Detailed Investigation of the Structural, Thermal, and Electronic Properties of Gold Isocyanide Complexes with Mechano‐Triggered Single‐Crystal‐to‐Single‐Crystal Phase Transitions

Abstract

Mechano-induced phase transitions in organic crystalline materials that alter their properties have received much attention. However, most mechano-responsive molecular crystals exhibit crystal to amorphous phase transitions on mechanical stimulation, and the intermolecular interaction patterns in the daughter phase are difficult to characterize. We investigated phenyl(phenylisocyanide)gold(I) (1) and phenyl(3,5-dimethylphenylisocyanide)gold(I) (2) complexes that exhibit a mechanotriggered single crystal to single crystal phase transition. Previous reports of 1 and 2 focused on relationships between the crystalline structures and photoluminescence properties; in this work we have focused on other aspects. The face index measurements of 1 and 2 before and after the mechano-induced phase transitions indicate they undergo non-epitaxial phase transitions without a rigorous orientational relationship between the mother and daughter phases. Differential scanning calorimetry analyses revealed the phase transition of 1 to be enthalpically driven by the formation of new aurophilic interactions. In contrast, the phase transition of 2 is entropically driven, with an empty void in the mother phase, not present in the daughter phase. Scanning electron microscopy observation showed that the degree of the charging effect of both 1 and 2 was changed by the phase transitions, suggesting that the formation of the aurophilic interactions affords more effective conductive pathways. Moreover, flashphotolysis time resolved microwave conductivity measurements revealed that 1 increased in conductivity after the phase change, whereas the conductivity of 2 decreased. These contrasting results were explained by the different patterns in the aurophilic interactions. Finally, an intriguing disappearing polymorphism of 2 is reported, in which a polymorph form could not be obtained again after some period of time even with repeated trials. The present studies provide us with a variety of hitherto unknown insights into mechano-responsive molecular crystals, which help us understand the phase transition behaviors upon mechanical stimulation and establish rational design principles.

Self‐Healing Behavior in a Thermo‐Mechanically Responsive Cocrystal during a Reversible Phase Transition

“…Forthe typical crystals used in the experiments with alength of more than 2mm, the speed of the phase transition is slower than 0.03 mm s À1 .Such aspeed is much slower than that of the thermosalient crystals (the duration time of thermosalient phase transition is normally within milliseconds), [25] suggesting that the phase transition is not martensitic and the mechanism including the nucleation and gradual growth of the daughter phase lattice should be described. [7,9,10,27,28] Moreover,r ecent studies in crystal chemistry have been shown that the long-range migration of mass or nanoparticles across the surface of crystals should be considered in the mechanism of the crystal growth. [29][30][31][32] We believe this process could also be involved in the SCSC phase transition and benefit the self-healing behavior of the crystal.…”

Molecular gold strings: aurophilicity, luminescence and structure–property correlations

“…202 In 2016, Ito and co-workers reported the synthesis of phenyl( phenylisocyanide)gold(I) (13a) and phenyl(3,5-dimethylphenylisocyanide)gold(I) (13b), which exhibit mechano triggered SCSC phase transformations and possess interesting optical and electronic properties. 23,[203][204][205] Complexes 13a and 13b were obtained as blue-and green-emitting single crystals respectively. However, a rapid phase transition was observed when the crystals were mechanically triggered.…”

Self‐Healing Behavior in a Thermo‐Mechanically Responsive Cocrystal during a Reversible Phase Transition

“…For the typical crystals used in the experiments with a length of more than 2 mm, the speed of the phase transition is slower than 0.03 mm s −1 . Such a speed is much slower than that of the thermosalient crystals (the duration time of thermosalient phase transition is normally within milliseconds), suggesting that the phase transition is not martensitic and the mechanism including the nucleation and gradual growth of the daughter phase lattice should be described . Moreover, recent studies in crystal chemistry have been shown that the long‐range migration of mass or nanoparticles across the surface of crystals should be considered in the mechanism of the crystal growth .…”