Magnetostructural correlations in parallel square-planar chloride bridged copper(II) dimers: structure, dynamic nuclear magnetic resonance study, and magnetic properties of [Cu2(terpy)2Cl2][PF6]2

Abstract

The crystal and molecular structure of [Cu₂(terpy)₂Cl₂][PF₆]₂(terpy = 2,2′:6′,2″-terpyridyl) has been determined from three-dimensional X-ray data. The complex crystallizes in the monoclinic space group P2₁/a with two dimeric formula units in a unit cell of dimensions a= 20.420(8), b= 13.383(1), c= 6.316 5(7)Å, and β= 97.42(4)°. The structure was determined by Patterson and Fourier methods and refined by full-matrix least-squares methods to R′= 0.054 from 715 independent reflections with I 2σ(I). The copper ion in each [Cu(terpy)Cl]⁺ monomer is slightly shifted (≃0.1 Å) from the plane defined by the chlorine and the three nitrogen atoms of the terpy ligand. Interactions between monomer units via long copper–chlorine bonds create discrete dibridged cationic species. Reorientations of the PF₆ ^– groups in the solid are discussed on the basis of ¹⁹F and ³¹P n.m.r. spectroscopic results. High-field magnetization measurements down to 2 K show the salt to be antiferromagnetically coupled and allow and evaluation of the singlet–triplet energy gap (2J=–5.9 cm^–1). The magnetic behaviour of this complex and other di-µ-chloro bridged parallel planar dimers is discussed on the basis of correlations with structural data.