Synthesis and spectral studies of diorganotin heterocyclic dithiocarbamate complexes: The crystal...

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SYNTHESIS AND SPECTRAL STUDIES OF DIORGANOTIN HETEROCYCLIC DITHIOCARBAMATE COMPLEXES :

THE CRYSTAL STRUCTURE OF I

JYOTI SHARMA, YASHPAL SINGH, RAKESH BOHRA and AUDHESH KUMAR RAT*

Department of Chemistry. LJniversity of Rajasthan, Jaipur 302004, India

Abstract-Some new diorganotin(IV) complexes of heterocyclic dithiocarbamates having

general formula [CH,CH,(X)CH,CH2NCS,],Sn Rz (where X = CH2, CH-CH,, N-CH,. 0 ; R = CH,) have been synthesized and characterized by IR and NMR (‘H, ‘C and “‘Sn)

spectral data. The crystal structure of (CH,)Sn[S,CNCH,CH,CHZCH2CH,12 has been determined.

Interest in dithiocarbamate complexes of diorganotin( IV) species arises because of their varied structures’ ’ and biological activities.5 On the basis of crystallographic studies’ ’ of the dithiocarbamate complexes of diorganotin( IV), a variety of coordination environments around the central tin atom, ranging from tetrahedral to distorted octahedral, with ligands having anisobidentate”.x or monodentate’,’ character, have been reported. In the present communication, we report the synthesis of some new dimethyltin derivatives of heterocyclic dithiocarbamate ligands having composition

CH2CH,(X)CH2CH,NCS2 and their character- ization using physico-chemical and I R, ‘H, ‘C and “‘Sn NMR spectral data. The structure for these complexes was finally confirmed by the X-ray crystallographic analysis of a representative complex.

(CH,)Sn [S,CNCH,CH2CH2CH,CH,1,.

RESULTS AND DISCUSSION

The interaction of Me,SnCl, with the sodium salt of the cyclic dithiocarbamates in 1 : 2 molar ratio yields the corresponding diorganotin(IV) derivatives :

* Author to whom correspondence should be addressed.

Me,SnCI,

I I $- 2CH,CH2(X)CH,CH2NCS, Na= \IlWI”f

I (C%ZCH,(X)CH,CH,NCS2)2SnMe, +2NaCIl

(whereX = CH1, CH-CH,, N-CHI, 0).

These dimethyltin derivatives are found to be crystalline solids having sharp melting points ; they are soluble in common organic solvents and mono- meric in chloroform solution.

The appearance of a strong band in the region 1465$15 cm- ‘, which may be assigned to r(C--N), indicates the bidentate nature of the ligand in the complexes and the band present at 985+ 15 cm ’ may be assigned “’ to v(C =S). The monodentate or bidentate behaviour of the dithiocarbamate moieties in the complexes may be pre- dicted on the basis of the C =S stretching mode.“’ The presence of only one intense absorption band at 98.5 + 15 cm ‘~’ indicates the bidentate”.” nature of the dithiocarbamate moiety in the complexes. The presence of a new band at 380 f 20 cm ’ may be attributed” to v(Sn-S), confirming the bonding of the central tin atom with the sulfur atom of the ligand.

1097

1098 J. SHARMA et al.

NMR spectra (‘H,“C and ““Sn)

The ‘H NMR spectra of these complexes display the characteristic proton signals due to CH,, ring CH2, N(CH,),, CH-CH, or N-CH, protons (Table 1). The singlet at 6 1.45-2.32 ppm may be assigned to methyl protons attached to tin.

A comparison of the ‘“C NMR spectra of the ligands14 with the corresponding diorganotin(IV) complexes (Table 2) shows a downfield shift in the position of C, and C, signals and an upfield shift in the position of the C, carbon signal. These shifts indicate the bidentate behaviour of the dithiocarbamate moieties in the complexes. The signals for the methyl carbon attached to tin have been observed in the range 6 15.77-15.28 ppm. The analysis of 270 MHz ‘%I NMR spectrum of (CH,),

Sn[SzCNCH,CH,CH,CH,CH1]2 indicates a tin carbon coupling constant ‘J (’ '"Sn, “C) of the order of 635.58 Hz. The appearance of coupling constant values in this region in the case of dimethyltin complexes has been attributed to the six-coordinate(‘.” environment around central tin atom. A correlation between ‘J (““Sn, “C) values and C-Sn-C angles (0) in dimethyltin complexes has been reported by Lockhart and Manders.lh The angle (3 is related to ‘Jas

‘J = 11.46-875

or 8 = 0.0877 (‘J) f76.7543.

