Wagner A. Alves

Using vibrational and electronic spectroscopies to investigate different complexes in the formamide/nickel chloride system

Raman, IR and UV-vis-NIR experiments of formamide (FA) and nickel chloride solutions at different compositions were carried out. The quantitative Raman study at the νCN region shows that 5 FA molecules are coordinated to Ni (II) and the sixth position of the octahedron is occupied by one chloride, with preferential formation of [Ni(FA)5Cl]Cl in concentrations near 0.1 mol kg(-1). In higher concentrations the [Ni(FA)4Cl2] complex becomes the most abundant. The downshift of the νCO mode of FA was evidenced by the appearance of a new band at 1640 cm(-1) in the IR spectra of the most concentrated salt solutions. Also, the downshift of the δOCN mode combined with the upshift of the νCN vibration have allowed us realize that Ni (II) is coordinated by the O atom of FA. The d orbital splitting (Δo) has been directly determined from the electronic spectrum of the [Ni(FA)6]Cl2 complex and FA has been included in the spectrochemical series.

FT-Raman spectroscopic analysis of the most probable structures in aluminum chloride and tetrahydrofuran solutions

A study by concentration-dependent Raman spectroscopy is presented for solutions of AlCl(3) in THF. The formation of small amounts of AlCl(4)(-) has been evidenced by the appearance of only one band at 348 cm(-1) in the most diluted salt solution. Another band at 330 cm(-1) starts rising with increasing salt concentration and it seems to belong to the [AlCl(3)(THF)(3)] complex. Indeed, this octahedral entity was confirmed by the quantitative analysis performed at the band envelope at 915 cm(-1). At this region, additional bands at 927 and 858 cm(-1) were observed and assigned to the C-C and C-O stretching modes, respectively, of THF molecules coordinated to the aluminum salt. Besides them, another band at 1042 cm(-1) clearly reveals the existence of this population of molecules. Although neutral octahedral complexes seem to be the major species in more concentrated salt solutions, the Raman spectra show the presence of complex ions in whole studied concentration range.

Novel 3-(aminomethyl)naphthoquinone mannich base-platinum(IV) complexes: synthesis, characterization, electrochemical and cytotoxic studies

Three novel platinum(IV) complexes cis,cis,trans-[Pt(HL1-3)Cl2(OH)2] 1b-3b (HL = 2-hydroxy-3-[(R1-amino)(pyridin-2-yl)methyl]-1,4-naphthoquinone, R1 = n-butyl, HL1; n-heptyl, HL2 and n-decyl, HL3) have been obtained from the oxidation of the respective precursors cis-[Pt(HL1-3)Cl2] 1a-3a. Cyclic voltammetry studies of 1b-3b in MeCN showed the quasi-reversible naphthoquinonate (NQO-, i.e. , L-) redox process and irreversible process attributed to the reduction of the Pt4+/Pt2+ pair, at potentials about 400 mV less negative than for the cisplatin precursor cis,cis,trans-[Pt(NH3)2Cl2(OH)2]. Hydrogen bond interaction between the naphthoquinone 2-hydroxyl group and an axially coordinated hydroxide ligand in 1b-3b has been proposed to favor the Pt4+/Pt2+ reduction. The cytotoxicity studies against four human cancer cell lines have shown that in general the platinum(IV) and platinum(II)derivatives exhibit the same cytotoxic profile and are all more active than cisplatin. The lowest in vitro IC50 values have been observed for 2b-3b, which bear ligands with the largest R1 groups (HL2-HL3) being the most lipophilic. Furthermore similar IC50 values for platinum(II) and platinum(IV) complexes of the same ligands have been associated with rapid in vitro reduction of the latter complexes to afford 1a-3a.

A Raman study on preferential interactions in the formamide/pyridine/pyridazine system and complementary thermodynamic information on the formamide/pyridazine mixture

The formamide (FA)/pyridine (py)/pyridazine (prd) system was investigated by FT-Raman spectroscopy and the results in situ show that FA is preferentially bound to py, as experimentally pointed out by the proton affinity (PA) values of these azabenzenes. Temperature-dependent further investigations for the FA/prd mixture clearly show that the 2:1 FA:prd complex is more stable than the 1:1 FA:py adduct, even though its formation is influenced by the extremely negative entropy of the system, which becomes the spontaneously unfavorable global process. Linear relationships of the complex formation enthalpies (ΔH°) with band shifts (Δν) and dipole moments (μ) of these azabenzenes are observed and are in excellent agreement with our recent studies.