Divalent metal phosphonate coordination polymers constructed from a dipiperidine-based bisphosphonate ligand

Area of Science:

• Coordination Chemistry
• Materials Science
• Crystallography

Background:

• The synthesis of novel coordination polymers with diverse structures and properties is an active area of research.
• Metal phosphonates are a class of coordination polymers with potential applications in various fields.
• Understanding the factors that control the formation and structure of these materials is crucial for their targeted design.

Purpose of the Study:

• To synthesize and characterize new metal phosphonate coordination polymers using the 4,4'-dipiperidine-N,N'-bis(methylenephosphonic acid) ligand.
• To investigate the structural diversity of these compounds, including layered, chain, and polymorph structures.
• To explore the influence of reaction conditions (solvent, temperature, irradiation) on the resulting structures and ligand protonation states.

Main Methods:

• Solvothermal and hydrothermal synthesis techniques were employed.
• Characterization involved elemental analyses and single-crystal X-ray diffraction.
• Microwave irradiation was used to obtain a polymorph of a cobalt compound.

Main Results:

• Seven new metal phosphonate coordination polymers were successfully synthesized with various divalent metal ions (Zn, Co, Mn, Sn).
• Diverse structural motifs were observed, including layered structures (Zn, Co, α/β-Co, Sn), a chain motif (Mn), and a layered structure with voids (Sn).
• The ligand's protonation state and coordination mode (N-binding vs. protonated N) varied depending on the metal ion and reaction conditions.
• Partial decomposition of the ligand was observed in reactions with Sn(II) oxalate, leading to phosphate incorporation.

Conclusions:

• The ligand 4,4'-dipiperidine-N,N'-bis(methylenephosphonic acid) can form diverse coordination polymer structures with different metal ions.
• Reaction conditions, including solvent choice and temperature, play a critical role in determining the final structure and protonation state of the coordination polymers.
• The study highlights the tunability of metal phosphonate structures through synthetic control.