Journal article
New iron(II) spin-crossover complexes with heterocyclic amine-derived ligands and STEPS experiments on photogenerated metastable high-spin states
Dalton Transactions, (11), pp 2621-263
1987
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Abstract
Cationic complexes of the type [Fe(L
NN
)
3
]
2+
and [Fe(L
NNN
)
2
]
2+
have been isolated as Cl
-
, ClO
4
-
, or BF
4
-
salts, where L
NN
and L
NNN
represent bidentate and tridentate nitrogen-donor ligands respectively. The bidentate ligands were 2-(2′-pyridyl) benzimidazole (pybtim), 2-(2′-pyridyl)-
N
-methylbenzimidazole (mpybzim); 2-(2′-pyridyl) benzothiazole (pybzt), 2,2′-dipyridylamine (dpya), and the tridentates di(2-pyridylmethyl)amine (dpyma), 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy), 2,6-bis(
N
-methylbenzimidazol-2′-yl)pyridine (mbzimpy), and 2,6-bis(benzothiazol-2′-yl) pyridine (bztpy). Except for [Fe(dpya)
3
][ClO
4
]
2
, all these FeN
6
chromophores exhibit strong absorption in the 550 nm region, which is assigned as a metal-to-ligand charge-transfer transition. Between 4 and 320 K, the iron(
II
) is in the low-spin form in the majority of these compounds; high-spin exceptions are [Fe(dpya)
3
][ClO
4
]
2
and [Fe(mbzimpy)
2
]Cl
2
. Other complexes show evidence of the onset of a spin transition near 40 °C, while the salt [Fe(bztpy)
2
][ClO
4
]
2
·CHCl
3
is a well defined spin-crossover system. The low-spin complex [Fe(bzimpy)
2
][ClO
4
]
2
was excited by irradiation with visible light, and the generation and decay of the resulting high-spin form was observed under cryogenic conditions. In solution, [Fe(bzimpy)
2
]
2+
acts as a weak diprotic acid and also exhibits quintet singlet spin crossover (Δ
H
=-42.7 kJ mol
-1
, Δ
S
=-140.9 J K
-1
mol
-1
). The complexes are all electrochemically oxidizable to their iron(
III
) forms in non-aqueous solution, but the dpyma, bztpy, pybtz, and dpya chelates thus formed are unstable. The iron(
III
) complex [Fe(H
-2
bzimpy)
2
]
-
containing the doubly deprotonated ligand was obtained as its low-spin triethylammonium salt. The high-spin chloro complexes [Fe(bzimpy)Cl
3
], [Fe(mbzimpy)Cl
3
], Fe(mbzimpy)Cl
2
, and the mixed-spin iron(
II
) complex salt [Fe(bzimpy)][FeCl
4
] were also isolated.
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Details
- Title
- New iron(II) spin-crossover complexes with heterocyclic amine-derived ligands and STEPS experiments on photogenerated metastable high-spin states
- Creators
- Anthony W Addison - Drexel UniversitySudhir Burman - Drexel UniversityCurtis G Wahlgren - Drexel UniversityOdatt A Rajan - University of VirginiaTeresa M RoweEkkehard Sinn - University of Virginia
- Publication Details
- Dalton Transactions, (11), pp 2621-263
- Publisher
- Royal Society of Chemistry
- Number of pages
- 1
- Resource Type
- Journal article
- Academic Unit
- Chemistry
- Web of Science ID
- WOS:A1987K924800017
- Scopus ID
- 2-s2.0-37049086857
- Other Identifier
- 991019174023604721
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- Collaboration types
- Domestic collaboration
- Web of Science research areas
- Chemistry, Inorganic & Nuclear