350 research outputs found

    Restyling museum role and activities: European best practices towards a new strategic fit

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    Challenged by market pressures and enduring funding constraints, museums are actually asked to reassess their traditional role of heritage custodians, rather becoming “more entrepreneurial”. The service orientation (Alcaraz et al, 2009) has become pivotal in the new museum management, by ensuring a kind of dictatorship of the consumer and the dominance of marketing oriented studies. Minor attention has been dedicated to the offer side as a determinant of museum innovation and competitiveness. By using a benchmarking approach, this paper aims at filling this gap, by unravelling museum functions into a set of value activities, in order to point out museum best practices at the activity level, ultimately attempting to reconstruct the picture of the museums today, in their struggle for survival.Di fronte alla sfida posta dall’ambiente competitivo e dalla scarsità di risorse finanziarie, i musei si trovano sempre più a dover fronteggiare l’esigenza di preservare il ruolo di “custodi” del patrimonio , pur diventando più imprenditoriali. . L’orientamento al servizio (Alcaraz and Gillian, 2009) è diventata la pietra miliare nella nuova era della gestione museale, assicurando una sorta di “dittatura” del consumatore e la dominanza di studi orientati al marketing. Una minore attenzione è stata dedicata al lato dell’offerta come determinante dell’innovaziopne e della competitività museale.Adottando un approccio dì benchmarking, questo articolo si propone di colmare tale lacuna, dipanando le funzioni museali in un set articolato di attività, al fine di individuare best practices a livello di attività, nel tentativo di ricostruire il volto dei musei oggi, colti in un momento cruciale della loro lotta per la sopravvivenza

    Influence of copper(I) halides on the reactivity of aliphatic carbodiimides

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    Carbodiimides are widely exploited in organic synthesis, and the reactivity of these compounds can be enhanced by the addition of copper(I) halides to the reaction medium. The mild reaction conditions provide an alternative and selective synthetic approach with respect to the utilization of Brønsted acids. The influence of copper(I) halides CuX (X = Cl, Br, I) on the electronic structure of diisopropylcarbodiimide and dicyclohexylcarbodiimide was investigated by means of DFT methods. The coordination of the considered carbodiimides occurs by one of the nitrogen atoms, with the formation of linear complexes having formula [CuX(carbodiimide)]. Besides varying the carbon-nitrogen bond lengths and orders, the interaction with Cu(I) reduces the electron density on the carbodiimides and alters the energies of the [NCN]-centred unoccupied orbitals, enhancing the reactivity towards nucleophiles. The computed Fukui functions suggest negligible interaction of Cu(I) with incoming nucleophiles, and the reactivity of carbodiimides is altered by coordination mainly because of the increased electrophilicity of the [NCN] fragments. CuX essentially behave as Lewis acids, and the nature of X influences the Cu-N bond strength, the carbodiimide→CuX donation and the energies of frontier unoccupied orbitals. CuCl is actually the most employed catalyst in combination with carbodiimides, but some of the results here provided suggest that the reactivity could be yet more enhanced by its replacement with CuI

    Luminescent Tetrahedral and Octahedral Manganese(II) Complexes with [O=P]-Donor Ligands

