1,721,012 research outputs found
Anion coordination directed synthesis patterns for [Ni4] aggregates: Structural changes for thiocyanate coordination and ligand arm hydrolysis
No full textThe coordination reactivity of ligand H5L1 (2,6-bis-(1,3-dihydroxy-2-methylpropan-2-ylimino)methyl-4-methylphenol) toward nickel(ii) ions in the presence of two different anions resulted in cubane and fused dicubane types of tetranuclear coordination aggregates. In the first case, utilization of two carboxylate (R = Me and Et in RCO2-) anions led to cubane type Ni4O4 aggregates [Ni4(H4L1)2(μ3-OH)2(μ1,3-O2CCH3)2](NO3)(CH3COO)·3H2O (1) and [Ni4(H4L1)2(μ3-OH)2(μ1,3-O2CC2H5)2](NO3)(C2H5COO)·CH3CN·1.5H2O (2). Whereas the use of thiocyanate anions triggered single imine arm hydrolysis of H5L1 and gave partial dicubane type Ni4N2O4 aggregates [Ni4(H2L2)2(HAMP)2(μ1,1-NCS)2](NO3)2 (3a) and [Ni4(H2L2)2(HAMP)2(μ1,1-NCS)2]Cl2·CH3OH·H2O (3b) (H2L2 = 3-(1,3-dihydroxy-2-methylpropan-2-ylimino)methyl-2-hydroxy-5-methylbenzaldehyde). Liberated 2-amino-2-methyl-1,3-propanediol from imine arm hydrolysis was successfully trapped in 3a and 3b for the growth and stabilization of different molecular architectures. Mass spectral evidence established that two types of dinuclear fragments Ni2(H4L1) and Ni2(H2L2), from the originally used and partially hydrolyzed ligand anions have been self-assembled for two types of NiII based coordination aggregates. Two sets of complexes were characterized by elemental analysis, FT-IR and optical spectroscopy, variable temperature magnetic measurements, and single crystal X-ray analysis. The magnetic behavior examined through the temperature interval of 1.9-300 K with experimental and theoretical corroboration support the exchange pathways within the two types of [Ni4] coordination aggregates
Hydroxido-supported and carboxylato bridge-driven aggregation for discrete [Ni4] and interconnected [Ni2]n complexes
Full text linkFour different carboxylato bridges have been efficiently utilized for growth of three tetranuclear nickel(II) complexes [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-CH3CO2)2](ClO4)2 (1), [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-C2H5CO2)2](ClO4)2·1/2H2O (2), and [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-O2C-C6H4-pNO2)2](ClO4)(p-NO2-C6H4-CO2)·DMF·5H2O (3) and one dinuclear nickel(II)-based chain complex {[Ni2(μ-H2L)(μ1,3-O2CCH2Ph)2(H2O)](ClO4)·1/2(CH3OH)}n (4). These were obtained via the reaction of Ni(ClO4)2·6H2O with H3L [2,6-bis((2-(2-hydroxyethylamino)ethylimino)methyl)-4-methylphenol] and RCO2Na (R = CH3,C2H5, p-NO2C6H4, and PhCH2). This family of complexes is developed from {Ni2(μ-H2L)}3+ fragments following self-aggregation. The complexes were characterized by X-ray crystallography and magnetic measurements. The changes from acetate, propionate, and p-nitrobenzoate to phenylacetate groups resulted in two different types of coordination aggregation. These compounds are new examples of [Ni4] and [Ni2]n complexes where organization of the building motifs are guided by the type of the carboxylate groups responsible for in-situ generation and utilization of HO– bridges with alteration in the aggregation process within the same ligand environment. Studies on the magnetic behavior of the compounds reveal that the exchange coupling within 1–4 is predominantly antiferromagnetic in nature
Dinuclear nickel complexes of divergent Ni⋯Ni separation showing ancillary ligand addition and bio-macromolecular interaction
No full textSchiff base ligand HL has been utilized to build up a new family of five [Ni2] complexes, [Ni2(μ-L)(μ-OH)](CIO4)2 [1(CIO4)2], [Ni2(μ-L)(μ-CF3CO2)2(C3H7NO)(H2O)]CF3CO2·H2O [2a(CF3CO2)·H2O], [Ni2(μ-L)(μ-CH3CH2CO2)2(C3H7NO)(H2O)]CIO4·C3H7NO [2b(CIO4)·C3H7NO], [Ni2(μ-L)(μ-CH3CO2)(μ-NCS)(NCS)(C3H7NO)] (3a) and [Ni2(μ-L)(μ-CH3CO2)(μ-N3)(N3)(C3H7NO)] (3b), in varying co-ligand environments. All the complexes have been characterized by elemental analyses, X-ray structure analysis and spectroscopic measurements. Three distinct types, dicationic, monocationic and neutral complexes, are synthesized using one pentadentate ligand HL. The NiII centers are bridged by three sets of bridging groups resulting in a wide variation in Ni⋯Ni separations from 2.897 to 3.475 Å. Doubly bridged NiII centers in the edge-shared square planar environment provide the shortest Ni⋯Ni separation in 12+. Whereas combination of other bridges from carboxylate, azide and isothiocyanate ancillary ligands results in cationic and neutral [Ni2] complexes 2+ and 3 having longer intermetallic separations. Modulation of Ni⋯Ni separation in synthetic complexes is fascinating in relation to the involvement and stabilization of the dinickel motif in the catalytic transition state of urease. Interaction and binding of cationic complexes (1–2b) with human serum albumin (HSA) and calf thymus-DNA have been examined using spectroscopic techniques. Tryptophan fluorescence quenching of HSA by cationic bimetallic complexes (1, 2a and 2b) featuring a hydrophobic ligand environment shows spontaneous and favorable interactions in the order of 2a > 2b > 1. For the interaction study with CT-DNA, nearly planar complex 1 binds more efficiently than 2a and 2b in octahedral coordination geometry
