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Au center dot center dot center dot H-C Interactions in Gold(I) Complexes with Benzyl Imidazolyl Phosphine Ligands
No full textSecondary interactions in gold(I) compounds have assumed
considerable interest, since they have a profound influence on
chemical and physics properties, structures and conformations
of gold complexes. In the last years a large number of secondary
bonding interactions has been discovered in compounds of
gold(I), mostly of the general type L-Au-X, where L is a
phosphine ligand and X is a halide or a pseudohalide. Distinct
kinds of interaction involving gold atoms are: Au•••Au
(aurophilic interaction), Au•••X where X is a halide,
Au••• -system, Au•••H-C. This last type of contact is very rare
either as hydrogen bond or as agostic interaction. The tertiary
phosphines (BzIm)Ph2P, 1-benzyl-2-imidazolyl diphenyl
phosphine, and (BzIm)3P, tris-(1-benzyl-2-imidazolyl)phosphine,
have features to systematically allow Au•••H-C contacts, also
coexisting with aurophilic interactions. In fact, they are able to
bring the hydrogen atoms of the benzyl groups in close position
to the gold atom by a change of conformation. In the complex
[(BzIm)Ph2PAuCl] [1], where only one benzyl imidazolyl
group is present, the assumed conformation is favourable for the
CH2 group to have one hydrogen atom at close distance from Au
(2.62 Å). In the complex, [(BzIm)3PAuCl], two benzyl
imidazolyl groups position one hydrogen atom of each CH2
group at close distances from gold (2.83 and 2.95 Å). In the
tetranuclear gold cluster [{(BzIm)3P}2Au4Cl2]2+ with the two
(BzIm)3P phosphines, which act as bihapto ligands, two gold
atoms each interact with one hydrogen atom at distances of 2.57
and 2.59 Å.
[1] Burini, A.; Pietroni, B. R.; Galassi, R; Valle, G.; Calogero, S.
Inorg. Chim. Acta 1995, 229, 299-305
Aurophilic interactions in polynuclear Au(I) complexes with phosphine ligands containing imidazole rings
Full text linkAurophilic interactions in polynuclear Au(I)
complexes with phosphine ligands containing
imidazole rings
Fiorella Bachechiaa*, Alfredo Burinib, Rossana Galassib
aIstituto di Strutturistica Chimica, C.N.R., Area della Ricerca di Roma,
C.P. 10, 00016 Monterotondo St. (Roma), Italy., bDipartimento di Scienze
Chimiche, Università di Camerino, 62032 Camerino, Italy. E-mail:
[email protected]
Keywords: gold complexes, aurophilicity, crystal
structures
The tertiary phosphines of the type (Bzim)3-nPhnP, where Bzim
is 1-benzyl-2-imidazolylphosphine and n varies from 0 to 2,
were synthesised as part of a program aimed to the study of
the coordination chemistry of phosphines containing imidazole
rings. The softer character of imidazole, with respect to other
heterocycles, turned out to be useful in the stabilization of
complexes with soft metals as those of Group 11 in low oxidation
states. These ligands can behave as monodentate or as P, N
bidentate forming dinuclear cationic complexes. With Au(I)
they were found to be able to favour the formation of intraand
intermolecular aurophilic interactions. TheAu(I) complexes
assume considerable interest when aurophilic bonds occur
between gold atoms, since their chemical and physical properties
change to particular characteristics with potential applications
in electronic, optical or sensor devices. In particular short
Au•••Au interactions are considered related to optoelectronic
properties as observed in a number of polynuclear gold
compounds. Here the structures of two Au(I) complexes are
reported. The binuclear complex [μ-(Bzim)Ph2PAu2(C6F5)2]
adopts a folded conformation with parallel, eclipsed C6F5
rings and a corresponding short AucccAu contact of 3.033(2)Å.
The tetranuclear cluster complex {[μ-N,N’-(Bzim)3PAuCl]2
Au2}2+c AuCl2
- c AuCl4
- consists in a 12-membered macrocycle
with two gold atoms coordinated to two (Bzim)3P
molecules, in bridging mode, through the nitrogen atoms of the
imidazole rings and two gold atoms coordinated to the
phosphorus atoms of the (Bzim)3P ligands. Two chloride atoms
complete the Au bicoordination. Three strong aurophilic interactions,
Au(1)cccAu(4) [2.989(2)Å], Au(2)cccAu(3) [3.014(2)Å]
andAu(1)cccAu(2) [3.257(3)Å], occur.Aweak gold-gold contact,
Au(3)cccAu(4) [3.766(2)Å], is also present.
Understanding molecular interactions
23r
Sensitivity of multi-temporal high resolution Polarimetric C and L-band SAR to grapes in vineyards
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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