Compartmental pyrazolate ligands providing two adjacent tris(pyridylalkyl)amine-type binding pockets and their dicopper(II) fluoride complexes featuring extremely short intramolecular O–H⋯F bridges

A set of pyrazolate-based compartmental ligands HL2–HL5 with pendent (pyridylalkyl)amine side arms in the 3- and 5-positions of the pyrazole has been prepared. The ligands differ by the number and lengths of the pyridylalkyl arms, and they can be described as dinucleating versions of well-known ligands such as tris(pyridylmethyl)amine (tpma) or tris(pyridylethyl)amine (tpea). Reaction of HL2, HL3 or HL5 with Cu(BF4)2 · 6H2O in the presence of base causes fluoride abstraction from the tetrafluoroborate and gives dicopper(II) complexes 1, 2, and 3a and b, respectively, which feature extremely short intramolecular F⋯HOMe or F⋯HOH bridges (d(F⋯O)=2.384(6)–2.507(3)). Molecular structures of all four complexes have been elucidated by X-ray crystallography and are compared to their mononuclear analogues. The influence of the intramolecular F⋯HO bridge on Cu–F and Cu–O bond lengths as well as on other structural characteristics is discussed.