Preparations, Magnetic Susceptibility and Structural Studies of Trinuclear Copper(II) Compounds of 4,4,9,9-Tetramethyl-5,8-diazadodecane-2,11-diol

Abstract

Reduction of 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione yields the meso and racemo isomers of 4,4,9,9-tetramethyl-5,8-diazadodecane- 2,11-diol which form trinuclear compounds [Cu₃( amat )₂](ClO₄)₂ with all ligand alcohol groups deprotonated . The structure of the compound of the racemo amino alcohol has been determined by X-ray diffractometry [space group, P2₁/c, a 1594.5(4), b 1786.0(5), c 1419.1(4) pm, β 104.84(2)°, R 0.040, R_w 0.049 for 3466 reflections]. The cation has three copper(II) ions close to colinear (Cu-Cu 294 pm, Cu-Cu-Cu 177°), with the terminal copper(II) ions coordinated by the two nitrogen and two oxygen atoms of the tetradentate diamine-diolato ligand, and the central copper(II) ion by the oxygen atoms of the two ligands . All copper(II) ions have coordination environments intermediate between square planar and tetrahedral, the distortion from square planar being greater for the central ion [angle between planes O₂Cu,CuO₂ is 45°, compared with 16° between the planes N₂Cu,CuO₂ of the terminal copper(II) ions]. The magnetic susceptibilities of the compounds, measured over the temperature ranges 96-269 and 99-360 K for the racemo and meso isomers, respectively, are similar. Calculated effective magnetic moments/copper atom range from 1.07 μ_B at 99 K to 1.28 μ_B at 360 K. The susceptibility values were fitted to the expression for three spin-coupled copper(II) ions, with resultant spin coupling parameters, J, between adjacent atoms of -212 cm^-1 ( meso-amat )and -230 cm^-1 (racemo-amat ).