Facile Preparation of Organometallic Nanorods from Various Ethynyl-Substituted Molecules.

A facile method to prepare one-dimensional (1D) organometallic nanomaterials from various ethynyl-substituted molecules is reported. The reactions of 3-chloro-1-ethynylbenzene, p-tBu-phenylacetylene and 4-ethynylbiphenyl with Cu+ ions in acetonitrile yield nanorod-shaped copper acetylides (Cu-C≡C-R) crystals. In the case of linear alkynes, namely, propyne, 1-pentyne and 1-hexyne, it was found that using an aqueous ammonia/ethanol mixed solvent instead of acetonitrile is a better approach to obtain 1D nanostructures. This procedure also enables us to prepare functional 1D nanomaterials. We demonstrate the preparation of a paramagnetic nanorod from the organic radical p-ethynylphenyl nitronyl nitroxide, and fluorescent nanorods from 9-ethynylphenanthrene and 2-ethynyl-9,9'-spirobifluorene.

A series of weak ferromagnets based on a chromium-acetylide-TTF type complex: correlation of the structures and magnetic properties and origin of the weak ferromagnetism.

The crystal structures and magnetic properties of a series of new weak ferromagnets containing a chromium-acetylide-tetrathiafulvalene (TTF) type complex, [CrCyclam(C≡C-5-methyl-4'5'-ethylenedithio-TTF)2](2+) ([1](2+)), were investigated. The six new isostructural weak ferromagnets [1][BF4]2(PhF)2(MeCN), [1][ClO4]2(PhF)2(MeCN), [1][ReO4]2(PhCl)2(MeCN), [1][ClO4]2(PhBr)3, [1][ReO4]2(PhBr)3, and [1][ClO4]2(PhI)3 contain ferrimagnetic chain structures of [1](2+)∞ with different interchain distances that are dependent on the sizes of the anions and solvent molecules. Magnetic measurements of the salts revealed that the weak ferromagnetic transition temperature gradually increases from 14.5 to 26.0 K as the interchain distance decreases from 3.997(2) to 3.803(2) Å, while the remanent magnetization at 2 K decreases from 0.0215 to 0.0079 µB. The observed magnetic properties and crystal structures suggest that the weak ferromagnetism originates from the single-ion anisotropy of [1](2+), where a stronger interchain antiferromagnetic interaction not only causes a higher transition temperature but also suppresses the noncollinear canted spin alignment.

Weak ferromagnetism and strong spin-spin interaction mediated by the mixed-valence ethynyltetrathiafulvalene-type ligand.

A new chromium complex with ethynyltetrathiafulvalene (TTF)-type ligands, [CrCyclam(C≡C-5-methyl-4'5'-ethylenedithio-TTF)(2)]OTf ([1]OTf), was synthesized. The cyclic voltammetry of the complex shows two reversible oxidation waves owing to the first and second oxidation of the TTF unit. The electrochemical oxidation of [1]OTf in a Bu(4)NClO(4) or Bu(4)NBF(4) solution of a 1:1 acetonitrile-chlorobenzene mixture gave isostructural crystals of [1][ClO(4)](2)(PhCl)(2)(MeCN) and [1][BF(4)](2)(PhCl)(2)(MeCN), where two mixed-valence TTF units of adjacent complexes form a dimer radical cation. The crystal structures are characterized by an alternating chain of S = 3/2 Cr(3+)Cyclam units and S = ½ (TTF)(2)(+) dimers. These two paramagnetic components are connected directly by an ethynyl group, resulting in a strong intrachain spin-spin interaction of 2J/k(B) = -30 and -28 K for [ClO(4)](-) and [BF(4)](-) salts, respectively (H = -2J∑(i)S(i)·S(i+1)). Both salts show a weak ferromagnetic transition at 23 K thanks to interchain antiferromagnetic interaction between TTF dimers. The remanent magnetizations and coercive forces of nonoriented samples at 1.8 K are 0.016 µ(B) and 90 mT for the [ClO(4)](-) salt and 0.010 µ(B) and 50 mT Oe for the [BF(4)](-) salt, respectively. The weak ferromagnetism is attributed to the Dzyaloshinsky-Moriya interaction between adjacent TTF dimers and/or the single-ion anisotropy of [1](2+).

