Di-μ-oxo Dimetal Core of Mn^IV and Ti^IV as a Linker Between Two Chiral Salen Complexes Leading to the Stereoselective Formation of Different <i>M</i>- and <i>P</i>‑Helical Structures

Because of restricted rotational freedom along the metal–metal axis, a di-μ-oxo dimetal core could be an excellent building block to create dinuclear compounds with well-defined stereochemistry, but their stereoselective synthesis remains a challenge. We herein report the formation of di-μ-oxo dimanganese­(IV) complexes with tetradentate salen ligands bearing different degrees of steric bulk, in order to study stereochemical aspects of the dimerization reaction that potentially generates multiple stereoisomers. X-ray crystallography shows that the di-μ-oxo dimanganese­(IV) complex with salen, where salen is (R,R)-N,N′-bis­(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, adopts a unique structure in which two salen complexes are arranged in an M-helical fashion. According to the solution study using 1H, 2H NMR, and circular dichroism spectroscopies, the dimerization reaction is highly diastereoselective in the presence of the tert-butyl group at the 3/3′ position as a determinant steric factor. In contrast, the di-μ-oxo dititanium­(IV) complex with the same salen ligand was previously reported to afford an opposite P-helical dimer. The present DFT study clarifies that a less-covalent Ti–O bonding causes a distortion of the di-μ-oxo dititanium­(IV) core structure, generating a completely different framework for interligand interaction. The present study provides a solid basis to understand the stereochemistry for the formation of the di-μ-oxo dimetal core

Critical Role of External Axial Ligands in Chirality Amplification of <i>trans</i>-Cyclohexane-1,2-diamine in Salen Complexes

A series of MnIV(salen)(L)2 complexes bearing different external axial ligands (L = Cl, NO3, N3, and OCH2CF3) from chiral salen ligands with trans-cyclohexane-1,2-diamine as a chiral scaffold are synthesized, to gain insight into conformational properties of metal salen complexes. X-ray crystal structures show that MnIV(salen)(OCH2CF3)2 and MnIV(salen)(N3)2 adopt a stepped conformation with one of two salicylidene rings pointing upward and the other pointing downward due to the bias from the trans-cyclohexane-1,2-diamine moiety, which is in clear contrast to a relatively planar solid-state conformation for MnIV(salen)(Cl)2. The CH2Cl2 solution of MnIV(salen)(L)2 shows circular dichroism of increasing intensity in the order L = Cl 3 ≪ N3 2CF3, which indicates MnIV(salen)(L)2 adopts a solution conformation of an increasing chiral distortion in this order. Quantum-chemical calculations with a symmetry adapted cluster-configuration interaction method indicate that a stepped conformation exhibits more intense circular dichroism than a planar conformation. The present study clarifies an unexpected new finding that the external axial ligands (L) play a critical role in amplifying the chirality in trans-cyclohexane-1,2-diamine in MnIV(salen)(L)2 to facilitate the formation of a chirally distorted conformation, possibly a stepped conformation

Computational Study on the Search for Non-Fullerene Acceptors, Examination of Interface Geometry, and Investigation of Electron Transfer

Extensive exploration of new non-fullerene acceptor materials in organic photovoltaics has led to enhancements in their power conversion efficiency. However, a comprehensive search for new non-fullerene acceptors with a detailed investigation of non-fullerene organic photovoltaic interface geometries has not been performed. In this study, we theoretically searched for new non-fullerene acceptors, modeled the interface of a non-fullerene acceptor and polymer, and estimated electron transfer rates for charge transfer and charge recombination processes via the Marcus formula. By examining more than 1850 candidate materials, promising acceptors were found. The theoretical investigation of the interface geometry revealed that steric hindrance restricts the possible interface geometries. Examination of the electron transfer rates suggested that the charge transfer process is more dominant than the charge recombination one, which is advantageous for high power conversion efficiency

Functionalization of Endohedral Metallofullerenes toward Improving Barrier Height for the Relaxation of Magnetization for Dy₂@C₈₀-X (X = CF₃, C₃N₃Ph₂)

We theoretically studied the electronic and magnetic properties of the exterior functionalized endohedral metallofullerenes (EMFs) of Gd2@­Ih-C80-X (where X is the exterior functional group). Molecular orbital analysis suggests that the presence of unpaired electron on the Ih-C80 cage is not favoring the observation of stable species. One of the effective strategies to address this problem is by attaching an exterior functional group to the fullerene cage. Out of the studied exterior functionalized EMFs, we were successful in finding two stable species such as Gd2@­Ih-C80-CF3 and Gd2@­Ih-C80-C3N3­Ph2 with no unpaired spin on the cage. Further, we utilized exterior functional groups such as −CF3 (1) and −C3N3­Ph2 (2) to model and to stabilize dinuclear Dy2@­Ih-C80 species, and we thoroughly investigated their magnetic properties using ab initio calculations. Within the single-ion paradigm, DyIII ions in 1 and 2 are magnetically anisotropic, and their magnetization-reversal energy barriers are estimated to be ∼698 and ∼705 cm–1, respectively. Furthermore, beyond the single-ion paradigm, i.e., considering a ferromagnetic coupling (∼30 cm–1) between the lanthanide ions and the radical spin, the energy barriers of 1 and 2 are estimated to be 79.8 and 73.0 cm–1, respectively

