Intercalation of 2,2'-bipyridyl into .alpha.-zirconium phosphate and in

Intercalation of 2,2'-bipyridyl into .alpha.-zirconium phosphate and in situ formation of cobalt(2+), nickel(2+), and copper(2+)/2,2'-bipyridyl comple...
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J . Phys. Chem. 1985, 89, 4762-4169

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Intercalation of 2,2‘-Bipyrldyl into cdlrconium Phosphate and in Situ Formation of Co2+, Ni2+, and Cu2+/2,2’-Blpyridyl Complex Pillars Carla Ferragina,?Aldo La Ginestra,: Maria Antonietta Massucci,+*Pasquale Patrono,’ and Anthony A. G. Tomlinsons* Istituto di Metodologie Avanzate Inorganiche, Area della Riterca di Roma del C.N.R., Monterotondo Stazione, 00016 Rome, Italy, Dipartimento di Chimica, Universitri di Roma, Rome, Italy, and Istituto di Teoria e Struttura Elettronica, Area della Ricerca di Roma, C.N.R., Monterotondo Stazione, 00016 Rome, Italy (Receiued: September 17, I984)

The intercalation of 2,2’-bipyridyl (bpy) into a-zirconium phosphate, and its subsequent coordination by Co2+,Ni2+,and Cu2+,has been investigated. Bpy will not readily intercalate into a-Zr(HP04)2.H20itself, nor into the half-sodium form, but easily diffuses into the layered a-zirconium phosphate under the same conditions (0.01 mol dm-3 solution in 1:l EtOH:H20; 25 “C) if the layers are first preswelled via preparation of the metastable ethanol intercalate a-Zr(HP04)2[2EtOH]. A material of composition a-Zr(HP04)2(bpy)o,2s.1 .5H20is given, and more concentrated solutions or higher temperatures (60 “C) lead only to a maximum loading of 35% bpy, Le., to a-Zr(HP04)2(bpy)o,3s.l .65H20. a-Zr(HP04)2(bpy)o,2s.1 .5H20 is well-ordered and has an interlayer distance of 10.90 A. From considerations of layer thickness after intercalation and the changes in UV spectrum of the bpy, it is suggested that the bpy is intercalated in a twisted transoid configuration and oriented sidewise to the zirconium phosphate layers. a-Zr(HP04)2(bpy)o.2s.1 .5H20takes up Co2+,Ni2+,and Cu2+ions from ( M = Cuz+,Ni2+;25 “C) EtOH/H20 solutions, giving materials of composition a-ZrH,,5[M(bpy)(OH2)]o,2s(P04)2-3H20 and a-ZrH1,S( [M(OH2),]o,12s[M(bpy)2Jo,12s](P04)2~4H20 (M = Ni2+,Co2+;60 “C). The former contains pseudooctahedral cis-MN204pillars (tetragonally distorted in the case of Cu2+)and the latter pseudooctahedral cis-MN402pillars + M(OH2), in solid solution, as deduced from electronic and EPR spectra and interlayer distances. The uptake rate follows the order Cu2+>> Co2+> Ni2+, whereas the rate of coordination to bpy follows the order Cu2+ > Nil+ >> Co2+. The two rates are sufficiently different that coordination of M2+to intercalated bpy can be followed. These are the first examples of (slow) coordination of metal ions to an intercalated organic ligand. The effects of dehydration on the geometry of the pillars are described. The pillared a-ZrH1,s[Cu(bpy)(OH2)]o,25(P04)2~3H20 exchanges further Cu2+or Ag+ to give solid solutions. This demonstrates that cavities are indeed formed between the layers, Le., the pillars are not too densely packed as to block access to further ions.

Introduction High surface area zirconium phosphates possess catalytic properties when loaded with transition-metal ions.’ The better characterized, crystalline C Y - Z ~ ( H P O ~ ) ~ (known . H ~ O to have a layered structure containing zeolite-like cavities between Zrcontaining layers) and its transition-metal ion exchanged forms are useful in acid catalysis and in catalyzed oxidation reactions2 However, all these materials have the drawback that the catalytic activity is confined to the crystallite surface, because the pore size (2.61 A in largest cavity opening3) is too small to allow substrates access between the layers. The most obvious way to increase the pore size in such layered materials is to introduce groups capable of holding the layers apart, Le., to form “pillars” so that the free height available to substrates between the layers ( a in Figure 1) is increased. Although the concept was put forward as long ago as 1955, experimental confirmation of its feasibility was not forthcoming until the pioneering experiments of Michel and W e k 4 However, the past decade has seen sustained efforts to prepare stable, pillared zirconium phosphates, and these have recently been reviewed by others.’ Basically, pillars have to date been introduced via the following routes: (i) preparing the phosphonate or bisphosphonate analogues, in which alkyl or aryl group(s) act as the pillars;6 (ii) directly inserting a metal complex by using forcing conditions (usually prolonged heating in acid media at reflux temperature);’ (iii) directly intercalating polar, usually linear, organic molecules* (in some cases, the layer-swelled material thus obtained has been subsequently exchanged with a transition-metal complex9). We report a further means of forming pillars in zirconium phosphate, in which a metal ion is coordinated in situ to a ligand (a large amine) intercalated between the layers. This strategy is the inverse of that utilized successfully by Pinnavaia et al.1° for the heterogenization of homogeneous catalysts, such as Rh-

’Istituto di Metodologie Avanzate Inorganiche. ‘Universitl di Roma. f Istituto di Teoria e Struttura Elettronica.

