Mononuclear and binuclear sandwich copper(II) complexes with poly(pyrazolyl)borate ligands: Syntheses, structures and properties

A series of Cu(II) complexes Cu2[μ-pz]2[HB(pz)3]2 (1), Cu[H2B(pz)2]2 (2), Cu[HB(pz)3]2 (3), Cu[HB(pzMe2)3]2 (4), Cu[B(pz)4]2 (5) (pz = pyrazole), have been synthesized and characterized by elemental analysis, IR, UV–vis, X-ray diffraction, thermal analysis and theoretical analysis. The IR spectra give the Cu–N vibration modes at 322, 366, 344, 387, and 380 cm−1 in complexes 1–5, respectively. The UV spectra show all the complexes have same UV absorption at 232 nm; there is another band at 332 nm for complexes 1, 2 and 4, while for complexes 3 and 5, the bands are at 272 and 308 nm, respectively. Complex 1 has a binuclear structure in which two pyrazole ligands bridge two Cu-Tp units. In 2–5, the Cu(II) centers are coordinated with dihydrobis(pyrazolyl)borate (Bp), hydrotris(pyrazolyl)borate (Tp), hydrotris(3,5-Me2pyrazolyl)borate (Tp′), tetrakis(pyrazolyl)borate (Tkp) respectively to form a mononuclear structure. The results of thermal analysis for complexes 1–5 are discussed too.