Substituting the relevant coupling constant data in the above equation, the C-Sn-C angle in di- methylbis(piperidinedithiocarbamate)tin(IV) complex has been found to be 132.28,‘, indicating a distorted octahedral environment around the central tin atom.

The “‘Sn chemical shift values in these complexes are found to be in the range of (-) 330.33 to (-) 336.47 ppm (Table 3). The appearance of chemical shift values in this region indicates a six-coordination environmenti around the central tin atom in these complexes.

Description and discussion qf structure

The predictions on the basis of spectroscopic data are entirely borne out in the structure of the title compound determined by single crystal X-ray analysis. The molecular structure of the complex,

I 1 (CH,),Sn[S,CNCH,CH,CH,CH,CH,]2, shown by a PLUTO diagram is depicted in Fig. 1. Bond leng- ths and bond angles are summarized in Table 4.

In the severely anisobidentate mode of bonding, the ester and dative pairs of Sn-S bonds are found to be on opposite sides of the girdle of the molecule

Diorganotin heterocyclic dithiocarbamate complexes 1099

Table 3. “‘Sn NMR spectral data of heterocyclic dithiocarbamate complexes of diorganotin(lV) (6, ppm)

1 (CH,)zSn(Pipdtc)z (-)334.86 2 CH 1),Sn(4-MePipdtc), ( - )336.47 3 (CH,),Sn(N-MePzdtc)? (-)33(X33 4 (CH &Sn( Morphdtc), ( - j324.79

i.e. c.is orientation. The dithiocarbamate ligand

m t- 2 m

w 6

I I moieties in (CH,)2Sn[S2CNCH,CH2CH2CH,CH,I, are anisobidentically chelated to the tin atom with one longer (av. 2.912 A) and one shorter (av. 2.53 A) Sn--S bond, respectively. These values are similar to those observed2,h earlier in Me,Sn(S2CN Me,), and MeSn [SzCN(CH2)4]2. The long Sn-S distances are significantly less than the sum of the van der Waal’s radii” (4.0 A). Thus, the coordination number of the tin atom is unambiguously assigned as six. In the analogous dithiocarbamate derivatives of the metals it has been noted that the more tightly the sulphur atom is bound to the metal atom. the longer is its bond with carbon. In other words, the shorter bonds to carbon can be written as C=S and are associated with the longer coor- dinated bond. These shorter C=S bond distances

in (CH,),Sn[S2CNCH,CH2CH,CH2CHJ2 are found to be (av.) 1.672 A. On the other hand, the longer bond distances, which can be written as C-S and are associated with shorter covalent bond. is found to be (av.) 1.749 A. Calculated C=S and C-S bond distances are 1.60 and 1.82 A, respectively. A comparison of the calculated values of the C-S (1.60 A) and C-S (1.82 A) bond distances with those of the observed C-S values (av. 1.672 A) indicates the involvement of electron delocalization with S-CLLLS system. It is, however, easy to dis- tinguish the ester from the dative portion of these chelating ligands.

m

The sulfur and carbon atoms of the dithiocarbamate moiety are co-planar with tin but are highly distorted from square planar geometry. The two sulphur atoms S(2) and S(4) form weak bonds and subtend an angle of 146.82(6)” at the tin atom. which is more than the normal bond angle of 90”. The difference of -57 is quite significant. In contrast, the bond angle S(l)-Sn-S(3) is 83.46(6)’ The S(l)-Sn-S(4) and S(2)-Sn-S(3) bond angles are 148.24(6)’ and 148.00(7) , respectively. However, there is no overall distortion in the basal plane. as the sum of the bond angle is found to be 359.24 ‘. The chelate angles, i.e. S( 1 )---Sn-S(2) and S(3)-Sn-S(4), are quite

