Spin Crossover in a Series of Non-Hofmann-Type Fe(II) Coordination Polymers Based on [Hg(SeCN)3]- or [Hg(SeCN)4]2- Building Blocks

Self-assembly of [Hg(SeCN)(4)](2)-tetrahedral building blocks, iron(II) ions, and a series of bis-monodentate pyridyltype bridging ligands has afforded the new heterobimetallic Hg-II-Fe-II coordination polymers {Fe[Hg(SeCN)(3)](2)(4,4'-bipy)(2)}(n) (1), {Fe[Hg(SeCN)(4)](tvp)}(n) (2), {Fe[Hg(SeCN)(3)](2)(4,4'-azpy)(2)}(n) (3), {Fe[Hg(SeCN)(4)](4,4'-azpy)(MeOH)} n (4), {Fe[Hg(SeCN)(4)](3,3'- bipy)} n (5) and {Fe[Hg(SeCN)4](3,3'-azpy)}(n) (6) (4,4-bipy = 4,4'-bipyridine, tvp = trans-1,2-bis(4-pyridyl)ethylene, 4,4'-azpy = 4,4'-azobispyridine, 3,3-bipy = 3,3'bipyridine, 3,3'-azpy = 3,3'-azobispyridine). Single-crystal X-ray analyses show that compounds 1 and 3 display a two-dimensional robust sheet structure made up of infinite linear [(FeL)n]2n+ (L = 4,4'-bipy or 4,4'-azpy) chains linked by in situ formed {[Hg(L)(SeCN)(3)](2)}(2)-anionic dimeric bridges. Complexes 2 and 4-6 define three-dimensional networks with different topological structures, indicating, in combination with complexes 1 and 3, that the polarity, length, rigidity, and conformation of the bridging organic ligand play important roles in the structural nature of the products reported here. The magnetic properties of complexes 1 and 2 show the occurrence of temperature-and light-induced spin crossover (SCO) properties, while complexes 4-6 are in the high-spin state at all temperatures. The current results provide a new route for the design and synthesis of new SCO functional materials with non-Hofmann-type traditional structures.

Automated summary

The self-assembly of tetrahedral building blocks and iron(II) ions resulted in a series of heterobimetallic Hg-II-Fe-II coordination polymers with diverse structural and magnetic properties. The nature of the bridging organic ligands plays a crucial role in determining the structural features of the products.