Silver-pyrazole complexes as hybrid multifunctional materials with metallomesogenic and photoluminescent behaviour

Paloma Ovejero, E. Asensio, José Vicente Heras, José A. Campo, M. M. Cano, M. R. Torres, Cristina Núñez, C. Lodeiro

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Abstract

New pyridine-functionalised pyrazole compounds [HpzR(n)py] (R(n) = C6H4OCnH2n+1; n = 12, 14, 16, 18; 1-4) and their corresponding silver complexes [Ag(HpzR(n)py) 2][A] ([A] = NO3-, BF4-; 5-12) have been synthesised and characterised. All of them, with the exception of 1, are liquid crystal materials exhibiting monotropic or enantiotropic SmA mesophases, in contrast to the non-mesomorphic related R(n)-monosubstituted compounds. Because the molecular shape is a factor determinant in the organisation of molecules in the liquid crystal phase, we were interested in solving the crystal structure of representative examples of the mentioned compounds, such as 1 and 6. So, the X-ray crystal structure of [Hpz R(12)py] 1 shows the presence of dimeric units through N-H⋯N hydrogen bonds, which conform to an elongated molecular shape containing a double chain length. On the other hand, the structure of [Ag(Hpz R(14)py)2][NO3] 6 also evidenced Ag-Ag bonded dimers from 'U'-shaped cationic entities. These dimers exhibit four chains, two by two alternated, so giving rise to a longer molecular length. Of particular interest was to observe that in both structures, the dimers are layer-like packed, their lamellar structures being related to that of the mesophases found in both kinds of compounds. Furthermore, the analysis of the optical data of the compounds 2 and 4 and the silver compounds 5, 6, 9 and 10 as representative examples pointed out their luminescent behaviour as well as their good ability to act as fluorescent probes for Zn2+, Cu2+ and Ag +. An increase in the fluorescence quantum yields is observed in the final complexes produced in the titrations, this fact being specially notable when 9 was used as the starting compound. © The Royal Society of Chemistry 2013.
Original languageEnglish
Pages (from-to)2107-2120
Number of pages14
JournalDalton Transactions
Volume42
Issue number6
DOIs
Publication statusPublished - 14 Feb 2013

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Keywords

  • Dimers
  • Hybrid materials
  • Hydrogen bonds
  • Liquid crystals
  • Quantum yield
  • Silver compounds
  • Dimeric units
  • Double chain
  • Fluorescence quantum yield
  • Fluorescent probes
  • Liquid crystal materials
  • Liquid crystal phase
  • Mesophases
  • Molecular length
  • Molecular shapes
  • Multi-functional materials
  • Non-mesomorphic
  • Optical data
  • Pyrazoles
  • Silver complexes
  • Starting compounds
  • X ray crystal structures
  • Silver

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