Synthesis and structural characterization of hybrid Group 12, 14, 15 metals–molybdenum (tungsten) cluster compounds

Polyhedron 20 (2001) 2339– 2352 www.elsevier.com/locate/poly

Synthesis and structural characterization of hybrid Group 12, 14, 15 metals–molybdenum (tungsten) cluster compounds Shao-Fang Lu *, Jian-Quan Huang 1, Rong-Min Yu, Xiao-Ying Huang, Qiang-Jin Wu, Ying Peng, Jin Chen, Zi-Xiang Huang, Yu Zheng, Da-Xu Wu State Key Laboratory of Structural Chemistry and Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China Received 15 August 2000; accepted 24 April 2001

Abstract For the heterometallic cluster compounds containing a core of [M3YS3M%](4 + n) + (M= Mo, W; Y= O, S; M%= metal atom except Mo, W), a relatively comprehensive understanding has already been made when M%n + appears to be a transition metal. When M%n + is a main group metal, however, what will be the situation? This certainly arouses the interest among the chemists. In this present work, the synthesis, new reaction types, crystal structures and spectroscopic characterization of a series of 33 hybrid Mo(W)–Group 12, 14, 15 metal clusters are summarized. These crystals can be put into three categories, i.e. the single cubane type which contains a [M3YS3M%] core (M = Mo, W; Y= O, S; M%=Sn, Pb, Sb, Bi) (SC type), the double cubane clusters coupled by two bridging oxygen atoms possessing a [Mo3OS3M% (m-O)]2 core (M%= Pb, Bi) (DC type) and the ionic clusters (IO type) which consists of a {Mo3} cluster cation and a M% complex anion (M%= Cd, Hg). It is shown that the incorporation of the main group metal M% is through M%S bonding between M% and three (m-S) atoms of the [M3YS3] cluster core, similar to the case when M% is a transition metal atom. The bonding is however comparatively looser than in the case of a transition metal. The synthetic reactions and structural features of these clusters are discussed. Furthermore, information on the third-order nonlinear optical property observed in some of these compounds is reported. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Hybrid Group 12, 14, 15 metals–Mo (W) cluster compound; Spectral characterization; Structural elucidation; Synthesis design; Third-order nonlinear optical property

1. Introduction Not until the 1980s were main group metal – transition metal hybrid clusters reported, and they have attracted considerable attention ever since. The main group metals may play a role in the stabilization of the cluster framework and at the same time enhance the catalytic activation and selectivity [1]. Moreover, the main group metals posses bonding characters different from those of the transition metals; for example, they can form inorganic polymers and new quasi-aromatic Abbre6iations: dtp, S2P(OC2H5)2− ; dtc, S2CN(C2H5)2− ; pyrdtc, S2CNC4H8; OAc, CH3COO−; py, NC5H5; DMF, OCHN(CH3)2; SC, single cubane type; DC, double cubane type; IO, ionic type. * Corresponding author. Tel.: +86-591-379-2835; fax: + 86-591371-4946. E-mail address: [email protected] (S.-F. Lu). 1 Invited Professor at the Fuzhou University.

systems [2]. Therefore, if the main group metals and transition metals can be combined by molecular design to form a hybrid metal cluster, it will be possible to give rein to the ‘hybrid advantage’ so as to lead to the formation of clusters that possess novel configurations and specific physico-chemical properties. Most of the hybrid clusters reported earlier are carbonyl-containing compounds [3]. In 1987, the Mo –Sb –S single cubane(dtp= like clusters [Mo3(SbCl3)S4(dtp)4·L] − S2P(OC2H5)2 , L= C2H5OH, C3H3ON) were first reported by us [4]. Later, the single cubanes [Mo3InS4]5 + [5], [Mo3(SnCl3)S4(NCS)9]6 − ] [6], n+ [Mo3SnS4(S2PEt2)6] [7], [Mo3GaS4(H2O)12 ] (n=5, 6) [8] and sandwich cubanes [Mo3S4SbS4Mo3]8 + [9], [Mo3S4SnS4Mo3]8 + [10], [Mo3S4HgS4Mo3]8 + [11], and [Mo3S4CdS4Mo3]8 + [12] clusters were successively reported by Shibahara, Keck, and others, but few systematic studies were conducted on the reaction of a

0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 1 ) 0 0 8 3 8 - 5

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particular trimolybdenum (or tungsten) compound with a variety of main group metal complexes. During recent years, efforts have been made by our research group to obtain 33 hybrid cluster compounds by using [M3(m3Y)S3]4 + (M= Mo, W; Y =O, S) as the starting materials through the reaction of these clusters with the complexes of 14, 15 main group metals (Sn, Pb, Sb, Bi) and Group 12 metals (Cd, Hg) in organic solvents. In this paper, the designed synthesis, structural characterization, the reactivity and nonlinear optical property of these cluster compounds are summarized. Some clusterforming rules and structural features are also discussed. The formulae of these compounds are listed below: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

Mo3(SnCl3)OS3(dtp)3(py)3 Mo3(SnCl3)S4(dtp)3(py)3 Mo3(SnCl3)YS3(dtp)3(py)3 (Y = 50% O+50% S) W3(SnCl3)S4(dtp)3(py)3 [Mo3(SnBr3)OS3(dtp)3(py)]·CH2Cl2 Mo3(SnI3)OS3(dtp)3(py)3 Mo3(PbI3)S4(dtp)3(py)3 [Mo3(PbI3)S4(dtp)3(C3H4N2)3][OC(CH3)2]2 W3(PbI3)S4(dtp)3(py)3 Mo3(PbI3)OS3(dtc)3(py)3 Mo3(SnI3)S4(dtp)3(py)3 [Mo3(SnCl3)OS3(OAc)(dtp)3(py)][(PPh3)2N] Mo3(SbCl3)YS3(OAc)(dtp)3(py) (Y= 90% O+ 10% S) [Mo3(SbBr3)OS3(OAc)(dtp)3(py)][OC(CH3)2] [Mo3(SbI3)OS3(OAc)(dtp)3(py)[OC(CH3)2] [Mo3(SbCl3)m3-S)(O,S)S2(dtp)4(H2O)]·2(H2O) [Mo3(SbCl3)S4(OAc)(dtp)3(py)](CH3COOH) [Mo3(SbBr3)YS3(OAc)(dtp)3(py)](0.5CH3COOC2H5) (Y = 90% S+10% O) [Mo3(SbI3)S4(OAc)(dtp)3(py)](0.5CH3COOC2H5) Mo3(SbI3)OS3(OOCClH2)(dtp)3(py) Mo3(SbI3)S4(pyrdtc)4(py) [W3(SbI3)S4(OAc)(dtp)3(DMF)] [Mo3(BiI3)S4(OAc)(dtp)3(py)][OC(CH3)2] [W3(BiI3)S4(OAc)(dtp)3(H2O)]·2[OC(CH3)2] [Mo3(SnCl3)OS3(OAc)2(dtp)2(py)]·(Et4N) [Mo3(SnCl3)OS3(OAc)2(dtp)2(py)](Et4N)·(CH2Cl2) [Mo3(SnI3)OS3(OOCC2H5)2(dtp)2(py)](Et4N) [Mo3(SbBr3)OS3(OAc)2(dtp)2(py)](0.5C2H5OH) Mo3(SbI3)OS3(OAc)2(dtp)2(py) {[Mo3PbOS3(OAc)2(dtp)2(py)3](m-O)}2 {[Mo3(BiI3)OS3(OAc)2(py)3](m-O)}2·2H2O [Mo3OS3(dtp)3(py)3]+[CdI(dtp)2]− {[Mo3S7 (dtp)3]4·I}3+{(HgI3)3}3−·4H2O

