Ray, Arabinda

Sathyanarayana, D. N.

English

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Il1dlan Journal of ChemistryVol. 15A, April 1977, pp. 306-309Normal Vibrations of Guanyl Thiourea-do & Thiourea-a,ARABINDA RAY & D. N. SATHYANARAYANADepartment of Inorganic & Physical Chemistry, Indian Institute of Science, Bangalore 560012Received 9 March 1976; accepted 23 August 1976The in-plane vibrations of guanyl thiourea-do and -d. have been calculated and the IRassignments obtained using the normal coordinate treatment. The infrared spectra of Ni(II),Cu(II) and Pd(lI) complexes of guanyl thiourea have been studied with the aid of the theoreticalband assignments regarding vC=S.GUANYL thiourea (GTU) is of considerableinterest because of its ability to readily forma variety of metal complexes. But thedetailed structures of these complexes are yet tobe establishedt-". Of particular interest in the1R spectra* of the complexes is the assignment ofstretching vibration of the C = S group". Onboth the counts a quan titative description of thenormal vibrations of GTU would be of much value.Further, GTU belongs to the class of S, N donorchelating ligan ds, which areof gre:at current interests.The frequencies of the in-plane vibrations ofGTU-do and -d6 assigned Oil the basis of normalcoordinate treatment are reported in this paper.The ba.ids of interest in relation to the spectra ofcomplexes belong to this category. The bandsdue to the out-of-plane vibrations have also beenassigned empirically for completeness. The 1Rspectra of the complexes of GTU with Ni(II), Cu(II)and Pd(II) are r ei.ivestigatcd with a view to knowingthe effect of coordination on the bands of GTU,especially the 'IC = S. Previous related studiesinclude an empirical assignments of some charac-teristic 1R bands of GTU-do and -d6 and theircomplexes with Ni(II), Cu(II) and Pd(II). A classi-fication of the thioarnide bands lias also beenreported by Rao et al.".Materials and MethodsGTU was prepared starting from dicyandiamide"and recrystallized from methanol, m.p. 170°.GTU-d6 was obtained by repeated exchange reactionof GTU with. D20 of over 99'4% purity. The com-plexes, Ni(GTU-H)2' Cu(GTU-H).2H20 and Pd(GTU-Hh, were prepared by known methodsr-",and their compositions checked by metal andsulphur analyses. The 1R spectra of the solidsamples were recorded on Carl-Zeiss UR 10 andBeckman 12 spectrophotorneters using mull andKBr techniques.Normal coordinate treatment - On the basis ofits close relationship with 2.4-dithiobiuret9 (DTB),the two planar configurations (I and II) of GTUwere considered for the normal coordinate treat-ment.• All the band positions are reported in cm'",306(I) (II)Both the configurations I and II of GTU belongto the point group C. The 33 normal modes ofGTU are classified into 23 in-plane (AI) ard 10 out-of-plane (A~) vibrations. ai.d ollly A' modes arecousidercd for the vibrational analysis. TIle in ternalcoordinates are shown in Fig. 1 and the internalsymmetry coordinates employed were coistructedusing the standard procedure'? and are not reportedhere for brevity. The structure parameters werethe same as used for DTB9 and are given in Table 1.Because of its effectiven ess for tltioamideo,11-l4and thiourcasw-!", theUrcy-Bradlcy force field wasused. The ini .ial force constan ts were transferredfrom DTU9. The fi.ial force constants ob.airiedafter refinement are shown in Table 2. As thecl:lemical environment of the two NH2 groups aredifferent, the force constants for the two NH2groups are different. The agreement between theobservcdan d calculated frequencies for both GTU-doand -d6 IS satisfactory. The values obtained forforce constants are reasonable and compare wellFig. 