The product of the examined reaction of Fe2+ and 2-nitroso-1-naphthol was confirmed to be the earlier assumed tris(2-nitroso-1-naphtholato)ferrate(II) by mass spectrometry

Blaženka Foretić

Nicoletta Burger

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ISSN-0011-1643CCA-2655 NoteThe Negative Ions’ Mass Spectrum oftris(2-Nitroso-1-naphtholato)ferrate(II)Bla`enka Foreti} and Nicoletta Burger*Department of Chemistry and Biochemistry, Faculty of Medicine, Universityof Zagreb, [alata 3, 10000 Zagreb, CroatiaReceived March 26, 1999; revised September 14, 1999; accepted September 20, 1999The product of the examined reaction of Fe2+ and 2-nitroso-1-naphth-ol was confirmed to be the earlier assumed tris(2-nitroso-1-naphth-olato)ferrate(II) by mass spectrometry.Key words: mass spectrometry, the tris(2-nitroso-1-naphtholato)fer-rate(II) ionINTRODUCTION2-Nitroso-1-naphthol is currently used as a complexing agent in cobaltanalysis.1,2 It is also a sensitive and specific histochemical reagent for fluo-rimetric determinations of tyrosine residues in proteins and peptides.3 Alongwith other phenols and naphthols, it belongs to biologically important com-pounds, especially because of its cytotoxic action.4Although there has been considerable interest in iron(II) complexes of1-nitroso-2-naphthol,1,5 surprisingly little work was carried out on chelatecomplexes of the same metal ion with the isomeric 2-nitroso-1-naphthol. Ear-lier, the structure of the iron(II) complex of 2-nitroso-1-naphthol was inves-tigated using magnetochemical and Mössbauer spectroscopic techniques.6 Theauthors suggested the existence of a complex of composition 1 Fe2+ : 2 ni-trosonaphthols with an oligomeric structure, which was prepared by mixingferrous ammonium sulphate and 2-nitroso-1-naphthol in a 1 : 2 molar ratio.* Author to whom correspondence should be addressed. (E-mail: bforetic@mef.hr)CROATICA CHEMICA ACTA CCACAA 73 (2) 417¿421 (2000)The complex was found to add two moles of pyridine to give a product of theformula Fe(C10H6O2N)2  2C5H5N.As a continuation of our studies on complexes of nitrosonaphthols, wehave also investigated the reaction between the iron(II) ion and 2-nitroso-1-naphthol, but the reaction product was isolated from a solution containingiron(II) ions and 2-nitroso-1-naphthol in a 1 : 3 molar ratio. The characteris-tics of the complex and the optimum conditions for its formation have beendescribed.7,8 Although the composition of the complex in solution was foundby spectrophotometric methods to be 1 Fe2+ : 3 nitrosonaphthols, a certaindoubt remained about its formula since the results of quantitative analysisof the isolated compound conform equally with FeFe(C10H6O2N)32 andFe(C10H6O2N)2. (The ratio of the metal toward the ligand is the same in bothformulas). The aim of this work was to establish which of the two formulasis the correct one, which has been done by mass spectrometry.EXPERIMENTALAll the chemicals used were of reagent grade. Redistilled water was used through-out. 2-Nitroso-1-naphthol was a Fluka Chemie AG (Buchs, Switzerland) reagent, furtherpurified by recrystallisation from water (m.p. 142–144 °C). Mohr’s salt, (NH4)2SO4  FeSO4  6H2O, was purchased from Kemika (Zagreb, Croatia) while Fe(ClO4)2  6H2Owas synthesized by a known procedure.9The tris(2-nitroso-1-naphtholato)ferrate(II) complex was prepared by mixingmethanolic solutions of 2-nitroso-1-naphthol with a methanolic solution of Fe(ClO4)2 6H2O or a water solution of Mohr’s salt in a 3 : 1 molar ratio. The precipitateddark-green solid was filtered off, washed with small portions of water and ethanoland dried in vacuo over phosphorus pentoxide. It was found to be anionic by treat-ment with a DEAE-Sephadex A-35 anion exchanger. Iron was determined as Fe2O3.Anal. Calcd. for FeFe(C10H6O2N)32: C 60.03, H 3.02, N 7.00, Fe 13.95%; found: C 59.94,H 3.28, N 6.85, Fe 14.36% and C 59.85, H 3.19, N 6.95, Fe 14.20% using ferrous per-chlorate and Mohr’s salt, respectively.The mass spectrum was recorded at the Ru|er Bo{kovi} Institute on an ExtrelFTMS 2001-DD