let Magna 750FT-IR spectrometer with KBr discs (4000–600 cm − 1) and CsI discs (600–100 cm − 1); Raman spectra, 910 Laser Raman FT spectrometer with SP grade KBr as the diluent for the sample; UV–Vis spectra, Shimadzu UV-3000 spectrometer with CH2Cl2 as the solvent; 95Mo NMR, Varian Unity 500 spectrometer, the samples were dissolved in CH2Cl2 as a saturated solution and 2 M solution of Na2MoO4 in D2O was used as the external reference; X-ray crystallography, Enraf–Nonius CAD4 or Rigaku AFC5R diffractometer using graphite-monochromatized Mo Ka radiation. With regard to the cluster compounds unreported before, brief synthetic procedures are presented here. Their crystallographic data have been deposited with the Cambridge Crystallographic Data Center. Details of the synthesis and crystal structure for these clusters will be published later separately. Brief synthesis for the cluster compounds unreported before are given below.

2.1. Mo3(SnCl3)S4(dtp)3(py)3 (2) (dtp= S2P(OC2H5) 2− ; py=NC5H5) Mo3S4(dtp)4·py (80 mg, 0.15 mmol) [13] and SnCl2·2H2O (34 mg, 0.15 mmol) were dissolved in 10 ml acetone and 5 ml CH3COOC2H5 under stirring, and then filtered. Three drops of pyridine were added to the filtrate. When the filtrate was left standing, the wadding-like precipitates that separated were continuously filtered off. After 10 days, a crystalline black product was isolated (40 mg, yield 18.6%).

2.2. Mo3(SnCl3)YS3(dtp)3(py)3 (3) (Y= 50% O +50% S) and W3(SnCl3)S4(dtp)3(py)3 (4) [Mo3(m3-Y)(m-S)3(dtp)4(H2O)] (Y =O,S) [14] (360 mg, 0.31 mmol), SnCl2·2H2O(90 mg, 0.40 mmol) and PPNCl (180 mg, 0.31 mmol) were dissolved in the mixed solvent of CH2Cl2 (10 ml) and C2H5OH (5 ml). Pyridine (0.06 ml) was added to the solution. The mixture was stirred for half an hour and then filtered. The green filtrate was evaporated in air. The next day, 150 mg of black crystalline 3 was obtained (yield 34%). Synthesis of 4 was carried out in a similar way to 3, except that W3S4(dtp)4·H2O [15] was used instead of [Mo3(m3-Y)(m-S)3(dtp)4(H2O)]. Finally the crystals of 4 were isolated (20 mg, yield 31.6%).

2. Experimental

2.3. Mo3(SnI3)OS3(dtp)3(py)3 (6) and Mo3(SnI3)S4(dtp)3(py)3 (11)

All the reactions and manipulations were performed in air. CP and SP grade reagents and solvents were used. The instruments used in this work are: IR, Nico-

Bu4NSnI3 (149 mg, 0.2 mmol) was dissolved in 10 ml acetone, and then 240 mg (0.2 mmol) of [Mo3(m3-O)(mS)3(dtp)4(H2O)] was added to the solution. The mixture

S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

was stirred and filtered. Three drops of pyridine were added. After 1 day, 50 mg of black rectangular crystals of 6 were obtained (yield 14.8%). Synthesis of 11 was carried out in a similar way to 6, except that [Mo3(m3-S)(m-S)3(dtp)4(H2O)] was used as the starting trinuclear cluster. At last, the crystal samples of 11 were isolated (23 mg, 9%).

2.4. W3(PbI3)S4(dtp)3(py)3 (9) and Mo3(PbI3)OS3(dtc)3(py)3 (10) (dtc = S2CN(C2H5) 2− ) KPbI3 (20 mg, 0.03 mmol) was added to the solution of W3S4(dtp)4·H2O (50 mg, 0.04 mmol) in 5ml of acetone. After stirring for 1 h, the reaction mixture was filtered. The filtrate was set openly in a container with 0.05 ml of pyridine and 5 ml of ethyl ether. The next day, 25 mg of black crystals were isolated (yield, 40.4%). The synthesis reaction of 10 was carried out in a similar way to 9 except that [Mo3(m3-O)(m-S)3(dtc)4· (H2O)] [16] was used instead of W3S4(dtp)4·H2O. Finally, the crystals of 10 were isolated (53 mg, 16%).

2.5. [Mo3(SbCl3)(v3 -S)(O,S)S2(dtp)4(H2O)] ·2(H2O) (16) Mo3OS3(OAc)(dtp)3·py [17] (360 mg,  0.3 mmol) was dissolved in 20 ml CH2Cl2 and 5 ml C2H5OH. To the solution was added 1 ml of C2H5OH – HCl in order to keep the acidity of the medium. Then SbCl3 (114 mg, 0.5 mmol) was also added. The mixture was stirred for 30 min and the orange solution was left standing to let it crystallize by volatilization. After 1 month, 100 mg of black crystals were collected (yield 23%).

2.6. [Mo3(SbCl3)S4(OAc)(dtp)3(py)] ·(CH3COOH) (17) The mixed solution of P2S5 (2.6 g, 11.71 mmol) in C2H5OH (10 ml) and MoCl3·3H2O (2.6 g, 10.18 mmol) in C2H5OH (10 ml) was bubbled with H2S for 2 h and then SbCl3 (680 mg, 3 mmol) was added. A black precipitate was obtained after 3 days. It was dissolved in CH2Cl2 (15 ml) and C2H5OH (5 ml). To the solution, HOOCCH3 (0.5 ml) and pyridine (0.2 ml) were added. The solution was allowed to vaporize in air for 1 week. The product of black crystals (450 mg) was obtained (yield 10%).

