Crystal structure and spectroscopic studies on metal complexes containing ns donor ligands derived from S-benzyldithiocarbazate andp-dimethylaminobenzaldehyde

PolyhedronVol. 15, N o 13. pp. 2263 2271, 1996

~

Pergamon 0277-5387(95)00477-7

Copyright ~'~ 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277 5387/96 $1500+0.01)

CRYSTAL STRUCTURE AND SPECTROSCOPIC STUDIES ON METAL COMPLEXES CONTAINING NS DONOR L1GANDS DERIVED FROM S-BENZYLDITHIOCARBAZATE AND p-DIMETHYLAMINOBENZALDEHYDE YU-PENG TIAN, CHUN-YING DUAN, ZHONG-LIN LU and XIAO-ZENG YOU* Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Centre for Advanced Studies in Science and Technology of Macrostructures, Nanjing 210093, P. R. China

and HOONG-KUN FUN and SIVAKUMAR KANDASAMY X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 118000 USM, Penang, Malaysia

(Received 25 August 1995; accepted 27 September 1995) Abstract--A series of neutral bis-ligand Cu H, Ni 11, Pd n and Pt H chelates with Schiff base ligands derived from S-benzyldithiocarbazate and p-dimethylaminobenzaldehydewere prepared and characterized. The Schiff base acts as a single, negatively charged bidentate ligand forming stable neutral metal complexes. Magnetic and spectroscopic data suggest a square-planar structure for the Ni H, Pd n and Pt n chelates. Also, ESR spectral and variabletemperature magnetic suspectibility data support the square-planar structure of Cu 1~chelate. Cyclic voltammograms show that the coordination ability of the metal is the main factor influencing the redox potential of the Schiff base ligand in the complexes. Single crystal Xray diffraction analysis of the nickel(II) chelate established that the Schiff base has lost a proton from its tautometric thiol form and coordinated to Ni H via the mercapto sulphur and//-nitrogen. The geometry around Ni H is square planar with two equivalent Ni--N and Ni--S bonds ; the two dimethylaminophenylrings and the coordinated plane are almost in one plane forming an electronic delocalization system.

In recent years there has been considerable interest in the chemistry of the metal complexes of Schiff base containing nitrogen and donors. ~8The interest in this field may be attributed to the striking structural features in the resultant metal complexes and their biological activities, as some of the metal complexes have anticancer activity.~ However, there are only a few examples of electrochemical and crystal structural studies of the complexes containing the sulphur-nitrogen ligands. 9'~° Herein we report the

* Author to whom correspondenceshould be addressed.

crystal structural, spectroscopic and electrochemical studies on the metal complexes with a new Schiff base ligand (HL) derived from S-benzyldithiocarbazate and p-dimethylaminobenzaldehyde.

EXPERIMENTAL All chemicals used were of analytical grade. The solvents were purified by conventional methods. Tetrabutylammonium perchlorate (Bu]NC104) was recrystallized twice. S-benzyldithiocarbazate was prepared by the literature method.l l

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YU-PENG TIAN et al.

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Preparation of S-benzyl-fl-N-(p-dimethylaminophen yl)methylendithiocarbazate (HL ) A solution of S-benzyldithiocarbazate (0.39 g, 2 mmol) in absolute ethanol (25 cm 3) was added to absolute ethanol (25 cm 3 1) containing p-dimethylaminobenzaldehyde (0.29, 2 mmol). The mixture was heated under reflux for 2 h. The solids formed were filtered off, washed with ethanol and recrystallized from benzene. Yellow pyramidal crystals were collected and dried in vacuo over P2Os, yield 0.56 g (85 %). I R data (KBr discs, cm-~) 3102, 2975 ( N - - H , m), 1589 ( C - - N , s), 1018 (C--S, s). FAB-MS m/z (relative intensity) 330 (5.4 ( M + 1)+). ~H N M R (chloroform-d, TMS). 61.65 (0.1H, s, SH), 3.04 (6H, s, (CH3)zN--), 4.55 (2H, s , - - S C H z p h ) , 6.72-7.58 (9H, m, aromatic), 7.76 (H, s, C H z N - - ) , 10.28 (0.9H, s, N H ) p p m ; m.p. 175~'C.

