ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P10. Silanethiolate Complexes of Bivalent Manganese, Cobalt, Iron and
Zinc with Water or Methanol as the Only Co-ligands
B. Becker, A. Kropidłowska
Chemical Faculty, Gdańsk University of Technology, 11/12 Narutowicza Str., 80-952 Gdańsk, Poland
e-mail bbecker@chem.pg.gda.pl
Zinc, with its d 10 electronic configuration and the peculiar properties of its coordination compounds plays a
specific role in bioinorganic processes. Zn(II) lacks the preference for a special coordination number and in
many metalloenzymes acts as Lewis acid, without changing its oxidation state. It means, e.g., that water bonded
to the Zn(II) center becomes more acidic and prone to dissociation. This is true for zinc and several other metals.
Cysteine is frequently found within coordination sphere of metaloproteins. Zinc fingers, liver alcohol
dehydrogenase or even metalothioneins may serve as examples. Being interested in metal thiolate chemistry we
asked ourselves how stable are complexes containing simultaneously these two ligands – thiolate and water. Can
they be prepared and stored? The search of Cambridge Crystallographic Database [1] revealed that despite the
simplicity of thiolate – water system, complexes bearing both these ligands are extremaly rare and in fact almost
unknown. The same was true for the complexes with such co-ligand as the simplest alcohol – methanol.
We limited our attention to four bivalent, essential trace elements: Mn(II) with high-spin d 5 configuration, d 6
Fe(II), d 7 Co(II) and closed shell d 10 Zn(II). As source of the thiolate ligand we used tri-tert-butoxysilanethiol
[2], stable, sterically encumbered and, because of oxygen atoms, able to serve as hydrogen bond acceptor. First
syntheses were performed for Zn(II) almost 15 years ago [3], and although we did success in isolation of
crystalline compounds they were not pure. Later we isolated and characterized structurally a Co(II) ionic
complex [4] [Co{SSi(OBu t )3}3(H2O)] – and only recently four Zn(II) complexes. One of them, shown in Fig. 1,
was isomorphous with the above mentioned Co(II) complex. Three others were neutral bimetallic molecules with
a formula [Zn{SSi(OBu t )3}2(H2O)]2. One of them is depicted in Fig. 2. In all complexes water was held in a
cavity formed by the proximal, spatially encumbered SSi(OBu t )3 silanethiolate ligands, and stabilized by
probably strong OSi…H–O–H…OSSi hydrogen bonds [5].
We did not prepare Co(II) and Zn(II) thiolates with methanol as the sole co-ligand, but it was possible in the case
of Mn(II) [6] and Fe(II) [7]. Again isomorphous complexes of formula [M{SSi(OBu t )3}2(MeOH)4] are stabilized
by a formation of four O–H … OSi hydrogen bonds – see Fig. 3.
Acknowledgement: The research was supported by the grant of the Polish Ministry of Education and Science
(No. 1 T09A 117 30). A. Kropidłowska thanks The Foundation for Polish Science for the fellowship.
References:
[1] Cambridge Structural Database, ver. 5.29, Cambridge 2008
[2] W. Wojnowski, B. Becker, L. Walz, K. Peters, E.-M. Peters, H.G. von Schnering
Polyhedron 11 (1992) 607-612.
[3] B. Becker, K. Radacki, W. Wojnowski, J.Organomet.Chem. 521 (1996) 39-49.
[4] B. Becker, A. Pladzyk, A. Konitz, W. Wojnowski, Appl. Organometal. Chem., 16 (2002) 517-524.
[5] A. Kropidłowska, J. Chojnacki, B. Becker, XVth Winter School on Coordination Chemistry, 4-8 December
2006, Karpacz - Poland, Proceedings, 34-35.
[6] A. Kropidłowska, J. Chojnacki and B. Becker, Inorg. Chem. Commun. 9 (2006) 383-387.
[7] L.Aparici-Plaza, K. Baranowska, B. Becker, 50 Crystallographic Meeting, Wrocław, 26-28.06.2008.
Abstracts, in print.
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