Ahmad Yavari

The preparation and characterisation of some complexes of iron(II) with amino acids

Abstract The following complexes of iron(II) with the amino acids glycine, alanine, phenylglycine, phenylalanine, leucine, serine, aspartic acid, glutamic acid, glutamine, tryptophan, histidine, methionine, S-methylcysteine, cystine, and glycylglycine have been isolated: Fe(Gly) 2 , Fe(Ala) 2 , Fe(Phegly) 2 , Fe(Phe) 2 ·2H 2 0, Fe(Leu) 2 ·2H 2 0, Fe(Ser) 2 , Fe(Asp)·2H 2 0, Fe(Glu)·2H 2 0, Fe(Gln) 2 , Fe(Trp) 2 , Fe(His) 2 ·H 2 0 and 2H 2 0, Fe(Met) 2 , Fe(MeCys) 2 , Fe(CysCys) and Fe(GlyGly) 2 . Their magnetic behaviour, reflectance spectra, and Mossbauer parameters are consistent with high spin, hexacoordinate iron(II), and imply extended structures involving carboxylate bridges.

Magnetic and spectroscopic properties of some heterotrinuclear basic acetates of chromium(III), iron(III), and divalent metal ions

Reaction of Fe3+, M2+, and acetate ions in aqueous solution gives [FeIII2MIIO(MeCO2)6(H2O)3]·3H2O (M = Mg, Mn, Co, Ni, or Zn), which on crystallisation from pyridine (py) is converted into [FeIII2MIIO(MeCO2)6(py)3]. Reaction of chromium(II) acetate with metal(II) acetate in pyridine in the presence of air gives [CrIII2MIIO(MeCO2)6(py)3](M = Mg, Co, or Ni), and with [FeIII2MIIO-(MeCO2)6(py)3] in pyridine inthe absence of air gives [CrIIIFeIIIMnIIO(MeCO2)6(py)3](M = Mn or Fe) and [CrIII2FeIIIO(MeCO2)6(py)3]. The compounds with co-ordinated pyridine have been examined crystallographically and magnetically. The Cr2Mg, Cr2Ni, Fe2Ni, and CrFeNi compounds crystallise in the monoclinic system, space group Cc or C2/c, Z= 4, but the other seven compounds are rhombohedral and isomorphous with [M3O(MeCO2)6(py)3]·py (M = Mn or Fe), indicating that the three metal atoms are crystallographically equivalent as a result of disorder in the molecular orientation. Powder magnetic susceptibilities for the Cr2Co and Cr2Ni compounds(4.2–60 K), for the Fe2Mn and Fe2Ni compounds (4.2–295 K), and for the Fe2Ni(aquo) and Fe2Mg compounds (80–295 K) have been fitted by use of an exchange Hamiltonian to yield values of the exchange parameters J for the Cr–Cr, Fe–Fe, Cr–Ni, Fe–Ni, and Fe–Mn interactions, which are discussed in terms of superexchange mechanisms. The values of JFeFe in the Fe2Mg, Fe2Mn, and Fe2Ni compounds and of JCrCr in the Cr2Co and Cr2Ni compounds are approximately twice their values in the cations [MIII3O(MeCO2)6(H2O)3]+(M = Cr or Fe), indicating that the µ3-O atom provides the main super-exchange pathway. Diffuse-reflectance and solution spectra (6 000–40 000 cm–1) of the compounds have been recorded at room temperature and are discussed in terms of the ligand-field model; a band in the spectra of the FeIII2FeII and CrIIIFeIIIFeIII compounds at ca. 7 000 cm–1 is assigned to intervalence transfer. The room-temperature spectra of [M3O(MeCO2)6L3]Cl (M3= CrIII3, CrIII2FeIII, CrIIIFeIII2 or FeIII3; L = H2O or py) have also been obtained, and intense absorption bands at ca. 19 000 and 26 000 cm–1 are tentatively assigned to simultaneous (Cr3+, Fe3+) double excitations.

Heterotrinuclear basic acetates containing chromium(III), iron(III), and a divalent metal: spectroscopic consequences of Metal–Metal interactions

Complexes [CrIII2MIIO(MeCO2)6py3](M = Mg, Fe, Co, Or Ni) and [CrIIIFeIIIMIIO(MeCO2)6py3](M = Mn, Fe, Co, or Ni; py = pyridine) are reported; their absorption spectra, together with those of the analogous Fe2IIIMIIcomplexes, provide new information about electronic properties of the M3O system.

Chromium(II) chemistry. Part 14. Ferromagnetic and antiferomagnetic tetrabromochromates(II)

The dihydrated chromium(II) complex bromides M2[CrBr4(OH2)2], where M = Cs, Rb, NH4, or Hpy (py = pyridine), are magnetically dilute, high-spin compounds. The ammonium salt is isomorphous with the analogous copper(II) bromide which is known to contain trans-[CuBr4(OH2)2]2– anions with two short and two long Cu–Br bonds. The piperazinium salts [H2pipz]2[CrBr6]·2H2O and [H2pipz]2[CrBr6], and the guanidinium salt [C(NH2)3]2[CrBr4]·2MeCO2H, are also magnetically dilute. Their reflectance spectra are as expected for tetragonally distorted octahedral anions. Thermal dehydration gives the compounds M2[CrBr4], where M = Cs, Rb, NH4′ NPhH3′ or Hpy, but the monoalkylammonium salts [NRH3]2[CrBr4], where R = Me, Et, Prn, Bun, n-C5H11,n-C8H17′, or n-C12H25′[NMe2H2]2[CrBr4], and [C(NH2)3]2[CrBr4]·2MeCo2H have been crystallised from glacial acetic acid, and [NEt4]2[CrBr4], from mixed organic solvents. Ferromagnetic behaviour is exhibited by Cs2[CrBr4] and the monoalkylammonium salts, but the other tetrabromochromates(II) are antiferromagnetic. The reflectance spectra indicate tetragonal six-co-ordination of CrII and hence polymeric structures. Like the analogous tetrachlorochromates(II), the magnetic data for the ferromagnetic tetrabromochromates from liquid-nitrogen to room temperature can be reproduced by the high-temperature series-expansion formula for a sheet ferromagnet with S= 2, and JBr > JCl. The reflectance spectra contain very sharp bands at ca. 15 600 and 18 400 cm–1 assigned to spin-forbidden transitions intensified by magnetic coupling. The magnetic behaviour of the antiferromagnetic complexes is reproduced by the high-temperature series-expansion formula with appropriate changes of sign. The stretching vibrations of the short Cr–Br bonds occur near 250 cm–1.

