NaCo(H2PO2)3: Crystal structure and physical study

• NaCo(H2PO2)3 is newly reported.
• Raman spectroscopy confirmed existence of H2PO22−.
• NaCo(H2PO2)3 was tested as electrode’s material and turned inactive in 2.4–4.5 V vs. Na/Na+.

NaCo(H2PO2)3 was synthesized in solution and its structure was studied by single-crystal X-ray diffraction. It crystallizes in the cubic space group P213 (#198), Z = 4, a = 9.2563(16) Å, V = 793.1(2) Å3. Final residual factors of the refined structure model R/Rw were 0.0367/0.0941. The cations Na+ and Co2+ are both octahedrally coordinated. [NaO6] and [CoO6] share edges to form channels propagating along [1,−1, −1] with the [H2PO2] pseudo-pyramids adjusted inside the channels to the above mentioned octahedra. The IR and Raman spectroscopic studies show the expected bands of the hypophosphite anion. NaCo(H2PO2)3 did not show any electrochemical activity under the electrochemical test conditions (2.4–4.5 V vs. Na/Na+).

The structure of NaCo(H2PO2)3 forms a 3D network built upon [NaO6] and [CoO6] octahedrons and [H2PO2] tetrahedrons which share corners and edges giving rise to a zig-zag channels running along [100]. One loop of this network can be formulated as [Co5H60Na5O60P30]. The PH bond was evidenced by the Raman study. The title compound was found inactive as electrode material for Li-Batteries.Figure optionsDownload as PowerPoint slide