0022-3654/85/2089-4762$0l.50/0

(PPh3)$+, via dispersion in smectite clays. It was hoped that the large metal complex pillar so formed would “spill over” the basal unit of the layer structure (which measures 5.2 X 5.3 8, in cyZr(HPO4),-H2O2) blocking too close an approach by the other pillars. This, in turn would mean that b in Figure 1 would be greatly increased via the formation of zig-zag channels. To be successful, this strategy requires a means of inserting large, nonlinear amines between the phosphate layers, preferably at room temperature. This is not always feasible because of steric hin(1) Onoue, Y.; Mizutani, Y.; Akiyama, S.; Izumi, Y . ; Watanabe Y . CHEMTECH 1977, 36. (2) The catalytic properties have been recently reviewed by: Clearfield, A. In “Inorganic Ion Exchange Materials”; Clearield, A,, Ed.; CRC Press: Bwa Raton, FL, 1982; Chapter 1. La Ginestra, A,; Ferragina, C.; Massucci, M. A.; Patrono, P.; Di Rocco, R.; Tomlinson, A. A. G. Gazz. Chim. Iral. 1983, 113, 357. (3) Clearfield, A.; Duax, W. L.; Medina, A. S.; Smith, G. D.; Thomas, J. R. J . Phys. Chem. 1969, 73,3424. Troup, J. M.; Clearfield, A. Inorg. Chem. 1977, 16, 3311. (4) Barrer, R. M. J . Chem. Sot. 1955, 434. Michel, E.; Weiss, A. Z. Naturforsch., E 1965, E20, 1307; 1967, B22, 1100. (5) Alberti, G.; Constantino, U. J . Mol. C u r d 1984, 27, 235. (6) Alberti, G.; Constantino, U.; Allulli, S.; Tomassini, N. J . Inorg. Nucl. Chem. 1978, 40, 1113. Dines, M. B.; Di Giacomo, P. M.; Callahan, K. P.; Griffith, P. C.; Lane, R. H.; Cooksey, R. E. ACS Symp. Ser. 1982, 192, 223 and references therein. The major problem with this method of forming pillars is that each phosphate group is derivatized, so that the lateral space available, b in Figure 1, is very limited. However, mixed component phase pillared phosphonate materials provide a more feasible route to interlayer cavities; see: Dines, M. B.; Cwksey, R. E.; Griffith, P. C.; Lane, R. H. Inorg. Chem. 1983, 22, 1003. ( 7 ) Yeates, R. C.; Kuznicki, S. M.; Lloyd, L. B.; Eyring, E. M. J . Inorg. Nucl. Chem. 1981,43,2355. Johnson, J. W. J . Chem. Sot., Chem. Commun. 1980, 263. Hasegawa, Y.; Kizaki, S. Chem. Lett. 1980, 241. (8) Alberti, G.; Costantino, U. In “Intercalation Chemistry”; Wittingham, M . S., Jacobson, A. J., Eds.; Academic Press: New York, 1982; Chapter 5. Costantino, U. In “Inorganic Ion Exchange Materials”; Clearfield, A,, Ed.: CRC Press: Boca Raton, FL, 1982; Chapter 3. (9) Clearfield, A.; Tindwa, R. M. Inorg. Nucl. Chem. Letr. 1979, 15, 251. (10) Pinnavaia, T. J.; Raythatha, R.: Lee, J. G. S.: Halloran. L. J.; Hoffman, J. F. J. Am. Chem. Sot. 1979, 101, 6891.

0 1985 American Chemical Society

Intercalation of Bpy into a-Zr(HP04)2.Hz0

The Journal of Physical Chemistry, Vol. 89, No. 22, 1985

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TABLE I: Analyses and Interlayer Distances of Materials calcd H20, % material d,,, A calcd bpv. % cavitya coordinated 1 10.90 11.3 (11.18) 7.9 (7.74) a-Zr(HP04)2(bpy)o,25.1 .5 H20e 10.0 (9.86) 13.3 (13.64) 1.1 (1.14) a-ZrHl.~[Cu(b~~)(OH2)10,2~(P04)2.3H20 2 13.0 10.0 (9.86) 13.4 (13.64) 1.2 (1.14) ~-Z~Hl,s[Ni(bPY)(OH2)10.2J(P04)2.3H20 3 12.44 9.50 (9.35) 16.20 (17.25) 1.97 (2.15) a-ZrH1,S([Ni(OH2)4]o,125[Ni(bpy)2]0.125)(P04)2~4H2O~,~ 4 14.47 9.5~(9.35) O ~ - Z ~ H ~ . ~ ( [ C O ( O H ~ ) ~ ] ~ . ~ ~ ~5[ C O14.47 (~~~) ] ~ , ~ ~17.0 ~ )(17.25) ( P ~ ~ ) 2.2 ~ ~(2.16) ~H~~ 8.9 (8.83) 12.5 (12.22) 1.0 (1.02) a-ZrCuo.,s[Cu(bPY)(OH2)10.2s(P04)2.3H20 6 13.0 8.7 (8.58) 11.7 (11.88) 0.9 (1.00) ~-Z~Ago,ssH0,9S [Cu(bPY)(OH2)10,2S(P04)2’3H20 7 13.0

M. %b 4.0 (4.01) 3.8 (3.72)

3.55 (3.51) 3.7 (3.52) 14.5 (14.36) 12.9 (13.04)

“From TG, not entirely reproducible results due to ready loss of small amounts of imbibed H 2 0 on standing in air. bVia back-titration of remaining metal ion in solution. CBpyalso confirmed by spectrophotometry. dBatch contact performed at 60 OC. ‘All coordinated H 2 0 attributed to metal in solid solution, i s . , to M(OH2):+ moiety; the intercalated [bpy]:[M2+]= 1:0 5 materials contained no water other than cavity water. ,pi I I a

r.5

a I

,

Zr(OP02) - f r a m e w o r k

I

I

Figure 1. The pillar concept (from ref 6). The cavity height a is defined by the size of the pillars, the cavity width 6 is defined by the lateral density of pillars between the layers. drance to diffusion between the layers. However, by first “preswelling” the phosphate layers in a-Zr(HP04)2.H20via the metastable alcohol intercalate,’ it is possible to diffuse large, aromatic amines (e.g., 2,2’-bipyridyl, 1,lO-phenanthroline) under mild conditions.12 This paper reports the preparation of a pure stable, nonstoichiometric pillared phase containing the common ligand 2,2’-bipyridyl (bpy) and its subsequent coordination by Coz+,NiZ+,and Cuz+.

1J‘i-

’

d

Experimental Section Materials. ZrOClZ.8H20and phosphoric acid were Erba R P products and 2,2’-bipyridyl was a Fluka product; all were used as received. Other reagents used throughout the course of this work were of the best available analytical purity. a-Zr( H P 0 4 ) 2 - H 2 0 and the half-sodium form a - Z r ( N a P 0 4 ) (HP04).5H20 were prepared, characterized, and stored as reported previously [C~(bpy)~](ClO was ~ ) prepared ~ as reported in the l i t e r a t ~ r eand ’ ~ gave satisfactory C, H, N analyses. Physical Measurements and Chemical Analyses. X-ray powder diffraction was used to follow phase changes undergone by materials (especially monitoring the dOo2reflection and its harmonics) with a Philips diffractometer. Ni-filtered Cu Ka radiation was used, and measurements of 28 are believed to be accurate to 0.05’. EPR spectra were registered on a Varian E9 spectrometer equipped with standard liquid nitrogen attachment. Field calibration was carried out routinely using DPPH (g = 2.0036) and were checked with a gaussmeter when greater accuracy was required. Electronic reflectance spectra were recorded on Beckmann DK 2A and Acta IV spectrophotometers against BaS04 or MgO as reflectance standards. Concentration changes in supernatant solutions were followed by conventional absorption spectrophotometry with a Perkin-Elmer 550s instrument for bpy-containing solutions. When M2+-containing solutions were used, the metal ion contents were found by EDTA titration or AA spectrophotometry before and after 13914

(1 1) Costantino, U. J . Chem. SOC.,Dalton Trans. 1979, 402. (12) Ferragina, C.; La Ginestra, A.; Massucci, M. A.; Patrono, P.; Tomlinson, A. A. G. J . Chem. SOC.,Chem. Commun. 1984, 1024. (13) Alberti, G.; Torracca, E. J . Inorg. Nucl. Chem. 1968, 30, 317. (14) Allulli, S.;Ferragina, C.; La Ginestra, A.; Massucci, M. A,; Tomassini, N. J. Chem. SOC.,Dalton Trans. 1977, 1879. (15) Hathaway, B. J.; Procter, I. M.; Slade, R. C.; Tomlinson, A. A. G. J . Chem. SOC.A 1969, 2219.

