Experimental and <i>ab Initio</i> Study of Catena(bis(μ₂‑iodo)-6-methylquinoline-copper(I)) under Pressure: Synthesis, Crystal Structure, Electronic, and Luminescence Properties

Copper­(I) iodine compounds can exhibit interesting mechanochromic and thermochromic luminescent properties with important technological applications. We report the synthesis and structure determination by X-ray diffraction of a new polymeric staircase copper­(I) iodine compound catena­(bis­(μ2-iodo)-6-methylquinoline-copper­(I), [C10H9CuIN]. The structure is composed of isolated polymeric staircase chains of copper–iodine coordinated to organic ligands through Cu–N bonds. High pressure X-ray diffraction to 6.45 GPa shows that the material is soft, with a bulk modulus K0 = 10.2(2)­GPa and a first derivative K′0 = 8.1(3), typical for organometallic compounds. The unit-cell compression is very anisotropic with the stiffest direction [302] arising from a combination of the stiff CuI ladders and the shear of the planar quinolone ligands over one another. Full structure refinements at elevated pressures show that pressures reduce the Cu···Cu distances in the compound. This effect is detected in luminescence spectra with the appearance of four sub-bands at 515, 600, 647, and 712 nm above 3.5 GPa. Red-shifts are observed, and they are tentatively associated with interactions between copper­(I) ions due to the shortening of the Cu···Cu distances induced by pressure, below twice the van der Waals limit (2.8 Å). Additionally, ab initio simulations were performed, and they confirmed the structure and the results obtained experimentally for the equation of state. The simulation allowed the band structure and the electronic density of states of this copper­(I) iodine complex to be determined. In particular, the band gap decreases slowly with pressure in a quadratic way with dEg/dP = −0.011 eV/GPa and d2Eg/dP2 = 0.001 eV/GPa2.碘化亚铜类化合物可展现出有趣的力致变色与热致变色发光性能，具备重要的技术应用价值。 本研究报道了一种新型聚合阶梯状碘化亚铜化合物——链状(双(μ₂-桥联碘)-6-甲基喹啉合亚铜(I))，化学式为[C₁₀H₉CuIN]，其合成与结构通过X射线衍射完成解析。该化合物的结构由孤立的铜-碘聚合阶梯链构成，此类链通过Cu-N键与有机配体配位。 对该材料开展最高至6.45 GPa的高压X射线衍射测试，结果显示其质地较软，体弹性模量（bulk modulus）K₀=10.2(2) GPa，一阶导数K'₀=8.1(3)，这与有机金属化合物的典型特征相符。该材料的晶胞压缩具有极强的各向异性，最刚性的晶向为[302]，这一特性源于刚性CuI阶梯链与平面喹啉配体间的相互剪切共同作用。 高压下的完整结构精修结果表明，压力会缩短化合物内的Cu···Cu间距。这一效应可在发光光谱中观测到：当压力高于3.5 GPa时，光谱中会出现位于515、600、647与712 nm处的四个子带。 实验观测到红移现象，初步将其归因于压力诱导Cu···Cu间距缩短后，亚铜离子间产生的相互作用——此时Cu···Cu间距已小于范德华极限（van der Waals limit，2.8 Å）的两倍。 此外，本研究还开展了从头算模拟（ab initio simulations），验证了该化合物的结构以及实验测得的状态方程（equation of state）结果。 该模拟得以确定该碘化亚铜配合物的能带结构与电子态密度。具体而言，带隙随压力升高缓慢降低，且符合二次方关系：dEg/dP = −0.011 eV/GPa，d²Eg/dP² = 0.001 eV/GPa²。