Aggregation of tetranuclear Mn4O2 building blocks with alkali ion was studied. Several Mn(III) complexes containing [Mn4O2(AcO)7(pyz)2]− (pyz = pyrazinate) anion(s) were obtained from an assembly system containing Mn(II), MnO4−, HOAc and Hpyz (Napyz or Kpyz). These [Mn4O2]8+ complexes have monomeric (1 and 2), dimeric (4 and 5) and one-dimensional chain (3) structures of which alkali metal ion connects the Mn ions of adjacent [Mn4O2]8+ units through µ1,1- and µ1,3-carboxylate bridges. Complexes 2 or 3 were converted into [Mn12O12(AcO)16(H2O)4] in EtOH solution in the presence of HOAc. However, in MeOH solution, a coordination polymer [Mn2(HCOO)4(H2O)4]n was obtained accompanying the oxidation of MeOH to become HCHO and HCOOH. Tracing the 1H NMR spectra of 2 or 3 in CD3OD, the disappearance of the resonance signals in 3 h indicated the decomposition of the [Mn4O2]8+ cores. Complex 2 exhibits its proton NMR signals in CDCl3 which are similar to those of its pic analogue but accompany downfield shift to various extents for all the corresponding signals. Variable-temperature magnetic susceptibilities of complexes 2–5 in the range 5–300 K were recorded and were fitted for an Mn4O2 butterfly core, giving the fitting parameters Jbb = −2.67 to −3.76 cm−1 and Jwb = −1.16 to −3.14 cm−1. Small J values indicate weak antiferromagnetic coupling interactions of the Mn(III) sites and the spin ground states are considered as ST = 0 based on the Jbb/Jwb ratio ≈1 for these complexes. The ESR spectra were recorded for complex 2 in dual-mode at liquid-helium temperatures and no obvious signal could be found. The addition of p-cresol gives rise to the reduction of the [Mn4O2]8+, resulting in observable signals.
研究了四核 Mn4O2 构建块与碱离子的聚合。从含有 Mn(II)、
MnO4-、HOAc 和 Hpyz(Napyz 或 Kpyz)的组装体系中获得了几种含有 [Mn4O2(AcO)7(pyz)2]-(pyz =
吡嗪酸盐)阴离子的 Mn(III) 复合物。这些[Mn4O2]8+ 复合物具有单体(1 和 2)、二聚体(4 和 5)和一维链(3)结构,其中碱
金属离子通过 µ1,1- 和 µ1,3-
羧酸桥连接相邻[Mn4O2]8+单元的
锰离子。络合物 2 或 3 在有 HOAc 存在的 EtOH 溶液中转化为[Mn12O12(AcO)16(
H2O)4]。然而,在 MeOH 溶液中,伴随着 MeOH 被氧化成 HCHO 和 HCOOH,得到了配位聚合物 [Mn2(HCOO)4( )4]n。追踪 2 或 3 在 CD3OD 中的 1H NMR 光谱,发现共振信号在 3 小时内消失,表明[Mn4O2]8+ 核心分解。络合物 2 在 CDCl3 中显示的质子核磁共振信号与其皮质类似物的质子核磁共振信号相似,但所有相应信号都有不同程度的下移。记录了复合物 2-5 在 5-300 K 范围内的变温磁感应强度,并对 Mn4O2 蝶形磁芯进行了拟合,得出拟合参数 Jbb = -2.67 至 -3.76 cm-1 和 Jwb = -1.16 至 -3.14 cm-1。小的 J 值表明 Mn(III)位点的反
铁磁耦合相互作用较弱,根据这些复合物的 Jbb/Jwb 比值≈1,可以认为自旋基态为 ST = 0。在液
氦温度下以双模式记录了络合物 2 的 ESR 光谱,没有发现明显的信号。加入
对甲酚会导致[Mn4O2]8+还原,从而产生可观察到的信号。