Structures and considerable static first hyperpolarizabilities: new organic alkalides (M+@n6adz)M'- (M, M'=Li, Na, K; n=2, 3) with cation inside and anion outside of the cage complexants

Eighteen structures of new organic alkalides (M+@n6adz)M'- (M, M'=Li, Na, K; n=2, 3) with the alkali-metal cation M+ lying near the center of the adz cage and the alkali-metal anion M'- located outside are obtained with all real frequencies. They exhibit very large static first hyperpolarizabilities (beta0) up to 3.2x10(5) au, which exceeds the record value of beta0=1.7x10(5) au for nonlinear optical compounds [Chem.-Eur. J. 1997, 3, 1091]. All potassides (M+@n6adz)K- (M=Li, Na, K; n=2, 3) have considerably large beta0 values (1.6x10(5)-3.2x10(5) au) much larger than the beta0 value (3.6x10(4) au) of the previously designed cuplike alkalide Li+(calix[4]pyrrole)K- [J. Am. Chem. Soc. 2006, 128, 1072]. This shows that the 26adz and 36adz cage complexants are preferable to cuplike calix[4]pyrrole complexant in enhancing the first hyperpolarizability. The effect of cage size of the complexant on the first hyperpolarizability is also presented here: in most cases, the smaller cage complexant corresponds to the larger beta0 value. Moreover, the crucial role by the alkali-metal anion in the large first hyperpolarizability of these alkalides is revealed. These results may provide new means for designing high-performance nonlinear optical materials.     

Effect of the complexant shape on the large first hyperpolarizability of alkalides Li+(NH3)4M-.

The effect of complexant shape effect on the first hyperpolarizability beta(0) of alkalides Li(+)(NH(3))(4)M(-) (M=Li, Na, K) was explored. At the MP2/6-311++G level, Li(+)(NH(3))(4)M(-) (M=Li, Na, K) have considerable beta(0) values due to excess electrons from chemical doping and charge transfer. By comparison with the alkalides Li(+)(calix[4]pyrrole)M(-), a complexant shape effect in Li(+)(NH(3))(4)M(-) is detected. The beta(0) values of Li(+)(NH(3))(4)M(-) with the "smaller", inorganic, T(d)-symmetric (NH(3))(4) complexant are more than four times larger than those of Li(+)(calix[4]pyrrole)M(-) with the "larger", organic C(4v)-symmetric calix[4]pyrrole complexant. The ratios of the beta(0) values of Li(+)(NH(3))(4)M(-) and Li(+)(calix[4]pyrrole)M(-) are 6.57 (M=Li ), 6.55 (M=Na), and 5.17 (M=K). In the Li(+)(NH(3))(4)M(-) systems, the NBO charge and oscillator strength are found to monotonically depend on the atomic number of the alkali metal anion. The order of the NBO charges of the alkali anions M(-) is -0.667 (M=Li )>-0.644 (M=Na)>-0.514 (M=K), while the order of the oscillator strengths in the crucial transition is 0.351 (M=Li )<0.360 (M=Na)<0.467 (M=K). This indicates that complexant shape effects are strong, and consequently the beta(0) values of Li(+)(NH(3))(4)M(-) are found to be beta(0)=70 295 (M=Li )<96 780 (M=Na)<185 805 a.u. (M=K). This work reveals that the use of a high-symmetry complexant is an important factor that should be taken into account when enhancing the first hyperpolarizability of alkalides by chemical doping.     

The structure and the large nonlinear optical properties of Li@calix[4]pyrrole

A new compound with electride characteristics, Li@calix[4]pyrrole, is designed in theory. The Li atom in Li@calix[4]pyrrole is ionized to form a cation and an excess electron anion. Its structure with C(4v) symmetry resembles a cup-like shape. It may be a stable organic electride at room temperature. The first hyperpolarizability of the cup-like electride molecule is first investigated by the DFT (B3LYP) method. The result shows that this electride molecule has a considerably large first hyperpolarizability with beta(0) = 7326 au (63.3 x 10(-30) esu), while the beta(0) value of the related calix[4]pyrrole system is only 390 au. Obviously, the Li atom doped in calix[4]pyrrole brings a dramatic change to the electronic structure, so that the first hyperpolarizability of Li@calix[4]pyrrole is almost 20 times larger than that of calix[4]pyrrole. We find that the excess electron from the Li atom plays an important role in the large first hyperpolarizability of Li@calix[4]pyrrole. The present investigation reveals a new idea and different means for designing and synthesizing high-performance NLO materials.     

