Iron(ii) complexes of 2,6-di(1H-pyrazol-3-yl)-pyridine derivatives with hydrogen bonding and sterically bulky substituents

Abstract

aSyntheses of 2,6-di(5-aminopyrazol-3-yl)pyridine (L 1 ), 2,6-di(5-tertbutylcarboxamido-pyrazol-3-reported. Iron complex salts of the first four ligands were crystallographically characterised. The structures exhibit intermolecular hydrogen bonding between the cations and the anions and/or solvent, leading to a fluorite (flu) net, a 1D ladder structure, and a homochiral self-penetrating helical network related to the (10,3)-a (srs) topology. All the complexes are high-spin in the crystal, and bulk samples are also fully or predominantly high-spin at room temperature and below although two of the dried materials exhibit partial spin-state transitions on cooling.

Spin state behavior of iron(II)/dipyrazolylpyridine complexes. New insights from crystallographic and solution measurements

“…). It is also unique among the compounds in this article in being sensitive to aerobic oxidation [60]. That …”

“…showing the hydrogen bonding between the complex dication and the perchlorate anions and diethyl ether molecules (which are de-emphasised for clarity). The cations and anions are respectively eight-connected and four-connected nodes in a distorted flu network topology [60].…”

“…(a helical self-penetrating network derived from the (10,3)-a {srs} net) [63]. However in the solid state they are all either high-spin, or show very poorly defined spin-crossover on cooling [60]. ).…”

The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

“…In that case, electron-withdrawing substituents would strengthen the ligand field by reducing ligand-metal π-donation. 2+ , since in that study both electron-donating and -withdrawing substituents led to a similar reduction in T ½ [98]. It may be relevant that those pyrazolyl substituents are adjacent to the 3-bpp NH groups, which could lead to them influencing hydrogen bonding by these groups.…”

“…This has been best studied in a series of complexes [Fe(bip) 2 [100] reported no measurable response to different anions in solution, that might reflect the aqueous solvents used for those measurements, which would disfavor intermolecular hydrogen-bonding and ion pairing [107]. 2+ , since in that study both electron-donating and -withdrawing substituents led to a similar reduction in T½ [98]. It may be relevant that those pyrazolyl substituents are adjacent to the 3-bpp NH groups, which could lead to them influencing hydrogen bonding by these groups.…”