Structural and Electronic Properties of the Iron(II) and Nickel(II) Bis(ligand) Complexes of 6-(5-Methyl-1,2,4-oxadiazol-3-yl)-2,2′-bipyridine— a Terpyridine-Based Tridentate

Abstract

Iron(II) and nickel(II) bis(ligand) complexes of 6-(5-methyl-1,2,4-oxadiazol-3-yl)-2,2′-bipyridine (L) are described. The ligand field in the iron complex is close to that at the singlet ( 1 A1) ? quintet ( 5 T2) crossover and magnetic and Mössbauer spectral evidence indicates that a spin transition occurs in salts of the iron complex but is centred above room temperature. The structures of [FeL2] [CF3SO3]2.CH3CN and [NiL2] [BF4]2.CH3CN were determined and both are very similar to the structures of the corresponding terpyridine complexes. Spectroscopic data indicate that for the iron complex π-interaction between the metal and the ligand is less than that in the terpyridine system. [FeL2] [CF3SO3]2.CH3CN is monoclinic, space group P 21/c; a 8 . 232(5), b 25 . 273(10), c 17 . 306(10) Å, β 92 . 37(3)°, Z 4; [NiL2] [BF4]2.CH3CN is monoclinic, space group P 21/c; a 8 . 136(2), b 17 . 558(2), c 23 . 783(7) Å, β 109 . 32(1)°, Z 4.

The first metal complexes of 3,3′-bi-1,2,4-oxadiazole: A curiously ignored ligand

“…1). The values for the bond lengths and angles within the 1,2,4-oxadiazole rings in this complex are similar to those reported in the other coordination complexes of ligands containing a 1,2,4-oxadiazole rings [13][14][15] and to those of the free ligand 1. As expected the palladium atom has square planar geometry, the largest deviation from idealized geometry being due to the presence of the five-membered chelate ring.…”

“…The reasons for this are uncertain, but are probably associated with the greater basicity of the N4 nitrogen donors compared to the N2 atoms. Support for this comes from the fact that, in all eight previously reported X-ray crystal structures of metal complexes of ligands containing a 1,2,4-oxadiazole ring, coordination occurs preferentially through the N4 nitrogen [13][14][15]. This aspect will be the subject of future studies.…”

“…Within this context, we noted that 1,2,4-oxadiazoles have been curiously ignored as subcomponents within ligands, be they monodentate, chelating or bridging. Indeed, a search of the Cambridge Crystallographic Database revealed that only three papers reported metal complexes of ligands containing a 1,2,4-oxadiazole subunit [13][14][15].…”

“…Within this context, we noted that 1,2,4-oxadiazoles have been curiously ignored as subcomponents within ligands, be they monodentate, chelating or bridging. Indeed, a search of the Cambridge Crystallographic Database revealed that only three papers reported metal complexes of ligands containing a 1,2,4-oxadiazole subunit [13][14][15].In continuation of our interest in the chemistry of biheterocycles [16], we realised that of the three isomeric bi-1,2,4-oxadiazoles, the 3,3'-isomer (1) represents a particularly interesting potential ligand. This compound has been known for over forty years [17] and could potentially chelate to a single metal in any of three modes (Fig.…”

A Route to 1,2,4-Oxadiazoles and Their Complexes via Platinum-Mediated 1,3-Dipolar Cycloaddition of Nitrile Oxides to Organonitriles

“…25 The crystallographic data indicate the presence of two 1,2,4-oxadiazole ligands bound to the Pt atom via their N 4 atoms. To the best of our knowledge, despite the wealth of structural chemistry of uncoordinated 1,2,4-oxadiazoles, 60 only three structures of complexed species are known, i.e., Sn(IV), 61 Fe(II), 62 and Ni(II) complexes. 62 The structures reported here are the first examples of (1,2,4-oxadiazole)-platinum compounds.…”