Syntheses, EPR spectral studies and crystal structures of manganese(II) complexes of neutral N,N donor bidentate Schiff bases and azide/thiocyanate as coligand

Abstract

a b s t r a c tFour manganese(II) complexes Mn 2 (paa) 2 (N 3 ) 4 (1), [Mn(paa) / 2 H 2 O (4) of three neutral N,N donor bidentate Schiff bases were synthesized and physico-chemically characterized by means of partial elemental analyses, electronic, infrared and EPR spectral studies. Compounds 3 and 4 were obtained as single crystals suitable for X-ray diffraction. Compound 4 recrystallized as Mn(dpka) 2 (NCS) 2 . Both the compounds crystallized in the monoclinic space groups P2 1 for 3 and C2/c for 4. Manganese(II) is found to be in a distorted octahedral geometry in both the monomeric complexes with thiocyanate anion as a terminal ligand coordinating through the nitrogen atom. EPR spectra in DMF solutions at 77 K show hyperfine sextets with low intensity forbidden lines lying between each of the two main hyperfine lines and the zero field splitting parameters (D and E) were calculated.Ó 2010 Elsevier Ltd. All rights reserved. IntroductionManganese complexes play important roles ranging from bioinorganic chemistry to solid-state physics. There has been considerable interest in synthesizing biomimetic complexes that can act as manganese containing enzymes such as superoxide dismutase (SOD) [1]. Interest in manganese complexes of varying nuclearities continues to be stimulated by the presence of manganese at the active sites of biological systems such as photosystem II in green plants, ribonucleotide reductase, superoxide dismutase, and the Mn catalases [2-9], the variability in magnetic behavior of polynuclear manganese clusters, which for some systems has been exploited in the development of information storage devices [10][11][12] and the use of such complexes as catalysts for bleaching and organic synthesis [13][14][15].In manganese biosystems, the azide ion is known to inhibit the superoxide dismutation in mononuclear superoxide dismutases via binding to the metal at the active site in both the Mn(II) and Mn(III) oxidation states [16]. The function of dinuclear active sites in Mn catalases, which catalyze the conversion of toxic peroxide to oxygen and water in certain bacteria, is also dramatically inhibited by azide [17][18][19][20][21][22].Gao et al. reports the structure and magnetism of Mn(II) one dimensional coordination polymers built from azide bridges and Schiff base obtained by the condensation of pyridine-2-carbaldehyde with aniline and its derivatives [23]. The complexes synthesized contain alternating end-on and end-to-end azide bridges, which mediate alternating ferromagnetic and antiferromagnetic exchange interactions, respectively. Wen and coworkers prepared one dimensional chiral coordination polymers of manganese(II) using azide and a Schiff base (obtained from pyridine-2-carbaldehyde and 1-phenylethyl amine) as the auxiliary ligand [24]. In these complexes, there is weak antiferromagnetic coupling between Mn(II) ions. The use of di-2-pyridyl ketone in conjugation with dicyanamide and azide gave cubane and defective doublecubane clusters of Mn(II) respectively, both of which are found to b...

Structural characterization, thermal investigation and biological activity of metal complexes containing Schiff Base ligand (Z)‐3‐(1‐((4,6‐dimethyl‐1H‐pyrazolo[3,4‐b] pyridin‐3‐yl)imino)ethyl)‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one

“…The ESR spectrum for complex ( 2 ) displays isotropic spectrum accompanied with (g) value of 2.12 and two broad signals with no hyperfine structure. It was concluded that the broadness of this peak is ascribed to dipolar interaction and a random orientation of Copper(II) ion in addition to the interaction between the unpaired electron and the magnetic nuclei …”

Synthesis, Characterization, DFT Study, Catechol Oxidase and Phenoxazinone Synthase Like Activities of Two New Manganese(IV) Schiff Base Complexes

“…Sharp and strong bands at 1094 cm −1 and 1100 cm −1 give evidence for the presence of ionic perchlorate in the spectra of 1 and 2 respectively . The appearance of a strong band at 2044 cm −1 in the IR spectrum of 2 indicates the presence of monodentate azide . Strong bands at 2926 cm −1 and 3451 cm −1 in the IR spectrum are assigned as alkyl C−H and N−H stretching vibrations in complex 2 respectively …”

Structural Insights and Third Order NLO Studies of Pseudohalide‐ Based Polymeric and Monomeric Congeners of Halo‐Substituted Parent Schiff Bases

“…A characteristic unsplit strong peak at 2049 cm −1 shown by complex 1 is attributable to asymmetric bridging nature of the azido ion . Further the symmetric stretching, ν s (N 3 ) and bending mode δ(N 3 ) of the azido group are ascertained from the peak positions at 1437 and 761 cm −1 respectively . In the case of dicyanamido complex 2 , the slight shift in frequency from that of the free dca anion [ν as + ν s (C=N) combination modes (2286 cm −1 ), ν as (C=N) (2232 cm −1 ) and ν s (C=N) (2179 cm −1 )] to 2288, 2231 and 2160 cm −1 respectively is indicative of the bridging bidentate dca .…”