Synthesis, structure, and properties of a new Co(II) diphosphonate based on auxiliary ligand 2,2'-bipyridine

ABSTRACT

The example of Co(II)-N-heterocyclic complex based on 1-hydroxyethylidenediphosphonic acid (H₅L = CH₃C(OH)(PO₃H₂)₂), namely [Co₂(H₃L)₂(2,2′-bipy)₂] 1, has been solvothermally isolated using the second ligand 2,2'-bipyridine (2,2'-bipy) and characterized by powder X-ray diffraction (PXRD), elemental analysis, IR, and thermal gravimetric analyses. The single-crystal X-ray diffractions show that complex 1 possesses a 0-D structure built from binuclear unit [Co₂(O–P–O)₂] by μ₂-(O–P–O) bridge. Then, H-bonding and π–π stacking interactions further expand this 0-D structure into a 3-D supramolecular framework. Fluorescent measurements reveal that the maximum emission peak is centered at 421.5 nm, mainly deriving from intraligand π*–π transition state of the second ligand 2,2'-bipy (λ_em = 419.5 nm, λ_ex = 235 nm). Magnetism data indicate that 1 exhibits ferromagnetic behavior within binuclear Co(II) unit via μ₂-(O–P–O) bridge in syn-anti mode.

KEYWORDS:

• Co(II)-diphosphonate
• synthesis
• structure
• fluorescence
• magnetism

Funding

The authors are grateful to the financial support from Jiangsu province college students innovation and entrepreneurship training programs, Open Fund of Jiangsu Key Laboratory for Chemistry of Low-dimensional Materials, Cultivation Fund of High Level Project of Huaiyin Normal University, the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province and National Natural Science Foundation of China (Projects Nos. 201410323004Z, JSKC13127, 11HSGJBZ12, 14KJA150003, and 21202058).