Crystal structures, proton conductivities and luminescence of two organic-inorganic hybrid materials based on Keggin-type clusters and Cu(II)/Cu(I)-bis(hydroxymethyl)-2,2′-bipyridine complexes

Abstract

Two proton-conductive and luminescent organic-inorganic hybrid materials, {[Cu^(II)(bhmbpy)(H₂O)(Cl)_0.5(CH₃CN)]₂[PW^(VI)₁₀W^(V)₂O₃₉]}·4H₂O(1) and {H₂[Cu^(I)(bhmbpy)₂(Cl)Cu^(I)(bhmbpy)₂][PW₁₂O₄₀]}·7H₂O (2) (where bhmbpy is bis(hydroxymethyl)-2,2′-bipyridine), were synthesized at room temperature. The two products were characterized by infrared spectroscopy, X-ray single-crystal diffraction, X-ray powder diffraction, elemental and thermogravimetric analyses. The proton conductivities and luminescence of 1 and 2 were studied by using alternating-current impedance spectroscopy and luminescence spectroscopy, respectively. X-ray diffraction analysis revealed that 1 includes a decorated polyanion chain {[Cu^(II)(bhmbpy)(H₂O)(Cl)_0.5(CH₃CN)]₂[PW^(VI)₁₀W^(V)₂O₃₉]}_n and forms a three-dimensional network structure depending on short Cl…Cl contacts and hydrogen-bonding interactions. X-ray diffraction analysis revealed that 2 includes a butterfly-like bi-nuclear copper cluster unit with a Cl-bridge, [Cu^(I)(bhmbpy)₂(Cl)Cu^(I)(bhmbpy)₂]⁺, and forms a three-dimensional network structure depending on hydrogen-bonding interactions. [PW₁₂O₄₀]^3– anions fill in the network based on hydrogen-bonding and electrostatic interactions. In them, the bhmbpy acts as a bidentate nitrogen donor ligand in the chelating fashion to coordinate with the Cu(II) center in 1 and the Cu(I) center in 2. The bhmbpy in 2 successfully constrains the Cu(I) within a rigid environment in a tetragonal-pyramidal geometry. The two compounds exhibit good proton conductivity (10⁻⁴ S·cm⁻¹) at 100 °C in the relative humidity range 35–98%. Their luminescence behaviors in the solid state at room temperature have also been investigated. Upon excitation at 384 nm, 1 exhibits three emission peaks centered at 439, 507 and 566 nm. When excited at 364 nm, 2 displays three emission peaks centered at 443, 501 and 553 nm.

Keywords:

• Polyoxotungstates
• crystal structure
• hybrid materials
• 4,4′-bis(hydroxymethyl)-2,2′-bipyridine
• copper complexes
• proton conductivity

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (grant numbers: 21501047 and 21171050).