J. Phys. Chem. 1987, 91, 6600-6606
6600
action, which is exothermic by approximately 6 kcal/mol. The subsequent rearrangement of cis-HCNH to trans-HCNH would have a barrier of 8 kcal/mol and would be exothermic by approximately 5 kcal/mol. Rearrangement of trans-HCNH to H2CN, while exothermic by some 14 kcal/mol, would have a relatively high barrier, near 38 kcal/mol, exceeding the threshold for the formation of H 2 C N . Thus, the stabilization of trans-HCNH, and possibly also of the cis rotamer, would be expected in the matrix experiments. The absorption a t 886 cm-I, contributed by a product that is photolyzed by visible radiation, is a candidate for assignment to one of the two HCNH rotamers. For both of these species, Bair and Dunning" have calculated the torsion and the CNH bending vibrations to lie between about 900 and 1050 cm-I. The assignment to the torsion vibration is readily tested, since for either the cis or the trans structure this vibration is the only out-of-plane mode. With the structures calculated by Bair and Dunning and the observed value of 886.3 cm-I, the calculated positions of the torsion vibration for cis- and trans-HI3CNH are 881.7 and 884.2 cm-I, respectively. The corresponding values for cis- and transHCI5NH are 883.5 and 885.8 cm-'. The agreement with the observed frequencies, given in Table I , is not sufficiently good to support assignment to the torsion mode of either rotamer of HCNH. While data do not suffice for similar calculations of isotopic shifts in the CNH deformation (a') of the HCNH species, the observation that the shift on nitrogen-15 substitution is greater than that on carbon-13 substitution would be consistent with the assignment of the 886.3-cm-l absorption to the in-plane CNH deformation fundamental of either cis- or trans-HCNH. It cannot be determined from the present experiments whether HCNH results from a second channel for the H HCN reaction or from the addition of H atoms to HNC, a product of the cage recombination of H + CN.*' The appearance of the 2046-cm-' absorption of CN in the mercury-arc photolysis experiments, in which photodecomposition of HCN should not occur, may result from the photolysis of HzCN
+
+
+
to form H , C N . A substantial barrier is ~ a l c u l a t e d ' ~for~ 'the ~ direct H HCN reaction to form these products, which is endothermic. The ESR signal of CN was suppressed in the earlier studies2 of this system, which gave a prominent H2CN signal. A low-pressure mercury-arc photolysis source was used for the ESR experiments on Ar:HCN:HI samples, whereas a medium-pressure mercury-arc lamp was used for the present experiments. The low-pressure lamp may have had a considerably lower radiation output near 280 nm, where the strongest H2CN absorption occurs.
+
Conclusions H atoms react with HCN isolated in solid argon at 14 K to form HzCN in sufficient concentration for detection of five vibrational fundamentals and of extended structure in one of the previously reported electronic transitions. The analysis of the infrared spectra for isotopically substituted HzCN is consistent with a planar molecular structure with partial triple bond character for the CN bond. The ultraviolet observations support the previous identification of two electronic transitions of HzCN. A Librational assignment has been proposed for structure in the 2Al-XZB2band systems of the H2CN-d,,species. An infrared absorption at 886 cm-' can be assigned to the in-plane CNH deformation fundamental of cis- or trans-HCNH, which has a photodecomposition threshold in the visible region of the spectrum. The mechanism by which HCNH is formed cannot be established from this series of experiments. Acknowledgment. The design and construction of the transfer optics for the Bomem Fourier transfer spectrophotometer by W. Bruce Olson were crucial to the detection of the weaker H2CN absorptions in the studies using that experimental system. This work was supported in part by the US.Army Research Office under Research Proposal 2 1495-CH. Registry No. H atomic, 12385-13-6;HCN, 74-90-8;Ar, 7440-37-1; HZCN, 15845-29-1;H2I3Cl4N,110905-04-9;H2I2Ci5N,110905-05-0; D2I2Ci4N,51624-18-1.
