Iron(II) complexes of (pyrazol-3-yl)pyrazine. Anion-dependent formation of a hydrogen-bonded, chiral nanoporous lattice

Abstract

Slow evaporation of aqueous solutions of (pyrazol-3-yl)pyrazine (L 1) and FeCl 2, Fe(ClO 4) 2 or Fe(BF 4) 2 yields [FeCl 2(L 1) 2]·H 2O ( 1·H 2O), [Fe(L 1) 3](ClO 4) 2·H 2O ( 2·H 2O) and [Fe(L 1) 3](BF 4) 2·2H 2O ( 3·2H 2O). The crystal structure of 1·H 2O shows a distorted cis-octahedral high-spin Fe(II) centre. Molecules of 1 associate in the crystal through hydrogen bonding into 1D chains, which are linked into a 2D lattice by OH⋯Cl hydrogen bonds to the lattice water. The structures of 2·H 2O and 3·2H 2O contain low-spin Fe(II) ions. In 2, the complex dication has a distorted mer-octahedral geometry, while in 3 the complex crystallises as its fac-octahedral isomer, with crystallographic C 3 symmetry. The complex dications in 3·2H 2O associate through hydrogen bonding into a hexagonal, chiral honeycomb structure with pores of diameter 5.3 Å. These channels are filled with a disordered region of electron density, which must contain one BF 4 − equivalent and lattice water. Attempts to remove the water from 3·2H 2O by heating under vacuum were unsuccessful, while partial replacement of the BF 4 − ions for Cl − in toluene results in decomposition of the crystalline sample.