Synthesis, X-Ray Crystal Structure and Magnetic Studies of a Biscopper(II) Complex of a C-Spiro Binucleating Linear Octadentate Ligand

Abstract

Reaction of the binucleating ligand 5,5-bis(4-amino-2-thiabutyl)-3,7- dithianonane-1,9-diamine (L¹) with a copper(II) salt in aqueous solution, and in the presence of lithium dithionate, results in the isolation of a dark blue crystalline solid identified as [Cu₂(L¹)](S₂O₆)₂.4H₂O. Crystals of the complex are triclinic, space group Pī , a 8.227(2), b 13.103(3), c 16.423(4) Ǻ, α 68.68(2), β 86.68(2), γ 75.50(2)°, Z 2, R 0.026 (5039 F). The structure consists of two copper(II) atoms each of which is coordinated through two thioether and two primary amine atoms. The two copper sites are linked through a saturated spiro carbon atom. Each copper atom is also coordinated to one water molecule; one of the copper atoms is coordinated to an oxygen atom of one dithionate anion. Thus, one copper atom is six-coordinate (4+2 tetragonally distorted), and the other is five-coordinate. The intramolecular Cu...Cu distance is 7.127 Ǻ; the shortest intermolecular Cu...Cu distance is 6.591 Ǻ. The angle between the two N₂S₂ planes is 92.2°. Low-temperature magnetic studies indicate weak intra- and inter-molecular antiferromagnetic interactions with a singlet-triplet splitting 2J of -10 cm^-1 and a θ of -5 K. E.p.r. studies indicate a magnetic dipole-dipole interaction between the two copper(II) sites and a weak intermolecular antiferromagnetic interaction.