Transition Met. Chem. 9, 469-473 (1984) Tetrafluoroaminechromate(III) anion complexes 469

Systematic Synthesis and Characterization of the Derivative Complexes of the Tetrafluoroaminechromate(III) Anions. - Crystal Structure of the (en-H2)[CrV4(en)]C1

Carmen Diaz, Alexandre Segui and Joan Ribas

Departament de Qufmica Inorg~nica. Facultat de Qufmica. Universitat de Barcelona, Barcelona. Spain

Xavier Solans and Manuel Font-Altaba

Departament de Cristallograffa. Facultat de Geologia. Universitat de Barcelona, Barcelona, Spain

Andreu Solans and Jaume Casab6*

Departament de Quimica Inorg~nica. Facultat de Ci~ncies. Universitat Aut6noma de Barcelona, Bellaterra, Barcelona, Spain

Summary

The new complexes (aa-Hz)[CrF4(aa)]Cl, where aa = ethyl- enediamine, 1,2-diaminopropane or 1,2-diaminocyclohexane, have been systematically synthesized and characterized. The crystal structure of (en-H2)[CrF4(en)]C1 (en = ethylene- diamine) has been resolved indicating that the four fluorine atoms are ligands and the chloride is ionic. The cation is the diprotonated ethylenediamine ligand. Synthesis of the analog- ous complex with 1,3-diaminopropane (tn) failed. The hy- drolysis of these complexes with concentrated HBr give com- pounds of formula [CrF2(HzO)z(aa)]Br, which upon solid phase heating yield the dehydrated [CrFzBr(HzO)(aa)].

Introduction

In the last few years we have studied the synthesis, charac- terization and solid state kinetics of trans-[CrF(HzO)(aa)2] z+ complexes (aa = ethylenediamine, en; 1,3-diaminopropane, tn and 1,2-diaminopropane, pn) (1-1~ It seemed of interest to carry out a similar study with mixed amines. Only two series of mixed amine complexes of chromium(III) have been described: trans-[CrF(HzO)(en)(pn)] 2+ and trans-[CrF- (HzO)(pn)(tn)]2+ (11 12).

These mixed amine complexes were obtained from [CrF2(H20)z(pn)]Br01-1z) which is produced from the doubly complexed salt [CrF4(pn)2][CrF4(pn)] by the reaction of HBr on the anionic part, according to the Dahme method (13). One of the objectives of this work is to systematize and to improve this method and apply it to the amines, pn, tn and chxn. We describe the single crystal x-ray structure determination of the compound with ethylenediamine as ligand. The hydrolysis of these single complexes in concentrated HBr, was studied also in order to give the desired [CrF2(HzO)z(aa)]Br salt, the pre- cursor to the possible mixed complex salts.

Experimental

New compounds

(en-H2)[CrF4(en)]Cl (1)

A solution of CrC13 �9 6 H20 (32 g, 0.20 tool) in/420 (40 cm 3) was placed in a polyethylene beaker and mixed with a 48% solution of HF (26g, 0.65mol). The resulting solution was stirred in an ice-bath for 5min and aqueous 98% ethyl-

* Author to whom all correspondence should be addressed.

enediamine (28.6 g, 0.476 mol) was added slowly. The mixture was subsequently heated for 2.5 h on a steam bath to complete the reaction. Finally, MeOH (200 cm 3) was added to the mix- ture, with stirring in an ice-bath. The blue precipitate was filtered, washed with EtOH until the filtrate was no longer red. (The red is due to residual [CrF2(en)2]+). Yield: 26g, 78%.

The crude material was dissolved in H20 (25 cm 3) at room temperature and the solution was filtered to remove a green undissolved material. A precipitate of blue crystals formed when MeOH (90 cm s) was added to the filtrate. The crystals were collected, washed with EtOH, Me2CO, Et20 and air- dried. Yield: 20g, 77%. (Found: C, 16.9; H, 6.4; C1, 12.4; N, 19.5. C4H18C1N4CrF4 calcd.: C, 16.8; H, 6,4; C1, 12.4; N, 19.6%).

(chxn-H2)[CrF4(chxn)]Cl (2)

This complex was prepared by the method described above for the complex (1) using aqueous 85% 1,2-diaminocyclo- hexane (64 g, 0.477 mol). Yield: 89%. The product was recrys- tallized from H20 after addition of MeOH : Me2CO 1 : 1. The powder so obtained is blue. Yield: 73%. (Found: C, 36.9; N, 14.3; H, 7.8; C1, 9.0. C12H30N4C1CrF4 calcd.: C, 36.6; H, 7.7; N, 14.2; C1, 9.0%).

