Dispersive Optical Properties and Refractive Index of [BMIM][SCN] Ionic Liquids with Transition Metal Coordination

Bilal S. Algnamat; Ahmad A. Abushattal; Amani F. Kraishan; Monther Alsboul; Mou’ad A. Tarawneh; Alá S. Alnaimat; Deshinta Arrova Dewi

doi:10.3390/sci8040069

journal article Open Access Mar 25, 2026

Dispersive Optical Properties and Refractive Index of [BMIM][SCN] Ionic Liquids with Transition Metal Coordination

Bilal S. Algnamat

Ahmad A. Abushattal Amani F. Kraishan

Monther Alsboul Mou’ad A. Tarawneh Alá S. Alnaimat Deshinta Arrova Dewi

Sci Vol. 8 No. 4 pp. 69 · MDPI AG

View at Publisher Save 10.3390/sci8040069

Abstract

We investigated the influence of transition metal coordination on the optical dispersion and thermo-optic behavior of the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]). Refractive index measurements in the visible–near-infrared range (400–1000 nm), combined with temperature-dependent characterization (298–323 K), demonstrate that coordination with Al3+, Cd2+, Zn2+, and Mn2+ consistently increases the refractive index relative to the neat ionic liquid. All systems exhibit normal dispersion, following the hierarchy n(Al) > n(Cd) ≳ n(Zn) > n(Mn) > n([BMIM][SCN]), which reflects cooperative contributions from metal-centerd polarizability and coordination-induced modifications to density and electronic structure. Negative thermo-optic coefficients are measured for all samples, with [BMIM]3[Al(SCN)6] displaying the highest temperature sensitivity. Abbe diagrams and group-velocity dispersion analyses confirm a predictable index–dispersion trade-off and show that dispersion-related transport parameters are less temperature dependent than n(T). Collectively, these findings establish a structure–property framework for tuning refractive index, chromatic dispersion, and thermo-optic response via coordination chemistry, supporting the targeted design of thiocyanate-based ionic liquids for photonic components, thermal lenses, and dispersion-managed optical devices.

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Published: Mar 25, 2026
Vol/Issue: 8(4)
Pages: 69
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Bilal S. Algnamat