Trialkylphosphine-Stabilized Copper(I) Gallium(III) Phenylchalcogenolate Complexes: Crystal Structures and Generation of Ternary Semiconductors by Thermolysis

A series of organometallic trialkylphosphine-stabilized copper gallium phenylchalcogenolate complexes [(R3P)mCunMe2–xGa­(EPh)n+x+1] (R = Me, Et, iPr, tBu; E = S, Se, Te; x = 0, 1) has been prepared and structurally characterized by X-ray diffraction. From their molecular structures three groups of compounds can be distinguished: ionic compounds, ring systems, and cage structures. All these complexes contain one gallium atom bound to one or two methyl groups, whereas the number of copper atoms, and therefore the nuclearity of the complexes, is variable and depends mainly on size and amount of phosphine ligand used in synthesis. The Ga–E bonds are relatively rigid, in contrast to flexible Cu–E bonds. The lengths of the latter are controlled by the coordination number and steric influences. The Ga–E bond lengths depend systematically on the number of methyl groups bound to the gallium atom, with somewhat shorter bonds in monomethyl compounds compared to dimethyl compounds. Quantum chemical computations reproduce this trend and show furthermore that the rotation of one phenyl group around the Ga–E bond is a low energy process with two distinct minima, corresponding to two different conformations found experimentally. Mixtures of different types of chalcogen atoms on molecular scale are possible, and then ligand exchange reactions in solution lead to mixed site occupation. In thermogravimetric studies the complexes were converted into the ternary semiconductors CuGaE2. The thermolysis reaction is completed at temperatures between 250 and 400 °C, typically with lower temperatures for the heavier chalcogens. Because of significant release of Me3Ga during the thermolysis process, and especially in case of copper excess in the precursor complexes, binary copper chalcogenides are obtained as additional thermolysis products. Quaternary semiconductors can be obtained from mixed chalcogen precursors.本研究合成了一系列由三烷基膦稳定的铜镓苯基硫族醇盐配合物[(R₃P)ₘCuₙMe₂–ₓGa­(EPh)ₙ₊ₓ₊₁]（其中R为Me、Et、iPr或tBu；E为S、Se或Te；x为0或1），并通过X射线衍射对其进行了结构表征。基于其分子结构，可将该系列化合物分为三类：离子型化合物、环系结构与笼状结构。所有此类配合物均含有一个与1个或2个甲基键合的镓原子，而铜原子的数目（即配合物的核数）可变，主要取决于合成过程中所用膦配体的空间尺寸与投料量。与灵活可调的Cu-E键不同，Ga-E键相对刚性；后者的键长由配位数与空间位阻效应共同调控。Ga-E键长会随结合在镓原子上的甲基数目呈现规律性变化：与二甲基取代的化合物相比，单甲基取代的配合物中Ga-E键长更短。量子化学计算重现了这一变化趋势，同时进一步证实，苯基围绕Ga-E键的旋转属于低能过程，存在两个不同的能量极小值点，分别对应实验中观测到的两种构象。在分子尺度上混合不同种类硫族原子的配合物是可行的，溶液中的配体交换反应会导致配位点的混合占据。热重分析实验表明，此类配合物可转化为三元半导体CuGaE₂，热解反应在250~400℃的温度范围内完成，通常硫族元素原子量越大，所需热解温度越低。由于热解过程中会大量释放三甲基镓，当前驱体配合物中铜过量时，还会额外生成二元铜硫族化合物作为热解副产物。以混合硫族前驱体为原料，则可制备得到四元半导体。