Inorganic Chemistry, Vol. 17, No. 1, 1978 191
Notes An x-ray crystallographic study of the cesium salt of the di-p-sulfido complex has been made and the structure is as i l l ~ s t r a t e d . This ~ is similar to that previously determined for
r
0
0
12-
[MO~O~(C~O~)~(H~O)~]~-.’~ Each oxalate ligand occupies coordination sites cis and trans to the terminal oxo ligand, and the Mo-O(oxa1ate) bond lengths are all identical. Assuming the same structure is retained in solution, complex formation involves replacement of an equatorial H 2 0 ligand by NCS-. The possibility of intramolecular rearrangement of the Mo coordination spheres in solution has been noted following I3C N M R experiments (see note, ref 3). There is no evidence as yet for such changes affecting interpretation of kinetic data, e.g., ref 3. Substitution of H20s cis to the terminal oxo ligands (probably by an Id mechanism) has been suggested for the aquo ions V02+, and Ti02+l 1 and would seem to provide a self-consistent interpretation with that for [ M O ~ O ~ ( C ~ O ~ ) ~ (ifHthe ~O H20’s ) ~ ] of ~ -the latter also occupy cis positions. In other words small amounts of the trans form may be present in solution but do not obviously contribute to the kinetics. Extreme caution is required here, however. Although equilibrium constants for 1:l complexing to both the di-p-sulfido and di-p-oxo complexes are of similar magnitude (see above), rate constants kf and k b are more rapid, both by a factor of ca. 40, in the case of the di-p-sulfido complex. These differences originate largely in the enthalpies of activation which are more favorable by 3.7 kcal mol-] ( k f ) and 5.0 kcal mol-’ (kb) for the di-p-sulfido complex, Table 11. The labilizing effect of S as compared to 0 bridges can be accounted for in terms of different bonding characteristics of these ligands. Spivack and Dori2have observed that the sulfido bridges in the di-p-sulfido aquo ion Mo2Sz022+ are extremely inert to cleavage even in concentrated acid. The di-p-oxo Mo203+aquo ion on the other hand undergoes bridge cleavage in HCl > 7 M to yield mononuclear complexes. This different behavior is attributable to strong Mo-S bonding which reduces the availability of electron pairs on the sulfur for protonation as a preliminary to bridge cleavage. The same Mo-S bonding is presumably responsible for the labilizing effect identified in this study. The Mo(V) atoms cannot donate P electrons to the S ligands since metal-metal bond formation4has already accounted for the single d electron on each metal. The strong Mo-S bonding must therefore originate from u and possibly P ligand to metal donations. The former would be expected to give a trans labilizing effect which is possibly enhanced (i.e., atoms drawn closer together) by the P bonding. Since the H20’s in each Mo coordination sphere of [Mo2S202(C204)2(H20)2]2are trans to one bridging sulfide and cis to the other, it is not possible to specify the position being labilized. Acknowledgment. F.A.A. and T.S. are grateful to the U.K. Science Research Council for postgraduate and postdoctoral support.
(6) (7) (8) (9) (10) (1 1)
G. G. Rao and M. Swyanarayana, Z . Anal. Chem., 168, 177 (1959). J. E. Crooks, M. S. Zetter, and P. A. Tregloan, J . Phys. E, 3,73 (1970). R. H. Moore and R. K. Zeigler, Los Alamos Report LA2367, 1959. W. S. McDonald, University of Leeds, unpublished work. F. A. Cotton and S. H. Morehouse, Inorg. Chem., 4, 1380 (1965). G. A. K. Thompson, R. S. Taylor, and A. G. Sykes, Znorg. Chem., 16, 2880 (1977).
