Isomeric 4,2′:6′,4″- and 3,2′:6′,3″-Terpyridines with Isomeric 4′-Trifluoromethylphenyl Substituents: Effects on the Assembly of Coordination Polymers with [Cu(hfacac)₂] (Hhfacac = Hexafluoropentane-2,4-dione)

• Main Authors: Giacomo Manfroni, Simona S. Capomolla, Alessandro Prescimone, Edwin C. Constable, Catherine E. Housecroft
• Format: Article
• Language: English
• Published: MDPI AG 2021-07-01
• Series: Inorganics
• Subjects: copper; 4,2′:6′,4″-terpyridine; 3,2′:6′,3″-terpyridine; coordination polymer; isomers
• Online Access: https://www.mdpi.com/2304-6740/9/7/54

The isomers 4′-(4-(trifluoromethyl)phenyl)-4,2′:6′,4″-terpyridine (<b>1</b>), 4′-(3-(trifluoromethyl)phenyl)-4,2′:6′,4″-terpyridine (<b>2</b>), 4′-(4-(trifluoromethyl)phenyl)-3,2′:6′,3″-terpyridine (<b>3</b>), and 4′-(3-(trifluoromethyl)phenyl)-3,2′:6′,3″-terpyridine (<b>4</b>) have been prepared and characterized. The single crystal structures of <b>1</b> and <b>2</b> were determined. The 1D-polymers [Cu₂(hfacac)₄(<b>1</b>)₂]<i>_n</i>·2<i>n</i>C₆H₄Cl₂ (Hhfacac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione), [Cu(hfacac)₂(<b>2</b>)]<i>_n</i>·2<i>n</i>C₆H₅Me, [Cu₂(hfacac)₄(<b>3</b>)₂]<i>_n</i>·<i>n</i>C₆H₄Cl₂, [Cu₂(hfacac)₄(<b>3</b>)₂]<i>_n</i>·<i>n</i>C₆H₅Cl, and [Cu(hfacac)₂(<b>4</b>)]<i>_n</i>·<i>n</i>C₆H₅Cl have been formed by reactions of <b>1</b>, <b>2</b>, <b>3</b> and <b>4</b> with [Cu(hfacac)₂]·H₂O under conditions of crystal growth by layering and four of these coordination polymers have been formed on a preparative scale. [Cu₂(hfacac)₄(<b>1</b>)₂]<i>_n</i>·2<i>n</i>C₆H₄Cl₂ and [Cu(hfacac)₂(<b>2</b>)]<i>_n</i>·2<i>n</i>C₆H₅Me are zig-zag chains and the different substitution position of the CF₃ group in <b>1</b> and <b>2</b> does not affect this motif. Packing of the polymer chains is governed mainly by C–F...F–C contacts, and there are no inter-polymer π-stacking interactions. The conformation of the 3,2′:6′,3″-tpy unit in [Cu₂(hfacac)₄(<b>3</b>)₂]<i>_n</i>·<i>n</i>C₆H₄Cl₂ and [Cu(hfacac)₂(<b>4</b>)]<i>_n</i>·<i>n</i>C₆H₅Cl differs, leading to different structural motifs in the 1D-polymer backbones. In [Cu(hfacac)₂(<b>4</b>)]<i>_n</i>·<i>n</i>C₆H₅Cl, the peripheral 3-CF₃C₆H₄ unit is accommodated in a pocket between two {Cu(hfacac)₂} units and engages in four C–H_phenyl...F–C_hfacac contacts which lock the phenylpyridine unit in a near planar conformation. In [Cu₂(hfacac)₄(<b>3</b>)₂]<i>_n</i>·<i>n</i>C₆H₄Cl₂ and [Cu(hfacac)₂(<b>4</b>)]<i>_n</i>·<i>n</i>C₆H₅Cl, π-stacking interactions between 4′-trifluoromethylphenyl-3,2′:6′,3″-tpy domains are key packing interactions, and this contrasts with the packing of polymers incorporating <b>1</b> and <b>2</b>. We use powder X-ray diffraction to demonstrate that the assemblies of the coordination polymers are reproducible, and that a switch from a 4,2′:6′,4″- to 3,2′:6′,3″-tpy metal-binding unit is accompanied by a change from dominant C–F...F–C and C–F...H–C contacts to π-stacking of arene domains between ligands <b>3</b> or <b>4</b>.