Understanding factors that underpin the signs and magnitudes of electron spin–spin couplings in biradicaloids, especially those that are integrated into highly delocalized electronic structures, promises to inform the design of molecular spintronic systems. Using steady-state and variable temperature electron paramagnetic resonance (EPR) spectroscopy, we examine spin dynamics in symmetric, strongly π-conjugated bis[(porphinato)copper] (bis[PCu]) systems and probe the roles played by atom-specific macrocycle spin density, porphyrin-to-porphyrin linkage topology, and orbital symmetry on the magnitudes of electronic spin–spin couplings over substantial Cu–Cu distances. These studies examine the following: (i) meso-to-meso-linked bis[PCu] systems having oligoyne spacers, (ii) meso-to-meso-bridged bis[PCu] arrays in which the PCu centers are separated by a single ethynyl unit or multiple 5,15-diethynyl(porphinato)zinc(II) units, and (iii) the corresponding β-to-β-bridged bis[PCu] structures. EPR data show that, for β-to-β-bridged systems and meso-to-meso-linked bis[PCu] structures having oligoyne spacers, a through σ-bond coupling mechanism controls the average exchange interaction (J_avg). In contrast, PCu centers separated by a single ethynyl or multiple 5,15-diethynyl(porphinato)zinc(II) units display a phenomenological decay of ln[J_avg] versus Cu–Cu σ-bond separation number of ∼0.115 per bond, half as large as for these other compositions, congruent with the importance of π-mediated spin–spin coupling. These disparities derive from effects that trace their origin to the nature of the macrocycle–macrocycle linkage topology and the relative energy of the Cu d_x²–y² singly occupied molecular orbital within the frontier orbital manifold of these electronically delocalized structures. This work provides insight into approaches to tune the extent of spin exchange interactions and distance-dependent electronic spin–spin coupling magnitudes in rigid, highly conjugated biradicaloids.

中文翻译：

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刚性分子系统中电子自旋-自旋耦合的拓扑，距离和轨道对称效应：对长距离自旋-自旋相互作用的影响。

了解支撑双自由基类电子自旋-自旋耦合的符号和强度的因素，尤其是那些集成到高度离域的电子结构中的因素，有望为分子自旋电子系统的设计提供参考。使用稳态和可变温度电子顺磁共振（EPR）光谱，我们研究了对称的强π共轭双[（卟啉））铜]（bis [PCu））系统中的自旋动力学，并研究了特定于原子的大环的作用自旋密度，卟啉-卟啉键合拓扑结构以及在相当长的Cu-Cu距离上电子自旋-自旋耦合的幅度的轨道对称性。这些研究中检查的情况如下：（ⅰ）内消旋-至-内消旋-连接的双[PCU]具有oligoyne间隔物系统，（II）内消旋-至-内消旋-bridged双[PCU]数组，其中PCU中心由一个单一的乙炔基单元或多个5,15-二乙炔（porphinato）锌（II）单元和分离（III）相应的β-TO- β桥双[PCu]结构。EPR数据表明，对于β-到-β-桥接体系和内消旋至-内消旋-连接的双[PCU]具有oligoyne间隔物结构中，通过σ键联接机构控制平均交换相互作用（Ĵ_平均）。相反，由单个乙炔基或多个5,15-二乙炔基（卟啉）锌（II）单元隔开的PCu中心表现出ln [ J _avg]与Cu-Cuσ-键的键间距约为每个键的0.115，是其他成分的一半，这与π介导的自旋-自旋耦合的重要性相吻合。这些差异源于效应的根源，这些效应的起源可追溯到大环-宏环链接拓扑的性质以及这些电子离域结构的前沿轨道流形内Cu d _{x ² - y ²}单占据的分子轨道的相对能量。这项工作为调节刚性，高共轭双基双基团中自旋交换相互作用和距离相关的电子自旋-自旋耦合幅度的方法提供了见解。