Synthesis and X-ray structure characterization of

Indian Journal of Chemistry Vol. 40A. June 200 I. pp. 563-567

Synthesis and X-ray structure characterization of ethylenediammonium tetrathiomol ybdate 8 R Srinivasan*, Beena K Vernekar& K Nagarajant Department of Chemi stry, Goa Uni ve rsity, Taleigao Plateau, Goa 403 206 Indi a email: srini @uni goa.ernet.in Received 29 Sep1e111ber 2000 revised 28 Februwy 2001 The passage of hydrogen sulphide gas into an aqueous ammonium heptamolybdate solution in the presence of ethylenediamine leads to the formation of stable ethylenediammonium tetrathiomolybdate 1 in good yields. The title compound has been characterized by IR , UV- Vis and elemental analysis and its structure has been determined by single crystal X-ray crystallography. Ethylenediammonium tetrathiomolybdate crystallizes in the orthorhombic space gro up P2 12 12 1 with the following unit cell dimensions for C2 H 10 N2 S4 Mo (M=286.3) a=8.582(5) A. b=9.276(5) A. c=ll.792(5) A, a=~= y = 90° v = 938.7(8) A\ Z=4. Dc=2.026 g.cm·3. The structure of the title compound consi sts of tetrahedral tetrathiomolybdate anions, which form an extended three dimensional network in the solid state, wi th the aid of N-H---S as well as C-H---S hyd rogen bonding interactions with the organic cation.

The chemistry of molybde num with sulphur donor li gands is unique when compared to other transition 1 metal ions • The diversity in structural and reactivity characteristics of Mo/S complexes is an important reason for th e continuing research in this rapidly grow ing field. Interest in sulphur containing compounds o f Mo and W is also due to their implications in bioinorganic chemi stry and industri al cataly sis 2 · 4 . Sulphur-coordinated tran sition metals engage in facile electron and proto n tran sfer processes w hi ch are important for active-site turnover in biosyste ms 5 . In industry, metal sulphides such as MoS 2 and WS 2 are central to hydrotreating catalysis includin g the removal of sulphur (hydrodesulphurization), nitrogen (hydrodenitrogenation), oxygen (hydrodeoxygenation) and metals (hydrode metalation) from petroleu m fractions. In view of th eir importance in existing system s and their poten ti al use in future sys tems, a better understanding of metal sulphide complexes may prove valu able in th e design of nex t-generation catalysts. The am monium sa lt of tetrathi o mo lybdate (N H4 h MoS 4 2 has been routinely used as the starti ng material in synthetic Mo/S c he mi stry for th e preparation of several compounds rang ing from inso lubl e sulphides 6 lik e MoS 3 and MoS 2 to so lubl e sulphur rich binary and terti ary thi omolybdates as well as he terobimetall ic co mpl exes 1.7 . However, in all the sy ntheses it has been recommended to use eith er fresh ly pre+Departmen t of Chem istry . Indian Inst itute of Technol ogy. Kanpur. UP 208 0 16. India

pared (or stored under inert atmosphere) sample of the a mmonium salt in view of its slow decomposition in air to (Mo 20 2 S 6 via an induced electron transfer reaction 8 . The tetrathi omolybdates can also function like bidentate ligands coordinating to a variety of tran sition metal ions forming sulphur bridged heterobimetallic complexes 7·9 . In recent years, the use of 10 11 piperidinium and benzyltriethy lam mo nium tetrathi ometalates as reagents in organic syntheses, for the facile formation of several no vel organi c sulphu r co mpounds has added an entire new dimension to thi s field . Although a few salts of tetrathi o molybdate other than the ammonium salt are known , there is a need to prepare other cationic te trathiomo lybdates in view of the rich synthetic chemistry associated with tetrathi omolybdate as men tioned above. Herein, we wish to re port on the sy nthes is and sin gle c rystal structural charac te ri zation of the stabl e ethylened iammonium tetrathi omolybdate.

f

Materials and Methods Solvents and reagents were used as obtained from commercial sources in thi s investi gation . Ammonium tetrathiomolybdate 2 was prepared by following a 12 published procedure • In fra red spectra were recorded on a Shimadzu DR-803 1 Ff-IR instrument. The samples were pressed as KBr pellets and referenced to polystyrene bands. UV -Vis spectra were recorded on a Shi madzu UV -160 I instrume nt us ing matched quartz ce lls. The X-ray structure determination was performed at the National Single Crystal X-ray facility

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INDIAN J CHEM , SEC. A, JUN E 2001

at liT Kanpur. C, H, N and S were analyzed at the Microanalytical Laboratori es liT Kanpur. Prepa ration of ethy /enediallllllOnium tetrathio lllo fybdate I Method 1

A steady stream of hydroge n sulphide gas was passed through an aqueous so lution of ammonium heptamolybdate (2g in 20 ml) containing 6 ml of 99% ethylenedi amine. The reacti on temperature was maintained at 60"C. Afte r 30-40 min of 0aas passin Oa ' co pi ous amounts of garnet red crystals slowl y separated. The gas passing was sto pped and th e reacti on mi xture cooled in an ice-bath fo r -15 min . The reel crystals were filtered at the pump, was hed with a few ml of ice-cold water followed by isopropanol and eth er and dri ed in vacuo. Yield 2.8 g (- 80%). IR data: 3000 (br), 1570, 1540, 1460, 1440, 1325, 1305, 1080, 1030, 10 10,970, 885,805,474 cm- 1 UV- Vi s data: 466, 316,240 nm Ana l. Found (Calcd): C 8.36 (8.39), H 3.7 (3 .50), N 9.98 (9.79), s 44.25 (44.75) %. Me thod 2

