Hydrophobic-exterior layer structures and magnetic properties of trinuclear copper complexes with chiral amino alcoholate ligands

The trinuclear secondary building unit (SBU) {Cu-3(mu-L)(4)X-2} constructed from chelating and alcoholate-O-bridging chiral amino alcoholate (amino alkoxido, mu-L) and terminal halide ligands (X) gives rise to two-dimensional (2D) homochiral supramolecular polymers through the bridging action of the halide ligand. Compounds 2D-[Cu-3(mu-L)(4)(mu(3)-X)(2)] {X = Br (1 to 4), X = Cl (5, 6); L = amino-ethanolate (1, 5), (R)-2-amino-propan-1-olate (2), (R)-2-amino-butan-1-olate (ab) (3, 6), (R)-2-amino-2-phenyl-ethanolate (4)} were synthesized from 2-amino alcohol, LH with CuBr2 or CuCl2, respectively, in the presence of triethylamine (TEA). The crystal packing of isomorphous 2D-[Cu-3(mu-L)(4)(mu(3)-X)(2)] shows a separation of the hydrophobic alkyl from the hydrophilic amino-/alcoholate-/Cu Br-region. Charge-assisted Cu(2+)center dot center dot center dot Br(-)- and hydrogen-bonding interactions in the hydrophilic region are the driving force of hydrophobic exterior layer formation with a hydrophilic interior exposing the hydrophobic alkyl groups to the exterior. Stacking of the layers through weak van-der-Waals interactions between the alkyl groups correlates with formation of thin crystal plates along the stacking direction. A lower ligand concentration yields both dinuclear and mononuclear SBUs in one-dimensional (1D-) homochiral coordination polymers 1D-[{Cu-2(mu-ab)(2)Br-2}(2){(mu(3)-Br)Cu(abH)(2)Br}{(mu(3)-Br)Cu(abH)(CH3OH)Br}] (7) and 1D-[{Cu-2(mu-ab)(2)Cl-2}(2){(mu(3)-Cl)Cu(abH)(CH3CH2OH)Cl}(2)] (8). In {[Cu(rac-abH)(rac-ab)H2O]ClO4}(2) (9) two SBUs combine through charge assisted H-bonds to a dimeric unit. Temperature dependent magnetic susceptibility measurements of 1 and 3 show ferromagnetic coupling but no magnetic ordering. However, at temperatures lower than 3 K an onset of long-range magnetic ordering can be observed. AC magnetic measurements in the range of 1.9 K to 5 K at different frequencies show that the long range magnetic ordering is achieved at lower temperatures than that. Correlation of magnetic coupling with the Cu-O-Cu angle is in agreement with the structural parameters of 1 and 3. Very good agreement between experimental and DFT calculated J, j coupling constants shows that the interaction between the terminal copper(II) ions in these linear trinuclear SBUs is operative and it cannot be neglected.