Preparation of the metal chelates A solution of the metal (Ni", Cu n) acetate (0.5 mmol) in ethanol (20 cm 3 1) was added to the ethanol solution (20 cm 3 1) of the ligand (1 mmol). The mixture was refluxed and stirred for 4 h after cooling to room temperature, and the crystals which formed were filtered off, washed with ethanol and dried in vacuo over P20> The P d " and Pt" chelates were prepared by the same procedure using KMUC14 (M = Pd, Pt). The prepared chelates with their analysis and I R data are listed in Table 1.

X-ray crystallography and structure solution Black crystals of the nickel chelate were isolated by slow evaporation of a dichloromethane solution containing isopropanol.

Table 2. Experimental data for crystallographic analysis Compound Formula Formula weight Crystal colour Crystal system Space group a (~) b (&) c (&) //(°) V (A) Z p (g cm ') /~ (mm -~) Crystal dimensions (ram) Temperature (K) Diffractometer Radiation (/~) Monochromator Scan technique 0 range for data collection Total reflections Unique reflections u Goodness of fit on F 2 (~/O')max Solution R Rw

NiL2 C34H36N6NiS 4

715.64 Black Monoclinic

P2t/n 7.9121 (4) 10.5254 (4) 20.177 (2) 98.59 (1) 1661.5 (2) 2 1.430 0.87 0.52 × 0.42 x 0.28 293 Siemens P4 Mo-K~, 0.71073 Graphite 0-20 scans 2.04~27.5 5106 3796 0.968 0.003 Direct methods 0.0334 0.0851

w = 1/[a2(F 2 + (0.0621p)2], where P = (F 2 +2F0:)/3 "All the unique data were used in refinement. Only the R factors are calculated for reflections with I > 2a(/).

Crystal data, intensity measurements and structure refinements are summarized in Table 2. Unitcell parameters and diffracted intensities were measured at room temperature using a Siemens P4

Table 1. Analytical" data and relevant IR frequencies (cm -t) of the ligand and its complexesb with their assignment (KBr discs) Compound

Colour

C

H

N

HL

Yellow

NiL2

Black

CuL2

Brown

PdL2

Brown

PtL2

Orange

62.2 (62.0) 57.0 (56.9) 57.0 (56.7) 53.8 (53.5) 48.0 (48.6)

5.8 (5.8) 5.3 (5.1) 4.9 (5.0) 4.8 (4.7) 4.2 (4.3)

12.5 (12.8) 11.8 (11.7) 12.0 (11.7) 10.6 (11.0) 9.8 (9.9)

v(N--H) v ( ~ N ) 3102 2975

v(~S)

v(M--N) v(M--S)

1589

1018

1552

944

455

1571

942

477

1563

943

453

1563

942

454

a Figures in parentheses are the calculated values. hAbbreviations : HL = S-benzyl-fl-N-(p-dimethylaminophenyl)methylendithiocarbazate.

371 356 362 339 369 351 370 354

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Metal complexes containing NS donor ligands diffractometer with graphite-monochromated MoK, radiation; the 0-20 scan mode was employed. Data were corrected for Lorentz and polarization effects and for absorption. The structure was solved by direct methods (SHELXS-86) ~2 and refined by full matrix least-squares method using SHELXL93. ~3 All the non-hydrogen atoms were refined anisotropically. The H atoms were located from difference-Fourier maps. S H E L X T L / P C t4 software was used for the molecular graphics and PARST j5 was used for all other geometrical calculations.

Physical measurements IR spectra were recorded on a Nicolet FT-IR170SX instrument (KBr discs) in the 4000-400 cm ~ region. The far-IR spectra (500-100 cm -j) were recorded as Nujol mulls between polyethylene sheets. Electronic absorption spectra were obtained on a Shimadzu UV 3100 spectrophotometer using a prepared dichlorethane solution. The solid-state electronic spectra were obtained by the reflectance technique on a Shimadzu UV240 spectrophotometer using MgO as the reference material. Magnetic susceptibility data were collected with a C A H N 2000 magnetobalance. Diamagnetic corrections for the constituent atoms were made using Pascal constants. ESR spectra were recorded on a Bruker ER 200-D-SRC spectrometer. The elemental analyses for carbon, nitrogen and hydrogen were performed on a Perkin-Elmer 240C analytical instrument. ~H N M R spectra were obtained on a Bruker AM-500 spectrometer using TMS as internal standard. The mass spectra were obtained on an ZAB-HS mass spectrometer (FAB source). Cyclic voltammetry was performed using an E G and G P A R model 273 potentiostat, in conjunction with a three-electrode cell fitted with a purged dinitrogen gas inlet and outlet, a platinum-wire working electrode, Ag/AgC1 as the reference electrode and a platinum auxiliary electrode. Current-potential curves were displayed on a Hewlett-Packard recorder. The voltammograms of the complexes were obtained in dichloromethane with