Exchange interactions in a series of novel heteronuclear basic carboxylate complexes containing two iron(III) ions and a divalent metal ion

Complexes [Fe2IIIMIIO(MeCO2)6py3]py (M = Mg, Mn, Co, Ni, or Zn; py = pyridine), isomorphous(except for M = Ni) with the mixed-valence compounds [M3O(MeCO2)6py3]py (M = Mn or Fe), are reported; their magnetic properties provide new information about superexchange pathways in the trinuclear basic carboxylate system.

Chromium(II) chemistry. Part 13. Thiocyanates

Chromium(II) forms the pentathiocyanatochromate(II), Na3[Cr(CNS)5]·9H2O, which from magnetic, diffusereflectance, and i.r. data contains a square-pyramidal arrangement of N-bonded thiocyanates. Attempts to prepare similar salts of other metal cations have been unsuccessful, and organic cations give a series of tetrathiocyanatochromates(II), [A]2[Cr(CNS)4][A = NMe4, NEt4, NPrn4, NBun4, Hhex, Hpy, 1/2H2en, or 1/2H2L; hex = hexamine (hexamethylenetetramine), py = pyridine, en = ethylenediamine, and L = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene]. In general these complexes show antiferromagnetic behaviour, and are belived to have thiocyanato-bridged structures. Monoethanol adducts of the [NEt4]+ and [NPrn4]+ salts have also been isolated, and found to be magnetically normal. The [NBun4]+ salt is isolated in two forms, one brown and magnetically normal, and the other blue and antiferromagnetic.

Chromium(II) chemistry. Part 12. Further examples of ferromagnetic chlorochromates(II)

The chlorochromates(II)[NMeH3]2[CrCl4], [NEtH3]2[CrCl4], [H2en][CrCl4], [H3dien][CrCl4]Cl, and [H4trien][CrCl4]Cl2(en, dien, and trien are ethylenediamine, 3-azapentane-1,5-diamine, and 3,6-diazaoctane-l,8-diamine respectively) are ferromagnetic whereas [NMe2H2]2[CrCl4] and [NMe2H2][CrCl3] are antiferromagnetic. The ferromagnetic complexes are isomorphous with the corresponding copper(II) complexes. These are known to contain two-dimensional networks of planar [CuCl4]2– units bridged by chloride ions of adjacent units so that the metal ions occupy tetragonally elongated octahedra. The magnetic behaviour of the ferromagnetic chromium(II) complexes from room to liquid-nitrogen temperature is reasonably represented by the high-temperature series-expansion formula for a sheet ferromagnet. The reflectance spectra of all the complexes are characteristic of six-co-ordinate CrII, and, in the case of the ferromagnetic complexes, contain very sharp bands at ca. 15 800 and 18 700 cm–1 assigned to spin-forbidden bands intensified by magnetic coupling. Absorption bands in the far-i.r. spectra near 300 cm–1 are assigned to Cr–Cl stretching vibrations within the planar [CrCl4]2– units.

Ferromagnetic monoalkylammonium tetrabromochromates(II)

The complex bromides of chromium(II), [MeNH3]2[CrBr4] and [EtNH3]2[CrBr4], are ferromagnetic.

Chromium(II) chemistry. Part IX. Ferromagnetic and antiferro-magnetic chlorochromates(II)

The new chromium(II) complex chlorides M2[CrCl4(OH2)2][M = NH4, Hpy (pyridiniurm). Rb,orCs] are magnetically dilute, high-spin compounds with reflectance spectra of the type expected for tetragonally distorted octahedral anions [CrCl4(OH2)2]2–. Several compounds are isomorphous with their copper(II) analogues of known structure. Thermal dehydration gives compounds M2[CrCl4](M = NH4, Rb, or Cs), which are ferromagnetic as is K2[CrCl4] obtained from a hydrate too unstable to be completely characterized. The reflectance spectra again indicate tetragonal six-co-ordination, and hence the anhydrous compounds have polymeric structures which permit the ferromagnetic interaction through 180° coupling. Unusually intense spin-forbidden absorptions are found in the reflectance spectra of these compounds. The complex Cs[CrCl3(OH2)2] is weakly antiferromagnetic and presumably has a similar structure to Li[CuCl3(OH2)2]. Chloride-bridged structures in [Hpy]2[CrCl4] and M[CrCl3](M = Hpy, Me4N, or Cs) produce antiferromagnetic behaviour which leads to slight intensification of the spin-forbidden bands.

Preparation and magnetic behaviour of complex bromides of chromium(II)

The complex bromides M2CrBr4(H2O)2 are paramagnetic (M = Rb, Cs,NH4,C5H5NH), but dehydration gives anti-ferromagnetic compounds except for Cs2CrBr4 which is ferromagnetic.