2734 J . Phys. Chem. 1988, 92, 2734-2738

Crystal Structure of the As-Synthesized Precursor (MnAI,)P,,O,,*C,H,,N to Molecular Sieve MnAPO- 1 1

Joseph J. Pluth, Joseph V. Smith,* and James W. Richardson, Jr.+

Department of Geophysical Sciences and Materials Research Laboratory, The University of Chicago, Chicago, Illinois 60637 (Received: June 19, 1987)

l h e crystal structure of the as-synthesized precursor to molecular sieve MnAPO- 11 was determined by single-crystal X-ray diffraction: ~(A19Mn)Plo040.C6H16N, M, = 2699, orthorhombic, Icm2, a = 13.472 (1) A, b = 18.712 (1) A, c = 8.4431 (3) A, V = 2128.4 (2) .A3, 2 = 2, D, = 2.14 g X(Cua,) = 1.54050 A, p = 86.1 cm-I, F(000) = 1398, T - 295 K, R = 0.055 for 1027 diffractions. A 4-connected framework, with PO4 tetrahedra alternating with (A1,Mn)04 tetrahedra, has the topology of net 263 in which there are isolated parallel elliptical channels parallel to c and bounded by 10-rings. Each channel contains one diisopropylamine species per unit cell in one out of four possible positions. The C and N atoms were located with a precision near 0.1 A. All distances from C atoms to framework oxygen atoms are greater than 3.7 A as expected for van der Waals bonding. The N atom lies at 2.8 A from two framework oxygen atoms, and it is proposed, bur nor proven experimentally, that two hydrogens are bonded to the N atom, instead of one hydrogen for un-ionized diisopropylamine. This would be consistent with charge compensation for occupancy of one tetrahedral A13+ site by Mnzf.

Introduction A new class of microporous materials was synthesized from

aluminophosphate gels by using a wide range of organic amines and quaternary ammonium cations as structuredirecting agents,'sZ and their physical and chemical properties are being studied intensively. The structural features of these microporous materials, and of other aluminophosphates with Al/P = 1, have been re- ~ i e w e d ; ~ additional structure types have been reported: or soon will be. Further generations of aluminophosphate-based molecular sieves, containing one or more of 13 additional elements, have been synthesized.5 Among these materials is a manganese-containing aluminophosphate,6 whose X-ray powder pattern indicates that its framework topology may correspond to that of AlPO.,-l 1.7*8 Determination of the crystal structure of MnAPO-11 is important for three reasons: first, to confirm the framework topology; second, to determine the location of the Mn; and third, to find out the structural relation between the encapsulated organic species and the enclosing tetrahedral framework. Furthermore, it was hoped that the geometrical relations might provide some clue to the valence state of the manganese.

Experimental Section Sample Description. The sample was supplied by S. T. Wilson

of Union Carbide Corp. It was synthesized using diisopropylamine as the structure-directing agent. Optical study with a petrographic microscope revealed a considerable range of crystal size and internal properties. Many crystals showed a faint hourglass structure. Others showed a complex lamellar texture, and some showed small amounts of trapped material at the center. A crystal with uniform straight optical extinction and no inclusions was selected. I t was bounded by flat (100) and (010) forms and was convex on (001); the dimensions on a, b, and c were 74, 36, and 7 1 (maximum) Fm. Weissenberg X-ray photographs showed single sharp spots with excellent a,, cyz resolution.

Electron microprobe analyses using A1PO4-5 as a standard for AI and P, and Corning W glass and Mn-hortonolite as standards for Mn, showed that crystals of MnAPO-11 contain -33 wt % A1,03, -54 wt '% P,O,, and 3.1-4.6 wt % MnO. A chemical analysis (wt %) of the bulk sample on a hydrated basis yielded 32.1 AlzO,, 53.0 P,O,, 4.26 MnO, 5.21 C, 0.91 N, and 10.6 loss on ignition (1000 "C). These compositions are consistent with the bulk chemical analysis (wt %) reported in ref 6 for preparation 74: 33.9 Al2O3, 51.1 P205, 5.6 C, 0.97 N , 3.5 Mn (=4.5 MnO), 9.4 loss on ignition.

'Also Intense Pulsed Neutron Source, Argonne National Laboratory, Argonne, IL 60439.

