Structural studies of phenanthrolineN-oxides. The problem of aromaticity and stability

Abstract

Our interest in synthesis and structural studies of 2-thione-and 2-cyanoiminepyrimidine derivatives is accounted by biological activity these compounds. We synthezed several compounds belonging to this family of substances with the radioprotector properties for applications in profilactic and medical treatments of different type of radiation damages of human organisms. By NMR-, IR-spectroscopy, neutron powder and single crystal X-ray diffraction methods we solved more than 10 crystal structures. The method of the synthesis, correlation between molecular structures of these compounds and their radioprotective properties tested on biological objects will be reported. Crystal structures are compared for the parent compound 2-(pyridin-2-ylhydrazonomethyl)-phenol (1) and its derivatives with methoxyl (2) and hydroxyl (3) groups at positions 5 and 6 respectively, along with the hydrochloride of (2). Two kinds of hydrogen bonding occur in (1). The phenolic OH group forms an intramolecular hydrogen bond to the unprotonated N8 atom in the hydrazone chain, while the adjacent NH group interacts with N1 of the pyridine ring in a centrosymmetric base-pair dimer. This pattern persists in (2). However, the extra OH group in (3) attracts a water molecule of crystallisation, which from a special position donates its protons to the pyridine N1 of two separate molecules. The dimer is thereby abolished, but the intramolecular O-H .. Keywords: PYRIMIDINE, RADIOPROTECTOR, BIOACTIVITYN8 hydrogen bond remains intact. Finally, protonation of (2) occurs on N1. This newly created proton donor group and the existing donors all form hydrogen bonds to the chloride ion, and both the dimer and the O-H ..N8 hydrogen bonds are lost. Ab initio (6-31G*) molecular orbital calculations comparing (1) The barium copper cyclosilicate BaCuSi2O6 was described in the tetragonal space group I-4m2 (No 119) at room temperature, with cell parameters a=7.042(3) Å and c=11.133(3) Å [1]. The structure consists of alternating Sr2-and Cu2Si4O12-layers normal to the c axis. The latter layers are in fact bilayers, containing four-membered rings of SiO4 tetraedra and Cu atoms. Four adjacent Si4O12 rings are connected within the bilayers by two Cu atoms coinciding in the (a,b) plane with a distance of 2.76 Å in the c direction. Thus, the Cu 2+ ions (S=1/2) form quasi-isolated dimers parallel to the c axis, arranged in a square lattice within the Cu2Si4O12-bilayers. These dimers have a very weak antiferromagnetic interlayer coupling. This arrangement leads to a disordered magnetic ground state at low temperatures, with a spin gap δ =4.1 meV between the singlet ground state S=0 and the first excited triplet state S=1 [2]. The Si4O12 rings are isolated from each other in the structure. Their study by means of Raman spectroscopy has been used to better understand the structure of amorphous SiO2 [3]. By means of single crystal X-ray diffraction on a Stoe IPDS diffractometer, we have observed at 295 K the presence of superstructure reflections, corresponding to a (a*sqrt(2...

A study of Fe3O4@ Si18O27 catalyst through Statistical-Nucleus Independent Chemical Shifts(S-NICS) method

“…For further investigation of aromaticity, another method called the harmonic oscillator model of aromaticity (HOMA) 6 has been applied, and is distinguished as a normalized sum of the squared deviations of bond length from the normal value 7 . An aromatic compound has a HOMA value of one whereas a non-aromatic compound has the value 0.…”