A temperature-dependent order-disorder and crystallographic phase transition in a 0D Feii spin crossover compound and its non-spin crossover Coii isomorph
作者:Tamsyn M. Ross、Boujemaa Moubaraki、Kia S. Wallwork、Stuart R. Batten、Keith S. Murray
DOI:10.1039/c1dt10961h
日期:——
The new dipyridylamino/triazine ligand DDE (N2,N2,N4,N4-tetraethyl-N6,N6-di(pyridin-2-yl)-1,3,5-triazine-2,4,6-triamine) has been incorporated into the mononuclear FeIISCO compounds cis-[FeII(NCSe)2(DDE)2] (1), cis-[FeII(NCBH3)2(DDE)2] (2), and cis-[FeII(NCS)2(DDE)2] (3). Magnetic susceptibility measurements reveal that each of 1, 2 and 3 undergoes a complete, continuous spin transition with a T½ of ∼260 K, ∼300 K and ∼205 K, respectively. An analogue and isomorph of 1, cis-[CoII(NCSe)2(DDE)2] (4), remains high spin down to low temperatures. Variable temperature single crystal data reveal that 1 and 4 undergo a crystallographic phase transition (from orthorhombic Pbcn at high temperatures to monoclinic P2/c at low temperatures) accompanied by an order-disorder transition of ethyl moieties of the DDE ligand. In the Pbcn phase, the structures of 1 and 4 contain one crystallographically unique MII centre, while in the P2/c phase, 1 and 4 contain two crystallographically unique MII centres. Variable temperature powder X-ray diffraction experiments reveal that the crystallographic phase transition occurs at ∼250 K for 1. The occurrence of the concomitant order-disorder and crystallographic phase transitions undergone by 1 and 4 is not directly apparent in their magnetic susceptibility measurements, and this is likely due to the local environment of the MII centres remaining largely undisturbed as the transitions occur. The compound 2 is isostructural to 1 and 4 at low temperatures.
新的二吡啶基氨基/三嗪配体DDE(N2,N2,N4,N4-四乙基-N6,N6-二(吡啶-2-基)-1,3,5-三嗪-2,4,6-三胺)已加入到单核FeIISCO化合物顺式-[FeII(NCSe)2(DDE)2](1)、顺式-[FeII(NCBH3)2(DDE)2](2)和顺式-[FeII(NCS)2(DDE)2](3)中。磁化率测量显示,1、2和3分别经历了完全、连续的自旋转变,T½分别为约260 K、约300 K和约205 K。顺式-[CoII(NCSe)2(DDE)2](4)是1的类似物和同素异形体,在低温下仍保持高自旋。可变温度单晶数据显示,1和4经历了晶相转变(从高温下的正交晶系Pbcn到低温下的单斜晶系P2/c),伴随着DDE配体乙基部分的有序-无序转变。在Pbcn相中,1和4的结构包含一个独特的晶相MII中心,而在