1100 J. SHARMA et (11.

Fig. 1. PLUTO diagram for (CH,),Sn[S,CN~CH,CH,CH&H$!H&

acute with the values 64.86(6)‘- and 65.10(6)“, ular structures are known ; the Me-Sn-Me angle respectively. The Me-Sn-Me angle (131.2”) is ranges from 135.6 to 142.8’ and in (CH,),

r I intermediate between cis and tram, similar to those Sn[S,CNCH,CH,CH,CH,CH,1, it is 131.2 . How- observed in Me$n(S,CNMe,), (136”) and Me,Sn ever, this bond angle is smallest among all the di- (S&N Et& (135.6”). Three different crystalline methyltinbisdithiocarbamate compounds reported modifications containing four independent molec- so far. The angle observed in solution (CDCl,) is

Table 4. Intramolecular distances (A) and angles (’ )”

Sn-S( 1) 2.540(2) Sn-S(2) 2.907(2) Sn-S(3) 2.520(2) Sn-C( 1) 2.140(9) Sn-C(2) 2.127(8) Sl-C(3) 1.747(7) S2-C(3) 1.676(7) s3-C(9) 1.751(8) S&-C(9) 1.669(8) Nl-C(3) 1.327(9) Nl-C(4) 1.505(9) Nl-C(8) 1.48(l)

S( I)-Sn-S(2) S( I)-Sn-S(3) S( I)-Sn-C( 1) S( I)-Sn-C(2) S(2)-Sn-S(3) S(2)-Sn-C( 1) S(2)-Sn-C(2) S(3)-Sn-C( 1) S(3)-Sn-C(2) C( I)-Sn-C(2) Sn-S( 1)-C(3) Sn-S(2)-C(3) Sn-S(3)-C(9) C(3)-N( 1)-C(4) C(3)-N( 1)-C(8) C(4)-N(l)-C(8) C(9)-N(2)-C(lO) C(9)-N(2)-C( 14) S(2)-Sn-S(4)

64.86(6) 83.46(6)

110.2(2) 105.5(2) 148.00(7) 82.8(3) 83.5(3)

105.6(2) 110.7(2) 131.2(3) 93.5(2) 82.9(3) 93.5(2)

124.4(6) 122.1(6) Il3.5(6) 122.6(6) 124.3(6) 146.82(6)

N(2)-C(9) 1.321(9) N(2)-C(10) 1.48(l) N(2)-C( 14) I .500(9)

C(4)-C(5) C(5)-C(6) C(6)-C(7) C(7)-C(8) C(lO)-C(l1) C(ll)-C(l2) C(12)-C(13) C(l3)-C(l4)

1.53(1 1.53(1 1.55(1 1.49( 1 1.54(1 1.55(1 1.53(1 ) 1.52(1 1

Sn-S(4) 2.918(2)

C(lO)-N(2)-C(l4) S( 1)-C(3)-S(2) S(l)-C(3)-N(1) S(2)-C(3)-N( 1) N( I)-C(4)-C(5) C(4)-C(5)-C(6) C(5)-C(6)-C(7) C(6)-C(7)-C(8) N( 1)-C(8)-C(7) S(3)-C(9)-S(4) S(3)-C(9)-N(2) S(4)-C(9)-N(2) N(2)-C(lO)-C(l1) C(lO)-C(1 I)-C(12) C(ll)-C(l2)-C(13) C(12)-C(l3)-C(l4) N(2)-C(l4)-C(l3) S( 1)-%--S(4) S(3)-Sn-S(4)

Il2.9(6) 118.2(4) 119.0(5) 122.9(5) 107.2(6) 111.3(7) 110.9(7) 109.6(7) 109.5(7) 1 I8.9(5) 119.1(5) 122.1(5) 106.3(7) 109.0(7) 110.2(7) 110.9(7) 108.4(6) 148.24(6) 65.10(6)

“Numbers in parentheses are estimated standard deviations in the least significant digits.

Diorganotin heterocyclic dithiocarbamate complexes 1101

slightly higher (132.28 ). This may be due to the absence of any solid state packing constraints due to the lattice effect.