0022-3654188 12092-2734%01 S o l 0

Data Collection. The selected crystal was coated with oil to control humidity, and mounted on an automated Picker-Krisel 4-circle diffractometer with a offset by 12O from the 4 axis. Refinement using 20 diffractions (58 < 20 C 80°), each the average of automatic centering of eight equivalent settings, gave the cell parameters in the abstract; the angles are consistent with orthorhombic geometry. 3832 intensities were collected with the 0 - 28 technique, scan speed 2O/min, scan width 1.8-2.5" for range 3-128" 20. Merging yielded 1027 intensities (Rint = 0.025), all of which were used in refinements; data collection range h f 15, k * 21, 1 9; maximum intensity variation of three standard reflections 0.5%. The absorption correction with an analytical method gave transmission factors 0.56-0.74.

The structure was solved from (a) refinement of trial positions of an averaged structure in Icmm with (Al,,5Po,5) on the tetrahedral nodes of net 263,7 (b) unsuccessful attempts to refine an ordered structure in Icm2 with (A1,Mn) and P alternating over the tet- rahedral nodes, (c) discovery of poorly defined positions for the C and N atoms of encapsulated diisopropylamine from a dif- ference-Fourier synthesis for the averaged structure, and (d) successful least-squares refinement of the ordered structure with the encapsulated diisopropylamine. This tedious process required perseverance and intuition based on chemical knowledge. Only at the end did the refinement proceed smoothly using standard least-squares techniques.

In the final model, 163 variables were refined: scale factor, atomic positions, anisotropic displacement factors for framework atoms, isotropic ones for C and N atoms, individual occupancy factors for A1 and P, and an overall occupancy factor for the C and N atoms. Neutral scattering factors' were used. The higher population factor for the A1 positions than for the P positions is consistent with the expectation from the chemical analysis that

(1) Wilson, S. T.; Lok, B. M.; Messina, C. A.; Cannan, T. R.; Flanigen, E. M. J . Am. Chem. Soc. 1982. 104. 1146.

1 ~~ ~ ~~ ~ ~ ~~~ ~ ~~

(2) wilson,S. T.; Lok, B. M.; Messina, C. A.; Cannan, T. R.; Flanigen,

(3) Bennett, J . M.; Dytrych, W. J.; Pluth, J . J . ; Richardson, J . W., Jr.;

(4) Rudolf, P. R.; Saldarriaga-Molina, C.; Clearfield, A. J. Phys. Chem.

E. M. ACS Symp. Ser. 1983, 218, 79.

Smith, J. V. Zeolites 1986, 6, 349.

1986, 90, 6122. ( 5 ) Flanigen, E. M.; Lok, B. M.; Patton, R. L.; Wilson, S. T. Pure ADPI. ._

Chem. 1986y58, 1351. (6) Wilson, S. T.; Flanigen, E. M. US. Patent 4567029, January 28, 1986. (7) Bennett, J . M.; Smith, J . V. Z . Kristallogr. 1985, 171 , 65. (8) Bennett, J. M.; Richardson, J . W., Jr.; Pluth, J . J.; Smith, J . V. Zeolites

(9) International Tables for X-ray Crystallography; Kynoch: Birming- 1987, 7, 160.

ham, U.K., 1974; Vol IV, pp 72-98.

0 1988 American Chemical Societv

Crystal Structure of (MnA19)P10040C6H16N The Journal of Physical Chemistry, Vol. 92, No. IO, 1988 2735

