Schiff Base Ligands from 3-aminopropanol

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Synthesis, magnetism, structure, and mass spectroscopy of the binuclear copper(II) complexes Cu₂Cl₂O₄N₂C₂0H₂0, Cu₂O₈N₄C₂0H₂0, and Cu₂O₄N₂C₂₈H₂₆


A series of binuclear copper(II) complexes has been synthesized using the Schiff base ligands derived from the condensation of 3-aminopropanol with 2-hydroxy aldehydes or ketones. For ligands derived from (1a) 5-chlorosalicyIaIdehyde, (1b) 3-nitrosalicylaldehyde, and (1c) 5,6-benzosalicylaldehyde, the binuclear complexes were studied by single-crystal x-ray diffraction, using counter methods, and their structures determined. Crystal data: 1a, Cu2Cl2O4N2C20H 20, space group P21/c, Z = 2, a = 9.475 (1) Å, b = 11.251 (3) Å, c = 9.857 (2) Å, β = 102.84 (2)°, V = 1025 Å3, R = 2.4%, 1608 reflections; 1b, Cu2O8N4C20H20, space group P21/c, Z = 2, a = 4.597 (1) Å, b = 15.515 (5) Å, c = 16.345 (4) Å, β = 113.28 (2)°, V = 1064 Å3, R = 4.2%, 1597 reflections; 1c, Cu2O4N2C28H26, space group P21/c, Z = 2, a = 10.982 (8) Å, b = 8.799 (2) Å, c = 12.322 (2) Å, β = 90.68 (3)°, V = 1191 Å3, R = 2.9%, 1275 reflections. The binuclear structure is held together by propoxy bridges between the copper atoms, and the ligand environment of the metal is quite close to square planar. The compounds all show very strong antiferromagnetic exchange interactions, as expected of the near-planar copper environment. In fact, the structures and magnetic properties fit into and give support to a general correlation between decreasing strength of antiferromagnetic interaction and increasing distortion toward tetrahedral metal environments in binuclear copper(II) complexes, and this correlation is strong enough to be used in the solution of the crystal structures. The bridging, via the highly electronegative propoxy oxygen, is readily reversed by electron impact to form the monomeric cation (three-coordinated copper), which is by far the strongest mass spectral peak. Comparison with other polymeric copper(II) complexes indicates that preferred bridging oxygens are given by the series alkyl-O- > aryl-O- > β-diketone enolic O- > ketonic O > alkyl-OH, which corresponds well to decreasing electronegativity.



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