synthesis and characterization of a novel c3-symmetric ... · pdf filechem. int. ed. 2008, 47,...
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ConclusionA new C3-symmetric ligand was prepared using standard procedures. The reaction se-quence can be monitored by 1H-NMR and ESI-MS easily.The steric properties of the ligand could be changed easily, as the reaction between thepyridine based aldehyde and triaminoguanidinium salts are simple Schiff-base type re-actions with nearly quantitative yields.The coexistence of different coordination geometries of cadmium in one complex meansa low energy barrier for the coordination transition.
Synthesis and Characterization of a Novel C3-symmetric Ligand and itsFirst Coordination CompoundC. R. Göb, I. M. Oppel
IntroductionC3-symmetric triaminoguanidinium based ligands are able to coordinate soft metal ionslike Zn(II)[1], Cd(II)[2] or Eu(III)[3] as well as hard metal ions like Ti(IV) or Zr(IV) in their tri-dentate chelating binding pockets. As the combination of ligands and metal ions providesflexible coordination environments, a variety of different discrete supramolecular coor-dination cages, such as tetrahedra[2], octahedra[4] and trigonal bipyramids[5], are accessi-ble.
Background and IdeaThis work is focused on the synthesis and characterization of positively charged coor-dination compounds and cages. This is achieved by the establishment of a new ligandtype. The 2-pyridylene-N-oxide based ligand is able to chelate metal ions like the alreadyliterature known benzylidene-type ligands.[3] Additionally, three positive charges are intro-duced to the ligand which allow the coordination complex to achieve an overall positivecharge.
Ligand Synthesis and AnalysisSimple five step synthetic routine:2 is produced by a standard routine with good yield (87%). The oxidation of 2 is per-formed from the crude reaction product quantitatively. The 1,3-dioxolane (acetal) in 3 issplit by acidic aqueous conditions. The triple Schiff-base reaction between 5 and varioustriaminoguanidinium salts (6) is carried out in aqueous ethanolic solutions and givesyields of 80-95 %. The anions of 6 can be exchanged by reaction with silver salts.
First Coordination Compound with Cadmium:Double-Decker
Institute for Inorganic Chemistry, Rheinisch-Westfälische Technische Hochschule Aachen Landoltweg 1, 52074 Aachen, [email protected], [email protected]
References[1] I. M. Oppel, K. Föcker, Angew. Chem. Int. Ed. 2008, 47, 402-405.[2] I. M. Müller, R. Robson, F. Separovic, Angew. Chem. Int. Ed. 2001, 40, 4385-4386.[3] M. L. Abraham, A. C. Schulze, A. Korthaus, I. M. Oppel, Dalton Trans. 2013, 42, 16066-16072.[4] I. M. Müller, S. Spillmann, H. Frank, R. Pietschnig, Chem. Eur. J. 2004, 10, 2207-2213.[5] I. M. Müller, D. Möller, Angew. Chem. Int. Ed. 2005, 44, 480-484.
2-formylpyridine-N-oxide (4)SG P21/n
a 6.821(2) Å
b 4.460(1) Å
c 18.425(6) Å
α 90.0 °
β 100.438(4) °
γ 90.0 °
V 551.2(3) Å3
Z 4
# solventδ [ppm]
H1 H3 H4 H5 H6
1 DMSO-D6 9.94 7.97 7.86 7.62 8.752 C6D6 6.03 7.41 7.11 6.64 8.43
3 CDCl3 6.307.52-7.48
7.25-7.18
7.25-7.18
8.20-8.15
4 CDCl3 10.61 7.81 7.45 7.32 8.207 DMSO-D6 9.12 8.31 7.49 7.45 8.36 d [Å] Cd1/Cd4 Cd2/Cd3/Cd5
Na 2.291(7) 2.255(7)Nb 2.375(7) 2.319(7)Ooxide 2.296(6) 2.622(6)Ochelate1 2.524(7) 2.388(6)Ochelate2 2.273(7) 2.304(6)Oeq 2.384(7)
Oax 2.422(6) 2.230(6)
crystallization from hot DMF solution(80 °C, cooling rate 0.25 Kh-1)
[°] Cd1/Cd4 Cd2/Cd3/Cd5Na-Cd-Nb 68.0(2) 69.6(2)Nb-Cd-Ooxide 73.8(2) 76.2(2)Na-Cd-Ooxide 132.4(2) 137.4(2)
entropy drivenself-organization
flexible coordi-
nation ofCd(II)
chelatingligands
rigid tridentatebindingpockets
flexible coordi-
nation ofCd(II)
fl
ligands
coordination number 6 and 7 for Cd(II)observed simultaneously
The reaction progress is easily monitored by 1H-NMR where a significant shifting of H1 is observed in every reaction step.The crystal structure of 4 is not described in literature yet.
[Cd6[(PyO)3]2(OAc)8(H2O)]SG P21/c
a 17.479(4) Å
b 18.752(4) Å
c 26.525(5) Å
α 90.0 °
β 93.836(3) °
γ 90.0 °
V 8674.5(3) Å3
Z 4
AcknowledgmentWe are grateful for all kinds of measurements around this topic to Mr. Toni Gossen (NMR), Mrs. Claudia Dittmer andDr. Wolfgang Bettray (ESI-MS). Furthermore we want to thank Mr. Kevin Lamberts for the collection of crystallographic dataconcerning the double-decker coordination complex and 2-formylpyridine-N-oxide crystals.