Computationally Assisted (Solid-State Density Functional Theory) Structural (X-ray) and Vibrational Spectroscopy (FT-IR, FT-RS, TDs-THz) Characterization of the Cardiovascular Drug Lacidipine

The structural properties of a second-generation dihydropyridine calcium antagonist, lacidipine, were explored by combining low-temperature X-ray diffraction with optical vibrational spectroscopy and periodic density functional theory (PBC DFT) calculations. Crystallographic analysis cannot discriminate between two possible molecular symmetries in crystals made of pure lacipidine: the space group <i>Ama</i>2, where the lacipidine molecule lies on mirror symmetry, or a <i>Cc</i> space group with distorted lacipidine molecules. Intermolecular interactions analysis reveals an infinite net of moderate-strength N–H···O hydrogen-bonds, which link the molecular units toward the crystallographic <i>b</i>-axis. Weak interactions were identified, revealing their role in stabilization of the crystal structure. The vibrational dynamics of lacidipine was thoroughly explored by combining infrared and Raman spectroscopy in the middle- and low-wavenumber range. The given interpretation was fully supported by state-of-the-art solid-state density functional theory calculations (plane-wave DFT), giving deep insight into the vibrational response and providing a complex assignment of spectral features. The vibrational analysis was extended onto the lattice-phonon range by employing time-domain terahertz spectroscopy. Analysis of the anisotropic displacement parameters suggests noticeable dynamics of the terminal (<i>tert</i>-butoxycarbonyl)­vinyl moiety. The terahertz study provides direct experimental evidence of “crankshaft” type motions in the terminal chain. By combining low-wavenumber vibrational spectroscopy with the first-principles calculations, we were able to prove that the quoted thermodynamically stable phase corresponds to the monoclinic <i>Cc</i> space group

Synthesis and Characterization of Redox-Active Mononuclear Fe(κ²‑dppe)(η⁵‑C₅Me₅)‑Terminated π‑Conjugated Wires

Several new redox-active Fe­(κ²-dppe)­(η⁵-C₅Me₅) arylacetylide complexes featuring pendant ethynyl (Fe­(κ²-dppe)­(η⁵-C₅Me₅)­[{CC­(1,4-C₆H₄)}_<i>n</i>CCH] (<b>1b</b>–<b>d</b>; <i>n</i> = 1–3), Fe­(κ²-dppe)­(η⁵-C₅Me₅)­[CC­(1,3-C₆H₄)­CCH] (<b>2</b>)) or ethenyl (Fe­(κ²-dppe)­(η⁵-C₅Me₅)­[CC­(1,4-C₆H₄)­CHCH₂] (<b>3</b>)) groups have been synthesized and characterized under their Fe­(II) and Fe­(III) states. In contrast to the known ethynyl Fe­(III) complex [Fe­(κ²-dppe)­(η⁵-C₅Me₅)­(CCH)]­[PF₆] (<b>1a</b>[PF₆]), most of the new Fe­(III) derivatives turned out to be kinetically stable in solution. A consistent picture of the electronic structure of the latter complexes in both redox states emerged from experimental data and DFT calculations. This study revealed that beyond the first 1,4-phenylene ring, modification or extension of the carbon-rich linker using (4-phenylene)­ethynylene spacers will have only a minor influence on their electronic properties in their ground state, while still maintaining some (weak) electronic interaction along the carbon-rich backbone

Synthesis and Characterization of Redox-Active Mononuclear Fe(κ²‑dppe)(η⁵‑C₅Me₅)‑Terminated π‑Conjugated Wires

Several new redox-active Fe­(κ²-dppe)­(η⁵-C₅Me₅) arylacetylide complexes featuring pendant ethynyl (Fe­(κ²-dppe)­(η⁵-C₅Me₅)­[{CC­(1,4-C₆H₄)}_<i>n</i>CCH] (<b>1b</b>–<b>d</b>; <i>n</i> = 1–3), Fe­(κ²-dppe)­(η⁵-C₅Me₅)­[CC­(1,3-C₆H₄)­CCH] (<b>2</b>)) or ethenyl (Fe­(κ²-dppe)­(η⁵-C₅Me₅)­[CC­(1,4-C₆H₄)­CHCH₂] (<b>3</b>)) groups have been synthesized and characterized under their Fe­(II) and Fe­(III) states. In contrast to the known ethynyl Fe­(III) complex [Fe­(κ²-dppe)­(η⁵-C₅Me₅)­(CCH)]­[PF₆] (<b>1a</b>[PF₆]), most of the new Fe­(III) derivatives turned out to be kinetically stable in solution. A consistent picture of the electronic structure of the latter complexes in both redox states emerged from experimental data and DFT calculations. This study revealed that beyond the first 1,4-phenylene ring, modification or extension of the carbon-rich linker using (4-phenylene)­ethynylene spacers will have only a minor influence on their electronic properties in their ground state, while still maintaining some (weak) electronic interaction along the carbon-rich backbone