Contribution from the Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700032, India
Metal Complexes of Sulfur-Nitrogen Chelating Agents. 7. N,N’-Ethylenebis( methyl 2-amino-1-cyclopentenedithiocarboxylate)Complexes of Ni(II), Pd(II), Co(II), and Cu(I1) S. K. Mondal, D. S.Joardar, and K. Nag*
Received December 13, 1976
Investigations on stereochemical nonrigidity in tetracoordinated metal(I1) chelates from the @-difunctional ligand systems I and I1 in terms of planar F= tetrahedral equilibrium
R’p;}a R2
I X = Y = NR, 0, S, Se X = O ; Y = NR, S X = S; Y = NR
R2
I1
x = 0 , s; Y = noncoordinating ring substituents
in noncoordinating solvents have been the subject matter of great interest.’ A comparative study with his(@-aminothione) and bis(@-ketoamine)complexes revealed2 that sulfur exerts a relatively greater stabilization of planar stereochemistry than does oxygen. In connection with our studies on NiN2S2 complexes from 2-amino-1-cyclopentenedithiocarboxylicacid, its N-ethyl derivative, and its S-alkyl ester we have o b s e r ~ e d ~ - ~ that only the spin-paired species exist both in the solid state and in solution. It is interesting to note that although extensive studies have been made on metal complexes derived from the related tetradentate N202 donors,6similar studies with corresponding Registry No. NCS-, 302-04-5; [Mo2S2O2(C204)2(H20)~I2-, NzS2 donor sets are scanty. The fact that N,N’-ethylene641 30-27-4; N a , [ M ~ ~ O , ( ~ - c y s t )64091-82-3; ~], Na2[Mo202S2(~bis(salicylideniminato)cobalt(II) and N,N’-ethylenebis(acecyst),], 3091 7-53-4; CS~[MO~S~O~(C~O~)~(H~O)~], 6409 1-8 1-2. tylacetoniminato)cobalt(II) chelates in the presence of DMF, References and Notes DMSO, and some other Lewis bases reversibly add molecular (1) R. C. Bray and J. C. Swann, Struct. Bonding (Berhn), 11, 107 (1972). 0xygen~9~ provided much stimulus for their investigation as (2) B. Spivack and 2. Dori, J . Chem. Sac., Chem. Commun., 909 (1973). model oxygen carriers.’ It is expected that the thio analogues (3) G. R. Cayley and A. G. Sykes, Znorg. Chem., 15, 2882 (1976). (4) A. Kay and P C. H. Mitchell, J. Chem. Sac. A , 2421 (1970); B. Spivack may also have similar interesting features. Indeed quite and 2.Dori, Chem. Commun., 1416 (1970). recently metal(I1) chelates of N,N’-ethylenebis(monothi0(5) W. E. Newton and J. W. McDonald, “Proceedings of the Second Inacetylacetonimine)1° and N,N’-ethylenebis(0-mercaptoternational Conference on the Chemistry and Uses of Molybdenum”, Oxford, England, 1976, p 25; J . Less-Common Met. (1977). benzaldiimine)’’Il2have been investigated. We wish to report 0020-1669/78/ 1 3 17-01 91 $01 .OO/O
0 1978 American Chemical Society
192 Inorganic Chemistry, Vol. 17, No. 1, 1978
Notes
Table I. Analytical Data %C Compd C16H22N2S4Ni
C16H2,N2S4Pd C,,H,,N2S4Co C,,H2,N,S4~
--___.
