The reaction of the metal-organic precursor Fe[N(SiMe3)2]2 with H2 in the presence of a long-chain acid and a long-chain amine in various proportions produces monodisperse zerovalent iron nanoparticles. These Fe particles display magnetic properties that match those of bulk iron as evidenced by magnetic and Mössbauer measurements. The nanoparticles adopt a cubic shape with edges of 7 nanometers and are incorporated into extended crystalline superlattices containing nanocubes in close proximity and with their crystallographic axes aligned. These superlattices are formed in solution, precipitate in high yield, and may be redissolved and redeposited as two-dimensional arrays.

Coalescence of initially produced nanospheres inside 3D super‐lattices may be the reason for the formation of ferromagnetic cobalt nanorods, monodisperse in length and diameter, from [Co(η3‐C8H13)(η4‐C8H12)] in the presence of stearic acid and hexadecylamine. The self‐organization of these nanorods into unprecedented hexagonal 2D and 3D super‐lattices has been studied by transmission electron microscopy (see picture).

The shape of things to come: Nanospheres, thermodynamically stable nanorods, and nanowires are selectively produced in solution from [Co(η3‐C8H13)(η4‐C8H12)] in the presence of oleic acid and various amines. The aspect ratio of the nanorods is controlled by the length of the alkyl chain of the amine. Nanorods with approximate dimensions of 9×40 nm (see Figure) are ferromagnetic at room temperature.

Nanokugeln, ‐röhrchen und ‐drähte nach Maß lassen sich selektiv aus einer Lösung von [Co(η3‐C8H13)(η4‐C8H12)] in Gegenwart von Ölsäure und verschiedenen Aminen herstellen. Dabei bestimmt die Alkylkettenlänge des Amins die Länge des Nanoröhrchens. Die Aufnahme zeigt Röhrchen von etwa 9×40 nm2, die thermodynamisch stabil und bei Raumtemperatur ferromagnetisch sind.

2 ] 2 . -Fe nanocubes are synthesized by decomposition of Fe[N(SiMe 3 ) 2 ] 2 in mesitylene under H2 atmosphere in the presence of hexadecylamine and oleic acid or hexadecylammonium chloride (150°C, 48 h, 50% yield). The samples are characterized by TEM, SEM, Moessbauer spectroscopy, and magnetic measurements. The nanoparticles adopt a cubic shape with edges of 7 nm and are incorporated into extended crystalline superlattices containing nanocubes in close proximity and with their crystallographic axes aligned. These Fe particles display magnetic properties that match those of bulk iron. -(DUMESTRE, F.; CHAUDRET*, B.; AMIENS, C.; RENAUD, P.; FEJES, P.; Sci.

Stable iron nanoparticles have been synthesised by the decomposition of {Fe(N[Si(CH(3))(3)](2))(2)}(2) under dihydrogen pressure. Those conditions lead to a system of monodisperse and metallic nanoparticles which diameter is less than 2 nm and stabilized by HN[Si(CH(3))(3)](2). The magnetization is found to be M(S)=1.92 mu(B)/at., i.e., 10% lower than the bulk value. The Mossbauer spectrum is fitted by two contributions of metallic iron. The magnetic anisotropy energy constant increases up to 5.2x10(5) J/m(3), i.e., ten times the bulk one

The dinuclear (Fe(II), Gd(III)) complexes studied in this report derive from hexadentate Schiff base ligands abbreviated H(2)L(i)() (i = 1, 2, 3). H(2)L(1) = N,N'-bis(3-methoxysalicylidene)-1,3-diamino-2,2'-dimethyl-propane, H(2)L(2) = N,N'-bis(3-methoxysalicylidene)-1,2-diamino-2-methylpropane, and H(2)L(3) = N,N'-bis(3-methoxysalicylidene)-1,2-diaminoethane. The crystal and molecular structures of three complexes have been determined at 160 K. Depending on the solvent used in the preparation, L(1)Fe(CH(3)OH)Gd(NO(3))(3)(CH(3)OH)(2), 1, or L(1)Fe((CH(3))(2)CO)Gd(NO(3))(3), 1', is obtained from H(2)L(1). A similar complex, L(2)Fe((CH(3))(2)CO)Gd(NO(3))(3), 2, is obtained from H(2)L(2). Complex 1 crystallizes in the orthorhombic space group Pca2(1) (No. 29): a = 22.141(3) A, b = 9.4159(16) A, c = 15.2075(17) A, V = 3170.4(7) A(3), Z = 4. Complexes 1' and 2 crystallize in the monoclinic space group P2(1)/c (No. 14): 1', a = 9.6264(17) A, b = 19.662(3) A, c = 16.039(3) A, beta = 95.15(2) degrees, V = 3023.6(9) A(3), Z = 4; 2, a = 9.7821(13) A, b = 18.7725(17) A, c = 16.100(2) A, beta = 96.497(16) degrees, V = 2937.5(6) A(3), Z = 4. Complexes 1, 1', and 2 possess an Fe(O(phenoxo))(2-)Gd core. The mononuclear L(3)Fe complex could be prepared from H(2)L(3) but not the related dinuclear (Fe, Gd) species. Mössbauer spectroscopy evidences that the iron center is in the +2 oxidation state for the six complexes. The experimental magnetic susceptibility and magnetization data of complexes 1, 1', and 2 indicate the occurrence of weak Fe(II)-Gd(III) ferromagnetic interactions. Single ion zero-field splitting of the iron(II) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry (1, J = 0.50 cm(-1), D = 2.06 cm(-1); 1', J = 0.41 cm(-1), D = 3.22 cm(-1); 2, J = 0.08 cm(-1), D = 4.43 cm(-1)).

Decomposition of the organometallic Co(η 3 -C 8 H 13 )(η 4 -C 8 H 12 ) complex in the presence of a 2/1 acid/amine mixture, or of cobalt stearate in the presence of 2 equiv. of amine leads to singlecrystalline hcp cobalt nanowires of a few nanometers in diameter and micrometers in length. These nanowires display high coercive fields (1.7 T) as well as the magnetization of bulk cobalt. To develop a method for the carbon coating of these nanowires and thus ensure their long-term air stability, the thermal stability of the nanowires is investigated. After being annealed at temperatures above 350 °C under static argon atmosphere, chains of cobalt nanoparticles embedded in a wirelike carbon matrix are obtained. This phenomenon is a consequence of the Rayleigh instability of the nanowires, which is enhanced during the decomposition of the stabilizing ligands. In high-vacuum conditions, in situ transmission electron microscopy (TEM) and high-resolution TEM studies show that the nanowires evaporate without any appearance of Rayleigh instability, and without any structural change. This suggests the crucial role played by the ligands in the fragmentation process. Annealing below 350 °C prevents the fragmentation process and yields carbon-coated cobalt nanowires.