Ligand Exchange Processes on Solvated Beryllium Cations. IV [Be(H₂O)₂(imidazole‐based Chelate)]¹⁾

Abstract

The water exchange reaction of [Be(H2O)2(1H‐imidazole‐4,5‐dicarboxylate)] and [Be(H2O)2(1H‐imidazol‐3‐ium‐4,5‐dicarboxylate)]+ in water was studied by DFT calculations (RB3LYP/6‐311+G**) and identified as an associative interchange mechanism. The activation barriers for [Be(H2O)2(1H‐imidazole‐4,5‐dicarboxylate)] (16.6 kcal/mol) and [Be(H2O)2(1H‐imidazol‐3‐ium‐4,5‐dicarboxylate)]+ (13.8 kcal/mol) are similar to the barrier for [Be(H2O)4)]2+ and independent of the overall charge. NICS calculations show no indication that the aromaticity of the imidazole ring is affected during the water exchange process.

Ligand‐Exchange Processes on Solvated Zinc Cations: Water Exchange on [Zn(H2O)4(L)]2+⋅2 H2O (L=Heterocyclic Ligand)

“…Comparison with literature values shows that NICS(1) values, considered not to be influenced by σ‐donor effects,32b show nearly the same values as for the protonated ligands. The observation that complexation with closed shell metal ions does not influence the NICS values is in accordance with earlier observations 27d. 47…”

“…This energy difference is in good agreement with the addition of molecules (such as water) to form the second coordination sphere, and is surely somewhat exaggerated as compared to the case with included solvent in earlier work. [24,27] Figure 2C). Note that the six-coordinate intermediate is only a metastable species and will loose one coordinated water molecule via a transition state similar to the first to form the more stable five-coordinate complex, Figure 2A).…”

“…Quantum-chemical methods: Following the approach used by Hartmann et al, [21] and for comparability with recent studies on solvent exchange on Li + , [26] Be 2 + , [27] and Al 3 + ions, [23,28] we fully optimized the structures at the RB3LYP/ 6-311 + G** level of theory [29] and evaluated the energy by RMP2A C H T U N G T R E N N U N G (full)/6-311 + G**//RB3LYP/6-311 + G**. [30] The influence of bulk solvent was probed by using the CPCM-formalism [31] and water as solvent, that is, RB3LYPA C H T U N G T R E N N U N G (CPCM)/6-311 + G**//RB3LYP/6-311 + G**.…”

“…The calculated reaction energies (RB3LYP/6-311 + G** + ZPE(RB3LYP/6-311 + G**)) can be corroborated by MP2A C H T U N G T R E N N U N G (full) energy calculations (MP2-A C H T U N G T R E N N U N G (full)/6-311 + G**//RB3LYP/6-311 + G** + ZPE(RB3LYP/ 6-311 + G**)), by which the well-documented energetic underestimation of transition states is shown. [27,30,35] Probing the solvent effects by CPCM single-point calculation (RB3LYPA C H T U N G T R E N N U N G (CPCM:H 2 O)/6-311 + G**//RB3LYP/6-311 + G** + ZPE(RB3LYP/6-311 + G**)), shows that the inclusion of solvent effects stabilizes the transition and intermediate states, and also lowers the activation barriers. The…”

Ligand Exchange Processes on Solvated Beryllium Cations, VI. Hydrogen Chalcogenide Exchange on [Be(Chelate)Sol2]2+ (Chelate: CH3–O–C2H4–O–CH3, CH3–S–C2H4–S–CH3, CH3–Se–C2H4–Se–CH3; Sol: H2O, H2S, H2Se)

“…The only observed variation in energy originates from a change of the solvent used, a behavior observed for other ligands as well, and can be easily accounted for by the tetragonal structure of beryllium complexes, which precludes a direct trans effect between chelate and bound solvent molecules. Mechanistically, the examined exchange processes follow an associative interchange (I a ) mechamism, like most of the previously‐examined exchange processes on beryllium,36–40 which can be concluded from the considerably shortened distances between the Be 2+ ‐ion and the entering and the leaving solvent molecules as compared to the non‐reacting solvent molecule. For instance, in [(CH 3 –O–C 2 H 4 –O–CH 3 )Be(H 2 O) 3 ] 2+ reacting solvent molecules' distances to Be 2+ are both 2.19 Å, whereas the non‐reacting solvent molecule's bond length is 1.61 Å.…”