title: Silver-pyrazole complexes as hybrid multifunctional materials with metallomesogenic and photoluminescent behaviour.
abstract: New pyridine-functionalised pyrazole compounds [Hpz(R(n)py)] (R(n) = C(6)H(4)OC(n)H(2n+1); n = 12, 14, 16, 18; 1-4) and their corresponding silver complexes [Ag(Hpz(R(n)py))(2)][A] ([A] = NO(3)(-), BF(4)(-); ) 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)][NO(3)] 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 Zn(2+), Cu(2+) 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.
authors.affiliation: Departamento de Química Inorgánica I, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain.
authors.forename: Paloma
authors.initials: P
authors.lastname: Ovejero
authors.forename: Eduardo
authors.initials: E
authors.lastname: Asensio
authors.forename: José Vicente
authors.initials: JV
authors.lastname: Heras
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Campo
authors.forename: Mercedes
authors.initials: M
authors.lastname: Cano
authors.forename: M Rosario
authors.initials: MR
authors.lastname: Torres
authors.forename: Cristina
authors.initials: C
authors.lastname: Núñez
authors.forename: Carlos
authors.initials: C
authors.lastname: Lodeiro
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D050866:Liquid Crystals / Q000737:chemistry; D008968:Molecular Conformation; D011720:Pyrazoles / Q000737:chemistry*; D011789:Quantum Theory; D012834:Silver / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D056831:Coordination Complexes; D011720:Pyrazoles; D012834:Silver; C031280:pyrazole