Stability, Molecular Dynamics in Solution, and X-ray Structure of the Ammonium Cryptate [NH4+C2.2.2]PF,Bernard Dietrich, Jean-Pierre Kintzinger, Jean-Marie Lehn,* Bernard Metz,+ and Assou Zahidi Laboratoire de Chimie Organique Physique (UA 422). Institut Le Bel, Universitt Louis Pasteur, 67000 Strasbourg, France, and Laboratoire de Chimie MinZrale (UA 4051, EHICS Strasbourg. and Laboratoire de Cristallographie Biologique, IBMC, CNRS, 67000 Strasbourg. France (Received: March 27, 1987; In Final Form: June 16, 1987)
The macrobicyclic ligand 1 [2.2.2] forms a highly stable complex with the NH4+cation in aqueous solution. Although the spherical macrotricycle 2 forms an even stronger complex, 1 is a more efficient binder of NH4+at pH 7-8 because of easier protonation of 2. Crystal structure determination indicates that the complex is of cryptate type [NH4+C1],the NH4+substrate being held in the macrobicyclic cavity by NH+-.X hydrogen bonds with one bridgehead nitrogen and three oxygens. Determination of the 'H, I3C, 15N,and I4N NMR relaxation times and calculation of the corresponding correlation times allow a detailed description of the molecular dynamics of the NH4+cryptates of 1 and 2. The [NH,+Cl] cryptate shows weak dynamic coupling between the receptor and the bound substrate, which reorients rapidly inside the cavity. On the other hand, the [NH4+C2]cryptate shows strong dynamic coupling, the receptor and substrate having similar molecular reorientation times. Nuclear Overhauser effects indicate that the orientation of the NH4+cation inside the cavity is similar in solution to that in the crystal.
Complexes of polyatomic cations such as ammonium, guanidinium, hydrazinium, diazonium, hydronium, etc. have been intensively studied in particular because of the biological role of substituted ammonium ions. The parent ion, the ammoTUA 405 and IBMC.
0022-3654/87/2091-6600$01.50/0
nium cation NH4+,is of special interest for two major reasons: (i) NH4+is on the border between inorganic and organic chem(1) Cram, D. J.; Cram, M. J. Acc. Chem. Res. 1978, 11, 8. (2) Lehn, J. M. Pure Appl. Chem. 1978, 50, 871. (3) Lehn, J. M. Pure Appl. Chem. 1979, 51, 919.
0 1987 American Chemical Society
Structure of Ammonium Cryptate
The Journal of Physical Chemistry, Vol. 91, No. 27, 1987 6601
TABLE I: 'H Chemical Shifts (in ppm) and J(I4N-H) (in Hz) for Ligand 1 and Its Cryptate [NH4'C1]"
solvent CDCI,
1
H2O/D20 (4/1)
PW'C 11 1 [NH4+ClI
OCH,CH,O 3.69 3.64 3.55 3.58
OCH&H,N 3.60 3.56 3.57 3.54
OCH,CH,N 2.65 2.57 2.16 2.50
NHa+ 6.92 (52.0) 6.98 (49.6)
"See also Figure 1. 1
i
- -. - - -. ppm
2
H
I
I
H
1
i
3
1
Figure 1. 'HNMR spectrum (200 MHz) of ligand 1 (L) and its cryptate [I4NH4+C1](C) in CDCI,.
istry, i.e., its behavior toward complexing agents can be related either to the alkali metal cation group or to its substituted derivatives; (ii) its simple structure and high symmetry allow a thorough analysis of its binding characteristics. Several structural studies have been published on NH4+ complexes with coronands and with antibiotic^.^^ Only one crystal structurelo and a detailed physicochemical study" of the NH4+ complex with a macropolycyclic ligand, the spherical macrotricycle 2, have been reported.
15
N
1
v
Figure 2. 'H, 2H, ISN,and I4N NMR spectra of the ammonium cation in the cryptate [NH4'C1] in CD2C12: (a) IH NMR signals of a I4NH4+/I5NH4+1:l mixture; (b) 2H NMR signals of I4N2H4'; (c) ISN NMR signals of 15NH4' obtained by an INEPT sequence;3o (d) 14N NMR signals of I4NH4+.IJ (15N,H)= 72.9 0.4 Hz; IJ (I4N,H) = 52.0 f 0.4 Hz; ' J (14N,2H)= 8.0 f 0.4 Hz.
