Interaction between a Transition-Metal Fluoride and a Transition-Metal Hydride: Water-Mediated Hydrofluoric Acid Evolution Following Fluoride Solvation

The reaction between the nickel­(II) PCP pincer fluoride complex (^<i>t</i>BuPCP)­Ni­(F) [^<i>t</i>BuPCP = 2,6-C₆H₃(CH₂P^<i>t</i>Bu₂)₂] and the tungsten­(II) carbonyl hydride CpW­(H)­(CO)₃ (Cp = η⁵-C₅H₅^–) leads to hydrofluoric acid evolution and formation of the bimetallic isocarbonylic species [CpW­(CO)₂(μ-κ,C:κ,O-CO)···Ni­(^<i>t</i>BuPCP)]. The process has been monitored through multinuclear (¹⁹F, ³¹P­{¹H}, ¹H) variable-temperature NMR spectroscopy, collecting ¹⁹F <i>T</i>₁ data values for a fluoride ligand bound to a transition metal. The extremely short relaxation time (minimum value of 13 ms at 193 K) is ascribed to the large chemical shift anisotropy of the Ni–F bond (688 ppm). The in-depth NMR analysis has revealed that the fluoride–hydride interaction is not direct but water-mediated, at odds with what was previously observed for the “hydride–hydride” case (^<i>t</i>BuPCP)­Ni­(H)/CpW­(H)­(CO)₃. Kinetic measurements have unveiled that the first step of the overall mechanism is thought to be solvation of the fluoride ligand (as a result of Ni–F···H₂O hydrogen bonding), while further reaction of the solvated fluoride with CpW­(H)­(CO)₃ is extremely slow and competes with the side reaction of fluoride replacement by a water molecule on the nickel center to form the [(^<i>t</i>BuPCP)­Ni­(H₂O)]⁺ <i>aquo</i> species. Finally, density functional theory analysis of the solvation process through a discrete + continuum model has been accomplished, at the M06//6-31+G­(d,p) level of theory, to support the mechanistic hypothesis

The Role of the Amino Protecting Group during Parahydrogenation of Protected Dehydroamino Acids

A series of dehydroamino acids endowed with different protective groups at the amino and carboxylate moieties and with different substituents at the double bond have been reacted with parahydrogen. The observed ParaHydrogen Induced Polarization (PHIP) effects in the ¹H NMR spectra are strongly dependent on the amino protecting group. DFT calculations allowed us to establish a relationship between the structures of the reaction intermediates (whose energies depend on the amido substitution) and the observed PHIP patterns

Coupling Solid-State NMR with GIPAW ab Initio Calculations in Metal Hydrides and Borohydrides

An integrated experimental–theoretical approach for the solid-state NMR investigation of a series of hydrogen-storage materials is illustrated. Seven experimental room-temperature structures of groups I and II metal hydrides and borohydrides, namely, NaH, LiH, NaBH₄, MgH₂, CaH₂, Ca­(BH₄)₂, and LiBH₄, were computationally optimized. Periodic lattice calculations were performed by means of the plane-wave method adopting the density functional theory (DFT) generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) functional as implemented in the Quantum ESPRESSO package. Projector augmented wave (PAW), including the gauge-including projected augmented-wave (GIPAW), methods for solid-state NMR calculations were used adopting both Rappe–Rabe–Kaxiras–Joannopoulos (RRKJ) ultrasoft pseudopotentials and new developed pseudopotentials. Computed GIPAW chemical shifts were critically compared with the experimental ones. A good agreement between experimental and computed multinuclear chemical shifts was obtained

Molecular Salts of Anesthetic Lidocaine with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study

Four lidocaine molecular salts of dicarboxylic acids (oxalic, fumaric, malonic, and succinic) were synthesized and characterized by a combined use of X-ray powder and single-crystal diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy (FT-IR), and solid-state NMR (¹H MAS and CRAMPS, and ¹³C and ¹⁵N CPMAS): all molecular salts show a dramatic increase in their melting point with respect to both lidocaine and lidocaine hydrochloride, and a higher dissolution rate and thermodynamic solubility in physiological solution with respect to the free base

Molecular Salts of Anesthetic Lidocaine with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study

