Chelates of nickel(I1) and copper(I1) with tridentate Schiff base formed by the condensation of S-benzyldithiocarbazate with benzoin

M. T. H. TARAFDER A N D M. AKBAR ALI Rajshrrhi Utlilvrsity, Rajslrnl~i, Bnt~gl(irles/r

Received August 3, 1977

M. T. H. TARAFDER and M. AKBAR ALI. Can. J. Chem. 56, 2000 (1978). New complexes with the Schiff base ligand derived from S-benzyldithiocarbazate

(NH2-NH-CSSCH2C,H5) have been prepared and characterized by elemental analyses, magnetic, conductometric, ir, and electronic spectral studies. The tridentate ONS Schiff base S-benzyl-~-N-(phenyl,phenylhydroxymethyl)methylenedithiocarbazate gave mono-ligand complexes with Ni(I1) and Cu(I1) having the general formula [MligandX] (M = Ni(I1) and Cu(l1); X = NO,, C1, Br, NCS). A proposed square-planar structure for the nickel complexes is supported by magnetic and spectral data. A square-planar struct~ire is also suggested for Cu(1l) complexes. The ir results give evidence of the different bondings present in the complexes.

M. T. H. TARAFDER et M. AKBAR ALI. Can. J. Chem. 56,2000 (1978). On a prepare de nouveaux con~plexes ~~til isant un ligand comportant une base de SchiK

provenant du S-benzyldithiocarbazate (NH2-NH-CSSCH2C6H5) et on les a caracterises par des analyses elementaires, magnetiques et conductinietriques et par des etudes de spectres ir et electroniques. La base de Schiff ONS tridentate S-benzyl-p-N-(pheny1,phenyl-hydroxy- n~ethyl)methylenedithiocarbazate reagit avec le Ni(l1) et le Cu(l1) pour conduire a des com- plexes ne comportant qu'un ligand ayant des formules generales [MligandX] (M = Ni(I1) et Cu(l1); X = NO,, CI, Br, NCS). La structure plan carre proposee pour 1es complexes du nickel est en accord avec les donnees magnetiques et spectrales. O n suggere aussi I'existence d'une structure plan carre pour les conlplexes du Cu(1l). L'infrarouge indique les diffirents types de liaisons q ~ ~ i sont presents dans ces complexes.

[Traduit par le journal]

Introduction and Cu(I1)) salt solution (0.01 mol) in hot absolute alcohol -. . . - - . - -. - . . - . . (20 n i l ) . ' ~ h e resulting mixture was kept under rellux for 3 h.

Nulnerous lnetal complexes of Schiff base deriva- The precipitate which settled was filtered, washed several tives havine nitroeen and s u l ~ h u r as donors have times with hot absolute alcohol so a s to remove unreacted been investigated ixtensively (1). However detailed Schiff base, and dried ill cncl,o over PZ05. The Schiff base

stlldies of schiff bases derived fro,,, ~ - b ~ ~ ~ ~ l d i ~ h i ~ - yielded conlplexes having a stoichiotnetry of I : 1 metal to ligand. The complexes isolated were analyzed as follows.

carbazate having Oxygen, and as 1 , A,m/, calcd. for [Ni(ONS)NO,]: C 51.58, H 3.7, N 8.2, M donors are lacking. We present a magnetic and I 1.47, s 12.5; found: c 51.3, H 3.4, N 8.0, M 11.3, S 12.1. spectroscopic study of Ni(I1) and Cu(I1) complexes 2. Atlal. calcd. for [Ni(ONS)CI]: C 54.4, H 3.9, N 5.77, M of a ONS Schiff base, i.e., S-benzyl-P-N-(pheny],- 12.09, S 13.18; found: C 54.2, H 3.6, N 5.62, M 12.1, S 12.7.

phenylhydroxymethyl)methylenedithiocarbazate 3. Atlnl. calcd. for [Ni(ONS)Br]: C 49.8, H 3.58, N 5.28, M 11.08. S 12.08: f o ~ ~ n d : C49.7, H 3.3, N 5.1, M 11.0, S 11.7.

derived from S-benzyldithiocarbazate.

