Cryptates crystal structures

F. Fages, J.-P. Desvergne, H. Bouas-Laurent, J.-M. Lehn, J. P. Konopelski, P. Marsau, and Y. Barrans, Synthesis and fluorescence emission properties of a bis-anthracenyl macrotricyclic ditopic receptor. Crystal structure ofits dinuclear rubidium cryptate, J. Chem. Soc., Chem. Commun. 655(1990). 

In the case of ligands E, F and H the chelate/cryptate nature of the complexes will depend on whether or not the cation is contained between a branch and a ring or between two rings, or included inside a ring. Of course, in such cases, the above definitions, which concern the limiting cases, are less clear and classification may have to await a crystal structure determination. Finally, complexes formed by inclusion of a cation in a cavity delimited by a monocyclic, bicyclic or tricyclic structure may... 

From various observations it has been inferred that most AC and AEC complexes formed by the ligands of type 6—45 are 1 1 inclusion complexes, cryptates 34), in which the cation is held in the central cavity of the ligand molecule 34, 61, 106). This has been amply confirmed by several crystal structure determinations which also provided fundamental information about the shape of the ligand in the complex. 

Fig. 7. Crystal structure and conformation of a) its RbSCN cryptate (from Ref. (103) and (125)) b) the free macrobicyclic ligand [2.2.2], 30...

Figure 6. X-ray crystal structure of the iodide cryptate of the macrotricyclic quaternary ammonium receptor 16." ...

The X-ray crystal structures of the F", Cl , and Br" cryptates of 19-6H demonstrate the inclusion of one of the halide anions in an unsymmetrical fashion. In the case of the small fluoride ion complex a tetrahedral coordination environment is observed for the guest anion with a mean N(H) - P hydrogen-bonding distance of 2.72(8) A. The CP and Br" cryptates exhibit octahedrally coordinated halide ions situated more centrally within the host framework with N(H) - X" distances in the ranges 3.19-3.39 A (X = CP) and 3.33-3.47 A (X = Br ). It is noteworthy that the hydrogen-bonded distances for the anion within the cryptand host are longer by up to ca 0.15 A than those for the other anions in the lattice, suggesting a particularly... 

Bkouche-Waksman, I. Guilhem, J. Pascard, C. Alpha, B. Deschenaux, R. Lehn, J.-M. 110. Crystal structures of the lanthanum(III), europium(III), and terbium(III) cryptates of tris(bipyridine) macrobicyclic ligands. Helv. Chim. Acta 1991, 74,1163-1170. 

Macropolycyclic ligands containing intramolecular cavities of a three-dimensional nature are referred to as cryptands. The bicyclic cryptands (73) exist in three conformations with respect to the terminal nitrogen atoms, exo-exo, endo-exo and endo-endo 6 these forms can rapidly interconvert via nitrogen inversion but only the endo-endo form has been found in the crystal structures of a variety of complexes372 and for the free ligand ([2.2.2], 73, m = n = / = l).449 In their complexes with alkali and alkaline earth cations, the cryptands exhibit an enhanced stability over the crown ethers and coronands dufe to the macrobicyclic, or cryptate, effect.33 202... 

Alkali metal anions have also been generated as a result of cryptand stabilization of the corresponding cation. Cryptands were found to enhance the solubility of zerovalent alkali metals in various organic solvents.156-157 Initially, the solutions apparently contain the cryptate cation and solvated electrons together with free ligand. When more metal is dissolved, metal anions, M , are formed.158 Dye and co-workers have isolated gold-colored crystals of [Na+ c 2.2.2]Na 159160 and the crystal structure has been determined.161,162 Anion clusters such as Sb] , Pb2 and Sn," have been isolated as crystalline salts of the [2.2.2] cryptate counterion [2.2.2].162,163... 

Linear recognition is displayed by the hexaprotonated form of the ellipsoidal cryptand bis-tren 33, which binds various monoatomic and polyatomic anions and extends the recognition of anionic substrates beyond the spherical halides [3.11, 3.12]. The crystal structures of four such anion cryptates [3.11b] provide a unique series of anion coordination patterns (Fig. 4). The strong and selective binding of the linear, triatomic anion N3" results from its size, shape and site complementarity to the receptor 33-6H+. In the [N3 pyramidal arrays of +N-H "N- hydrogen bonds, each of which binds one of the two terminal nitrogens of N3-. 