S C6H5

/

II

Bu]NC104 (0.1 mol dm 3) as the supporting electrolyte. R E S U L T S AND D I S C U S S I O N

Synthesis and spectrum of the Schiff base ligand The Schiff base (I), hereafter abbreviated as HL, was obtained in good yield by condensation of S-benzyldithiocarbazate with p-dimethylaminobenzaldehyde (see Scheme 1). The important IR bands of the H L together with those of their metal complexes are included in Table 1, where the assignments shown are tentative and are based on assignments made on similar compounds. ~6 The H L has a thione group ( k S ) and a proton adjacent to the thione group. It has been stated that the thione group (C~-S) is relatively unstable in the monomeric form and tends to form a stable C - - S single bond by ethioenolization, if there is at least one hydrogen atom adjacent to the ~ S bond. ~7The IR spectra of the H L do not display v(S--H) at ca 2570 c m - ~, indicating that in the solid state they remain in the thione form (I). However, ~H N M R spectra support the fact that the thione form (I) and the thiolo tautometric form (II) are in equilibrium in solution by the presence of proton - - N - - C - - S H (chemical shift 1.65). The calculated fractions of the protons o f - - N H - - C - - S and - - N z C - - S H are ca 0.9 and 0.1, respectively. This result indicates that in the solution the thione form (I) and thiol form (II) existed in the ratio 9 : 1.

IR spectra of the metal complexes The spectra of the H L exhibit strong bands at 2975 and 3102 cm -t, respectively, which can be assigned as the v ( N - - H ) of the free ligand. These bands disappear in the IR spectra of the metal complexes, which suggest that the proton on the enitrogen atom is lost upon complex formation with a metal ion. A strong band at 1355 cm 1 in the IR spectrum of the H L is assigned as v(C--N). This band is shifted to higher frequencies by ca 20 cm in the IR spectra of its complexes. This increase of

CH 3

H S

CH 3

I

H

CH3

CH3

(II)

(I)

Scheme 1.

YU-PENG TIAN et al.

2266

they are essentially diamagnetic in nature. For the d 8 electronic configuration, diamagnetism generally implies that the metal ion has a four-coordinate square-planar configuration. The electronic spectra of the complexes both in Nujol mulls as well as in dichloromethane solution are not very well resolved owing to the tails of very intense charge-transfer bands extending to the visible portion of the spectrum (Table 4). However, the absence of any band in the range 1.0-15.5 kk is strong evidence that octahedral or tetrahedral structures are absent. 22 Three bands corresponding to the transitions tAtu~ IA2u, I A l u ~ JBla and I A l g ~ JEiq, are expected in the electronic spectrum of a squareplanar d 8 complex. However, in many instances, especially with sulfur ligands, the bands corresponding to the transitions 1A~q~ IBlu, ~A~q ~ IAzu and IAjg ~ ~F~u are submerged under very intense inter-ligand and charge-transfer bands and only one in the range 16.0-20.0 kk is observed. The shoulder is around 660 nm for Ni H, 590 nm for P d " and 609 nm for Pt" in the electronic spectra of the present complexes and therefore may be assigned to the ~Alq*--IA2g transition. The bands around 440 nm are assigned to the metal-to-ligand charge transfer of the Ni", Pd n and Pt" complexes. Such transitions are known in thiocarbazide and thiocarbazone complexes 23'24 as the S - - M n transition. Other bands, especially bands III and IV, in the case of the H L complexes shift to lower frequencies relative to the corresponding bands of the ligand, as the proton on the c~-nitrogen atom is lost upon metal complex formation.

