Showing papers by "Peter S. White published in 1985"
01 Jan 1985
1,219 citations
TL;DR: In this paper, small canopy gaps dominated the natural disturbance regime of old-growth spruce-fir forests in the Great Smoky Mountains, North Carolina and Tennessee, and new gaps ≤200m2 in size were formed.
Abstract: Spatially small canopy gaps dominated the natural disturbance regime of old-growth spruce–fir forests in the Great Smoky Mountains, North Carolina and Tennessee. New gaps ≤200 m2 in size were forme...
157 citations
01 Jan 1985
84 citations
TL;DR: Transition probability analysis of an undisturbed spruce-fir forest was used to evaluate the sensitivity of the overstory/understory comparison to underlying assumptions and found that the species that was densest in the understory species (Abies) had the shortest lifespan and thus, the fastest canopy turnover rate.
Abstract: Compositional stability in forests has traditionally been evaluated by comparing understory with overstory composition. Such comparisons have generally been qualitative. Transition probability analysis has recently allowed quantitative prediction of future community states. We used transition probability analysis of an undisturbed spruce-fir forest to evaluate the sensitivity of the overstory/understory comparison to underlying assumptions. The predictions of future composition differed widely depending on understory size class used, ecological situation (gap versus forest plots), and stand descriptor (density versus frequency). Species longevities and interactions between understory and overstory species also affected the predictions. Understory data generally led to a predicted increase in importance for the most tolerant species (Abies fraseri) and the conclusion that a previous disturbance allowed the least tolerant species (Betula lutea) to become established. Inventory of stems in gaps led to a predicted increase in importance for the least tolerant species (Betula) and the conclusion that disturbance frequency was increasing in the stand. Data incorporating more detailed observations of the gap capture process led to the inference that this old growth stand was in compositional equilibrium. In this community, the species that was densest in the understory species (Abies) had the shortest lifespan and thus, the fastest canopy turnover rate. This lead to counter-intuitive behavior in the models; in some cases Abies had a 40% higher relative density in the understory than in the overstory at equilibrium.
43 citations
42 citations
TL;DR: In this paper, a planar CH3[graphic omitted] cations and AsF6-anions with some cation-anion interactions were solved from low-temperature diffractometer data by direct methods and refined by least-squares techniques to a final R of 0.049 for 1 077 observed reflections.
Abstract: Crystalline CH3[graphic omitted] AsF6–, CH3[graphic omitted] AsF6–, and [graphic omitted] AsF6– were prepared in essentially quantitative yield by the reaction of S2NAsF6 with CH3CN, CH3CCH, and HCCH respectively, in sulphur dioxide solution. The compounds have been characterised by elemental analysis, i.r. and mass spectrometry. The compound CH3[graphic omitted] AsF6– crystallizes in the monoclinic space group P21/c, with unit-cell dimensions a= 8.182(7), b= 9.822(3), c= 11.515(7)A, β= 110.91(6)°, and Z= 4. The structure was solved from low-temperature diffractometer data by direct methods and refined by least-squares techniques to a final R of 0.12 for 893 observed reflections. The structure consists of discrete, planar CH3[graphic omitted] cations and AsF6– anions with some cation–anion interactions. The compound CH3[graphic omitted] AsF6– crystallizes in the monoclinic space group P21/c, with unit-cell dimensions a= 8.539(5), b= 9.941 (2), c= 12.053(5)A, β= 116.69(4)°, and Z= 4. The structure was solved by direct methods and refined by least-squares techniques to a final R of 0.049 for 1 077 observed reflections. The structure contains the hitherto unknown CH3[graphic omitted] cation and the AsF6– anion with some cation–anion interaction. Both CH3[graphic omitted] and [graphic omitted] (R = H or CH3) can be regarded as 6π cyclic systems. The cations have been reduced chemically and electrolytically to form long-lived free radicals identified by their e.s.r. spectra; INDO calculations have yielded values of hyperfine coupling constants in good agreement with those obtained experimentally.
38 citations
32 citations
TL;DR: S7IMF6 and S7IAsF6 were prepared essentially quantitatively by a variety of similar routes to those that led to S7IMf6; and in addition, by the reaction of bromine and s7IASF6 as mentioned in this paper.
Abstract: S7BrMF6 (M = As, Sb) were prepared essentially quantitatively by a variety of similar routes to those that led to S7IMF6; and in addition, by the reaction of bromine and S7IAsF6. (S7Br)4S4(AsF6)6 w...
28 citations
27 citations
TL;DR: In this paper, a trigonal bipyramidal geometry was assigned to tellurium trifluoride by using X-ray diffraction, with the lone pair and C2F5 groups in equatorial, and the halogens in the axial positions.
