Coordination, second-sphere

The specific structure of [(H20)5Ni(py)]2+ was observed in the complexes with the second-sphere coordination of calix[4]arene sulfonate.715 There are two different [(H20)5Ni(py)]2+ cations in the complex assembly. In one the hydrophobic pyridine ring is buried in the hydrophobic cavity of the calixarene with the depth of penetration into the calixarene cavity being 4.3 A (Figure 9). The second independent [(H20)5Ni(py)]2+ cation is intercalated into the calixarene bilayer. 

Most network structures involving crown ethers are simple hydrogen bonded chains where the crown forms second sphere coordination interactions with a complex ion. These are known for [18]crown-6, [15]crown-5 and [12]crown-4 hosts with a variety of metal complexes [17-25]. For instance when combined with the small [12] crown-4, the perchlorate salts of Mn(II), Ni(II) and Zn(II) form polymeric chain structures with alternating crown ethers and [M(H20)6]2+ cations [19]. Similarly the larger [18]crown-6 forms simple linear chains with metal complexes and cations such as fra s-[Pt(NH3)2Cl2] [20], [Cu(NH3)4(H20)]2+ (Fig.2) [21],and [Mg(H20)5(N03)] + [22],... 

Scheme 10.26 Metallomacrocyclic/[2]catenane formation templated by second-sphere coordination of the PdCI2 subunit reported by Wisner and coworkers.

Wu B, Liang JJ, Yang J et al (2008) Sulfate ion encapsulation in caged supramolecular structures assembled by second-sphere coordination. Chem Commun 1762-1764... 

Second Sphere Coordination coordination of molecules in the layer just beyond the ligands bound to the metal center... 

The complexes discussed so far all involve direct interaction between the metal ion and the crown ether. Another important class of crown ether derivatives is that involving second sphere coordination. These compounds involve interaction between the ligands in the primary coordination sphere (such as H2O in M(H20)6"" cations), and the second sphere ligand, the crown ether, often by means of hydrogen bonds. Such a sttuctme is foimd in the [Mn(0H2)6](C104)2 adduct of 18-crown-6 (94). It is not surprising that transition metal/crown ether chemistry often involves adducts, since... 

The concept of coordination in the second sphere was introduced by Werner. All authors agree that such outer-sphere association exists in solution, hut they disagree about the kind and the extent of this association. Some advocate a second-sphere coordination which is closely analogous to the inner-sphere coordination. The data which support this hypothesis are not very convincing and can be criticized in various ways. The present author finds that the electrostatic theories of N. Bjerrum, Fuoss, and Kraus, according to which the formation of the ion-associates is a result of coulombic attraction, both qualitatively and quantitatively, give the most trustworthy picture of the outer-sphere association. However, this does not exclude the fact that some preferred mutual orientation exists in the ion pairs. 

This type of reaction is a special case of the more general category— reactions of coordinated ligands—which has recently been discussed 19). However, one has the feeling that the concept second-sphere coordination, as understood by modern research workers, no longer includes this category of important reactions. 

Colquhoun HM, Stoddart JF, Williams DJ (1986) Second-sphere coordination-a novel role for molecular receptors. Angew Chem Int Ed 25 487-507... 

S.h.f.s. are observed (208, 662) in F , S, Se , and Te crystals and in all cases are attributable to interaction with first and, in some cases, second sphere coordination of the anion (see Table XXXIII). In ZnS, S splittings are observed, a rare event since the isotope is only in 0.74% natural abundance. The decrease in Ag (g — 2.0023) and in Cr h.f.s. in the series of host lattices ZnS, ZnSe, and ZnTe follows the order of increase in covalency as expected. There are no paramagnetic chemical compounds of Cr+ with 8 =. ... 

First examples of second-sphere coordination adduct between a CD and such organometallic complexes were observed with the ferrocene and its derivatives. Thus, Breslow was the first to report in 1975 that ferrocene forms a 1 1 adduct with the /3-CD in both A/T-dimethylformamide and dimethyl sulfoxide. Nevertheless, the first crystalline inclusion complexes of ferrocene and its derivatives were prepared by Harada and Takahashi in 1984. The inclusion complexes were obtained by direct addition of crystals of ferrocene or its derivatives into aqueous solutions of CD. The stoichiometry of the inclusion complexes was found to be dependent on the sizes of the CD. The /3-CD and y-CD formed 1 1 stoichiometric inclusion complexes whereas a-CD formed a 2 1 (CD guest) complex with ferrocene. From induced circular dichroism experiments, three structures were proposed for these adducts as shown in Figure... 

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