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Investigations into the Targeted Design of Solids Hydrothermal Synthesis and Structures of One- Two- and Three-Dimensional Phases of the OxovanadiumЦOrganodiphosphonate System.

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Scheme 3. Establi\hment of the absolute configuration of ether 2
ca illary GC analysis at 35 'C on a Chiraldex G-TA column
(A TEC. Whippany, NJ. USA) shows that the anesthetic 6 produced @om the reaction is the levorotatory isomer, based on its
longer retention time.[' 31 Because it is known[141that the absolute configuration of (-)-6 is (S), it is now certain that the
absolute configuration of ether (-)-2 is also (S).
The above data indicate that acid 1 undergoes highly
stereospecific C - C bond cleavage, producing ether 2 with
99.5% inversion of configuration at the chiral carbon atom.
This result is surprising. considering that in acyclic systems certain decarboxyIation~['~~
and such related C - C bond breaking
processes as the cleavage of tertiary alcohols" 61 and HallerBauer cleavage" in most cases exhibit retention of configuration in the product, sometimes as high as 98 YO.The reaction is
less selective in other solvents. In the present case, the very high
level of inversion of configuration may be due to the highly
electronegative z substituents of acid 1 . These, through hydrogen bonding. may cause the quenching proton of triethylene
glycol to be in the required position opposite the carboxyl leaving group, assuming decarboxylation and quenching of the resultant organopotassium intermediate occur heterolytically ; a
concerted mechanism is also possible.
We have shown that under relatively harsh conditions an
enantiomerically pure acyclic carboxylic acid can be decarboxylated to give a product with nearly complete inversion ofconfiguration. This result is especially significant considering that carboxylic acids are known to produce products with a medium to
high degree of configurational retention or racemization when
subjected to much less drastic conditions." 5J To our knowledge,
this is the most stereospecific C-C bond cleavage ever seen in an
acyclic system. Future reports from this laboratory will describe
use of this reaction in the synthesis of optically active anesthetics
as well as new mechanistic data which will clarify the basic
concept of configurational retention versus inversion in these
Received: August 15, 1994 [Z 7238 IE]
German version: Angeir. Chrnr. 1995. /07. 254
Keywords: configuration determination . fluorohydrocarbons .
inhalational anesthetics
[ l ] A . C' Hdl. W R. Lich, N . P. Franks. Br. J Pliurrnurol. 1994, 112,906: B. D.
S. Bade. P Skolnick. Eirr. J Phurniurol. 1994. 267.
Hairi.;. E J Moody. .4.
269. G. Lqsko. J. Robinson. R. Cnsto. R. Ferrone. ihrd., 1994, 213. 25.
[?I D. L. Pe;ir\on. Dissertation. Cornell University, 1990:DIFs. Ahsrr. Inr. B 1992.
52. 6400, C G. Huang, L. A. Rozov, D. F. Halpern. G. G. Vernice. J. Org.
( ' / i n n . 1993. SK. 73x2; L. A. Rozov. C. G. Huang. D. F. Halpern, G. G. Vernice
(Anaquest) US-A 5283372. 1994 [Chem. Ahstr. 1994. 120, 322704~1.
[3] D. U.Stwrk. A . Sliitnngkoon. G. Vigh, J C h r o m m q r . A 1994. 663. 79; F. V.
Schurig. H . Grosenick. ihid. 1994. 666. 617.
[ l l ] Single crystals of amine (R)-( +)-4 were grown by d o n eiaporation froin a
solution of 1 2 % vjv water in acetone. In the crystal atructui-cdetcrmination the
asymmetric unit contains two crystallographically independent molecules exhibiting similar configurational and geometric parameters. Represcntative
molecule A is depicted in Figure 1. All bond lengths and bond angles arc as
expected. M , = 301.71, inonoclinic. space group P 2 , , t i =11.140(6). h =
17.27.((5). r.=7.290(4),&. ,B=90.19(5). V=1403(2),&'. % = 4 . pLdlc=
1.43 gcm-3. ji = 28.28 c m - l . Data were collected on a colorless crqst'al measuring 0.25 x 0.25 x 0.10 mm at T = - 160 C with n Rig:iI\ti AFCSS diffrac20 scans with a scan speed of 8 - 3 ? ;min in and ;L s u n Nidth of
(1.47 + 0.30 tan@)' using graphite-nionochroinated Cu,, iadiatlon. Lattice
parameters were determined by least squares iising 75 rcflections with
37.3 c 20 <77.2 . Three standards monitored every 150 ri.tlections indicated
no significant decay. A full set of Friedel mates was collucted totaling 3918
r e f l e c t i o n s ( s i n ~ , , , ~ i = 0 . 5 6 A ~ ' : O ~ h ~ 1 3 . O ~ X 8- ~< 1/ <98. ) . 3 5 3 5 o f
which were unique with merging R = 0.055. (The Fiiedcl mates were not
merged.) The structure was solved using MlTHRlL .ind refined (P. W.