Structures and static electric properties of novel alkalide anions F-Li+Li- and F-Li3+Li3-

Novel cluster anions Li2F- and Li6F- with alkalide character have been studied in the present paper. In contrast to a typical neutral alkalide, Li2F- contains a F- anion instead of the neutral ligand and forms an alkalide anion F-Li+Li-. In addition to a F- anion ligand, Li6F- contains a Li3+ superalkali cation instead of the alkali metal cation and a Li3- superalkali anion instead of the alkali metal anion, and this alkalide anion can be denoted by F-Li3+Li3-, which is supported by NBO charge results. The results indicate that the F- anion can polarize not only the Li atom but also the Li3 superalkali to form alkalide anions with excess electrons. For Li2F-, two linear structures (1Sigma+ and 3Sigma+ states) are obtained. For Li6F-, the structure of the 1A1 state is a trigonal antiprism capped by the F- anion with C3v symmetry, while the structure of the 7A' state is a slightly distorted trigonal antiprism with Cs symmetry. Due to the excess electrons on the alkali metal and superalkali anions (Li- and Li3-), the alkalide anions Li2F- and Li6F- have large first hyperpolarizabilities (beta0=1.116x10(4)-1.764x10(5) au). For the spin multiplicity effect on electric properties, in these two alkalide anions, the values of the static electric properties, especially the first hyperpolarizabilities, of the high spin states are larger than the corresponding values of the low spin states. For the substitution effect of superalkali atoms, in the two singlet states, as the Li3 superalkalis substitute the Li atoms, the value of the mean of polarizability increases, while the values of dipole moment and the first hyperpolarizability decrease.     

Substituent Effects on the Structural Features and Nonlinear Optical Properties of the Organic Alkalide Li+(calix[4]pyrrole)Li−

The effects of substituents on the structure, character, and nonlinear optical (NLO) properties of the organic alkalide Li⁺(calix[4]pyrrole)Li^? were studied by density functional theory. Natural bond orbital analysis and vertical ionization energies reveal that electron‐donating substituents strengthen the alkalide character of Li⁺(calix[4]pyrrole)Li^? and that they are beneficial for a larger first hyperpolarizability (β₀) value. However, electron‐withdrawing substituents have the opposite effect. The dependence of the NLO properties on the number of substituents and their relative position was detected in multisubstituted Li⁺(calix[4]pyrrole)Li^? compounds. For both the amino‐ and methyl‐substituted derivatives, the polarizabilities and the first hyperpolarizabilities increase as more pyrrole β‐H atoms are substituted. Moreover, distribution of the substituents so that they are as far away from each other as possible resulted in an increase in the β₀ value. The new knowledge obtained in this study may provide an effective approach to enhance the NLO responses of alkalides by employing pyrrole derivatives as complexants.     

What is the role of the complexant in the large first hyperpolarizability of sodide systems Li(NH3)(n)Na (n = 1-4)?

To explore the coordination number (around the cation) dependence of the nonlinear optical (NLO) properties in alkalides, this paper studies the structures and large NLO responses of model alkalides, Li(NH3)(n)Na (n = 1-4). At the MP2/aug-cc-pVDZ level, the structural characteristic is determined to be that the Li-Na distance increases (from 3.030 to 4.646 angstroms) with the increasing of the number of NH3 (n from 1 to 4). Results show that Li(NH3)(n)Na (n = 1-4) have considerably large first hyperpolarizabilities (beta0). Especially, a prominent coordination number dependence of the beta0 value is found as follows: beta0 = 13 669 (n = 1) < 26,840 (n = 2) < 39 764 (n = 3) < 77 921 au (n = 4) at the MP2 level. With the same coordination number (four N atoms) of Li+ cations, the beta0 value (77,921 au) of this "small" inorganic molecule Li(NH3)(n)Na is over five times larger than that of the "big" organic molecule Li@Calix[4]pyrrole-Na (14,772 au). This indicates that the beta0 value is strongly related to the flexibility of the complexant. Obviously, the flexibility of (NH3)4 is much greater than that of the cup-like shaped Calix[4]pyrrole. This work suggests that two important factors should be taken into account to enhance the first hyperpolarizability of alkalide, i.e., the coordination number around the cation and the flexibility of the complexant.     