R

e h 35

30

25

20

15

10

2

op

5

Figure 2. X-ray diffraction patterns of intercalated bpy and complexpillared materials: (a) a-Zr(HP04)2(bpy)o.2s-l .5H20; (b) a-ZrHl,S[C~(bpy)(OH~)]~,~~(P0~)~-3H~0; (c) [ C ~ ( b p y ) ~diffused ] ~ + int oa-Zr(HP04)2[2EtOHl(see text); (dl a-ZrHl,S[Ni(b~~)(OH2)lo.2s(P04)2 3H2Q (e) ~-Z~H19[Co(OH2)~l~.l~~[C~(b~~)21~.12S(P04)2~4H (obtained by carrying out batch preparation at 60 “C). contacting. The organic ligand contents of solids were confirmed via TG-DSC analysis (ignition up to 1200 OC to constant weight in an air flow) with a Stanton Model STA 781 simultaneous thermoanalyzer, heating rate 5 OC/min. The water content of solids was also found by T G methods. Preparation of a-Zr(HP04),/bpyIntercalated Compounds. The bpy-intercalated materials were all prepared from the metastable alcohol phase a-Zr(HP04),[2EtOH] (dOo2= 14.20 A) by contacting a-Zr(HPO4)(NaPO4).5HZO(0.5 g) with absolute EtOH 0.1 mol dm-3 in HC104 (100 mL) for 24 h.” The suspension was then centrifuged (at low rpm, otherwise layer collapse of the material occurs, giving a-Zr(HP04)2.Hz0,dOo2= 7.6 A) the supernatant decanted, and the white solid washed with absolute EtOH to neutrality. Aliquots of 250 mL of 0.01 mol dm-3 solution of bpy in 1:l EtOH:H,O were added to samples of 1.26 mmol of alcohol phase (left wet to avoid any layer collapse) and the suspensions left to stand for 24 h at 25 OC. The resulting pink solid was filtered off and dried in air. The chemical analyses and the T G measurements, referring to four preparations, give the formula Zr-

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The Journal of Physical Chemistry, Vol. 89, No. 22, 1985

Ferragina et al. SCHEME I

'

1 -

e 0

0 0

4

e

TT7-)-TTT

A

0

C

another metastable alcohol phase having an interlayer distance larger than that with EtOH, led to exactly the same result. In either case, when the blue solid was filtered off and subsequently batch-contacted with a solution of copper acetate, the a-Zr(HP04)z(bpy)o,zs.l. 5 H 2 0 phase was entirely consumed, to leave the pure dOo2= 13.00 8, phase. I I I I I 1 2 3 4 5 Exchange Behavior of Cuz+ Complex Pillared Phase. atimo/h ZrHl,5[Cu(bpy)(OH2)]o,25(P04)2~3H20 was chosen to see if free Figure 3. Time course of metal ion uptake into ~ t - z r ( H P 0 ~ ) ~ - OH groups are still available in the interlayer region. In a typical (bpy)025-1.5H20 at 25 OC. procedure, the pillared material was batch-contacted with agitation, with 1 X lo-, mol dm-, solution of Cu(OAc), or AgNO, (HP04)2(bpy)o,25-1 .5H20 (Table I). The material is well-ordered, until no further uptake occurred. The blue solids obtained were with an interlayer spacing of 10.90 A (Figure 2a). then filtered off and dried in air. Analyses and interlayer distances On repeating the uptake with more concentrated solutions (0.1 are listed in Table I. mol dm-,) of bpy at 25 "C, more highly loaded materials were obtained. The maximum loading after 24 h contacting corresponds Results and Discussion to the formulation a-Zr(HP04)2(bpy)o,35-l .65H20. The X-ray pattern is identical with that of a-Zr(HP04)2(bpy)o,2s~1 .5H20, The X-ray pattern of a-Zr(HP04)2(bpy)o,25.1 .5H20shows that apart from a lower degree of crystallinity. On carrying out the the material is highly crystalline and has an interlayer distance same experiment at 60 OC, after 4 days of contact a phase with of 10.90 A. On a very crude picture, when bpy diffuses into a somewhat better crystallinity than that obtained at 25 "C, the a-Zr(HP04),[2EtOH] it may pack between the layers in one (or same bpy loading, and the same interlayer spacing (10.90 A) but more) of three ways: flat (A), sidewise slanted (B), or lengthwise otherwise different X-ray patterns, was obtained. (C) (Scheme I). All subsequent experiments were carried out with a-ZrThat the phase given is a pure, highly crystalline one with a (HP04)z(bpy)o,25.1.5H20, which was chosen because it is the most well-defined interlayer distance strongly suggests that a single type crystalline, least loaded, pure material of the series; Le., it provides of orientation is present. We further assume that on intercalation, the most open structure. Uptake of eo2+, Ni2+, and Cu2+ by a-Zr(HP04)2(bpy)o,25. the layer thickness remains more or less the same as in the parent C X - Z ~ ( H P O ~ ) ~ . Le., H ~ O6.3 , A.3 (This is a common assumption 1 .5H20and Formation of Metal Complexes in Situ. The uptake in intercalation chemistry,* and is based on the assumption that of metal ions by a-Zr(HP04)z(bpy)o,25.1 S H 2 0was carried out little "ruffling" of the intralayer Zr out of the plane of the layers by a batch procedure. Samples of 1 mmol of bpy compound were takes place on inter~alation.'~) The free height available in contacted with agitation with 50 mL of a 5 mmol dm-3 metal ion a-Zr(HP04)2(bpy)o,25.1.5H20, Le., a in Figure 1, is then ca. 4.6 acetate solution such that [M2+]:[bpy] = 1.1 (although the acetates A. This value is somewhat larger than the thickness of bpy, are usually used to facilitate exchange,I6 the nitrates here gave estimated to be 3.2-3.3 A from crystallographic studies.'* This the same results; no elution of bpy ensued despite the p H drop would argue against a completely flat orientation, as in A. Simto -2.0). At set time intervals the solids were filtered off and ilarly, the lengthwise orientation, C, would be expected to give the changes in pH and metal ion concentration in the supernatant an interlayer distance much larger than that found in practice. monitored. The contact times required for complete uptake were The X-ray evidence alone thus points to the presence of the 30 min for Cu2+,4 h for Co2+,and 5 h for Ni2+ (Figure 3). X-ray orientation B, although the angle between intercalant plane and patterns of the wet (and dried) solids were also taken and the inorganic layer is expected to be small. The area convered by formation of the coordination compounds between the layer could the projection of the bpy molecule on the basal plane is then more be followed by monitoring both the decrease and eventual disthan sufficient to cover two basal units of the phosphate layer (each appearance of the dOo2peak or a-Zr(HP04)z(bpy)o,25'1.5H20 at of which measures 5.3 X 5.2 A)., Further, if the bpy is indeed 28 = 8.1" and the dOo2peak of the new phases at lower 20 angles. trans in configuration, molecular models show that in order to Coordination went to completion in 90 min for Cu2+, 24 h for allow Ne-HOP interactions to be operative, the projection of bpy Ni2+, and 4 days for Co2+at 60 "C ( > l o days at 25 "C). These will overlap into more than two basal units. This would nicely times refer to the case of solids left in their mother liquors until rationalize why not much further bpy will be taken up by acomplexation was accomplished. Final products and their inZr(HP04)2(bpy)o.25.1.5H20 at 25 "C, and then only with loss of terlayer distances are listed in Table I. crystallinity. Diffusion of Cu(bpy),2+into a-Zr(HP04),[2EtOH].An attempt was made to intercalate C ~ ( b p y ) ~ ,into + the metastable What evidence is there for the trans configuration, B? In both alcohol intercalate to see if complex pillars could be prepared solid-state and in nonpolar solvents, pure bpy exists in the trans directly: 0.76 mmol of a-Zr(HP04),[2EtOH] was contacted with configuration, whereas bpyH+ exists in the cis configuration, and 0.76 mequiv of [Cu(bpy),](ClO,), (210 mL, 1.8 mmol dme3 bpyHZ2+(in strong H2S04solutions) is believed to exist as the solution). After 24 h, two phases were obtained, having similar trans form.19 High intensity bands in the UV spectra are X-ray intensities for the dso2peaks, which lie at 10.90 and 13.00 A (see Figure 2b). These interlayer distances are identical with those for a-Zr(HP04)2(bpy)o,z5-l . 5 H z 0 and the in situ prepared (17) Alagna, L.; Tomlinson, A. A. G. J . Chem. SOC.,Faraday Trans. 1 Cuz+complex (Table I). Similarly, batch contacting of [Cu1982, 78, 3009, reports indirect evidence, from EXAFS s ctroscopy, for the ( b p ~ ) ~solution ] ~ + with freshly prepared a-Zr(HP04),[2BuOH], presence of interlayer distortions in dehydrated fully Cu p" +-exchangeda-Zr(16) Allulli, S.; La Ginestra, A.; Massucci, M. A,; Tomassini, N.; Ferragina, C.; Tomlinson, A. A. G. J . Chem. SOC.,Dalton Trans. 1976, 2115.

