1,721,175 research outputs found
A NEW INSIGHT FROM QUALITATIVE MO THEORY INTO THE PROBLEM OF THE FE-FE BOND IN FE2(CO)9
No full textA revision of EHMO calculations with FMO analysis has provided new qualitative insight into the bonding network in Fe2(CO)9 and reconciled the previous diverging interpretations. After separation of all of the Fe(CO)bridge bonding/antibonding levels (12 electrons for six FeC bonds) there remains a two-electron/two-orbital interaction (σ/σ{black star}) that is ultimately responsible for a direct (through-space) FeFe bond. However, predominant repulsive interactions via the CO bridges (through-bond) may hide the linkage
Aromaticity and Agostic Interactions as Stabilizing Factors in Trinuclear Rhenium Clusters with Low Electron Count
No full textMetal-metal bonding network in tetranuclear planar clusters
No full textIn order to understand the trends of the M4 skeleton to deform in planar clusters of type M4(CO)16, extended Hückel calculations have been performed. Depending on the total electron count the shape transforms ideally from square to rhombus through the formation of one diagonal M-M bond (64 → 62e-). The nature of the annular and transannular M-M σ-interactions is illustrated
Stabilisation of trivalent nickel through 1 : 2 co-ordination by cyclic terdentate ligands CH2CH2NH(CH2)2NH(CH2)2X (X = NH, O, or S)
No full textThe octahedral six-co-ordinated complexes [Ni(L2)2]2+ and [Ni(L3)2]2+(L2 and L3= 1 -oxa- and 1 -this-4,7-diazacyclononane, respectively)(donor set: N4O2 and N4S2, respectively) undergo a reversible one-electron oxidation process in MeCN and dimethyl sulphoxide (dmso) solution to give authentic NiIII species. These NiIII complexes present a distorted stereochemical arrangement, with the O and S heteroatoms occupying the axial sites of an elongated octahedron, and persist in solution for hours. Comparison with the corresponding complexes of 1,4,7-triazacyclonanane (L1)(donor set: N6) indicates that the relative stability of the trivalent species, expressed by the value of E1⁄2(NiIII–NiII), decreases along the series: L1 > L3 > L2, the trend reflecting the decrease in the strength of the Ni–X interactions (X = N, S, or O). The corresponding NiIII complexes of the open-chain analogues of the macrocycles L1 or L3 form at comparable potentials, but persist in solution only in the time-scale of the voltammetry experiment, thus demonstrating the existence of a purely kinetic macrocyclic effect in the stabilisation of high oxidation states of metals.
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INTERMETAL BONDING NETWORK IN 2-DIMENSIONAL TETRANUCLEAR CLUSTERS
No full textThe present study deals with the small number of structurally characterized 64 → 60e- tetranuclear clusters containing metals of the groups 7 → 10 and having in common the primary feature of planarity. The M4 skeleton has a variety of shapes: square, rhombus, or more generally quadrilateral. Empirical electron counting rules do not always provide a sufficient description of the bonding in these two-dimensional compounds nor is the viewpoint unique for different cases. In order to determine the electronic distribution, hence the trends of the M4 skeleton to deform, extended Hückel calculations have been carried out for a number of models. The nature of the outer M-M σ interactions and the distribution of the metal lone pairs are illustrated for 64e- square clusters. Then, it is shown that 62e- M4(CO)16 rhombuses correlate ideally with 64e- squares through the formation of one diagonal bond. Five M-M bonds are also ascertained in the 62e- quadrilateral Os4(CO)15 that is short one ligand. In any case, the fifth bond is shown to involve "t2g" orbitals in an unforeseen way. The distribution of the M-M bonds in 64e- clusters, containing π-donor coplanar phosphido bridges, is irregular. In Ru4(CO)13(μ-PPh2)2, formed by two condensed triangles sharing one side, only two outer consecutive Ru-Ru linkages have bond order 1, whereas the other three (including the quadrilateral's diagonal) are assigned bond order 2/3. In Ru4(CO)10(μPPh2)4 the M4 bonding network is something intermediate between two limiting viewpoints. The first one assigns a total of three bonds to the four sides of the Ru4 rhombus. The fourth linkage, coinciding with one diagonal, is best described as an uncommon four electron/three orbitals bond. The other description indicates that a fourth cyclic M-M bond is formed at expenses of part of the M-P bridge-bonding network. The theoretical result has also an experimental confirmation. Finally, there are planar tetranuclear clusters having all of the metal atoms square planarly coordinated by ligands and a reduced number of M-M connectivities. Among the latter, Ni4(μ-SR)8 (64 electrons) has a square Ni4 skeleton but no M-M bond, whereas Pd4(μ-CO)4(μ-CH3CO2) 4, with 60 electrons, is a parallelogram with two M-M bonds at those sides doubly bridged by the carbonyl ligands