Rafalko. R. I. Fryer. L. V. Kudzma. A ~ . I NC I W / ~ / O .Sw/
~ F . C 1993, 49. 116.
and references therein) using 2706 reflections b i t h / > 3.0Ori(/).All non-hydrogen atoms were refined anisotropically. The hydrogen iiioms w r e assigned
calculated positions and temperature factors (H -C = O.(JS
B,,(H) = 1.2 B,,
(C or N)). The final R and R, values R R = 0.086 and K{ = 0.1 16. respectively.
/ o g r .A
with GOI: = 2.64. The Hamilton R-test (D. Rogers, A r r < r ( ~ r ~ ~ . ~ r u /Secr.
1981. 37. 734) confirms that the absolute configuration o f ainine (R)-( +)-4 is
as shown. Both data for stereoisomers (R)-(+)-4and ( S ) - ( -)-4 were fully
refined: RS/RR R$R: =1.07 (R' = 0.093. RS, = 0.124. GOF = 2.82 for
(S)-(-)-4. Calcubated x <10-" for h' = 2364 cstahlishe\ the validity of the
assignment. Further details of the crystal structure inres~iyiilionare available
from the Director of the Cambridge Crystallographic Data Centre. 1 1 Union
Road. GB-Cambridge. CB2 1EZ (UK). on quoting the tull journal citation.
[12] T. Ishihara, M. Kuroboshi, Chem. Lert. 1987. 1145.
1131 It has been established that ( - ) - 6 elutes after its ( + ) enaiitiomer on this
stationary phase. L. A. Rozov, C. G. Huang. D. F, Halpern. G G. Vernice.
abstract F L U 0 # 19 presented a t the 206th ACS National Meeting. Chicago,
IL, August, 1993. Coinjection ofthe reaction product with authentic (&)-desflurane verifies the peak assignment.
[14] P. L. Polavarapu, A. L. Cholli, G. G. Vernice, J. Phuriri Sci. 1993. 83, 7Yl.
[tS] T. R. Doyle, 0. Vogl, J. Am. Chrm. Soc. 1989. l / l . 8510: D. J. Cram, A . S.
Wingrove. ;hid. 1963. 85,1100. and references therein.
[16] T. D. Hoffmann, D. J. Cram. J Am. C h m . Sor.. 1969. Y / . 1009. and earlier
papers in this series; D. J. Cram. Fundrrmenruls of CurhmroJiCh~nmtrv.Academic Press. 1965. Chapter 4.
[I71 J. P. Gilday. L. A. Paquette, Org. Prep. Proc. h i ( . 1990. 33. 169.
Investigations into the Targeted Design of Solids:
Hydrothermal Synthesis and Structures of One-,
Two-, and Three-Dimensional Phases of the
Oxovanadium-Organodiphosphonate System"*
Victoria Soghomonian, Qin Chen,
Robert C. Haushalter," and Jon Zubieta*
The recent expansion of the chemistry of the metal
organophosphonate systems" - 31 reflects their practical applications as catalysts, hosts in intercalation compounds, and
protonic c o n d u ~ t o r s . [ ~Vanadyl
organophosphonates such
as [VO(RPO,)]. x H , O [ * - * ~ ~and [ ( V O ) ~ { ( O ~ P ) ~ C' H ~ ) l
4 H,O,[' possess structurally well-defined internal void spaces
[4] L A. Romv. K. Ramig, Terrohrdron Lrrr. 1994. 35. 4501.