(HP0.+)2*H20. (18) Kitaigorodsky,A. I. "MolecularCrystals and Molecules";Academic Press: New York, 1973. A recent example is: Morpugo, G. 0.; Dessy, G.; Fares, V. J . Chem. Soc., Dalron Trans. 1984, 461 and references therein.

The Journal of Physical Chemistry, Vol. 89, No. 22, 1985 4765

Intercalation of Bpy into a-Zr(HP04)2.H20

A

L c

c m a

P

TG

C

6

A

10-

+

gao-

B

A

h

k

h

2

4h

C 20-

Ol 10 i

k 6

Figure 5. Changes in dw2reflections of metal ion exchanged material (batch conditions; [intercalated bpy]:[M2+] = 1; 25 O,c): (A) Cu2+ (recorded a t different times on a single sample withdrawn after 5 min of batch contact, Le., after 75% Cu2' exchange). a is the dw2peak of a-Zr(HP04)2(bpy)o.2s.1.5H20, b the dW2 peak of a-ZrHI,?[?(bpy)(OH2)]o.2s(P04)2-3H20; (B) Ni2'; (C) Co2+;the dw2 peak a IS identical with the dw2peak of Figure 2e. B and C were recorded on a series of samples, each of which was filtered off after different contact times (the (' (bpy)o 2sS1.5H20; (B) ~-Z~HI.S[C~(~PY)(OH~)IO.~~(P~~)~'~H~~; complete uptake of M2' is 5 h for Ni2+ and 4 h for Co2+. a-ZrHl.~[Ni(bpy)(OH2)I~.2~(P04)2.3H20; (D) a - z r H ~ . ~ [ C o -

Figure 4. TG and DTA analyses of materials: (A) a - Z r ( H P 0 4

(OH2)41o,125[Co(bpy)2]0.~~S(P04)2~4H~O (note separation between cavity water and coordinated water).

characteristic for each configuration, the main bands for bpy itself lying at 35 590 and 42 920 cm-I, those for bpyH+ at 33 220 and 41 494 cm-I, and those for at 34 600 and 45 000 cm-I. The reflectance spectrum of ~ t - Z r ( H P O ~ ) ~ ( b p yS) ~ -l H,2~0~shows a high intensity UV absorbance with a peak at 34 850 cm-', in agreement with a trans configuration and strong interaction with the acidic matrix phosphate groups. In addition, the presence of a second UV band ascribable to bpy, lying at ca 46 500 cm-', indicates that the bpy is only slightly twisted, if at Further evidence in support of the presence of very strong interaction between trans N atoms and matrix >P-OH groups is available from the change in interlayer distance when a-Zr(HP04)2(bpy)0,25-1 S H 2 0is dehydrated. In all the cases reported in the literature to date, removal of intercalated water leads to partial, or total, layer collapse;* in the present case, there is a distinct expansion of the interlayer distance, from 10.90 to 11.62 A. This is highly suggestive of a "straightening out" of the bpy between the layers.21 (19) Remyga, S. A.; Myasnikova, R. M.; Kitaigorodsky, A. I. Kristallogruj?ya 1%7,12,900 (Engl. Edn., 1967, p. 784). Lmel, R. H.; Kaczmarczyk, A. J . Phys. Chem. 1961,65, 1196. Bray, R. G.; Ferguson, J.; Hawkins, C. J. J . Phys. Chem. 1961, 65, 1196. Bray, R. G.; Ferguson, J.; Hawkins, C. J. Aust. J. Chem. 1969, 22, 2091. The pale pink material also shows weak bands in the near UV-vis region (Table 11). They became weaker when the material was dehydrated. They were at first believed to be due to impurities of iron, because Fe"-diimine bonds give c.t. bands in the same region (1700C-20000,25000-30000 cm-I; see: Krumholz, P. Srruct. Bonding 1971, 9, 147). However, both chemical analysis and the XPS spectrum (Vacuum Generators ESCA MkIII instrument) provided no evidence for the presence of iron impurities. We speculate that the bands may arise via intensity enhancement of otherwise forbidden transitions. (20) Nakamoto, K. J. Phys. Chem. 1960, 64, 1420. (21) It is a moot point whether this strong bpy-matrix interaction constitutes a protonation in the usual sense of the word, because the bpy is quite free to coordinate metal ions.

