Rational Design and Self-Assembly of Molecular Squares Featuring Cp*M (M = Rh, Ir) Vertices Bridged by Phenanthroline-Derived Ligands

Abstract

Herein, we describe the design and synthesis of three tetranuclear complexes, [(Cp*Rh)­(L 1 )]4­(OTf)4 (1a, HL 1 = 2-(pyridin-4-yl)-1H-imidazo­[4,5-f]­[1,10]­phenanthroline), [(Cp*Ir)­(L 1 )]4­(OTf)4 (1b), and [(Cp*Rh)­(L 2 )]4­(OTf)4 (2, HL 2 = 2-(4-(pyridin-4-yl)­phenyl)-1H-imidazo­[4,5-f]­[1,10]­phenanthroline). Owing to the precise design of the phenanthroline-derived ligands, these complexes exhibit perfect square-shaped structures with side lengths of 13.53, 13.57, and 17.95 Å, respectively. These molecules orderly align and assemble into square-shaped, one-dimensional nanotubes. The molecular structures and arrangement of the nanotubes were evidenced by single-crystal X-ray diffraction. Solution behavior was studied by NMR spectroscopy. Fourier transform infrared spectroscopy and elemental analysis were also employed to characterize these complexes.

Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions

“…Phendione 867 is probably one of the most versatile building blocks ever used to functionalize phen. A plethora of articles describes the synthesis of 867 . ,,,− The common point to all the reported procedures is the strongly acidic (ensuring phen is protonated and increasing the solubility) and oxidizing conditions. Phendione can be further transformed into precious synthons for numerous applications.…”

“…From these pioneering works, some minor variations in this synthesis of 867 have been described. Some authors first dissolve phen in sulfuric acid then add sodium bromide and then nitric acid (refs , , , − , , , ), others first mixed phen with potassium or sodium bromide and cool down the mixture before adding sulfuric acid and nitric acid at −78 (refs , , , , ) or 0 °C (refs , , , , , ,, , , , − ,,, , , , − , , , , ), and others cool the sulfuric acid solution at 0 or −78 °C and add a mixture of phen and KBr or NaBr then add nitric acid (refs , , , , , , , , − ). Other reports advise to cool the sulfuric acid and nitric acid at 0 °C before phen and NaBr are added to the mixture and heated, , or some directly prepare the phen and KBr solid mixture and add the latter to the acidic mixture before heating. , Finally, some authors first dissolved phen in sulfuric acid then add potassium bromide; in this case, no nitric acid was used before heating the reaction. , …”

“…The design of the imidazo­[4,5- f ]­[1,10-phenanthroline] ligands relies on the condensation of 867 and aromatic aldehydes. Many variations have been made on the aldehyde backbone for various applications (biology (refs , , , , , , , , ), detection/sensors (refs , , , , , , , ), supramolecular chemistry (refs − , , , ), coordination chemistry (refs , , − , , , ), non-linear optics, photoinduced electron transfer, ,, etc.) and thus only selected examples will be presented.…”

Redox‐Active Supramolecular Heteroleptic M4L2L′2 Assemblies with Tunable Interior Binding Site

“…There are examples of homoleptic squares using as ingle ditopic ligand based on porphyrin, [1] perylene bisimide [2] or 4,4'-bipyridine frameworks. [3][4][5] By using two different ligands in as ingle assembly,h eteroleptic M 4 L 2 L' 2 analogues are accessible that offer more control over the dimensions of the molecular assemblies. [6][7][8][9][10] To date, supramolecular interactions and host-guest chemistry with 2D architectures is relatively limited in comparison to 3D-analogues.…”

“…Over the last decades, numerous M 4 L 4 metallo‐squares have been synthesized. There are examples of homoleptic squares using a single ditopic ligand based on porphyrin, perylene bisimide or 4,4′‐bipyridine frameworks . By using two different ligands in a single assembly, heteroleptic M 4 L 2 L′ 2 analogues are accessible that offer more control over the dimensions of the molecular assemblies .…”