[ 5 ] G.Siegeiiiund, R. Muschaweck (Hoechst) US-A 3981 927. I976 [Chem. Absrr.
1975. 8,. 155327dI
[6] L. A. Ro/oi. C. G. Huang. G. G. Vernice (Aniiquesl) US-A 5205914. 1993
[Chr.iii. .Ih\rr. 1993. 119. 116811v]
171 G.Siegeinund. R. Muschaweck (Hoechst) DE-B 2361 058, 1975[Chem. Ahsrr.
1975. 83. 103636q].
[XI I). Sianeu. .4. Pasetti, F. Tarli. J Org. Cl7em. 1966, 31. 2312.
[Y] H . C. Bictwii. P. Heim, J Org. Clxw. 1973, 38, 912.
[l I)]All ncu compounds provided satisfactory spectral data and correct combustion analyses.
Prof. J. Zubieta, V. Soghomonian, Q. Chen
Department of Chemistry. Syracuse University
Syracuse. NY 132444100 (USA)
Telefax: Int. code t ( 3 1 5 ) 443-4070
e-mail : jazubietw
Dr. R. C . Haushalter
NEC Research Institute. 4 Independence Way
Princeton, NJ 08540 (USA)
Telefax: Int. code +(609) 951-2483
e-mail: haushalterro
The work at Syracuse was supported by the National Science Foundation
(Grant CHE 9318824).
and coordination sites which allow such materials to intercalate
alcohols by coordination of the substrate molecule to the vanadium sites of the V-P-0 layer. When combined with readily
modified organic substituents, the thermal stability and reactivity of transition metal oxide moieties, and the interplay of hydrophilic and hydrophobic domains, such substrate-specific
recognition and incipient coordinative unsaturation of the
vanadium sites offers an approach to the design of highly selective oxidation catalysts.["We have sought to expand the
chemistry of the V-O-RP0:- system by the introduction of
various templates as structure-directing units, a methodology
which results in a dramatic expansion of the range of materials
(with respect to structure and composition) of the analogous
oxovanadium phosphate phases." 5 - 1 8 1 Encouraged by our success in introducing progressively more radical modifications
in the layered structures of V-O-RPOi- phases by exploitation of appropriate templates,[" - '11 we have turned our attention to the oxovanadium diphosphonate system, V-O[0,P(CH,),P0,J4-, where "engineering" of the material could
be accomplished both by introduction of different templates
and by changes in the length of the diphosphonate space group
R. Pursuing this strategy, one-, two- and pillared two- or threedimensional phases, 1, 2, and 3 respectively, have been synthesized and structurally characterized.
The materials 1-3 were prepared by hydrothermal syntheBy employing temperatures in the 150 "C to 250 "C
range under autogenous pressures, self-assembly from simple
molecular precursors of metastable phases which retain the
bond relationships between most of the constituent atoms may
be accomplished. A variety of precursors may be introduced
since all precursors are soluble under the conditions of the synthesis. Furthermore, a variety of templating cations may be
employed to direct the organization of the solid and to induce
crystallization, since templates of appropriate size or geometry
may be selected from the reaction mixture to fill the crystal
vacancies. In this way, compounds 1-3 were prepared from
mixtures of VCI,, H,O, the appropriate diphosphonates, and
templates at 200 "C for periods of 50-96 h. The IR spectra of
each of the materials exhibited a band in the 968 to 985 cm-'
range assigned to v(V=O) and several bands in the 1000 to
1200 cm-' region characteristic of the (PO,) group.