Thermal Behauior and Stability. a-Zr(HP04)2(bpy)o,251.5H20 loses all its zeolitic water rapidly and reversibly between 110 and 160 O C (Figure 4A). This is very different from the parent a-Zr(HP04)2-H20,which loses its water with difficulty and not reversibly,2q22and reflects the presence of larger cavities in the intercalated bpy material. This zeolitic type water is lost in two steps. Bpy is then lost slowly between 330 and 400 OC;Le. there is some stabilizing effect on intercalation (bpy itself has mp 71-2 "C and bp 272-5 0C23). Most of the water content in the metal-complexed materials is also zeolitic, being lost in at least two steps between 70 and 160 OC. The weight loss is reversible. The remaining water is then lost in a slow, but clearly distinguishable, process at 250 "C, giving rise to structural rearrangements as suggested by the exothermic peak in the DTA curve (see Figure 4B-D). This allowed determination of the water molecules coordinated to the metal ions as 1 H 2 0per Ni2+ (or Cu2+) and 2 H 2 0 per Co2+ion. This dehydration was accompanied by color changes: blue pale blue (Cu2+), blue green (Ni2+), yellow bright blue (Co"). Elimination of bpy begins at 380 OC (Cu2+ and Co2+)and 390 OC (Ni2+) as judged from the DTA curves. The exothermic reactions occurring above these temperatures indicate that the bpy decomposes in stages, all being finally lost (as carbon) only at 1100 OC;Le., complexation stabilizes the pillars as expected. The loss of bpy overlaps with condensation of the phosphate groups to pyrophosphate, typical of layered group 436phosphates.22 At 1200 O C , a mixture of crystalline ZrP20, and ZrMP208is given. Metal Zon Uptake and Interlayer Coordination. The most interesting novelty to emerge from this attempt to produce large

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-

-

(22) La Ginestra, A.; Ferragina, C.; Massucci, M. A.; Tomassini, N. Therm. Anal. Proc. In?. C o n ! , 4th. 1974 1975, 1 , 631. (23) "Handbook of Chemistry and Physics", 60th ed.; CRC Press: Boca Raton, FL, 1979.

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The Journal of Physical Chemistry, Vol. 89, No. 22, 1985

TABLE 11: Electronic Spectra (em-’) no.a 1 2 and 2-anhyd 3 3-anhyd 4 4-anhyd 5

5-anhyd 6 7

d - d transitions

c.t.

14800; 1570 sh 9100 sh; 10750; 16500 sh; 26500 5600 sh; 8500; 12500 sh; 13300 sh; 25300 sh 9000; 1570Oe; 12400; 18800d; 27800 5700 sh; 6200; 8700; 12000; 14300 sh; 20400; 27,000 8550; 21400; 28100 5700; 7300 sh; 8900; 15700; 17400; 20000; 28200 sh 14300; 15100 sh 14900; 15900 sh

+ intraligandb

20000; 28400; 34850; 36100; 39700; 43100 32300; 33700; 40000 33100 sh; 34200; 40000 32800; 33900; 39200; ca 46000 31750; 32600; 40000 32700; 38900 31250; 33300; 39200 26000; 32000; 33300; 40000

ONumbering of materials as in Table I. *All c.t. bands between 34400 and 43000 undergo shifts expected for cisoid-bpy after coordination; see ref 19. ‘Bands due to NiO, moiety. dBands due to cis-NiN,O, moiety.

cavities in a-zirconium phosphate by in situ coordination of a metal ion to an intercalated ligand is that the uptake via ion exchange and the coordination to the ligand occur in well-defined and separable stages. Chemical analysis shows that at 25 “C the metal ion exchange rates follow the order: Cuz+ >> Coz+ > Ni2+. This is the same order as that found for diffusion of the hydrated metal ions into a-Zr(NaP04)(HP04).5H20.14 The Cuz+ is exchanged in a single step, all metal ion being removed from a 1:l [intercalated bpy]: [Cuz+] suspension within 30 min. Conversely, both Co2+ and Ni2+ are exchanged in two steps. The uptake curve for Coz+shows a very indistinct break after 1.5 h contact time (ca. 60% Co2+exchange) whereas that for Niz+has an unusual “pause” after 2 h contact time (50% NiZ+ exchange). This “pause” lasts for ca. 2 h, after which the remaining Ni2+ in the supernatant is exchanged over a period of 1 h (see Figure 3). The rate of coordination, as measured by disappearance of the dOo2peak for (~-Zr(HPO~)~(bpy)~,~~~1.5H~0 (+M2+ in solid solution) and growing in of that due to complex-pillared species, follows the order: Cu2+ > NiZ+>> Co2+ (see Figure 5). The complexation of Cuz+ was (relatively) fast, so that the solid had to be removed from the suspension after 5 min contact (Le., ca. 75% Cu2+exchange) in order to observe the initial stage and subsequent development of coordination (Figure 5A). Simply removing the material from the supernatant and following the coordination rate on the diffractometer-mounted sample was not feasible for Ni2+ and Co2+, however, because coordination was too slow. The batch method (see Experimental Section) was more convenient; even then, complete coordination of Co2+ to intercalated bpy had still not gone to completion after 10 days contact at 25 ‘C. In both cases, two coordinated phases were apparent (see Figure 5B,C). To the best of our knowledge, these are the first examples of slow coordination of a transition-metal ion to a ligand, in the solid state at low temperature. In solution, substitution of coordinated water in Cuz+, NiZ+,and Coz+ hydrates occurs with rates of 104-10-5 (Note that the X-ray patterns of the materials obtained after monitoring coordination were identical with those of the pure products shown in Figure 2; i.e., the intensity changes are not caused by exposure to X-rays.) It seems reasonable to assume that initially the exchanged M2+ ions are present in the bpy-pillared material as a solid solution and anchored to acidic phosphate groups. For Cuz+,by analogy with solution studies, coordination may be expected to occur via the following steps: (i) diffusion of bpy to the Cuz+;(ii) coordination of one N atom of bpy to the Cu2+; (iii) rotation of the bpy between the layers to allow cis-bidentate coordination to the metal ion. Qualitatively, it appears that step (iii) is the rate-determining step, although a detailed reaction mechanism cannot yet be put forward because the role of intercalated water is unknown. Nevertheless, the site available for the metal complex pillar between the layers is very selective for the attainment of a monobpy complex only. All attempts to intercalate

