Palladium(II) complexes with 1,2,4-triazole derivative & ethylene diamine as ligands, synthesis, characterization, luminesence study & crystal structure determination

Abstract

Complexes [Pd(aemptrz)Cl2] (1) and [Pd2(μ-mptrz)2(mptrz)2(en)]·CH3OH (2) (where aemptrz is 1‐(1‐(λ2‐azanyl)ethyl)‐4‐methyl‐5‐(λ1‐sulfanyl)‐4H‐1λ4,2,4‐triazole, mptrz is 4-methyl-4H-1,2,4-triazole-3-thiolato and en is ethylene diamine) were synthesized by the reaction of 4-methyl-4H-1,2,4-triazole-3-thiol (Hmptrz) (1) or a mixture of (Hmptrz) and ethylene diamine (2) with PdCl2. Complexes [Pd2(μ-mptrz)4] (3) and [Pd2(μ-mptrz)2(mptrz)2(en)] (4) were obtained by similar methods, but using Pd(OAc)2 instead of PdCl2. The four complexes were thoroughly characterized by elemental analysis, IR, UV–Vis, 1H NMR, luminescence spectroscopy as well as single-crystal X-ray diffraction method. Central Pd(II) ions in 1 are tetra-coordinated by two chloride atom in the cis-positions, one sulfur atom and one nitrogen atom to form PdNSCl2 coordination sphere, presenting slightly distorted square planar geometry around Pd atom. In complex 2, the Pd1 atoms are coordinated to four triazole units via four PdS bond (PdS4 square-plane) and the Pd2 atoms are coordinated to two of these triazole units together with the two N atoms of ethylene diamine ligand (PdN4 square-plane). In complex 3 the two Pd(II) centers are connected together by four bridging triazole ligands providing a paddle wheel-like arrangement. The Pd1 atom in complex 4 has a square-planar coordination involving the S atoms from four mptrz− ligands (two terminals and two bridged triazole) and the Pd2 atom is coordinated by two nitrogens of ethylene diamine and two nitrogens of the two bridged triazole ligand. Complex 1 has τ4 value (the geometric parameter) of 0.043, which fits with a slightly distorted square planar geometry. Considering the Pd⋯Pd contact, the stereochemistry of the palladium(II) ion in 2, 3 and 4 suggest a distorted square pyramid with a geometrical factor τ5=0.042, 0.013 and 0.040, respectively. The luminescence properties of the free ligand as well as the complexes 1–4 were investigated in solution.