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    Luminescent Mn(II) complexes are of potential interest for lighting applications, for instance as replacement of expensive rare earths-based phosphors in fluorescent lamps [1]. The emission is related to the 4T1(G)→6A1(6S) transition and is strongly dependent upon the coordination geometry: tetrahedral complexes are normally green emitters, while octahedral species emit in the red range. However, the luminescent properties can be enhanced by the presence of rigid structures and light harvesting fragments, able to reduce the non-radiative decay and improve the absorption in the UV region [2]. On the basis of recent outcomes on dihalide derivatives with phosphine oxides, our research group exploited phosphoramides, arylphosphonic diamides, amidophosphates and phosphonates as ligands for the preparation of tetrahedral Mn(II) complexes having general formula [MnX2L2] (X = Cl, Br, I). The complexes were isolated from the reaction between the proper anhydrous MnX2 salt and L under mild conditions. The structure of the derivatives was ascertained by single-crystal X-ray diffraction. The species revealed to be appreciably luminescent in the green region upon excitation with UV-light, with emission maxima centered between 510 and 535 nm. The luminescence lifetimes are in the hundreds of μs range, strongly influenced by the choice of the coordinated halide. In general, the lifetime decreases passing from the chloro- to the bromo- and the iodo- derivative as a consequence of the increased spin-orbit coupling effect [3-5]. Instead, when 2-naphthyl or carbazolyl fragments were introduced in the skeleton of the [O=P]-donor ligands the corresponding tetrahedral Mn(II) complexes were characterized by dual emissions, with a band in the green region attributable to the metal center and another one, centered in the red region, ascribed to triplet states of the aromatic substituents [6-7]. Similar results were achieved with [O=P]-ligands based on P(III) such as dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) and 9,10-dihydro-9-oxa-10phosphaphenantrene-10-oxide (DOPO) [8]. On the other hand, the coordination of Mn(II) to phosphonates containing the (R/S)-BINOL fragment determined an almost pure 3LC emission with complete disappearance of the green band. Bidentate ligands prepared from DOPO allowed the isolation of the corresponding octahedral Mn(II) complexes characterized by intense emissions centered at 611 nm. Differently from tetrahedral derivatives the luminescent lifetimes are in tens of ms range for octahedral derivatives as the 4T1(G)→6A1(6S) transition is both parity and spin forbidden

    Intense red-emitting three-coordinated benzothiadiazole-based copper(I) complexes

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    2,1,3-benzothiadiazole (BTD) is a fluorophore commonly exploited as luminescent material for advanced applications, such as organic light-emitting diodes (OLEDs), dyes, solar and photovoltaic cells[1-4]. Ligands containing the benzothiadiazole heterocycle allowed the isolation of luminescent complexes applied in OLED technology[5,6]. In this communication we report the synthesis and characterization of heteroleptic three-coordinated Cu(I) complexes based on the benzothiadiazole heterocycle. Triphenylphosphine, diphenylphosphinomethane (dppm) and bis[(2-diphenylphosphino)phenyl] ether (DPEphos) were used as P-donor ligands. The derivatives were prepared starting from CuCl or by acidolysis of borohydride Cu(I) complexes. When [Cu(NCCH3)4][BF4] was used as precursor, four-coordinated derivatives characterized by one acetonitrile molecule in the coordination sphere were isolated. After being excited with light below 450 nm the complexes exhibited intense emissions in the red region, lifetimes up to 2 ms long and high quantum yields. XRD data highlighted that at solid state the tetrafluoroborate used as counterion is interacting with the metal centre through a fluorine. In the case of dppm, binuclear species were isolated. The replacement of tetrafluoroborate with perchlorate showed the non-innocent role of the counter-anion, affecting in particular the luminescence lifetimes. The wide emission bands were attributed to 3LC transitions on the basis of luminescence lifetime measurements and TD-DFT calculations

    N,N-dimethyl-4-amino-2,1,3-benzothiadiazole: synthesis and luminescent solvatochromism

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    2,1,3-benzothiadiazole (BTD) derivatives were widely applied as herbicides, fungicides and antibacterial agents. The strong withdrawing ability of BTD and its fluorescent properties make it appealing also for the preparation of luminescent materials. Polymers containing the BTD fragment were successfully exploited for advances applications such as organic light-emitting diodes (OLEDs), dyes, solar and photovoltaic cells, as recently reported by B.A.D. Neto et al. [Eur. J. Org. Chem. (2013) 228]. To the best of our knowledge, a complete synthetic procedure for N,N-dimethyl-4-amino-2,1,3-benzothiadiazole (BTDNMe2) from the commercially available 2,1,3-benzothiadiazole was never reported. The only reference available dates back to 1976 and describes the thermal decomposition of the corresponding ammonium salt [N.M. Slavachevskaja et al., Pharm. Chem. J. 10 (1976) 327]. The synthetic route here proposed involves nitration of BTD in sulfonitric mixture, followed by reduction of the nitro-group and subsequent methylation with iodomethane. BTDNMe2 was isolated as dark red oil and it was fully characterized by means of nuclear magnetic resonance (NMR) and infrared spectroscopy. Solutions of BTDNMe2 in common organic solvents revealed to be appreciably luminescent in the visible range. The increase of dielectric constant caused a non-linear red shift of the absorption and emission maxima, an increase of the Stokes shift and a reduction of the photoluminescence quantum yield. The electronic transitions related to the absorption and emission properties were associated to the HOMO-LUMO energy gap by means of electrochemical measurements and DFT calculations. Finally, BTDNMe2 was successfully used for the preparation of luminescent doped polymethylmethacrylate samples with intense orange emission