consists of infinite
As shown in Figure 1 , the structure of 1
puckered chains of [(VO)(0,P(CH,)P0,)]2- units with piperazinium ions occupying the interstrand regions. The V" sites
exhibit square pyramidal coordination geometry with the apical
position occupied by a terminal oxygen atom and the four equatorial positions defined by phosphonate oxygen atoms, two
from each of two diphosphonato ligands. Each diphosphonate
group symmetrically bridges two vanadium centers, and each
PO, unit of the ligand retains a pendant (P-0) group. While
pendant (P-OH) groups are more common in organophosphonate coordination chemistry, the uncoordinated (P=O) group
has been demonstrated in the structure of [nBu,N],[V,O,(RP03),].[21The structure of this (P-0) moiety in 1 receives
contributions from the multiply bonded (P=O) form, as suggested by the relatively short P - 0 distance of 1.518(6) A, and
more significantly from the charge interaction [-PO- . . . 'HN-]
with the cation in 1 as indicated by O . . . H distances in the
2.1 -2.5 8, range. This diphosphonate coordination mode con-
Fig. 1. Two views of the [(VO)(O,PCH,PO,)]:"- chains of 1. Middle: View of the
zigzag pattern adopted as a result of folding of (V=O) groups into the vacant
coordination site of the neighboring vanadyl unit. Left: View of the chain showing
the atom-labeling scheme. which is also applicable in all subsequent figures: V
atoms are crosshatched, P atoms are lined bottom left to top right. 0 atoms are open
circles. and C atoms are lightly shaded small circles. Right: A view of neighboring
[(VO)(O,PCH,PO,)],Z"- chams and the intervening piperazinium ions.
trasts with that of the layered solid [ (VO),(O,P(CH,)PO,)(H20),] wherein all phosphonate oxygen donors are coordinated to metal centers. The unusual chain-puckering in 1 is attributed to the long-range axial interactions between adjacent (VO)
sites which cause folding of the one-dimensional strands
through an alternating short-long ( V = O . . . V = O . . . V = O )
zigzag motif. This structural feature is also observed in the structure of the V-P-0 plane of [(VO)(O,PC,H,)(H,O)]. Valence
sum calculations'261confirmthat vanadium is in the +rv oxidation state.
The structure of 2["] consists of layers of square pyramidally
surrounded V'' sites; the pyramids corner-sharing with diphosphonate tetrahedra to produce [(VO)(O,PCH,CH,PO,)J~"layers. The ethylenediammonium ions occupy the interlamellar
regions (Fig. 2). In addition to the apical oxygen atom, each
Fig. 2. The structure of 2 viewed along the CryStdllOgrdphiC u axis, illustrating the
interlamellar location of the organic cations.
vanadium(1v) site is bonded in the equatorial positions to four
diphosphonate oxygen donors, one from each of four diphosphonate groups. Hence, each diphosphonato ligand bridges
four vanadium centers in a monodentate fashion through two
oxygen donors of each (PO,) unit. In a fashion akin to that in
1, each PO, group exhibits a pendant (P-0) group, which
projects into the interlamellar space, as d o the vanadyl oxygen
atoms. Again, the structure exhibits hydrogen bonding between
the pendant group and the organic cations. In comparison to the
prototypical layered structures [(VO)(0,PC,H,)(H,0)]r91 and
[(VO) { (0,PCH ,PO (H ,O)J ,[I and V-0-RPO: - layer of 2
exhibits a more open net as a consequence of the presence of
14-membered (V-0-P-C-C-P-0), rings (see Fig. 4 b). The layer
also exhibits eight-membered (V-0-P-0-V-0-P-0-) rings, char-
acteristtc of both molecular and solid-phase structures of the
V-O-RP0:- system.
The dramatic structural variations attendant to expansion of
the phosphonate tether group are evident in the “pillared”
structure adopted by 3 (Fig. 3). The structure of 3[281may be
described in terms of inorganic V-P-0 layers joined covalently
Fig. 3 . .A view 01‘ thc three-dimensional V-0-P-C framework adopted by 3. highlighting the positions of the organic cations which penetrate the inorganic V-0-P
layers. Dotted circles are N atoms.
by the trimethylene bridges of the diphosphonate groups. Since
the covalently linked framework includes the ligand carbon
framework. the solid may alternatively be described as a threedimensional V-P-0-C framwork with ethylenediammonium
cations occupying the channels parallel to the crystallographic a
axis. There are two distinct vanadium(1v) environments (see
Fig. 4c): the V1 site is square pyramidal, surrounded by an
apical oxygen atom, three oxygen donors of PO, groups and an
oxygen atom of a bridging hydroxy group, while the V2 site is
distorted octahedral, surrounded by an apical oxygen atom,
three oxygen donors of PO, groups, the oxygen atom of a bridging hydroxy group, and an oxygen atom of a terminal aquo
ligand. The binuclear [V:vO,(OH)] unit provides an unusual
structural motif within the V-P-0 layers. The diphosphonato
ligands span adjacent layers such that one of the PO, groups
symmetrically bridges the V” sites of a [V,O,(OH)] unit and
coordinates through the remaining oxygen donor to the V2 site
of an adjacent binuclear unit, while the second (PO,) group
bonds to two V1 sites and one V2 site of three proximal
[V,O,(OH)] units from a neighboring layer. In contrast to the
structures of 1 and 2. all the oxygen donors of the diphosphonato ligand in 3 coordinate to metal centers.