Chromium acetylide complex based ferrimagnet and weak ferromagnet.

The crystal structures and magnetic properties of new molecule-based magnets, [CrCyclam(C[triple bond]C-3-thiophene)(2)][Ni(mdt)(2)] (1) and [CrCyclam(C[triple bond]C-Ph)(2)][Ni(mdt)(2)](H(2)O) (2) (Cyclam = 1,4,8,11-tetraazacyclotetradecane, mdt = 1,3-dithiole-4,5-dithiolate), are reported. The crystal structures of both compounds are characterized by ferrimagnetic chains of alternately stacked [CrCyclam(C[triple bond]C-R)](+) cations and [Ni(mdt)(2)](-) anions with intrachain exchange interactions of 2J = -6.1 K in 1 and -5.7 K in 2 (H = -2J Sigma(i) S(i) x S(i+1)). The material 1 exhibits ferrimagnetic transition at 2.3 K owing to weak interchain antiferromagnetic interactions between cations and anions. In the case of 2, cations in adjacent ferrimagnetic chains are bridged by a water molecule, resulting in an interchain antiferromagnetic coupling. Despite a centrosymmetry of a whole crystal of 2, one bridging water molecule occupies only one of the two centrosymmetric sites and breaks a local centrosymmetry between adjacent cations. The interchain antiferromagnetic interaction and Dzyaloshinsky-Moriya interaction originated from the local symmetry breakdown of 2 bring a weak-ferromagnetic transition at 3.7 K with a coercive force of less than 0.8 mT, followed by the second magnetic phase transition at 2.9 K. Below this temperature, the coercive force rapidly increases from 1 to 11.8 mT as the temperature decreases from 2.9 to 1.8 K, while the remanent magnetization monotonically increases from 0.008 mu(B) at 3.6 K to 0.12 mu(B) at 1.8 K.

d-Electron-induced negative magnetoresistance of a pi-d interaction system based on a brominated-TTF donor.

A new pi-d interaction system (EDT-TTFBr2)2FeBr4 (EDT-TTFBr2 = 4,5-dibromo-4',5'-ethylenedithiotetrathiafulvalene) and its nonmagnetic anion analogue (EDT-TTFBr2)2GaBr4 based on a brominated TTF-type organic donor are investigated. The salts featured by quasi-1D pi-electronic systems are metallic with metal-insulator transitions taking place at about 20 and 70 K for the FeBr4- and GaBr4- salts, respectively, where the low-temperature insulating state is associated with charge ordering or a Mott insulator followed by an antiferromagnetic transition at lower temperatures. The FeBr4- salt is featured with an antiferromagnetic transition of the anion d spins at a Neel temperature (TN) = 11 K, which is significantly high despite its long anion-anion Br-Br contact, suggesting the importance of the pi-d interaction in the magnetism. The surprisingly strong pi-d interaction, ca. -22.3 K estimated from the magnetization curve, evidences the usefulness of the chemical modification of the donor molecule with bromine substitution to achieve strong intermolecular interaction. The antiferromagnetic state of the anion d spins affects the transport of the conducting pi electrons through the strong pi-d interaction, as evidenced by the presence of a resistivity anomaly of the FeBr4- salt at TN. Below TN, the FeBr4- salt shows negative magnetoresistance that reaches -23% at the highest magnetic field investigated (B=15 T), whereas only a small positive magnetoresistance is observed in the pi-electron-only GaBr4- salt. The mechanism of the negative magnetoresistance is explained by the stabilization of the insulating state of the pi electrons by the periodic magnetic potential of the anion d spins in the FeBr4- salt, which is modified by applying the external magnetic field.