[ C ~ ( b p y ) ~into ] ~ +cu-Zr(HP04),[2EtOH] led to dissociation to give bpy and Cu(bpy)’+ intercalated between the layers (see Figure 2B). This is not simply a steric effect because [Cu(phen)J2+, which is considerably larger than its bpy analogue, will intercalate without dissociation into a-Zr(HP04)z[2EtOH].25 For Ni2+and Co2+,diffusion effects and intercalated water play a more important role during coordination. To clarify the reasons for the appearance of the pause in uptake at 50% Ni2+exchange, two batches each with [intercalated bpy]:[Ni22+] = 1:0.5 were left in contact. One, “Ni-A”, was contacted for 4 h, and the other, “Ni-B”, for 24 h. Both materials were filtered off and their X-ray patterns registered immediately and then at set times. As shown in Figure 6, the dOo2regions are very different. For Ni-A, there is initial formation of two phases, having dooz= 12.44 and dOo2 = 14.47 A, and the former then grows in at the expense of the latter, the process going almost to completion after 6 days. By way of contrast, Ni-B gives initial, predominant formation of the dooz= 14.47 8, phase, which then slowly, and partially, undergoes

(24) Roche, T. S.; Wilkins, R. G . J . Am. Chem. Soc. 1974, 96, 5082. Cayley, G . R.; Margerum, D. W. J. Chem. Soc., Chem. Commun. 1974, 1003.

(25) Ferragina, C.; La Ginestra, A.; Massucci, M. A.; Patrono, P.; Tomlinson, A. A. G. J . Chem. Soc., Dalton Trans., submitted for publication.

i- h

1

6d

0

tdkk

‘ 1 0 8 6 -2e

(O)

Figure 6. Changes in dW2reflections of cu-Zr(HP04)2(bpy)o,2,.1.5H,O charged with Ni2+ [intercalated bpy]:[Ni2+] = 1:0.5): (A) on removing solid after 4 h exchange; (B) after digesting solid in mother liquor for 24 h. The x-rays refer to samples A and B left in air and registered at invervals.

Intercalation of Bpy into a-Zr(HP04)2.H20 SCHEME I1

The Journal of Physical Chemistry, Vol. 89, No. 22, 1985 4767

999

L 9 R

[ i n t e r c a l a t e d bipy]:[Ni"]

inn e r

'."

= 1

: 0.5

o u t e r

25OC

air

I

qI-' gl 2.07 (1

, 30

25

20

'4 -53 Energy/cm- ( x 10 1 15

lzooq

I2.07(1)

g

Figure 7. Electronic reflectance spectra of materials of Figure 6 .

solid-state transformation to the 12.44-8, phase. The formation of two different layered phases suggests that more than one complex forms between the layers. This is confirmed by inspection of electronic reflectance spectra. Ni-A gives d - d bands at 9100,10750, 16500, and 26500 cm-I, as expected for a cis-NiN,O, moietyz6and identical with the band energies found in pure a-ZrHl.5[Ni(bpy)(OHz)]0.25(P04)2~3H20 (see Table 11). The d-d spectrum of Ni-B is significantly different, with bands at 11 150, 18 700, and 27 800 cm-I (see Figure 7); the spectrum well compares with complexes having a cis-NiN402 chr~mophore.~' The reactions involved may be visualized as illustrated in Scheme I1 (ignoring cavity water molecules). The main factors involved are (i) diffusion of NiZ+ions between the layers; (ii) complex formation; (iii) partial complex dissociation. Ni2+diffuses only slowly, so that during the initial stages of uptake it is still mainly localized on the external parts of a-Zr(HP04)2(bpy)0,25-1 .5H20 crystallites. There is thus a greater probability of finding [intercalated bpy]:[Ni2+] ratios of 1:l in (26) Tomlinson, A. A. G.; Bonamico, M.; Dessy, G.;Fares, V.; Scaramuzza, L.J. Chem. Soc., Dalron Trans. 1972, 1671. (27) Harris, C. M.;McKenzie, E. D. J . Inorg. Nucl. Chem. 1967, 29, 1047.

~ P hP Figure 8. EPR spectra of Cu2+-containing materials: (i) 2% Cu2+-ex~ ) a~- Z,r~ H ,~S ~ [ C~ u (. b p~yH )-~ O ; changed O I - Z ~ ( H P O . , ) ~ ( ~ ~(ii) (OH2)]o.2s(P04)2.3H20;(iii) as for ii, after heating a t 140 "C in vacuo for 2 h.

this region. On removal from supernatant after 4 h (Ni-A) the diffusion of Ni2+greatly slows down, and coordination of the bpy proceeds, giving mainly the 1:1 phase, as in Figure 6A. Conversely, after 24 h contact with supernatant, (Ni-B), the solution-like interlayer region now has a more homogeneous distribution of Ni2+ ions, and the equilibrium Ni2+ + bpy

-

[Ni(bpy)I2+

-

[Ni(b~y)~]~+

is set up. This would account for the predominant formation of the [Ni(bpy),12+ phase in Figure 6B, 3 min after removal from supernatant. This complex then dissociates back to the monobpy

4768

The Journal of Physical Chemistry, Vol. 89, No. 22, 1985

\ 1

I 40

35

i

30

25

I-

I

20

15

--._ I

30

I

30

I

I

1

25

20

F,

I

25

I

20

1 10

I 5

1

I I 10 5 Energy/ c~n-'~.llxlO-~i

15

Figure 9. Electronic reflectance spectra: (i) a-Zr(HP04)2(bpy)o,2s. 1.5H20; (ii) -, a-ZrH,5[Cu(bpy)(OH2)]02s(P04)2~3H20, and -, after heating a t 140 OC in vacuo for 2 h; (iii) -, a-ZrH,,[Ni(bpy)(OH2)]o,2s(P04)2.3H20, and - - -, after heating at 140 OC in vacuo for 2 h; ( i d -, a-ZrH1 sI[C~(~H~)~I~.,~~[C~(~PY)~IO lzsl(PO4)2-4H@, and - - - ,after heating in vacuo at 140 OC for 2 h.

