CO₂还原始终是能源和环境领域的重要挑战。 二亚胺羰基Mn配合物价格低廉, 稳定性好, 可调变性强, 成为近年来光催化还原CO₂的热门催化剂。 紫外-可见光谱和红外光谱研究有助于调控CO₂光还原催化剂性能。 基于密度泛函理论(DFT)和含时密度泛函理论(TD-DFT), 对系列二亚胺羰基锰配合物[Mn(bpy)(CO)₃Br], (简写为1), [Mn(phen)(CO)₃Br], (简写为2), [Mn(phen-dione)(CO)₃Br], (简写为3), [Mn(phen-dione)(CO)₃CH₃CN]⁺, (简写为4) (bpy=2,2'-bipyridine, phen=1,10-phenan-throline, phen-dione=phenanthroline-5, 6-dione)的紫外-可见光谱和红外光谱进行研究。 基于TD-DFT方法, 采用多种泛函, 对紫外-可见光谱进行模拟。 结果显示1和2主要有两个最大吸收峰, 分别位于371 nm (1), 408 nm (1)和361 nm (2), 414 nm (2), 其电子跃迁类型均为由金属Mn中心基团向二亚胺配体的电荷转移(MLCT)跃迁。 而3和4均具有三个吸收峰, 分别位于290 nm (3), 337 nm (3), 431 nm (3)和294 nm (4), 319 nm (4), 371 nm (4)。 其中, 除了4的294 nm吸收峰对应了二亚胺配体内部的π—π^*跃迁, 3和4的其余吸收峰均为MLCT跃迁。 伴随着二亚胺配体电负性的增强, 吸收峰向可见光区移动(红移), 而因Mn中心配体电负性的增强, 导致吸收峰向紫外光区移动(蓝移)。 一旦电子从Mn中心基团转移至二亚胺配体, Mn中心基团成为缺电子中心, 有利于外界电子进入。 因Mn中心基团的轨道主要由金属Mn和配体的 σ^*反键轨道组成, 有利于Mn中心基团配体Br^-/CH₃CN解离, 形成活性中间体。 红外光谱计算结果显示1, 2, 3和4的特征振动峰主要分为两类: 金属Mn中心的C=O键伸缩振动(1, 2, 3和4的1 920~2 020 cm^-1)和二亚胺羰基的C=O键伸缩振动(3的1 690 cm^-1和4的1 694 cm^-1)。 伴随着二亚胺羰基配体和Mn中心配体电负性的增强, 1到4的特征峰波数略微增加。 计算的分子结构, 紫外-可见光谱和红外光谱与实验结果符合很好, 能够为二亚胺羰基锰配合物的合成和光还原CO₂性能调变提供可靠的理论参考。

The reduction of CO₂ is still a challenge in energy sources and the environmental field. Diamine coordinated manganese tricarbonylcatalysts containing diamine ligands, as inexpensive molecule based inorganic materials, become a potentially interesting catalyst in the photoreduction of CO₂. The ultraviolet-visible (UV-Vis) and infrared (IR) spectra are beneficial to the modulation of catalysts for the photoreduction of CO₂. TheUV-Vis and IR spectra of a series of diamine coordinated manganese tricarbonyl catalysts, [Mn(bpy)(CO)₃Br], (1), [Mn(phen)(CO)₃Br](2), [Mn(phen-dione)(CO)₃Br](3), [Mn(phen-dione)(CO)₃CH₃CN]⁺(4) (bpy=2,2'-bipyridine, phen=1,10-phenan-throline, phen-dione=phenanthroline-5,6-dione) has been investigated using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations. The UV-Vis spectrawere obtained using several TD-DFT calculations. The simulated UV-Vis spectra of 1 and 2 all show two peaks centered at 371 nm (1), 408 nm (1) and 361 nm (2), 414 nm (2), respectively. Absorption peaks of 1 and 2 arise from a metal-to-ligand charge transfer (MLCT) transition. The simulated UV-Vis spectra of 3 and 4 show three absorption peaks centered around 290 nm (3), 337 nm (3), 431 nm (3) and 294 nm (4), 319 nm (4), 371 nm (4), respectively. Herein, except for the peak of 294 nm (4) generated by the ligand-to-ligand π—π^* transition, the remain absorption peaks of 3 and 4 all arise from MLCT absorption. The increased electronegativity of diamine ligands is responsible for shifting absorption peak from the UV region to the visible region (red). The increased electronegativity of the Mn-centeredligand is responsible for shifting absorption peak from the visible region to the UV region (blue). Once an electron is transferred from the Mn-centered unit to the diamine ligands, the Mn center will become anelectron-deficient unit. Herein, the Mn-centeredunit contributes from the σ antibonding orbital between the Mn atom and ligand in the MLCT states. Thus, when the populated excited MLCT states are hit, the release of Mn-centered ligand (Br^-/CH₃CN) becomes favorable, and the system can form the active species. The simulated IR spectra show that two kinds of characteristic peaks are obtained, that is, (1) stretching vibration of Mn-centered C=O unit at 1 920~2020 cm^-1 (1, 2, 3, and 4) and (2) stretching vibration of C=O unit of diamine ligands at 1 690 cm^-1 (3) and 1 694 cm^-1 (4), respectively. The increased electronegativity of diamine ligands and Mn-centered ligand strengthens the C=O bond, which increases the stretching vibration frequency of the C=O units from 1 to 4. The calculation results, including molecular structures, the UV and IR spectra show good agreement with those obtained by experiment and provide the reasonable theoretical guide for the synthesis and regulation of diamine-coordinated manganese tricarbonyl catalysts.