Characterization of Incomplete Cubane-Type and Cubane-Type Sulfur

Chapter 13 Characterization of Incomplete Cubane-Type and Cubane-Type Sulfur-Bridged Clusters

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Genta Sakane and Takashi Shibahara Department of Chemistry, Okayama University of Science, 1-1 Ridai-cho, Okayama 700, Japan Incomplete cubane-type clusters with M3S4 cores and cubane-type clusters withM3M'S4cores are characterized (M3 =Mo3,Mo2W,MoW2,W3; M'= metal). The clusters [M3NiS4(H2O)10]4+ take up ethylene to give [Μ3ΝiS4(C2Η4)(Η2O)9] : an increase in the number of tungsten atoms results in the upfield chemical shift of ethylene-signal in the 1H-NMR spectra. The molybdenum-iron cluster[Mo3FeS4(H2O)10] (Mo3Fe) does not react with ethylene. The formal oxidation states of metals in Mo3Fe and [Mo3NiS4(H2O)10] (Mo3Ni) are assigned as MoIVMoIII2M'II(Μ'=Fe, Ni). The oxygen/sulfur-bridged clusters[Mo3S4(H2O)9] +(Mo3)and [Mo3OS3(H2O)9] (Mo3OS) react with acetylene to give clusters with carbon-sulfur bonds. The reactivities ofMo3NiandMo3are interpreted by the electronic structures calculated by the Discrete Variational (DV)-Xαmethod. EPR studies of the mixed-metal cluster with Mo3CuS4 core are also described. 4+

4+

4+

4

4+

4+

2

2

Sulfide (S~), disulfide (S2 "), and thiolate (SR") ligands combine metal ions to give varied types of metal clusters. Much attention has been paid not only to metal-centered chemistry but also to ligand-centered chemistry, which is interesting inherently and of potential use in catalysis. Especially, molybdenum sulfur compounds have attracted much attention, and a large number of sulfur-bridged molybdenum compounds have appeared (/). In this article, some of our recent results on incomplete cubane-type clusters with M3S4 cores and cubane-type clusters with M3M'S4 cores (M3 =Mo3,Mo2W, MoW2, W3; M' = metal) will be summarized. Comparison of Molybdenum-Iron and Molybdenum-Nickel Clusters, [Mo3FeS4(HO) ] (MoFe) and [Mo NÎS (H O) ] (M03N1) 4+

2

4+

10

3

3

4

2

10

The report (2) that the incomplete cubane-type sulfur-bridged molybdenum aqua cluster [Mo3S4(H20)9] (Mo3) reacts with iron metal to give the molybdenum4+

0097-6156/96/0653-0225$15.00A) © 1996 American Chemical Society In Transition Metal Sulfur Chemistry; Stiefel, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

226

TRANSITION M E T A L SULFUR CHEMISTRY

iron mixed-metal cluster [ M o 3 F e S 4 ( H 2 0 ) i o ] (Mo3Fe; Scheme 1) engendered much research on this type of metal incorporation reaction. This reaction is the first example where the missing corner of the incomplete cubane-type core is filled with another metal atom. Many metal incorporation reactions of the aqua cluster have been reported by us (3) and by other groups (4) to give mixed-metal clusters with M o 3 M ' S 4 cores (M' = metal). We can think of two kinds of driving force for the formation of the cubane-type mixed-metal clusters from the incomplete cubane-type aqua cluster M 0 3 and metals. One factor is the affinity of the metal for the bridging sulfur atoms, and another is the reducing ability of the metal (2, 3b). In addition to direct reaction of M 0 3 , with metals or metal ions (e. g., S n ) , NaBIfy reduction of M 0 3 in the presence of M has also been used (4b, 4c). The reaction of M 0 3 with [Cr(H20)6] to give [Mo3CrS4(H20)i2] (4d), and other routes to clusters with M o M ' S cores (M' = Cu (5a, 5c, 5d) M ' = Sb (5b, 5c), M ' = W (6), M ' = Co (7)) have also been reported. Metal atom replacement of the incorporated metal atom M in the cubane-type M o 3 M ' S 4 core with C u to give the cluster with M03Q1S4 " " core has been reported (8), and the existence of a new oxidation state of M03CUS45+ is known (9). The strong coloration on the reaction of the cluster M 0 3 with mercury can be used for the analysis of mercury (JO). The reactivity of clusters with the Mo3PdS4 (77) or M03N1S4 (12) core toward small molecules such as CO, alkenes, and alkynes has been reported.


