Raman Scattering Spectra of Boron Imidazolate Frameworks Containing Different Magnetic Ions

TL;DR

This study uses Raman spectroscopy to analyze vibrational modes in boron imidazolate frameworks with different magnetic ions, revealing how local and lattice vibrations depend on structure and metal nodes.

Contribution

It provides detailed vibrational spectra of BIFs with various metal ions, highlighting the energy hierarchy and structural dependence of local and collective vibrations.

Findings

Local linker vibrations are consistent across BIFs and independent of structure.

Collective lattice vibrations distinguish cage and 2D BIFs, weakly dependent on metal.

Vibrations around 200 cm$^{-1}$ are specific to each metal node.

Abstract

We present a Raman scattering spectroscopic study of boron imidazolate metal-organic frameworks (BIFs) with three different magnetic metal ions and one non-magnetic in a wide frequency range from 25 to 1700 cm$^{-1}$, which covers local vibrations of the linkers and well as collective lattice vibrations. We show that the spectral region above 800 cm$^{-1}$ belongs to the local vibrations of the linkers, which have the same frequencies for the studied BIFs without any dependence on the structure of the BIFs, and are easily interpreted based on the spectra of imidazolate linkers. In contrast, collective lattice vibrations, observed below 100 cm$^{-1}$, show a distinction between cage and two-dimensional BIFs structures, with a weak dependence on the metal node. We identify the range of vibrations around 200 cm$^{-1}$, which are distinct for each MOF, depending on a metal node. Our work demonstrates the energy hierarchy in the vibrational response of BIFs.