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

Slow evaporation of aqueous solutions of (pyrazol-3-yl)pyrazine (L-1) and FeCl2, Fe(ClO4)(2) or Fe(BF4)(2) yields [FeCl2(L-1)(2)] . H2O (1 . H2O), [Fe(L-1)(3)](ClO4)(2).H2O (2.H2O) and [Fe(L-1)(3)](BF4)(2).2H(2)O (3.2H(2)O). The crystal structure of 1.H2O 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.H2O and 3.2H(2)O 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(2)O associate through hydrogen bonding into a hexagonal, chiral honeycomb structure with pores of diameter 5.3 Angstrom. These channels are filled with a disordered region of electron density, which must contain one BF4- equivalent and lattice water. Attempts to remove the water from 3.2H(2)O by heating under vacuum were unsuccessful, while partial replacement of the BF4- ions for Cl- in toluene results in decomposition of the crystalline sample. (C) 2002 Elsevier Science Ltd. All rights reserved.