Competitive coordination aggregation for V-shaped [Co3] and disc-like [Co7] complexes: Synthesis, magnetic properties and catechol oxidase activity
No full textUnique dependence on the nature of metal salt and reaction conditions for coordination assembly reactions of varying architecture and nuclearity have been identified in V-shaped [Co3L4] and planar disc-like [Co7L6] compounds: [CoII3L2(μ-L)2(μ-OH2)2(CF3CO2)2] (1) and [CoII7(μ-L)6(μ-OMe)6]Cl2 (2) (HL = 2-(3-ethoxypropylimino)methyl-6-methoxyphenol). At room temperature varying reaction conditions, cobalt-ligand ratios and use of different bases allowed unique types of coordination self-assembly. The synthetic marvel lies in the nature of aggregation with respect to the two unrelated cores in 1 and 2. Complex 1 assumes a V-shaped arrangement bound to L-, water and a trifluoroacetate anion, while 2 grows around a central CoII ion surrounded by a CoII6 hexagon bound to methoxide and L-. Magnetic measurements revealed that the intermetallic interactions are antiferromagnetic in nature in the case of complex 1 and ferromagnetic in the case of 2 involving high spin cobalt(ii) ions with stabilization of the high-spin ground state in the latter case. In MeCN solutions complexes 1 and 2 showed catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in air. The kinetic study in MeCN revealed that with respect to the catalytic turnover number (kcat) 2 is more effective than 1 for oxidation of 3,5-DTBCH2
Strategic synthesis of [Cu2], [Cu4] and [Cu5] complexes: inhibition and triggering of ligand arm hydrolysis and self-aggregation by chosen ancillary bridges
Full text linkThe Schiff base ligand HL1 ({2,6-bis(allylimino)methyl}-4-methylphenol) having no coordinating donor arm has been examined for its reaction medium and ancillary bridge dependent reactivity for hierarchical family of CuII complexes. The ligand showed unique reactivity pattern toward CuII in solution. The bridging nature of in situ generated HO− ions in absence and presence of externally added carboxylates (RCOO−; R= CF3, C6H5 and CH3) has been utilized to produce complexes {[Cu2(µ–L2)2(H2O)]2[Cu2(µ–L2)2(H2O)2](ClO4)6} (1) (HL2 = 3-{(allylimino)methyl}-2-hydroxy-5-methylbenzaldehyde), [Cu4(µ4–O)(µ–L1)2(µ1,3–O2CCF3)4] (2), [Cu4(µ4–O)(µ–L1)2(µ1,3–O2CC6H5)4]∙H2O (3), [Cu5(µ3–OH)2(µ–L1)2(µ1,3–OAc)2(OAc)2(H2O)4][Cu5(µ3–OH)2(µ–L1)2(µ1,3–OAc)2(OAc)3(H2O)](ClO4)3∙2C2H5OH (4). Absence of carboxylate anions did not yield HO− ions in situ and triggered single ligand arm hydrolysis. The formation of tetra- and pentanuclear aggregates as well as ligand hydrolyzed dinulcear products has been rationalized to identify the possible roles of carboxylate anions in solution. Detailed characterization of the complexes in the solid state and in solution have been carried out using spectroscopic measurements, X-ray crystallography, variable temperature magnetic measurements and functional behavior. In MeOH solutions at 298 K, the complexes 1-4 showed catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) saturated with O2 of air
Two types of nitrito support for μ4-oxido-bridged [Cu4] complexes: synthesis, crystal structures, magnetic properties and DFT analysis
No full textNovel nitrito supported and μ4-oxido bridged CuII aggregates have been found in two tetranuclear complexes, [Cu4(μ4-O)L2(μ1,3-ONO)4] (1) and [Cu4(μ4-O)L2(μ1,3-OAc)2(μ1,2-NO2)2] (2), of the chiral Schiff base HL (HL = 4-methyl-2,6-bis-(1-phenyl-ethylimino)-methylphenol). The structures contain either in situ generated or externally added peripheral μ-nitrito groups, in κ2O/O and κ2N/O bridging modes. Four NO2 - bridges in 1 and two AcO- co-ligands along with two NO2 - bridges in 2 are essential for the stabilization of these tetranuclear aggregates. The complexes have been characterized by X-ray crystal structure determination, spectroscopic and magnetic measurements, and density functional theory (DFT) analysis. They are formed from the assembly of two [Cu2L]3+ fragments around a water-derived oxido ligand under the control of nitrite or mixed nitrite/acetate bridges. Variable temperature magnetic susceptibility measurements reveal strong intramolecular antiferromagnetic exchange interactions within the tetranuclear clusters to yield ST = 0 ground state. The capacity of the two different nitrite bridging modes to mediate magnetic coupling has been examined through measurements and numerical fitting procedures, and rationalized by means of DFT calculations
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
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