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)

Abstract

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.

Does the Central Nitrogen Atom Make a Difference? A Comparison of Non‐Coordinating Pyridine and Benzene Spacers in Multitopic Ligands

“…have commented: “Planar bis(β‐diketonato) complexes can accept additional ligands at the axial sites keeping their planar structures.” [78] This preference (while not guaranteed) can be used to direct the assembly of 1D‐coordination polymers and circumvents the competitive assembly of metallamacrocycles when using 4,2′:6′,4“‐tpy ligands (see Section 2.4). This strategy is demonstrated in [Co(acac) 2 ( 20 )] n ( Figure 17 a ), [78] [Cu(hfacac) 2 ( 46 )] n ( Figure 17 b ), [79] [Cu(hfacac) 2 ( 47 )] n , [79] [Cu(hfacac) 2 ( 48 )] n , [80] and [Cu(hfacac) 2 ( 49 )] n , [80] (all structurally like [Cu(hfacac) 2 ( 46 )] n , Figure 17 b ). While the structure of [Zn(acac) 2 ( 50 )] n ( Figure 17 c ) resembles those cited above, it is noteworthy that 4′‐(4‐(pyrimidin‐5‐yl)phenyl)‐4,2′:6′,4′′‐terpyridine ( 50 ) coordinates through one pyridine and one pyrimidine ring rather than through the outer rings of the 4,2′:6′,4′′‐tpy domain [81] …”

“…Ligand 52 (Scheme 16) adopts conformation II (Scheme 4) in [Cu(hfacac) 2 (52)] n and the structure of the 1D-coordination polymer resembles that of [Cu 2 (OAc) 4 (34)] n (34 with R = n-hexyl or n-heptyl), [Cu 2 (OAc) 4 (38)] n , [Cu 2 (OAc) 4 (39)] n , and [Cu 2 (OAc) 4 (40)] n (compare Figures 18a and 12c, and see Table 1). [80] In contrast, ligand 53 exhibits conformation I (Scheme 4) in [Cu(hfacac) 2 (53)] n and the 1D-chain resembles that of [Cu 2 (OAc) 4 (34)] n (34 with R = Me) shown in Figure 12b. [80] Conformer I is also observed for the 3,2':6',3''-tpy unit in [Cu-(hfacac) 2 (54)] n , but in this case, a cis-arrangement of Ndonors at the Cu(II) center is observed (Figure 18b).…”

“…[80] In contrast, ligand 53 exhibits conformation I (Scheme 4) in [Cu(hfacac) 2 (53)] n and the 1D-chain resembles that of [Cu 2 (OAc) 4 (34)] n (34 with R = Me) shown in Figure 12b. [80] Conformer I is also observed for the 3,2':6',3''-tpy unit in [Cu-(hfacac) 2 (54)] n , but in this case, a cis-arrangement of Ndonors at the Cu(II) center is observed (Figure 18b). [79] Again, we note that Toledo et al suggest that packing requirements may dictate the preference for a cis versus trans-arrangement of N-donors.…”

Multitopic 3,2′:6′,3′′-terpyridine ligands as 4-connecting nodes in two-dimensional 4,4-networks

“…This journal is © The Royal Society of Chemistry 2022 (hfacac) 4 (L2) 2 ] n •nC 6 H 5 Cl the 3,2′:6′,3″-tpy domains exhibit conformation C, while with [Cu(hfacac) 2 (L2)] n •nC 6 H 5 Cl conformation B is adopted (Scheme 1). 26 Structures of ligands L1 and L2 are shown in Scheme 2.…”

Cornerstones in Contemporary Inorganic Chemistry

“…The theme of copper coordination polymers is continued in the paper by Housecroft et al, which elegantly demonstrated how ligand conformation can dictate the way in which coordination polymers pack, even when such packing is governed by relatively weak intermolecular interactions [2]. The ligands in question are isomers of terpyridine (4,2 :6 ,4 and 3,2 :6 ,3 ), and it is the positions of the N donor atoms that are crucial in determining the type of 1D chain that is observed in the resulting coordination polymers formed by reactions with Cu(hfacac) 2 ]•H 2 O.…”