Characterization of silver(I) complexes with mono- and dihalo-substituted derivatives of pyridine in solution and in solid state

Reakcijom srebrova(I) nitrata s mono- i dihalogen derivatima piridina u molarnom omjeru 1 : 2 u smjesi vode i alkohola priređeno je 12 novih kompleksa srebra(I) opće formule [Ag(NO3)(Xnpy)2], X = Cl, Br, I; n = 1 – 2. Pripravljeni kompleksni spojevi identificirani su pomoću elementne analize, dok je njihova struktura u otopini okarakterizirana tehnikama višenuklearne spektroskopije NMR (1H, 13C, 15N, 109Ag) i spektrometrije masa. Kompleksi su u čvrstom stanju okarakterizirani spektroskopijom IR, a kristalna i molekulska struktura im je određena metodama rentgenske strukturne analize. Molekule liganda su u svim kompleksima na srebrov(I) ion vezane preko atoma dušika piridinskog prstena. U koordinacijskoj sferi srebra(I) dokazan je i nitratni ion koji ovisno o načinu koordiniranja na srebro omogućava stvaranje koordinacijskih polimera ili supramolekulskih struktura. Koordinacijski broj srebra kod sintetiziranih spojeva varira između tri, četiri, pet ili šest i to čak ponegdje i unutar istog spoja. Pored kovalentnih veza, Ag–N i Ag–O, u strukturama su pronađene i nekovalentne interakcije (vodikove i halogenske veze te π···π interakcije) koje pridonose konačnoj dimenzionalnosti spoja. Slaba veza Ag–Ag otkrivena je u kompleksu s 3-Ipy kao ligandom. Priređeni spojevi pokazuju bolju antibakterijsku aktivnost u uvjetima in vitro spram Gram-negativnih nego spram Gram-pozitivnih bakterijskih vrsta. Twelve 1:2 complexes of silver(I) nitrate with mono- and dihalopyridine of the general formula [Ag(NO3)(Xnpy)2], X = Cl, Br, I; n = 1–2, were prepared by reaction of AgNO3 and corresponding pyridine derivative in water-alcohol solution. All synthesized complexes were identified by elemental analysis and characterized in solution by multinuclear NMR spectroscopy (1H, 13C, 15N, 109Ag) and mass spectrometry. In solid state the complexes were characterized by IR spectroscopy, while their crystal and molecular structures were revealed by single crystal X-ray analysis. It was established that in all complexes, besides pyridine nitrogen atoms, the oxygen atoms belonging to nitrate ion are also coordinated to silver ion thus providing not only different coordination numbers of Ag(I) which vary from three, four, five and six but also a formation of coordination polymers or supramolecular structures. It is interesting that in the molecule of one complex, which is dinuclear, there are even two differently coordinated silver ions (3, 4). Beside covalent Ag–N and Ag–O bonds present in complex molecules, there are various non-covalent interactions such as hydrogen bonding, halogen bonds and halogen-halogen interactions thus contributing to final dimensionality. Moreover, a weak Ag–Ag bonding was determined in complex with 3-Ipy as a ligand. In vitro tests of all complexes gave better antibacterial activity against Gram-negative than Gram-positive strains.