Halide Influence on Molecular and Supramolecular Arrangements of Iron Complexes with a 3,5-Bis(2-Pyridyl)-1,2,4,6-Thiatriazine Ligand

A series of iron centered complexes,
namely, [Fe­(Py2TTA)­Cl2] (1), [Fe­(Py2TTA)­Br2] (2), and [Fe­(μ-F)­(Py2TTAO)­F]∞ (3), were isolated
via complexation of 3,5-bis­(2-pyridyl)-1,2,4,6-thiatriazine (Py2TTAH) with various ferric halides (e.g., FeF3,
FeCl3, and FeBr3). Comparison of the optical
and electrochemical spectroscopy, structural analysis, and magnetic
studies reveal numerous similarities between the chlorido (1) and bromido (2) derivatives, which crystallize as
discrete five-coordinate iron centered complexes with coordination
geometries that are intermediate between trigonal bipyramidal and
square base pyramid. Conversely, the fluorido derivative (3) results in a completely different structure due to oxidation of
the ligand and the formation of a one-dimensional coordination polymer
held together through a bridging fluoride ion. Consequently, the spectroscopic
and magnetic behavior of 3 differs significantly compared
with 1 and 2. Complexes 1 and 2 exhibit paramagnetic properties typical for a mononuclear S = 5/2 system with weak intermolecular antiferromagnetic
interactions at low temperatures, whereas complex 3 demonstrates
significant exchange couplings within the chain and weak antiferromagnetic
interchain interactions, which stabilize a canted antiferromagnetic
state below 4.2 K.