Synthesis, structure, and magnetic properties of the halide-bridged dimeric complex [(bpmaL₁)Fe(μ-Cl)Cl]₂

Complexation of FeCl₂·4H₂O with N,N-Bis{(1-H pyrazole-1-yl)methyl}aniline [bpmaL₁] gave air-stable dichloro-bridged binuclear iron(II) species (1a) having five-coordinated iron, which was characterised by X-ray crystallography and magnetic susceptibility. The geometry at each iron centre of 1a is a distorted trigonal bipyramid with two equivalent half-molecules providing overall C_i symmetry. One of the pyrazolyl nitrogen atoms (N1) and a chlorine atom (Cl2)^# form one apex of the distorted trigonal bipyramid. The magnetic parameters indicated only a weak antiferromagnetic coupling, despite the presence of two chloro ions, and dominant zero-field-splitting parameters. The relatively long Fe⋯Fe distance of 3.8118(6) Å within the chloro-bridged dimer excludes direct interaction between the iron(II) ions. Thus, the antiferromagnetic coupling between the two iron(II) ions of 1a is attributed to superexchange through the chloride ions. Compared to the analogous cobalt complexes, the activity of α-olefin polymerization towards ethylene, norbornene, 1-octene and methyl methacrylate (MMA) was virtually zero, 1a is the first bis-pyrazole based dinuclear and five-coordinated iron(II) complex.