1 -Internal coordinates of GTURAY & SATHYANARAYANA: NORMAL VIBRATIONS OF GTU-do & -d.with those for DTB9 and other thioamide systemsU-14,indicating the transferability of these force constants.TABLE 1 - STRUCTUREPARAMETERSOF GTUBond lengths Bond angles(A)-----N-H 1·020 HNH 120°C=N 1·300 HNC 120°C-N 1·345 HN'C 116°C-N' 1·395 CNC 128°C=S 1·713 NCS 120°NCN' 120°TABLE 2 - FORCE CONSTANTS(mdyn/A) OF GTUStretching Bending RepulsionKNHKN(3)HKN'HKNC(I)KNC(2)KC=NKN'C(I)KN'C(2)KcsfNH,NH5·724·905·606·706·156·753-404·253·50-0,28HNH(I)HHHl'(l)CHHN(:!)HHHN(:!)CHSCN(l)Hscx:H!'I'CN(I)HHN'C(I)HCNCHHN'C(2)HN'CN(2)HN'CN(3)HCI'(3)HHN(2)CN(3)0·390·300·37.0·34.0·260·210·320·160·420·300·140·200.2450·17FHNHFHN(l)CFHN(2)CFSCN(I)FSCN'FN'CN(l)FHN'C(I)FCNCFHN'C(2)F:-I'CN(2)FN'CN(3)FCN(3)HFN(2)CN(3)Results and Discussion0·00·550·651·200·900·650·450·300·560·850·950·751·30Configuration IThe observed and calculated frequencies (valuesin cm ") together with their potential energy distri-butions (PED) are presented in Table 3 for GTU-doand -d6 [co.ifiguration I). . .,A' oibrations - The assignments of different l)l-plane vibrations are discussed below.Reeion 3500-3000 - Six bands due to the NHan d NH2 stretc'ring modes are expected. Of these,the bald at 3115 is attribu.ted to the im ir.e (= NH)stretching as in kctimines". The other vNH occursat 3320. The remaining bands at 3450, 3430 and3200 are attributed to the stretching modes of thetwo NH2 groups. The bands due to ND stretchingmodes of GTU-d6 are exhibited in the range2300-2600.Region 1700-1400 - A band at 1655 is due to amixed vibration of C-N and C=N stretching modesand NH2 bending. The corresponding band occursin the deute rated molecule at 1625.The bands at 1630 and 1615 are predominantlydue to NH2 bending, the former is coupled withTABLE 3 - INFRARED FREQUENCIES(em-I) OF GTU-do AND -d6 AND THEIR MAIN ASSIGNMENTSGTU-d. GTU-do Main assignment (PED, %)HObs. Calc. Deviation Obs. Calc. Deviation(%)* (%)*2565 2550 0·9 3450 3448 0·6 vaNH.(2) (100)2524 2520 0·9 3430 3434 0·1 vaNH.(I) (100)2446 2424 0·0 3320 3325 0·2 vNH(I00)24002365 2315 0·4 3200 3203 0·1 vsNH.(2) (100)2325 2302 0·0 3200 3185 0·5 vsNH.(I) (99)2295 2269 1-1 3tt5 3111 0·1 v=NH(100)1625 1623 0·1 1655 1667 0·7 vCN(2) (32) + vC=N(23) + 8NH.(2)(28)1305 1286 1·2 1630 1634 0·2 8NH.(1) (58) + vCN(l) (27)12701220 1227 0·6 1615 1627 0·7 8NH.(2) (54) + vC=N(20)1550 1545 0·3 1513 1537 0·5 vCN'(2) (16) + vCN(I) (16) + WH.(l) (15)+ 8NH(15) + vCN(2) (13)1500 1477 1·5 1500 1482 1·2 vCN'(2) (19) + vCN(2) (17) + vCN'(l) (13)+ rNH.(2) (13)1128 1119 0·8 1428 1405 0·8 vNH(48) + vCN(l) (27)1400865 845 2·3 1330 1334 1-1 rNH.(l) (41) + vCN'(I) (24) + vCS(15)13101035 967 6·6 1195 1189 0·5 rNH.(2) (66) + vC=N(23)815 817 0·2 1075 1088 1·1 ilC=NH(48) + vCN'(2) (17) + rNH.(l) (12)815 817 0·2 1075 1051 2·0 IIC=NH(4l) + vCN(2) (19) + vCN'(1) (13)910 898 1·3 955 990 3·7 rNH.(l) (23) + vCN'(2) (t 8) + "CS(12)735 709 3·5 750 752 0·3 vCS(65)580 588 1·4 640 633 H ilNCS(27) + IlNCN(2) (21) + ?CNC(19)450 463 2·9 505 520 3·0 8NC=N(48) + 8NCS(2l) + 8NCN(l) (18)§ 335 370 369 0·3 8NCN(I) (38) + 8NC=N(29)§ 311 330 331 0·3 8NCN(2) (49) + 8NCS(27)§ 124 § 130 8CNC(54) + 8NCN(2) (16) + 8NCS(14)·Calculated from [Ivobs -r-vcalc] X 100J/voh,.tv = stretching, 8 = bending, r = rocking. 