Experimental A11 the chemicals used were reagent grade and were used

without further purification. Preparation of the Schiff base, S-benzyl-~-N-(phenyl,phenylhydroxymethyl)methylenedithio- carbazate (1): this compound deposited as yellow crystals after solutions containing S-benzyldithiocarbazate (0.1 mol) in 50 ml hot absolute alcohol and benzoin (0.1 niol) in hot alcohol (50 ml) had been heated on the steam bath for a few minutes, m p 205°C. Anal. calcd. for C22H2001\JZS2: C67.33, H 5 . 1 , N 7 . 1 , S 16.3;found: C67.1, H 5 .0 ,N6.8 , S 15.8. Preparation of complexes: the ONS ligand (0.01 mol) in hot absolute alcohol (300 ml) was mixed with metal (Ni(I1)

4. Atrol. calcd. for [Ni(ONS)NCS]: C 54.3, H 3.7, N 8.08, M 11.5, S 18.9; found: C 54.1, H 3.4, N 7.7, M 11.38, S 18.5. 5. Atrnl. calcd. for [Cu(ONS)NO,]: C 51.1, H 3.67, N 8.1, M 12.2, S 12.3: found: C 50.8, H 3.5, N 7.9, M 12.1, S 11.9. 6. Atrrrl. calcd. for [Cu(ONS)CI]: C 58.87, H 3.8, N 5.7, M 12.96, S 13.05; found: C 53.65, H 3.5, N 5.35, M 11.8, S 12.7. 7. Atinl. calcd. for [Cu(ONS)Br] : C 49.39, H 3.5, N 5.2, M 11.8 ,S11.97;found:C49.1 ,H3.3 ,N 5.01,M11.75,S 11.45. The preparation of [Cu(ONS)NCS] was ~~nsuccessful.

S~)ectt'rr The solid-state electronic spectra of the conlplexes were

obtained in a Carl Zeiss PMQ I1 spectrophotometer with a solid-reflectance attachnlent using MgO as the calibrant. The ir spectral data have been recorded in the range 4000-200 cnl-I, with Perkin-Elmer 457 and 225 spectrophotometers, as Nujol nulls between KBr or as KBr discs. The far ir spectra (400-200 cm-') were recorded as Nujol mulls between polyethylene sheets. The electrical co~lductance nleasurerllents were made at room tenlperature with a conductivity bridge type E 756613 of the M.E.L. Equipment Company Limited,

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TARAFDER AND ALI

TABLE 1. Infrared frequencies (cm-I) of the Ni(l1) and Cu(l1) complexes and thei~ assignments*

Complex v(C=N) v(M-N) v(C=S) v(M-S) v(M-0) v(M-X)

I . [Ni(ONS)NO,] 1510 510 950 395 S 550 S 2. [NI(ONS)CI] 1500 530 962 395 S 545 260 3. [Ni(ONS)Br] 1495 51 5 960 396 S 540 200 4. [Ni(ONS)NCS] 1515 570 955 394 S 550 S 5. [Cu(ONS)NO,] 1500 500 955 3 60 470 6. [Cu(ONS)CI] 1505 490 S 965 365 485 3 20 7. [CLI(ONS)B~] 1505 480 964 3 70 490 220

*S = strong

Sussex, using a Griffin and George NO-S75-915/010 con- ductiv~ty cell with platinum black electrode. Millimolar solutions of the metal-chelates were used. Magnetic suscep- tibility measurements were made on solld samples at room temperature by the Faraday method. All the values were corrected for diamagnetism according to the method of Selwood (2).

Atinlysis Metal analyses were made by means of EDTA t~tration aftel

decomposing the coniplexes w~th a nilxture of n ~ t r ~ c , sulphuric, I and perchloric ac~ds. Carbon-hydrogen-nitrogen analyses

were made Llslng ~liicroanalyt~cal techniques. The sulphur analysis was carried out according to the method described

1 by Vogel (3).

I Results and Discussion

The Schiff base ONS (I) was formed by the con- densation of S-benzyldithiocasbazate with benzoin

I With Ni(1l) and Cu(I1) mono-ligand nitrate, I chloride, bromide, and thiocyanate complexes have , been assigned the structures [MligandX] on the basis

of molecular conductivities and is absorptions (Table 1). The conductance measurements were done in nitrobenzene medium in which the metal chelates behaved as non-electrolytes because they have very low conductance values, 0-2.5 and 0-2.1 Q-' cm2 mol-' for the nickel and copper complexes, respec- tively, suggesting anion coordination to the metal ion which is also supported by the ir absorptions of the complexes.

