Synthesis, structural characterization and catalytic activity study of Mn(II), Fe(III), Ni(II), Cu(II) and Zn(II) complexes of quinoxaline-2-carboxalidine-2-amino-5-methylphenol: Crystal structure of the nickel(II) complex

Synthesis and characterization of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with new Schiff base derived from 6,7-dimethyl-quinoxaline-2,3(1H,4H)-dione and thiosemicarbazide

“…However, the shielded protons of -CH3 groups are recorded at 3.40 ppm as singlet peak. In addition, 13 C NMR spectra data of LH also entirely agree with the data of 1 H NMR spectra [27][28][29].…”

Synthesis and Characterization of Template Cr(III),Fe(III), Mn(II), Cd(II) and V(IV), Complexes Derived from 2,6- Diaminopyridine and 1,4-Dihydro-Quinoxalin-2,3-dione.

“…The preliminary identification of the acyclic metal template complexes has been obtained from its IR spectrum, which shows the absence of uncondensed functional groups -NH2 and C=O of 1,2-phenylenediamine and quinoxalin-2,3-dione(i.e., stretching modes of starting materials) and suggests the formation of the proposed acycle.The appearance of strong absorption band in the region 1600-1650 cm-¹ corresponds to υ>C=N stretching frequency (where, υ = frequency).A single sharp band observed for the ligand at 3300 cm-¹ corresponds to υN-H of secondary -CO-NH group, confirms the presence of lactam form corresponding to quinoxaline moiety.It was noted that a pair of bands are present in the spectrum of 2,6-diaminopyridine at 3200-3400 cm -1 corresponding to ν(NH 2 ) but are absent in the infrared spectra of all the complexes (15) .Furthermore, no indicating the absence of >C=O of quinoxalin-2,3-dione at 2-position,this confirms the condensation of carbonyl group of quinoxaline and amino groups of 2,6-diaminopyridine (10) ,figure2.These results provide strong evidence for the formation of acyclic frame (14) . A strong absorption band in the region ~1595-1633 cm -1 may be attributed to the C=N group (15) .The lower values in the wave numbers of ν(C=N) may be explained on the basis of drift of lone pair density of azomethine nitrogen towards metal atom (1516) .The bands present at ~33050-2966 cm -1 may be assigned due to ν(C-H) vibrations of quinoxaline and pyridine moietyies.…”

“…The most abundant fragments with relatives isotopic abundances at m/e=557 and 561of Cr and Fe(III)complexes respectively.The other fragments that close to base peak may be assigned to departure of SO 2 gas and hydroxyl ions for VO(IV) complexes which were displayed in table2 (14) Figure (1). Where * refers to the molecular ion peak of the complex in gm./mole …”

Theoretical and experimental studies on three new coordination complexes of Co(II), Ni(II), and Cu(II) with 2,4-dichloro-6-{(E)-[(5-chloro-2 sulfanylphenyl)imino]methyl}phenol Schiff base ligand

“…The characteristic υ (-HC=N-) stretching vibration, found in the H 2 L at 1614.5 cm −1 , shifted to lower wave numbers in complexes which indicates the azomethine nitrogen participats in coordination with metal ions (M-N) [46]. The participation of deprotonated phenolic moiety in complexes is verified by the shifting of ν(C-O) stretching band about 15-25 cm −1 from the original; found at 1272.1 cm −1 in the H 2 L after chelation [47,48]. This may be due to the weakening of ν(C-O) and formation of stronger M-O bond.…”