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dissolved in 10 ml of acetone and 5 ml of CH3COOC2H5 under stirring at room temperature. On standing for 1 week, a crystalline product (120 mg, 68%) was obtained. Recrystallization by CH2Cl2CH3COOC2H5 resulted in the production of crystals suitable for X-ray structure analysis. For synthesis of 19, the procedure was similar to that for 18, except that SbI3 (76 mg, 0.15 mmol) was used rather than SbBr3. After 3 days, crystals (200 mg) of 19 were isolated (82%). For the syntheses of 20 and 21, the reactions were also carried out in a similar way to 18, except that Mo3OS3(OOCCH2Cl)(dtp)3·py [18] and Mo3S4(pyrdtc)4·H2O [19] were used as starting materials, respectively. Crystals of 20 (310 mg, yield 95%) and 21 (48 mg, yield 15%) were obtained, respectively.

2.8. [W3(SbI3)S4(OAc)(dtp)3(DMF)] (22) SbI3 (20 mg, 0.04 mmol) was added to the solution of W3S4(dtp)4·H2O (50 mg, 0.04 mmol) in CH2Cl2 (3 ml) and C2H5OH (2 ml). After stirring for 1 h, the mixture was filtered. DMF (0.05 ml) and HOAc (0.05 ml) were added to the filtrate. The resultant solution was allowed to crystallize under air. After 3 days, 10 mg of black crystals were isolated (yield 13.4%).

2.9. [W3(BiI3)S4(OAc)(dtp)3(H2O)] ·2[OC(CH3)2] (24) BiI3 (20 mg,0.034 mmol) was added to the solution of W3S4(dtp)4·H2O (50 mg, 0.04 mmol) in CH2Cl2 (3 ml) and C2H5OH (2 ml). After stirring for 1 h, the reaction mixture was filtered. 0.05 ml of HOAc was added to the filtrate. The resultant solution was allowed to crystallize under air. After 5 days, 5 mg of black crystals were isolated (yield 7.7%).

2.10. [Mo3(SnCl3)OS3(OAc)2(dtp)2(py)](Et4N) ·(CH2Cl2) (26) SnCl2·2H2O (100 mg, 0.44 mmol), Et4NCl·H2O (100 mg, 0.37 mmol) and pyridine (0.06 ml) were added into the brown solution of [Mo3(m3-O)(m-S)3(dtp)2(OAc)2(py)] [20] (360 mg, 0.33 mmol) in 15 ml of CH2Cl2 and 5 ml of C2H5OH. The solution color turned to green immediately. After stirring for 1 h, the mixture was filtered. The filtrate was kept openly in air to crystallize by vaporization at room temperature. Black crystals (150 mg) were isolated, washed with absolute alcohol and petroleum ether, and then dried in air (yield 32%).

2.7. [Mo3(SbBr3)YS3(OAc)(dtp)3(py)] (0.5CH3COOC2H5) Y = (90% S +10% O) (18), [Mo3(SbI3)S4(OAc)(dtp)3(py)](0.5CH3COOC2H5) (19), Mo3(SbI3)OS3(OOCClCH2)(dtp)3(py) (20) and Mo3(SbI3)S4(pyrdtc)4(py) (21) (pyrdtc =S2CNC4H 8− ; OAc =CH3COO−)

2.11. [Mo3(SnI3)OS3(OOCC2H5)2(dtp)2(py)](Et4N) (27)

For synthesis of 18, Mo3S4(OAc)(dtp)3·py (140 mg, 0.125 mmol) and SbBr3 (35.3 mg, 0.125 mmol) were

[Mo3(m3-O)(m-S)3(dtp)4(H2O)] (360 mg, 0.31 mmol), SnI2·2H2O(90 mg, 0.40 mmol), and Et4NI (90 mg, 0.35

S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

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mmol) were dissolved in 10 ml of CH2Cl2 and 5 ml of C2H5OH. Pyridine (0.15 ml) and C2H5COOH (0.5 ml) were added to the solution. The mixture was stirred under reflux for half an hour and then filtered. The filtrate was evaporated in air. Black crystals (50 mg) suitable for X-ray diffraction work were obtained in 10 days (yield 10%).

3. Results and discussion

3.1. Structural types The formulae and selected structural data of the clusters are given in Table 1. Among the 33 cluster compounds, the first 31 have a cubane-like core of [M3YS3M%] (M =Mo, W; M% =Sn, Pb, Sb, Bi; Y= S, O) and can be divided into two types: single cubane (SC) and double cubane (DC). As far as the SC type is concerned, according to the number of bridging ligands around the core, they can be further divided into three types: SC0, in which no bridging ligand is contained; SC1 and SC2 containing one or two bridging ligands, respectively [21]. The latter two possess an ionic configuration. Fig. 1 shows five configurations of these clusters. The structures of clusters 1 –11 belong to the SC0 type and each molecule has C3 symmetry, while clusters 12 – 24 belong to the SC1 type with C1 symmetry. Furthermore, clusters 25– 29 belong to SC2 with Cs symmetry and clusters 30 and 31 to DC type with Ci symmetry. The last two clusters, 32 and 33 belong to an ionic type (abbreviated to IO). All the M (Mo, W) atoms in the cubane-like core possess a six-coordinated octahedral geometry whereas the main group metal M% contains a distorted octahedral coordination sphere. The DC type coupled by two oxygen atoms is a novel cubane configuration first reported by us.

3.2. Designed synthesis and reaction 3.2.1. Direct addition reaction Mo3(m3-Y)(v-S)3(dtp)4(H2O) + SnX3− +py “Mo3(SnX3)(YS3)(dtp)3(py)3 +dtp− (X= Cl, Br, I; Y= O, S)

(1)

Mo3(v3-Y)(v-S)3(OAc)(dtp)3(py) +SbX3 “ Mo3(SbX3)(YS3)(OAc)(dtp)3(py) (X =Cl, Br, I; Y=O, S)

(2)

Mo3(v3-S)(v-S)3(dtp)4(H2O) + PbI3− +L “ Mo3(PbI3)S4(dtp)3(L)3 +dtp− (L=py, C3H4N2)

(3)

Mo3(v3-S)(v-S)3(OAc)(dtp)3(py)+ BiI3 “ Mo3(BiI3)S4(OAc)(dtp)3(py)

(4)

Mo3(v3-O)(v-S)3(dtp)4(py)+ CdI2 + Bu4NI + py “ [Mo3OS3(dtp)3(py)3]+[CdI(dtp)2]−

(5)