EXPERIMENTAL

Precautions were taken to exclude moisture throughout the experimental manipulations. Me,SnCl, was distilled before use. Tin was estimated gravimetrically as tin(IV) oxide and sulphur was estimated gravimetrically using Messenger’s method.‘” Molecular weights of the complexes were determined by an osmometric method using a Knauer Vapour Pressure Osmometer, in chloroform solution at 45 C. IR spectra of the compounds were recorded in the range 4000-400 cm-’ on a Perkin-Elmer 577 spectrophotometer using KBr pellets. ‘H, “C and “‘Sn NMR spectra were recorded in CDCI, and CHCll solutions on a Jeol FX 90 Q (90 MHz) NMR spectrometer. “C NMR spectra of the compound (C)-i,), Sn

(SJZNCH,CH2(CHZ)CH2CFl,)z were recorded in CDCI; solution on a WH-270 NMR spectrometer at 270 MHz using TMS as an external reference. For ““Sn NMR spectra tetramethyltin was used as external reference. The ligands were prepared by literature method.“’

Since all the complexes have been synthesized by similar methods. the synthesis of a representative complex is described below and the synthetic details and analytical data of the other complexes are summarized in Table 5.

Preparation of’ dimeth~~lhis(piperadine dithiocarha-

mate)tin(lV). (CH~)$n(S2CNCH,CH2CH2CH,C H,),

A weighed amount of the dimethyltin dichloride (0.81 g, 1.72 mmol) was mixed with the sodium salt of the ligand (I .62 g, 3.45 mmol) piperidine dithiocarbamate in 1 : 2 molar ratio in benzene solution. The reaction mixture was stirred for -4 h at room temperature and finally refluxed for about 30 min to ensure completion of the reaction. The NaCl thus formed was filtered off and the excess solvent was removed from the filterate under reduced pressure. The compound thus obtained was dried in cucuo and recrystallized from a solution of dichloromethane and n-hexane.

Crystals of Me,Sn (S2CNCH2CH2CH2CH2CH2)1 were obtained by recrystallizing the complex from a solution of dichloromethane and n-hexane. All diffraction measurements were recorded at room

1102 J. SHARMA et al.

temperature on an Enraf-Nonius CAD-4 diffract- rometer using graphite-monochromated MO-K, radiation. The unit cell parameters were determined from 25 (7” < 0 < 11”) randomly selected reflections by using the automatic search index and least square routines. The crystal used was a colourless plate (size 0.20 x 0.25 x 0.10 mm). Reference inten- sity reflections (4 2 4 and 2 2 6) measured every 1800 s showed no variations.

All the data were corrected for Lorentz and pol- arization effects. An empirical absorption cor- rection was applied to the data by measuring the intensities of four reflections with x near 90“ for different Ic/ values (0 < $ <: 360’, every 10 ‘), using the EAC programme from the Enraf-Nonius package. The maximum and minimum transmissions were 1.25 and 0.73, respectively.

Crystals of C,4H26N2S4Sn (469.30) are mon- oclinic with space group P2,/c, a = 17.326(j), h = 8.573(4), c = 13.248(8) A, h = 90.32(4)“, V = 1967.8 A’; Z = 4, D,,,, = 1.584 g cmp3, monochromated MO-K, radiation, ;( = 0.71069 A, p = 17.07 cm-’ T = 295 K and F(OOO) = 952 ; number of data collected = 3979, unique data = 3705, number of unique reflections used with I > 3cr(Z) = 2581.

The structure was solved by routine heavy atom methods and refined by full matrix least squares refinement techniques using anisotropic thermal parameters for all non-hydrogen atoms. Hydrogen atoms were omitted. The weighing scheme was M‘ = l/a’(F) and the final residuals were R = 0.054 and R, = 0.072, where w = l/02(F0). A final difference map had maximum density of 0.63 e A-’ near tin. Programs from the Enraf-Nonius SDP Plus Package2’ were run on a PDP 1 l/73 computer.

Acknowledgements-The authors thank the University Grants Commission, New Delhi, for providing X-ray diffraction facilities in the Department of Chemistry, University of Rajasthan, Jaipur. One of the authors (J. S.) is also grateful to the UGC, New Delhi and the State Government of Rajasthan for providing financial assist-

ante under a special assistance programme, and Prof. C. L. Khetrapal, IISc Bangalore for recording 270 MHz ‘jC NMR spectra.

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