%H
%N -___-_
Calcd
Found
Calcd
Found
Calcd
Found
Yellow Green Orange Maroon Red
51.61 44.78 40.30 44.75 44.29
51.45 44.55 40.46 44.63 44.50
6.45 5.13 4.97 5.12 5.07
6.55 5.20 4.70 4.98 5.00
7.52 6.53 5.88 6.52 6.46
7.77 6.58 5.77 6.45 6.35
____
C16H24N2S4
-
Color
--__
%M -________ Calcd Found -
13.70 22.33 13.74 14.65
13.80 22.25 13.94 14.58
Table 11. Infrared Data Ligand
Ni L
Pd L
c uL
c oL
15 80 (s) 1565 (s) 1405 (w) 1320 (m) 1302 (m) 1260 (s) 1230 (m) 1210 (w) 1030 (w) 1000 (m) 960 (w) 940 (m) 910 (s)
1560 (s)
1562 (s)
1570 (s)
1565 (s)
u(C-C)
1420 (w) 1310 (m)
1300 (w)
1420 (w) 1302 (m)
1415 (w) 1300 (m)
u(C'" C) v(SCHJ
1280 (s) 1212 (m)
1275 (m) 1210 (w)
1280 (s) 1210 (m)
1280 (s) 1210 (w)
u(CLN)
1085 (w) 1010 (w) 975 (w) 940 (m) 910 (s)
1070 (w) 1005 (w) 963 (w) 940 (w) 903 (s)
1070 (m)
1070 (m) 1002 (w) 965 (w) 935 (m) 900 (s)
820 (m) 760 (m) 730 (m) 5 80 (w) 430 (w)
820 (w) 790 (w) 720 (w) 5 7 0 (m) 5 2 0 (w, b) 450 (w)
720 (w) 570 (m) 515 (w) 450 (sh)
here that another interesting series of metal(I1) chelates can be readily generated from N,N'-ethylenebis(methy1 2amino- 1-cyclopentenedithiocarboxylate). Experimental Section T h e ligand was prepared according to Bordis et a1.l' and was purified by recrystallizing twice from benzene (mp 205-207 "C (lit. 210-213 "C)). Preparation of Metal Chelates. Typically the Ni(I1) chelate was obtained by slowly adding a methanolic solution (30 mL) of hydrated nickel chloride ( 2 mmol) and 2 g of ammonium acetate to a solution of freshly recrystallized ligand (2 mmol) in hot benzene (50 mL). The solution was refluxed for 1 h during which shining crystals began to separate. After cooling of the mixture to room temperature, the compound was filtered and washed first with a small portion of benzene and then with methanol and water. For preparing the Pd(I1) chelate potassium tetrachloropalladate and for Co(I1) and Cu(I1) chelates their acetates in methanol were used. In the case of Co(II), complex solvents were deaerated and the preparation was carried out in nitrogen atmosphere. All compounds were recrystallized from chloroform and the yields obtained were in the range 50-70%. Analysis. Carbon, hydrogen, and nitrogen were analyzed by Mrs. C. Dutta in the Microanalytical Laboratory of this institute and the metals were estimated by the usual procedures.14 Physical Measurements. The electronic spectra of the complexes in solution and in Nujol mull were recorded in a Spectro MOM 201 spectrophotometer. T h e infrared spectra were recorded with a Beckman IR-20 spectrometer in the range 4000-400 cm-' in Nujol mull. The 'H N M R spectra of the ligand in CDC13 and the Ni(I1) and Pd(I1) chelates in DMSO-& were recorded in a Varian T-60 spectrometer using T M S as the internal standard. The mass spectrum of t h e Ni(I1) chelate was recorded in a Varian M A T S,M1 mass spectrometer a t 70 eV (the sample was heated to 220 "C). Conductivity measurements were performed in a Philips P R 9500 conductance bridge. Magnetic moment measurements were made on a Gouy balance. Thermal analyses were carried out with a M O M Derivatograph and powder diffraction patterns were photographed with a Nonius Guinier camera using C u Kcu radiation.
Results and Discussion The analytical data of the compounds are shown in Table I which indicates the formation of 1:l chelates. The none-
965 (w) 935 (m) 902 (s) 890 (s) 820 (w) 790 (w) 720 (w) 565 (m) 520 (w) 440 (b)
Assignments
+ v(C--N)
+ u(C-S)
CH, rocking v,,,,(CSSCH,
815 (w) 790 (w) 720 (w)
u(c-
5 2 0 (w) 450 (b)
1
S)
v(M-N)
Table 111. Proton Magnetic Resonance Dataa
Compd Ligandb Ni Lc Pd Lc
-CH,3,5-CH, CH,-
4-CH, S-CH, 1.82 1.80 1.85
2.58
2.78 2.53d 2.52d
a Chemical shifts are in ppm (6).
In CDC1. Center of gravity of broad complex multiplet.
