Grignard reagents that are at the simplest level described as "RMgX" (where R is an organic substituent and X a halide) are one of the most widely utilized classes of synthetic reagents. Lately, especially Grignard reagents with amido ligands of the type R1R2NMgX, so-called Hauser bases, and their Turbo analogue R1R2NMgX·LiCl play an outranging role in modern synthetic chemistry. However, because of their complex solution behavior, where Schlenk-type equilibria are involved, very little is known about their structure in solution. Especially the impact of LiCl on the Schlenk-equilibrium was still obscured by complexity and limited analytical access. Herein, we present unprecedented insights into the solution structure of the Hauser base (i)Pr2NMgCl 1 and the Turbo-Hauser base (i)Pr2NMgCl·LiCl 2 at various temperatures in THF-d8 solution by employing a newly elaborated diffusion ordered spectroscopy (DOSY) NMR method hand-in-hand with theoretical calculations.

Within this work, the field of bulky methanides in metal coordination is exceeded by the synthesis of the versatile and promising bis(4,6-isopropylbenzoxazol-2-yl)methane (7) ligand platform. As an enhancement in this class of ligands, isopropyl (iPr) substituents as steric-demanding groups have been successfully introduced in proximity to the coordination pocket, mimicking the shielding abilities of the ubiquitous NacNac ligand scaffold to improve the steric protection of a coordinated s-block metal cation. A percent buried volume (% V) calculation as well as an electronic structure analysis shades light onto the shielding and electronic abilities of the ligand in comparison to other selected methanides and diketiminates. Upon deprotonation with a variety of different group 1 and 2 metalation agents, a row of novel s-block metal complexes of the parent deprotonated monoanionic ligand 7 was obtained and structurally, as well as spectroscopically, characterized. In particular, in this context, the alkali-metal precursor complexes [Li(THF){(4,6-iPr-NCOCH)CH}] (8) and [K{μ-(4,6-iPr-NCOCH)CH}] (9) as well as the alkaline-earth-metal compounds [MgCl(THF){(4,6-iPr-NCOCH)CH}] (10) and [M(THF){(4,6-iPr-NCOCH)CH}] [M = Mg, n = 0 (11); M = Ca, n = 1 (12); M = Sr, n = 1 (13); M = Ba, n = 1 (14)] were successfully synthesized. Especially, the latter four exhibit interesting trends in the solid state as well as in solution within the metal series.

Fluorescence spectroscopy investigations of the new acridine derivative bis(N,N-dimethylaminemethylene)acridine (3) show remarkable selectivity and sensitivity towards Zn(2+) and Cd(2+) ions in methanol and for the latter even in water. Through the chelation of the metal ions the present PET effect is quenched, significantly enhancing the emission intensity of the fluorophore. In solution, the bonding situation is studied by fluorescence and NMR spectroscopy, as well as ESI-TOF mass-spectrometry measurements. The solid state environment is investigated by X-ray diffraction and computational calculations. Here, we can show the complexation of the zinc and cadmium ions by the methylene bridged amine receptors as well as by the nitrogen atom of the acridine system.

An additive quantum mechanics/molecular mechanics (QM/MM) model for the theoretical investigation of molecular crystals (AC-QM/MM) is presented. At the one-body level, a single molecule is chosen as the QM region. The MM region around it consists of a finite cluster of explicit MM atoms, represented by point charges and Lennard-Jones potentials, with additional background charges to mimic periodic electrostatics. Cluster charges are QM-derived and calculated self-consistently to ensure a polarizable embedding. We have also considered the extension to many-body QM corrections, calculating the interactions of a central molecule to neighbouring units in the crystal. Full gradient expressions have been derived, also including symmetry information. The scheme allows for the calculation of molecular properties as well as unconstrained optimisations of the molecular geometry and cell parameters with respect to the lattice energy. Benchmarking the approach with the X23 reference set confirms the convergence pattern of the many-body extension, although comparison to plane wave DFT reveals a systematic overestimation of cohesive energies by 6-16 kJ•mol −1 . While the scheme primarily aims to provide an inexpensive and flexible way to model a molecule in a crystal environment, it can also be used to reach highly accurate cohesive energies by the straightforward application of wave function correlated approaches. Calculations with local coupled cluster with singles, doubles, and perturbative triples, albeit limited to numerical gradients, show an impressive agreement with experimental estimates for small molecular crystals. File list (2)download file view on ChemRxiv acQMMM_paper.pdf (3.41 MiB) download file view on ChemRxiv acQMMM_si.pdf (146.30 KiB)

An additive quantum mechanics/molecular mechanics (QM/MM) model for the theoretical investigation of molecular crystals (AC-QM/MM) is presented. At the one-body level, a single molecule is chosen as the QM region. The MM region around it consists of a finite cluster of explicit MM atoms, represented by point charges and Lennard-Jones potentials, with additional background charges to mimic periodic electrostatics. Cluster charges are QM-derived and calculated self-consistently to ensure a polarizable embedding. We have also considered the extension to many-body QM corrections, calculating the interactions of a central molecule to neighbouring units in the crystal. Full gradient expressions have been derived, also including symmetry information. The scheme allows for the calculation of molecular properties as well as unconstrained optimisations of the molecular geometry and cell parameters with respect to the lattice energy. Benchmarking the approach with the X23 reference set confirms the convergence pattern of the many-body extension, although comparison to plane wave DFT reveals a systematic overestimation of cohesive energies by 6-16 kJ·mol⁻¹ . While the scheme primarily aims to provide an inexpensive and flexible way to model a molecule in a crystal environment, it can also be used to reach highly accurate cohesive energies by the straightforward application of wave function correlated approaches. Calculations with local coupled cluster with singles, doubles, and perturbative triples, albeit limited to numerical gradients, show an impressive agreement with experimental estimates for small molecular crystals.<br><br>