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The synthesis and structural and magnetic characterization of a new tridentate 2,2'-bipyridine dicarboxamide ligand obtained from 3,3'-diamino-2,2'-bi-pyridine and 2-pyridine carbonyl chloride is presented.

The preparation, X-ray crystal structure, electrochemical and magnetic characterization of a 1:1 copper complex [C[u.sup.II][(hfac).sub.2](TTF-CH=N-Py)] (imine-bridged pyridyltetrathiafulvalene building block) are reported. The crystal structure reveals that the imine N atom participates in chelation to the paramagnetic center which makes the ligand an attractive precursor for assembly of [pi]-d systems.

The synthesis, crystal structure, and magnetic properties of a series of [Mo.sub.3]Co[S.sub.4] clusters with three different populations to their selenium analogues are reported. The results provide insights into the nature of bonding for [Mo.sub.3]Co[Q.sub.4] (Q = S, Se) complexes.

The preparation and characterization of a novel dimeric [Mn.sup.II] complex [{[Mn([N.sub.3][O.sub.2])]Cl(O[H.sub.2])}.sub.2]2Cl of a macrocyclic Schiff base ligand derived from the condensation of 2,2',6,6'-tetraacetyl-4,4'-bipyridine with 3,6-dioxaoctane-1,8-diamine in the presence of a stoichiometric amount of [Mn.sup.II] is reported.

The synthesis, crystal structure and physical characterization of new radical salts formed by the organic donor bis(ethylenediseleno)tetrathiafulvalene (BEST) and the paramagnetic tris(oxalato)metalate anions [[M[([C.sub.2][O.sub.4]).sub.3]].sup.3-] (M = [Fe.sup.III] and [Cr.sup.III]) are described. The results have shown that all the compounds are paramagnetic semiconductors with high room-temperature conductivities and magnetic susceptibilities dominated by the Fe- or Cr-containing anions.

The synthesis, crystal structure, and magnetic properties of [Mo3(CoCO)Se4(dmpe)3Cl3] (1), [Mo3(CoCI)Se4(dmpe)3Cl3] (2), and [Mo3(CoCI)Se4(dmpe)3Cl3](TCNQ) ([2](TCNQ)) (dmpe 1,2-bis(dimethylphosphanyl)ethane; TCNQ = 7,7,8,8- tetracyanoquinomethane) cubane-type complexes with 16, 15, and 14 metal electrons, respectively, are reported. These compounds complete the series of cobalt-containing Mo3CoQ4 (Q = S, Se) cubane-type complexes, which allows a complete analysis of the consequences of replacing the inner chalcogen and the metal electron count on the structural, magnetic, and electrochemical properties. The experimental evidence is theoretically supported and rationalized on the basis of density-functional theory calculations. For the 15-metal electron [Mo3(CoCI)Se4(dmpe)3Cl3] complex with S = 1/2, both electron paramagnetic resonance and theoretical studies give support to a spin density mainly located on the heteroatom. The nature of the highest occupied molecular orbital upon chalcogen exchange within the Mo3CoQ4 (Q = S, Se) series remains essentially unchanged, whereas the nature of the ligand attached to Co (Cl or CO) results in a different ordering of the molecular orbital scheme. This behavior is explained by the absence of backdonation between an occupied d orbital of Co to an empty π Cl orbital, to yield frontier orbitals that differ from those of previous models. [ABSTRACT FROM AUTHOR]

The incorporation of the electronegative cyano group into the structure of the title dithiazolyl radical 1 induces a lamellar packing motif that favors spin-transition behavior. Variable-temperature magnetic studies on 1 reveal a reversible phase transition at 250 K between a diamagnetic low-temperature phase and a paramagnetic high-temperature phase. X-ray crystal structures at 180(2) and 300(2) K reveal that both phases crystallize in the space group P21/c, with the phase transition associated with a doubling of the crystallographic a axis. The concomitant change in magnetic properties is associated with a change from a paramagnetic regular stack of radicals and a diamagnetic distorted π stack in which an energy gap opens up at the Fermi level corresponding to a Peierls-like transition. [ABSTRACT FROM AUTHOR]

A novel dimeric MnII complex {[Mn(N3O2)]Cl(OH2)}(2)2Cl (2) of a macrocyclic Schiff base ligand derived from the condensation of 2,2',6,6'-tetraacetyl-4,4'-bipyridine with 3,6-dioxaoctane-1,8-diamine in the presence of a stoichiometric amount of MnII has been prepared and characterized. The X-ray analysis of 2 reveals that the two Mn ions assume a pentagonal-bipyramidal geometry, with the macrocycle occupying the pentagonal plane and the axial positions being filled by a halide ion and a H2O molecule. Magnetic susceptibility data (2-270 K) reveal the occurrence of weak antiferromagnetic interactions between covalently tethered MnII-MnII dimeric units.