4-Cyanopyridine, a versatile mono- and bidentate ligand. Crystal structures of related coordination polymers determined by X-ray powder diffraction

• Published in: CrystEngComm Vol. 19; no. 16; pp. 2216 - 2228
• Main Authors: Zhao, Haishuang, Bodach, Alexander, Heine, Miriam, Krysiak, Yasar, Glinnemann, Jürgen, Alig, Edith, Fink, Lothar, Schmidt, Martin U.
• Format: Journal Article
• Language: English
• Published: 2017
• Subjects: Coordination compounds; Crystal structure; Ligands; Linearity; Nitrogen atoms; Pyridines; Transition metals; X rays
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/C7CE00425G

4-Cyanopyridine (4-CNpy, also known as isonicotinonitrile) can act as a monodentate ligand in transition metal complexes via the pyridine nitrogen atom (N py ), or as a bidentate ligand via both nitrogen atoms (N py and N CN ), resulting in a linear bridge between two metal atoms. Seven new polymeric transition metal compounds, [CuCl 2 (4-CNpy)] n ( 1b ), [MnCl 2 (4-CNpy)] n ( 2b ), [NiCl 2 (4-CNpy) 2 ] n ( 3a ), [NiCl 2 (4-CNpy)] n ( 3b ), [CoBr 2 (4-CNpy) 2 ] n ( 4a ), [NiBr 2 (4-CNpy) 2 ] n ( 5a ) and [NiBr 2 (4-CNpy)] n ( 5b ), are reported. Compounds 1b , 2b , 3b and 5b were obtained from the corresponding [M( ii )X 2 (4-CNpy) 2 ] n compounds by careful thermal decomposition under controlled conditions. Compounds 3a , 4a and 5a were synthesized from 4-cyanopyridine and transition metal halides. For all compounds, IR-spectroscopy was used to distinguish between mono- or bi-coordination of the 4-cyanopyridine ligand: in bi-coordinated compounds the asymmetric stretching vibrations of the cyano group v as (CN) are shifted to higher frequencies. All crystal structures were determined from X-ray powder diffraction data. Compounds 1b , 3a , 4a and 5a consist of polymeric chains of octahedra (double chains for 1b ; single chains for 3a , 4a and 5a ), in which 4-cyanopyridine acts as a monodentate ligand via the N py atom. Compound 1b exists in two polymorphs, a triclinic ( α - 1b ) and a monoclinic phase ( β - 1b ); both exhibit a strong Jahn–Teller distortion of the CuCl 5 N-octahedra. On the other hand, 2b , 3b and 5b exhibit layered structures, in which the 4-cyanopyridine acts as a bidentate ligand. Both nitrogen atoms coordinate to metal atoms, resulting in a linear M( ii )-py-CN–M( ii ) bridge. These are the first examples of Mn and Ni compounds in which two 3d metal atoms are connected by a 4-cyanopyridine bridge. Due to the linearity of this bridge, 4-cyanopyridine lends itself to the construction of new metal–organic frameworks.