Theoretical study on nonlinear optical properties of the Li+[calix[4]pyrrole]Li−dimer,trimer and its polymer with diffuse excess electrons

The static (hyper)polarizabilities of the dimer and trimer with diffuse excess electrons, [Li⁺[calix[4]pyrrole]Li^?]_n, are firstly investigated by the DFT(B3LYP) method in detail. For the dimer and trimer, a Li atom inside each calix[4]pyrrole unit is ionized to form a diffuse excess electron. The results show that the dimer and trimer containing two and three excess electrons, respectively, have very large first hyperpolarizablities as 2.3 × 10⁴ and 4.0 × 10⁴ au, which are 30 and 40 times larger than that of the corresponding [calix[4]pyrrole]_n (n = 2, 3) without Li atom. Also, β values of dimer and trimer are twice and four times as large as that of monomer containing one excess electron. Obviously, not only excess electron but also the number of excess electron plays an important role in increasing the first hyperpolarizability. Moreover, the (hyper)polarizabilities of the [Li⁺[calix[4]pyrrole]Li^?]_n polymer are investigated at ab initio level by using the elongation finite‐field (elongation FF) method. All the oligomers of the [Li⁺[calix[4]pyrrole]Li^?]_n with many excess electrons exhibit very large first hyperpolarizability and large second hyperpolarizability. The present investigation shows that by introducing several and more excess electrons into the nonlinear optical (NLO) materials will be an important strategy for improving their NLO properties, which will be helpful for design of NLO materials. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Theoretical investigation of the large nonlinear optical properties of (HCN)n clusters with Li atom

Two new classes of (HCN)(n)...Li and Li...(HCN)(n) (n = 1, 2, 3) clusters with the electride characteristic are formed in theory by the metal Li atom attaching to the (HCN)(n) (n = 1, 2, 3) clusters. Because of the interaction between the Li atom and the (HCN)(n) part, the 2s valence electron of the Li atom becomes a loosely bound excess electron. Our high-level ab initio calculations show that these new clusters with the excess electron have large first hyperpolarizabilities, for example, beta(0) = -15,258 au for (HCN)...Li and beta(0) = -3401 au for Li...(HCN) at the QCISD/6-311++G(3df,3pd) level (only beta(0) = -2.8 au for HCN monomer(26)). Obviously, the excess electron from the Li atom plays a crucial role in the large first hyperpolarizabilities of these clusters. The beta(0) value of (HCN)(n)...Li (beta(0) > 10(4) au, from sigma --> pi* transition) is larger than that of Li...(HCN)(n) (beta(0) > 10(3) au, from sigma --> sigma* transition) for n = 1, 2, or 3. In addition, two interesting rules have been observed. They are that |beta(0)| decreases with lengthening of the HCN chain for (HCN)(n)...Li clusters and that |beta(0)| increases as n increases for Li...(HCN)(n) clusters. In this paper, we discuss two classes of clusters that are highly similar to the electride structure model, of which the structural characteristics are that alkali metal atoms ionize to form cations and trapped electrons under the action of other polar molecules. Thus, the investigation on the large first hyperpolarizabilities of (HCN)(n)...Li and Li...(HCN)(n) (n = 1, 2, 3) may prompt one to study the unusual nonlinear optical responses of some electrides.     

Oligoether-strapped calix[4]pyrrole: an ion-pair receptor displaying cation-dependent chloride anion transport

A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1·F](-) and [1·Cl](-)) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li(+), Na(+), K(+), Cs(+), as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1·F](-), no appreciable interaction with the K(+) ion was seen. On the other hand, when this complex was treated with Li(+) or Na(+) ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li(+), Na(+), K(+), treating [1·F](-) with Cs(+) ions gave rise to a stable, host-separated ion-pair complex, [F·1·Cs], which contains the Cs(+) ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1·Cl](-). Here, no appreciable interaction was observed with Na(+) or K(+). In contrast, treating with Li(+) produces a tight ion-pair complex, [1·Li·Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1·F](-), treatment of [1·Cl](-) with Cs(+) ions gives rise to a host-separated ion-pair complex, [Cl·1·Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism.     

