Macrocyclic selenoether complexes of nickel(II). Synthesis and properties of [NiX2([16]aneSe4)] ([16]aneSe4 = 1,5,9,13-tetraselenacyclohexadecane, X = Cl, Br or I) and [NiX2(MeSeCH2CH2SeMe)2]*

Abstract

Reaction of NiX₂ (X = Cl, Br or I) with [16]aneSe₄ (1,5,9,13-tetraselenacyclohexadecane) under anhydrous conditions in n-butanol yielded trans-[NiX₂([16]aneSe₄)]. Similar reactions using MeSeCH₂CH₂SeMe produced trans-[NiX₂(MeSeCH₂CH₂SeMe)₂]. The complexes have been characterised by IR and UV/VIS spectroscopy and magnetic measurements. The crystal structure of [NiCl₂(MeSeCH₂CH₂SeMe)₂] showed an octahedral nickel centre co-ordinated to trans chlorines [2.370(2)–2.376(2) Å] with the diselenoethers present as chelating ligands in the DL conformation [2.522(1)–2.5623(8) Å]. Structural data on the very poorly soluble [16]aneSe₄ complexes were obtained via nickel K-edge EXAFS (extended X-ray absorption fine structure), and the results compared with related complexes. A ligand field analysis of the UV/VIS spectra of [NiX₂([16]aneSe₄)] and of the tetrathioether analogues [NiX₂([16]aneS₄)] ([16]aneS₄ = 1,5,9,13-tetrathiacyclohexadecane) showed that the ligand fields produced by 16-membered ring macrocycles [Dq(xy)] lie in the order N₄ > S₄ > Se₄, with MeSeCH₂CH₂SeMe affording a stronger field that [16]aneSe₄ due to the smaller chelate ring size.