Insight on thermal, spectral, magnetic and biologic behaviour of new Ni(II), Cu(II) and Zn(II) complexes with a pentaazamacrocyclic ligand bearing nicotinamide moieties
Journal of Thermal Analysis and Calorimetry
Rodica Olar1, Florentina Pătraşcu1, Carmen Mariana Balotescu2, Emilia Elena Iorgulescu3, Coralia Bleotu4, Luminiţa Măruţescu2, Veronica Lazar2, Dana Marinescu1, Nicolae Stanică5and Mihaela Badea1
1Department of Inorganic Chemistry, Faculty of Chemistry, University of Bucharest, 90-92 Panduri Str., 050663 Bucharest, Romania
2Department of Microbiology,Faculty of Biology, University of Bucharest, 1-3 Aleea Portocalelor Str., 06601Bucharest, Romania
3University of Bucharest, Faculty of Chemistry, Department of Analytical Chemistry, 90-92 Panduri Str., 050663 Bucharest, Romania
4Stefan S Nicolau Institute of Virology, 285 Mihai Bravu Ave., Bucharest, Romania
5Romanian Academy, “Ilie Murgulescu” Physical Chemistry Institute, 202 Splaiul Independenţei, 060021 Bucharest, Romania
Electrochemistry
The cyclic voltammograms of the ligand (L) and complexes (1) and (2) were recorded both in the cathodic and in anodic potential range while the voltammetric investigation of the complex (3) was performed only in the cathodic range.
Cathodic investigation of the 10-3M ligand solution indicates a quasireversible reduction on the platinum electrode surface assigned to the carbonyl group from its structure. Complex [NiLCl2] (1) in DMSO undergoes a Ni(II)/Ni(I) reduction at more negative potential in comparison with the cathodic potential peak observedfor [Ni(DMSO)6]Cl2. This behaviour could beexplainedconsidering that the macrocyclic ligand stabilized the oxidation state two in the complex (1) (Table 1). In the anodic range thevoltammograms show the irreversible Ni(II)/Ni(III) oxidation both for [Ni(DMSO)6]Cl2 and complex(1). It is worth to mention that azamacrocyclic ligand stabilise easier the unusual oxidation states like Ni(III), aspect reflected by the lower value of oxidation potential(Fig. 1, Table 2).
In DMSO solution both [CuLCl2]∙H2O (2) and [Cu(DMSO)4]Cl2 complexes exhibit a chemically reversible transformation of Cu(II) to Cu(I) (ipa/ipc=1) but an electrochemically quasireversible reduction (Ep=222 mV and respectively Ep=131 mV at 0,10 Vs-1) in the cathodic range.The Cu(II)/Cu(III) oxidation process is also chemically reversible (ipa/ipc=1) and electrochemically irreversible (Ep=161 mV for [Cu(DMSO)4]Cl2 and respectively Ep=211 mV for [CuLCl2] H2O at 0.10Vs-1). The shift of the Epc peak to a cathodic potential and Epa peak to an anodic one in the case of complex (2) indicates that the two oxidation state for copperis better stabilised by the macrocyclic ligand. This voltammogram displays also the cathodic peak of the ligand shifted at more negative potential(Fig. 2, Table 1 and Table 2).
Fig. 1Cyclic voltammograms of ligand(▬), [Ni(DMSO)6]Cl2(▬) and complex (1) (▬) recorded in DMSO at Pt electrode (concentration 10-3 M, supporting electrolyte 10-1 M [Bu4N]ClO4, reference electrode Ag/AgCl/KCl sat., scan rate 10-1V s-1)
Fig. 2Cyclic voltammograms of ligand(▬), [Cu(DMSO)4]Cl2(▬) and complex (2) (▬) recorded in DMSO at Pt electrode (concentration 10-3 M, supporting electrolyte 10-1 M [Bu4N]ClO4, reference electrode Ag/AgCl/KCl sat., scan rate 10-1 V s-1)
The zinc complexes exhibit only a two electron reduction as result of the electronic saturation of d orbitals for this ion. The cyclic voltammogram recorded for the [Zn(DMSO)4]Cl2solution exhibits a cathodic peak thatcorresponds to the reduction of the Zn(II) ion while in thebackscanmode an anodic stripping peak due to the oxidation process of the metallic zinc electrodeposited on the electrode surface can be observed. The voltammogram recorded for the complex (3) displays a two electron reduction wave corresponding to the Zn2+/Zn(0) process and the ligand reduction respectively.In the backscan mode only the peak corresponding to the reduced form of the ligand is observed.The anodic stripping peak is not observedprobably due to formation of the metallic zinc aggregates with the macrocyclic ligand(Fig. 3, Table 1).
Fig. 3Cyclic voltammograms of ligand(▬), [Zn(DMSO)4]Cl2(▬) and complex (3) (▬) recorded in DMSO at Pt electrode (concentration 10-3 M, supporting electrolyte 10-1 M [Bu4N]ClO4, reference electrode Ag/AgCl/KCl sat., scan rate 10-1 V s1)
Table 1 The electrode potentials (vs. Ag/AgCl/KCl sat.) for the reduction process ofthe ligand and complexes in DMSO (supporting electrolyte 10-1 M [Bu4N]ClO4, scan rate 10-1 V s-1)
Compound / Epc /V / ipc/A / Epa/ V / ipa / AL / -0,856 / -5.968·10-7 / -0,604 / 2,127·10-7
[Ni(DMSO)6]Cl2 / -0,745 / -2,099·10-6 / -0,584 / 3,039·10-7
[NiLCl2] (1) / -0,685
-1,042 / -7,093·10-7
-4,151·10-6 / -0,141 / 4,703·10-6
[Cu(DMSO)4]Cl2 / -0,504 / -3,358·10-6 / -0,373 / 3,33·10-6
[CuLCl2]∙H2O(2) / -0,524
-0,997 / -4,316·10-6
-5,834·10-7 / -0,302 / 6,13·10-6
[Zn(DMSO)4]Cl2 / -1,057 / -3,457·10-6 / -0,322 / 7,007·10-6
[ZnLCl2] (3) / -0,735
-1,068 / -6,352·10-7
-2,12·10-7 / -0,604 / 2,904·10-6
Table2 The electrode potentials (vs. Ag/AgCl/KCl sat.) for the oxidation process of the ligand and complexes in DMSO (supporting electrolyte 10-1 M [Bu4N]ClO4, scan rate 10-1 V s-1)
Compound / Epa / V / ipa/ A / Epc/ V / ipc/ AL / - / - / - / -
[Ni(DMSO)6]Cl2 / 1,577 / 8,023·10-5 / - / -
[NiLCl2] (1) / 1,295 / 3,266·10-5 / - / -
[Cu(DMSO)4]Cl2 / 0,413 / 5,992·10-6 / 0,252 / -5,533·10-6
[CuLCl2]∙H2O(2) / 0,433 / 3,732·10-5 / 0,222 / -3,521·10-6
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