--

complex as shown by the progressive decrease in the peak height at 14.47 A and concomitant increase in that at 12.44 A. The matrix phosphate groups may be involved in this dissociation, and an analogous reaction has been reporteda2* Returning to the phase changes in Figure 5B, and the pause in uptake of Figure 3, we speculate that the block to entry of Ni2+ occurs because of the gross rearrangements occurring at the pause time in the interlayer. Two interlayer bpy complexes are also present during uptake and coordination of Coz+. Takeup clearly slows down, after ca. 60% Co2+ exchange (Figure 3) and two doo2peaks grow in as coordination proceeds, at the same basal spacing as for Ni2+ (Figure 5C). However, in this case there does not appear to be a subsequent dissociation of [ C ~ ( b p y ) ~to ] ~[Co(bpy)12+. + At 25 "C, the [Co(bpy)]*+ phase grows in at the expense of intercalated bpy but further coordination to the bpy is extremely slow, even though a [intercalated bpy]:[exchanged Co2+]ratio of 1 : l is present. Further support for the importance of diffusion in the uptake and coordination is provided by the phases obtained by carrying out exchange at 60 "C. For both Co2+and Ni2+, and for ratios of [intercalated bpy]:[Me++] = 1:l or 1:0.5, only the almost pure 14.47-A phases alone are obtained. The TG and DTA curves for the "1:O.S' materials do not show weight losses and thermal effects around 250 OC, the temperature at which the water coordinated to the metal is lost. This is indeed observed for the 1:l phases. This implies that these 1:l phases formed at 60 OC should be (28) Hathaway, B. J.; Billing, D. E. Coord. Chem. Reu. 1970, 5 , 143. Hathaway, B. J.; Tomlinson, A. A. G. Ibid. 1970, 5, 1.

Ferragina et al.

formulated as ~ - ~ ~ ~ 1 , 5 ~ ~ ~ ~ ~ ~ 2 ~ , 1 0 . 1 2 5 ~ ~ ~ ~ P Y ~ mH20. Geometry of the Complex Pillars. Further evidence for the above formulations is available from the electronic reflectance and (where utilizable) EPR spectra of a-Zrl,s[Cu(bpy)(OH2)]o,25(P04)2.3H20, its anhydrous analogue, and a low-loaded material. The g values are all of the "normal" type; Le., they all have gl,> g N 2.03, values diagnostic of a geometry giving rise ~* or to a d+2 (or d,) ground ~ t a t e . ' ~ ,Trigonal-bipyramidal cis-octahedral geometries can then be excluded. In addition, the gllvalue for the 2% Cu2+-exchanged material is not in the range characteristic of a cis-Cu(bpy)2z+moiety (2.22-2.2329), and the d-d bands are not at the low energies characteristic of pseudotetrahedral geometries.)O The spectral properties are in agreement with a tetragonal octahedral C u N 2 0 2+ 2 (or 1) 0 moiety. The Ail = (165-5) X lo4 an-'found in the diluted case provides further evidence that the Cu2+is indeed coordinated to the bpy and is not merely exchanged into the cavity formed by the bpy. According to Marev et al.,31a [ C ~ ( b p y ) ( 0 H ~ )moiety ~ ] ~ + gives (in aqueous solution): Ail = (165-2) X lo4 cm-l and gll = 2.310 (5). In a borate buffer, the parameters change slightly, to All = (174-3) X lo4 cm-], gll = 2.295.)] Similarly, we ascribe the small differences in EPR parameters between aqueous [Cu(bpy)(OH2)2]2+and the 2% Cu2+-exchangedform to bonding by lattice phosphate oxygen atoms. Given that only one H 2 0molecule is coordinated to the Cu2+ in a-ZrHl,5[Cu(bpy)(OH2)]o,25(P04)2-3H20, this information implies that the matrix is coordinated to Cu2+via more than two ?-P-0- groups. Presumably, two floor ?-P-0- groups and a roof +P-0- group (see Figure 1) are involved in forming the pillar. Such a CuN,Ox,O (Ox = matrix oxygen) moiety must cause considerable local distortion in the matrix. Curiously, removal of all the coordinated water leads to little change in EPR parameters or electronic spectra; Le., the pillar geometry changes very little. However, there is considerable amorphization on dehydration (although the material given is still layered) which presumably reflects the fact that in order to coordinate with a further matrix oxygen, the CuZ+may affect the coordination of the intralayer Zr atoms. The pillar geometry in L U - Z ~ H [Ni(bpy)(OH2)]0,25(P04)2-3H20 ,,~ is clearly pseudooctahedral, as deduced from the electronic spectra, and band energies are in agreement with a cis-MN204chromophore26(see Figure 9). In a-ZrHl.75[Ni(bpy)2]o,125(P04)2-4H20, the electronic spectra clearly show that a cis-pseudo octahedral NiN,02 pillar is present27 and the same comments apply to the Co2+analogue. In these cases, the metal ion cannot coordinate to two ?-P-0- groups, one from the "floor" and the other from the ''roof'. Presumably, the matrix provides two oxygen atoms from the floor (see Scheme 11). In the final, pure products obtained at 60 "C, i.e., ~ - ~ ~ ~ ~ , ~ ~ ~ ~ ~ ~ ~ ~ ~ (P04)2.mH20,M = Co, Ni, this M N 4 0 2pillar remains as such the hydrated metal ion portion being present in solid solution. The electronic spectroscopic evidence for this is particularly clear for the Ni2+case, where bands characteristic of both cis-NiN402and N i 0 6 are evident (Table 11). Dehydration of both types of Co2+and NiZ+complex pillared materials leads to considerable amorphization and gross changes in pillar geometry. The pillar geometry in a-ZrH,,S{[Co~ ~ ~ 2 ~ 4 1 0 . 1 2 s ~ ~ ~ ~ ~ P Y ~ changes 2 1 0 . 1to2 mainly 5 ~ ~ ~ ~ 4 ~ 2 ~ ~ pseudotetrahedral when all water is removed, although there is some evidence for the presence of more than one species.32 In

(29) Lever, A. B. P. "Inorganic Electronic Spectroscopy", 2nd ed.;Elsevier: Amsterdam, 1984. Attanasio, D.; Tomlinson, A. A. G.; Alagna, L. J . Chem. SOC.,Chem. Commun. 1977, 618. (30) Bencini, A.; Gatteschi, D. Inorg. Chem. 1977, 16, 1994. In any case, the presence of a Cu(bpy)22+moiety can be excluded because it would give rise to a partitioning of Cu2+between cavity and pillar. This is expected to give two EPR signals (probably showing strong magnetic exchange effects due to the proximity of the Cu2+ions); only a single is observed. - signal (31j Marev,-I. N.; Belyaeva, V. K.; Smirnova, E. B.; Dolmanova, I. F. Inorg. Chem. 1978, 17, 1667.

