Structure and Magnetic Studies on a Series of Two-Dimensional Iron(II) Framework Materials with Varying Ligand Characteristics

Targeting the general (4,4)-grid structural motif, we have prepared seven new coordination polymers in the general family [Fe(NCX)(2)(L)(2)]center dot(guest) (L = bis-pyridyl-type bridging ligands; X = S, Se) as an extension of the well-established spin crossover framework (SCOF) family. In all cases, the (4,4)-grid topology is formed by the bridging of octahedral iron(II) sites in the equatorial plane by bis-pyridyl ligands of varying length, flexibility, and intermolecular interaction capacity. In particular, the six ligands n-(4-pyridyl)-isonicotinamide (pin), trans-1,2-bis(40-pyridyl) ethane (tvp), 1,2-dibromo-1,2-bis(40-pyridyl) ethane (dbbpe), bis(4-pyridyl)-1,2,4,5-tetrazine (bptz), 4,40-bis(pyridyl) acetylene (bpac), and 1,4-bis(4-pyridylethynyl)benzene (bpeben) have been utilised. The seven newmaterials [Fe(NCS)(2)(pin)(2)]center dot 2(MeCN) (pin-S), [Fe(tvp)(2)(NCS)(2)]center dot 1/2(tvp)center dot(CH3CH2OH) (tvp-S), [Fe(dbbpe)(2)(NCS)(2)]center dot 6(CH3CN) (dbbpe-S), [Fe(NCS)(2) (bptz)(2)]center dot 2(CHCl3)center dot 6(EtOH) (bptz-S), [Fe(NCSe)(2)(bptz)(2)]center dot 4(CHCl3)center dot(EtOH)center dot(H2O) (bptz-Se), [Fe(NCS)(2)(bpac)(2)]center dot 2(PrOH) (bpac-S), and [Fe(NCS)(2)(bpeben)(2)]center dot 2(CHCl3) (bpeben-S) all form(4,4)-grids of varying size that are arranged in a parallel stacked topology. Despite being in the [FeN6] coordination environment known to be conducive to spin crossover, these materials all remain high-spin with thermal variation. These results are discussed in context with the large family of SCOFs that show varied spin crossover behaviours.