Structure of di(salicylaldehyde benzoylhydrazonato) zinc(II), an unusual staircase polymeric structure formed via E -> Z isomerization on complexation

A bicomplex of salicylaldehyde benzoylhydrazone (SBH) with Zn(II) was synth esized in ethanol and single crystals were obtained in DMSO. The compound c rystallizes in the orthorhombic system with the space group Pna2(1)(33) and crystal data: a = 22.573(3) A, b = 6.1208(5) A. c = 17.881(2) A. V = 2470. 5(5) A(3). Z = 4. d(calc) = 1.462 g(.)cm(-3). (2633 reflections with I > 2 sigma (I); final R = 0.0509: R-w = 0. 1099). The asymmetric unit is a nearly planar bicomplex built up from one Zn atom linked to two monodeprotonated SBH ligands. The compound can be described a s formed of chains extended along the b axis. This linear polymeric charact er results from the linking of each asymmetric unit to two neighbouring one s via four (2 x 2) covalent Zn-O bonds involving three Zn atoms and four ph enolic oxygens. These covalent bonds are related to the very unusual Z conf iguration of the ligand. The three-dimensional cohesion of the compound is obtained by van der Waals forces between the polymeric chains. El Hage Chah ine. 1997). The title compound was prepared and characterized as a part of this work. In other respects, metal cations were classified as hard and soft Lewis aci d - HSAB concept (Pearson, 1963). Soft acids form unexpected complexes with Lewis bases. Therefore, it seemed interesting to study the behavior of a c helator designed as a hard and/or a borderline Lewis base towards complex f ormation with a borderline Lewis acid, Zn++.