Stabilities and coordination modes of histidine in copper(II) mixed-ligand complexes with ethylenediamine, diethylenetriamine or N,N,N′,N″,N″-pentamethyldiethylenetriamine in aqueous solution

Stabilities and Coordination Modes of α-Alaninephosphonic Acid in Copper(II) Heteroligand Complexes with Ethylenediamine, Diethylenetriamine or N,N,N′,N′,N″-Pentamethyldiethylene Triamine in Aqueous Solution

“…The detailed discussions about the acid-base properties of these ligands can be found in earlier papers [6][7][8][9][10][11][12][13]. The results for the binary systems Cu 2+ -en [14][15][16][17][18], Cu 2+ -dien [5,6,[17][18][19], Cu 2+ -Me 5 dien [15,20,21] and Cu 2+ -α-Ala(P) [22,23] are in good agreement with the literature data.…”

“…The values of log 10 K, close to −1, were obtained earlier for heteroligand species of tetragonal geometry formed by ethylenediamine and glycinephosphonic acid [1], aminoacids [22,23] or aminohydroxamic acids in the copper(II) solution [8]. Distinctly lower values of log 10 K are observed in the case of heteroligand complexes [Cu(L 1 )(α-Ala(P))] with dien or Me 5 dien (Table 1, row 6).…”

“…So, the formation of the heteroligand species [Cu(dien)(α-Ala(P))] can be supported. The EPR parameters obtained for this species correspond well to a five-coordinate species formed by dien and amino acids or glycinephosphonic acid in the copper(II) frozen solution (Table 2) [1,22,23]. The presence of a weak rhombic distortion suggests that the geometry is slightly deviated from square pyramidal towards trigonal bipyramidal [27].…”

“…Furthermore, as was observed for the ternary systems with the same simple polyamines [1,22,23], the formation of heteroligand complexes is especially preferred in the system with dien (the log 10 X [Cu(L 1 )(α-Ala(P))] is distinctly higher than the value for the system with en). This is a reflection of the ratio of the stepwise formation constants for the binary Cu 2+ -amine system (log 10 (K Cu(dien) /K Cu(dien) 2 ) = 11.26 which is significantly greater than log 10 (K Cu(en) /K Cu(en) 2 ) = 1.43.…”

“…The electronic absorption spectra at pH range 9.0-9.5 ( Fig. 3) are characteristic for a five-coordinate asymmetric complexes with 4N coordination mode [1,7,22,23]. So, α-Ala(P) completes the coordination number of five by binding with the amine nitrogen in Cu 2+ plane and the phosphonic oxygen in an axial position.…”