Correlation between Metal–Insulator Transition and Hydrogen-Bonding Network in the Organic Metal δ‑(BEDT-TTF)₄[2,6-Anthracene-bis(sulfonate)]·(H₂O)₄

The sensitivity of electronic properties of organic conductors to minute modifications of their solid-state structure is investigated here within BEDT-TTF (ET) salts with organic bis-sulfonate anions, where specific hydrogen bonds between water molecules and sulfonate moieties are shown to dynamically control the organic slabs’ electronic structure. While the mixed-valence, 2,6-naphthalene-bis­(sulfonate) salt, (ET)₄­(NBS)·​4H₂O, exhibits a charge order state already at room temperature, the corresponding salt with the 2,6-anthracene-bis­(sulfonate) dianion, formulated as (ET)₄­(ABS)·​4H₂O, is metallic at RT and exhibits a metal–insulator transition at <i>T</i>_MI = 85 K. The origin of the MI transition is revealed from a combination of temperature-dependent spectroscopic (Raman) measurements, X-ray structure elucidations (from 300 to 15 K), and theoretical investigations, demonstrating that the charge disproportionation observed below <i>T</i>_MI is associated here with the progressive switching of bifurcated OH···O hydrogen bonds between the sulfonate moieties of the anion and the trapped water molecules. These movements within the anion layer are transmitted through weaker C–H···O interactions to the two A and B donor molecules, modifying the details of the overlap interactions within AA and BB pairs and opening a gap in the band structure

Correlation between Metal–Insulator Transition and Hydrogen-Bonding Network in the Organic Metal δ‑(BEDT-TTF)₄[2,6-Anthracene-bis(sulfonate)]·(H₂O)₄

The sensitivity of electronic properties of organic conductors to minute modifications of their solid-state structure is investigated here within BEDT-TTF (ET) salts with organic bis-sulfonate anions, where specific hydrogen bonds between water molecules and sulfonate moieties are shown to dynamically control the organic slabs’ electronic structure. While the mixed-valence, 2,6-naphthalene-bis­(sulfonate) salt, (ET)₄­(NBS)·​4H₂O, exhibits a charge order state already at room temperature, the corresponding salt with the 2,6-anthracene-bis­(sulfonate) dianion, formulated as (ET)₄­(ABS)·​4H₂O, is metallic at RT and exhibits a metal–insulator transition at <i>T</i>_MI = 85 K. The origin of the MI transition is revealed from a combination of temperature-dependent spectroscopic (Raman) measurements, X-ray structure elucidations (from 300 to 15 K), and theoretical investigations, demonstrating that the charge disproportionation observed below <i>T</i>_MI is associated here with the progressive switching of bifurcated OH···O hydrogen bonds between the sulfonate moieties of the anion and the trapped water molecules. These movements within the anion layer are transmitted through weaker C–H···O interactions to the two A and B donor molecules, modifying the details of the overlap interactions within AA and BB pairs and opening a gap in the band structure

2,7-Fluorenediyl-Bridged Complexes Containing Electroactive “Fe(η⁵‑C₅Me₅)(κ²‑dppe)CC–” End Groups: Molecular Wires and Remarkable Nonlinear Electrochromes

The 2,7-fluorenyl-bridged Fe­(η⁵-C₅Me₅)­(κ²-dppe)­[CC­(2,7-C₁₃H₆Bu₂)­CC]­Fe­(η⁵-C₅Me₅)­(κ²-dppe) (<b>1a</b>), its extended analogue Fe­(η⁵-C₅Me₅)­(κ²-dppe)­[CC­(1,4-C₆H₄)­CC­(2,7-C₁₃H₆Bu₂)­CC­(1,4-C₆H₄)­CC]­(η⁵-C₅Me₅)­(κ²-dppe)Fe (<b>1b</b>), and the corresponding mononuclear complexes Fe­(η⁵-C₅Me₅)­(κ²-dppe)­[CC­(2-C₁₃H₇Bu₂)] (<b>2a</b>) and Fe­(η⁵-C₅Me₅)­(κ²-dppe)­[CC­(1,4-C₆H₄)­CC­(2-C₁₃H₇Bu₂)] (<b>2b</b>), which model half of these molecules, have been synthesized and characterized in their various redox states. The molecular wire characteristics of the dinuclear complexes were examined in their mixed-valent states, with progression from <b>1a</b>[PF₆] to <b>1b</b>[PF₆] resulting in a sharp decrease in electronic coupling. The cubic nonlinear optical properties of these species were investigated over the visible and near-IR range, a particular emphasis being placed on their multiphoton absorption properties; the complexes are shown to function as redox-switchable nonlinear chromophores at selected wavelengths, and the more extended derivatives are shown to exhibit the more promising NLO performance