Tuning of crystallization method and ligand conformation to give a mononuclear compound or two-dimensional SCO coordination polymer based on a new semi-rigid V-shaped bis-pyridyl bis-amide ligand.

With the new semi-rigid V-shaped bidentate pyridyl amide com­pound 5-methyl-N,N′-bis­(pyridin-4-yl)benzene-1,3-dicarboxamide (L) as an auxiliary ligand and the FeII ion as the metal centre, one mononuclear com­plex, bis­(methanol-κO)bis­[5-methyl-N,N′-bis­(pyridin-4-yl)benzene-1,3-dicarboxamide-κN]bis­(thio­cyanato-κN)iron(II), [Fe(SCN)2(C19H16N4O2)2(CH3OH)2] (1), and one two-dimensional coordination polymer, catena-poly[[[bis­(thio­cyanato-κN)iron(II)]-bis­[μ-5-methyl-N,N′-bis­(pyridin-4-yl)benzene-1,3-dicarboxamide-κ2N:N′]] methanol disolvate dihydrate], {[Fe(SCN)2(C19H16N4O2)2]·2CH3OH·2H2O}n (2), were prepared by slow evaporation and H-tube diffusion methods, respectively, indicating the effect of the method of crystallization on the structure type of the target product. Both com­plexes have been structurally characterized by elemental analysis, IR spectroscopy and single-crystal X-ray crystallography. The single-crystal X-ray diffraction analysis shows that L functions as a monodentate ligand in mononuclear 1, while it coordinates in a bidentate manner to two inde­­pendent Fe(SCN)2 units in com­plex 2, with a different conformation from that in 1 and the ligands point in two almost orthogonal directions, therefore leading to a two-dimensional grid-like network. Investigation of the magnetic properties reveals the always high-spin state of the FeII centre over the whole temperature range in 1 and a gradual thermally-induced incom­plete spin crossover (SCO) behaviour below 150 K in 2, demonstrating the influence of the different coordination fields on the spin properties of the metal ions. The current results provide useful information for the rational design of functional com­plexes with different structure dimensionalities by employing different conformations of the ligand and different crystallization methods.