Halogen⋯halogen interactions in the self-assembly of one-dimensional 2,2′-bipyrimidine-based CuIIReIV systems

Abstract

Two one-dimensional Cu^IIRe^IV coordination polymers of the general formula {[Re^IVCl₄(μ-bpym)Cu^IIX₂]·solvent}_n [where bpym = 2,2′-bipyrimidine, X = Cl (1) and Br (2), and solvent = H₂O (1) and CHCl₃ (2)] have been prepared and characterised structurally and magnetically. Both compounds crystallise in the monoclinic system with space groups P2₁/c (1) and P2₁/n (2). Each Cu^II ion is bonded to two cis nitrogen atoms from the bpym ligand and to four halogen atoms. Two of these halogen atoms are placed in the equatorial plane and the other two are filling the axial positions of the Cu^II ion, thus generating a distorted octahedral environment for this metal ion in 1 and 2. In both compounds, the Re^IV ion is six-coordinate and bonded to four chloride ions and two nitrogen atoms of the bpym ligand giving rise to a distorted octahedral geometry. In the crystal packing of both compounds, hydrogen bonds (1), short intermolecular Re^IV–Cl⋯Cl–Re^IV contacts (1 and 2), and X⋯π type interactions (1 and 2), the intermolecular interactions causing the self-assembly of these novel one-dimensional 2,2′-bipyrimidine-based Cu^IIRe^IV systems, are present. Variable-temperature magnetic measurements performed on microcrystalline samples of 1 and 2 reveal an antiferromagnetic behaviour for both compounds. Several magnetic interactions take place in 1 and 2, both intermolecular (Re^IV–Re^IV) and intramolecular (Re^IV–Cu^II and Cu^II–Cu^II) magnetic exchanges, which account for the maxima observed in their respective magnetic susceptibility versus temperature curves at ca. 6.0 (1) and 18.0 K (2).