Synthesis, structural versatility and magnetic properties of a series of copper(ii) coordination polymers based on bipyrazole and various dicarboxylate ligands

Abstract

Seven new copper(II) coordination networks combining flexible 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) and diverse dicarboxylates, [Cu(bpz)_0.5(adip)]_n (1), [Cu₂(bpz)₄(sub)₂]_n (2), [Cu₄(bpz)_1.5(aze)·H₂O]_n (3), [Cu₂(bpz)(pta)₂(H₂O)·H₂O]_n (4), [Cu₂(bpz)(ipa)]_n (5), [Cu₂(bpz)(o-pda)₂·H₂O]_n (6), and [Cu₂(μ₃-OH)(bpz)(p-pda)_1.5·H₂O]_n (7) (H₂adip = adipic acid, H₂sub = suberic acid, H₂aze = azelaic acid, H₂pta = phthalic acid, H₂ipa = isophthalic acid, H₂o-pda = o-phenylenediacetic acid, H₂p-pda = p-phenylenediacetic acid), have been obtained under solvothermal conditions and structurally verified by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), UV-vis spectroscopy and thermogravimetric analyses (TGA). Single crystal X-ray diffraction analysis revealed that both 1 and 6 are 6-connected pcu networks (point symbol: {4¹²·6³}) based on paddle-wheel [Cu₂(COO)₄] secondary building units (SBU). Complexes 2 and 4 are 2D 4⁴-sql networks based on a single metal ion node and a binuclear [Cu₂(COO)₄(H₂O)] SBU, respectively, while complex 3 features an extremely rare 3D 5-connected hxg-d-5-C2/c (point symbol: {4²·6⁷·8}) network. Complex 5 shows a 1D tape structure built from bpz sealed 1D helical Cu₂(ipa) chains along the b axis, and 7 is a 3D 8-connected hex (point symbol: {3⁶·4¹⁸·5³·6}) network based on a centrosymmetric [Cu₄(μ₃-OH)₂(COO)₄] SBU. A thorough structural comparison of these coordination networks suggests that the coordination fashions, conformations of dicarboxylates along with the different inorganic Cu(II) SBUs simultaneously play a significant role in constructing the diverse networks. Variable-temperature magnetic susceptibility data denote that 4 and 7 display antiferromagnetic interactions in binuclear [Cu₂(COO)₄(H₂O)] and [Cu₄(μ₃-OH)₂(COO)₄] SBUs. Moreover, the thermal stability and UV-vis spectra of 1–7 are discussed in detail.