The design of the above reactions is based on the following considerations: (1) The [M3YS3]4 + type clusters are of an incomplete cubane configuration for lack of a metal corner. Therefore, there is hope of adding another main group metal M% to form a complete cubane core [M3YS3M%](4 + n) + . (2) In order to promote this addition reaction, the main group metal M%n + should have a relatively strong affinity for S2 − and the additive units M%X, M%X2 or M%X3 should possess a suitable stereo-configuration. In the reactions mentioned above, SbX3, BiI3, SnX3 and PbI3 all exhibit a trigonal pyramidal geometry and a good affinity for S2 − as well, thus leading to a smooth addition of the M% complex. With regard to BiCl3, BiBr3, PbCl3− and PbBr3− , owing to the fact that no appropriate solvent can be found, the corresponding reactions have not yet been achieved. At the same time, analogous reactions have been carried out for Group 13 metals (AlCl3, GaCl3, etc.) and a Group 2 metal (MgCl2), but no successful result can be achieved. This may be due to the fact that these main group metals and their complexes cannot satisfy the above two conditions. Another analogous study has also been conducted on the Subgroup 12 with a filled d orbital namely Zn, Cd, Hg. Among them, there occurs a distinct reaction in the case of HgI3− that results in a novel compound {[Mo3(m3-S)(m-S2)3(dtp)3]4·I}{(HgI3)3}·4H2O (here S22 − = [Sax –Seq], Seq is in {Mo3} plane, Sax is out-of{Mo3}plane) [30]. (see Fig. 2(a)). This reaction will be described later. In the case of CdI-3, reaction (5) is seen to form the cluster [Mo3OS3(dtp)3(py)3][CdI(dtp)2] whose structure is very similar to [Mo3S4(R2PS2)3(py)3]][MI3]− reported by Diller et al. [31]. Obviously, these products cannot be said in a strict sense to be additive clusters. (3) Electrovalent balance is another factor to be considered in the design of the reaction. A neutral reagent like SbX3 (X=Cl, Br, I) or BiI3 can be added to the [M3YS3] core by simple combination to form new clusters [M3(SbX3)YS3]4 + or [M3(BiI3)YS3]4 + as shown in reactions (2) and (4). For the anionic reagent SnX3− (X=Cl, Br, I) and PbI3− , as shown in reactions (1) and (3), however, the bidentate bridging ligand (dtp)− always drops off and is replaced by two neutral pyridine or imidazole molecules in order to satisfy electrovalent neutralization, thus forming a neutral cluster with a [M3(SnX3)YS3]3 + or [M3(PbI3)YS3]3 + core.

S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

2343

Table 1 The main structural data Number

Compound

Space group

MM (A, )

MM% (A, ) (average)

M%X (A, ) (average)

Ref. a

SC0 1

Mo3(SnCl3)OS3(dtp)3(py)3

P1(

3.8334

2.409 (Cl)

[22]

2

Mo3(SnCl3)S4(dtp)3(py)3

3.845

2.409 (Cl)

CCDC No. 149888

3

Mo3(SnCl3)YS3(dtp)3(py)3 (Y= 50% O+50% S)

P1(

3.843

2.404 (Cl)

CCDC No. 149884

4

W3(SnCl3)S4(dtp)3(py)3

P1(

3.905

2.430 (Cl)

CCDC No. 149621

5

[Mo3(SnBr3)OS3(dtp)3(py)] (CH2Cl2)

P21/n

3.837

2.563 (Br)

[23]

6

Mo3(SnI3)OS3(dtp)3(py)3

P1(

3.876

2.806 (I)

CCDC No. 149885

7

Mo3(PbI3)S4(dtp)3(py)3

P1(

4.207

2.932 (I)

[24]

8

[Mo3(PbI3)S4(dtp)3(C3H4N2)3][OC(CH3)2]2

Pbca

4.077

2.959 (I)

[25]

9

W3(PbI3)S4(dtp)3(py)3

P1(

4.224

2.947 (I)

CCDC No. 149620

10

Mo3(PbI3)OS3(dtc)3(py)3

R3

4.135

2.950 (I)

CCDC No. 143598

11

Mo3(SnI3)S4(dtp)3(py)3

P1(

2.614(8) 2.6103(7) 2.6015(7) 2.7131(9) 2.716(1) 2.725(1) 2.647(2) 2.656(2) 2.654(2) 2.706(1) 2.709(1) 2.720(1) 2.616(2) 2.620(2) 2.618(2) 2.607(2) 2.612(2) 2.603(2) 2.744(2) 2.747(2) 2.751(2) 2.737(3) 2.752(3) 2.749(3) 2.739(2) 2.741(2) 2.749(3) 2.627(3) 2.627(3) 2.627(3) 2.718(3) 2.723(3) 2.710(3)

3.867

2.731 (I)

CCDC No. 149890

SC1 12

[Mo3(SnCl3)OS3(OAc)(dtp)3(py)][(PPh3)2N]

P1(

3.789

2.420 (Cl)

[22]

13

Mo3(SbCl3)YS3(OAc)(dtp)3(py) (Y = 90% O+10% S)

P1(

3.834

2.373 (Cl)

[26]

14

[Mo3(SbBr3)OS3(OAc)(dtp)3(py)][OC(CH3)2]

P1(

3.843

2.543 (Br)

[26]

15

[Mo3(SbI3)OS3(OAc)(dtp)3(py)[OC(CH3)2]

P1(

3.834

2.770 (I)

[26]

16

[Mo3(SbCl3)(m3-S)(O,S)S2(dtp)4(H2O)]·2(H2O)

P21/n

3.830

2.387 (Cl)

CCDC No. 150281

17

[Mo3(SbCl3)S4(OAc)(dtp)3(py)](CH3COOH)

P1(

3.855

2.380 (Cl)

CCDC No. 149892

18

[Mo3(SbBr3)YS3(OAc)(dtp)3(py)](0.5CH3COOC2H5) (Y =90% S+10% O)

P1(

3.850

2.550 (Br)

CCDC No. 149891

19

[Mo3(SbI3)S4(OAc)(dtp)3(py)](0.5CH3COOC2H5)

P1(

3.865

2.778 (I)

CCDC No. 149889

2.5644(2) b 2.6088(3) 2.6111(3) 2.609(2) b 2.637(2) 2.643(2) 2.598(6) b 2.635(6) 2.628(6) 2.605(2) b 2.629(2) 2.642(2) 2.700(5) b 2.734(5) 2.718(5) 2.679(1) b 2.733(1) 2.750(1) 2.663(2) b 2.714(2) 2.731(2) 2.680(2) b 2.747(2) 2.740(2)

S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

2344 Table 1 The main structural data Number

Compound

Space group

MM (A, )

MM% (A, ) (average)

M%X (A, ) (average)

Ref. a

20

Mo3(SbI3)OS3(OOCClCH2)(dtp)3(py)

P1(

3.869

2.767 (I)

CCDC No. 149887

21

Mo3(SbI3)S4(pyrdtc)4(py)

Cc

3.781

2.789 (I)

CCDC No. 143599

22

[W3(SbI3)S4(OAc)(dtp)3(DMF)]

P1(

3.902

2.785 (I)

CCDC No. 149619

23

[Mo3(BiI3)S4(OAc)(dtp)3(py)][OC(CH3)2]

P1(

4.033

2.856 (I)

[24]

24

[W3(BiI3)S4(OAc)(dtp)3(H2O)]·2[OC(CH3)2]