4+

2+

2 +

2+

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4

y

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clusters [ Μ θ 3 Ρ β 8 4 ( Η Ο ) ] (Mo Fe) and [ M c p N i S 4 ( H O ) ] are obtainable through the reaction of [M03 §/β\2®)9\ ( 3 ) with * and nickel, respectively, and are crystallized from 4 M Hpts solution to give [Mo3M'S4(H O) ](pts)4 7 H 0 ( M ' = Fe (Mo Fepts), N i (Mo Nipts); Hpts = /Moluenesulfonic acid). X-ray structural analyses of Mo3Fepts and Mo3Nipts revealed that the clusters, M o 3 F e and M03N1, have an approximate symmetry of C3 , with the iron and nickel atoms having fairly regular tetrahedral geometry in both clusters (2, 3h). The ^Fe-Môssbauer spectroscopy showed that the oxidation state of the iron atom in the mixed metal cluster Mo3Fepts was assignable as +2.39 (75), which indicates that the reaction is reductive addition of iron to the M o 3 S core in the molybdenum aqua cluster M03. Figure 1 shows cyclic voltammograms of M 0 3 , Mo3Fe, and M03N1. The cyclic voltammogram of M 0 3 shows three consecutive one-electron reduction processes (the cathodic peak potentials, Ep , are -0.45, -1.01, and -1.74 V, respectively), similar to those observed in [M3S4(Hnta)3] " obtained from [M S4(H 0)9] and H nta ( M = M03, M o W , M o W , W ) (14) and [Mo3S4(ida)3] ~ (75). These processes correspond to the change of oxidation states of the three metal atoms in each cluster: 4+

The

2

4+

10

3

2

(M03N1)

2

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10

r o n

M o

3

v

4

C

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M

IV

3

_

M

IV

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M

ni

-* M l V M i n 2

M %

The cyclic voltammogram of M o 3 F e also shows three reduction peaks with E p = -0.91, -1.47, and -1.81 V. The cathodic peak currents are close to each other and almost the same as those of M 0 3 after being normalized by concentration, indicating that M o 3 F e undergoes consecutive one-electron reduction processes. Four combinations of the oxidation states of the metals in M o 3 F e before reduction are possible: M o ^ F e , M o ^ M o F e , M o ^ M o ^ F e , M o 3 F e . Of these oxidation states, M o ^ M o ^ 2 ^ * appropriate, because the oxidation state of the iron atom in M o 3 F e has been determined to be +2.39 by Fe-Môssbauer C

0

I

l n

I

1 1

m

m

2

F e

sm o s t

57

In Transition Metal Sulfur Chemistry; Stiefel, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

SAKANE & SHIBAHARA

i4+

\/ Mo

S

[ M o 0 ( H 0 ) 9 ] (M03O4). While the sulfur-bridged cluster M 0 3 reacts with acetylene, the oxygen-bridged 4 +

3

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Mo

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d

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234

TRANSITION METAL SULFUR CHEMISTRY

400

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600 700 800 900 Wavelength/nm

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Figure 4. Electronic spectra: , [Μθ3(μ .8)(μ.θΧμ-8)2(Η9θ)9]4+ ( M 0 3 O S ) in 1 M HC1; , [ M o t o - S ) ^ - S ) 3 ( H 0 ) 9 f + ( M o ) in 1 M HC1; , [Μθ3(μ3.8)(μ.Ο)(μ3-82α Η2)(Η2θ)9]4+ ( M o O S A c ) obtained by passing acetylene through M 0 3 O S in 1 M HC1; — · , [Μθ3(μ3-8)(μ-8)(μ3-82α Η2)(Η 0)9]4+ ( M o A c ) obtained by passing acetylene through M o in 1 M HC1. 3

3

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Figure 5. Atomic orbital components constituting H O M O ' s : a, [Mo3FeS4(H2O)i0] ( M o F e ) ; b, [Mo3NiS4(H20)io] ( M o N i ) . Reproduced with permission from reference 3h. 4+

4+

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3



13. SAKANE & SHIBAHARA

235

Cubane-Type Sulfur-Bridged Clusters

C H 2

2

Figure 6. L U M O ' s for CO, C2H2, and C2H4. permission from reference 3h.

