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 1D-zigzag chains which pack into 2D sheets. In {[Cu(3)(OMe)(MeOH)][CF3SO3].MeOH}n, the solvent is both a ligand and 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 (STM). On Au(111), 1 and 2 assemble into close-packed assemblies, whilst 3 forms a regular porous network. The deposition of Cu ad-atoms 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 ad-atoms 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.