Hquids, ionic, metallic, molecular

The strengths of intermolecular forces vary over a wide range but are generally much weaker than intramolecular forces—ionic, metallic, or covalent bonds ( Figure 11.3). Less energy, therefore, is required to vaporize a liquid or melt a solid than to break covalent bonds. For example, only 16 kj/mol is required to overcome the intermolecular attractions in Hquid HCI to vaporize it. In contrast, the energy required to break the covalent bond in HCI is 431 kJ/mol. Thus, when a molecular substance such as HCI changes from solid to liquid to gas, the molecules remain intact. 

Obviously, with the development of the first catalytic reactions in ionic Hquids, the general research focus turned away from basic studies of metal complexes dissolved in ionic Hquids. Today there is a clear lack of fundamental understanding of many catalytic processes in ionic liquids on a molecular level. Much more fundamental work is undoubtedly needed and should be encouraged in order to speed up the future development of transition metal catalysis in ionic liquids. 

Despite the great potential of these weakly coordinating ionic hquids in combination with highly dectrophilic, polar or ionic catalyst complexes, it should be noted that the anions of an ionic hquid are more likdy to coordinate to the metal center of a dissolved complex than the same anions dissolved in a molecular solvent would do [16], This point becomes understandable considering a cationic metal center (coordinatively unsaturated with vacant orbitals) dissolved in a molecular solvent. The possibilities are (i) an anion can directly coordinate to the metal center,... 

The metal precursor is generally the ion, whereas the chalcogenide precursor can be thiosulfate (S2O] ) [25], selenosulfate (SSeO] ) [51], or HTeOJ [24] for sulfides, selenides, and tellurides, respectively. In the case of oxides such as ZnO, the chalcogen precursor can be molecular oxygen or hydrogen peroxide [13]. II-VI compounds have also been synthesized electrochemicaUy from non-aqueous organic solvents [52, 53] and from ionic Hquids [54]. II-VI compounds have also been synthesized by ECALE [22, 55], but this process is not suited for large-scale fabrication. 

Another probe that is of particular interest to SILP is [Cu(acac)(tmen)]+ (Figure 2.5) [96, 102]. As a transition metal complex, it is a model for how ionic hquids might interact with transition metal catalysts. It has been shown that for the d - d band correlates weU with the Gutmann donor numbers of molecular solvents [103], and is dominated by the anion in ionic hquids. The values vary greatly, with [C,Ciim]rrfO] (2cu = 602) > [G,Giim][Tf2N] = 546) > [C,Ciim][PF,] (k = 517), which compares to DMF (2, = 602) > acetone (2 = 569) > CH2CICH2CI... 

Zabet-Moghaddam et al. ° characterized five different ionic liquids by LDI and by MALDl-MS. Signals of both anions and cations of the ionic liquids could be observed both in LDI- and in MALDI-MS without any metal adducts. Low-molecular-mass compounds and peptides could be analyzed best in the presence of water-immiscible ionic liquids, whereas proteins gave the best results in water-miscible ionic liquids. Optimal analytical conditions depend on the molar ratio of matrix-to-analyte and ionic hquid-to-matrix, although the homogeneity of samples in the presence of ionic liquids was reduced compared with classical MALDl preparations. 

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