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 inNew journal of chemistry Vol. 42; no. 13; pp. 10898 - 10905
Main Authors Gong, Xiaoli, Zhu, Liyao, Zhao, Jufeng, Cui, Guangmang, Lu, Xinmiao, Xie, Yaoming, King, R. Bruce
Format Journal Article
LanguageEnglish
Published Cambridge Royal Society of Chemistry 2018
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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.
ISSN:1144-0546
1369-9261
DOI:10.1039/C8NJ01434E