Syntheses and structural characterization of ferrocene-containing double-helicate and mononuclear copper(II) and silver(I) complexes

The self-assembly and structural characterization of the new ferrocene-containing dicopper-(II) double helicate [Cu2L21] (1) and related copper(II) complex [CuL2(CH3CN)] [ClO4](2) (2) and silver(I) complexes [AgL2(CH3CN)][BF4] (3) and [AgL2][BF4] (4) have been achieved. These complexes are derived from inexpensive and easy-to-prepare ferrocene-containing bisbidentate Schiff-base ligands H2L1, [(C6H4)(OH)CHNNC(CH3)(C5H4)](2)Fe, and L-2, [(C5H4N)-CHNNC(CH3)(C5H4)](2)Fe. . The neutral double-helical dicopper(II) complex 1 crystallizes in a polar space group. The two ferrocene-containing ligands strand interwined about each other and around the two tetrahedral copper ions in a double-helical fashion, with the Cu Cu separation being 9.45 Angstrom. The four metal centers are coplanar and form a slightly distorted rhombus with sides of ca. 5.8 Angstrom. Reaction of the ligand L2 and copper(II) constructed a mononuclear copper complex, 2. X-ray structural analysis reveals that the copper(II) atom is coordinated in a distorted square pyramidal geometry, with four nitrogen atoms from the two bidentate bind sites forming the basal plane; the acetonitrile nitrogen atom occupies the apical position. The molecular structure of the silver(I) complex 3 is quite similar to that of copper complex 2, with the silver(I) surprisingly coordinated in a square pyramidal geometry. The silver(I) atom in mononuclear silver complex 4 is coordinated in a new square planar fashion. The result presented here shows that while the ligand (L-1)(2-) can bridge two metal ions to give a double helicate with Cu(II), the ligand L2 acts as a tetradentate ligand chelate to a single metal center in its structurally characterized complexes with Cu(II) and Ag(I). Crystal structures of the free ligand H2L1 and L-2 are also reported for comparison.