TABLE I: Atomic Positional and Displacement Parameters for MnAPO-11 atom populationb X Y Z uwa P(1) 8 X 0.913 (14) 0.1464 (2) 0.0365 (2) 0.170 (2) 0.0421 (10) AW) 8 X 1.034 (16) 0.1390 (2) 0.0331 (2) -0.203 (2) 0.0450 (12) P(2) 8 X 0.912 (14) 0.9515 (2) 0.10846 (14) -0.334 (2) 0.0383 (1 1) AI@) 8 X 1.028 (17) 0.9501 (3) 0.1060 (2) 0.294 (2) 0.0450 (13) P(3) 4 X 0.904 (18) 0.8621 (3) 0.25 0.163 (2) 0.0337 (14) ~ 3 ) 4 x 1.010 (11) 0.8565 (3) 0.25 -0.208 (2) 0.037 (2) O(1) 8 x 1 0.1430 (6) 0.0364 (4) 0.0 0.119 (4) O(2) 8 x 1 0.9515 (6) 0.1120 (4) 0.491 (2) 0.129 (4) o(3) 4 x 1 0.8542 (9) 0.25 0.001 (2) 0.132 (5) O(4) 8 x 1 0.2455 (8) 0.0612 (3) 0.228 (2) 0.085 (2) o(5) 8 x 1 0.0690 (7) 0.0874 ( 5 ) 0.234 (2) 0.084 (4) O(5’) 8 x 1 0.0564 (7) 0.0974 ( 5 ) -0.277 (2) 0.086 (4) O(6) 8 x 1 0.1250 (8) 0.9611 (4) 0.232 (2) 0.090 (4) O(6’) 8 x 1 0.1158 (8) 0.9498 (5) -0.276 (2) 0.100 (4) o(7) 8 x 1 0.9175 (9) 0.1863 ( 5 ) 0.221 (2) 0.111 (5)

O(8) 4 x 1 0.7620 (1 1) 0.25 0.227 (4) 0.121 (5) N 8 X 0.323 (4) 0.301 (3) 0.206 (3) 0.242 (1 0) 0.22 (3)

o ( 7 7 8 x 1 0.9169 (10) 0.1786 (5) -0.267 (2) 0.1 13 (5)

C(1) 4 X 0.646 (7) 0.250 (6) 0.25 0.073 (11) 0.27 (2) C(2) 4 X 0.646 (7) 0.246 (8) 0.25 0.346 (12) 0.27 (2) (33) 4 X 1.292 (14) 0.3449 (13) 0.25 0.457 (4) 0.174 (8) C(4) 4 X 1.292 (14) 0.161 (2) 0.25 0.448 (5) 0.220 (1 1)

is defined as ‘/a~::I,C:-,U~~,*u,*(aia,). bPopulation defined as site multiplicity X fractional occupancy.

Figure 1. Stereoview of the 4-connected 3 D net connecting the tetrahedral nodes of net 2633. Two channels parallel to the c axis are present for each unit cell. The 3D net can be constructed from 3-connected 2D nets, each of whose nodes is connected either upwards or downwards to an adjacent 2D net. Each 2D net contains 4-, 6-, and 10-rings. There is strict alternation of upward and downward connections in each 2D net. In pure AlP0,-1 1 alternate nodes are occupied by AI (circle) and P (no circle).

Figure 2. Stereoview of a piece of an infinite channel with the NC6 skeleton of an encapsulated diisopropylamine species. Each tetrahedral atom is connected to four oxygen atoms, and each oxygen atom to two tetrahedral atoms, except at the arbitrary boundary of the stereoview. All framework atoms are represented by a displacement ellipsoid at 20% probability. The atoms of the NC6 skeleton are represented by an arbitrary sphere. Dashed lines show the inferred hydrogen bonding between N and O(4) and O(5’).

10% of the Al sites are occupied by Mn. Because X-ray scattering factors depend on the state of ionization, there was no point in replacing the A1 scattering factor with an interpolated one for Alo.9Mno.l; any difference would be within experimental uncer- tainty. The final least-squares refinement minimized all Fs with uF computed from uI the square root of [total counts + (2% of total counts)*], w = uF-*, R = 0.055, w R = 0.042, S = 2.13;

maximum shift/e.s.d. = 0.1 for U,, of Al(2); maximum and minimum heights on final difference-Fourier map are 0.5 and -0.5 e A-’; computer programs for local data reduction were S H E L X ~ ~ , ~ ~ ORFFE,” ORTEP,’~ AGNOST.’~ Protons were not located from the

(10) Sheldrick, G. M. Computer program, Cambridge University, Eng- land.

