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February 12, 2026Open Access

Structure and optical properties of a trimetallic cobalt–molybdenum–sodium metal–organic framework

M1Moore, Benjamin, 1748-1816University of Manchester JTJeremiah P. TideyUniversity of Warwick CHCraig I. HileyUniversity of Warwick

Key Points

Investigate the structure and optical properties of a trimetallic cobalt–molybdenum–sodium metal-organic framework.
Achieved crystallization through solvothermal synthesis using specific metal sources and a ligand precursor.
Analyzed the structure via 3D electron diffraction and confirmed phase purity with synchrotron powder X-ray diffraction.
Assessed optical characteristics using UV–Vis spectroscopy, determining a bandgap of 1.8 eV.
Evaluated thermal stability through thermogravimetric analysis and variable-temperature powder X-ray diffraction.
The framework crystallizes in a monoclinic space group with specific lattice parameters.
Co exhibits trigonal bipyramidal coordination, while Mo shows tetrahedral geometry in the structure.
The optical study reveals four visible-light peaks linked to d–d transitions of cobalt, supporting its bandgap determination.
Thermal stability of the material extends to 410 °C, after which structural collapse leads to other compound formations.

Abstract

The crystallization of a trimetallic cobalt–molybdenum–sodium metal–organic framework, polyμ-benzene-1,3,5-tricarboxylato-tetra-μ-oxido-cobaltmolybdenumtrisodium, UOW-10 or Na 3 Co(MoO 4 )(BTC) n , is achieved by solvothermal synthesis using benzene-1,3,5-tricarboxylic acid (H 3 BTC, C 9 H 6 O 6 ) as a ligand precursor, Na 2 MoO 4 ·2H 2 O and Co(NO 3 ) 2 ·2H 2 O as metal sources, and N , N -dimethylformamide (DMF) as the solvent. 3D electron diffraction (3D ED) reveals that the structure crystallizes in the monoclinic space group P 2 1 / c , with lattice parameters of a = 9.718 (2), b = 18.250 (3), c = 6.892 (9) Å, α = γ = 90, β = 96.156 (15)°, V = 1214.7 (4) Å 3 and Z = 4. The phase purity of the bulk sample was confirmed using synchrotron powder X-ray diffraction. The organic ligands form a 2D layer, where cobalt and molybdenum are found, with sodium cations located between the layers. There are four crystallographically distinct sodium sites: three exhibit a distorted octahedral coordination geometry, while the remaining site is seven-coordinate. The cobalt has trigonal bipyramidal coordination geometry and molybdenum exhibits a tetrahedral coordination geometry. Half the sodium cations in the structure forms 1D column-like motifs via shared oxygen edges along the crystallographic c axis, which are cross-linked in b by the cobalt and molybdenum sites via bridging O atoms, while the other half of the sodium cations form 2D ribbons in the ac plane, propagating along c , linked by sharing oxygen edges and faces. The optical properties of UOW-10 were investigated through the use of UV–Vis spectroscopy, showing a bandgap of 1.8 eV. Deconvolution of the features in the visible-light region reveals that four peaks are present, which can all be ascribed to the d–d transitions from the trigonal bipyramidal cobalt. By means of thermogravimetric analysis (TGA) and variable-temperature powder X-ray diffraction (VT-PXRD), it is demonstrated that the material has thermal stability to 410 °C, after which structure collapse occurs, leading to a mixture of Na 2 MoO 4 , CoO and Co 3 Mo above 900 °C.

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