Freshl y prepared ammoniu m tetrath iomolybdate 2 (260 mg, I mmo l) was di ssolved in water ( 15 ml ). To th is solu tion et hylenedi ami ne ( I ml ) was added and the reactio n mixture filtered and kept in the refrigerator fo r crystalli zati on. After 3-4 clays deep garn et red blocks of the title compo un d had formed. The crysta ls were isolated by fi ltration , washed wi th a small amount of water foll owed by isopropanol and ether and air dri ed. The prod uct obtained (170 mg) in this meth od had an identi cal IR, UV-Vis and an alysed satisfactoril y as th e product fro m Meth od I. The crysta ls obtai ned in thi s method were suitable fo r Xray stud ies . Results and Discussion Synlhesis

The synthesis of th e title compoun d can be readil y acco mpli shed in good yi elds by the ex hausti ve hyd roge n sulphide treatment of an aqueo us heptamolybdate solution in the presence of eth ylenedi amine. The replace ment of oxo groups in the startin g materi al by the sulphiclo groups in the title compound can be represe nted by th e following Eq. (1 ). H,S

( N H~)c,( Mo7024)+en(excess)---7(enH 2 )( M o04 ) ~ 1 ... ( I)

where en slands fo r eth ylenediamine. The first step in the sy nthes is is the formation of ethylcnediammonium tetraoxomolybdate (e nJ-1 2 ) (Mo0~)

in the presence of excess ethyl enediamine. Th is th en undergoes ligand exchange on treatment with J-J 2S res ulting in the formation of the product. The form ati on of 1 from th e preformed 2 on treatment with eth ylenediamine can be explained as a cation exchange reaction by the stronger base ethy lenedi amine as shown in Eq. (2) . Our efforts to isolate th e co rrespondin g W analog ue under identical conditions have not been fruit ful. (NJ-I4)zMoS4 +en (excess) ---7 1 + 2 NH3

...

(2)

The produ ct sy nthesized from both th e above methods is ex tremely ai r stable and very less solu ble in water unlike the ammonium salt. Ethylenediammonium tetrath io moly bdate 1 is solu ble in DMF but insolu ble in CH3CN. It has bee n reported8 that ammonium tetrathi omolybdate 2 slowly decomposes in air, via an induced electron trans fe r reaction resu lting in the for mat ion of th e din uc lear (Mo20 2S(l· species and thi s process is quite fac ile under laboratory atmos phe re. In contrast, 1 is extremely stab le. The unu sual stab ility of 1 co mpared to th at of 2 can be attributed to th e nature of the cou nter cati on in the title complex. It may be noted th at all prev ious know n salts of (MoS4) 2 . co ntain two monovalent cati ons whi ch are ei th er am mon ium or ces ium or tetraa lky lammonium . It appears that th e diffe rence in stabilty is due to the di cati oni c nature of ethylenediammonium cati ons. Such a behaviour is not unprecedented, as it is well establi shed th at the charae 0 on the cati on is cru cial for th e stabilizati on of a parti cul ar ani on. Thi s is well demonstrated 13 by the isolati on of pentacoo rclinate [Ni (CN) 5 t triani oni c co mplex as the salt of [Cr(en).,]3+. The ex tra stability of th e title compound can be furth er attributed to the hydrogen bondin g interactions of the tetrathi omol ybclate ani on and the ethy lenedi ammoniu m cati on via both N-J-1---S and C- 1-1 ---S bonds res ulting in the formati on of a three dimensional network (vide infra) as establi shed by X-ray an alys is. Spectral studies

A combinati on of IR, UV-Vis and elemental an alysis techniques has been employed to characteri ze 1. The solid state infrared spectrum of 1 ex hibits a strong signal at 474 cnf 1 and th is is ass igned to the V Mo=S (asymmetric) vibrati on while all th e other signal s can be attributed to as ori ginatin g from the organic ethylenediammonium co unter cati on. The tripl y dege nerate Mo=S asy mmetric stretching vibration occurs at a lower energy compared to that in th e ammonium salt

SRINIY ASAN et al .: X-RAY STRUCTURE OF ETHYLENEDIAMMONIUM TETRATHIOMOL YBDATE

Table I -Crystal data and structure refinement for (enH 2)MoS 4

Table 2 - Bond lengths [A]and bond angles [deg]for 1

(enH 2)MoS4

S(4)-Mo(l)

2. 1846(17)

Molecular formula

C2H10MoN2S4

S(2)-Mo(l)

2. 1735( 18)

Formula weight

286.30

C(I)-N( l )

1.474(11)

Temperature

293(2) K

C( I )-C(2)

1.493(1 0)

Wavelength

0.71069 A

N(2)-C(2 )

1.478( 10)

Crystal system, space group

orthorhombic, P2 12 12 1

Mo( I )-S(3)

2.17 83( 17)

Unit cell dimensions

a= 8.582(5) 90.000 deg.

Mo(l )-S( I)

2.1792( 19)

Identification code

8=9.276(5) 90.000 deg.

A

alpha=

A

beta=

c = 11.792(5) A ga mma= 90.000 deg. Volume

938.7(8) A3

Z, Calculated density

4, 2.026 g.cm·3

Absorption coefficient

2.214 mm· 1

F(OOO)

568

Crystal size.

2 x 2x2 mm

Theta range for data collection

2.79 to 22.55 de g.

Limiting indices

-9