The ONS Schiff base S-benzyl-j3-N-(pheny1,phenyl- hydroxymethyl)methylenedithiocarbazate acts as a tridentate ligand coordinating the metal ion via the j3-n~trogen atom, th~oketo sulphur, and the oxygen of the hydroxyl group as evident from ir spectral data (Table I). The C=N stretching vibration in the free ONS Sch~ff base occurs at ca. 1535 cm-' (4) but on complexation the bands in all the complexes are shifted towards the lower frequency regions (Table I). This lowering of C=N stretching mode on complexation may tentatively be attributed to a

j lowering of the C=N bond order as a result of M-N bond formation ( 5 ) as evident from the appearance ' of v(Ni-N) and v(Cu-N) bonds at 510-570 (6)

! and 480-500 cm-' (7) respect~vely (Table I). The

a-nitrogen atom is not bonded with the ~iietal a s v(N-H) band (ca. 3080 cm-' (8)) of the free ligand does not suffer any shift in the complexes. The ir spectruin of the uncomplexed ligand shows v(C=S) at ca. 1000 cm-' ; it undergoes considerable shift towards lower frequencies in the metal complexes (Table 1). This negative shift of v(C=S) bands lnay be taken as an indication of coordination by the thioketo sulphur. This shifting may be due to a lowering of C=S bond order as a result of M-S bond formation.

The far ir spectra of the metal complexes were measured in order to locate metal-sulphur stretching frequencies. The appearance of v(Ni-S) and v(Cu-S) bands at ca. 395 cm-' and 36@370 cm-' is indicative of the presence of Ni-S (9) and Cu-S (10) bonds in the nickel and copper complexes. Ali and Livingstonc (1) have established in the cases of S-methyldithiocarbazate and its various Schiff bases that the thioether sulphur does not coordinate to the metal ion. The disappearance of v(0-H) observed in the free ligand around 3300 cm-' (1 1) clearly indicates the loss of the proton from 0-H on coordination and formation of a new bond between metal and oxygen as evident from ir spectral data. The absorptions in the region 540-550 and 470-490 cm-' (Table 1) lnay be due t o Ni-0 (12) and Cu-0 (7) linkages in the nickel and copper com- plexes respectively.Comp1ex 1 gives ir bands at 1485 and 1260 cm-' indicative that NO, occupies one of the stereochemical sites of Ni(I1) (13). The complexes [Ni(ONS)X](X = C1,Br) show ir bands a t ca. 260 and 200 cm- ' corresponding to v(Ni-C1) a n d v(Ni-Br) vibrations respectively. The complex [Ni(ONS)NCS] has thiocyanate v(C-N) absorption a t 2105 cm-I suggesting the presence of terminal N-bonded thio- cyanate (14). [Cu(ONS)NO,] gives ir bands at 1480 and 1255 cm-' characteristic of coordinated NO,. The complexes 6 and 7 display v(Cu-CI) and v(Cu-Br) a t 320 and 220 cm-I respectively.

The brown [Ni(ONS)X] complexes are low-spin type (diamagnetic) suggesting square-planar struc- ture. The three coordination positions a re occupied

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2002 CAN. J . CHEM. VOL. 36, 1978

b y t h e O N S sequence a n d t h e fou r th coord ina t ion site o f t h e Ni(I1) ion is occupied by e i ther NO, , CI, Br, o r NCS. T h e e lec t ronic spect ra o f t h e meta l complexes provide evidence regarding thei r struc- tures . T h e spect ra or t h e nickel complexes give an envelope wi th a shou lde r a t 20 000 - 20 100 c m - I which co r re sponds to 'A2 , + ' A l g t rans i t ion (15). T h e o t h e r t w o 6 d t rans i t ions , 'B,, + ' A , , a n d ' E , + ' A , , (15), in t h e present cases were no t observed b u t p robab ly were h idden b y t h e cha rge t ransfer b a n d . T h e green pa ramagne t i c c o p p e r com- plexes [Cu(ONS)X] yield magnet ic m o m e n t (1.8-1.87 B M ) co r re spond ing t o o n e unpaired e lec t ron. T h e c o p p e r c o ~ n p l e x e s a r e said t o possess squa re -p lana r s t e reoche~n i s t ry since t h e c o p p e r ion h a s been f o u n d t o be reluctant t o t a k e u p a regular te t rahedral geomet ry (16). T h e e lec t ronic spect ra o f t h e c o m - plexes give t h e t w o b a n d s at 16 000 - 16 100 c m - I ('A,, + 'B,,) a n d 19 000 - 19 600 c m - ' ('E,, +

'B1 , ) which co r re sponds to t h e squa re -p lana r stereochelnistry (1 7, 18).

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