Reproduced with

cluster M 0 3 O 4 does not react with acetylene. This difference can be understood in terms of the DV-Χα calculations of M 0 3 and M 0 3 O 4 (36). Reports have appeared on the calculation of clusters with M o 3 S 4 or Μ θ 3 θ 4 cores. Several calculation methods having been employed: 1) bare cores, M o S + (37a, 37b, 37d, 37e), M o 0 (37a, 37e, 37f), and M o S _ O + (n=0-4) (38). 2) full clusters, [Mo S Cl (PH3)3] - (37c\ [ M o 0 ( O H ) (H 0)3] " (37c, 37f) However, no reports on the full aqua clusters, M 0 3 and M 0 3 O 4 , have appeared to the best of our knowledge. Fairly large mixing of Mo 4d and S 3 ρ (or Ο 2p) atomic orbitals has been observed in some of the orbitals, regardless of the method of calculation. As for the HOMO of the bare cores of M o 3 S 4 and Μθ3θ4 +, however, the CNDO/2 calculation (37a, 37b) indicates no contribution of bridging-sulfur (or -oxygen) orbitals, while SCCC-EHMO (37e\ Fenske-Hall (57/), and ab initio (38) methods indicate contribution of both molybdenum and sulfur (or oxygen). Our results on the bare cores, M o 3 S 4 and Μ θ 3 θ 4 , as well as the full clusters, M 0 3 and M 0 3 O 4 , indicate the mixing of Mo 4d and S 3p (or Ο 2p) orbitals in each HOMO. If the HOMO (45e, X-Z plane; Figure 7a) of M03 and the HOMO (40e, X-Z plane; Figure 7b) of M 0 3 O 4 are compared, it is found that the orbital lobe of μ-S expands toward the Z-axis, which is favorable to the overlapping of the μ-S orbital lobe with the π-orbital of acetylene. On the other hand, the orbital lobe of μ-O does not expand toward Z-axis; furthermore, the magnitude of expansion of the lobe is much less than that in M03. Therefore, the possibility of the orbital lobe of μ-0 overlapping with the π-orbital of acetylene is much less than the case of M03. Another factor for the reactivity difference in M 0 3 and M 0 3 O 4 clusters is the difference in energy levels. However, the energy differences in HOMO's (0.84 eV) and in LUMO's (0.67 eV) are not so large, and the different shapes seem to be the larger factor for the C-S bond formation. Calculated transition energies are in fairly good agreement with experimental ones for both clusters. 4+

4 +

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4 +

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a

b

4

Figure 7. Contour maps: a) HOMO (x-z plane) for [Mo3S4(H20)9] + (M03).

The x-z plane contains one Mo, one μ-S, one μ3-8, one Ο

(water), and two Η atoms (water), [Μθ3θ4(Η2θ)9]

4 +

(M03O4).

b) HOMO (x-z plane) for

The x-z plane contains one Mo, one μ-Ο,

one μ 3 - 0 , one Ο (water), and two Η atoms (water).

Solid, dotted, and

dashed lines indicate positive, negative, and zero contour lines, respectively. Reproduced with permission from reference 36.



Cubane-Type Sulfur-Bridged Clusters 237


Acknowledgments This work was partly supported by a Grant-in-Aid for Scientific Research Nos. 59470039, 02453043, and 04241102 (on Priority Area of "Activation of Inactive Small Molecules")fromthe Ministry of Education, Science and Culture of Japan.