P1(

2.606(3) b 2.636(3) 2.643(3) 2.708(2) b 2.729(2) 2.757(2) 2.680(1) b 2.741(1) 2.735(1) 2.693(2) b 2.750(2) 2.754(2) 2.686(3) b 2.728(3) 2.740(3)

4.013

2.847 (I)

CCDC No. 149622

SC2 25

[Mo3(SnCl3)OS3(OAc)2(dtp)2(py)]·(Et4N)

P21/n

3.7844

2.401 (Cl)

[22]

26

[Mo3(SnCl3)OS3(OAc)2(dtp)2(py)](Et4N)·(CH2Cl2)

P21/n

3.777

2.415 (Cl)

27

[Mo3(SnI3)OS3(OOCC2H5)2(dtp)2(py)](Et4N)

Pccn

3.798

2.849 (I)

CCDC No. 149886

28

[Mo3(SbBr3)OS3(OAc)2(dtp)2(py)](0.5C2H5OH)

P1(

3.820

2.543 (Br)

[26]

29

Mo3(SbI3)OS3(OAc)2(dtp)2(py)

P1(

2.5517(9) b 2.548(1) b 2.6089(9) 2.549 b 2.561 b 2.608 2.553(3) b 2.553(3) b 2.610(3) 2.575(2) b 2.571(2) b 2.638(2) 2.57(1) b 2.58(1) b 2.63(1)

3.897

2.747 (I)

[26]

DC 30

{[Mo3PbOS3(OAc)2(dtp)2(py)3](m-O)}2

P21/n

4.041

31

{[Mo3(BiI3)OS3(OAc)2(py)3] (m-O)}2·2H2O

P21/n

2.610(2) b 2.611(2) b 2.647(2) 2.630(2) b 2.633(2) b 2.639(2)

IO 32

[Mo3OS3(dtp)3(py)3]+[CdI(dtp)2]−

P1(

33

{[Mo3S7(dtp)3]4·I}3+{(HgI3)3}3−·4H2O

F23

a b

2.651(1) 2.652(1) 2.652(1) 2.734(2) 2.734(2) 2.734(2)

[27]

3.936

I···Sax 3.590(4) I···Seq 3.405(5)

2.896 (I)

[28]

2.717 (I) (CdI)

[29]

2.645(2) (HgI)

CCDC No. 149896

Reference or deposition number in the Cambridge Crystallographic Data Centre. The distance of MM bond bridged by ligand.

3.2.2. Certain new reaction types In addition to the direct addition reactions mentioned above, several new reaction types unreported before in the synthesis of [M3YS3M%](4 + n) + clusters have also been found.

3.2.2.1. The substitution reaction for metal M% complexes. Mo3(SbCl3)S4(dtp)4(H2O) +SnCl3− + py  

Red-brown crystal

“ Mo3(SnCl3)S4(dtp)3(py)3  

Greenish-black crystal

(6)

S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

Fig. 1. Five types of configurations: (a) SC0 type; (b) SC1 type; (c) SC2 type; (d) DC type; (e) IO type.

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S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

2346

Fig. 1. (Continued)

The IR and UV – Vis spectra of the product are identical to those of Mo3(SnCl3)S4(dtp)3(py)3 of reaction (1). This confirms the substitution of SnCl3− for SbCl3 in the reaction.

3.2.2.2. The additi6e-coupled reaction. 2{Mo3(m3-O)(m-S)3(OAc)2(dtp)2(py)} + 2BiI3 + py + 2H2O “{[ Mo3(BiI3)OS3(OAc)2(py)3](m-O)}2 +4Hdtp (7) 2{Mo3(m3-O)(m-S)3(dtp)4(H2O)} + 2Pb(OAc)2 +py “{[Mo3PbOS3(OAc)2(dtp)2(py)3](m-O)}2 +4Hdtp (8) In these two occasional reactions, accompanying the addition of BiI3 and Pb(OAc)2 to {Mo3}, two [Mo3OS3M%] (M% =Pb, Bi) cluster cores have further been coupled by two (m-O) bridging atoms to constitute a novel double cubane cluster molecule, of which the reactive mechanism is not yet clear. It seems that in order to keep electrovalent balance before and after the reaction, the bridging oxygen atoms originate from H2O during the reaction and cleave the Hdtp group in the meantime. However, (m-O) may also come from O2 and the (dtp)− comes off in the form of (dtp)2. This means that oxidation– reduction of the ligand takes place.

3.2.2.3. The recombination– polymerization reaction of clusters. [Mo3(m3-O,S)(m-S)3(dtp)4(H2O)] + HgI4 Bu4NI, air

 {[Mo3S7(dtp)3]4·I}{(HgI3)3}·4H2O

3.2.2.4. Ligand competiti6e reaction promoted by metal. [Mo3S4(dtp)4(H2O)] + CdCl2 + EtOH + CH3C6H4SO3Na “ Mo3S4(m-O3SC6H4CH3)(dtp)3(EtOH) (see Fig. 2(c)) [33]

(9)

CH2Cl2, CH3CN

2[Mo3(m3-O)(m-S)3(dtp)4(H2O)] BiI3 + HOAc

 [Mo6(m3-S)3(m-S%)3(m-S2)3(dtp)5(m-OAc)] py

These two reactions are also found accidentally. In reaction (9), as shown in Fig. 2(a), the [Mo3(m3-O,S)(mS)3] core has already changed to [Mo3(m3-S)(m-S2)3]. It can be seen that an iodine atom interacts with four [Mo3S7(dtp)3]+ units at a distance of about 3.5 A, for I···Sax. Each of the four {[Mo3S7(dtp)3]4·I} tetramers provides one [Mo3S7(dtp)3] and these four [Mo3S7(dtp)3] can be looked upon as a ‘tetrahedron’. Three (HgI3)− units are located statistically at the ‘face’ of the ‘tetrahedron’ and have a weak interaction with [Mo3S7(dtp)3] through I···Seq with a distance of 3.4 A, . This structure provides a typical example of the cluster recombination–polymerization reaction. In reaction (10), it can be seen from the structure of the product [Mo6(m3-S)3(m-S)3(m-S2)3(dtp)5(m-OAc)] [32] (see Fig. 2(b)) that the (m3-O) in the original {Mo3} cluster has been transformed to (m3-S). Of two {Mo3} units which constitute the {Mo6} cluster, one {Mo3} unit has still a [Mo3S4] core whereas the other one contains a [Mo3(m3S)(m-S2)3] core, where three (m-S) have already changed into (m-S2). Two {Mo3} units are linked by (m3-S) and (h3-S2) to form a pseudo-raft {Mo6} framework. In this reaction, whenever one {Mo6} cluster is formed, six S atoms are needed and these are provided by just three (dtp) ligands coming off. It is obvious that the addition of BiI3 has not been realized in this reaction.

