A Comprehensive Review on Cu(II) Complexes With Pyrazine or Pyrazine Derivatives: Synthesis, Characterization, Crystal Engineering, Magnetic, and Biological Applications

ABSTRACT We report on Cu(II)‐PYZ (Pyrazine) or derivative complexes, covering review areas e.g., synthetic advances; rationales for the advantages/disadvantages of several synthetic techniques; characterization; and crystal engineering. It covers the review period from 1970 to date, including initial research on PYZ ligands by C.W. REIMANN et al. The review addressed a synthetic weakness in complex solvent media such as H 2 O, DMF, or ethanol, and highlights the need for greener or other advanced synthetic methods. Moreover, the review explains PYZ's bridging affinity to Cu(II) centers (2N atoms), resulting in 1D/2D/3D infinite networks. This stems from PYZ's weak σ‐donating ability and the flexible coordination geometries of Cu(II) ions, which affect the complexes' stability and magnetic properties. Thus, the comparative metric magnetic exchange coupling constant ( J ) shows that structural dimensionality directly dictates coupling strength, and the complexes transition from weak antiferromagnetic frameworks to highly ordered ones. Electronic limitations such as orbital overlap, electron‐electron repulsion, and Jahn‐Teller distortions govern magnetic behavior. Furthermore, Cu(II) complexes show considerable promise as anticancer and antimicrobial agents, where stereochemistry and the PYZ ligands electron‐withdrawing/donating groups influence monomeric vs. polymeric networks, affecting biological properties, solubility, cellular uptake, and complex stability in biological fluids. Finally, the review explains limitations and future challenges.