Copper–nitroxide based breathing crystals: a unified mechanism of gradual magnetostructural transition supported by quantum chemistry calculations†‡,Inorganic Chemistry Frontiers

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Copper–nitroxide based breathing crystals: a unified mechanism of gradual magnetostructural transition supported by quantum chemistry calculations†‡
Inorganic Chemistry Frontiers ( IF 6.1 ) Pub Date : 2019-03-26 00:00:00 , DOI: 10.1039/c9qi00129h
Rocío Sánchez-de-Armas _{1,

2} , Norge Cruz Hernández _{2,

3,

4,

5} , Carmen J. Calzado _{1,

2}

Affiliation

The molecular magnets Cu(hfac)₂L^R based on copper(II) and pyrazolyl-substituted nitronyl nitroxide radicals L^R exhibit thermally and optically-induced magnetostructural transitions, similar to the spin-crossover and light-induced excited spin state trapping phenomena. The mechanism of the gradual change in the magnetic moment in Cu(hfac)₂L^R remains unclear. Herewith, we report a detailed study of this mechanism at the molecular level based on DDCI and periodic DFT+U calculations. Three representative members of the Cu(hfac)₂L^R family have been selected, with different substituents (R = Pr, Bu) and solvents (octane, o-xylane, without solvent). Our results indicate that the magnetostructural transition can be related to the coexistence of two limit structures, the low temperature (LT) phase with a strong coupling between the Cu(II) and nitronyl nitroxide spins and the high temperature (HT) phase, where the spins are weakly coupled. In this scenario, the gradual change in the magnetic moment with temperature just reflects the thermally weighted ratio of the two limit LT and HT phases. Our findings support the changes observed in the variable temperature-FTIR spectra of Cu(hfac)₂L^Pr, manifested by the increase/decrease of certain vibrational bands with temperature and suggest a unified mechanism governing the gradual magnetic anomalies of the Cu(hfac)₂L^R complexes.

中文翻译：

铜氮氧呼吸基于晶体：由量子化学计算支持逐步过渡magnetostructural一个统一的机制† ‡

基于铜（II）的分子磁体Cu（hfac）₂ L ^R和吡唑基取代的亚硝酰基硝基氧自由基L ^R表现出热和光诱导的磁结构转变，类似于自旋交叉和光诱导的自旋态俘获现象。Cu（hfac）₂ L ^R中磁矩逐渐变化的机理尚不清楚。因此，我们在DDCI和定期DFT + U计算的基础上，报告了在分子水平上对该机理的详细研究。选择了Cu（hfac）₂ L ^R族的三个代表性成员，它们具有不同的取代基（R = Pr，Bu）和溶剂（辛烷，o-二甲苯，无溶剂）。我们的结果表明，磁结构转变可能与两种极限结构的共存相关，即低温（LT）相与Cu（II）和亚硝酰亚硝酸根自旋之间的强耦合以及高温（HT）相，其中自旋是弱耦合的。在这种情况下，磁矩随温度的逐渐变化仅反映了两个极限LT和HT相的热加权比。我们的发现支持在Cu（hfac）₂ L ^Pr的可变温度FTIR光谱中观察到的变化，其表现为某些振动带随温度的增加/减少，并提出了控制Cu（hfac）逐渐磁异常的统一机制。_2个L ^R配合物。

更新日期：2019-03-26

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