A Modified Synthetic Pathway for the Synthesis of so far Inaccessible N1‐Functionalized Tetrazole Ligands – Synthesis and Characterization of the 1D Chain‐Type Spin Crossover Compound [Fe(3ditz)₃](BF₄)₂

Abstract

A modified phase-transfer-catalyst-assisted synthetic pathway was developed that widens the pool of accessible 1-substituted tetrazoles, which are possible ligands for iron(II) spin-crossover compounds. Within the family of α,ω-bis(tetrazol-1-yl)alkanes, a series of ligands and their respective iron(II) spin-crossover compounds were synthesized and structurally and spectroscopically characterized in the past. The classical route to prepare these ligands is based on the respective amino-precursors. Hence the pool of accessible compounds is limited by the commercial or synthetical availability of α,ω-diaminoalkanes. Furthermore, the concomitant transformation to the tetrazole moieties turns out to be easier for diamino-alkanes with an even number of carbon atoms than for those with an odd number. In line with this observation, the shortest odd-numbered homologues such as 1,1-bis(tetrazol-1-yl)methane (<i>1ditz</i>) and 1,3-bis(tetrazol-1-yl)propane (<i>3ditz</i>) were inaccessible so far. In this paper, we report the successful preparation and characterisation of the classically inaccessible 1,3-bis(tetrazol-1-yl)propane (<i>3ditz</i>) and of its spin-crossover complex [Fe(<i>3ditz</i>)₃](BF₄)₂, which features an abrupt and almost complete spin transition at <i>T</i>[Formula: see text] = 159 K. The single-crystal X-ray structure of the low-spin and the high-spin species is presented. The magnetic data are supported by variable-temperature IR, UV/Vis/NIR, and ⁵⁷Fe Mössbauer spectra.