Four lidocaine molecular salts of dicarboxylic acids (oxalic, fumaric, malonic, and succinic) were synthesized and characterized by a combined use of X-ray powder and single-crystal diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy (FT-IR), and solid-state NMR (¹H MAS and CRAMPS, and ¹³C and ¹⁵N CPMAS): all molecular salts show a dramatic increase in their melting point with respect to both lidocaine and lidocaine hydrochloride, and a higher dissolution rate and thermodynamic solubility in physiological solution with respect to the free base

Solvent-Free Synthesis of Luminescent Copper(I) Coordination Polymers with Thiourea Derivatives

This communication reports the solvent-free synthesis of a series of copper­(I) cyanide (CuCN) -based coordination polymers showing interesting luminescence properties and specific three-dimensional structures. The new compounds have been achieved by directly grinding CuCN together with thiourea (tu), <i>N</i>-methylthiourea (mtu), <i>N</i>-phenylthiourea (ptu), <i>N</i>,<i>N</i>′-diphenylthiourea (dptu), and 2,4-difluorophenylthiourea (fptu). The resulting compounds are [(CuCN)₂(tu)]_<i>n</i>, [(CuCN)₅(mtu)₃]_<i>n</i>, [(CuCN)₃(mtu)₂]_<i>n</i>, [CuCN­(ptu)]_<i>n</i>, [CuCN­(dptu)]_<i>n</i>, and [(CuCN)₃(fptu)₂]_<i>n</i>. “Seeding” crystallization was successful for [(CuCN)₂(tu)]_<i>n</i>, [CuCN­(ptu)]_<i>n</i>, [CuCN­(dptu)]_<i>n</i>, and [(CuCN)₃(fptu)₂]_<i>n</i>, and their structures have been resolved using X-ray single crystal diffraction. Owing to the microcrystalline powdered nature of compounds [(CuCN)₅(mtu)₃]_<i>n</i> and [(CuCN)₃(mtu)_<b>2</b>]_<i>n</i>, their characterization was mainly based on solid-state NMR, via ¹³C cross polarization magic angle spinning for ligand coordination and ¹H magic angle spinning for the weak interactions involving hydrogen atoms. Other solid-state techniques (infrared spectroscopy, X-ray powder diffraction, differential scanning calorimetry, and thermogravimetric analysis) completed the characterization. Finally, the luminescence properties were explored by recording emission and excitation spectra and by evaluating the luminescence quantum yields and lifetimes. Such in-depth study gives promising results for the potential application as luminescent sensors of such compounds

Probing Hydrogen Bond Networks in Half-Sandwich Ru(II) Building Blocks by a Combined ¹H DQ CRAMPS Solid-State NMR, XRPD, and DFT Approach

The hydrogen bond network of three polymorphs (<b>1α</b>, <b>1β</b>, and <b>1γ</b>) and one solvate form (<b>1·H</b>_<b>2</b><b>O</b>) arising from the hydration–dehydration process of the Ru­(II) complex [(<i>p</i>-cymene)­Ru­(κN-INA)­Cl₂] (where INA is isonicotinic acid), has been ascertained by means of one-dimensional (1D) and two-dimensional (2D) double quantum ¹H CRAMPS (Combined Rotation and Multiple Pulses Sequences) and ¹³C CPMAS solid-state NMR experiments. The resolution improvement provided by homonuclear decoupling pulse sequences, with respect to fast MAS experiments, has been highlighted. The solid-state structure of <b>1γ</b> has been fully characterized by combining X-ray powder diffraction (XRPD), solid-state NMR, and periodic plane-wave first-principles calculations. None of the forms show the expected supramolecular cyclic dimerization of the carboxylic functions of INA, because of the presence of Cl atoms as strong hydrogen bond (HB) acceptors. The hydration–dehydration process of the complex has been discussed in terms of structure and HB rearrangements

Probing Hydrogen Bond Networks in Half-Sandwich Ru(II) Building Blocks by a Combined ¹H DQ CRAMPS Solid-State NMR, XRPD, and DFT Approach

The hydrogen bond network of three polymorphs (<b>1α</b>, <b>1β</b>, and <b>1γ</b>) and one solvate form (<b>1·H</b>_<b>2</b><b>O</b>) arising from the hydration–dehydration process of the Ru­(II) complex [(<i>p</i>-cymene)­Ru­(κN-INA)­Cl₂] (where INA is isonicotinic acid), has been ascertained by means of one-dimensional (1D) and two-dimensional (2D) double quantum ¹H CRAMPS (Combined Rotation and Multiple Pulses Sequences) and ¹³C CPMAS solid-state NMR experiments. The resolution improvement provided by homonuclear decoupling pulse sequences, with respect to fast MAS experiments, has been highlighted. The solid-state structure of <b>1γ</b> has been fully characterized by combining X-ray powder diffraction (XRPD), solid-state NMR, and periodic plane-wave first-principles calculations. None of the forms show the expected supramolecular cyclic dimerization of the carboxylic functions of INA, because of the presence of Cl atoms as strong hydrogen bond (HB) acceptors. The hydration–dehydration process of the complex has been discussed in terms of structure and HB rearrangements