Ion-controlled on-off switch of electron transfer from tetrathiafulvalene calix[4]pyrroles to Li+@C60

Binding of chloride anion to a tetrathiafulvalene calix[4]pyrrole (TTF-C4P) donor results in ET to Li(+)@C(60) to produce the radical pair (TTF-C4P(?+)/Li(+)@C(60)(?-)), the structure of which was characterized by X-ray crystallographic analysis. The addition of tetraethylammonium cation, which binds more effectively than Li(+)@C(60)(?-) as a guest within the TTF-C4P cavity, leads to electron back-transfer, restoring the initial oxidation states of the donor and acceptor pair.     

Analytical applications of nano-baskets of calix[4]pyrroles

Calix[4]pyrrole is one such class which holds a great promise in the fields of sensors and their unique behavior as sensors owes to its structural flexibility. Anion binding ability of calix[4]pyrrole has been modified in a variety of ways. Introduction of electron releasing and electron withdrawing groups at the meso position or at β-pyrrolic positions leads to calix[4]pyrrole with deep cavities and fixed walls which shows increased selectivity and modified binding effects. Strapping of calix[4]pyrrole is another way to modify its structural behavior which is responsible for its binding behavior. Choice of strap could play a profound role not only in increasing the intrinsic anion binding affinity of calix[4] pyrrole, but also in modulating the receptor anion stoichiometry, thereby modifying potentially the inherent anion binding selectivity. Calix[n]pyrroles with extended cavities have also been synthesized. Such as calix[3]bipyrrole binds bromide substantially with high affinity than calix[4]pyrrole. Calix[4]pyrrole has also been used to produce anion sensors that can report the presence of anion by means of a color change. The medium effect on the complexation of calix[4]pyrrole and anion has been investigated in various solvents. Calix[4]pyrrole has also been used to increase the ionic conductivity of solid polymer electrolyte by anion complexation of the metal salt. Calix[4]pyrrole has been used to obtain optical sensors using surface plasmon resonance technique. Composite films of cellulose acetate containing calix[4]pyrrole has also been reported which has potential usage in packaging, storage and preservation. In nut shell, calix[4]pyrrole can be modified in a variety of ways to form versatile sensors which can be used in variety of ways in various areas.     

Alkali metal atom-aromatic ring: a novel interaction mode realizes large first hyperpolarizabilities of M@AR (M=Li, Na, and K, AR=pyrrole, indole, thiophene, and benzene)

Several new electride compounds M@pyrrole (M = Li, Na, and K), Li@AR (AR = indole, thiophene, and benzene), Li@tryptophan and Li@serotonin were designed and investigated, which exhibit considerably large first hyperpolarizabilities (β(0)) (6705, 1116, 11399, 5781, 4808, 1536, 8106, and 9389 au, respectively) by comparison with their corresponding sole molecules pyrrole (β(0) = 30 au), indole (104 au), thiophene (6 au), benzene (0 au), tryptophan (159 au) and serotonin (151 au), respectively. The computational results revealed that the interaction of the alkali metal atom with π-conjugated aromatic ring (AR) is one effectively new approach to produce diffuse excess electron to get a large β(0) value, which is advantageous for the design of the novel high-performance NLO materials with π-conjugated AR: alkali metal atoms doped nanomaterials and biomolecules.     

[Li…X]e-[1](X=FH,OH2, NH3)的光电性质从头算

在MP2理论水平上采用6-311G基组系列计算了一价阴离子van der Waals复合物[Li…X]e-[1](X=FH, OH2, NH3)的偶极矩(μ)、平均极化率(α)以及平均一阶超极化率(β), 讨论了基组效应和电子相关效应对计算结果的影响, 比较了价电子对复合物一阶超极化率的贡献. 在MP4(SDQ)/6-311++G(2df, 2pd)水平上计算得到[Li…FH]e-[1]的μ=2.5633 a.u., α=1.0476×10³ a.u., β=1.0948×10⁵ a.u.；[Li…OH2]e-[1] 的μ=2.3204 a.u., α=1.2201×10³ a.u., β=2.1410×10⁵ a.u.；[Li…NH3]e-[1]的μ=2.4687 a.u., α=1.4817×10³ a.u., β=3.4040×10⁵ a.u.. 计算结果表明, 三种一价阴离子复合物分子均具有非常大的一阶超极化率, 而一个价电子对复合物的一阶超极化率的贡献超过1.0×10⁵ a.u..     

