Lattice Vibrational Anisotropy in a Potentially Porous Diiron Paddle-Wheel Coordination Polymer

A new three-dimensional potentially porous coordination polymer {[Fe₂(bdc)₄(Me₄bpz)₂]·solv}[1], where bdc = terephthalic acid and Me₄bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole, was successfully synthesized. Single-crystal X-ray structural elucidation confirmed that [1] comprises 2-fold interpenetrated nets with accessible pores for solvent exchange. Variable-temperature Mössbauer spectroscopy revealed a temperature dependence of relative line intensities of the quadrupole doublet spectral profile associated with the iron sites in the paddle-wheel structure. As the temperature decreased, the asymmetry in line intensities of the quadrupole doublet diminished. This is attributable to vibrational anisotropy (Goldanskii-Karyagin effect), which may be important for pore dynamics and sorption characteristics.