Theoretical studies on the structure and protonation of Cu(II) complexes of a series of tripodal aliphatic tetraamines: Good correlations with the experimental data

Abstract

DFT(B3LYP) studies on first protonation step of a series of Cu(II) complexes of some tripodal tetraamines with general formula N[(CH(2))(n)NH(2)][(CH(2))(m)NH(2)][(CH(2))(p)NH(2)] (n = m = p = 2, tren; n = 3, m = p = 2, pee; n = m = 3, p = 2, ppe; n = m = 3, tpt; n = 2, m = 3, p = 4, epb; and n = m = 3, p = 4; ppb) are reported. First, the gas-phase proton macroaffinity of all latter complexes was calculated with considering following simple reaction: [Cu(L)](2+)(g) + H(+)(g) --> [Cu(HL)](3+)(g). The results showed that there is a good correlation between the calculated proton macroaffinities of all complexes with their stability constants in solution. Then, we tried to determine the possible reliable structures for microspecies involved in protonation process of above complexes. The results showed that, similar to the solid state, the [Cu(L)(H(2)O)](2+) and [Cu(HL)(H(2)O)(2)](3+) are most stable species for latter complexes and their protonated form, respectively, at gas phase. We found that there are acceptable correlations between the formation constants of above complexes with both the -Delta E and -Delta G of following reaction: [Cu(L)(H(2)O)](2+)(g) + H(+)(g) + H(2)O(g) --> [Cu(HL)(H(2)O)(2)](3+)(g). The -Delta E of the latter reaction can be defined as a theoretically solvent-proton macroaffinity of reactant complexes because they have gained one proton and one molecule of the solvent. The unknown formation constant of [Cu(epb)](2+) complex was also predicted from the observed correlations. In addition, the first proton affinity of all complexes was studied in solution using DPCM and CPCM methods. It was shown that there is an acceptable correlation between the solvent-proton affinities of [Cu(L)(H(2)O)](2+) complexes with formation constants of [Cu(HL)(H(2)O)(2)](3+) complexes in solution.

Theoretical studies on the proton affinities of four different series of nano-size diamines and designing strong superbases based on fullerene(C60) molecule

“…Protonation of different sites will release different amounts of energy which are correspond to different proton microaffinities [22][23][24][25][26][27][28][29]. In the case of present A 2 -type diamines, two available basic sites are equal and in the first step of protonation, L + H + ?…”

“…Following our interest in the theoretical studies on proton affinities of polybasic compounds [22][23][24][25][26][27][28][29], we decided to compare proton affinities of some nano-size diamines (1-2.3 nm) including long spacers between the amino groups with those containing fullerene molecule as a big spacer. Indeed, in the past decade, C 60 and its derivatives have become an attractive tool in various biological models [30][31][32].…”

The Solution Chemistry of Cu2+–tren Complexes Revisited: Exploring the Role of Species That Are Not Trigonal Bipyramidal

“…Therefore, along with the protonation of [Cu(L)(H 2 O)] 2+ complexes in solution, a molecule of water is added to the complex. [37] During the acid-promoted decomposition of the complexes there is formation of an intermediate that could correspond to a higher protonated species, thus, H 2 CuL 4+ and H 3 CuL 5+ were also included in the calculations. The structure of the most stable geometry that was optimized for each species is presented in Figure 8, whereas Table 2 includes the τ values and the relative energy in solution for all of the optimized geometries that were found for each of the species.…”

What causes the weakest host to act as the strongest one? A theoretical study on the host–guest chemistry of five azacryptands and fluoride anions

“…[45][46][47][48][49][50][51][52][53] In our previous works we have been successful in calculating the macroscopic and even microscopic protonation constants of polybasic molecules. 53 We have also been successful in predicting the formation constants of metal complexes of a series of tripodal tetraamines 54,55 and/or macrocyclic ligands 56 by studying their proton affinities. Also in the present work we have tried to calculate directly the formation constants of the host-guest complexes studied here.…”