Critical Role of External Axial Ligands in Chirality Amplification of <i>trans</i>-Cyclohexane-1,2-diamine in Salen Complexes

A series of MnIV(salen)(L)2 complexes bearing different external axial ligands (L = Cl, NO3, N3, and OCH2CF3) from chiral salen ligands with trans-cyclohexane-1,2-diamine as a chiral scaffold are synthesized, to gain insight into conformational properties of metal salen complexes. X-ray crystal structures show that MnIV(salen)(OCH2CF3)2 and MnIV(salen)(N3)2 adopt a stepped conformation with one of two salicylidene rings pointing upward and the other pointing downward due to the bias from the trans-cyclohexane-1,2-diamine moiety, which is in clear contrast to a relatively planar solid-state conformation for MnIV(salen)(Cl)2. The CH2Cl2 solution of MnIV(salen)(L)2 shows circular dichroism of increasing intensity in the order L = Cl 3 ≪ N3 2CF3, which indicates MnIV(salen)(L)2 adopts a solution conformation of an increasing chiral distortion in this order. Quantum-chemical calculations with a symmetry adapted cluster-configuration interaction method indicate that a stepped conformation exhibits more intense circular dichroism than a planar conformation. The present study clarifies an unexpected new finding that the external axial ligands (L) play a critical role in amplifying the chirality in trans-cyclohexane-1,2-diamine in MnIV(salen)(L)2 to facilitate the formation of a chirally distorted conformation, possibly a stepped conformation

Critical Role of External Axial Ligands in Chirality Amplification of <i>trans</i>-Cyclohexane-1,2-diamine in Salen Complexes

A series of MnIV(salen)(L)2 complexes bearing different external axial ligands (L = Cl, NO3, N3, and OCH2CF3) from chiral salen ligands with trans-cyclohexane-1,2-diamine as a chiral scaffold are synthesized, to gain insight into conformational properties of metal salen complexes. X-ray crystal structures show that MnIV(salen)(OCH2CF3)2 and MnIV(salen)(N3)2 adopt a stepped conformation with one of two salicylidene rings pointing upward and the other pointing downward due to the bias from the trans-cyclohexane-1,2-diamine moiety, which is in clear contrast to a relatively planar solid-state conformation for MnIV(salen)(Cl)2. The CH2Cl2 solution of MnIV(salen)(L)2 shows circular dichroism of increasing intensity in the order L = Cl 3 ≪ N3 2CF3, which indicates MnIV(salen)(L)2 adopts a solution conformation of an increasing chiral distortion in this order. Quantum-chemical calculations with a symmetry adapted cluster-configuration interaction method indicate that a stepped conformation exhibits more intense circular dichroism than a planar conformation. The present study clarifies an unexpected new finding that the external axial ligands (L) play a critical role in amplifying the chirality in trans-cyclohexane-1,2-diamine in MnIV(salen)(L)2 to facilitate the formation of a chirally distorted conformation, possibly a stepped conformation

Critical Role of External Axial Ligands in Chirality Amplification of <i>trans</i>-Cyclohexane-1,2-diamine in Salen Complexes

A series of MnIV(salen)(L)2 complexes bearing different external axial ligands (L = Cl, NO3, N3, and OCH2CF3) from chiral salen ligands with trans-cyclohexane-1,2-diamine as a chiral scaffold are synthesized, to gain insight into conformational properties of metal salen complexes. X-ray crystal structures show that MnIV(salen)(OCH2CF3)2 and MnIV(salen)(N3)2 adopt a stepped conformation with one of two salicylidene rings pointing upward and the other pointing downward due to the bias from the trans-cyclohexane-1,2-diamine moiety, which is in clear contrast to a relatively planar solid-state conformation for MnIV(salen)(Cl)2. The CH2Cl2 solution of MnIV(salen)(L)2 shows circular dichroism of increasing intensity in the order L = Cl 3 ≪ N3 2CF3, which indicates MnIV(salen)(L)2 adopts a solution conformation of an increasing chiral distortion in this order. Quantum-chemical calculations with a symmetry adapted cluster-configuration interaction method indicate that a stepped conformation exhibits more intense circular dichroism than a planar conformation. The present study clarifies an unexpected new finding that the external axial ligands (L) play a critical role in amplifying the chirality in trans-cyclohexane-1,2-diamine in MnIV(salen)(L)2 to facilitate the formation of a chirally distorted conformation, possibly a stepped conformation