1 and 2 in parentheses after the groups indicate groups as shown in Fig. 1.tThe potential energy distributions given are for GTU-do and the assignments approximately correspond to GTU-d.bands as shown; PEDs less than 10% are omitted.§Not investigated.307INDIAN ], CHE.M., VOL. 15A, APRIL 1977C-N stretching an~ the latter with C=N stretchingmodes. These assignments are compatible withthe NH2 modes observed in DTB9. In GTU-d6,the bands at 1220, 1160 and 1128 are due to NDbending modes. The NH bending is associatedchiefly with a split band near 1430 and is coupledwith vC-N. In GTU-d6, the ND bending modecontributes to the bands at 1160, 1128 and 910..The C-N stretching modes are highly coupledwith other vibrations and the contribution fromC-N stretching to anyone band does not exceed32%.Re.gion 135.0-900 - The imine (=. H) bendingoccurs at a fairly low frequency (1075) and is weaklycoupled, mainly with C-N' stretching. The C=NDbending in GTU-.d6 is associated with the bands at865 and 815. O.le of the NH2 rocking modes maybe assigned at 1195, the analogous vibration inGTU-d6 is identified at 1035. The other NH2 rockingmode contributes to the bands at 1330, 1075 and955 crrr". In the comparable molecule, DTB9, theNH2 rocking modes occur at 1350, 1280, 1120 and1010.Region 850-700 - A fundamental problem ininterpreting the IR spectra of thiocarbonyl com-pounds with =N-C=S group is the assignmentof an absorption band to the stretching vibrationof the C=S group4,l1-16. The 750 band in GTUis mostly due to a C=S stretching mode. It isexpected to shift slightly On deuteration and theband is observed at 735 in GTU-d6. The positionof vC=S in GTU is comparable to that of vC=Sin simple thio compounds like thioureal", thioacet-amide--, etc., and to that of the 780 band in DTB9.Region below 650 - The bands due to skeletalbending modes appear in this region. The NCSbending is highly coupled and contributes to thebands at 640, 505 aid 330. The bands at 370 and330 could be attributed to NCN bending modes.In DTB, the corresponding band is observed at396. The band at 505 may be assigned to NC=Nbending. The CNC bending at 130 is compatiblewith the corresponding band at 135 in DTB. TheCNC bending mode couples with NCS and NCNbending modes, both in GTU and DTB.A" vibration - A tentative assignment of theout-of-plane vibrations is given below:An intense broad band at 955 in GTU is attributedto NH out-of-plane bending, overlapping with anin-plane band, and is comparable to the band at955 DTB. The bands at 770 and 710 are assignedto NH2 torsional modes and are compatible withthe bands at 735 and 710 in DTB, whereas the NH2wagging modes of GTU are assigned at 648 and485, the corresponding bands in DTB occurring at600 and 550. The =NH out-of-plane bendingexpected around 700 may be presumed to havemerged with the NH2 torsional modes. The bandat 438 may be assigned to C=S bending. The re-maining bands at 390 and 270 can also be attributedto skeletal bending vibrations.In GTU-d6, there are five bands; at 678, 650, 540,485 and 405, which are not assigned to A' vibrations.In comparison with the spectrum of DTB-d5, thebands occurring at 678, 540 and 650 may beassigned to ND bending, CS bending and a coupled308~H2<, /N=C,Ni NH.",'N--C"H II2 Srnn (IT)vibration. of CS and CN ~endi!lg m?des respectively .The torsional and wagging vibrations of ND2 maybe assigned at 485 and 405 respectively.Configuration IIFor configuration II, o~e does Hot expect muchG1\a ge In ~he nature ~f vibrations and assignments.Tlte potential energy dIst~lbu.tlOllS for the frequenciescalculated for cOllfigurahoJ.l II were practically thesame as those for configuration I, except for the bandsat 640 an.d 505. The vibrational assignments forconfiguration II are, therefore, not tabulated. Inconfiguration II, the band at 640 is mainly due toNC~N and NCS bending modes, and the con tri-butio.i from the former is more than 35<;.