(10)

(11)

In this reaction, the p-toluenesulfonic acid group is CH3C6H4SO3− substituted for (dtp). The (CH3C6H4SO3− ) ligand can be regarded as a non-coordinated radical in general and its ligation to Mo is weaker than that of (dtp). In reaction (5), the product [Mo3OS3-

S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

2347

Fig. 2. (a) The parts of structure of {[Mo3S7(dtp)3]4·I}{(HgI3)3}·4H2O; (i) [Mo3S7(dtp)3]; (ii) {HgI3}; (iii) {[Mo3S7(dtp)3]4·I}; (iv) interaction between [HgI3] and [Mo3S7(dtp)3]. (b) The structure of [Mo6(m3-S)3(m-S)3(m-S2)3(m-OAc)(dtp)5] (dtp ligands are omitted for clarity). (c) The structure of Mo3YS3(m-SO3C6H4CH3)(dtp)3·L.

(dtp)3(py)3][CdI(dtp)2] resulted from [Mo3OS3(dtp)4(py)] reacting with CdI2 and Bu4NI. From this fact, it is reasonable to assume that the substitution of reaction (11) may be attributed to the promotion of CdCl2. Cd2 + causes the (m-dtp) in the original {Mo3} cluster to drop off and produces a stable Cd-containing complex with it. Thus the (CH3C6H4SO3− ) ligand occupies the site of (m-dtp) to complete this new substitution.

3.3. Spectral characterization 3.3.1. IR and Raman spectra Based on the empirical assignment, the w(Mm3S) stretching vibration of the compounds in the present work is located in the 420–430 cm − 1 region whereas the w(Mm3S%) (S% is a triple bridge linking two M atoms and one main group metal atom) lies between 440–460

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S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

Fig. 2. (Continued)

cm − 1. We note that both the frequencies are lower than those in the original {Mo3} clusters (the corresponding stretching vibration bands lie between 445– 457 and 457–485 cm − 1, respectively [34]). This fact can be explained to be due to the formation of M%S bonding, which leads to the weakening of the MS bond. It is interesting to note that the (Mom3O) vibration falls in the 690–695 cm − 1 region for SC0 and SC1 species but at approximately 717 cm − 1 for SC2 and DC types, a very characteristic band in the identification of these two types of structures [26]. On the other hand, the Raman spectra indicate that the w(MM) band is assigned to 213–250 cm − 1. Comparison can be made

with the pair of clusters, Mo3(SbI3)OS3(OAc)(dtp)3(py)[OC(CH3)2] (15) and [Mo3(SbI3)S4(OAc)(dtp)3(py)](0.5CH3COOC2H5) (19) (with a difference in m3-Y and the values of w(MoMo) are 213 and 221 cm − 1, respectively). A further comparison of Mo and W analogues, e.g. Mo3(PbI3)S4(dtp)3(py)3 (7) and W3(PbI3)S4(dtp)3(py)3 (9), indicates that w(MoMo) and w(WW) are located at 221 and 228 cm − 1, respectively. These frequencies are higher than those of the original {Mo3} cluster (approximately 170–200 cm − 1 [35]). All this suggests that a strengthening of M–M interaction occurs when M% complex is bound to the {Mo3} fragment. Moreover, it can be seen that w(SnS%) lies at approxi-

S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352 Table 2 IR data of some representative clusters (w in cm−1) Clusters

a

13

14

15

28

w(Mom3O) w(Mom3S) w(MoO(OAc))

694.3 453.2 676.9, 530.3 636.4, 499.5

w(MoS(dtp)) w(Sbm3S) w(SbX)

310–300 330–350 306 (315.6) b

w(MoMo)

213.4

694.3 454 676.9, 532.3 634.5, 495.6 310–300 330–350 167.8 (163.2) b 213.4

717.4 450 676.9,530.3

w(MoN(py))

696.2 454 676.9, 532.3 634.5, 497.6 310–300 330–350 210.2 (209.5) b 213.4

638.3 310–300 330–350 210.2 (211.4) b 230

a 13, [Mo3(SbCl3)OS3(m-OAc)(dtp)3(py)]; 14, [Mo3(SbBr3)OS3(mOAc)(dtp)3(py)]; 15, [Mo3(SbI3)OS3(m-OAc)(dtp)3(py)]; 28, [Mo3(SbBr3)OS3(m-OAc)2(dtp)2(py)]. b Raman spectra.

Table 3 UV–Vis data for some representative clusters u (nm) (m, M−1 cm−1) a 1 420 (8.87×103) 380 (1.44×104)

2 430 (8.85×103) 395 (1.55×104) 325 (9.66×103) 4 240 (4.66×104) 248 (4.82×10 ) Mo3SnOS3 “Mo3SnS4 Red shift b 12 440 (6.37×104) 370 (1.36×104)

242 (4.96×104) Sn“ Sb red shift

13 465 405 310 238

(8.58×103) (1.37×104) (1.23×104) (4.74×104)

c Mo3(SbX3)OS3(m-OAc)(dtp)3(py) (X = Cl, Br, I) Cl (13) Br (14) I (15) 465 (8.58×103) 500 (7.98×103) 570 (1.01×104) 4 4 415 (1.47×10 ) 405 (1.37×10 ) 425 (1.30×104) 310 (1.23×104) 325 (1.00×104) 330 (1.14×104) 238 (4.74×104) 238 (4.88×104) 245 (4.82×104) Cl“ Br“ I red shift

mately 297 cm − 1, w(SbS%) at 330– 350 cm − 1, w(PbS%) at approximately 191 cm − 1 and w(BiS%) at 198–210 cm − 1. All these values are lower than those of the corresponding M%S covalent bond [36], thus indicating a loose combination of the M% complex with [M3YS3]. In addition, a very intense band for M%X can be observed in the far-IR and Raman spectra owing to the relatively independent coordinated situation of M%X3 (X= Cl, Br, I). These M%X vibration bands are comparable with those of the corresponding covalent bond [37]. Table 2 lists the values of the pertinent IR, far-IR and Raman absorption bands for clusters 13 – 15 and 28 containing the same [Mo3OS3Sb] core as an example.

