Synthesis, Characterization and Coordination Chemistry of Some Selenium‐Containing Macrocyclic Schiff Bases

Abstract

AbstractThe condensation of bis(o‐formylphenyl) selenide with 1,2‐diaminoethane or 1,3‐diaminopropane yielded the new macrocyclic ligands 1 and 2 in very good yields. Crystals of 1 are monoclinic, space group P21/c with a = 10.0648(10) Å, b = 37.390(4) Å, c = 8.0073(11) Å, Z = 4 and those of 2 are triclinic, space group P$\bar {1}$ with a = 7.200(3), b = 9.137(3), c = 12.780(6) Å, Z = 1. The coordination chemistry of 1 and 2 has been studied with the “soft” metal ion PdII and “hard” metal ions NiII and CoII. Reaction of [PdCl2(COD)] with 1 mol‐equiv. of 1 or 2 in refluxing methanol and addition of NH4PF6 afforded the PdII complexes 5 and 6, respectively. Compound 5 is an unexpected partially hydrolyzed complex. It crystallizes in the tetragonal space group P41212 with a = 10.7737(10) Å, b = 10.7737(10) Å, c = 28.190(5) Å, Z = 4. The structure shows the PdII ion coordinated to a square‐planar arrangement of two selenium and two nitrogen atoms. Reaction of NiCl2·6H2O with 1 or 2 and NH4PF6 yielded complexes 7 and 8, respectively. The assignment of octahedral geometries to [Ni(L)](PF6)2] (7: L = 1; 8: L = 2) follows from their paramagnetism [μeff = 3.23 (7), 1.81 (8) B.M.] and their UV/Vis spectra. This was also confirmed by single‐crystal X‐ray studies. The crystal structures of 7 and 8 showed a distorted octahedral nickel center coordinated by two selenium and four nitrogen atoms. 7: Monoclinic, space group P21/c; a = 9.979(2) Å, b = 18.901(4) Å, c = 19.333(4) Å; Z = 4. 8:Orthorhombic, space group Pna21; a = 20.277(5), b = 20.865(5), c = 9.416(2) Å; Z = 4. The cyclic voltammograms of 7 and 8 in MeCN solution show well‐behaved quasi‐reversible NiIII/NiII couples. The analogous CoII complex, [Co(1)](PF6)2] (9) also shows a quasi‐reversible CoIII/CoII couple. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)