2736 The Journal of Physical Chemistry, Vol. 92, No. 10, 1988

TABLE IL MnAPO-11 Framework: Interatomic Distaocea (A) and Angles (den)

centroid riding”

1.438 (13) 1.493 (13) 1.510 (12) 1.531 (11) 1.493

1.702 (12) 1.720 (13) 1.743 (13) 1.752 (12) 1.729

1.481 (22) 1.501 (12) 1.503 (13) 1.506 (12) 1.498

1.667 (22) 1.683 (14) 1.696 (11) 1.718 (11) 1.691

1.364 (24) 1.454 (19) 1.491 (13) 1.450

1.643 (13) 1.688 (18) 1.767 (24) 1.685

1.521 (13) 1.534 (13) 1.552 (12) 1.572 (11) 1.545

1.749 (12) 1.787 (13) 1.776 (13) 1.783 (12) 1.774

1.573 (21) 1.560 (12) 1.575 (13) 1.551 (12) 1.565

1.743 (21) 1.736 (14) 1.733 (12) 1.751 (12) 1.741

1.482 (23) 1.544 (18) 1.562 (13) 1.538

O(l)-R1)-0(4) O( 1 )-P(1)-0(5) O(l)-p(1)-0(6) 0(4)-P(1)-0(5) 0(4)-P(1)-0(6) 0(5)-P(1)-0(6)

O(6’)-AI( 1)-0( 1) O(6’)-AI( 1)-0(4) O(6’)-AI( 1)-0(5’) 0(1)-A1( 1)-0(4) O(l)-AI(l)-0(5‘) O(4)-AI( 1)-0(5’)

0(2)-P(2)-0(6’) 0(2)-P(2)-0(7’) O(Z)-P(Z)-O( 5’) 0(6’)-P(2)-0(7’) 0(6’)-P(2)-0(5’) O( 7’)-P( 2)-O(5’)

0(2)-A1(2)-0(7) 0(2)-A1(2)-0(6) 0(2)-A1(2)-0(5) 0(7)-A1(2)-0(6) 0(7)-A1(2)-0(5) 0(6)-A1(2)-0(5)

0(3)-P(3)-0(8) 20(3)-P(3)-0(7) 20(8)-P(3)-0(7) 0(7)-P(3)-0(7)

110.7 (10) 109.4 (9) 109.4 (8) 107.9 (8) 110.1 (8) 109.3 (8)

113.4 (8) 108.7 (7) 112.6 (8) 107.1 (8) 110.4 (8) 104.0 (7)

111.1 (9) 109.7 (9) 109.0 (9) 108.9 (9) 111.2 (8) 106.9 (9)

108.0 (8) 111.5 (8) 107.4 (8) 113.0 (8) 108.3 (8) 108.3 (7)

107.5 (14) 111.6 (10)

106.3 (12) 110.0 (10)

1.711 (13) 0(7’)-A1(3)-0(7’) 108.9 (11) 1.764 (18) 20(7’)-A1(3)-0(8) 111.7 (8) 1.857 (23) 20(7’)-A1(3)-0(3) 108.2 (9) 1.761 0(8)-A1(3)-0(3) 108.1 (12)

178.0(6) P(1)-0(6)-A1(2) 154.2 (7) 173.5 (6) P(2)-0(6’)-AI(l) 153.3 (8) 174.6 (9) P(3)-0(7)-A1(2) 165.0 (9) 144.4 (4) P(2)-0(7’)-A1(3) 168.1 (10) 151.3 (7) P(3)-0(8)-A1(3) 177.1 (23)

P(2)-0(5’)-Al( 1) 143.5 (6)

‘Oxygen riding on tetrahedral atom.

final difference-Fourier map, and the residual peaks appeared to be random and not interpretable in terms of atoms bonded to framework oxygens or to the diisopropylamine species. Final atomic coordinates and displacement factors are given in Table I, and interatomic distances (with and without riding motion) and angles in Tables I1 and 111. A table of anisotropic thermal parameters (Table IV) and a listing of observed and calculated structure factors are available as supplementary material. (See Supplementary Material Available paragraph at the end of this article.)

Discussion Figure 1 shows the 4-connected net linking the tetrahedral nodes

of the AIP0,-1 1 type of framework. Figure 2 shows both tet- rahedral and oxygen atoms of the framework together with the NC6 skeleton of a diisopropylamine species lying in a channel. In this view, which is nearly down the c axis, a piece of the infinite channel is bounded by three ellipsoidal 10-rings of linked (Ab9M% ,)04 and PO4 tetrahedra, related by pseudomirror planes displaced by cl2. The topological mirror symmetry is destroyed by the alternation of (Ab9Mno.J and P atoms in tetrahedral sites. The channel wall is lined by a curved two-dimensional net of 6-rings. Each channel is isolated from adjacent channels by a wall composed of linked 4- and 6-rings of tetrahedra.