Fourier transform spectrometer using the direct laser desorption/ioni-zation technique. A few micrograms of the isolated compound was dissolved in etha-nol and the solution was allowed to evaporate on the stainless steel disk of the di-rect-insertion probe. A pulsed Nd : YAG laser (moderated at the 1065 nm wavelength)Quanta Ray DCR-11 was used to desorb/ionize the solid.RESULTS AND DISCUSSIONOrtho-substituted nitrosonaphthols can undergo tautomerisation to giveoxo-oximes:418 B. FORETI] AND N. BURGERIn the case of 2-nitroso-1-naphthol, the equilibrium is greatly displacedtoward the keto-form and the compound has, in solid state and in solution, apredominately quinone-oximic structure.8 The product of the reaction of 2-nitroso-1-naphthol (also referred to as 1,2-naphthoquinone-2-oxime) and theFe2+ ion is identical to the one which forms in the second stage of the reac-tion between the same ligand and the aquapentacyanoferrate(II) ion in thepresence of Hg2+, provided the concentration ratio of Hg2+ ions toward aq-uapentacyanoferrate(II) is greater than 2 (Ref. 8). It was assumed to be thetris(2-nitroso-1-naphtholato)ferrate(II) ion, a green complex (lm = 700 nm,Kstability(24 °C) = 7.58  1013 M–3, e = 23400 M–1 cm–1)7,8 where the ligand boundsto iron as an anionic moiety, which is also similar to other metal chelates of2-nitroso-1-naphthol1 and other nitroso compounds.10,11 To prove the correct-TRIS(2-NITROSO-1-NAPHTHOLATO)FERRATE(II) 419NO OHNOOHFigure 1. The LD FTMS spectrum of the negative ions of complex FeFe(C10H6O2N)32.ness of the above assumption, the mass spectrum of the isolated compoundwas recorded and is presented in Figure 1. The characteristic fragments inthe spectrum are described in Table I. The peak at 572 m/z provides con-vincing evidence for the presence of the tris(2-nitroso-1-naphtholato)ferrate(II)ion. Peaks arising from associated complexes earlier observed in the massspectra of related compounds12 were of extremely low relative abundances(2–3%) and were not found. Additional fragmentations are due to the loss ofO, CO and the ligand from the complex. A similar fragmentation patternwas found in the mass spectrum of the nickel(II) complex of 2-nitroso-1-naphthol12 and confirms the earlier statement deduced from IR data thatthe deprotonated oxime group coordinates to the metal centre through thenitrogen atom.7REFERENCES1. A. Chakravorthy, Coord. Chem. Rev. 13 (1974) 1–45.2. M. Sugawara, T. Ucida, and T. Kambara, Bull. Chem. Soc. Jpn. 55 (1982) 3175–3178.3. F. Sundler, L. J. Larsson, and R. Hakanson, Histochemistry 50 (1976) 39–46.4. M. P. M. Portela, S. H. F. Villamil, L. J. Perissinotti, and A. O. M. Stoppani, Bio-chem. Pharmacol. 52 (1996) 1875–1882.5. J. Charalambous, M. J. Fraser, and R. Sims, Inorg. Chim. Acta 18 (1976) 247–251.6. D. K. Allen, J. Charalambous, M. H. Johri, and R. Sims, Inorg. Chim. Acta 29(1978) 235–236.7. B. Foreti} and N. Burger, Monatsh.Chem. 127 (1996) 227–230.8. B. Foreti}, N. Burger, and V. Hankonyi, Polyhedron 14 (1995) 605–609.9. F. Linstrand, Z. Anorg. Allgem. Chem. 230 (1936) 187–208.10. M. S. Masoud, A. M. Hindawey, M. A. Mostafa, and A. M. Ramadan, Spectrosc.Lett. 30 (1997) 1227–1247.11. M. S. Masoud, S. S. Haggag, and A. M. Ramadan, Transition Met. Chem. 23 (1998)343–347.12. J. Charalambous, P. Maple, N. A. Nassef, and F. B. Taylor, Inorg. Chim. Acta 26(1978) 107–111.420 B. FORETI] AND N. BURGERTABLE IMajor ions in the mass spectrum of thetris(2-nitroso-1-naphtholato)ferrate(II) complexm/z Assignment572 Fe(C10H6O2N)3–528 Fe(C10H6O2N)3 – CO – O–399 Fe(C10H6O2N)2 – H–355 Fe(C10H6O2N)2 – H – CO – O–172 C10H6O2N–SA@ETAKMaseni spektar negativnih iona kompleksatris(2-nitrozo-1-naftolato)ferata(II)Bla`enka Foreti} i Nicoletta BurgerProdukt ispitivane reakcije `eljezova(II) iona i 2-nitrozo-1-naftola jest tris(2-nitrozo-1-naftolato)ferat(II) {to je potvr|eno masenom spektrometrijom.TRIS(2-NITROSO-1-NAPHTHOLATO)FERRATE(II) 421

The Negative Ions\u27 Mass Spectrum of tris(2-Nitroso-1-naphtholato)ferrate(II)

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