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

Abstract

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.