The diisopropylamine species lies in the middle of the channel with the carbon atoms on a mirror plane perpendicular to the b

(1 1) Busing, W. R.; Martin, K.; Levy, H. A. Report ORNL-TM-306. Oak

(12) Johnson, C. K. Report ORNL-3794. Oak Ridge National Labora-

(13) Ibers, J., personal communication.

Ridge National Laboratory, TN, 1964.

tory, TN, 1965.

Pluth et al.

TABLE III: MnAPO-11: Interatomic Distances (A) and Angles (deg) Involving C and N Atoms

Intramolecular N-C(l) 1.78 (11) C(1)-N-C(2) 92 (5) N-C(2) 1.41 (11) C(3)-C(l)-C(4) 101 (5) C(I)-C(3) 1.61 (9) N-C(l)-C(3) 142 (4) C(I)-C(4) 1.59 (9) N-C(l)-C(4) 104 ( 5 ) C(2)-C(3) 1.63 (11) C(3)-C(2)-C(4) 108 (7)

N-C(2)-C(4) 142 (4) C(2)-C(4) 1.43 (1 1) N-C(2)-C(3) 86 (6)

Proposed Hydrogen Bonding N-O(5’) 2.81 (5) 0(4)-N-0(5’) 59 (1) N-O(4) 2.82 (5) C(l)-N-0(4) 108 (3)

C(1)-N-O(5’) 123 (4) C(2)-N-0(4) 116 (4) C(2)-N-0(5’) 145 ( 6 )

Van der Waals Bonding to Framework Oxygen Atoms N-O(7‘) 3.83 (5) C(3)-2 O(5’) 3.72 (2) N-0(5) 3.84 (5) C(3)-2 O(7’) 3.96 (3)

C(1)-2 O(4) 3.77 (3) C(4)-2 O(2) 3.84 (2)

C(2)-2 O(5) 3.98 (7) C(4)-2 O(7) 3.98 (3)

Distance between Carbon Atoms of Adjacent Molecules

N-O(1) 3.93 (7) C(4)-2 O(5) 3.75 (3)

C(2)-2 O(4) 3.67 (3) C(4)-2 O(5’) 3.95 (3)

C(3)-C(4) 4.14 (11)

axis and the central nitrogen atom displaced to one side or the other of the mirror plane in the space group Zcm2. This dis- placement is the key to interpretation of the stereochemistry. It allows the N atom to approach two framework oxygens O(4) and O(5’) a t 2.82 (5) and 2.81 (5) A, respectively. These short distances are consistent with the attachment of two hydrogen species to the N atom thereby providing hydrogen bonding to the framework oxygens. A neutral diisopropylamine molecule has the composition (CH3)2CHNHCH(CH3)2 = C6NH1,. Addition of the second hydrogen to the nitrogen atom generates an ionized species with one positive charge; this requires a negative charge in the tetrahedral framework for overall charge balance. Indeed, there is approximately one Mn atom within the uncertainty of the chemical analysis for each diisopropylamine species, and the occupancy of an A13+ site by Mn2+ provides the desired negative charge; see later for details.

It must be emphasized that this implication for the stereo- chemistry of the as-synthesized MnAPO-1 1 lacks rigorous ex- perimental justification because the noise in the final difference map is too large for detection of the proposed two protons. Nevertheless the experimental data strongly support the above interpretation. If only one proton were attached to the nitrogen, only one framework oxygen would be within range of hydrogen bonding; all other framework oxygens would lie a t appropriate distances for van der Waals bonding (Le., >3.5 A). Note that all the C atoms lie a t >3.7 A from framework oxygens. Because manganese can assume a range of valence states, including di- and trivalent ones, under ambient conditions, it is prudent to consider the possibility that not all diisopropylamine species are coupled to Mn2+ ions. Furthermore, it is necessary to consider the possible occurrence of some framework hydroxyl species. Nevertheless, there is no firm experimental evidence from the present data to support these possibilities.

To summarize at this point: the simplest interpretation of the present data is that (Alo93+Mno,12’) ions alternate with Ps+ ions in the tetrahedral framework and that charge balance is main- tained with diisopropylammonium ions. Various details ensue.

