1D and 2D assembly structures by imidazole•••chloride hydrogen bonds of iron(II) complexes [FeII(HLn-Pr)3]Cl•Y (HLn-Pr=2-methylimidazol-4-yl-methylideneamino-n-propyl; Y = AsF6, BF4) and their spin states

Two FeII complexes fac-[Fe-II(HLn-Pr)(3)]Cl center dot Y (Y = AsF6 (1) and BF4 (2)) were synthesized, where HLn-Pr is 2-methylimidazole-4-yl-methylideneamino-n-propyl. Each complex-cation has the same octahedral N-6 geometry coordinated by three bidentate ligands and assumes facial-isomerism, fac-[Fe-II(HLn-Pr)(3)](2+) with Delta- and K-enantiomorphs. Three imidazole groups per Delta- or K-fac-[Fe-II(HLn-Pr)(3)](2+) are hydrogen-bonded to three Cl- ions or, from the viewpoint of the Cl- ion, one Cl- ion is hydrogen-bonded to three neighbouring fac-[Fe-II(HLn-Pr)(3)](2+) cations. The 3 : 3 NH center dot center dot center dot Cl- hydrogen bonds between Delta- or K-fac-[Fe-II(HLn-Pr)(3)](2+) and Cl- generate two kinds of assembly structures. The directions of the 3 : 3 NH center dot center dot center dot Cl- hydrogen bonds and hence the resulting assembly structures are determined by the size of the anion Y, though Y is not involved into the network structure and just accommodated in the cavity. Compound 1 has a 1D ladder structure giving a larger cavity, in which the Delta- and K-fac-[Fe-II(HLn-Pr)(3)](2+) enantiomorphs are bridged by two NH center dot center dot center dot Cl- hydrogen bonds. Compound 2 has a 2D network structure with a net unit of a cyclic trimer of {fac-[Fe-II(HLn-Pr)(3)](2+) center dot center dot center dot Cl- } 3 giving a smaller cavity, in which Delta- or K-fac-[Fe-II(HLn-Pr)(3)](2+) species with the same chirality are linked by NH center dot center dot center dot Cl- hydrogen bonds to give a homochiral 2D network structure. Magnetic susceptibility and Mossbauer spectral measurements demonstrated that compound 1 showed an abrupt one-step spin crossover with 4.0 K thermal hysteresis of T-c down arrow = 125.5 K and T-c up arrow = 129.5 K and compound 2 showed no spin transition and stayed in the high-spin state over the 5-300 K temperature range.