Complexes of BiCl3 with hydrazone derived ligands: a Möbius-like discrete metal chelate versus a salt-like porous polymeric structure

Abstract

In this work we have synthesized and characterized a new helical complex of BiCl₃, namely [Bi(L^I)Cl₃], fabricated with an extremely bulky ligand, 1,2-diphenyl-1,2-bis((phenyl(pyridin-2-yl)methylene)hydrazono)ethane (L^I). The same reaction of BiCl₃ with N′-(4-hydroxybenzylidene)isonicotinohydrazide (HL^II) has allowed us to obtain a salt-like porous polymeric structure ([H₂L^II]₂[BiCl₅]·EtOH)_n. As evidenced from the single crystal X-ray analysis data, complex [Bi(L^I)Cl₃] is a Möbius-like discrete metal chelate, where the Bi^III atom is seven-coordinated in a distorted pentagonal bipyramidal N₄Cl₃ geometry and the organic ligand L^I adopts a helical twist conformation. The structure of compound ([H₂L^II]₂[BiCl₅]·EtOH)_n comprises monoprotonated non-coordinated organic molecules [H₂L^II]⁺ counterbalanced by a [BiCl₅]²⁻ anionic fragment, which, in turn, forms a 1D zig-zag polymeric chain. The organic molecules are arranged in a centrosymmetric fashion yielding a hydrogen bonded tetramer with a rectangular cavity of dimensions 7.55 × 9.02 Å. The tetramers are stacked through weak intermolecular interactions, yielding 1D infinite channels. Thus, complex ([H₂L^II]₂[BiCl₅]·EtOH)_n was found to be a porous organic–inorganic hybrid compound. By using DFT calculations we have analyzed and rationalized the molecular electrostatic potential (MEP) surfaces and, through the quantum theory of the “atoms-in-molecules” (QTAIM) computational tool, the hydrogen bonding interactions observed in the solid state of both crystal structures, focusing on the competition between O–H⋯O and N–H⋯O hydrogen bonds in ([H₂L^II]₂[BiCl₅]·EtOH)_n.