Synthesis of the dioxidomolybdenum(VI) complexes [MoO2(HLR)(MeOH)]Cl (1–3) was carried out by using MoO2Cl2 and the corresponding ONO aroylhydrazone ligand H2LR (ligand H2LR is salicylaldehyde isonicotinoylhydrazone (H2LSIH), 2-hydroxy-naphthaldehyde isonicotinoylhydrazone (H2LNIH), or p-(N,N′-diethylamino)salicylaldehyde isonicotinoylhydrazone (H2LEt2NSIH) in methanol. Compounds [MoO2(HLR)(H2O)]Cl (1a–3a) were obtained upon exposure of the corresponding mononuclear complexes 1–3 to moisture. Deprotonation of the mononuclear complexes 1–3 was performed by using Et3N as a base (by the conventional solution based-method and by the mechanochemical approach) as well as by UV-light assisted reactions yielding [MoO2(LSIH)(MeOH)] (4), [MoO2(LNIH)(MeOH)] (5) and [MoO2(LEt2NSIH)]n (6), respectively. Crystal and molecular structures of all complexes were determined by the single crystal X-ray diffraction method. The complexes were further characterized by elemental analysis, IR spectroscopy, TG analysis, one- and two-dimensional NMR spectroscopy and powder X-ray diffraction.

NMR spectroscopy in combination with statistical methods was used to study vacuum residues and vacuum gas oils from 32 crude oils of different origin. Two chemometric metodes were applied. First- ly, principal component analysis on complete spectra was used to perform classification of samples and clear distinction between vacuum residues and vacuum light and heavy gas oils were obtained. To quanti- tatively predict the composition of asphaltenes, principal component regression models using areas of res- onance signals spaned by 11 frequency bins of the 1 H NMR spectra were build. The first 5 principal com- ponents accounted for more than 94 % of variations in the input data set and coefficient of determination for correlation between measured and predicted values was R 2 = 0.7421. Although this value is not signifi- cant, it shows the underlying linear dependence in the data. Pseudo two-dimensional DOSY NMR exper- iments were used to assess the composition and structural properties of asphaltenes in a selected crude oil and its vacuum residue on the basis of their different hydrodynamic behavior and translational diffusion coefficients. DOSY spectra showed the presence of several asphaltene aggregates differing in size and interactions they formed. The obtained results have shown that NMR techniques in combina- tion with chemometrics are very useful to analyze vacuum residues and vacuum gas oils. Furthermore, we expect that our ongoing investigation of asphaltenes from crude oils of different origin will elucidate in more details composition, structure and properties of these complex molecular systems.