Alkali metals coordination geometry

ESR and ESEM studies of Cu(II) in a series of alkali metal ion-exchanged Tl-X zeolites were able to demonstrate the influence of mixed co-cations on the coordination and location of Cu(II) (60). The presence of Tl(l) forces of Cu(II) into the -cage to form a hexaaqua species, whereas Na and K result in the formation of triaqua or monoaqua species. In NaTl-X zeolite, both species are present with the same intensity, indicating that both cations can influence the location and coordination geometry of Cu(II). The Cu(II) species observed after dehydration of Tl-rich NaTl-X and KT1-X zeolites was able to interact with ethanol and DMSO adsorbates but no such interaction was observed with CsTl-X zeolites. This interaction with polar adsorbates was interpreted in terms of migrations of the copper from the -cages. 

For alkali metals (i) is applicable but the oxidation state is always (I). Concept (ii) is applicable but the coordination geometry does not (in the... 

Many polypodands having terminal donor groups are also available, e.g. (39)-(41).33 These also exhibit cation complexation and phase transfer properties. KMn04 and aqueous alkali metal picrates are much more readily taken into organic phases in the presence of these podands than with dibenzo-18-crown-6.239 The KSCN complex of (39) exhibits a novel coordination geometry as all 10 donor atoms participate in coordination of the metal cation, and in order to do this the three arms wrap around the cation in a propeller-like fashion.240... 

Whether the use of 1,3-interactions in place of L-M-L force constants is a valid approach depends on the metal ion being considered. If it is a metal for which the M-L bonding is primarily electrostatic, such as an alkali, alkaline earth or rare earth metal, then 1,3-interactions are definitely preferable. In such cases it may be important to include an electrostatic component in the 1,3-interactions in addition to the usual van der Waals term. If, however, the metal ion is one that has a clear preference for a particular coordination geometry, then inclusion of at least a component of the L-M-L force constants may be indicated (see Chapter 11, Section 11.1). Recently, a model which includes both 1,3-interactions and force constants for the L-M-L angles has been described1 lsl Other approaches are discussed in Chapter 2, Section 2.2.2. 

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