{. Theba:d at 504 is a coupled vibration of NCS, NC=Nand N<:N beudi.ig modes with major contributions,appro~lmately 30% from NC=N aud NCS bendingvibratio.is.Metal ComplexesRecently ~aiga.l.kar a.id Hlaldar2 have investigatedthe electronic and infrared spectra of GTU complexesof ~i.(II), Cu(II), and Pd(II), and have madeempirical ba.id assignments», On the basis of struc-tures proposed by them we discuss below the effectof coordination of GTU on its vC=S. A broaderinvestigation on the basis of theoretical bandassignments will be presented later for a numberof metal complexes of GTU.On the basis .of the previously proposed structure(III) for the NI(II) complex, the vC=S is expectedto show blue-shift ~n coordination of GTU throughthe NH2 gr01!p adjacent 10 the C=S group. Theband at 750 In .GTU due to \lC=S is accordinglyobserved at a hIgher-frequency (815) in the Ni(lI)complex. (The C-NR2 stretching frequency maybe expected to undergo red shift in complex). Thespectrum of the Cu(II) complex is very similar totha~ ?f the Ni(II) complex. The Cu(II) complexexhibits C=S stretching as an intense band at 802..The IR spectrum of the Pd(II) complex isd~fferent from that of the Ni(II) complex. Pall a-dium, beI!lg ~ soft metal, has a greater tendencyfor coordination through. the. soft donor sulphur,and hence one of the bO_ld1ngSItes may be the thio-carb?nyl sulphu.r (structure IV), and consequentlyco.isiderable shift In v.C=.S to lower frequenciesmay be expected. From ItS shape and intensitya strOJ.lg band at 655 in. the Pd(II) complex maybe assigned to vC=S which shows a large decreaseof ~earIy 100 ~rom the band position in free ligand.ThIS decrease IS comparable to that in S-coordinatedtransition metal complexes of dithiooxamide+.References1. RAY, P., cu«. Reu., (1961), 313; and the r-eferencestherein.RAY & SATHYANARAYANA: NORMAL VIBRATIONS OF GTU-do & -ds2. PAIGANKAR, A. & HALDER, B., C. J. Indian chem, Soc.,47 (1970), 135.3. BELLAMY, L. J., The infrared spectra of complex molecules(Chapman & Hall, London), 1975.4. ALI, M. A. & LIV'INGSTONE, S. E., Coord. chem, Rev., 13(1974), rot.5. RAo, C. N. R. & VENKATARAGHAV'AN, R., Spectrochim,Acta, 18 (1963), 54t.6. KURZEV', F., Org. Synth., 35 (1955), 69.7. RAY, P. & CHAUDHURY, A. K., J. Indian chem, Soc. 27(1950), 673.8. PODDAR, S. N. & RAY, P., J. Indian chem, Soc., 29 (1952),279.9. RAY, A. & SATHYANARAYANA, D. N., Spectrochim. Acta,31A (1975) 899.10. WILSON, E. B., DECIUS, J. C. & CROSS, P. C. Molecularvibrations (McGraw-Hill, New York). 1955.11. SUZUKI, I., Bull. chem. Soc. Japan, 35 (1962). 1286; 1449;1456.12. RAY, A. & SATHYANARAYANA, D. N., Bull. chem, Soc.Japan, 45 (1972), 2712; 46 (1973), 1969.13. RAo, C. N. R. & CHATURV'EDI, G. c., Spectrochim. Acta,27A (1971), 520.14. RAY, A. & SATHYANARAYANA, D. N., Indian J. Chern.,12 (1974), 1092.15. GOSAV'I, R. K., AGARWALA, U. & RAo, C. N. R., J. Am.chem. Soc., 89 (1967), 235.16. HADZI, D., KIDRICK, J., KNEZEV'IC, Z. V. & BARLIC, B.,Spectrochim. Acta, 32A (1976), 693.309

Normal Vibrations of Guanyl Thiourea-d0 & Thiourea-d6

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Normal Vibrations of Guanyl Thiourea-d0 & Thiourea-d6

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