(pn-H2)lCrF4(pn)]Cl (3)

The procedure used for corresponding en and chxn com- pounds was employed, using aqueous 97% 1,2-diaminop- ropane (35.6 g, 0.466 mol). In this case the precipitation was carried out by the addition of absolute EtOH to the filtrate. Yield: 69%.

The crude material (6 g) was dissolved in H20 (2 cm 3) at room temperature and the solution filtered to remove the undissolved material. A blue resin was formed when a Me2CO:Et20 (1:2) mixture was added to the filtrate. By stirring it with absolute EtOH for 10 rain a t -20 ~ the resin was converted into a blue dust precipitate. It was cooled and washed with EtOH, MezCO, Et20 and air-dried. Yield : 60%. (Found: C, 23.2; N, 17.9; H, 7.2; C1, 11.4. C6HzzC1N4CrF 4 calcd.: C, 23.0; N, 17.9; H, 7.1; C1, 11.3%).

All similar attempts to develop a suitable synthetic method for the preparation of (tn-H2)[CrF4(tn)]C1 failed. When MeOH, Me2CO, EtOH or mixtures of these solvents with Et20 were added to the blue solution a blue resin always

�9 Verlag Chemie GmbH, D-6940 Weinheim, 1984 0340-4285/84/1212-0469502.50/0

470 C. Diaz, A. Segui, J. Ribas, X. Solans, M. Font-Altaba, A. Solans and J. Casab6 Transition Met. Chem. 9, 469-473 (1984)

appeared, which could not be broken up. When the resin was dried in vacuo over P2Os, or was slowly heated in an oven, decomposition always set in yielding green products. Attempt- ed precipitations with voluminous cations, eg. Bu4 N+, were unsuccessful.

[CrF2(H20)2(en)]Br (4)

When (1) was placed in a beaker and diluted with a 48% solution of HBr (40 cm3), a white powder, (en-H2)Br2, insolu- ble in aqueous HBr was formed immediately. At the same time, red crystals of [CrF2(H20)2(en)]Br precipitated. Frac- tional recrystallization gave a low yield of product (< 10%). The elemental analysis were not always satisfactory. (Found: C, 9.1; H, 4.8; N, 10.7. C2Ha2N2BrCrF2Oz calcd.: C, 9.1; H, 4.6; N, 10.6%.) This complex was also satisfactorily prepared from [CrF2(en)2][CrF4(en)] by the method of Vaughn and coworkers(lg).

[CrF2Br(H20)(en)] (5)

This product was prepared by heating (4) at 150 ~ over- night. A gradual colour change occurred during this time and the sample lost 6.9% by weight (corresponding to 1 mol of H20: 6.77%). Since the product is very hygroscopic, anhy- drous conditions were utilized for its conservation. Hydrolysis gave the initial compound (4).

The synthesis of the analogous compounds with 1,2- diaminopropane or 1,2-diaminocyclohexane were carried out without problems because the respective (aa-H2)Br2 are very soluble in H20/HBr.

[CrF2(H20)2(chxn)]Br. 1.51-120 (6)

The compound (2) (18 g) wasflaced in a beaker, an aque- ous solution of 48% HBr (45 cm ) was added and the mixture was stirred for l h at room temperature. The resulting blue- purple crystals were collected and washed with 95% EtOH, Me2CO and Et20. (The product should have been violet-pur- ple but it is blue due to the presence of blue Formula: [CrF2Br(HgO)(chxn)]). The latter was removed by hydrolysis. Fw: The crude material (20 g) was dissolved in water (100 cm 3) and System: the solution was filtered. 48% HBr (120 cm 3) was added to the Space group: a : well-stirred filtrate. The mixture was cooled in the freezer and b: the resulting crystals were collected, washed with EtOH, c: Me=CO and EtzO. Yield: 8.4 g, 63%. (Found: C, 20.7; H, 6.2; 13: N, 8.1; Br, 22.9. C6H21N2BrCrF201,5 calcd.: C, 20.8; H, 6.1; V: N, 8.1; Br, 23.0%). 0:

Z: ~.(Mo K~): ~t (Mo K~): [CrF2Br (H20)(chxn)] (7)

This complex was prepared in the same fashion as (5), except that the product (6) was heated at 80-90 ~ for 3 h. During this interval the solid changed from purple to blue and a 13.2% weight loss occurred (12.98% is the weight loss for 2.5 mol of 1-120).

