Concomitant dimorphism in poly[di- μ -azido-(5,5 ′ -dimethyl-2,2 ′ -bipyridine)iron(II)]

The title metal – organic polymer, catena-poly[[(5,5 ′ -dimethyl-2,2 ′ -bipyridine- κ 2N,N ′ )iron(II)]-di- μ -azido- κ 2N1:N3-[(5,5 ′ -dimethyl-2,2 ′ -bipyridine- κ 2N,N ′ )iron(II)]-di- μ -azido- κ 2N1:N1], [Fe(N3)2(C12H12N2)]n, features alternating μ -1,1 (end-on mode of coordination) and μ -1,3 (end-to-end mode of coordination) double azide bridges, forming chains running in the [100] direction. The octahedral coordination geometry around the FeII centre is completed by a bidentate 5,5 ′ -dimethyl-2,2 ′ -bipyridine ligand. Two polymorphs for this compound were obtained from the crude reaction product, the first in the space group P\overline{1} and the other in P21/c. The molecular and crystal structures are very similar for both forms, the main difference being that the eight-membered Fe( μ -1,3-N3)2Fe metallacycle formed with end-to-end azide ligands has a nearly flat conformation in the triclinic form and a chair conformation in the monoclinic form. In spite of this geometric difference, both forms have the same density, the same packing index and similar arrangements of the one-dimensional chains in the crystal. As a consequence, they also share very similar Hirshfeld surfaces and fingerprint plots. However, a density functional theory (DFT) computational study showed that the monoclinic form is more stable than the triclinic form by ca 30.5   kJ   mol − 1.

Source: Acta Crystallographica Section C - July 21, 2022 Category: Chemistry Authors: Setifi, Z. Bern è s, S. Geiger, D.K. Setifi, F. Reedijk, J. Tags: concomitant polymorphs inorganic polymer azide bridge concomitant crystallization crystal structure DFT research papers Source Type: research