Variable behaviour of a flexible bispyrazole ligand: A Co(II) polymer and a unique Cu(II) penta-coordinated dimer

Hoping to highlight the flexibility of a bispyrazole ligand possessing an ether chain including a weak spot (1,2-bis([4-(3,5- dimethyl-1H- pyrazol-1- yl) -2-oxabutyl]benzene (L)), its reactivity against coordinatively flexible metal centres has been assayed. Thus Co(II) and Cu(II) coordination complexes of L have been synthesized and fully characterized by analytical and spectroscopical methods. Their X-ray crystal struc-ture elucidation has allowed to ascertain that while the Co(II) compound {[Co(L)Cl-2]center dot 1/2H(2)O}(n) (1) possesses a polymeric structure, much like its Zn(II), Cd(II) and Hg(II) analogues, the Cu(II) compound [Cu2LCl4] (2) displays a completely unexpected dimeric architecture. The previously unreported coordi-nation mode of the ligand in the Cu(II) compound causes dramatical changes in the morphology of the resulting complexes. Their crystal structures are discussed in deep, and the causes behind their differing architectures are examined through comparison with bibliographical references. (C) 2023 The Authors. Published by Elsevier B.V.