Tetranuclear iron carbonyl complexes with a central tin atom: relationship to iron carbonyl carbides
The two tetranuclear iron carbonyl systems EFe 4 (CO) n (E = Sn, C) containing central group 14 interstitial atoms differ in that spiropentane-like SnFe 4 (CO) 16 has been synthesized in the tin system whereas the butterfly CFe 4 (CO) 13 , with three fewer carbonyl groups is the carbonyl-richest tet...
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Published in | New journal of chemistry Vol. 42; no. 13; pp. 10898 - 10905 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Cambridge
Royal Society of Chemistry
2018
|
Subjects | |
Online Access | Get full text |
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Summary: | The two tetranuclear iron carbonyl systems EFe
4
(CO)
n
(E = Sn, C) containing central group 14 interstitial atoms differ in that spiropentane-like SnFe
4
(CO)
16
has been synthesized in the tin system whereas the butterfly CFe
4
(CO)
13
, with three fewer carbonyl groups is the carbonyl-richest tetranuclear iron carbonyl carbide that has been synthesized. In order to clarify this point, the complete SnFe
4
(CO)
n
(
n
= 16, 15, 14, 13, 12) series has been studied by density functional theory for comparison with earlier similar studies on their CFe
4
(CO)
n
analogues. The experimentally observed spiropentane-like Sn[Fe
2
(CO)
8
]
2
structure is found to be the lowest energy structure for the SnFe
4
(CO)
16
system as it is for the experimentally unknown CFe
4
(CO)
16
system. Loss of a CO group from Sn[Fe
2
(CO)
8
]
2
joins the two Fe
2
(CO)
8
units by a third Fe–Fe bond to give an SnFe
4
(CO)
15
structure with a bonded four-atom Fe–Fe–Fe–Fe chain. Further CO loss from SnFe
4
(CO)
15
adds a fourth Fe–Fe bond in the lowest energy SnFe
4
(CO)
14
structure. The lowest energy SnFe
4
(CO)
13
structure is analogous to that of the experimentally known iron carbonyl carbide CFe
4
(CO)
13
with a central Fe
4
butterfly having five Fe–Fe bonds. The energetics of CO dissociation from the EFe
4
(CO)
n
(E = C, Sn;
n
= 16, 15, 14, 13) species account for the experimentally observed differences between the systems with central tin and central carbon atoms. Thus for the tin systems the CO dissociation energy from SnFe
4
(CO)
16
is relatively high at ∼50 kcal mol
−1
consistent with its experimental observation as a stable species. However, for the tetranuclear iron carbonyl carbides CFe
4
(CO)
n
, the CO dissociation energies of the species with more than 13 CO groups are all very small or even negative suggesting CFe
4
(CO)
13
to be the carbonyl-richest viable iron tetracarbonyl carbide consistent with experiment. |
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ISSN: | 1144-0546 1369-9261 |
DOI: | 10.1039/C8NJ01434E |