The significance of the alkene size and the nature of the metal ion in metal–alkene complexes: a theoretical study

Abstract

Cation interactions with π-systems are a problem of outstanding contemporary interest and the nature of these interactions seems to be quite different for transition and main group metal ions. In this paper, we have systematically analyzed the contrast in the bonding of Cu(+) and main group metal ions. The molecular structures and energetics of the complexes formed by various alkenes (A = C(n)H(2n), n = 2-6; C(n)H(2n- 2), n = 3-8 and C(n)H(2n + 2), n = 5-10) and metal ions (M = Li(+), Na(+), K(+), Ca(2+), Mg(2+), Cu(+) and Zn(2+)) are investigated by employing ab initio post Hartree-Fock (MP2/6-311++G**) calculations and are reported in the current study. The study, which also aims to evaluate the effect of the size of the alkyl portion attached to the π-system on the complexation energy, indicates a linear relationship between the two. The decreasing order of complexation energy with various metal ion-alkene complexes follows the order Zn(2+)-A > Mg(2+)-A > Ca(2+)-A > Cu(+)-A > Li(+)-A > Na(+)-A > K(+)-A. The increased charge transfer and the electron density at (3,-1) intermolecular bond critical point corroborates well with the size of the π-system and the complexation energy. The observed deviation from the linear dependency of the Cu(+)-A complexes is attributed to the dπ→π* back bonding interaction. An energy decomposition analysis via the reduced variational space (RVS) procedure was also carried out to analyze which component among polarization, charge transfer, coulomb and exchange repulsion contributes to the increase in the complexation energy. The RVS results suggest that the polarization component significantly contributes to the increase in the complexation energy when the alkene size increases.

A first-principles investigation of histidine and its ionic counterparts

“…Further, frequency calculations at B3LYP/6-31G(d) level of theory characterized all monomers as minima on the PES. From the literature, it is well known that the M05-2X functional is suitable for treating non-covalent interactions [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. In our previous studies of phenylalanine, tyrosine and tryptophan monomers, we have also found the M05-2X functional to give satisfactory results [17][18][19].…”

“…Chakrabarti et al [20] reported that the His ring interacts with other aromatic and basic residues and forms hydrogen bonds (HBs) with polar and charged (both negative and positive) residues in proteins. Recent studies on the cooperativity of non-covalent interactions reveal that the manifestation of cooperativity is essential to understand various phenomena such as formation of supramolecular assemblies, catalysis and biological functions [1,[21][22][23][24]. His is an important model for the understanding of cation-π interactions due to its imidazole side chain [25][26][27][28][29][30][31][32][33][34][35][36].…”

Cation–Alkane Interaction

“…The modulation in the strength of cation−π interactions due to the size of the π-system and the nature of the cation have already been demonstrated by our group. 22,24 The present study shows that the larger the alkane size, the stronger the cation−alkane interaction, and thus provides an explanation for the decrease of cation mobility in liquid alkanes as the alkane size increases. 74 The BE of Li + -A10 (34.51 kcal/mol) is competitive with the BE of Li + -H 2 O (experimental value = 34.02 kcal/mol 75 and computed value = 32.69 kcal/mol 95 ).…”

Method and basis set analysis of oxorhenium(V) complexes for theoretical calculations

“…This choice is supported by numerous previous studies that have employed MP2 optimized or reoptimized structures as a reference for transition metal complexes, especially for (but not limited to) closed-shell, singlet species [24-33]. The computed structures of the literature compounds were compared directly to the experimentally determined crystal structures from the cif file from the CCDC [12].…”