3.62 3.22 3.20
Hydrogenbonded proton -11.5
In DMSO-d,.
lectrolytic behavior of these compounds is evident from their low A M values (- 1 mho cm2 mol-') in nitrobenzene. Molecular weight determinations (by depression of freezing point method) in nitrobenzene indicate the monomeric composition of the Ni(I1) and Cu(I1) chelates.l5 Further confirmation of the monomeric composition of the Ni(I1) chelate is obtained from its mass spectral data which show that the molecular ions m/e 428 (I = 100) and 430 ( I = 6 5 ) derived from 58Niand 60Niisotopes form the most intense peaks. The fragmentation pattern of the compound is rather complicated but it is certain that initial fragmentations take place only at the peripheral parts of the molecule since the presence of the positive ions devoid of a CH3 group ( m / e 413, I = 8), a SCH3 group ( m / e 383, I = 5; mle 381, I = 13), and two SCH3groups (m/e 333, I = 8) could be detected. The Ni(I1) and Pd(I1) chelates are diamagnetic. The room-temperature magnetic moment of the Cu(I1) complex is 1.93 pB and that of Co(11) chelate is 2.02 bB. These values suggest square-planar configuration of the chelates although tetragonal distortion cannot be entirely ruled out. However, the powder diffraction pattern of the metal chelates shows that they are isomorphic with the Pd(I1) complex which strongly suggests a square-planar configuration. Table I1 shows the characteristic infrared frequencies of the ligand and its complexes. In the ligand no band due to S-H stretching in the region 2500 cm-' could be observed and N-H stretching appears only as a very weak and broad band at ca.
Inorganic Chemistry, Vol. 17, No. 1, 1978 193
Notes Table IV. Electronic Spectra
%
log E
Assignment
25 000 31 250 15 380 22 220 30 000 37 310 20410 23 810 32 570 10 530 17 240 21 740 30 120 35 710 1 2 270 20 830 26 310 31 440
4.43 4.34 2.01 3.76 4.29 4.57 2.85 3.89 4.37 1.55 2.70 3.77 4.11 4.29 1.87 3.20 4.18 4.47
d-d CT L-L* L-L* d-d CT L-L* d-d d-d CT L-L* LL* d-d CT L-L* L-L*
Compda Ligand NiL
Pd L coL
cu L
In chloroform.
3200 cm-'. This indicates that the ligand has the hydrogen-bonded structure 111. The 'H NMR spectrum of the
S'C H 3
SC H 3
Ill
ligand (shown in Table 111) confirms the above structure. The assignment of the infrared bands has been made in accordance with our previous ~ t u d i e s . ~It- ~may be noted that the two strong bands at 1580 and 1565 cm-l in the ligand get collapsed to a single band in the chelates which appears to be consistent with the assumption that there is more delocalization of the double bonds in the chelates compared to that in the ligand. The presence of discrete C=C or C=N bonds can be ruled out on the grounds that these vibrations appear at considerably higher energy range, ca. 1650 cm-'. Indeed a similar observation made in tetradentate thioiminato Schiff base complexes has been rationalized by invoking d.rr-d.rr interaction of the sulfur donors with metal ions.1° A comparison of the 'H N M R spectral data of the ligand and its Ni(I1) and Pd(I1) chelates (Table 111) reveals that 4-CH2 protons are least affected due to chelation. On the other hand, the -CH2CH2- bridge and SCH3 and 3,5-CH2 protons have undergone considerable upfield shift due to chelation. In fact, SCH3 and 3,5-CH2protons get very much overlapped. The stereochemical rigidity in the coplanar form (IV) coupled
/ SCH,
SC H3
IV
with electron flow from the metal onto the chelate ring (T back-bonding) induces more electron delocalization which in effect causes better shielding of the protons in the metal chelates. The electronic spectral features of the compounds are shown in Table IV. In the absence of detailed MO calculation it is difficult for the most part to make definite assignments of the transitions. In the Ni(I1) and Pd(I1) chelates the bands
-