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(10) a) Aikoh, H.; Shibahara, T. Physiol. Chem. Phys. &Med.NMR 1990, 22, 187-192. b) Aikoh, H.; Shibahara, T. Analyst 1993, 118, 1329-1332. (11) Murata, T.; Mizobe, Y.; Gao, H.; Ishii, Y.; Wakabayashi, T.; Nakano, F.; Tanase, T.; Yano, S.; Hidai, M.; Echizen,I.;Nanikawa, H.; Motomura, S. J. Am. Chem. Soc. 1994, 116, 3389-3398. (12) Shibahara, T.; Mochida, S.; Sakane, G. Chem. Lett. 1993, 89-92. (13) Katada, M.; Akashi, H.; Shibahara, T.; Sano, H. J. Radioanal. Nucl. Chem., Letters 1990, 145, 143-149. (14) Shibahara, T.; Yamasaki, M.; Watase, T.; Ichimura, A. Inorg. Chem. 1994, 33, 292-301. (15) a) Shibahara, T.; Kuroya, H. Polyhedron 1986, 5, 357-361. b) Akashi, H.; Shibahara, T.; Kuroya, H. Polyhedron 1990, 9, 1671-1676. (16) Although the first reduction wave seems to be splitting into two peaks, the magnitude of the second shoulder peak is less than 5% of that of thefirstmain peak, and the second is ignored. (17) Akashi, H.; Uryu, N.; Shibahara, T., to be published. (18) Kobayashi, H.; Shibahara, T.; Uryu, N. Bull. Chem. Soc. Jpn. 1990, 63, 799-803. (19) a) Miyamoto, R.; Kawata, S.; Iwaizumi, M.; Akashi, H.; Shibahara, T., The 40th Symposium on Coordination Chemistry ofJapan, Kanazawa, October 1990, Abstr. No. 2BP15. b)submitted for publication. (20) a) Shibahara, T.; Yamasaki, M.; Sakane, G.; Minami, K.; Yabuki, T.; Ichimura, A. Inorg. Chem. 1992, 31, 640-647. b) Yamasaki, M.; Shibahara, T. Anal. Sciences 1992, 8, 727-729. (21) Watase, T.; Yamasaki, M . ; Ishigaki, Y.; Honbata, Α.; Shibahara, T. The 42nd Symposium on Coordination Chemistry ofJapan, Nara, October 1992, Abstr., No. 1AP02. (22) a) Sakane, G.; Watase, T.; Yamate, M.; Shibahara, T. The 44th Symposium on Coordination Chemistry ofJapan, Yokohama, November 1994, Abstr. No 1B07. b) to be published. (23) Shibahara, T.; Yamamoto, T.; Sakane, G. Chem. Lett., 1994, 1231-1234. (24) W3SnS: a) Ref. 19. b) Müller, A.; Fedin, V. P.; Diemann, E.; Bogge, H.; Krickemeyer, E. Solter, D.; Giuliani, A. M.; Barbieri, R.; Adler, P. Inorg. Chem. 1994, 33, 2243-2247. (25) W CuS : a) Zheng, Y.-F.; Zhan, H.-Q.; Wu, X.-T.; Lu, J.-X. Transition Met. Chem. 1989, 14, 161-164. b) Zhan, H.-Q.; Zheng, Y.-F.; Wu, X.-T.; Lu, J.X. Inorg. Chim. Acta 1989, 156, 277-280. (26) For example, a) P. W. Jolly, "Comprehensive Organometallic Chemistry", ed by G. Wilkinson, F. G. A. Stone, and E. W. Abel, Pergamon Press, Oxford, New York, Toronto, Sydney, Paris, Frankfurt (1982), Vol. 6, p. 1. b) "Dictionary of Organometallic Compounds", ed by J. Buckingham and J. Macintyre, Chapman and Hall, London, New York, Toronto(1984), Vol. 2, p. 1320. (27) a) Sakane, G.; Yamamoto, T.; Yamada, T.; Shibahara, T. 41st Symposium on Organometallic Chemistry, Japan, Osaka, October 1994, Abstr., No. A208 b) Shibahara, T.; Sakane, G.; Maeyama, M.; Kobashi, H.; Yamamoto, T.; Watase, T., Inorg. Chim. Acta, in press. (28) Shibahara, T.; Sakane, G.; Mochida, S. J. Am. Chem. Soc. 1993, 115, 1040810409. (29) a) Tanner, L. D.; Haltiwanger, R.C.;Rakowski DuBois, M. Inorg. Chem. 1988, 27, 1741-1746. b) Rakowski DuBois, M.; VanDerveer, M.C.;DuBois, D. 4