Topological relations between three-periodic nets. II. Binodal nets
Full text linkThe TOPOS program package was used to generate all subnets of 3- to 12-
coordinated binodal nets taken from the Reticular Chemistry Structure
Resource database. 38 304 binodal nets with novel topologies were revealed
and stored in the TTD collection. A new invariant, the adjacency matrix of the
shell graph of a node, is proposed to distinguish the node local topology. With
this invariant, the first six examples of binodal-quasi-uninodal nets were
discovered. 4604 organic and metal-organic frameworks were analyzed to find
examples of the topologies generated. It was shown that many edge-transitive
nets as well as unknown topologies occur in crystal structur
Parallel and inclined (1D -> 2D) interlacing modes in new polyrotaxane frameworks [M-2(bix)(3)(SO4)(2)] [M = Zn(II), Cd(II); Bix=1,4-bis(imidazol-1-ylmethyl)benzene]
No full textThe reactions of M-II sulfates (M = Zn, Cd) with the flexible ligand 1,4-bis(imidazol-1-ylmethyl)benzene (bix) yield the novel interesting coordination networks [M-2(bix)(3)(SO4)(2)], containing 1D polymeric motifs of alternating rings and rods, which show extended rotaxane-like mechanical links producing 2D sheets via unprecedented parallel (M = Zn) or inclined (M = Cd) interlacing modes of the chains
Borromean links and other non-conventional links in 'polycatenated' coordination polymers: re-examination of some puzzling networks
No full textA number of coordination networks, exhibiting novel and fascinating types of entanglements of individual motifs have been reported throughout the years by many groups. The structural complexity of these species has caused, in some cases, misinterpretations regarding the correct nature of the entanglement. In this article, we analyse the structures of some polymeric networks of the 'polycatenanes' class, which have the peculiar feature of all the constituent motifs having lower dimensionality than that of the overall array. Unexpected topological features and new linkages, that had previously been overlooked, have been discovered. The most relevant finding concerns the first observation of examples of Borromean links in 3D and 2D arrays. These systems are comprised of layers that are not catenated but, nonetheless, inseparably entangled in an uncommon topological fashion.A number of coordination networks, exhibiting novel and fascinating types of entanglements of individual motifs have been reported throughout the years by many groups. The structural complexity of these species has caused, in some cases, misinterpretations regarding the correct nature of the entanglement. In this article, we analyse the structures of some polymeric networks of the 'polycatenanes' class, which have the peculiar feature of all the constituent motifs having lower dimensionality than that of the overall array. Unexpected topological features and new linkages, that had previously been overlooked, have been discovered. The most relevant finding concerns the first observation of examples of Borromean links in 3D and 2D arrays. These systems are comprised of layers that are not catenated but, nonetheless, inseparably entangled in an uncommon topological fashion
A new type of supramolecular entanglement in the silver(I) coordination polymer [Ag-2(bpethy)(5)](BF4)(2) [bpethy = 1,2-bis(4-pyridyl)ethyne]
No full textThe polymeric compound [Ag-2(bpethy)(5)](BF4)(2), obtained from AgBF4 and 1,2-bis(4-pyridyl)ethyne (bpethy) in molar ratio 1:3, contains infinite molecular ladder motifs with monodentate ligands as sidearms on both sides, that are threaded through the squares of adjacent polymeric units in a mutual relationship, to give infinite 'polythreaded' bidimensional layers
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