at 15380 and 20410 cm-' respectively are due to a d-d transition which may be due to either lAlg 1A2,'4J6or 'A, 'BI, transition." Although the usual energy range for this band in [NiN2S2]chromophores is 18 000 cm-', however, in both bi~(bidentate)~-~ and tetradentatelo [NiN2S2]complexes, where there is extensive delocalization in the chelate ring, this band is observed in the range 15 000-16 500 cm-' and they behave more like [NiS4] chromophores in the spectrochemical series. Crystal field stabilization energies A, evaluated from the relation E ( v ) = A, - 35F4 (F4= 80 cm-') are 18 180 and 22 510 cm-' respectively for the Ni(I1) and Pd(I1) chelates. It may be noted that the energy sequence of the charge transfer band in these two compounds is Ni(I1) < Pd(I1) which acL charge transfer. cording to GrayI8 may be assigned to M The electronic spectrum of the Ni(I1) chelate has been examined in the solid state (mull) and in a number of coordinating solvents, e.g., pyridine, DMSO, DMF, etc., and it shows identical spectral features. Thus tetragonal distortion in the solid or the expansion of coordination number through solvent participation appears unlikely. This behavior is identical with malononitriledithiolato type complexes which possess remarkably stable square-planar configuration.18 The electronic spectrum of the Co(I1) complex shows two bands due to d-d transition and occurs almost in the same energy observed in the corresponding tetradentate thioiminato Schiff base complexes.1° Chloroform solution of the Co(I1) complex apparently reacts with oxygen since the spectrum slowly changes with time. In the Cu(I1) chelate d-d transition occurs at rather relatively low energy (12 270 cm-l)19 compared with those normally observed in square-planar complexes.20 However, in several [CuN2S2]square-planar chelates this band has been observed in the range 13 000-14000 cm-'.'O The stable square-planar configurationsin the metal chelates are also apparent from their high thermal stability. For example, the Ni(I1) complex begins to decompose above 280 OC and the Co(I1) complex at 220 OC.
-
-
Acknowledgment. Thanks are due to Dr. D. R. Chowdhury of Cogswell Polytechnic Institute, Rensselaer, Troy, N.Y., for 'H N M R spectra and Dr. T. Seshadri of the Institut fur Anorganischen Chemie, Karlsruhe, for mass spectra. D.S.J. is indebted to CSIR, India, for awarding a PDF. Registry No. Ligand, 34281-33-9; N i L , 63665-43-0; PdL, 63625-65-0; COL,63641-42-9; CUL,63665-42-9.
References and Notes (1) (2) (3) (4) (5)
R. H. Holm and M. J. O'connor, Prog. Inorg. Chem., 14, 241 (1971). D. H. Gerlach and R. H. Holm, J . Am. Chem. Soc., 91,3457 (1969). K. Nag and D. S. Joardar, Inorg. Chim. Acta, 14, 133 (1975). K. Nag and D. S . Joardar, Can. J . Chem., 54, 2827 (1976). D. S. Joardar, S. K. Mondal, and K. Nag, Bull. Chem. SOC.Jpn., 50,
1489 (1977). (6) R. H. Holm, G. W. Everett, and A. Chakravorty, Prog. Inorg. Chem., 7, 83 (1966). (7) C. Floriani and F. Calderazzo, J . Chem. SOC.A, 946 (1969). (8) A. L. Crumbliss and F. Basolo, J . Am. Chem. Soc., 92, 55 (1970). (9) F. Basolo, B. M. Hoffman, and J. A. Ibers, Acc. Chem. Res., 8,384 (1975). (10) P. R. Blum, R. M. C. Wei, and S. E. Cummings, Inorg. Chem., 13,450 (1974). (11) I. Bertini, L. Sacconi, and G. P. Speroni, Inorg. Chem., 11, 1323 (1972). (12) M. F. Corrigan and B. 0. West, Aust. J . Chem., 29, 1413 (1976). (13) B. BordBs, P. Sohar, G. Matolcsy, and P. Berencsi, J . Org. Chem., 37, 1727 (1972). (14) Nickel and palladium were estimated gravimetrically as their di-
(15) (16) (17) (18) (19) (20)
methylglyoximates, cobalt was weighed as CoS04, and copper was volumetrically determined by titrating with EDTA using PAN as the indicator. Molecular weight: for the Ni(1I) complex, found 398, calcd 429; for the Cu(I1) complex, found 385, calcd 434.5. C. Furlani and M. L. Luciani, Inorg. Chem., 7, 1586 (1968). B. G. Warden, E. Billig, and H. B. Gray, Inorg. Chem., 5, 78 (1966). H. B. Gray, Transition Met. Chem., 1, 239 (1965). This band arises probably due to 2BI, ZAl transition. B. J. Hathaway, Coord. Chem. Rev., 5, 143 f1970).
-
