RESUMEN
The magnetism of a series of tetranuclear complexes of the [Fe4IIL4]8+ [2x2]-grid-type was investigated, revealing the occurrence of spin transition behavior within this class of compounds. The phenomenon depends directly on the nature of the substituent R(1) in the 2-position on the central pyrimidine group of the ligand L. All Fe(II) ions in compounds with R(1) substituents favoring strong ligand fields (R(1)=H; OH) remain completely in the diamagnetic low-spin state. Only complexes bearing R(1) substituents attenuating the ligand field by steric (and to a lesser extent electronic) effects (R(1)=Me; Ph) exhibit spin transition behavior triggered by temperature. In general, gradual and incomplete transitions without hysteresis were observed for magnetically active complexes. The systems described provide approaches to the development of (supra)molecular spintronics.
RESUMEN
The [M(4)(II)L(4)](8+) [2 x 2]-grid-type complexes 1-8 present a set of features of particular interest for potential applications. All complexes exhibit multiple reduction levels at low reduction potentials paired with rather high stability. The modulation of the reduction potentials is possible by introduction of appropriate substituents on the ligands. The Co(II)(4) complexes 1-5 present a remarkable regularity in the disposition of the reduction levels, indicating the ability of the Co(II) sites to transmit electronic interactions between reduced ligands. In general, all investigated molecular systems 1-8 show characteristics typical for multilevel supramolecular electronic devices.
RESUMEN
The self-assembly of new multimetallic complexes of grid-type architecture is described. The binding of a set of tris-terdentate ligands, 1 a-1 d, based on terpyridine-like subunits, with different octahedrally coordinated metal ions leads to the formation of species whose structure depends strongly on the ligand, the metal ion, the counterion, the solvent, and the reaction conditions. Under suitable conditions, the [3 x 3] grid was obtained from the reaction of ligand 1 a with zinc tetrafluoroborate and from ligand 1 b with mercury triflate. The other ligands led to the formation of mainly one compound of composition [M(6)L(5)](12+), which has the structure of an incomplete [2 x 3] grid. The crystal structure of such a [2 x 3] grid, [Co(6)(1 d)(5)](12+), has been determined. In this complex, the three central pyrimidine-pyridine-pyrimidine non-coordinating sites adopt transoid NCbond;CN conformations. The much less stable cisoid conformations, the "pinching" of the coordination sites in the complex, the weaker donor strength of the central binding site, and the steric demand of the substituents are all factors contributing to the reluctance to produce the [3 x 3] structure. A subtle interplay between the nature of the metal, the steric demand of the ligand, the reaction conditions, and the type of counterion determine the product of self-assembly. The results obtained show that by tuning the parameters, complexes containing six or nine octahedrally coordinated metal ions in a well-defined grid-type arrangement are accessible. Both types of arrays, [2 x 3] and [3 x 3 ], are of interest as self-assembled inorganic architectures of well-defined structure and nuclearity that may be suitable prototypes for selective information storage media.
RESUMEN
The self-assembly of the terdentate ligands 1a-h, based on terpyridine-like binding sites, with octahedrally coordinated metal ions, such as Fe(II), Co(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II), leads to the formation of the supramolecular grid-type complexes 2a-c(M(II)), 3d-g(M(II)) and 4h(M(II)). The structures and compositions of these coordination complexes in solution were deduced from electrospray mass spectrometry (ESMS) measurements. The results agree with the data available from x-ray radiocrystallography in the solid state and/or NMR spectroscopy in solution. ESMS may be applied in cases where other methods are difficult to use or inconclusive. This study stresses the power of ESMS in supramolecular chemistry.