A Homologous Series of [Fe(H2Bpz2)2(L)] Spin-Crossover Complexes with Annelated Bipyridyl Co-Ligands
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- 作者：Rafal Kulmaczewski ; Helena J. Shepherd ; Oscar Cespedes ; Malcolm A. Halcrow
- 刊名：Inorganic Chemistry
- 出版年：2014
- 出版时间：September 15, 2014
- 年：2014
- 卷：53
- 期：18
- 页码：9809-9817
- 全文大小：696K
- ISSN：1520-510X
文摘
Four new iron(II) complexes [Fe(H2Bpz2)2(L)] were prepared (pz = pyrazolyl), where L is dipyrido[3,2-f:2鈥?3鈥?h]quinoxaline (dpq), dipyrido[3,2-a:2鈥?鈥?c]phenazine (dppz), dipyrido[3,2-a:2鈥?鈥?c]benzo[i]-phenazine (dppn), and dipyrido[3,2-a:2鈥?3鈥?c](6,7,8,9-tetrahydro)phenazine (dppc). Crystal structures of [Fe(H2Bpz2)2(dpq)], [Fe(H2Bpz2)2(dppz)], and [Fe(H2Bpz2)2(dppn)] all reveal stacks of complex molecules formed through 蟺鈥撓€ stacking between interdigitated bipyridyl chelate ligands, often with additional intercalated toluene or uncoordinated bipyridyl ligand (dpq). Molecules of [Fe(H2Bpz2)2(dppc)] form a different stacking motif in the crystal, with weaker contacts between individual molecules. Many of the structures also contain channels of disordered solvent, running between the molecular stacks. Despite their different stacking motifs, all these compounds exhibit very gradual thermal spin-crossover (SCO) on cooling, which occur over different temperature ranges but are otherwise quite similar in form. Weak thermal hysteresis in one of these spin equilibria can be attributed to the effects of a change in bipyridyl ligand conformation in the molecular stacks around 150 K, which was observed crystallographically. These results demonstrate that strong mechanical coupling between molecules in a crystal is not sufficient to engineer cooperative SCO switching, if other regions of the lattice are less densely packed.