the v ( C - - N ) on complexation may be attributed to an increase of the C ( 1 ) - - N (1) bond order as a result of the deprotonation from the a-nitrogen atom. This tendency of the H L to deprotonate may be attributed to the stabilization of the deprotonated form by conjugation of the - - ~ N - - N ~ C - group. TM A strong band at 1018 cm ~ in the IR spectrum of the H L is tentatively assigned as v ( ~ S ) . This band is absent in the spectra of the metal complexes. This observation can be explained by the change in the nature of the C ~ S bond on coordination of the ligand through the sulfur atom, which is proven by crystal structure determination [ ~ S , 1.671(3) A, C - - S , 1.726(4)/~]. The two very strong peaks at ca 1606 and 1589 cm l in the IR spectra of the H L may be attributed to the aromatic C ~ - C vibration and the C ~ N stretching. Although these two vibrational modes may be coupled to each other, the peak at ca 1589 cm ~ may be safely assigned to the C - - N stretching vibrations of the azomethine group, since the frequency of the bands are lowered by ca 20 cm ~ in the spectra of the metal complexes. The band at ca 1606 cm ~ in the spectra of the ligand is very little affected upon complex formation and is, therefore, assigned to the aromatic C z C vibrations. This lowering of the v ( C - - N ) on complexation may be attributed to a decrease in the C - - N bond order as a result of the M - - N bond formation. The far-IR spectra (500-100 cm ~) of the complexes display a medium to strong band in the region 354-371 cm -I and in most cases another band in the range 335-356 cm -~ (see Table 1), which may be assigned to the metal sulfur stretching frequenciesJ 9'2° A band at higher frequencies in the range 453~477 cm ~ can be assigned as the metal-nitrogen stretching vibrations. 2~

Magnetic, E S R and electronic spectra o f the Cu H chelate

Magnetic and electron spectra o f Ni u, P d H and Pt H chelates

The room-temperature magnetic moments of the Ni", P d " and Pt n complexes (Table 3) suggest that

The room-temperature magnetic moments of the Cu n chelate (1.86 BM) are as expected for a squareplanar d 9 ion. Variable-temperature magnetic susceptibility measurement is more helpful in this respect. The ground state of a square-planar Cu" species is not degenerate and, therefore, it should

Table 3. The redox potentials and magnetic data of the dithio-compound" Compound

HL NiL2 CuL2 PdL2 PtL2

El~2 (Peak I)

-

1.341 0.956 0.544 1.201 1.094

El~ 2 (Peak II)

Pen"(300.3 K)

0.834 0.867 0.999 0.782 0.859

-0.46 1.85 diam diam

"Measured at Pt wire electrodes in dichloromethane, 0.1 x 10 4 mol dm -3, 0.1 mol dm 3 Bu]NC104, sweep rate: 250 m V s --~.

Metal complexes containing NS donor ligands

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Table 4. Electronic spectral data (nm) of the ligand and its complexes in dichloromethane and in the solid state

d-d

L-L* Compound

Band I

HL

198 (4.18)4 198 (4.64) 198 (4.42) 198 (4.45) 198 (4.45)

NiL2 CuL2 PdL2 PtL2

Band II

Band III

Band IV

Band V

Band VI

230 (4.19) 216 (4.51 ) 230 (4.48) 218 (4.45) 228 (4.63)

240 (4.14)

278 (4.11) 292 (4.64) 290 (4.40) 286 (4.51) 282 (4.33)

326 (3.90)

390 (4.69) 402 (4.72) 406 (4.80) 396 (4.62) 392 (4.85)

254 (4.43) 246 (4.56) 242 (4.58)

MLCT Band VII

Band VIII (solid)

450 (4.66) 454

674

434 (4.69) 452 (4.48)

590

782

609

"Band maxima in mm (log e).

have a magnetic moment close to the spin-only value of 1.73 BM. A tetrahedral Cu n complex, on the other hand, possesses a degenerate ground state and, consequently, the magnetic moment should be associated with some orbital contributions and should be dependent on temperatureY The magnetic behaviour of the Cu n chelate was studied over the temperature range 300-375 K. The plot of the reciprocal of the molar susceptibility corrected for both diamagnetism and temperature-independent paramagnetism vs temperature afforded the calculation of the values 0 and g (Fig. 1) as 8 K and 2.06, respectively. The magnetic data do not suggest the presence of any anomalous magnetic behavior in the Cu" chelates and support a square-planar configuration. Room-temperature ESR spectra give the 9 value at 2.058, which is in accordance with the data of the magnetic data and supports a square-planar configuration. The electronic spectrum of the Cu n chelate in a Nujol mull shows a broad band with a maximum

600-

~" 400

~,~ 200

y s

0

I 100 Temperature

I 200 (K)

I 300

Fig. 1. Plot of inverse magnetic susceptibility vs temperature for CuL>

at 782 nm. Three bands corresponding to the transitions 2Blg --+2B2g, 2Big -+ 2E2g and 2B~a ~ 2Alg are expected in the electronic spectrum of a strongly distorted octahedral copper(II) complex. However, in the limit of this tetragonal distortion such a complex reaches square-planar geometry and exhibits only one band in the 500-800 nm range, which can be resolved into at least three components. The appearance of only one band at 782 nm in the electronic spectrum of Cu n chelate is in agreement with a square-planar structure. This band may be assigned to all the three transitions expected in the electronic spectrum of a square-planar copper n species. 26 The shoulder at 454 nm may be assigned as an M L C T and other bands of the electronic spectrum in the dichloromethane may be assigned to L-L* charge transfer.