Chemical Composition. The proposed ideal composition of M ~ A ~ $ ~ o O ~ O - C ~ H ~ ~ N corresponds to the following weight frac- tions: Mn 4.07, A1 17.99, P 22.95, 0 47.42, C 5.34, H 1.19, N 1.04. Because the ideal value for Mn (4.07) is greater than the range found for electron microprobe analysis (2.4-3.6) and the value for bulk chemical analysis (3.41, dehydrated), and because the ideal values for C and N (5.34 and 1.04) are near the values for bulk chemical analysis (5.4 and 0.94, anhydrous basis), it appears that there is not a strict charge coupling between the

Crystal Structure of (MnA19)P100404!6H16N

screw 1 diad A -2.2 prone y * 0.25

0 0 e

c4q c3 A c4- 2.1

first observed second - 1LI - 0.1 025 0.4 0.1 025 0.4 0.1 025 0.4

X

choke posltlons choice

Figure 3. Positions observed for C and N atoms of the diisopropylamine species in the mirror plane y = 0.25. The central diagram shows the observed positions. The C positions are in the plane, but the N position is projected onto the plane from the two positions above and below. The left and right drawings show the two choices of positions along a channel. Note that the C(3) and C(4) positions overlap, whereas the C(1), C(2), and N positions do not.

diisopropylamine species and the Mn. Perhaps some diiso- propylamine species are neutral. Further work is needed to sort out the details of the chemistry, but the present data are com- patible with essentially full occupancy of the channels by diiso- propylamine species, and somewhat less than the ideal value of two Mn per unit cell for the present single crystal and bulk samples.

Location of Mn. It is inferred that the Mn is in a tetrahedral site. All peaks in the difference-Fourier synthesis are accounted for by framework atoms and by the C6N skeleton of the encap- sulated species. Furthermore, all the pore volume is needed for the van der Waals and hydrogen bonding around the diiso- propylamine species. The Mn is assumed to occupy an A1 rather than a P tetrahedral site because (a) the chemical analyses show P > Al, and (b) the Mn is likely to have a valence not greater than 3 in a hydrous ambient environment, and the ionic radii for divalent and trivalent Mn match better with that of A13+ than of PS+.

Framework Ordering. The distances in the tetrahedra (Table 11) are consistent with the alternation of P and Alo,9Mno,l. Within experimental uncertainty, there is no evidence from the population factors and tetrahedral distances that Mn is preferentially dis- tributed among the three AI-rich tetrahedra (Tables I and 11). However, from the viewpoint of charge balance, Mn would be expected to favor the Al( 1) tetrahedron which contains the two oxygen atoms O(4) and O(5’) selected earlier for hydrogen bonding. Such a preferential occupancy is allowed by the un- certainty in bond lengths and population factors, but must be tested by further experimental data.

Disorder of the Diisopropylamine Species. There are four possible positions of the diisopropylamine species in each segment of channel. The central part of Figure 3 shows the positions of N and C atoms in or near the plane y = 0.25, as determined from structure refinement. Only the positions for C(3) and C(4) have full occupancy within experimental error (Table I). Those for N, C( l ) , and C(2) occur at half-occupancy; furthermore, the N position is split into two, which effectively gives quarter-occupancy. [Note that the experimental occupancy for the C6N skeleton (2 X 0.323 (4)) corresponds to the expected value of 2 X 0.25 for two diisopropylamine species per cell, when scaled for the presence of hydrogen atoms.] The obvious interpretation is that there are

The Journal of Physical Chemistry, Vol. 92, No. 10, 1988 2737

four choices of equal probability for the encapsulated species (Figure 3, left and right), which are averaged by the X-ray dif- fraction process. In addition to the twofold choice of position along the channel, there is a twofold choice of displacement out of the plane y = 0.25 for the N atom (Figure 2). Each N atom is displaced toward one pair of O(4) and O(5’) atoms, or to the other pair of O(4) and O(5’) atoms formally related to the mirror plane in space group Zcm2. Because there is no experimental evidence for a lower symmetry than Zcm2 in the present set of data, it was assumed that displacements occur randomly. However, it must be emphasized that ordered regions, either in single channels or in domains, might occur. In particular, for any one channel, space restrictions enforce a single choice of z unless a vacancy allows a switch to the other choice. Selected-area electron diffraction and imaging studies should be useful in resolving the uncertainty.

