Ligand Exchange Processes on Solvated Beryllium Cations. II [Be(solvent)(12‐Crown‐4)]²⁺

Abstract

The solvation and solvent exchange mechanism of [Be(12-crown-4)] 2ϩ in water and ammonia was studied by DFT calculations (RB3LYP/6-311ϩG**). In solution, five-fold coordinated Be 2ϩ species of quadratic pyramidal [Be(H 2 O)(12-crown-4)] 2ϩ and [Be(NH 3 )(12-crown-4)] 2ϩ exist. The water and ammonia exchange reactions follow an associative interchange mechanism, similar to 735 that found for the pure solvent complexes [Be(H 2 O) 4 ] 2ϩ and [Be(NH 3 ) 4 ] 2ϩ . The activation barriers are clearly smaller than for the pure solvent complexes, viz. [Be(H 2 O)(12-crown-4)] 2ϩ : 6.0 kcal/mol and [Be(NH 3 )(12-crown-4)] 2ϩ : 15.3 kcal/mol.

Recent Contributions to the Coordination Chemistry of Beryllium

“…[60] Quantum-chemical calculations indicatet hat also dicationic complexes [( [12]crown-4)Be(L)] 2 + (L = H 2 O, NH 3 )e xhibit as imilars tructure. [61] More recentN MR spectroscopic studies suggest that complexc ation 63 is also formed when only BeCl 2 is reacted with [12]crown-4. [62] In contrastt o [ 12]crown-4, larger crown ethers no longer bind through all oxygen atoms; k 2 -O-coordinated mono-and dinuclear complexesa re formed with [15]crown-5 (64) [63] and [18]crown-6 (65), [64] respectively.B oth complexes are also the dominant species in solution according to NMR spectroscopy.…”

“…Cation 63 presents one of only three beryllium compounds that have been characterized by single‐crystal X‐ray diffraction and in which the metal atom is fivefold coordinated . Quantum‐chemical calculations indicate that also dicationic complexes [([12]crown‐4)Be(L)] 2+ (L=H 2 O, NH 3 ) exhibit a similar structure . More recent NMR spectroscopic studies suggest that complex cation 63 is also formed when only BeCl 2 is reacted with [12]crown‐4 .…”

Application of High Pressure in the Elucidation of Inorganic and Bioinorganic Reaction Mechanisms

“…178 Aqua and ammonia analogues of this novel fivecoordinate species (the crown ether (12-crown-4) is planar with the Cl positioned above the central Be atom) have been subjected to quantum mechanical calculations and it was concluded that exchange of either water or ammonia proceeds by an I a mechanism. 179 Volumes of activation (experimental) are available for water exchange on Al 3 þ (I d ) and Ga 3 þ (I d ) and (theoretical) for In 3 þ (A); the mechanistic diagnosis is based on the sign and magnitude of the parameters. The rate of solvent exchange increases with increasing size of [M(S) 6 ] 3 þ .…”

“…It was concluded on the basis of the calculations that both water and ammonia exchange on [Be(H 2 O)(12-crown-4)] 2 þ and [Be(NH 3 )(12-crown-4)] 2 þ , respectively, by an I a mechanism. 179 Since compounds of lithium are used extensively in chemical synthesis, industrial applications, and medicine, fundamental knowledge of processes such as solvent exchange on solvated lithium(I) cations and ligand substitution reactions involving lithium(I) ions is important. A wide-ranging program combining experimental investigations, where these are possible, with computations employing principally DFT methods has been initiated.…”

Ligand‐Exchange Processes on Solvated Beryllium Cations. Part III

“…We recently demonstrated the impressive advantage of the application of modern quantum-chemical methods for the investigation of the mechanism of solventexchange reactions around lithium [31 -33], beryllium [1] [34], aluminum [35], titanium [36], and zinc [37] cations. In all cases, we applied cluster models.…”