Dear Andrii Tupys

Thank you very much for your professional answer, I agree with you that the oxalate used as reducing agent in many reactions, my main point is to explain the convert the paramagnetic VO(II) to diamagnetic complexes with good H1 NMR spectra. Recently our teamwork has published an article about ruthenium(II) and diamine complexes, our study and the literature confirmed that the amines reduce the Ru(III) to Ru(II).

Soluble ruthenium(II) with 3,4-diaminobenzoic acid complexes

Preparation, thermal study, theoretical calculations and in vitro cytotoxic activity, (2018) Journal of Thermal Analysis and Calorimetry, DOI: 10.1007/s10973-018-7405-6. On this point of view do you mean that the amine and oxalate may be reduced the vanadium(IV) to vanadium (III)?@Andrii Tupys

Dear Andrii Tupys

Thank you very much for your explanation, I would like to tell you that the oxalate complex (NH4)2VO(C2O4)2 has been prepared by the direct reaction between the vanadyl sulfate and the oxalate in 1:2 mole ratio as I had mentioned previously by literature method and the oxalate doesn't reduce the V(V) to V(IV), the main point in my question is the H1NMR of the ternary complexes vanadium, diamine and oxalate, please find attaché figure of the spectrum of one of the complexes, if the oxalate doesn't reduce the vanadium may be the amine does the reduction as like as what had happened with the ruthenium

Best wishes

@Andrii Tupys

Dear Andrii Tupys

Thank you very much for your openion and I have attached the file for HNMR spectrum for one of the complexes. I am very sorry for the delay in the contact with you.

best regards

Andrii Tupys@

Dear Andrii Tupys

Thank you very much for your discussion and your interest, the diamine used is 4-chloro-o-phenylenediamine and there are three types of protons 2 for the benzene ring with different media and protons for the amine groups. I have compared the experimental spectrum with the calculated one had been calculated DFT by use of (GAUSSIAN 09), B3LYP, and LanL2DZ basis set. There is agreement between the excluded data between the two ways especially in the point of view the experimental data measured for the solid state complexes and for the calculated one in the gaseous state. @Andrii Tupys

I enjoyed very much by the discussion above and the sincere interpretation of Andrii Tupys . Oxovanadium(IV) (VO2+ ) or vanadyl ion is stable in acid medium and has d1 configuration i.e paramagnetic. Both the oxalate or CPDA can not oxidise V(IV) to V(V), rather it may help in reduction of V(V) to V(IV). The VO2+ solution should be blue in colour, other colours may indicate different oxidation sates. What is the acid used =? Strong oxidizing acids may oxidise V(IV) to (V(V). The structure of your complex need more investigations as the six position in the VO SqPy geometry may be occupied and a covalent character may be considered to explain the diamagnetism.

Thank you very much for your comment my supervisor Prof. Ahmed Soliman; vanadyl ion solution was blue color in the beginning before the preparation of the precursor salt [NH4)2[VO(C2O4)2] which was prepared by literature method. There is no any type of oxidizing agents added to the reaction, there is no acid has been used in the preparation of the complexes and the complexes prepared in the physiological pH=7.2 by use of sodium carbonate. @Ahmed A Soliman