Bonding of the Diisopropylamine Species: Template Model of Crystallization. The apparent shape of the diisopropylamine species (Table 111) is partly determined by the arbitrary restriction that the C atoms lie in a mirror plane at y = 0.25. Any release of this restriction rules out stability of the least-squares refinement. Nevertheless, listed distances and angles are chemically reasonable within the 3a experimental uncertainty. All the distances to framework oxygens are consistent with either hydrogen or van der Waals bonding; furthermore, the range of distances (A) for the shortest van der Waals contact from the carbon atoms (3.67 (3), 3.72 (2), 3.75 (3), 3.77 (3)) are equal within experimental uncertainty. I t is concluded that the encapsulated species fits neatly within the tetrahedral framework and that this neatness is consistent with the template model of crystalli~ation;’~ see ref 3 for a general discussion of the application of this crystallization model to aluminophosphate molecular sieves.

Atomic Displacements. The “temperature” factors for the oxygen atoms are too large for simple thermal motion when compared with those for many framework structures with ordered tetrahedral atoms. Some of the additional displacement must result from the occupancy of Mn in A1 sites, and from the disorder of the encapsulated species, but a further contribution is likely for the oblate ellipsoids of the 0(1), 0(2), and O(3) atoms (Figure 2). These atoms lie near the pseudomirror planes between the 2D nets of 4-, 6-, and 10-rings. They are analogous to the O(2) atom in the A1PO4-5 structure,ls which is related to the AlP04-1 1 structure by a a-tran~formation.~ Because there was a definite threefold pattern of electron density for the O(2) atom in A1PO4-5, the final difference-Fourier map for MnAPO-11 was checked for similar patterns. Although no clear pattern emerged within the random experimental error, it is likely that the centroid of electron density for the 0 (1 ) , 0 (2 ) , and O(3) atoms of MnAPO-11 rep- resents an average of more than one center of motion, as for the O(2) atom of A1P04-5. This would reduce the P(1)-O(1)-Al(l), P(2)-0(2)-A1(2), and P(3)-0(3)-A1(3) angles from the exper- imental values of 178.0 (6), 173.5 (6), and 174.6 (9)O. A fourth type of oxygen atom O(8) also has a high value of the intertet- rahedral angle, P(3)-0(8)-A1(3) = 177 (2)’. This atom lies in the mirror plane ( l m l ) between adjacent 6-rings of a 2D net. Its oblate ellipsoid is foreshortened in Figure 2, but the inferred averaging of more than one center of motion would reduce the P(3)-0(8)-A1(3) angle.

All other framework oxygen atoms have smaller “temperature” factors, and it is concluded that the framework oxygen atoms tend to adopt positions which reduce the range of P-0-AI angles from the formal spread of 178-143’ (Table 11). This corresponds chemically to a tendency for all the framework oxygen atoms in A1P04-5 and MnAPO- 1 1 to have similar values for overlap of the molecular orbitals. Further study of aluminophosphate structures is underway to test whether this is a general rule. Complications must arise for structures with hydroxyl species (e.g., as-synthesized A1P04-17), and the role of thermal motion must

(14) Flanigen, E. M. Adv. Chem. Ser. 1973, 121, 119. (15) Bennett, J . M.; Cohen, J . P.; Flanigen, E. M.; Pluth, J . J.; Smith, J .

(16) Pluth, J . J.; Smith, J. V.; Bennett, J. M. Acra Crystallogr. 1984, C40, V. ACS Symp. Ser. 1983, 218, 109.

283.

2738 J . Phys. Chem. 1988, 92, 2138-2745

be evaluated by studying structures over a range of temperatures.

Conclusion This structure determination has opened up a new area of

research on the structural chemistry of the new families of alu- minophosphate-based molecular sieves containing framework transition metals. Specifically for MnAPO- 1 1, the encapsulated diisopropylamine species fits neatly into the micropore, and Mn occupies an A1 site. There is charge linkage between the framework and the encapsulated species, and hydrogen bonding between nitrogen and framework oxygens. The stage is set for application of various spectral and resonance techniques for further characterization of the crystal-chemical properties.

