Synthesis and structure of mixed-ligand complexes of copper (II) with ditiolfenols and heterocyclic diamines

The present work is devoted to the investigation of the interaction of copper (II) with dithiolphenols (2,6-dithiol-4-methylphenol (DTMP) and 2,6-dithiol-4-ethylphenol (DTEP)) in the presence of heterocyclic diamines (AM). Among the het-erocyclic diamines, phenanthroline (Phen), batofenantroline (bphen) and 2,2'-dipyridyl (Dip) were used. DTMP and DTEP with copper form colored complexes insoluble in nonpolar organic solvents. The charge of the complexes is established by the method of electromigration of ions and by the method of electrophoresis on paper. When studying the electromigration of this complex in a U-shaped tube with two cranes, the motion of the orange-colored ions to the positive pole was observed. On this basis, we concluded that the colored complexes are anions. When an amine system is introduced into the system, the transition of anionic complexes to the organic phase is observed in the form of a mixediligand complex (MLC). In the electrolysis of solutions of complex MLC complexes, their movement neither to the anode nor to the cathode was observed even after a long current transmission, i.e., they are electrically neutral. The experiments were carried out in the usual way, in a u-shaped tube with two cranes at a voltage of180-200 V and in a current of 0.5-0.8 ma. Electrolysis was carried out for 3 hours. Complexing reagents (DTMP and DTEP) are a tribasic weak acid and, depending on the Ph of the medium, can exist in molecular and two anionic forms. The reagents were synthesized according to a known method. Synthesized compounds are characterized by physicochemical methods: IR and NMR spectroscopy. DTMP-IR (KBr, sm^-1): - 3460 v (OH), 2570 v(SH), 2962 и 2872 v(-CH₃), 1555 8{CHs), 1450 8_as (CH3). 1H NMR (300.18 MHZ, CgD₆): 85.24 (s, 1H- OH), 8 3.38 (s,2H - 2SH), 8 7.11 (s,2HAr-H), 8 2.38 (s,3H-CH₃). DTEP-IR (KBr, sm^-1) - 3460 v (OH), 2575 v(SH), 2965 и 2874 v(-CH₃), 1555 8(CH5), 1460 8as (-CH2-CH3). 1H NMR (300.18 MHZ, C₆D₆): 8 5.19 (s, 1H- OH), 8 3.32(s, 2H- 2SH), 8 7.11 (s, 2H Ar-H), 8 2.59 (s, 2H -CH₂-), 8 1.22 (s, 3H -CH₃). Non-aqueous solvents were tested for the extraction of MLC: chloroform, 1,2-dichloroethane, carbon tetrachloride, benzene, chlorobenzene, toluene, xylene, n-butanol, isopentanol and diethyl ether. The best extractants were chloroform, dichloroethane and carbon tetrachloride. With a single extraction with chloroform, 98.2-98.8% of copper (II) is recovered in the form of MLC. Further studies were carried out with chloroform. The copper content in the organic phase was determined by photometric-diethyldithiocarbaminate after stripping, and in the aqueous phase by the difference. A study of the dependence of complexation on Ph showed that the optimum acidity interval at which the optical density is maximal and constant is at Ph = 5.8-8.5. At the Ph of solution 10, the extraction of MLC is practically not observed, which is apparently due to an increase in the concentration in the aqueous solution of the non-extracting complex [CuR₂]⁴~, since the dissociation of H₃R on the second sulfhydryl group continues to increase. The presence of a single maximum of the optical density in the indicated Ph range confirms the assumption of the formation of one complex compound. MLC of copper is formed in the presence of a large excess of complexing reagents. The optimum condition for the formation and extraction of these compounds is 0.8*1^³ mol/l and 1.0*10^-3 mol/l concentration of DF and am, respectively. MLC copper with DP and Am are stable in aqueous and organic solvents and do not decompose for three days, and after extraction - more than a month. The maximum optical density is reached within 5 minutes. The maximum analytical signal for the complex formation of copper with dithio-phenols and am is observed at 629-640 nm. Dithiolphenols are maximal absorbed at 274-276 nm. The contrast of the reactions is high: the initial reagents are almost colorless, and