Abstract: The reaction of (C2F5)2Te and XeF2 in a slurry of SO2ClF yielded (C2F5)2TeF2 essentially quantitatively. Chlorine and (C2F5)2Te gave (C2F5)2TeCl2. Both (C2F5)2TeF2 and (C2F5)2TeCl2 were assigned a trigonal bipyramidal geometry, on the basis of their 19F nmr and vibrational spectra, with the lone pair and C2F5 groups in equatorial, and the halogens in the axial positions. Perfluoroethyl tellurium trifluoride was prepared essentially quantitatively by the reaction of C2F5TeTeC2F5 and XeF2 in liquid SO2F2. The generally inert SO2ClF was found to react with C2F5TeTeC2F5 to give C2F5TeClxF3−x, and sulphur dioxide. The structure of C2F5TeF3 was determined by X-ray diffraction. The crystals are tetragonal with a = 10.129(4), c = 25.561(6) A, and Z = 16. The structure was refined in space group I41/a to a conventional R factor of 0.051 for 901 observed reflections with I ≥ 3σ(I). Each tellurium atom is surrounded by two terminal fluorine atoms and two bridging fluorine atoms and a C2F5 group in an axial position ...
16 citations
TL;DR: In this paper, a single-crystal X-ray diffraction study of (β) 6SbF3·5SbFsbF5 was performed and the results showed that it is monoclinic, space group P21/c with cell dimensions a= 11.638, b= 8.995, c= 16.723, β= 106.81, and Z= 2.041.
Abstract: (β)6SbF3·5SbF5was prepared by the reduction of SbF3·SbF5 with a slight excess of phosphorus trifluoride relative to the stoicheiometric amount, in arsenic trifluoride solution. It was also prepared by the reduction of antimony pentafluoride in sulphur dioxide solution and a stoicheiometric quantity of iodine. The Raman spectrum of (β)6SbF3·5SbF5 is identical to that of a material designated SbF5·SbF3(B) by previous workers. A single-crystal X-ray diffraction study of (β) 6SbF3·5SbF5shows that it is monoclinic, space group P21/c with cell dimensions a= 11.638(1), b= 8.995(1), c= 16.723(2)A, β= 106.81(1)°, and Z= 2. The structure was refined to a final R of 0.041 for 2 440 reflections. The structure consists of discrete Sb6F135+ cations and SbF6– anions with cation-anion interactions. The cation can be viewed as being built of strongly interacting Sb2F5+ and SbF2+ units. The geometries of the fluorine atoms about the various SbIII species are described and discussed. The structure of (β)6SbF3·5SbF5 is similar to, but different from, (α) 6SbF3·5SbF5, previously prepared at high temperatures by the fluorination of antimony metal.
TL;DR: Se6I2(AsF6)2· 2SO2 has been prepared and its structure determined by single crystal X-ray diffraction; the cation contains a hexaselenium ring of chair conformation with iodine substituents in the axial 1,4 positions.
Abstract: Se6I2(AsF6)2· 2SO2 has been prepared and its structure determined by single crystal X-ray diffraction; the cation contains a hexaselenium ring of chair conformation with iodine substituents in the axial 1,4 positions.
TL;DR: In this paper, it was shown that the reaction between [V(η-C5H5)2(CO)] and NO has a 2: 1 stoicheiometry and gave a complex containing NCO which could not be separated from a polymeric oxide.
Abstract: The reaction between [V(η-C5H5)2] and NO has been shown to have a 1 : 1 stoicheiometry but the initial product, presumed to be [V(η-C5H5)2(NO)], undergoes disproportionation to give a mixture of final products. The reaction between [V(η-C5H5)2(CO)] and NO occurred with a 2: 1 stoicheiometry and gave a complex containing NCO which could not be separated from a polymeric oxide. The complex [V(η-C5H5)2(NCO)] was obtained independently from [VCl(η-C5H5)2] and NCO– in aqueous solution. The reaction between [V(η-C5H5)2(CO)] and NOCl gave a mixture of products including one or more containing NCO–, and there was no reaction between NO and [V(η-C5H5)2(CO)2]+. The reaction between [VI(η-C5H5)2] and NO gave two products, both analysing as VI(C5H5)2NO. One was a brown insoluble polymer with ionic iodide which is believed to have bridging N2O22– ligands. The second product was green, monomeric [VI(C5H5)2(NO)]. This is a fluxional molecule as shown by e.s.r. and i.r. spectroscopy in tetrahydrofuran (thf) solution. The two forms of the molecule have different ν(NO) frequencies (1 670 and 1 590 cm–1). The form with the lower frequency [which is presumed