Acknowledgment. We thank S. T. Wilson and E. M. Flanigen for synthesis of the MnAPO-11 and discussion of the results, J. M. Bennett for proposing the topology of the AlP04-1 1 prototype, I . M. Steele for electron microprobe analysis, and N. Weber for manuscript preparation. Financial support was provided by NSF grants CHE8405 167 and DMR8216892 (Materials Research Laboratory), and by Union Carbide Corp.

Registry No. MnAPO-11, 113893-23-5.

Supplementary Material Available: Table of anisotropic displacement parameters (Table IV, 1 page) and observed and calculated structure factors (6 pages). Ordering information is given on any current masthead page.

Is CN- Significantly Anisotropic? Comparison of CN- vs CI-: Clustering with HCN and Condensed-Phase Thermochemistry

Michael Meot-Ner (Mautner),*

Chemical Kinetics Division, Center for Chemical Physics, National Bureau of Standards, Gaithersburg, Maryland 20899

S. M. Cybulski, Steve Scheiner,*

Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, Illinois 62901

and Joel F. Liebman*

Department of Chemistry, University of Maryland, Baltimore, Maryland 21228 (Received: July 1, 1987; In Final Form: November 6. 1987)

Pulsed high-pressure mass spectrometry shows that the clustering thermochemistry of the CN- anion with HCN behaves in a fashion quite similar to C1-, Br-, and I-, indicating CN- acts very much like a spherical ion with radius slightly larger than CI-. The falloff of binding energy with increasing number of HCN molecules provides no evidence of any significant shell structure. Ab initio calculations support the low degree of anisotropy of CN-. While the most stable complex with HCN is CN--HCN, there is little loss of stability when CN- and HCN do not form a linear complex. The central CN- may rotate almost freely in clusters with two or three molecules of HCN, suggesting a nearly spherical character for the anion within these complexes. The calculations also confirm the lack of shell structure since complexes of the type CN--HCN-HCN are nearly equal in energy to NCH-CN--HCN. The behavior of CN- as a nearly spherical anion is further supported by a survey of condensed-phase thermochemistry wherein properties such as lattice energies and solvation energies are closely matched by C1-.

Introduction The energies and structures of cluster ions are subjects of active

current interest. Thermochemical data now extend from simple diatomic dimers to ionic clusters of large organics with complex structures.' The simplest core ions for clusters are spherical monatomic ions, but the spherical symmetry breaks down when proceeding to polyatomic core ions. It is of interest to examine whether the loss of symmetry has a significant effect on the stabilities of clusters. In the present study we examine whether the anisotropy of the CN- anion affects its interactions with ligand molecules in clusters and its thermochemistry in condensed phases.

In relation to strong covalent interactions at short distances, CN- is obviously anisotropic. Thus, the recombination energy with H+ to form H C N is more exothermic by 10-20 kcal/mol than the recombination to form HNC.* On the other hand, in complexes where the interaction is mostly electrostatic, the in-

(1) Keesee, R. G.; Castleman, A. W. J . Phys. Chem. Ref. Data 1986, 15,

(2) Pau, C. F.; Hehre, W. J. J . Phys. Chem. 1982, 86, 321. Lias, S.; 101 1.

Holmes, J . , private communication.

homogeneity of the field about the ion may become negligible at longer distances. For example, K+ and NH4+, which have similar ionic radii, also show similar energies of clustering to H 2 0 , NH3, CH3CN, and C6H6, as well as similar solvation and crystal lattice energies, and even similar activities in e n ~ y m e s . ~ The similarity results from the cancellation of various electrostatic terms at realistic ion-ligand distances from NH4+. As a result, NH4+ behaves as a spherical entity with unit charge, regardless of the actual charge distribution in the ion. In clusters and condensed systems where electrostatic interactions predominate, CN- may similarly behave as a spherical core ion. It is of interest to compare the thermochemistry of CN- with C1- and Br- in this regard and to examine by theoretical calculations the energetic effects of moving a ligand molecule around CN-.

For clustering studies we selected HCN as a model polar ligand. HCN bonds strongly to the anions and therefore allows clustering measurements by up to seven molecules, Le., up to and beyond the first solvent shell in which anisotropy may be significant. Also,

(3 ) Liebman, J. F.; Meot-Ner (Mautner), M.; Castora, F. P., unpublished results.

0022-3654/88/2092-2738$01.50/0 0 1988 American Chemical Society