*
1
2
TABLE II: Protonation Constants and Stability Constants of the NH4+ and K+ Complexes of Cryptands 1 and 2 cryptand PKI PK~ NHa+" " ' K 1 9.6 7.45 4.5 5.3 (9.6)b (7.3)b (5.4)b 2 10.2c 10.9c 6.lC 3.4d
"log K , in aqueous solution. bReference 1 3 . 'Reference 11. Reference 14. crobicyclic ligand 1 [2.2.2]. The syntheses of 1 and 2 and their binding properties toward alkali and alkaline-earth metal cations have been described in earlier
IN+
1I
We describe here the X-ray structure and the physicochemical properties (stability constants, bonding scheme, molecular dynamics) of the cryptate complex formed by NH4+ with the ma(4) De Jong, F.; Reinhoudt, D. N. Adu. Phys. Org. Chem. 1980,17,279. ( 5 ) Behr, J. P. In Bioenergetics and Thermodynamics: Model Systems; Braibanti, A., Ed.; Reidel: Dordrecht, The Netherlands, 1980; p 425. (6) Dobler, M. Ionophores and their Sfructures; Wiley: New York, 1981. (7) Goldberg, I. In Inclusion Compounds; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Eds.; Academic: London, 1984; Vol. 2, p 261. (8) Sutherland, I. 0. J . Chem. SOC.,Faraday Trans. 1 1986, 82, 1145; Chem. SOC.Rev. 1986, 15, 63. (9) Nagano, 0.;Kobayashi, A.; Sasaki, Y. Bull. Chem. SOC.Jpn. 1978, 51. - ,790 - (10) Metz, B.; Rosalky, J. M.; Weiss, R. J . Chem. S O ~ Chem. ., Commun. 1976, 533. (1 1 ) Graf, E.; Kintzinger, J. P.; Lehn, J. M., Le Moigne, J. J . Am. Chem. SOC.1982, 104, 1672.
Formation of the Ammonium Complex of Cryptand [2.2.2] in Solution Addition of a solid ammonium salt NH4X (X = NO3-, C1-, C104-) to a solution of 1 in CDC13 or CDzClzwas followed by the progressive disappearance of the original IH N M R spectrum and by the appearance of a new spectrum. The signals corresponding to the ligand protons were shifted to higher field; at the same time a triplet corresponding to the ammonium protons appeared at low field (Figure 1; Table I). The ammonium complex was similarly formed in aqueous solution: in this spectrum the ammonium triplet was also observed, proving that the exchange of the ammonium cation and of its protons was slow. The 'H, 2H, l5N, and 14N ammonium N M R spectra of [NH4'C1] are (12) Dietrich, B.; Lehn, J. M., Sauvage, J. P., Blanzat, J. Tetrahedron 1973, 29, 1629, 1647. (1 3) Lehn, J. M.; Sauvage, J. P. J. Am. Chem. SOC.1975,97,6700. Lehn, J. M. Acc. Chem. Res. 1978, 1 1 , 49. (14) Graf, E.; Lehn, J. M. J. Am. Chem. SOC.1975, 97, 5022; Helu. Chim. Acto 1981, 64, 1040.
Dietrich et al.
6602 The Journal of Physical Chemistry, Vol. 91, No. 27, 1987 1,3H+ L , 2 H + L,fH+C C' LfH+ I
1
L3H+
c' c
L:ZH+
PH
I
1
methanol solution, (dimensions 0.18 X 0.20 X 0.27 mm), was fixed in a Lindemann glass capillary. X-ray diffraction measurements were performed on a CAD4 diffractometer (Cu K a radiation, graphite monochromator, room temperature ca. 20 "C). Cell dimensions were obtained by least squares from 21 centered reO~P, flections (18 o < 6 < 34'). Crystal data: cl H ~ o F ~ N ~ fw = 539.50, trigonal, R k , a = b = 11.880 (1) c = 33.113 (6) A, a = p = 90°, y = 120°, V = 4047 (1) A3, 2 = 6, D, = 1.33 g cm-j, Dq = 1.31 (1) g cm-3 (by flotation in a heptane/carbon tetrachloride solution), F(000) = 1716, = 16.0 cm-'. A total of 732 reflections was measured in the w/26 scan mode (scan width: 0.70 0.14 tan 0 deg; variable scan speed; data collection range: 2' < 8 < 63'). The intensities of three standard reflections were measured every 2 h of X-ray exposure time, and no decay was observed. The intensities were corrected for Lorentz and polarization effects, but not for absorption. A $ scan showed the absorption effect to be weak (dispersion less than 5% on intensities). The structure was solved by direct methods15 and refined by full-matrix least-squares analysis. All calculations were done using SDP.16 Only the 533 reflections with I > 341) were included in the refinement. Weights were assigned as w = 4F02/U2(Fo2), with u(Fo2) = + (0.07 F02)2]1/2,u(1) based on counting statistics. Atomic scattering factors were taken from the usual tab~lation,"~ and the effects of anomalous dispersion were included ' ~ ~ of Af' and Af". in F, by using Cromer and I b e r ~ values The structure was initially solved in space group R3c (no. 161). All non-hydrogen atoms were located on the best E map.I5 In this model, the threefold axis passes through the nitrogen atoms of the complex cation and the phosphorus atom of the anion. After examination of the atomic positions, it appeared that the crystal structure was centrosymmetric. Thus space group Rgc (no. 167) was chosen. Consequently, the