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3.3.2. UV –Vis spectra The electronic absorption bands and their extinction coefficients for some representative clusters are listed in Table 3. In (a), [Mo3(SnCl3)YS3 (dtp)3(py)3] (Y=O, S referring to clusters 1 and 2, respectively) are a pair of representative clusters of the same SC0 type but with a difference in (m3-Y). In (b), [Mo3(SnCl3)OS3(m-OAc)(dtp)3(py)]− (12) and [Mo3(SbCl3)OS3(m-OAc)(dtp)3(py)] (13) are a pair of clusters belonging to the same SC1 type but containing different main group metals. In (c), [Mo3(SbX3)OS3(m-OAc)(dtp)3(py)] (X=Cl, Br, I) represents a set of clusters (13–15) with different halogen atoms. 3.3.3. 95Mo NMR A comparison of the 95Mo chemical shifts for three sets of compounds is given in Table 4(a)–(c): (a) gives the spectra of [Mo3(SnCl3)YS3(dtp)3(py)3] (1) (2) (Y= (m3-O) and (m3-S), respectively); (b) shows the spectra of [Mo3(SnCl3)OS3(dtp)3(py)3] (1), [Mo3(SnCl3)OS3(mOAc)(dtp)3(py)][(PPh3)2N] (12) and [Mo3(SnCl3)OS3(mOAc)2(dtp)2(py)](Et4N) (25). They possess the same cluster core but have different (m-OAc) numbers. The spectra of Mo3(SbX3)OS3(m-OAc)(dtp)3(py) (X=Cl, Br, I) with different halogen atoms are shown in (c). 3.4. Some discussions concerning the structural features 3.4.1. The difference lies in whether M% is a main group metal or a transition metal in [M3YS3M%] clusters When the cluster core [M3YS3M%] (M= Mo, W; Y= O, S) (M% = Sn, Pb, Sb, Bi) is compared with the same kind of clusters in which M% is a transition metal, Table 4 95 Mo NMR data of some representative clusters (in ppm) a (1) (2) 1317.574 1525.790 The chemical shift increases with the replacement of (m3-O) by (m3-S) b (1) SC0 type 1317.574

(12) SC1 type 1517.700 1324.314 1264.407 The chemical shifts increase (to low field region) with (OAc) bridging ligands around the cluster core c Mo3(SbX3)OS3(m-OAc)(dtp)3(py) (X =Cl, Br, I) X =Cl (13) X =Br (14) 1442.697 1493.975 1245.447 1289.800 1176.016 1218.873 The chemical shifts increase in Cl “Br“I order

(25) SC2 type 1515.079 1445.625 more

X=I (15) 1589.793 1378.133 1319.370

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S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

several striking differences can be seen in the structures. Firstly, MM% bondings exist normally when M% is a transition metal, but when M% is a main group metal as in the present series, no MM% bonding has been found since all the MM% distances lie in the 3.8– 4.2 A, region. Secondly, the formation of such clusters is through M%S bonding. In the present series of clusters, the M%S bond lengths are always longer than the usual covalent bond lengths. For example, the covalent bond length of SnS should have a value of 2.52.6 A, [38a], in clusters 1 –6, however, it is in the range of 2.7– 2.8 A, . Similarly, the covalent bond lengths of SbS should also be about 2.5 A, [38b], but they are found in the range of 2.7–2.8 A, . In contrast, when M% is a transition metal like in [Mo3NiS4(H2O)10]4 + [39], the average NiS bond length is 2.20 A, , comparable to the corresponding NiS covalent bond length (approximately 2.19 A, ). Relatively speaking, the lengthening of the Mo(m-S) bond in the original {Mo3} clusters due to the formation of the M%S bond is significantly smaller when M% is a main group metal than that when M% is a transition metal. The maximum lengthening can reach a value of approximately 0.04 and 0.07 A, , respectively. This indicates that the combination of M% with [M3YS3] is comparatively close when M% is a transition metal while it is comparatively loose when M% is a main group metal. It also means both the parts of the M% complex and the [M3YS3] unit here have retained their identities. Thirdly, in the present series, the degree of shortening of MM bond lengths on the addition of the main group metal M% is more apparent than that when M% is a transition metal. For instance, the average MoMo bond length is 2.75 A, in the [M3S4] core and this distance can be reduced by 0.04– 0.06 A, in the series [M3YS3M%] (M% =Sn, Pb, Sb, Bi). When M% = Ni, however, no noticeable reduction has been found in the value of the MoMo bond length and it is still 2.75 A, [36]. The IR and Raman spectra also confirm this rule. Thus, from the fact mentioned above, it is clear that when M% is a main group metal, M%X3 (M% =Sb, Bi) or M%X3− (M% =Sn, Pb) having lone pair electrons, it will offer electrons to the [M3YS3] core and thus enhance the MM bonding. The main group metal seems to be oxidized formally upon its incorporation into the {Mo3} cluster. These results are consistent with the analysis of the bonding of [M3S4M%] reported by Bahn [40].

3.4.2. The difference in the effect of 6arious main group metals M% on the [M3YS3M%] core It can be seen from the structures of this series of clusters that the addition of a Group 14 metal may cause the bridging (dtp) to leave the original {Mo3} cluster, thus forming a SC0 configuration with C3 or pseudo-C3 symmetry. But no SC0 structures have been obtained for Group 15 metals so far, where the struc-

ture of the original {Mo3} or {W3} clusters is basically retained. On the other hand, as far as the electronic structure is concerned, comparing SnCl3 with SbCl3 in SC1 type clusters, the peaks of UV–Vis spectra of the latter are red-shifted more than those of the former. For DC type clusters, to compare {[Mo3PbOS3(OAc)2(dtp)2(py)3](m-O)}}2 (30) with {[Mo3BiI3OS3(OAc)2(py)3](m-O)}}2 (31), the peaks of cluster 31 are essentially red-shifted. This indicates that although main group metals M% can provide two 5s electrons for {Mo3} clusters, the M%S bondings of Sb and Bi are weaker than those of Sn and Pb, respectively, and therefore the transition energies in [M3YS3] of MoSb and MoBi clusters are smaller than those of MoSn and MoPb, respectively. It is shown from the above observations that the oxidation state of the M% metal and its affinity for S atom are the important factors in the effect on the stereo-configuration and electronic structure of the [M3YS3M%] compounds.

3.4.3. The difference of 6arious X in M%X3 Taking the Mo3(SbX3)OS3(m-OAc)(dtp)3(py) cluster as an example, when X=Cl, Br, I, there is no obvious alteration in their molecular stereo-configuration, but great changes take place in their electronic structures. The spectroscopic data of IR, Raman, UV–Vis and 95 Mo NMR for these clusters are listed in Tables 2– 4. It can be seen from these tables that the UV–Vis peaks are red shifted in the order Cl“Br “ I. This is consistent with the rule that the more reduction ability of the ligand, the less the energy of the charge-transfer transition and the longer wavelength of the absorption. The shielding order of 95Mo NMR I B Br B Cl exhibits an effect of ‘inverse halogen dependence’ [41]. This is probably due to the less than half-filled valence shell electron configuration of Mo(IV). 3.4.4. The difference between [Mo3S4M%] and [Mo3OS3M%] cores It is shown from the structure analysis that the difference between [Mo3S4M%] and [Mo3OS3M%] is the same as that between [Mo3S4] and [Mo3OS3] before the addition of M% [42]. For example, the average MoMo bond length falls between 2.71–2.75 A, for [Mo3S4M%] and 2.59–2.63 A, for [Mo3OS3M%]. The average bond lengths of Mo(m3-S) and Mo(m3-O) are 2.34 and 2.05 A, , respectively. As for the spectral data, in the case of the same M%X3 such as SnCl3, the red shift in the absorption band from [Mo3OS3Sn] to [Mo3S4Sn] is observed as shown in the UV–Vis spectra (see Table 3(a)). That means the transition energies of [Mo3S4Sn] are lower than those of [Mo3OS3Sn]. Besides, the 95Mo NMR peak of [Mo3S4Sn] is also shifted to a low-field region with respect to [Mo3OS3Sn] (see Table 4(a)). Based on these two facts, it is held that the degree of

