New metal complexes of N-benzyl-N-nitrosohy-droxylamine (BNHA) are isolated and characterized by elemental analysis, IR and UV-VIS spectroscopy. Spectrophotometric titration of aqueous solutions of BNHА by salts of some transition metals allowed to calculate the composition and formation constants of the metal complexes. The crystal structure of Cu (BNHА)2 is studied by X-ray diffraction. The Cu atom is coordinated by four O atoms of two bidentate ligands, which close 5-membered chelate rings. The N-O (1.306 ? - 1.320 ?) and N-N (1.274 ? and 1.275? ) bond lengths indicate that π electrons are delocalized over the chelating groups. Complexes form stacks with intermolecular Cu…N contacts equal to 3.118 ? and 3.306 ?.
The feature of chelate-forming derivatives of N-nitrosohydroxylamines is the possibility to form stable complexes with the metallic ions of various natures (for example, Al and Pd).
The ammonium salt of N-nitroso-N-phenylhydroxylamine, is a well known (as cupferron) analytical reagent and it was very popular especially during the classical period of analytical chemistry [1-3]. This ligand is known to form complexes with many metals but only few of them have been structurally characterized [4-15].
Recently it was shown that many ortho-substituted N-nitroso-N-oxybenzenamines are good NO donors for both in vitro and in vivo assays [
In addition, cupferron is a biologically active compound, known to display carcinogenic, genotoxic, mutagenic and DNA-damaging effects [17,18]. The knowledge of the chemistry of cupferron and its analogues containing N-nitrosohydroxylamine fragments could contribute to a better understanding of the interaction of nitrogen oxide with metal centers of biologically important species.
Here we report the isolation and characterization of some transition metal complexes with N-benzyl-N-nitrosohy-droxylamine (BNHА).
The electronic spectra in the 200 - 800 nm range were obtained on a Varian spectrophotometer “Cary 50 scan”, using aqueous 10−4 M solutions. IR spectra were recorded in KBr on a Varian “Excalibur HE 3100” FT spectrophotometer. Single crystal was characterized by a Bruker APEX II diffractometer. All the chemicals are commercially available and they were used without further purification. All the solvents were dried using standard methods before use.
K(BNHA) and Cu(BNHA)2. The synthesis was performed according to the procedure described in [
The above mentioned complexes were prepared by the reaction of the corresponding metal chloride with K(BNHA). In a typical reaction, an aqueous solution containing 1 mmol of MCl2∙xH2O was slowly mixed with 2 mmol of the K(BNHA) under vigorous stirring. The obtained precipitates were collected and re-crystallized from ethanol. Yields 50% - 70%.
The formulae of the obtained complexes are derived from the elemental analysis and presented in the
Spectrophotometric titration of solutions of K(BNHA) with the solutions of metal salts in water was carried out in neutral and alkaline media. Based on the results of titration, the saturation curves were drawn for several wavelengths, and the metal-to-ligand ratios were calculated. The formation constants of metal complexes were determined by the procedure described by Beck & Nadypal [
Light blue needles of Cu(BNHA)2 suitable for X-ray data collection were obtained while re-crystallisation from ethanol. The diffraction data were collected on a Bruker APEX-II CCD diffractometer at room temperature and processed using the Bruker software [
1M.p. 157˚C (dec.) [
Structure solution and refinement were performed using the SHELX97 program package [
The electronic absorption spectrum of K(BNHA) (
ax, y + 1, z; bx, y − 1, z.
is characterized by one wide absorption band in the range 230 nm - 260 nm with the lmax 252 nm (log e 4.06).
The addition of metal salts to the solutions of K(BNHA) provokes the hypsochromic shift and decrease in intensity of the ligand absorption band which indicates the change of the electronic structures of the organic anions due to their complexation and formation of coordinate bonds of a co-valent character. Dlmax 1 - 19 nm. The presence of isobestic points in the spectra indicates the reversible equilibria in the “ligand-complex” systems. The metal-to-ligand ratio and formation constants of the complexws in aqueous solutions are presented in the
As the K-BNHA bonds may be considered to be of
100% ionic character, the Dlmax value may indicate the increase in the degree of co-valency of M-BNHA interaction. Thus, from the data of the
The major IR absorption bands of K(BNHA) and its Cu(II) and Co(II) complexes are presented in the
The assignments of the various absorption bands in K(BNHA) and the transitional metal complexes were performed according to N. Thakur et al. [
The copper atom has a nearly planar square coordination formed by oxygen atoms of two BNHA-ligands, which close 5-membered ONNOCu chelate rings (
The Cu(1) atom lies in the plane of the O(1)N(1) N(2)O(2) fragment (its deviation is 0.022 Å) and deviates from the O(3)N(3)N(4)O(4) plane by 0.194 Å. In both BGA-molecules, the planar O2N2CH2 and PhCH2 fragments lie in approximately perpendicular planes (the dihedral angles are 93.3˚ and 109.9˚). The phenyl rings of the two NBHA-molecules are bent in opposite directions with respect to the coordination plane and form an angle of 139.4˚ with each other. The geometric parameters of the NBHA-ligands in Cu(BNHA)2 are close to those in Zr(cp)2(BNHA) [
The N-benzyl-N-nitrosohydroxylamine (BNHА) ligand coordinates metal ions by two oxygen atoms. The bonding of the ligands to metal ions is confirmed by spectroscopic and single-crystal X-ray diffraction studies. The composition and the formation constants of the complexes in aqueous solutions were determined by UV spectroscopic titration.
The crystallographic data for Cu(BNHA)2 have been deposited with the Cambridge Crystallographic Data Centre (CCDC 910807).
This study was supported by the Russian Foundation for Basic Research (project 10-03-00003-а).