Rational Design of Zero-dimensional Manganese(II) Halide Hybrids with Suppressed Melting Temperatures

Melt processability of metal halide hybrids (MHH), suitable for fabricating thin-film devices and accessing glassy phases of compounds, has received current research interest. Successful melt processability requires suppressing melting temperatures (Tm) well below the decomposition temperature (Td). However, the absence of a clear structure–property correlation renders the suppression of Tm challenging for low-dimensional MHH. Here, the suppression of Tm of zero-dimensional (0D) Mn(II) halide hybrids is reported with rational choice of ammonium organic cation (length of aliphatic organic chain, aromatic substitution of tertiary ammonium tethering group, and halide variation). A clear structure–property correlation is observed with the structure of the organic cation and the Tm of the MHH. A delicate balance between ΔHfus and ΔSfus is at play in determining the melting temperature. Experimental ΔHfus and ΔSfus values support the observed qualitative trend in the melting points, as highlighted by the detailed Hirshfeld surface analysis. Among the various compounds reported here, (BzBu3N)2MnBr4 (Bz = benzyl; Bu = butyl) shows the lowest Tm of 96 °C (with Td = 180 °C). Furthermore, successful melt processability of the low-melting hybrids is demonstrated for doctor-bladed molten samples, maintaining purity and crystallinity. The present work provides chemical and thermodynamic insights into lowering of melting points of MHH and unravels the operative structure–property relationship, highlighting the melting mechanism that is of vital importance in designing low-melting 0D hybrids appropriate for melt processability.