J. Phys. Chem. 1985, 89, 4169-4113

4769

give a plastic coordination sphere,34 i.e., to change geometry so much as to still preserve a layered structure. A Metal Zon Exchange into C W - Z [Cu(bpy)(0H2)],,,,~H~.~ (PO4),.3H2O. The pillars formed are quite wide and it might be expected that remaining exchangeable H+ would be "covered" by + the pillar and hence become inaccessible to incoming ions. Fortunately, pillar density is low; Le., b in Figure 1 is large, so v) B that there should still be much cavity space available. This is '2. indeed found to be the case. All the remaining protons in the Cu2+-complex pillared material are exchanged on contact with I I I a Cu2+-containing solution to give a-Zr-Cuo,75[Cu(bpy)35 30 25 20 15 10 5 (OH2)]0,25(P04)2.3H20. Conversely, Ag+ will exchange only 55% 2 o/" of the available protons, giving a-ZrAgo,,,Ho,,5[Cu(bpy)(OHz)]o,2s(P04)2~3H20, The X-ray patterns (Figure 10) show Figure 10. X-ray powder diffraction patterns of cavity exchanged Cu that both materials are pure solid solutions with dW2= 13.0 A. complex pillared materials: (A) a-ZrCuo.~~[Cu(bpy)(OH2)]0.~~(P04)2~ The difference between Cu2+ and Ag+ presumably reflects dif3HzO; (B)~-Z~A~~.s~Ho.sstC~(b~~)(OHz)lo.zs(P~~)2~~~~~~ ferences in steric constraints and is being further investigated. the case of the NiZ+analogue, two species are again present and Conclusions it is not possible to unambiguously assign a geometry (Table 11). This paper has demonstrated that large amines can be interHowever, the electronic spectrum of the monobpy form, acalated into a layered phosphate under mild conditions, if a ZrHI.s[Ni(bpy)(OHz)]0.25(P04)~3H20 (dW2= 12.44 A) when metastable preswelled alcohol intercalate is used as an intermecompletely dehydrated is simpler (Figure 9). The presence of very diate. Pillars can then be formed in situ, via the formation of low energy bands between 5000 and 10000 cm-I indicates that intercalated analogues of simple inorganic complexes. This method an octahedral geometry is no longer present, and the spectrum provides an entry to an "intercalation coordination chemistry". would suggest the presence of a five-coordinate moiety.33 However, as regards the particular ligand utilized here, bpy, the On complete dehydration, all the Co2+-and Niz+-containing materials gave X-ray patterns indicating a greater degree of usual processes of coordination chemistry intervene (formation of more than one complex, dissociation, hydration phenomena, amorphization than in the case of the Cu2+-containing materials. . . . .) so that the layers are not held apart rigidly. A more adThis presumably reflects the much greater capability of Cu2+ to vantageous strategy for obtaining more stable pillared materials would utilize not only ligands containing coordination sites, but (32) The very weak shoulders at ca. 10000 and 21 000 cm-' still visible also further groups capable of holding the layers apart more rigidly. after dehydration may be due to the Co2+in solid solution. The absence of Work is under way in this direction.35 a shoulder between 11 500 and 13 000 cm-', which is characteristic of fivecoordinate geometries (see: Bertini, I.; Gatteschi, D.; Scozzafava,A. Inorg. Chem. 1975,14,512 and references therein) and the band shape suggests a Acknowledgment. This paper forms part of the C.N.R. finalized tetrahedral geometry about the Co2+. The low-energy ,T,(F) band center is research project "Chimica Fine e Secondaria", Settore Ossidazioni. closer to those found in CoN202moieties than in CoN4 ones (Gatteschi, D. Registry No. bpy, 366-18-7; Zr(HP04), 13772-29-7; Zr(HP0,)Struct. Bonding 1982,52, 37), implying that dissociation occurs on heating. (NaPO,), 34370-53-1; EtOH, 64-17-5; Cu, 7440-50-8; Ag, 7440-22-4. Further, the splittings of both *rl(F) and *rl(P) are very large, especially that of "T,(P),which gives a splitting of ca. 4300 cm-', much larger than is usually observed (see: Bellitto, C.; Tomlinson, A. A. G.; Furlani, C.; De Munno, G. Inorg. Chim. Acta 1978, 27, 269). This suggests that the pillar in the an(34) See, e&,; Hathaway, B. J. Strucr. Bonding 1984, 57, 55. hydrous, highly amorphized material must be extremely distorted. (35) Ferragina, C.; La Ginestra, A.; Massucci, M. A,; Patrono, P.; Tom(33) Lever, A. B. P. "Inorganic Electronic Spectroscopy", 2nd ed.;Elsevier: linson, A. A. G. Atti XVII Congr. Naz. Chim., Inorg., Cefalri (Italy),Oct 1984 Com. E9. Amsterdam, 1984; Chapter 6.

A

Catalytic Role of Copper( I)Ion on the Propargylic Transposition. A Theoretical Study M. Mercbin, J. AndrBs, I. Nebot-Gil, E. Siiia, and F. Tomis* Departamento de Quimica Fisica, Facultad de Ciencias Quimicas, Universidad de Valencia, Burjassot (Valencia), Spain (Received: January 8. 1985)

Pseudopotential ab initio calculations have been performed for the K- and u-type interactions between the copper monoion and the propyne, the allene, and the propargylium ion, which are taken as models for the reactive systems involved in the propargylic transposition reactions. The most striking conclusion obtained is that the presence of the copper ion makes energetically favorable the linear bending of the molecules studied, in contrast to the isolated molecules, where the linear bending is endoenergetic. For strong bent conformations a stable 0-type interaction is present for the copper(1)-propargylium ion system, which is explained by means of the analysis of the carbocation electronic structure. These facts explain qualitatively the catalytic role played by the copper monoion in the propargylic transposition reactions and account for the lack of stereospecificity of the catalytic rearrangement of the a-acetylenic alcohols to a,@-unsaturated carbonyl compounds.

Introduction Among the reactions of propargylic transposition, the rearrangement of a-acetylenic alcohols to oc,P-unsaturated carbonyl compounds is an efficient tool in organic for instance, (1) Vartanyan, S . A,; Babayan, S . 0. Rum. Chem. Rev. 1967, 36, 670. (2) Olsson, L. I.; Claesson, A.; Bogentoft, C. Acta Chem. Scand. 1973,27,

1629.

ethylene carbonyl derivatives are intermediates in the synthesis of a great number of co"ercia1 Products, such as fragances, carotenoids, and vitamins.4 These rearrangements are often (3) Pauling, H.; Andrews, D. A,; Hindley, N. C. Helv. Chim. Acta 1976, 59, 1233. (4) Olson, G. L.; Cheung, H. C.; Morgan, K. D.; Borer, R.; Saucy, G. Helv. Chim. Acta 1976, 59, 567.

0022-3654/85/2089-4169$01.50/00 1985 American Chemical Society