complex cation and the anion have crystallographic site symmetry 32 and 3, respectively. The hydrogen atoms of ligand 1 were located on difference Fourier maps in the course of the refinement and included in the model. Two peaks appeared then at ca. 1 A from the nitrogen of the ammonium ion, one on the threefold axis, the other in a general position. These were interpreted as half-weight hydrogen atoms and included in the refinement. The NH4+ orientation so found was in agreement with results of molecular mechanics calculations of this complex,'* which showed that starting structures with different NH4+ orientations converged toward the same minimum. This optimized complex has C, symmetry with one N-H bond lying on the ligand threefold axis, and the other three N-H bonds oriented toward the ligand oxygens (see Figure 4). During refinement, the hydrogen atom in the general position moved somewhat nearer to the nitrogen of the ammonium ion. An extinction correction was applied according to the equation F, = (1 gIc)F,. The value of g determined by least-squares refinement is 4.8 X 10". The refinement of the structure with all the atoms converged to R , = CIFol- IFcl/CIFol = 0.044 and R2 = [Cw(lFol - IFcl)2/CwlFo12]'/2 = 0.065. The number of parameters refined was 84. The largest shift/error ratio in the last cycle was 0.06, and the goodness-of-fit indicator = [Cw(lFol- IFcl)2/(m- n ) ] ' / 2 = 1.47, where m and n are the numbers of observations and variables, respectively. The highest peak on the final difference Fourier map was 0.07 e A-3. The final values for the atomic positional and thermal parameters are presented in Table 111.
A,
+
I
1
4
.
.
.
.
1
.
3.5
. . .
oom
I
1
.
.
3
.
.
1
2.5
Figure 3. 'H NMR (200 MHz) observation of the evolution of the amounts of cryptates [NH4+C1](C) [NH4+C2](C') and of the diproionated species [2,2H+] as a function of the pH of the solution (D2O); L = 1; L' = 2. represented in Figure 2. These results clearly demonstrate the actual complexation of NH4+ by 1.
Stability Constants of the Ammonium Cryptates of 1 and 2 The stability constants K , defined by the equilibrium 1 were obtained by pH metric titration after determination of the protonation constants K l and K2 (equilibria 2 and 3) as reported earlier.I3 The protonation constants of ligands 1 and 2 and the L
+ M+ + (L,M+) LH++L+H+
LH?+ + LH+
+ H+
K,
K1 K2
(2) (3)
stability constants of their complexes with NH4+ and K+ are indicated in Table 11. Ligands 1 and 2 have different selectivities towards NH4+ and K+. 1 is selective for K+ and 2 for NH4+;" it forms a more stable complex with K+ than 2, whereas the reverse is observed with NH4+. However, the relative efficiency of ion binding by 1 and 2 depends on the pH because of competition with protonation. Thus, progressive acidification of the solution leads to much more extensive protonation of the more basic 2 than of 1, so that the latter becomes a more efficient binder of NH4+ than the f ~ r m e r . ~ ' .Figure '~ 3 shows spectra of an equimolecular mixture of 1 and 2 in the presence of one equivalent of NH4+ for each ligand. At pH 9.6, ligand 1 is completely in its ammonium complex form, whereas 2 is partially protonated. On lowering the pH, the proportion of [NH4+C2] with respect to the diprotonated species [2, 2H+] falls off rapidly. At pH 8.6 the [NH4+C2]complex is undetectable, ligand 2 being entirely diprotonated; at this pH, 1is still present as its ammonium complex, and 35% of [NH4+C1] remain at pH 7.4.
Crystal Structure of the [NH4+C2.2.2] Cryptate Hexafluorophosphate Salt Data Collection, Structure Solution, and Refinement. A crystal of [NH4+C1]PF6-, obtained by slow evaporation of a water-
+
(15) Main, P.; Fiske, S.; Hull, S.E.; Lessinger, L.; Germain, G.; Declercq, J. P.; Woolfson, M. M. MULTAN 80; Universities of York, England, and Louvain, Belgium, 1980. (16) All calculationswere carried out on a DEC PDP 11/44 with the use of the Enraf-Nonius CADGSDP-PLUS programs. This crystallographic computing package is described by: Frenz, B. A. In Computing in Crystallography, Schenk, H., Olthof-Hazekamp, R., Van Konigsveld, H., Bassi, G. C., Eds.; Delft University Press: Delft, Holland, 1978; p 64. Frenz, B. A. Structure Determination Package and SDP-PLUS User's Guide; Frenz: College Station, TX, 1982. (17) (a) Cromer, D. T.; Waber, J. T. International Tables for X-Ray Crystallography; Kynoch: Birmingham, England, 1974; Vol. IV, Table 2.2B. (b) Cromer, D. T.; Ibers, J. A. Ibid. Table 2.3.1. (18) Wipff, G.; Gehin, D., unpublished results.