An unusual feature of the V-0-RPOi- system is the range of
connectivity patterns which are beginning to emerge for vanadium polyhedra and phosphonate tetrahedra within the V-P-0
layers. As shown in Figure 4a, [(VO)(O,PC,H,)(H,O)] exhibits
vanadium octahedra corner-sharing through short-long V - 0
interactions into infinite chains, while [(VO){(O,P),CH,}(H,O),1
contains isolated (VO,) octahedra, that is, no V-0-V bonding.
While the structure of 2 resembles the latter with respect to the
absence of V-0-V bonds, the vanadium sites are square pyramidal and as noted previously the details of the polyhedral connectivity are quite distinct. The V-P-0 structure of 3 is unique in
presenting [V,O,(OH)] binuclear units with both octahedral and
square-pyramidal vanadium sites. While the structure of
(Et,N)[(VO),(OH)(H,O)(O,PEt),] . H,0[2’1 also displays the
[v,O,(OH)] motif, the detailed connectivity within the plane is
quite distinct from that of 3.
The preparation of compounds 1-3 illustrates the power of
hydrothermal synthesis, since in this way compounds can be
formed by “self-assembly” from molecular precursors of
metastable phases not accessible through conventional hightemperature solid-state techniques. While “designed” synthesis
in the sense of predictability of product identity has yet to be
achieved, it i s clear that the combination of hydrothermal synthesis methods, appropriate adjustment of organic spacers in
the ligand component, and suitable templates for framework
organization allows modification both of framework dimensionality, and of V-P-0 layer separation, and isolation of a
range of phase compositions of dramatic structural variability
limited only by the flexibility of polyhedral connectivity of the
component moieties. Modification of the length of the organic
buttress of the diphosphonato ligand should allow the engineering of materials with specific interlayer spacings and hence tailored micropor~sities.[~.
Experimental Procedure
I : A mixture of VCI,, methylenediphosphonic acid, piperazine, and water in the
mole ratio 1 : 1.1.93:945 was heated at 200 C and autogenous pressure for 50 h in
a 23 m L Teflon-lined Parr acid digestion bomb (50 % fill volume). Green crystals of
1 were isolated in 80% yield. IR (KBr pellet) i.[cm-’] = 3024 (w). 2958 (w), 2758
(m). 2526 (n). 1621 (m).1505 (m), 1449 (m), 1156 (s). 1084 (s). 1029 (vs), 968 (s).
907 ( w ) , 785 (s). 530 (m). 475 (w). Anal. calcd. for C,H,,N,O-P,V: C 18.3; H 4.28;
N 8.56; found: C 18.3; H 4.39; N 8.55.
2: A mixture of VCI,. ethylenediphosphonic acid, ethylenediamine, and water in the
mole ratio 1 :3.11:5.1:1890 was heated at 200 “C and antogenous pressure for 96 h
in a quartz glass tube. Green crystals of 2 were collected in 90% yield. I R (KBr
pellet) C[cm-’] = 3448 (w), 2925 (m). 1181 (w). 1109 (s), 1076 (s). 1037 (sh). 1014
(vs), 975 (5). 775 (m). 545 (m), 463 (w). Anal. calcd. for C,H,,N,O,P,V: C 15.2;
H 4.44: N 8.89: found: C 14.9; H 4.14, N 8.67
3: A mixture of VCI,, propylenediphospbonic acid, ethylenediamine. piperazine.
and H,O in the mole ratio 1:1.47:4.8:945 was heated at 200 C and autogenous
pressure for 80 h in a quartz glass tube. Blue crystals of 3 were isolated in 40% yield
along with [H,N(CH,CH,)2NH,][(V0)2(H0,PCH,CH2CH,P0,)2](4), a layered
material whose properties will be discussed elsewhere. While the piperazine template
does not appear in the product 3. it is necessary for the isolation ofcrystals suitable
for X-ray crystallography. In the absence of piperazine. compound 3 was obtained
as a microcrystalline material whose identity has been confirmed by powder diffraction. IR(KBrpellet)~[cni-'] = 3433(s. br).2757(w), 1250(w), 1144(m). 1072(s).
