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PubMed1987

Dynamics and stability in coevolutionary ecological systems. I. Community stability and coevolutionarily stable states.

An extension of J. Roughgarden's [1979, Theor. Pop. Biol. 9, 388; 1979, "An Introduction to Evolutionary Ecology and Population Genetic Theory," Macmillan, New York] formalism for investigating the effects of coevolution on community structure is presented. The extension assumes the result that a coevolved community is asymptotically stable when coevolution takes place at a genetically noninvasible boundary. This is proved for the general case of n interacting species. From this a community persistence function, phi (P), is defined that allows measuring the domain of attraction for the community as well as the resilience time, that is, the time taken for a perturbation to decay to 1-1/e (63%) of its initial value.

Animals↗
PubMed2006

Stability and porosity enhancement through concurrent ligand extension and secondary building unit stabilization.

A trigonal nanosized carboxylate ligand, 1,3,5-tris[4'-carboxy(1,1'-biphenyl-4-yl)]benzene (TCBPB), has been synthesized and applied in the construction of porous metal-organic frameworks (MOFs). A solvothermal reaction of TCBPB and a zinc salt in the presence of pyridine produces 1, an unstable MOF consisting of a tetrazinc secondary building unit (SBU) with labile terminal ligands. Changing pyridine to a noncoordinating base in the assembly procedure affords 2, a stable MOF with permanent porosity containing an octazinc SBU without labile terminal ligands.

Journal Article↗
PubMed1999

Two Novel Lithium-15-Crown-5 Complexes: An Extended LiCl Chain Stabilized by Crown Ether and a Dimeric Complex Stabilized by Hydrogen Bonding with Water.

Two lithium chloride-15C5 (15C5 = 15-crown-5) complexes, [Li(15C5)(&mgr;-Cl)(2)Li](infinity), 1, and {[Li(15C5)(H(2)O)]Cl}(2), 2, were synthesized. Their structures, characterized by single-crystal X-ray diffraction analyses, are dictated by the absence of or presence of water. Complex 1, prepared in an anhydrous environment, is the first example of an extended LiCl chain structure. It contains repeating units Li(&mgr;-Cl)Li(15C5) that are connected by additional bridging Cl atoms. One Li has close contacts with one Cl and all five O atoms of 15C5 and the other Li with three Cl and one O of 15C5. However, the chain structure cannot form in the presence of water. Instead dimeric complex 2 was formed when LiCl.xH(2)O (x = 1.14) was the starting material. In this case H(2)O is coordinated to lithium through a Li-O linkage and is hydrogen bonded to Cl(-) (H.Cl). The Li(+) cation is coordinated to the five O atoms of 15C5 as well as the O atom from H(2)O, and the Cl(-) counteranion is isolated from Li(+) by two hydrogen bonds with one H atom each from two H(2)O molecules with H.Cl distances of 2.30(4) and 2.35(4) Å, respectively. A crystallographically imposed center of symmetry generates a dimer that resembles a 2:2 anion-paired encapsulate. Crystal data for 1: space group Pna2(1) (no. 33), a = 14.974(1) Å, b = 13.553(1) Å, c = 7.160(1) Å, V = 1453.0(2) Å(3), Z = 4. Crystal data for 2: space group P2(1)/n (no. 14), a = 10.353(1) Å, b = 7.9070(1) Å, c = 17.741 Å, beta = 100.50(1) degrees, V = 1427.9(2) Å(3), Z = 4.

Journal Article↗