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

The 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 P 2 1 / 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 Pd II and “hard” metal ions Ni II and Co II . Reaction of [PdCl 2 (COD)] with 1 mol‐equiv. of 1 or 2 in refluxing methanol and addition of NH 4 PF 6 afforded the Pd II complexes 5 and 6 , respectively. Compound 5 is an unexpected partially hydrolyzed complex. It crystallizes in the tetragonal space group P 4 1 2 1 2 with a = 10.7737(10) Å, b = 10.7737(10) Å, c = 28.190(5) Å, Z = 4. The structure shows the Pd II ion coordinated to a square‐planar arrangement of two selenium and two nitrogen atoms. Reaction of NiCl 2 · 6H 2 O with 1 or 2 and NH 4 PF 6 yielded complexes 7 and 8 , respectively. The assignment of octahedral geometries to [Ni(L)](PF 6 ) 2 ] ( 7 : L = 1 ; 8 : L = 2 ) follows from their paramagnetism [ μ eff = 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 P 2 1 / c ; a = 9.979(2) Å, b = 18.901(4) Å, c = 19.333(4) Å; Z = 4. 8 :Orthorhombic, space group Pna 2 1 ; 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 Ni III /Ni II couples. The analogous Co II complex, [Co( 1 )](PF 6 ) 2 ] ( 9 ) also shows a quasi‐reversible Co III /Co II couple. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)