Pentapyrrolic calix[4]pyrrole

A new calix[4]pyrrole has been synthesised that contains a 3,4,5-trisbromopyrrole appended to a meso-position which shows enhanced anion affinity as compared to the parent meso-octamethylcalix[4]pyrrole macrocycle.     

碱金属掺杂叔丁基杯[4]芳烃体系的结构及非线性光学性质

采用密度泛函理论B3LYP方法得到了M@t-Bu-calix[4]arene和（M@t-Bu-calix[4]arene）Li'（M=Li,Na,K）体系的几何结构. 其中（M@t-Bu-calix[4]arene）Li'（M=Li,Na,K）三个体系各有5个稳定异构体,在前三个异构体中,碱金属与t-Bu-calix[4]arene分子间具有很强的相互作用能,说明了体系的稳定性. 在部分（M@t-Bucalix[4]arene）Li异构体中Li'原子以阴离子形式存在,整个体系表现出碱金属化物的特性. 此外,使用CAMB3LYP方法计算了t-Bu-calix[4]arene及碱金属掺杂后体系的非线性光学性质. 结果表明,t-Bu-calix[4]arene内部掺杂一个碱金属原子M后,体系的一阶超极化率（β₀）有较大提高,而在配体外部又掺杂一个Li原子后,体系具有更大的β₀值. 其中（M@t-Bu-calix[4]arene）Li'体系的MLi'-4异构体表现出最高的β₀值（41827-114354 a.u.）,并且随着M原子序数的增加而逐渐增大. 可见,碱金属掺杂是提高t-Bu-calix[4]arene非线性光学响应的一种有效策略.     

Cation- and anion-assisted binding of triethylenediamine by zinc bisporphyrinates

The complexation of zinc calix[4]arene or calix[4]pyrrole bisporphyrinates with alkali metal cations, halide anions, and triethylenediamine was studied by ¹H NMR spectroscopy. It was established that the binding of molecules and/or charged particles by various fragments of calix[4]arene and calix[4]pyrrole porphyrins are interrelated processes. This makes it possible to use one process (for example, complexation of the calix[4]arene fragment of the macrocycle with alkali metal cations or complexation of the calix[4]pyrrole fragment with halide ions) as a tool for controlling another process (complexation of the porphyrin fragments of the macrocycle with neutral molecules).     

杯[4]吡咯-阴离子体系相互作用的理论研究——杯[4]吡咯-卤素阴离子体系的密度泛函研究

用密度泛函B3LYP/LANL2DZ方法对自由杯[4]吡咯的最低能量构象和卤素阴离子-杯[4]吡咯复合物进行了计算研究.结果表明,杯[4]吡咯与卤素离子能通过彼此间的相互作用形成复合物,并且这种相互作用在本质上应为分子间的氢键相互作用;杯[4]吡咯与卤素阴离子形成的复合物在构型变化、电荷转移、前线轨道及其作用方式、成键布居以及能量和热力学参数等方面均按元素周期律有规律地变化,杯[4]吡咯与卤素阴离子间的相互作用沿元素周期依次减少.     

Theoretical study of anion binding to calix[4]pyrrole: the effects of solvent,fluorine substitution,cosolute, and water traces

The binding of different anions to calix[4]pyrrole has been studied by means of molecular dynamics coupled to thermodynamic integration calculations. The effect of different apolar solvents, octafluoro substitution, and the change in binding free energy derived from the presence of cosolute and water traces (the hydrated salt used to introduce the anion in the solution) were examined. Calculations allow us to rationalize the differential binding of ions to calix[4]pyrrole and octafluorocalix[4]pyrrole as well as to predict the behavior in new solvents for which experimental data are not available yet. It is found that both calix[4]pyrrole and octafluorocalix[4]pyrrole have a dramatic preference for F- in the gas phase and pure aprotic solvents, but the situation can change dramatically in protic solvents or in the presence of the hydrated cation which is used as cosolute of the anion. Overall, our results provide interesting clues for a better understanding of the process detected experimentally as "binding".     