S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352 Table 5 The third-order nonlinear optical susceptibility Clusters

 (3) (esu)

k (esu)

Mo3OS3(OAc)(dtp)3(py) Mo4S4(dtp)6 Mo3S4(SnI3)(dtp)3(py)3 Mo3OS3(SbBr3)(OAc)2(dtp)2(py) [Mo3OS3(SnCl3)(OAc)2(dtp)2(py)]Mo3OS3(PbI3)(dtc)3(py)3 Mo3S4(PbI3)(dtp)3(py)3 a

2.9×10−13 3.41×10−13 3.72×10−12 2.29×10−13 3.06×10−13 2.24×10−12 5.31×10−13

2.08×10−31 4.82×10−30 2.82×10−31 2.62×10−31 5.64×10−31 1.70×10−30

a The values of  (3) and k were measured by using 532 nm wavelength and  (3) (CS2) as 6.8×10−13 esu.

delocalization in [Mo3S4Sn] is more predominant than that in [Mo3OS3Sn].

3.4.5. The stability of [M3YS3M%] and the relati6e independence of M% complex It is shown from the above structural analysis and reactivity experiment of the clusters that the [M3YS3M%] cluster core possesses rather good stability. For instance, upon the addition of SnCl3, the three hybrid clusters 1, 12 and 25 belong to SC0, SC1 and SC2 type configurations, respectively. Of these, cluster 1 is a neutral cluster whereas clusters 12 and 25 are anionic clusters. It is interesting to note that cluster 25 of SC2 type can be obtained from the reactions using clusters 1 (SC0) and 12 (SC1) as starting materials. That means when the peripheral ligands undergo a chemical reconstitution, the [Mo3OS3(SnCl3)] cluster core is still unchanged and exhibits good stability. In addition, it can be seen from the formation of two double cubane clusters 30 and 31 that although their formation mechanism is not yet known, there surely occurs a reaction of rather complex ligand-rearrangement including the cleavage of (dtp) ligands from the original {Mo3} cluster and substitution by (H2O). Even under such circumstances, the [Mo3OS3Pb] and [Mo3OS3Bi] cluster core can still remain unchanged, thus indicating their considerable stability. On the other hand, as already described, no M–M% bonding exists in the [M3YS3M%] cluster core and the SM% bond length is also relatively long. This means that a rather loose combination exists between the M% complex and [M3YS3]; in other words, the M% complex preserves its integrity. This is reflected in the chemical reaction like reaction (6), for example, SnCl3− can substitute for SbCl3 in [Mo3S4(SbCl3)]4 + to convert it into [Mo3S4(SnCl3)]3 + . Such an intersubstitution reaction between the main group metals M% is discovered for the first time in our study. 3.5. The third-order nonlinear optical property During recent years, attention has been attracted to the fact that many cubane-like mixed metal clusters can

2351

exhibit significant nonlinear optical properties such as optical limiting capability [43] and third-order nonlinear optical effects [44]. As most of the crystals of the clusters discussed in this text possess these configurations, it naturally leads us to make efforts to explore the relationship between the structure and the third-order nonlinear optical property of these compounds in our work. By means of the forward degenerate four-wave mixing (DWFM) technique [45], with a Nd:YAG laser of 1064 nm and 8 ns pulse width as the light source and using CS2 as a reference sample ( (3)(CS2)=1.9× 10 − 12 esu [46]), the third-order nonlinear susceptibility  (3) and k of some crystals have been measured. Here k is defined as the third-order nonlinearity of each individual molecule. The measured results under the same condition are listed in Table 5. It can be seen from the table that the tetranuclear cluster displays a better nonlinear optical property than that of the trinuclear compound in general. Of the tetranuclear compounds, the  (3) values of hybrid metal clusters are higher than those of homo Mo-containing clusters. As far as the main group metal M% is concerned, the Sn–Mo hybrid cluster, particular ‘SnI3’, exhibits the best  (3) and k. Additionally, the cluster Mo3OS3(PbI3)(dtc)3(py)3 (10) with (dtc) as the ligand exhibits a significantly higher  (3) than that of the analogous cluster containing a (dtp) ligand, i.e. Mo3S4(PbI3)(dtp)3(py)3 (7). This indicates that the better the conjugation of the ligand, the greater the thirdorder nonlinear optical susceptibility will be. All this provides evidence for the potential application of the cubane-like configuration in fine-tuning the third-order nonlinear optical property. More work regarding the influence of composition and structure on the property as well as their potential application is in progress.

4. Summary and outlook In this work, designed synthesis via the [3+ 1] reaction mode has been established, which generates altogether 33 new hybrid clusters. Among them, the single cubane-like Mo(W)-containing tetranuclear cluster with M%n + = Sb3 + , Bi3 + , Pb2 + , the unusual [Mo3OS3M%] cluster core containing mixed S/O bridging atoms and the novel double cubane cluster coupled by two bridging oxygen atoms are synthesized and their crystal structures reported for the first time. It is shown from the structural analysis that the addition of the main group metal to [M3YS3] causes the enhancement of MoMo (or WW) bonding and exerts a significant influence on their electronic structures. A study on their physical property shows that some types among these clusters exhibit good third-order nonlinear optical susceptibility. Specific areas worthy of further study are

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S.-F. Lu et al. / Polyhedron 20 (2001) 2339–2352

numerous, including the elucidation of the factors controlling cluster formation, the use of other main group metals and the potential application of these hybrid clusters in functional materials.

5. Supplementary material Crystallographic data for the structural analysis have been depositd with the Cambridge Crystallographic Data Centre, CCDC Nos. 149888, 149884, 149621, 149885, 149620, 143598, 149890,150281, 149892, 149891, 149889, 149887, 143599, 149619, 149622, 149886, 149896 for compounds 2 – 4, 6, 9 – 11, 16–22, 24, 27 and 33, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: + 44-1223-336033; e-mail: [email protected]. ac.uk or www: http://www.ccdc.cam.ac.uk).

Acknowledgements This work was financially supported by the National Natural Science Foundation (NNSF) of China, NSF of Fujian Province and the State Key Laboratory of Structural Chemistry. The authors would like to thank Professor Bo-Chang Wu, Dr Jin-Hai Si, Dr Qi-Guang Yang, Dr Xu-Chun Liu (Institute of Physics, Chinese Academy of Sciences, Beijing, China) for the measurement of the nonlinear optical property and Professor Yi-Xiong Fang for his kind help in preparing this manuscript.

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