Ferric wheels

When triethanolamine H3L13 (35) was reacted with sodium hydride and iron(III) chloride, the hexanuclear centrosymmetric ferric wheel [Nac Fe6(L13)6 )Cl (36) was isolated. Amidst a set of possibilities in the template-mediated self-assembly of a supramolecular system, the one combination of building blocks is realized that leads to the best receptor for the substrate [112]. Therefore, the six-membered cyclic structure 36 is exclusively selected from all the possible iron triethoxyamine oligomers, when sodium ions are present. The iron(III) complex 36 is present as an Sg-symmetric wheel, with an encapsulated sodium ion in the center and a chloride counterion. Consequently, the trianion (L13)3- acts as a tripodal, tetradentate, tetratopic ligand, which each links three iron(III) ions and one sodium ion. In the presence of cations with different ionic radii, different structures are expected. Therefore, when triethanolamine H3L13 (35) was reacted with cesium carbonate and iron(III) chloride, the octanuclear centrosymmetric ferric wheel [Csc Fe8(L13)8 ]Cl (37) was isolated (Scheme 13) [113]. 

A common feature of the complexes [Nac Fe6(L13)6 ]Cl (36) and [Csc- Fe8(L13)g ]Cl (37, Sect. 6) is that one p -OT ethoxide donor of the triethano-lateamine ligands [N(CH2CH20)iCH2CH20 ] of (L13) 3 does not participate in the formation of the ferric wheels. They function solely as ligands for the coordi-native saturation of the iron centers. Therefore, any monoanionic donor, such as a chloride ion, could also be a candidate for this function. As expected, reaction of /V-alkyldiethanolamines H2L14 17 (38) with calcium hydride and iron(III) chloride yielded the neutral iron coronands [Fe6Cl6(L14 17)6] (39) with unoccupied centers (Scheme 14) [114-116],... 

In principle, all the six-membered ferric wheels [Fe6CI6(LM l7)6] (39) are isostructural and have idealized S g-molecular symmetry. However, there are fundamental differences concerning their crystal packing. For example, all the disk-like molecules of 39a are arranged in parallel and are piled in cylindrical columns, with all the iron centers superimposed. Each column is surrounded by six parallel columns, which are alternately dislocated by 1/3 c and 2/3 c against the central one (Fig. 13). 

An additional interesting feature of some ferric wheels is their readiness to create various superstructures, depending on the nature of their side arms. For instance, van der Waals interactions cause the side arms of [Fe6Cl6(L15)6] (39b) to interlock... 

Fig. 13 Stereo representations of the schematic unit cell top) and the crystal packing bottom) of the ferric wheel [Fe6Cl6(L14)6] (39a), view along the c axis...

An especially interesting example of crystal packing, leading to porous three-dimensional frameworks, is caused by ji-ji stacking of the naphthyl groups of the side arms of the ferric wheels [FegClgCL16 ] (39c) (Fig. 15). 

Unlike [Fe6Cl6(L14)6] (39a) (Sect. 7.1), the ferric wheels of [Fe6Cl6(L17)6] (39d) are not arranged in parallel but rather are three-dimensionally perpendicular (Fig. 16) [114-116], a well-known arrangement for 3D-coordination polymers (Sect. 9.2, Fig. 18). 

It is evident that the majority of different structures given above provides excellent sources for further development, as illustrated exemplarily by the ferric wheels. A general feature of the metallo-coronands [Fe6Cl6(L)6] (39 Sect. 7) is the fact that the N-alkyl substituents are alternately arranged above and below the plane of the six iron ions. Interestingly, this molecular geometry offers the possibility to construct container molecules. 

The final iron cage discussed is the largest known ferric wheel. The octadecanuclear wheel, [Fe(0H)(XDK)Fe2(0Me)4(02CMe)2]e (70) [XDK = the dianion of m-xylylenediamine bis(Kemp s triacid imide) see Scheme 2] (164), shown in Fig. 29, is made from reaction of the di-nuclear iron complex of XDK with [NEt4](02CMe) in methanol, followed... 

Stephen J. Lippard Molecular ferric wheel , [Fe(OCH3)2(02CCH2Cl)]io... 

One example of such systems is the circular molecule (Fe(OMe)2(02CCH2Cl)]1o denominated ferric wheel [84], of which the ground state is antiferromagnetic (S=0). A transition-metal molecule of this size constitutes a challenge for DF calculations. 

Electronic structure SCF spin-polarized calculations were performed with the DV method for the cluster [Fe(OC)2(02CC)]io formed by stripping the ferric wheel molecule of its peripheral H and Cl atoms (see Fig. 8) [85]. Mossbauer spectroscopy measurements have been reported [84] calculations of the hyperfine parameters were performed and compared to experiment. The magnetic moment obtained on the Fe was 4.3/ib and the charge +2.3 [85]. 

Fig. 8 - Views of the cluster (Fe(OC)2(02CC))io, representing the molecule ferric wheel a) Top view (z=0 plane), b) Side view.

Figure 16), better known as ferric wheel [11,48,53]. The wheel is prepared in methanol solution from the reaction between [Fe30(02CCFl2Cl)6(H20)3](N03) and Fe(N03)3-9H20. Four p2-OMe donors and two monochloroacetate ions link three Fe(lII) ions each out of the 10 Fe(Ill) ions of 25 and is unoccupied in the center. 

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