Di-μ-oxo Dimetal Core of Mn^IV and Ti^IV as a Linker Between Two Chiral Salen Complexes Leading to the Stereoselective Formation of Different <i>M</i>- and <i>P</i>‑Helical Structures

Because of restricted rotational freedom along the metal–metal axis, a di-μ-oxo dimetal core could be an excellent building block to create dinuclear compounds with well-defined stereochemistry, but their stereoselective synthesis remains a challenge. We herein report the formation of di-μ-oxo dimanganese­(IV) complexes with tetradentate salen ligands bearing different degrees of steric bulk, in order to study stereochemical aspects of the dimerization reaction that potentially generates multiple stereoisomers. X-ray crystallography shows that the di-μ-oxo dimanganese­(IV) complex with salen, where salen is (<i>R</i>,<i>R</i>)-<i>N</i>,<i>N</i>′-bis­(3,5-di-<i>tert</i>-butylsalicylidene)-1,2-cyclohexanediamine, adopts a unique structure in which two salen complexes are arranged in an <i>M</i>-helical fashion. According to the solution study using ¹H, ²H NMR, and circular dichroism spectroscopies, the dimerization reaction is highly diastereoselective in the presence of the <i>tert</i>-butyl group at the 3/3′ position as a determinant steric factor. In contrast, the di-μ-oxo dititanium­(IV) complex with the same salen ligand was previously reported to afford an opposite <i>P</i>-helical dimer. The present DFT study clarifies that a less-covalent Ti–O bonding causes a distortion of the di-μ-oxo dititanium­(IV) core structure, generating a completely different framework for interligand interaction. The present study provides a solid basis to understand the stereochemistry for the formation of the di-μ-oxo dimetal core

First-Principles Calculations of the Rotational Motion and Hydrogen Bond Capability of Large Organic Cations in Hybrid Perovskites

The organic cation dynamics in organic–inorganic hybrid perovskites affect the unique physical properties of these materials. To date, the rotational dynamics of methylammonium (CH₃NH₃⁺) and formamidinium (CH­(NH₂)₂⁺) have been studied both experimentally and from first-principles calculations. Recently, a novel hybrid perovskite with large organic cation guanidinium (C­(NH₂)₃⁺, GA), which exhibited extraordinarily long carrier lifetimes, was reported. In order to analyze physical properties of GA, we examined the detailed rotational potential energy surfaces and rotational energy barriers of GA in cubic-phase GASnI₃ and alternative perovskites using first-principles calculations. The analysis revealed that the principal rotations of GA involve six hydrogen bonds between the organic cation and the inorganic framework in the crystals. Our results suggest that GA can effectively passivate under-coordinated iodine ions using its high hydrogen bond capability, which is consistent with the experimental speculation that GA can suppress iodine defects by the hydrogen bonds

Density Functional Study on the Photopolymerization of Styrene Using Dinuclear Ru–Pd and Ir–Pd Complexes with Naphthyl-Substituted Ligands

A density functional study was performed to investigate the mechanism of the photocatalytic reactivity of styrene polymerization using dinuclear Ru–Pd and Ir–Pd catalytic complexes. In previous experiments with these catalysts, the reactivity increased, and more polymer products were yielded compared to dimers under visible light irradiation. The best catalytic reactivity was obtained using an Ir–Pd complex containing naphthyl substituents at the phenyl ligands coordinated to Ir (Ir–Pd1). In contrast, Ir–Pd2, an isomer of Ir–Pd1, containing naphthyl substituents at the pyridine ligands, did not show good reactivity, which may be related to the stability of the excited state of the catalytic complexes. In this study, we calculated the radiative lifetimes of these catalytic complexes and Ir–Pd1 had the longest lifetime; this result was consistent with the experimental results. The longest lifetime of the Ir–Pd1 was attributed to the destabilization of the highest occupied molecular orbital (HOMO) energy by π*−π* interactions between the naphthyl and phenyl ligands. Further, this destabilization of the HOMO energy afforded a small energy gap between the HOMO and lowest unoccupied molecular orbital, enhancing the metal-to-ligand charge transfer to the bridging ligand between Ir and Pd. Additionally, we focused on the reaction of the second insertion of styrene, which was identified as the rate-determining step of the polymerization cycle in a previous study. The singlet–triplet crossing points of the intermediates were estimated, and the barrier heights of the intersystem crossing were much lower than those in the thermal paths, which explained the efficiency of the photocatalytic reactivity in the experiment