Two Bulky Conjugated 4′-(4-Hydroxyphenyl)-4,2′:6′,4′′-terpyridine-based Layered Complexes: Synthesis, Structure, and Photocatalytic Hydrogen Evolution Activity

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)

The isomers 4′-(4-(trifluoromethyl)phenyl)-4,2′:6′,4″-terpyridine (1), 4′-(3-(trifluoromethyl)phenyl)-4,2′:6′,4″-terpyridine (2), 4′-(4-(trifluoromethyl)phenyl)-3,2′:6′,3″-terpyridine (3), and 4′-(3-(trifluoromethyl)phenyl)-3,2′:6′,3″-terpyridine (4) have been prepared and characterized. The single crystal structures of 1 and 2 were determined. The 1D-polymers [Cu2(hfacac)4(1)2]n·2nC6H4Cl2 (Hhfacac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione), [Cu(hfacac)2(2)]n·2nC6H5Me, [Cu2(hfacac)4(3)2]n·nC6H4Cl2, [Cu2(hfacac)4(3)2]n·nC6H5Cl, and [Cu(hfacac)2(4)]n·nC6H5Cl have been formed by reactions of 1, 2, 3 and 4 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(1)2]n·2nC6H4Cl2 and [Cu(hfacac)2(2)]n·2nC6H5Me are zig-zag chains and the different substitution position of the CF3 group in 1 and 2 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(3)2]n·nC6H4Cl2 and [Cu(hfacac)2(4)]n·nC6H5Cl differs, leading to different structural motifs in the 1D-polymer backbones. In [Cu(hfacac)2(4)]n·nC6H5Cl, the peripheral 3-CF3C6H4 unit is accommodated in a pocket between two {Cu(hfacac)2} units and engages in four C–Hphenyl...F–Chfacac contacts which lock the phenylpyridine unit in a near planar conformation. In [Cu2(hfacac)4(3)2]n·nC6H4Cl2 and [Cu(hfacac)2(4)]n·nC6H5Cl, 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 1 and 2. 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 3 or 4.

The terpyridine isomer game: from chelate to coordination network building block

The first 4,2':6',4''-terpyridine (4,2':6',4''-tpy) containing coordination polymer was reported over 20 years ago and in the last decade, there has been increased interest in the use of ditopic 4,2':6',4''-tpy ligands as linkers in coordination polymers and 2D-networks. Functionalization in the 4'-position of 4,2':6',4''-tpy is synthetically straightforward, giving access to a large suite of building blocks. Less well explored is the coordination chemistry of 3,2':6',3''-tpy ligands which exhibit greater conformational flexibility than 4,2':6',4''-tpy. One approach to making the transition from 2D- to 3D-networks is to utilize tetratopic bis(4,2':6',4''-tpy) and bis(3,2':6',3''-tpy) ligands which act as 4-connecting nodes. In this highlight, we survey recent progress towards a better understanding of the design principles associated with the use of ditopic and tetratopic 4,2':6',4''-tpy and 3,2':6',3''-tpy containing ligands and their roles both as linkers and nodes in coordination assemblies.