The Different Faces of 4′-Pyrimidinyl-Functionalized 4,2′:6′,4′′-Terpyridines: Metal–Organic Assemblies from Solution and on Au(111) and Cu(111) Surface Platforms

A comparative investigation
of crystal growth from solution and
on-surface assembly in vacuo between copper and three
4′-(2-R-pyrimidin-5-yl)-4,2′:6′,4′′-terpyridines,
with R = H (1), Me (2), or Et (3), is presented. In solution, ligand 3 combines with
copper­(II) acetate or copper­(I) triflate in MeOH solution to give
[Cu2(OAc)4(3)]n or {[Cu­(3)­(OMe)­(MeOH)]­[CF3SO3]·MeOH}n. In [Cu2(OAc)4(3)]n, paddle-wheel
{Cu2(μ-OAc)4} nodes direct the assembly
of one-dimensional (1D) zigzag chains which pack into two-dimensional
(2D) sheets. In {[Cu­(3)­(OMe)­(MeOH)]­[CF3SO3]·MeOH}n, the solvent is
a ligand and also generates {Cu2(μ-OMe)2} units which function as planar 4-connecting nodes to generate a
2D (4,4) net with ligand 3. On Au(111) or Cu(111) surfaces in vacuo, no additional solvent or anions are involved in
the assembly. The different substituents in 1, 2, or 3 allow precise molecular resolution imaging
in scanning tunneling microscopy. On Au(111), 1 and 2 assemble into close-packed assemblies, while 3 forms a regular porous network. The deposition of Cu adatoms results
in reorganization leading to ladder-shaped surface metal–organic
motifs. These on-surface coordination assemblies are independent of
the 4′-substituent in the 4,2′:6′,4′′-tpy
and are reproduced on Cu(111) where Cu adatoms are available during
the deposition and relaxation process at room temperature. Upon annealing
at elevated temperatures, the original surface assemblies of 1 and 3 are modified and a transition from ladders
into rhomboid structures is observed; for 2, a further
quasi-hexagonal nanoporous network is observed.