Structure of Ammonium Cryptate
The Journal of Physical Chemistry, Vol. 91, No. 27, 1987 6603
Figure 4. ORTEP stereoscopic view of the cation [NH,+Cl]. The ammonium ion is represented in its two possible orientations (see text). Hydrogen atoms are represented by spheres of arbitrary size. Thermal ellipsoids are drawn at the 30% probability level. TABLE III: Atomic Positional and Thermal Parameters with Their Estimated Standard Deviations in Parentheses' U(1,l) or atom Y Z B h , A2 U(2,2) X U(3,3) U(1 2 ) 0.000 0.1586 (1) N1 1.000 U(1,l) U(1,l) 0.055 (1) 0.039 (2) 0.065 (1) 0.078 (1) 0.041 (1) 0.0383 (9) 0.0209 (3) 0.14377 (8) C2 0.8945 (3) 0.028 (1) 0.076 (2) 0.055 (2) -0.0475 (3) 0.1685 (1) 0.051 (1) C3 0.7728 (3) 0.0599 (9) 0.0491 (9) 0.0222 (6) 0.20652 (6) 0.0444 (8) 0.0167 (2) 04 0.7939 (2) C5 0.6784 (2) -0.0338 (3) 0.23031 (8) 0.043 (1) 0.071 (1) 0.063 (2) 0.0278 (9) 0.250 N 1.000 0.000 U(1,l) U(1,l) 0.044 (2) 0.046 (3) 0.000 P 1.ooo 0.000 U(1,l) U(1,l) 0.0501 (6) 0.063 (1) F 1.1000 (2) 0.1163 (2) 0.02708 (7) 0.093 (1) 0.080 (1) 0.126 (2) 0.0288 (9) 4.7 (6) -0.014 (2) 0.1159 (8) H2a 0.871 (2) 5.2 (7) 0.123 (2) 0.1444 (7) H2b 0.929 (2) 0.1751 (8) 5.1 (6) -0.140 (3) H3a 0.744 (2) 6.8 (8) -0.056 (3) 0.1534 (9) H3b 0.693 (3) -0.031 (2) 0.2158 (8) 5.1 (7) H5a 0.611 (2) 0.2340 (8) 5.1 (7) H5b 0.637 (2) -0.124 (2) 0.000 HNl 1.000 0.215 (3) 5(2) 1.052 (5) 0.064 (4) HN2 0.258 (2) 5(1)
+
'The form of the anisotropic thermal parameter is e x p [ - 2 ~ ~ ( h ~ a * ~ U ( l k2b*W(2,2) ,l) 2klbsc*U(2,3)}].
