Understanding Electronic Structure and Bonding in Uranium Complexes by Using Computational Methods

The electronic structure of actinide-containing complexes is often complex due to the near degeneracies present in the valence orbitals and the ability of both the 5f and 6d orbitals to engage in bonding. Herein we explore the electronic structure of uranium-arene complexes. Previous research has shown that the f orbitals on uranium and electrons from the arene can engage in different types of bonding ranging from strong, highly covalent bonds to polarized donor-acceptor interactions between occupied orbitals on the ligand and empty orbitals on the metal. By using a combination of density functional theory (DFT) and complete active space second order perturbation theory (CASPT2), we can study large complexes while ensuring that the electronic structure is properly described at the DFT level. Specifically, we are studying the[U(anth)2(hmpa)2] complex, 1, (where anth=anthracene and hmpa=hydroxymethylphosphoramide). In addition to the electronic structure, we will explore the nature of bonding in the complex and which orbitals are contributed to forming the bond. Future work will extend this study to 1) larger uranium-arene complexes containing more than one uranium center and 2) packing effects including the role of counterions on the geometry and electronic structure

ELECTRONIC STRUCTURE AND MOLECULAR GEOMETRIES OF METAL COMPLEXES WITH DFT AND MULTIREFERENCE METHOD

Metal complexes are ubiquitous for their diverse applications including catalysis, sensing, medicine, and environmental applications. For effective use of metal complexes, understanding their electronic structure is essential. In most cases, molecules can be represented as a single electron configuration. However, in some cases, especially transition metal and actinide complexes, multireference electronic structures are observed. This is because the valence d (and f) orbitals in metals are often nearly degenerate, leading to close-lying energy states and the subsequently more frequent presence of multiconfigurational electronic structures. The traditional approach to modeling these systems is to use density functional theory to optimize the geometry of the molecule. In most cases, this assumption holds; however, we are interested in cases where it is less obvious. This thesis focuses on the relationship between molecular geometry and electronic structure in metal complexes using DFT and multireference methods. In some cases, high-level multireference methods are used to obtain geometries and compute vibrational frequencies. Specifically, the copper corrole was studied, which has been the subject of long-standing debate due to its unique geometry and electronic structure. Complete active space multireference methods were employed to optimize unsubstituted and a set of meso-functionalized copper corroles, and their electronic structure was studied with a larger active space, comparing the results with available DFT and experimental data. On the other hand, other questions involving changes in molecular geometry can be addressed using structures from density functional theory. Specifically, a series of uranium-arenide complexes were investigated to understand their ground state electronic configurations and bonding between uranium and anthracene ligands. Finally, the nature of uranium-pnictogen bonds was explored and a unique metal-ligand structural distortion observed in the solid state was understood

Molecular Geometry and Electronic Structure of Copper Corroles

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

DNA–melamine hybrid molecules: from self-assembly to nanostructures

Single-stranded DNA–melamine hybrid molecular building blocks were synthesized using a phosphoramidation cross-coupling reaction with a zero linker approach. The self-assembly of the DNA–organic hybrid molecules was achieved by DNA hybridization. Following self-assembly, two distinct types of nanostructures in the form of linear chains and network arrays were observed. The morphology of the self-assembled nanostructures was found to depend on the number of DNA strands that were attached to a single melamine molecule

Molecular Geometry and Electronic Structure of Copper Corroles

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 the Hartree–Fock exchange. Using extended multireference perturbation theory methods (XMS-CASPT2), the functional choice can be assessed. The molecular geometries and electronic structures of both the unsubstituted and the 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 with that in 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 toward 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

Supporting Data: Molecular Geometry and Electronic Structure of Copper Corroles

Supporting computational data for the following publication:R. Bhowmick, S. Roy Chowdhury, and B. Vlaisavljevich “Molecular Geometry and Electronic Structure of Copper Corroles" Inorg. Chem. Chem. Phys. 2023. DOI: 10.1021/acs.inorgchem.3c01779</p

Molecular Geometry and Electronic Structure of Copper Corroles

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 the Hartree–Fock exchange. Using extended multireference perturbation theory methods (XMS-CASPT2), the functional choice can be assessed. The molecular geometries and electronic structures of both the unsubstituted and the 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 with that in 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 toward 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

Synthesis, characterization and DNA interaction studies of new triptycene derivatives

A facile and efficient synthesis of a new series of triptycene-based tripods is being reported. Using 2,6,14- or 2,7,14-triaminotriptycenes as synthons, the corresponding triazidotriptycenes were prepared in high yield. Additionally, we report the transformation of 2,6,14- or 2,7,14-triaminotriptycenes to the corresponding ethynyl-substituted triptycenes via their tribromo derivatives. Subsequently, derivatization of ethynyl-substituted triptycenes was studied to yield the respective propiolic acid and ethynylphosphine derivatives. Characterization of the newly functionalized triptycene derivatives and their regioisomers were carried out using FTIR and multinuclear NMR spectroscopy, mass spectrometry, and elemental analyses techniques. The study of the interaction of these trisubstituted triptycenes with various forms of DNA revealed interesting dependency on the functional groups of the triptycene core to initiate damage or conformational changes in DNA