade rearrangement pathways, whereas regioselective E → Z isomerization of the more dienophilic double bond takes place exclusively in nitromethane. On the basis of intermediate isolation and computational DFT studies, the dimerization reaction is proposed to proceed via s-trans to s-cis isomerization/regioselective E → Z isomerization/Diels-Alder cycloaddition.

Accurate treatment of electron correlation and spin-orbit coupling is essential for understanding the electronic structure and spectroscopy of high-spin, open-shell transition metal dihalides. The experimental photoelectron spectra of MnX2, X = Cl, Br, I, have been interpreted on the basis of multi-configurational ab initio electronic structure calculations. The intensity of the photoelectron bands have been calculated from the norms of the Dyson orbitals, which represent the transition probability to a particular ionic state from a given starting state. The present study provides a detailed account of the contribution of the one- and two-electron transitions in the experimental photoelectron spectra of the title molecules and outlines the nature of the photoelectron bands in terms of the closely spaced quintet and septet states of the cationic species.

In the search for a low molecular weight organo gelator, sodium-4-oxo-4-((11-phenoxyundecyl)oxy)but-2-enoate (PUDMS) was designed and synthesized using phenol, 11-bromoundecanol, and maleic anhydride as starting materials. The maleate based amphiphile entrap hydrocarbon solvents like cyclohexane, hexane, and heptane in the presence of 25 μL water, interestingly in pure solvents no gelation was observed. Among the hydrocarbon solvents, cyclohexane shows excellent gelation with lowest critical gelation concentration (0.44 mg/mL) value with higher gelation number (8005) in an optimal water volume of 25 μL. The organogels were characterized by various conventional techniques such as rheology, DSC, FE-SEM, and XRD. The dynamic mechanical strength is independent of the angular frequency ranging between 0.1 Hz to 12 Hz irrespective of the organic solvent used, though cyclohexane showed little higher magnitude in the storage modulus (G') value. The microstructure observed by the FE-SEM study suggested PUDMS has emulsified morphology for cyclohexane and hexane solvent where as sheet like structure observed for heptane. Further, the bilayer thickness for the gel network structure was calculated from XRD studies. The pH-induced release of vitamin B 12 from the vitamin B 12 -loaded PUDMS organogel, showing potential application in pH-triggered nutraceutical release.

Linear or near linear bicoordinated mononuclear Co(II) complexes are studied as potential single molecule magnets due to the strong spin-orbit constant of Co(II) and its low coordination number that retains the metal orbital angular momentum unquenched. The spin-orbit coupled unquenched orbital angular momentum of the metal center upon interaction with ligand field produces strong magnetic anisotropy. The role of ligand environment, structural distortion and conformational change on the magnetic anisotropy of the Co(II) complexes are investigated employing ab initio electronic structure calculations. The zero-field splitting parameters, g-tensors, and the transition magnetic moment matrix elements among the Kramer's pairs are evaluated to obtain the effective anisotropy barriers (Ueff) and mechanism of relaxation of magnetization in a series of Co(II) complexes, where the estimated values of Ueff range between 394 cm-1 to 974 cm-1, representing the largest effective anisotropy barrier reported for transition metal complexes. The calculations reveal that the ligand field strength, structural distortion and conformational changes not only affect the magnetic anisotropy barrier but also significantly alter the mechanism of relaxation of magnetic moments.

In the search for single molecule magnets, metal ions are considered pivotal towards achieving large magnetic anisotropy barriers. In this context, the influence of ligands with heavy elements, showing large spin-orbit coupling, on magnetic anisotropy barriers was investigated using a series of Mn(ii)-based complexes, in which the metal ion did not have any orbital contribution. The mixing of metal and ligand orbitals was achieved by explicitly correlating the metal and ligand valence electrons with CASSCF calculations. The CASSCF wave functions were further used for evaluating spin-orbit coupling and zero-field splitting parameters for these complexes. For Mn(ii) complexes with heavy ligand atoms, such as Br and I, several interesting inter-state mixings occur via the spin-orbit operator, which results in large magnetic anisotropy in these Mn(ii) complexes.

(PMe3)2FeCl3 is an Fe(III) complex that exists in the intermediate-spin ground state in a distorted trigonal bipyramidal geometry. An electronic state with high-spin configuration lies in close vic...

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with -C[triple bond, length as m-dash]C-H termini have been successfully synthesized through stepwise Pd(0)/Cu(i)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(ii) diacetylide complexes (O1-Ru2, O3-Ru2, O5-Ru2 and O7-Ru2, respectively) have been prepared by the reaction of cis-Ru(dppe)2Cl2 and NaPF6 in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(ii)-Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(ii)-C[triple bond, length as m-dash]C-Ph]-capped diacetylide organometallic wires (O1-Ru2-Ph, O3-Ru2-Ph, O5-Ru2-Ph and O7-Ru2-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(ii)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(ii)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(ii) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.

Mononuclear Fe(iii) complexes commonly exist in high-spin or low-spin states, whereas their occurrence in the intermediate-spin state (S = 3/2) is scarce. The magnetic anisotropy in two trigonal-bipyramidal mononuclear Fe(iii) complexes, (PMe3)2FeCl3 (1) and (PMe2Ph)2FeCl3 (2), in their intermediate-spin ground state has been examined by ab initio electronic structure calculations. The calculations successfully reproduce the experimental magnetic anisotropic barrier, Ueff in 1 (81 cm−1) and 2 (42 cm−1), which is shown to arise due to thermally assisted quantum tunneling of magnetization from the second Kramer’s doublets. The magnetic anisotropy in both the complexes is found to be significantly influenced by the axial ligands, while the equatorial ligands have negligible contribution. The large reduction in Ueff of 2 has been shown to arise due to the phenyl groups, which results in the lifting of orbital degeneracy of e″ and e′ frontier orbitals and leads to a net quenching of the orbital angular momentum of the metal center causing a diminished spin-orbit splitting in 2. While the crystal structure of 2 shows two phenyl rings out of plane to each other, the present study discovered another stable conformation of 2, where the two phenyl rings are in the same plane (2a). Unlike 2, the planarity of the two phenyl rings in 2a restores the degeneracy of the frontier orbitals, thereby increasing the spin-orbit splitting and a consequent rise in Ueff from 42 to 80 cm−1 in 2a.