Organic crystal engineering with 1,4-piperazine-2,5-diones. 6. Studies of the hydrogen-bond association of cyclo[(2-methylamino-4,7-dimethoxyindan-2-carboxylic acid)(2-amino-4,7-dimethoxyindan-2-carboxylic acid)

[structure: see text] The title 1,4-piperazine-2,5-dione was synthesized in 23% yield over six steps from ethyl 2-amino-4,7-dimethoxyindan-2-carboxylate. Crystallization by slow diffusion of ether into a chloroform solution and by slow evaporation of an ethanol-chloroform-benzene solution produced polymorphic crystalline forms as determined by single-crystal X-ray analysis. The polymorphs exhibited different hydrogen-bonding networks. The association of this piperazinedione in solution was studied using mass spectrometric and nuclear magnetic resonance spectroscopic techniques. The MS and NMR data were interpreted using the solid-state structures as models for solution aggregation. Association constants extracted from the NMR data are in line with those of other cyclic cis amides in chloroform solvent.     

Magnetically ordered (Tc= 200 K) bis(tetracyanopyrazine)vanadium, V[TCNP]2.yCH2Cl2

A new organic-based magnet, V[TCNP]2.yCH2Cl2 (TCNP = tetracyanopyrazine), has been synthesized, and its magnetic properties have been examined. The amorphous nature of V[TCNP]2.yCH2Cl2 makes it difficult to determine the structure of the material; however, ac and dc magnetic measurements indicate that it is a ferrimagnet below 200 K with a small coercive field of 8 Oe at 5 K.     

Homogeneous catalytic hydrogenation of diethyland biphenyl-acetylene and isomerization ofCis-Stilbene in the presence of [(C5H5)2Ru3(CO)3(μ-CO)(μ3-CO)(C2Ph2)]

The title complex (1) is a good hydrogenation catalyst tar diphenylacetylene in homogeneous conditions; it comparison with the activity of other ruthenium clusters is made. Apparently cluster catalysis occurs, but fragmentation to binuclear metallacyclic products containing two alkyne molecules was also observed: these 40 not been previously described and have been characterized by elemental analyses and mass spectrometry. Complex1 contains all alkyne bound parallel to one metal-metal edge. The results obtained support the hypothesis that transition metal clusters with alkynes bound in this fashion could ad as catalysts precursors or as intermediates in the homogeneous hydrogenation of alkynes; this behavior would be an example of structure-reactivity relationship in homogeneous catalysis. An erratum to this article is available at .     

Supramolecular architectures featuring stereoisomeric cluster complexes of the [Re6(μ3-Se)8]2+ core

The [Re₆(μ₃-Se)₈]²⁺ core-containing cluster complexes of the general formula [Re₆(μ₃-Se)₈(PEt₃)₄L₂]²⁺ (both trans- and cis-isomers) site-differentiated with inert PEt₃ and functional L ligands that are capable of hydrogen bonding or secondary (with respect to primary coordination with the cluster core) metal-ligand coordination interactions have been prepared. The applications of such stereospecific cluster isomers as building blocks for supramolecular construction have been studied. A great variety of multicluster arrays mediated by intercluster hydrogen bonding or cluster ligand coordination with secondary metal ions have been obtained and structurally characterized. The findings from this research clearly establish the superior utility of these novel building blocks for the creation of structurally sophisticated architectures and possibly functional materials.