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Cubane-Type Sulfur-Bridged Ousters 239

L.; Haltiwanger, R.C.;Miller, W. K. J. Am. Chem. Soc. 1980, 102, 7456-7461. c) Rakowski DuBois, M. Chem. Rev. 1989, 89, 1-9. d) Ropez, L.; Godziela, G.; Rakowski DuBois, M. Organometallics 1991, 10, 2660-2664. (30) Weberg, R.; Haltiwanger, R.C.;Rakowski DuBois, M. Organometallics 1985, 4, 1315-1318. (31) Bolinger, C. M.; Rauchfuss, T. B.; Rheingold, A. L. J. Am. Chem. Soc. 1983, 105, 6321-6323. (32) a) Halbert, T. R.; Pan, W.-H.; Stiefel, Ε. I. J. Am. Chem. Soc. 1983, 105, 5476-5477. b) Pilato, R. S.; Eriksen, Κ. Α.; Greaney, M. Α.; Stiefel, Ε. I. J. Am. Chem. Soc. 1991, 113, 9372-9374. (33) a) Draganjac, M.; Coucouvanis, D. J. Am. Chem. Soc. 1983, 105, 139-140. b) Coucouvanis, D.; Hadjikyriacou, Α.; Draganjac, M.; Kanatzidis, M. G.; Ileperuma, O. Polyhedron 1986, 5, 349-356. c) Coucouvanis, D.; Hadjikyriacou, Α.; Toupadakis, Α.; Koo, Sang-Man; Ileperuma, O.; Draganjac, M.; Salifoglou, A. Inorg. Chem. 1991, 30, 754-767. (34) Kanatzidis, M. G.; Coucouvanis, D. Inorg. Chem. 1984, 23, 403-409. (35) a) Ansari, M. Α.; Chandrasekaran, J.; Sarkar, S. Polyhedron 1988, 7, 471-476. b) Ansari, M. Α.; Chandrasekaran, J.; Sarkar, S. Inorg. Chim. Acta 1987, 130, 155-156. (36) Sakane, G.; Shibahara, T.; Adachi, H. J. Cluster Science 1995, 6, 503-521. (37) a) Chen, Z.-D.; Lu, J.-X.; Liu, C.-W.; Zhang, Q.-N. Polyhedron 1991, 10, 2799-2807. b) Chen. Z.-D.; Lu, J.-X.; Liu, C.-W.; Zhang, Q.-E. J. Mol. Struct. (Theochem) 1991, 236, 343-357. c) Cotton, F. Α.; Feng, X.-J. Inorg. Chem. 1991, 30, 3666-3670. d) Wang, Y.; Wang, J.; Li, J. J. Mol. Struct. (Theochem) 1991, 251, 165-171. e) Chen, W.-D.; Zhang, Q.-N.; Huang, J.S.; Lu,J.-X.Polyhedron 1990, 9, 1625-1631. f) Bursten, Β. E.; Cotton, F. Α.; Hall, M. B.; Najjar, R. C. Inorg. Chem. 1982, 21, 302-307. (38) a) Li, J.; Liu, C.-W.; Lu, J.-X. J. Chem. Soc. Faraday Trans. 1994, 90, 39-45 b) Li, J.; Liu, C.-W.; Lu, J.-X. J. Polyhedron 1994, 13, 1841-1851. [Μo3O4(Η2O)9] (Mo3O4). The x-z plane contains one Mo, one μ-Ο, one μ3-O, one Ο (water), and two Η atoms (water). Solid, dotted, and dashed lines indicate positive, negative, and zero contour lines, respectively. Reproduced with permissionfromreference 36. 4+


Characterization of Incomplete Cubane-Type and Cubane-Type Sulfur

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