Halogen Bonding and Pharmaceutical Cocrystals: The Case of a Widely Used Preservative

3-Iodo-2-propynyl-<i>N</i>-butylcarbamate (IPBC) is an iodinated antimicrobial product used globally as a preservative, fungicide, and algaecide. IPBC is difficult to obtain in pure form as well as to handle in industrial products because it tends to be sticky and clumpy. Here, we describe the preparation of four pharmaceutical cocrystals involving IPBC. The obtained cocrystals have been characterized by X-ray diffraction, solution and solid-state NMR, IR, and DSC analyses. In all the described cases the halogen bond (XB) is the key interaction responsible for the self-assembly of the pharmaceutical cocrystals thanks to the involvement of the 1-iodoalkyne moiety of IPBC, which functions as a very reliable XB-donor, with both neutral and anionic XB-acceptors. Most of the obtained cocrystals have improved properties with respect to the source API, in terms, e.g., of thermal stability. The cocrystal involving the GRAS excipient CaCl₂ has superior powder flow characteristics compared to the pure IPBC, representing a promising solution to the handling issues related to the manufacturing of products containing IPBC

[MnBrL(CO)₄] (L = Amidinatogermylene): Reductive Dimerization, Carbonyl Substitution, and Hydrolysis Reactions

The manganese­(I) carbonyl complex [MnBr­{Ge­(^<i>i</i>Pr₂bzam)­^<i>t</i>Bu}­(CO)₄] (<b>1</b>; ^<i>i</i>Pr₂bzam = 1,3-di­(isopropyl)­benzamidinate), which contains an amidinatogermylene ligand, reacts with LiPh or Li^<i>t</i>Bu at room temperature undergoing a reductive dimerization process that leads to the manganese(0) dimer [Mn₂­{Ge­(^<i>i</i>Pr₂bzam)­^<i>t</i>Bu}₂­(CO)₈]. This complex and the monosubstituted derivative [Mn₂­{Ge­(^<i>i</i>Pr₂bzam)­^<i>t</i>Bu}­(CO)₉] have also been prepared by reacting [Mn₂(CO)₁₀] with Ge­(^<i>i</i>Pr₂bzam)^<i>t</i>Bu at high temperature (110 °C). These binuclear complexes contain their germylene ligands in axial positions (<i>trans</i> to the Mn–Mn bond). The large volume of the germylene ligand clearly affects the reactivity of complex <b>1</b> with neutral two-electron donor reagents, since for bulky reagents, the CO substitution occurs <i>trans</i> to the germylene ligand, as in <i>trans-mer</i>-[MnBrL­{Ge­(^<i>i</i>Pr₂bzam)­^<i>t</i>Bu}­(CO)₃] (L = Ge­(^<i>i</i>Pr₂bzam)^<i>t</i>Bu, PMe₃), whereas for small reagents, the CO substitution occurs <i>cis</i> to the germylene ligand, as in <i>fac</i>-[MnBr­(CN^<i>t</i>Bu)­{Ge­(^<i>i</i>Pr₂bzam)­^<i>t</i>Bu}­(CO)₃]. The IR spectra (ν_CO) of these complexes have confirmed that the germylene Ge­(^<i>i</i>Pr₂bzam)^<i>t</i>Bu is a very strong electron-donating ligand, even stronger than the most basic trialkylphosphanes and N-heterocyclic carbenes. The hydrolysis of complex <b>1</b> leads to the salt [^<i>i</i>Pr₂bzamH₂]­[MnBr­{Ge­(OH)₂^<i>t</i>Bu}­(CO)₄], the anion of which contains an unprecedented germanato­(II) ligand, [Ge­(OH)₂^<i>t</i>Bu]⁻, in <i>cis</i> to the Br atom. This hydrolysis product and its precursor <b>1</b> have been tested as catalyst precursors for the electrolytic reduction of CO₂, showing no significant activity