Reactions of Fe(II) with the tripodal chelating ligand 1,1,1-tris(2-pyridyl)ethoxymethane (py3C-OEt) and (NCE)− co-ligands (E = S, Se, BH3) give a series of mononuclear complexes formulated as [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1) and BH3 (2). These compounds are the first Fe(II) spin cross-over (SCO) complexes based on the tripodal ligand tris(2-pyridyl)ethoxymethane and on the versatile co-ligands (NCS)− and (NCBH3)−. The crystal structure reveals discrete monomeric isomorph structures formed by a cationic [Fe(py3C-OEt)2]2+ complex and by two equivalent anionic [Fe(py3C-OEt)(NCE)3]− complexes. In the cations the Fe(II) is facially coordinated by two py3C-OEt tripodal ligands whereas in the anion the three nitrogen atoms of the tripodal ligand are facially coordinated and the N-donor atoms of the three (NCE)− co-ligands occupy the remaining three positions to complete the distorted octahedral environment of the Fe(II) centre. The magnetic studies show the presence of gradual SCO for both complexes: A one-step transition around 205 K for 1 and a two-step transition for compound 2, centered around 245 K and 380 K.

Two new mononuclear Fe(II) polymorphs, [(C2H5)4N]2[Fe(py3C-OEt)(NCS)3]2 (1) and [(C2H5)4N][Fe(py3C-OEt)(NCS)3] (2) (py3C-OEt = tris(pyridin-2yl)ethoxymethane) have been synthesized and characterized by single crystal X-ray diffraction, by magnetic and photomagnetic measurements, and by detailed variable temperature infrared spectroscopy. The molecular structure, in both complexes, is composed by the same anionic [Fe(py3C-OEt)(NCS)3] -complex (two units for 1, and one unit for 2) generated by a coordination, to the Fe(II) metal centre, of one tridentate donor molecules such tetrathiafulvalene (TTF) derivatives for the design of multifunctional systems, such as fluorescent or conducting switchable materials. 6,60 ■ ASSOCIATED CONTENT Supporting informationThe Supporting Information is available free of charge on the ACS Publications website at DOI: XXXXX/acs.inorg-chem.XXXXXXX X-ray crystallographic data in CIF format: CCDC numbers 2025933-2025936 (CIF). This material is available free of charge via the Internet at http://pubs.acs.org. Syntheses details and figures S1-S19 (pdf)

Reactions of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in presence of the pseudohalide ancillary NCE- (E = S, Se, BH3) ligands led to a series of three mononuclear complexes formulated as [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1), BH3 (2) and Se (3). Single crystal characterizations (complexes 1-2) and X-ray powder diffraction (complexes 1-3) reveal monomeric isomorph structures formed by the spin crossover (SCO) anionic [Fe(py3C-OEt)(NCE)3] complex, associated with the low spin (LS) cationic [Fe(py3C-OEt)2]2+ complex and two solvent acetonitrile molecules. In the [Fe(py3C-OEt)2]2+ cation, the Fe(II) is coordinated by two py3C-OEt tridentate ligands, while the [Fe(py3C-OEt)(NCE)3] anion displays a hexacoordinated environment involving three N-donor atoms of one py3C-OEt ligand and three nitrogen atoms arising from of the three (NCE) coligands. The magnetic studies show the presence of gradual SCO behavior for the three complexes: a one-step transition around 205 K for 1 and two step-transitions for compounds 2 and 3, centred at 245 K and 380 K for 2, and at 170 K and 298 K for 3. The magnetic behaviors of complexes 1 and 2 remain unchanged when heating up to 500 K, while complex 3 shows significant changes which are caused by the crystallisation solvent loss above room temperature.

A new 1D coordination polymer, [Fe3(2-bntrz)6(bntrz)2(2-tcnsme)2](tcnsme)4.4H2O (1∙4H2O), based on the [Fe3(2-bntrz)6] trinuclear units covalently linked by symmetric double cyanocarbanion coligands involving 12-membered metallacycles has been prepared and characterised. The crystal...