1034 (vs). 1012 (sh), 985 (w), 801 (w). Anal. calcd. for C,H,,N,O,,P,V,:
C 11.0:
H 4.13: N 3.21: found: C 11.6; H 3.11: N 3.00. Heating of 3 at 100 C for 5 h
result$ in removal of six equivalents of water to give the material
( 3 a ) . Anal. calcd. for
C 12.6; H 3.14: N 3.66; found: C 12.3: H 3.02; N 3.41.
Received: July 4. 1994
Reviacd version: September 6. 1994 [Z 7093 IE]
German version: Angew. Clicm. 1995. 107. 229
Keywords: hydrothermal synthesis . polyoxometalates . solidstate structures . vanadium compounds
[ I ] J. Zubieta. Comnient\ I m r g . Chetii. 1994, 16. 153. and reference$ therein
[2] Q. Chen, J. Salta, J. Zubieta. Itiorg. Chwi. 1993. 32. 4485.
[3] C. Bhardwaj, H. Hu. A . Clearfield, Imirg. C h w ~1993.32.4294,
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(41 G. Alberti. U.Constantino, F. Marmottini. R. Vivani. P. Zappelli. A/igc.w
Chem. 1993, 105. 1396; A n g m . Chum. I n ( . Ed. EngI. 1993. 32. 1357. and references therein.
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[6] D. A. Burwell. M. E. Thompson, SiI/~runiolrr.rr/ar
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[I I ] G. H u m . A. J. Jacobson. J. W. Johnson, D. P. Goshorn, C h m . Murcr. 1992.4,
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[I41 A. Stein. S. W Keller. T. E. Mallouk. S c i e m ~ 1993,
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[I 51 V. Soghomonian. Q. Chen, R. C. Haushalter, J. Zubieta, C. J. O'Connor. S c m cc 1993. 259, 1596.
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105, 601 : Angrw. Cheni. I n / . 6 1 . €n,q/. 1993. 32, 610.
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[I91 [Et,NH,l[Me,NH,][(VO),(OH)Z(O,PC,H,),]:
M. I. Khan.
Lee. C. J.
1994. 116, in press.
OConnor. R. C. Haushalter. J. Zubieta, J. An?. C l i ~ mSoc.
1201 [EtNH,],[(VO),(H,O)(O,PC,H,),I: M. 1. Khan. Y.-S. Lee. C. J. O'Connor.
Cliem 1994. 33. 1855.
R. C. Haushalter. J. Zuhieta, IFKJFX.
1211 [Et,NJ[(VO),(OH)(H20)(03PCzH~)3]~
H,O: M. I. Khan. Y.-S. Lee, C. J.
O'Connor. R. C. Haushalter. J. Zubieta. C/JWII.
MUIW.1994, 6. in press.
1221 M. Figlarr, Climi. Scr. 1988. 28. 3.
[23] J. Rouxel, Chow. Scr. 1988. 28. 33.
[24] R. A. Laudise. C l r ~ wG. i g . Ncii..~1987, Sept. 8. 30.
[ 2 5 ] 1: orthorhombic Pnmu. a = 8.012(2). h = 18.191(4). L' =7.744(2) .&.V =
Z = 4.plrlCd= 1.925 gcin-"; structure solution and refinement
= 0.71073 .&) converged at
based on 1452 reflections with I,, 2 3u(/,) (Mo,,. i.
R = 0.0374. Further details of the crystal structure investigations of 1-3 may
be obtained from the Fachinformationszentrum Karlsruhe. D-76344
Eggenstein-Leopoldshafen (Germany). on quoting the depository number
1261 I . D. Brown in Structure undBondrrig iii Crysrul.~,V d . 2(Eds.: M . O'Keeffe, A.
Navrotsky), Academic Press, New York, 1981, p. 1
1271 2: monoclinic P2,:n. u = 5.023(1). h =16.306(3). c =13.304(2) A. /j =
92.54(3) V = 3088.9(7) A', Z = 4. pcllCd= 1.919 gem-': structure solution
and refinement based on 1358 reflections with /" 2 3n(/,) (Mo,,.