    Green-emitting Zn(II) halide complexes with N,N,N',N'-tetramethyl-P-indol-1-ylphosphonic diamide as ligand

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    Zn(II) derivatives are of current interest for photophysical applications because they can enhance the emission of fluorescent ligands upon coordination. In addition, LMCT transitions involving the low-lying s or p empty orbitals of the metal center have been reported [1,2]. Herein we report the synthesis and characterization of tetrahedral Zn(II) complexes having general formula [ZnX2L2] (X = Cl, Br, I; L = N,N,N',N'-tetramethyl-P-indol-1-ylphosphonic diamide). The species were isolated from the reaction between the proper anhydrous ZnX2 salt and L under mild conditions. The structure of all the three derivatives was ascertained by single-crystal X-ray diffraction. The three species revealed to be appreciably luminescent in the green region upon excitation with UV-light below 300 nm, with emission bands centered between 520 and 530 nm. The high Stokes shifts and the luminescence lifetimes in the μs range suggest that triplet excited states are involved in the emission. On the other hand, the absorption bands are essentially ascribable to the π*←π transition of the indolyl fragment, as confirmed by DFT calculations

    Copper(I) borohydride complex with bis[(2-diphenylphosphino)phenyl] ether. Structure investigation by single-crystal X-Ray diffraction and DFT calculations

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    The borohydride anion is characterized by a rich coordination chemistry because of the variable denticity and the possibility of behaving as terminal or bridging ligand. The copper(I) complex Cu(k2-BH4)(DPEphos), where DPEphos is bis[(2-diphenylphosphino)phenyl] ether, was recently synthesized from CuCl using NaBH4 as borohydride source. The product crystallized from dichloromethane/ethanol (space group P1 ̅). The asymmetric unit contains two non-equivalent molecules, both exhibiting k2 coordination mode of the borohydride ligand, as suggested also by IR and 1H NMR spectra. The same Cu(I)-BH4 interaction was already observed for the related bis(triphenylphosphine) complex. The Cu-H distances are comprised between 1.67(3) and 1.75(2) Å, while the B-H distances are in the 1.07(2) – 1.20(2) Å range. The H-Cu-H angles for the two non-equivalent molecules are 62.7(12) and 66.3(10)°. DPEphos behaves as chelating ligand, with bite angles of 111.663(16) and 116.190(17)°. The Cu-P distances are between 2.2300(4) and 2.2776(5) Å. Bond lengths and angles of the first coordination sphere were compared with those obtained from DFT geometry optimizations, carried out using hybrid and range-separated functionals with variable percentage of Hartree-Fock exchange

    N,N-Dimethyl-4-amino-2,1,3-benzothiadiazole: Synthesis and Luminescent Solvatochromism

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    N,N-Dimethyl-4-amino-2,1,3-benzothiadiazole (BTDNMe2) was synthesized from the commercially available 2,1,3-benzothiadiazole (BTD) by nitration in a sulfonitric mixture, followed by a reduction of the nitro group and subsequent methylation with iodomethane. BTDNMe2 was fully characterized by means of nuclear magnetic resonance (NMR) and infrared spectroscopy. The solutions of BTDNMe2 in common organic solvents revealed to be appreciably luminescent in the visible range. The electronic transitions related to the absorption and emission properties were associated with the HOMO–LUMO energy gap by means of electrochemical measurements and DFT calculations. Finally, BTDNMe2 was successfully used to prepare luminescent-doped poly(methyl methacrylate) samples

    Tris-isocyanide copper(I) complex enabling copper azide-alkyne cycloaddition in neat conditions

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    The three-coordinated homoleptic Cu(I) complex with 2,6-dimethylphenyl isocyanide in the coordination sphere was easily synthesized and isolated as tetrafluoroborate salt. The structure of the compound was determined by single-crystal X-ray diffraction. The complex is highly stable, active and selective toward the copper-catalyzed azide-alkyne cycloaddition, working in neat conditions and in the absence of bases at room temperature. Substrate scope was assessed by testing several different alkynes and azides. In most cases the corresponding 1,4-disubstituted-1,2,3-triazoles were isolated in high yields
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