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

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Tetratopic ligands are crucial building blocks for constructing complex coordination networks.
• The precise arrangement of metal centers and ligands dictates the resulting network topology and properties.
• Understanding structure-property relationships in metal-organic frameworks is essential for materials design.

Purpose of the Study:

• To synthesize and characterize novel tetratopic ligands: 1,4-bis(2-phenylethoxy)-2,5-bis(3,2':6',3''-terpyridin-4'-yl)benzene (1) and 1,4-bis(3-phenylpropoxy)-2,5-bis(3,2':6',3''-terpyridin-4'-yl)benzene (2).
• To investigate the self-assembly of coordination polymers using these ligands with copper(II) and zinc(II) metal precursors.
• To elucidate the structural characteristics and network topology of the resulting metal-organic assemblies.

Main Methods:

• Synthesis and full characterization of tetratopic ligands 1 and 2.
• Crystal growth by layering of ligands with metal precursors ([M(hfacac)2]·xH2O, M = Cu, Zn).
• Single-crystal X-ray diffraction analysis to determine the solid-state structures.

Main Results:

• Formation of five distinct coordination polymers: [Cu2(hfacac)4(1)], [Zn2(hfacac)4(1)], [Cu2(hfacac)4(2)], [Cu2(hfacac)4(2)], and [Cu2(hfacac)4(2)].
• Single-crystal X-ray analysis revealed the assembly of planar (4,4)-nets, with ligands 1 or 2 acting as nodes.
• Copper(II) centers exhibited trans-arrangement of N-donors, while zinc(II) centers showed cis-arrangement, influencing the network architecture.

Conclusions:

• The synthesized tetratopic ligands successfully directed the formation of (4,4)-net coordination polymers.
• The choice of metal ion (Cu(II) vs. Zn(II)) dictates the coordination geometry around the metal center.
• Differences in metal coordination geometry modify the supramolecular assembly architecture without altering the fundamental (4,4)-network topology.