Mononuclear, dinuclear, hexanuclear, and one-dimensional polymeric silver complexes having ligand-supported and unsupported argentophilic interactions stabilized by pincer-like 2,6-bis(5-pyrazolyl)pyridine ligands

Abstract

The mononuclear complexes [Ag(H₂L¹)(Py)₂](NO₃)·H₂O (1, H₂L¹ = 2,6-bis(5-methyl-1H-pyrazol-3-yl)pyridine) and [Ag(NO₃)(L²)] (2, L² = 2,6-bis(5-methyl-1-isopropyl-1H-pyrazol-3-yl)pyridine), dinuclear complex [Ag₂(H₂L³)₂(HL⁴)₂] (3, H₂L³ = 2,6-bis(5-phenyl-1H-pyrazol-3-yl)pyridine, HL⁴ = 6-(5-phenyl-1H-pyrazolyl-3-yl)picolinate), one-dimensional polymer {[Ag₂(H₂L¹)₂](NO₃)₂·H₂O}_n (4), and hexanuclear clusters [Ag₆(HL¹)₄](X)₂ (X = NO₃⁻, 5; BF₄⁻, 6; ClO₄⁻, 7) stabilized by pincer-like bispyrazolyl ligands have been prepared and characterized using ¹H NMR spectroscopy, elemental analysis, IR spectroscopy, luminescence spectroscopy and X-ray diffraction. In complex 3, there is a ligand unsupported Ag–Ag bond between the two silver atoms. Complex 4 displays a one-dimensional polymer consisting of an infinite Ag–Ag chain and every two adjacent silver ions are bridged by an H₂L¹ ligand. Complexes 5 and 7 have the same Ag₆ cores in which six silver atoms are held together by four HL¹ and five Ag–Ag bonds, while complex 6 was held together by six Ag–Ag bonds. The silver–silver distances in these complexes are found in the range of 2.874(1)–3.333(2) Å for ligand supported, and 3.040(1) Å for ligand unsupported Ag–Ag bonds, respectively. Complexes 3–7 are strongly luminescent due to either intraligand or metal–ligand charge transfer processes.