0.71073 A) converged at R = 0.0557 [ 2 5 ] .
[28] 3: monoclinic C2ic. a =14.870(3). h = 10.245(2). c =18.868(4) A. /i=
99.50(3) , I/ = 2835.0(12) A'. Z = 4, L J ' , , , ~ ~= 2.015 gcm-', structure solution
and refinement based on 1266 reflections with 1" t ?u(I,J (Mo,,. L =
0.71073 A) converged at R = 0.0533 [XI.
[29] J. Alper. Chem. Ind. f l o n d m i ) 1986, 335.
Dimensional Reduction of Re6Se,C1, :
Sheets, Chains, and Discrete Clusters
Composed of Chloride-Terminated
[Re6Qs]2' (Q = S, Se) cores**
Jeffrey R. Long, Andrew S. Williamson, and
Richard H. Holm*
Lack of access to certain transition metal halide and chalcohalide clusters through self-assembly methods has enkindled
interest in cluster excision, a low-temperature procedure in
which the desired cluster is removed intact in molecular form
from its covalently bound environment within an extended solid
framework."] As demonstrated for the n-dimensional phases
Re6Ses+nCl,o-*,, (n = I - 3),12] the effective use of current excision methodology is largely contingent upon the clusters being
loosely bound in one or two
This, however, is not
always the case, and many clusters exist in a three-dimensional
andlor more tightly bound framework. Our recent efforts have
therefore focused on the development of a general high-temperature technique for producing frameworks of reduced connectivity, in hope of thereby gaining entry to a wealth of formerly
inaccessible cluster chemistry. Herein, we describe such a technique, and demonstrate its efficacy by application to the
Re6Se,CI2 parent structure.
The premise underlying our approach is exemplified in Figure 1 , which illustrates the srepwise deconstruction of a rudimentary three-dimensional cluster framework. The initial structure consists of [M,Q,] cluster cores linked in three dimensions
by bridging anions X. Successive incorporation of additional
equivalents of X reduces the overall dimensionality of the
framework by terminating intercluster bridges, producing structures containing sheets, chains and. finally, discrete clusters. To
preserve the original cluster electron count, each X added is
accompanied by a charge-compensating cation A, which resides
external to the framework (i.e.. between sheets, chains, or isolated clusters). The scheme presented in Figure 1 is not necessarily
intended to imply a specific reaction pathway (although it may
do so in some cases), but rather to provide a formalism with
which new lower dimensional compounds may be derived from
existing structures. Thus, this process of dimensional reduction,
when applied to a known parent phase, serves as a means of
formulating synthetic targets with structures amenable to excision or direct dissolution, ultimately affording the desired cluster in molecular form. Substitution of single metal centers M for
the [M,Q,] cores in Figure 1 creates an analogous formalism for
metal- anion frameworks, useful in relating covalent structures
throughout the solid state.[41
Many of the more intractable cluster frameworks are partially
o r entirely linked by bonding interactions directly between
cores, rather than through some intermediate bridging ligand,
as in Figure 1 .['I The two-dimensional framework in Re,Se,CI,
( & [Re,Se4Se4;;"]Se",,'Cl~)[51 provides such an example. Its
structure[61 (Fig. 2) is built up from electron-precise, facecapped octahedral [Re,Se,]*+ cluster cores, each with two attendant terminal chlorides at frans rhenium apices and four
[*] Prof: R. H. Holm, J. R. Long, A. S. Williamson
Department of Chemistry. Harvard University
Cambridge. MA 02138 (USA)
Telefax: Int. code + (617)496-9289
This work was supported hy the National Science Foundation (Grant C H E
92-08387). X-ray equipment was obtained through the National Institutes of
Health (Grant 1 S10 RR 02247). We thank the Office of Naval Research for
their support of J. R. L. in the form oTa predoctoral fellowship (1991 - 1994).
a n d M. J. Scott. D. Lange. and B. Souza for technical assistance.
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two, dimensions, solids, hydrothermal, three, system, phase, investigation, structure, synthesis, design, one, oxovanadiumцorganodiphosphonate, targeted
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