to be VI(C5H5)2(NO) with either a bent {VNO} group or a linear {VNO} group but a long N–O bond] predominates at low temperature. The form with the higher ν(NO) frequency has a linear {VNO} group with a short N–O distance and is presumed to have at least one C5H5 ring with less than pentahapticity. When a solution of [VI(C5H5)2(NO)] in thf was set aside at room temperature, diamagnetic [{VI(η-C5H5)}2{V(η-C5H5)(NO)}2(µ-O)4] was formed. The structure of this complex, determined by X-ray diffraction, showed that it has an eight-membered ring of alternating V and O atoms with a two-fold axis in the centre of the ring. The V atoms alternately carry I or NO ligands, which are arranged in trans fashion to one another. The O–V–O angles are all similar, averaging 104.7(3)°, but the V–O–V angles are in two sets, two of 179.3(3) and two of 148.1(3)°. The four oxygen atoms lie in a plane with the V atoms carrying the iodo-ligand displaced 0.261 A out of the plane towards the iodo-ligand and the V atoms carrying the NO ligand displaced 0.157 A in the opposite direction. The reaction between [VBr(η-C5H5)2] and NO gave a complicated mixture of insoluble nitrosyl products and a soluble green monomer, [VBr(C5H5)2(NO)] which was analogous to [VI(C5H5)2(NO)] but lost NO far more readily. With [VCl(η-C5H5)2] and NO insoluble nitrosyls were again produced, as well as N2O and [V2O2Cl2(η-C5H5)3] which could also be obtained from [VCl(η-C5H5)2] and O2. There was no reaction between [VCl2(η-C5H5)2] and NO, but on addition of BF3 reduction of [VCl2(η-C5H5)2] to [VCl(η-C5H5)2] occurred.
TL;DR: In this article, the structure of (cp)2Cr (cp = η5-C5H5) with Me3NO produces a mixture of the previously reported (4Cr4O4 and (cp 4Cr 4O3(η2-C 5H4); the latter has been determined by X-ray crystallography.
Abstract: Oxidation of (cp)2Cr (cp =η5-C5H5) with Me3NO produces a mixture of the previously reported (cp)4Cr4O4 and (cp)4Cr4O3(η2-C5H4); the structure of the latter has been determined by X-ray crystallography.
TL;DR: In this article, a phase diagram for the system BiF5-SbF5 was constructed and the structure of the adducts was further supported by their vibrational spectra.
Abstract: Adducts between BiF5 and SbF5 were prepared in liquid WF6 at room temperature. Sublimation of the product gave various volatile crystalline products with analyses corresponding to BiF5(SbF5)3, BiF5(SbF5)2, BiF5(SbF5)1.5, and (BiF5)nSbF5(n= 2, 3, or 20.6). The adducts (BiF5)nSbF5(n= 1 or 1.5), were also prepared. The BiF5(SbF5)n(n= 1.5, 2, or 3) adducts were of low melting point and of higher volatility than (BiF5)nSbF5(n 1). Single-crystal X-ray diffraction studies showed that BiF5(SbF5)n(n= 2 or 3) were isomorphous with tetrameric (NbF5)4, and an X-ray powder diffraction photograph of BiF5(SbF5)1. was very similar to that of BiF5(SbF5)n(n= 2 or 3), indicating that it was also isostructural with (NbF5)4. The BiF5(SbF5)3 structure likely consists of disordered BiF5(SbF5)3 tetramers, and BiF5(SbF5)2 likely consists of a mixture of disordered BiF5(SbF5)3 and (BiF5.SbF5)2 tetramers in the appropriate ratios. The molecular-beam mass spectra of SbF5(BiF5)n(n= 2 or 3) show fragment ions attributable to BiF5 and SbF5 as well as various associated pentafluoride clusters, including BiF5(SbF5)3 for the n= 3 adduct. The vibrational spectra of BiF5(SbF5)n(n= 1.5, 2, or 3) were similar and indicative of the presence of SbF5 and BiF5 units joined by cis-bridged fluorine atoms. (BiF5)nSbF5(n= 1, 1.5, 2, 3, or 20.6), were shown by X-ray powder diffraction photography to be isomorphous with polymeric trans-bridged BiF5 and therefore to consist of disordered BiF5 and SnF5 units linked by trans-bridged fluorine atoms. The trans-bridged polymeric BiF5-type structure of the adducts was further supported by their vibrational spectra. The behaviour of BiF5-(SbF5)n(n= 2 or 3) in WF6 solution is discussed. An estimated phase diagram for the system BiF5–SbF5 was constructed.
TL;DR: In this article, the Reaktion des Dicarbonyls (I) mit gasformigem H2S liefert die Titelverbindung (II) als ersten trigonalbipyramidalen Thiocluster.
Abstract: Die Reaktion des Dicarbonyls (I) mit gasformigem H2S liefert die Titelverbindung (II) als ersten trigonalbipyramidalen Thiocluster.