Conformational features and anion-binding properties of calix[4]pyrrole: a theoretical study

The conformational preference of calix[4]pyrrole and its fluoride and chloride anion-binding properties have been investigated by density functional theory calculations. Geometries were optimized by the BLYP/3-21G and BLYP/6-31G methods, and energies were evaluated with the BLYP/6-31+G method. To model the effect of medium, the SCIPCM solvent model was also employed. Four typical conformations of the parent substituent-free calix[4]pyrrole were studied. Both in the gas phase and in CH(2)Cl(2) solution, the stability sequence is predicted to be 1,3-alternate > partial cone > 1,2-alternate > cone. The cone conformation is predicted to be about 16.0 and 11.4 kcal/mol less stable in the gas phase and CH(2)Cl(2) solution, respectively. This is mainly due to electrostatic repulsions arising from the all-syn pyrrole/pyrrole/pyrrole/pyrrole arrangement present in this conformer. The existence of possible 1:1 and 1:2 anion-binding modes were explored in the case of fluoride anion, and the factors favoring the 1:1 binding mode are discussed. The calculated binding energy for fluoride anion is about 15 kcal/mol larger than that for chloride anion. The calculated binding energy for chloride anion agrees with the experimental value very well. The presence of meso-alkyl substituents destabilizes the cone conformer with respect to the 1,3-alternate conformer and, therefore, reduces the anion-binding affinity by 3-4 kcal/mol. The strength of N-H- - -anion hydrogen bonds in the various structures subject to study were estimated on the basis of the calculated anion-binding energies and the predicted structural deformation energies of substituent-free calix[4]pyrrole.     

Synthesis,structures, and conformational characteristics of calixarene monoanions and dianions

The synthesis, complete characterization, and solid state structural and solution conformation determination of calix[n]arenes (n = 4, 6, 8) is reported. A complete series of X-ray structures of the alkali metal salts of calix[4]arene (HC4) illustrate the great influence of the alkali metal ion on the solid state structure of calixanions (e.g., the Li salt of monoanionic HC4 is a monomer; the Na salt of monoanionic HC4 forms a dimer; and the K, Rb, and Cs salts exist in polymeric forms). Solution NMR spectra of alkali metal salts of monoanionic calix[4]arenes indicate that they have the cone conformation in solution. Variable-temperature NMR spectra of salts HC4.M (M = Li, Na, K, Rb, Cs) show that they possess similar coalescence temperatures, all higher than that of HC4. Due to steric hindrance from tert-butyl groups in the para position of p-tert-butylcalix[4]arene (Bu(t)C4), the alkali metal salts of monoanionic Bu(t)C4 exist in monomeric or dimeric form in the solid state. Calix[6]arene (HC6) and p-tert-butylcalix[6]arene (Bu(t)C6) were treated with a 2:1 molar ratio of M(2)CO(3) (M = K, Rb, Cs) or a 1:1 molar ratio of MOC(CH(3))(3) (M = Li, Na) to give calix[6]arene monoanions, but calix[6]arenes react in a 1:1 molar ratio with M(2)CO(3) (M = K, Rb, Cs) to afford calix[6]arene dianions. Calix[8]arene (HC8) and p-tert-butylcalix[8]arene (Bu(t)()C8) have similar reactivity. The alkali metal salts of monoanionic calix[6]arenes are more conformationally flexible than the alkali metal salts of dianionic calix[6]arenes, which has been shown by their solution NMR spectra. X-ray crystal structures of HC6.Li and HC6.Cs indicate that the size of the alkali metal has some influence on the conformation of calixanions; for example, HC6.Li has a cone-like conformation, and HC6.Cs has a 1,2,3-alternate conformation. The calix[6]arene dianions show roughly the same structural architecture, and the salts tend to form polymeric chains. For most calixarene salts cation-pi arene interactions were observed.