The non-complementarity between the ellipsoidal 33-6H+ and the spherical halides results in much weaker binding and appreciable distortions of the ligand, as seen in the crystal structures of the cryptates 35 where the bound ion is F , Cl-, or Br-. In these complexes, F- is bound by a tetrahedral array of hydrogen bonds whereas Cl- and Br- display octahedral coordination (Fig. 4). Thus, 33-6H+ is a molecular receptor for the recognition of linear triatomic species of a size compatible with the size of the molecular cavity [3.11]. 

Fig. 4. Crystal structures of the anion cryptates formed by the hexaprotonated receptor molecule 33-6H+ with fluoride (left), chloride (centre), and azide (right) anions.

The crystal structure 57 of the strong and selective complex formed by the terephthalate dianion with a hexaprotonated macrobicyclic polyamine shows that it is a molecular cryptate 56 with the dianion tightly enclosed in the cavity and held by formation of three hydrogen bonds between each carboxylate and the ammonium groups [4.19]. Both structures 53 and 57 illustrate nicely what supermolecules really are they show two covalently built molecules bound to each other by a set of non-covalent interactions to form a well-defined novel entity of supramolecular nature. Acyclic [4.20a,b] and macrobicyclic [4.20c] hydrogen bonding receptors... 

Dietrich, B., Dilworth, B., Lehn, J.-M., etal, Anion cryptates Synthesis, crystal structures, and complexation constants of fluoride and chloride inclusion complexes of polyammonium macrobicyclic ligands. Helv. Chim. Acta 1996, 79, 569-587. 

Figure 12. Crystal structure of the bromide complex with 6 showing the side (A) and end-on (B) views for the bromide and one water molecule, and the side (C) and end-on (D) views for the bromide and three water molecules in the two crystallographically independent cryptates.

Menif, R. Reibenspies, J. Martell, A. E. Synthesis, protonation constants, and copper(II) and cobalt(II) binding constants of a new octaaza macrobicylic cryptand (MX)3crystal structures of the cryptand and of the carbonato-bridged dinuclear copper(II) cryptate, Inorg. Chem. 1991, 30, 3446-3454. 

Ciampolini, M., Dapporto, P., and Nardi, N. (1979) Structure and properties of some lanthanoid(III) perchlorates with the cryptand 4,7,13,16,21,24-hexaoxa-l,10-diazabicyclo[8.8.8]hexacosane, Dalton Trans, 974-977 Hart, F. A., Hursthouse, M. B., Abdul Malik, K. M., and Moorhouse, S. (1978) X-ray crystal structure of a cryptate complex of lanthanum nitrate, Chem. Commun. 549-50. 

Fie. 10. Crystal structure of the dinuclear cryptate (Na -ll C (reproduced with permission). 

Various homo- and heteropolyatomic anions have been stabilized with cryptate counterions. (Na 2.2.21) forms stable complexes with Pb52 (139), Sn94 (140), and Sb73 (141) by inhibiting reversion to the initial sodium-metal alloy phase. In a similar vein, the crystal structures of (K[2.2.2])+(HgTe2) containing a linear anion (142) and (K[2.2.2]+)2Sn42 have been described (143). 

Fig. 26. Template formation of the C3-symmetrical cryptates [R(L6)]3+ in water with numbering scheme. The representation of [R(L6)(NC>3)]2+ corresponds to the crystal structure of [Eu(L6)(N03)](N03)2(H20)4 (Platas et...

Several Ln(II) coronates and cryptates have been isolated, but few crystal structures are known. One example is given in Fig. 4.22 in which Eu(II) is sandwiched between two B15C5 coronands. The metal ion lies on an inversion centre and is ten coordinate with an environment close to a pentagonal antiprism, with approximate Dsa geometry. From the Eu-O distances, an ionic radius of about 1.39 A can be calculated, as compared to the standard value of 1.33 A, which means that the Eu-O bond lengths are somewhat longer than usual. 

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