Electrochemical behaviour The redox potentials of the ligand and its metal complexes are listed in Table 3. The cyclic voltammograms of the H L and its metal complexes show that their redox processes are semi-reversible without coupled reactions. In the metal complexes, the redox potential of the dithiocarbazate - - C S S R - is in the range 0.5-1.0 V, while the redox potential of the methylidenes is in the range - 0 . 5 1.5 V. The EI/2(Q+/Q) (the redox potential of the dithiocarbazate) and the Et/2(Q/Q-) (the potential of the methylidene) are obtained by the formula Ell2 = (Epa+ Evc)/2. From Table 3 it is very obvious that the redox potential of the methylidene in the ligand is substantially lower than that in the metal chelates, demonstrating that the presence of the metal made the double bond of the Schiff base ligand more easily reduced. This result is very

YU-PENG TIAN et al.

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~

1.0

c~ 0.9

CuL2

NiL2

Pdtq , , ~ 0.8 -1.3

I -1.1

I -0.9

I --0.7

I -0.5

Eu2(Q ! Q-, V)

Fig. 2. Plot of E,/2(Q+/Q) vs E,/z(Q/Q ).

important in the catalytic reaction of the reduction of unsaturated organic compounds. Moreover, it is found that the higher the redox potential of the dithiocarbazate, the lower the redox potential in the methylidene, as shown in the plot of EI/2(Q+/Q) vs E,/2(Q/Q-) (Fig. 2). This result indicates that the factor influencing the redox potential in both methylidene and dithiocarbazate is the same, which is the coordinating ability of the metal in the complex. The stronger the coordinating ability, the higher the redox potential of the dithiocarbazate and the lower the redox potential of the methylidene. The same conclusions have already been reached by us. ~°

Single-crystal structure for NiL2 The ORTEP drawing of NiL2 with the atomic numbering scheme is shown in Fig. 3. Selected bond

~ )

lengths and angles are given in Table 5. A view of the molecular packing in the crystal is given in Fig. 5. The nickel atom is coordinated in a square-planar configuration with two equivalent N i - - N bonds [1.931(1)/~] and a Ni--S bond [2.180(1)/~]. The HL has lost a proton from its tautometric thiol form and acts as a single negatively charged bidentate ligand coordinating to the nickel ion via the mercapto sulfur and fl-nitrogen atoms. The dimethylaminophenyl ring is completely planar and forms a dihedral angle of 8.81(5) ° with the metalcoordinated plane; the very small dihedral angle indicates the high delocalization of electrons in the zc-system of the two Schiff base ligands and the nickel(II) ion. It is interesting to compare the structure of the HL in the free state 27 and in the nickel complex. The largest difference may be found in the bond distances around atom C(1). In the free ligand, the bond distances of C(1)--N(1) [1.324(3)/~] and C(1)--S(1) [1.671(3) /~] suggest that C(1)--N(1) has near single bond character and C(1)~S(1) near double bond, while in the complex the bond distances of C(1)--N(1) [1.270(3)/~] and C(1)--S(1) [1.726(3) ~] show that C(1)--N(1) is the double bond and C(1)--S(1) is a single bond. These results, together with the spectral characterization of the nickel complex, indicated the presence of the C - - S - - M group formed by the enolization of the --NH--~S group in the free ligand to - - N - - C - - S H and coordination of the metal through the sulfur after deprotonation. The deprotonation and the formation of the metal complexes made the configuration of the ligand quite different. The ligand undergoes some

coo)

--

c(7) c(8)

~ ~ ~ "f~ ~

~

~

c04) Fig. 3. ORTEP drawing of NiL2 with the atomic numbering scheme.

