Copper phosphates and phosphinates with pyridine/pyrazole alcohol co-ligands: Synthesis and structure

Copper phosphates, [Cu(dtbp)2(pzet)2]·H2O (1) and [Cu(dtbp)2(pyme)2] (2), as well as copper phosphinate, [Cu(dppi)2(pyet)2] (3) have been synthesized by the reaction of copper acetate with di-tert-butyl phosphate (dtbp) or diphenyl phosphinate (dppi) in the presence of pyridine base having hydroxyl group, namely, 3,5-dimethylpyrazole-2-ethanol (pzet) or 2-(hydroxymethyl)pyridine (pyme) or 2-(2-hydroxyethyl)pyridine (pyet). Single crystal X-ray diffraction studies reveal that copper ion in all the three complexes is bonded to two phosphoryl ions (P(O)O−) and two pyridine co-ligands. The crystal structure of 1 reveals that the hydroxyl group of the CH2CH2OH moiety of pzet ligand exhibits a positional disorder between the non-bonding position and the bonding position with respect to the central copper ion along the Jahn–Teller axis. Hence, the structure of 1 can be considered to exhibit both ‘square-planar’ and ‘octahedral’ coordination geometries simultaneously for the copper ion in the same complex. A similar situation for the –OH groups has not been observed in the complexes 2 and 3 and hence the coordination geometry around the copper ion is axially elongated octahedron.

Graphical abstractSynthesis and structural characterization of Cu(II) complexes bearing monoprotic phosphorus acids is presented. The use of co-ligands such as 2-pyrazole ethanol and 2-pyridine methanol/ethanol serves to block the oligomerization through chelation. Conformationally flexible ethanol side chain leads to the realization of both square planar and octahedral coordination environments for copper in the same complex.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Copper phosphonates and phosphinates have been synthesized and characterized. ► Effect of pyrazole or pyridine alcohol coligands on the product is investigated. ► Rare ethanol-in and ethanol-out form for coligand established in the same crystal. ► Molecular structures are established by single crystal X-ray diffraction studies.