Bond distances, bond angles, and torsional angles appear in Table IV. A listing of the observed and calculated structure amplitudes are available as supplementary material (see the paragraph at the end of the paper). Discussion. The crystal structure consists of discrete complex cations and anions, with no unusual interactions between them. The shortest nonbonded distances between the fluorine atoms of the PF6- group and hydrogen atoms of [2.2.2] are close to the sum of the Van der Waals radii (2.67 A) of these atoms;lg the shortest value is 2.62 (4) A for F-Ii3b (C3-.F = 3.473 (4) A), and the shortest Ne-P distance is 7.39 A. Thus, the cation is far from the PF6- anion, which appears to be ordered, with P-F bond lengths of 1.576 (2) A. As expected, the cation is a cryptate complex [NH4+C1] (Figure 4). Its symmetry is C, or D3 if the two orientations of the NH4+ ion are averaged. The ammonium ion occupies the center of the cavity and is bound by hydrogen bonds to the heteroatoms of the ligand. The lone pairs of the two nitrogen atoms of the tertiary amines point toward the ammonium ion; thus the ligand has the in-in conformation. The oxygen atoms also point toward the center of the cavity. The ammonium ion is surrounded by the eight heteroatoms of 1 in a slightly distorted bicapped trigonal prism with D3 point symmetry; the two triangles formed by the oxygen atoms are twisted. The twist angle a is equal to 16.0' and the distance d between the two triangles is 2.88 A. The distance between the two apical nitrogen atoms is 6.052 (7) A, similar to that observed in the [Cs+C1] cryptate.20 The coordination polyhedron of the
u(1,3) 0 -0.005 (1) -0.012 (1) -0.0010 (8) 0.003 (1) 0 0 -0.036 (1)
u(2,3) 0 0.002 (1) -0.009 (1) -0.0014 (8) 0.016 (1) 0 0 -0.039 (1)
+ 12c*2U(3,3)+ 2hka*b*U(1,2) + 2hla*c*U(1,3) +
TABLE I V Selected Distances and Bond and Torsion Angles" (a) Distances, A Nl-C2 1.478 (3) C5-C5(i) 1.479 (6) 04-.-04(i) 2.900 (4) C2-C3 1.499 (4) P-F 1.576 (2) 04.a.N 2.931 (2) C3-04 1.428 (3) Nl.s.04 3.006 (2) C ~ * * * F ( V )3.473 (4) 04-C5 1.428 (3) N1.S.N 3.026 (3) C2-Nl-C2(ii) N 1-C2-C3 C2-C3-04 C3-04-C5 04-CS-C5(i)
(b) Bond Angles, deg 109.5 (2) F-P-F(ii) 113.3 (3) F-P-F(iv) 109.1 (2) Nl**-N*..04 112.7 (2) Nl.-.N..-04(i) 108.4 (2) 04...N...04(i)
C2(ii)-Nl-C2-C3 Nl-C2-C3-04 C3-04-CS-CS(i)
(c) Torsion 8 1.5 71.9 176.9
Angles, deg C2(iii)-Nl-C2-C3 C2-C3-04-C5 04-C5-C5(i)-04(i)
90.8 (1) 89.2 (1) 60.6 (1) 119.4 (1) 59.3 (1) -1 58.4 173.7 -75.5
'Symmetry transformations: (i) x-y, -y, - z; (ii) 1 - y , x - y 1, z; (iii) 2 y - x, 1 - x, z ; (iv) 1 + y , 1 + y - x , -2; (v) I / , y , 2/3 x - 2, - z . Numbers in parentheses are estimated standard deviations in the least significant digits.
+
+
+
ammonium ion is a tetrahedron formed by N I and three oxygen atoms. Bond lengths and angles in 1 (Table IV) are similar to those found in other cryptates.*I The O-.O and N-0 contacts have (20) Moras, D.; Metz, B.; Weiss, R. Acra Crystallogr.,Secr. B 1973, B29,
388. (21) Metz, B.; Weiss, R. Inorg. Chem. 1974, 13, 2094 and references
(19) Bondi, A. J . Phys. Chem. 1964, 68, 441.
therein.
Dietrich et al.
6604 The Journal of Physical Chemistry, Vol. 91, No. 27, 1987 TABLE V Characteristic Structural Parameters for [MtC2.2.2] Cryptates M+ =
Kt
Rb+
cs+
TIt
NH4+
22.5 2.65 2.785 2.874 5.74 4.255 1.38 1.38
14.9 2.82 2.897 3.002 6.00 4.388 1.50 1.52
15.3 2.87 2.966 3.034 6.07 4.498 1.56 1.71
15.3 2.79 2.904 2.946 5.89 4.418 1.49 1.51
16.0 2.88 2.931 3.026 6.05 4.422 1.53
Na'
parameter
45.8 2.11 d," 8, 2.574 M- * *O, 8, 2.752 M**.N,8, N.*.N, 8, 5.50 4.07 0.. .0,6A cavity radius R,,' 8, 1.21 1.02 ionic radius,d 8, a,' deg
"See text and ref 23. bDistance between the two O3 triangular planes of the bicapped prism. cThe definition of R, is given in ref 22. dCalculated values, using the ionic radii of Pauling, revised by Ahrens, and corrected for o c t a c o ~ r d i n a t i o n . ~ ~ ~ * ~
h A
x
-
*
1631
I83 K
/I
4XB
-
XB
1
1
'
I
'
p m
x 1
"C
TC,"
15N
Tam
'H lSNo
1.52 s 1.43 s 1.54 s 2.50 s 20 s 0.12 s 15.1 ps 2.1 ps
1
3
'
0.80 s 0.84 s 2.5 s 26.7 ps 17 ps
"See ref 30.
single AA'XX' spectrum. At low temperature (
