Thermally triggered solid-state single-crystal-to-single-crystal structural transformation accompanies property...

Area of Science:

• Coordination Chemistry
• Materials Science
• Solid-State Chemistry

Background:

• The study focuses on the transformation of a 1D copper complex, [(CuL0.5H2O)⋅H2O]n, derived from 2,2'-bipyridine-3,3',6,6'-tetracarboxylic acid (H4L).
• This complex exhibits interesting structural and magnetic properties.

Purpose of the Study:

• To investigate the thermally triggered single-crystal-to-single-crystal (SCSC) transformation of the 1D complex to a 3D anhydrous complex.
• To characterize the structural and property changes associated with this transformation.
• To evaluate the catalytic performance of both complexes in the synthesis of 2-imidazolines derivatives.

Main Methods:

• Single-crystal X-ray diffraction
• Thermogravimetric (TG) analysis
• Powder X-ray diffraction (PXRD) and variable-temperature PXRD (VT-PXRD)
• IR spectroscopy
• Magnetic analyses

Main Results:

• The irreversible SCSC transformation from the 1D hydrated complex (1) to the 3D anhydrous complex (2) was confirmed. The 1D chain structure is retained, but coordination geometries around Cu(II) ions change from distorted trigonal bipyramid to distorted square pyramid with the removal of coordinated water and formation of new carboxylate-Cu bonds.
• Magnetic properties shifted from antiferromagnetism to weak ferromagnetism due to a new Cu-O-C-O-Cu bridge.
• Both complexes demonstrated high catalytic activity for 2-imidazolines synthesis and recyclability, with complex 2 showing lower activation temperature than complex 1.

Conclusions:

• The SCSC transformation leads to significant structural and magnetic property changes in the copper complex.
• The resulting anhydrous complex exhibits enhanced catalytic efficiency for 2-imidazolines synthesis.
• A potential pathway for the observed SCSC structural transformation is proposed.