Nikolia Lalioti

Ising‐Type Magnetic Anisotropy in a Cobalt(II) Nitronyl Nitroxide Compound: A Key to Understanding the Formation of Molecular Magnetic Nanowires

The compound [Co(hfac)2-(NITPhOMe)2] (2) (hfac = hexafluoroacetylacetonate, NITPhOMe = 4-methoxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) crystallizes in the triclinic P1 space group, a= 10.870(5), b = 11.520(5), c = 19.749(5) A, alpha = 78.05(5), beta = 84.20(5), gamma = 64.51(5) degrees, Z = 2. It can be considered a model system for studying the nature of the magnetic anisotropy of [Co(hfac)2(NITPhOMe)] (1), which was recently reported to behave as a molecular magnetic wire. The magnetic anisotropy of 2 was investigated by EPR spectroscopy and SQUID magnetometry both in the polycrystalline powder and in a single crystal. The experimental magnetic anisotropy was related to the anisotropy of the central ion and to the exchange interaction between the cobalt(II) ion and the radicals.

Glauber slow dynamics of the magnetization in a molecular Ising chain

The slow dynamics (10−6 s–104 s) of the magnetization in the paramagnetic phase, predicted by Glauber for the 1d Ising model, has been observed with ac susceptibility and SQUID magnetometry measurements in a molecular chain comprising alternating Co2+ spins and organic radical spins strongly antiferromagnetically coupled to give a 1d ferrimagnet. An Arrhenius behavior with activation energy Δ = 152 K has been observed for ten decades of relaxation time and found to be consistent with the Glauber model. We have extended this model to take into account the ferrimagnetic nature of the chain as well as its helicoidal crystal structure.

New metal-binding modes for 5-aminoorotic acid: preparation, characterization and crystal structures of zinc(II) complexes

Treatment of ZnCl2 with 2 equivalents of 5-aminoorotic acid (5-amino-2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid, H4L) and 2 equivalents of NaOH in water–methanol yielded a mixture of crystals and powder of complexes [{Zn(H2L)(H2O)2}n] 1 and [Zn(H3L)2(H2O)4] 2, respectively. A good yield (ca. 70%) of pure 2 can be obtained by the reaction of Zn(O2CMe)2·2H2O and 2 equivalents of H4L in refluxing water. The crystal structure of 1 consists of neutral octahedral [Zn(H2L)(H2O)2] units which form polymer chains along the b axis; H2L2– behaves as a bis(bidentate) bridging ligand co-ordinating to two zinc atoms via the amino nitrogen, the oxygen of the neutral carboxamide group, the deprotonated carboxamide nitrogen and one of the carboxylate oxygens and forming two five-membered chelate rings. The 1H NMR spectra of 1 in (CD3)2SO at 290 and 310 K suggest that its solid-state structure is not retained in solution. Slow crystallization of 1 or 2 from dmso solutions yielded crystals of the monomeric octahedral complex [Zn(H3L)2(dmso)2(H2O)2] 3 the structure of which was solved by single-crystal X-ray crystallography. The monoanion H3L– utilizes only one carboxylate oxygen for metal binding in the centrosymmetric complex 3. The difference in anionic charge and co-ordination mode between H2L2– and H3L– leads to different hydrogen-bonded supramolecular structures for 1 and 3. The IR and 1H NMR spectra of the prepared complexes are discussed.

Supramolecular interactions and magnetism of metal–radical chains

The combination of organic imidazoline-1-oxyl-3-oxide radicals as building blocks with metal ions can yield 1-D magnetic chains in various conformations, depending on the metal ion and the 2 substituent of the radicals.

Tetranuclear iron(III) carboxylate clusters with 1,10-phenanthroline and 2,2'-bipyridine: a new [Fe4(μ4-OHO)(μ-OH)2]7+ core

The reactions between Fe(ClO4)3·6H2O, NaO2CMe·3H2O and L–L (L–Lxa0=xa02,2′-bipyridine, 1,10-phenanthroline) in MeCN give complexes [Fe4(OHO)(OH)2(O2CMe)4(L–L)4](ClO4)3 whose cations contain the novel [Fe4(μ4-OHO)(μ-OH)2]7+ core; magnetic studies indicate that both complexes have Sxa0=xa00 ground states, consistent with the presence of strong antiferromagnetic exchange interactions.

Rare M7O2 double tetrahedral core in molecular species: preparation, structure and properties of [Zn7O2(O2CMe)10(1-Meim)2] (1-Meim = 1-methylimidazole)

The 2:1 reaction between Zn(O2CMe)2·2H2O and 1-Meim in refluxing MeCN gives [Zn7O2(O2CMe)10(1-Meim)2] 1 which comprises two vertex-sharing tetranuclear Zn4(µ4-O)(η1: η1:µ2-O2CMe)5(1-Meim) units; solid-state 13C and 15N NMR spectra reveal structural details of the complex.

A Mn-4(II) cubane and a novel (Mn10Mn4III)-Mn-II cluster from the use of di-2-pyridyl ketone in manganese acetate chemistry

The employment of di-2-pyridyl ketone, (py)2CO, in manganese(II) acetate chemistry is reported. The syntheses, crystal structures and magnetochemical characterisation are described for [MnII4(O2CMe)4{(py)2C(OH)O}4] () and [MnII10MnIII4O4(O2CMe)20{(py)2C(OH)O}4] (), where (py)2C(OH)O- is the monoanion of the gem-diol form of the ligand. The reaction of Mn(O2CMe)(2).4H2O with one equivalent of (py)2CO in Me2CO gives . Complex was obtained from the 1:1 reaction, in EtOH, between Mn(O2CMe)(2).4H2O and (py)2CO in the presence of NEt3. The tetranuclear molecule has a cubane topology with the MnII and the deprotonated oxygen atoms from the eta1:eta3:eta1:micro3 ligands occupying alternate vertices of the cube. The core of consists of two mixed valence cubane {MnII2MnIII2(micro3-O)2(micro3-OR)2}4+ subunits that are linked through an unusual {MnII6(eta1:eta2:micro-O2CMe)6(eta2:eta2:micro3-O2CMe)2}4+ moiety via twelve eta1:eta1:micro MeCO2- groups. Some suggestions have been made concerning the possible assembly of from . The magnetic properties of in the 300-5 K range have been modelled with two J values, which reveal weak antiferromagnetic interactions within the molecule. Complex has a low spin ground state. This work demonstrates the flexibility, versatility and synthetic potential of combining (py)2CO with carboxylate ligands.