Metal complexes containing NS donor tigands Table 5. Selected bond lengths (A) and angles (°) for NiL2

Ni--S(l) N--N (2) S(1)--C(1) S(2)--C(1) S(2)--C(11) N(I)--C(1) N(I)--N(2) N(2)--C(2) N(3)--C(6) N(3)--C(10) N(3)--C(9) C(2)--C(3) C(3)--C(4) C(3)--C(8) C(4)--C(5) C(5)--C(6) C(6)--C(7) C(7)--C(8) C(11)--C(12) C(12)--C(13) C(12)--C(17) C(13)--C(14) C(l 4)--C (15) C(15)--C(16) C(16)--C(17) N(2)--Ni--N(2') N(2)--Ni--S(I') N (2')--Ni--S (1 ') N(2)--Ni--S(1) N(2)'--Ni--S(1) S(I')--Ni--S(l) C(1)--S(I)--Ni C( 1)--S (2)--C(11 ) C(1)--N(1 )--N(2) C(2)--N(2)--N(1) C (2)--N(2)--Ni N(1)--N(2)--Ni C(6)--N(3)--C(10) C(6)--N(3)--C(9) C(10)--N(3)--C(9) N(1)--C(1)--S(I) N(1)--C(1)--S(2) S(1)--C(I)--S(2) N(2)--C(2)--C(3) C(4)--C(3)--C(8) C(4)--C(3)--C(2) C(8)--C(3)--C(2) C(5)--C(4)--C(3) C(4)--C(5)--C(6) N(3)--C(6)--C(7) N(3)--C(6)--C(5) C(7)--C(6)--C(5) C(8)--C(7)--C(6) C(7)--C(8)--C(3)

2.180(1) 1.931(1) 1.726(2) 1.759(2) 1.805(2) 1.278(2) 1.413(2) 1.303(2) 1.360(2) 1.444(3) 1.444(3) 1.445(2) 1.400(3) 1.404(3) 1.371(3) 1.409(3) 1.405(3) 1.370(3) 1.511(3) 1.382(3) 1.390(3) 1.387(3) 1.370(4) 1.377(3) 1.379(3) 180.0 93.78(4) 86.22 (4) 86.22(4) 93.78(4) 180.0 95.97(6) 103.24(9) 112.73(14) 113.34(14) 126.49 ( 11) 120.12(10) 121.1 (2) 121.2(2) 117.5(2) 124.95(13) 120.56(13) 114.48(10) 133.3(2) 116.1 (2) 128.0(2) 115.9(2) 121.7(2) 121.8(2) 121.7(2) 121.5(2) 116.8(2) 120.6(2) 122.9(2)

Symmetry transformations used to generate equivalent atoms: (i) - x , - y + 1, - z + 1.

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YU-PENG TIAN et al.

2270

Ni

,

~

~C3

//

/SI'

Sl "-NI~cI S~

I iCll

Fig. 4. Superposition of the ligand molecule in the complex (solid line) and free state (dashed line).

Fig. 5. A view of the molecular packing in the crystal.

conformational changes during the complex formation. Fig. 4 shows the superposition of the ligand in the complex and in the free state. The major conformational changes are in the carbazate moiety. The trans ~ cis and cis ~ t r a n s transitions around certain bonds facilitate the H L to coordinate the metal ion as a bidentate ligand using the /~-nitrogen atom and the thio S atom. The relevant torsion angles are given in Table 6. S u p p l e m e n t a r y m a t e r i a l . Tables of coordinates,

thermal parameters, bond distances and angles, least-squares planes equations, and observed and calculated structure factors are available from the authors on request. A c k n o w l e d g e m e n t s - - T h i s work was supported by grants for the major research project from the State Science and Technology Commission and the National Natural Science Foundation of China, and by research R&D No. 123-3417-2201 by the Malaysian Government and Universiti Sains Malaysia.

Metal complexes containing NS donor ligands

2271

Table 6. Comparison of the torsion angle in free and coordinated ligand

Torsion angle (°)

Free ligand 23

Coordinated ligand (present work)

179.8 180.0 178.7 1.3 179.9 0.1 178.0 82.4

2.2 179.2 0.8 178.1 1.5 179.5 76.3 0.8

C (3)---C(2)--N (2)--N(I) C(2)--N(2)--N(1)--C(1) N(2)--N(1)--C(1)--S(1) N(2)--N(1)--C(1)--S(2) N(1)--C(1)--S(2)--C(11) S(1)--C(1)--S(2)--C(11) C(1)--S(2)--C(11)--C(12) S(2)--C(11)--C(12)--C(13)

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