Charalambous Maria, Moushi Eleni E, Nguyen Tu N, Papatriantafyllopoulou Constantina, Nastopoulos Vassilios, Christou George, Tasiopoulos Anastasios J
Department of Chemistry, University of Cyprus, Nicosia, Cyprus.
Department of Chemistry, University of Florida, Gainesville, FL, United States.
Front Chem. 2019 Mar 5;7:96. doi: 10.3389/fchem.2019.00096. eCollection 2019.
We report the synthesis, crystal structures and magnetic properties of the giant heterometallic [MnNi] (compounds , )/[MnCo] (compound ) "loops-of-loops-and-supertetrahedra" molecular aggregates and of a [MnNi] compound (cation of ) that is structurally related with the cation co-crystallizing with the anion of . In particular, after the initial preparation and characterization of compound [MnNi(μ-O)(μ-OH)(μ-Cl)(OCCH)(py)][MnNi(μ-O)(μ-O)(μ-Cl)Cl(OCCH)(pd)(py)] () we targeted the isolation of (i) both the cationic and the anionic aggregates of in a discrete form and (ii) the Mn/Co analog of [MnNi] aggregate. Our synthetic efforts toward these directions afforded the discrete [MnNi] "loops-of-loops-and-supertetrahedra" aggregate [MnNi(μ-O)(μ-O)(μ-Cl)Cl(OCCH)(pd)(py)(HO)] (), the heterometallic Mn/Co analog [MnCo(μ-O)(μ-O)(μ-Cl)Cl(μ-OCHCH)(OCCH)(pd)(py)] () and the discrete [MnNi] cation MnNi(μ-O)(μ-OH)(μ-Cl)(OCCH)(py)(OH) (). The structure of consists of a mixed valence [ ] molecular aggregate that contains two loops separated by two supertetrahedral units and a [ ] cation based on two [Mn (μ-O)(μ-OH)(μ-Cl)] cubane sub-units connected through both mono- and tri-atomic bridges provided by the μ-O and carboxylate anions. The structures of - are related to those of the compounds co-crystallized in exhibiting however some differences that shall be discussed in detail in the manuscript. Magnetism studies revealed the presence of dominant ferromagnetic interactions in - that lead to large ground state spin (S) values for the "loops-of-loops-and-supertetrahedra" aggregates and antiferromagnetic exchange interactions in that lead to a low (and possibly zero) S value. In particular, dc and ac magnetic susceptibility studies revealed that the discrete [MnNi] aggregate exhibits a large S value ~ 26 but is not a new SMM. The ac magnetic susceptibility studies of the [MnCo] analog revealed an extremely weak beginning of an out-of-phase tail indicating the presence of a very small relaxation barrier assignable to the anisotropic Coions and a resulting out-of-phase ac signal whose peak is at very low T.
我们报道了巨型异金属[MnNi]（化合物 、 ）/[MnCo]（化合物 ）“环中环和超四面体”分子聚集体以及与 阴离子共结晶的阳离子结构相关的[MnNi]化合物（ 的阳离子）的合成、晶体结构和磁性。特别是，在最初制备并表征化合物[MnNi(μ - O)(μ - OH)(μ - Cl)(OCCH)(py)][MnNi(μ - O)(μ - O)(μ - Cl)Cl(OCCH)(pd)(py)]（ ）之后，我们的目标是分离出（i）离散形式的 的阳离子和阴离子聚集体，以及（ii）[MnNi]聚集体的Mn/Co类似物。我们朝着这些方向的合成努力得到了离散的[MnNi]“环中环和超四面体”聚集体[MnNi(μ - O)(μ - O)(μ - Cl)Cl(OCCH)(pd)(py)(HO)]（ ）、异金属Mn/Co类似物[MnCo(μ - O)(μ - O)(μ - Cl)Cl(μ - OCHCH)(OCCH)(pd)(py)]（ ）和离散的[MnNi]阳离子MnNi(μ - O)(μ - OH)(μ - Cl)(OCCH)(py)(OH)（ ）。 的结构由一个混合价态的[ ]分子聚集体组成，该聚集体包含两个由两个 超四面体单元隔开的 环，以及一个基于两个通过μ - O和羧酸根阴离子提供的单原子和三原子桥连接的[Mn (μ - O)(μ - OH)(μ - Cl)]立方烷亚单元的[ ]阳离子。 - 的结构与在 中共结晶的化合物的结构相关，然而存在一些差异，将在稿件中详细讨论。磁性研究表明， - 中存在占主导地位的铁磁相互作用，导致“环中环和超四面体”聚集体具有较大的基态自旋（S）值，而 中存在反铁磁交换相互作用，导致S值较低（可能为零）。特别是，直流和交流磁化率研究表明，离散的[MnNi]聚集体表现出较大的S值~26，但不是一种新的单分子磁体。[MnCo]类似物的交流磁化率研究揭示了一个非常微弱的异相尾部开始，表明存在一个可归因于各向异性Co离子的非常小的弛豫势垒，以及一个其峰值在非常低温度T下的异相交流信号。