the complexes are green. Painted chloroform extracts of dithiol-phenolate-amine (nonmetallic) complexes absorb maximum at 320-330 nm. The molar absorption coefficients are (3.28-4.82) * 10⁴. With increasing molar mass, the molar absorption coefficients of the complexes increase. The stoichiometry of the comlexes studied was established by the methods of shifting the equilibrium and the relative yield. The ratio of components in the MLC Cu:DF:Am = 1:1:1. By Nazarenko's method, it was established that the complexing form of copper is Cu²⁺. The number of protons displaced by Cu²⁺ from one molecule of dithiolphenol turned out to be 1. The IR spectra of the complex Cu (DTMP) Phen in the region of950-960 sm^-1, an intense absorption band appears, which is absent in the spectra of the reagent. This band is due to the valence vibration of the metal-ligand bond. The disappearance of a pronounced band at 2580 sm^-1, observed in the DTMF spectrum and the appearance in the IR spectra of a complex of two absorption bands, one of which is shifted toward smaller frequencies, indicates that one of the -SH groups participates in the formation of the complex. The disappearance of the absorption band in the 32003600 sm^-1 region with a maximum at 3460 sm^-1 shows that the hydroxyl group takes part in the formation of a bond with a metal. The detection of absorption bands at 1370 sm^-1 indicates the presence of coordinated phenanthroline. The calculations showed that the MLC in the organic phase does not polymerize and is in monomeric form (у = 1.05-1.08). The thermogravimetric study of the complex Cu(DTMP)Phen has shown that its thermal decomposition proceeds in three stages: at 60-120 °C water evaporates (mass loss is 4.16%), at 340-390°C, Phen decomposes (weight loss 41.7%), and at 490-510°C - DTMP (weight loss 39.35%). The final product of thermolysis of the complex is CuO. A single crystal of the complex with DTMP and Phen was studied by a X-ray diffraction method. The molecular structure of this compound was established by the X-ray diffraction method. Investigation of the compound [Cu(H₂O)(DTMP)(Phen)] by the X-ray diffraction method has shown that its crystal structure consists of discrete single-nuclear complexes. The resulting compound (green-colored single crystal) is insoluble in water and many organic solvents. In mineral acids, the complex dissolves with destruction. The complex monomeric and central atom is coordinated by 5 donor atoms. The donor environment of copper in the complex under study is made up of 2 nitrogen atoms, 2 oxygen atoms and a sulfur atom (CuN₂O₂S). The mechanism of MLC formation can be represented as follows. Copper ions interacting with two molecules of dithiolphenols form double-charged anionic complexes. The addition of am forms MLC, which is extracted with organic solvents. Based on the equations of the calibration graphs, the limit of photometric detection (LOD) and the limit of quantitative determination (LOG) of copper in the form of mixed ligand complexes were calculated. To assess the applicability of ionic associates for the separation and determination of copper, the interfering effect of foreign ions has been studied. The citrates and tartrates interfere with the determination, J^-, CNS₂O₃^2-, thiourea. The interfering effect of Fe (III) was eliminated with oxalic acid; Ti (IV) - sodium fluoride or a tyrone; Hg (II) -sulfite by ion; Nb (V) and Ta (V) -oxalic acid, and Mo (VI) and W (VI) sodium fluoride and oxalic acid. When using a 1% solution of ascorbic acid, Mn (VII), V (IV), Nb (V), Cr (VI), Mo (VI) and Fe (III) do not interfere with determination. When using a 0.01 M solution of oxalic acid, V (IV), Nb (V), Ta (V), Cr (III), Mo (VI), W (VI) and Fe (III) do not interfere with the determination. Highly sensitive, selective methods for extrac tion-photometric determination of copper. The methods are used to determine copper in food products: beans, wheat bran, gelatin, and also in steels of different brands.

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