[CrF2(H20)2(pn)]Br" H20 (8)

A solution of (3) (lg) in 48% HBr (2cm 3) was stirred for 30 rain at room temperature. The reaction mixture was cooled subsequently in an ice-bath and the product was collected by filtration, washed with absolute EtOH and MezCO. Yield: 0.5g; 54%: less than for the analogous en and chxn com-

pounds, due to the high solubility of the pn compounds 0~ The complex with pn is very pure. The crude material (0.2 g) was dissolved in a minimum amount of H20. After filtering, the same volume of 48% HBr was added. Yield: 0.06 g; 30%. (Found: C, 12.1; H, 5.4; N, 9.4. C3H16NBrCrF203 calcd.: C, 12.1; N, 9.4; H, 5.4%.)

[CrF2Br(H20)(pn)] (9)

This complex was prepared in a similar manner as previ- ously described. When the product (8) was heated at 110 ~ for 3 h it changed from purple to blue. The weight loss is 12.3% (calcd. weight loss for H 2 0 (2mol) 12.1%).

Techniques

I.r. spectra were recorded on a Beckman IR 20A spec- trophotometer purged with dry air. Samples were prepared using the KBr technique. Electronic absorption spectra were recorded in solution and in solid phase (KBr disck) on a Beck- man 5230 UV spectrophotometer. Conductivity measure- ments were carried out with a conductivity bridge Radiometer CDM-3.

Intensity measurements and crystal structure determination

A small crystal was selected for intensity measurements on a Philips PV-1000 four-circle diffractometer. The unit cell was obtained by automatic centering of 25 independent reflections and refining the orientation matrix and cell-parameters by least-squares. Intensities were collected with Mo-K~ radiation monochromatized by reflexion from a graphite crystal. 1000 intensities within the range 2~<0<~25 ~ were considered, applying the condition: I >I 2.5 o (I). Lorentz polarization cor- rections were made, but absorption was ignored. Main crys- tallographic data are given in Table 1.

Table 1. Crystallographic data for (en-H2)[CrF4(en)]C1.

(C2HsN2)GCr �9 C2H10N2 �9 C1 285.7 Monoclinic P21

7.364(1) A 10.510(2) 7.540(1)

100.13(2) ~ 574.5(2)/~a 1.65 g cm -3

2 0.71069

13.0 cm -1 Measured intensities: 1002 Observed reflections: 1000 (I I> 2.5 o (I))

The structure was solved by direct methods, using the MUL- TAN system of computer programs (15). An E-map computed from the set of phases with the highest combined figures of merit revealed peaks for all non-hydrogen atoms. The struc- ture was isotropically and anisotropically refined by full-matrix least-sozuares method, using the SHELX-76 computer pro- gram 06), where anomalous scattering factors were of Interna-

(17) tional Tables of Crystallography . The function minimized was w(IFoHFc[) 2, were w = (o2lFol + 0.002691Fol2) -1. A different synthesis revealed peaks for 25 hydrogen atoms,

Transition Met. Chem. 9, 469-473 (1984) Tetrafluoroaminechromate(III) anion complexes

Table 2. Final atomic coordinates and temperature coefficients of (en-Hz)[CrFa(en)]C1.

471

X/A Y/B Z/C Ull U22 U33 U23 U13 U12

Cr 5333(2) 3172(0) 2674(2) 203(8) 209(7) 297(8) -33(17) 21(5) 33(18) F(1) 5348(14) 4973(10) 2689(13) 259(48) 157(53) 370(58) -36(39) 100(46) 75(40) F(2) 7374(7) 3180(14) 4668(7) 276(25) 298(27) 366(25) -70(62) -46(20) 83(70) F(3) 5306(18) 1379(12) 2718(16) 484(85) 274(62) 494(75) -32(46) -44(68) 98(53) F(4) 3558(7) 3188(18) 4204(7) 328(28) 357(29) 485(28) -7(78) 174(22) -132(79) N(5) 3307(11) 3134(24) 372(11) 312(39) 226(50) 429(36) 102(92) 23(30) -66(89) C(6) 4134(18) 3520(15) -1204(16) 506(71) 719(140) 275(53) 87(59) 56(48) 27(64) C(7) 5997(18) 3540(14) -1023(17) 558(71) 722(136) 376(58) 16(62) 121(51) 22(65) N(8) 7077(14) 3200(20) 787(11) 732(59) 775(70) 751(48) 1'65(99) 226(45) 560(89) N(9) -2156(27) 713(26) 5875(23) 176(98) 653(133) 412(77) 323(83) 9(60) 66(84) C(10) -766(23) 241(16) 4890(23) 87(66) 199(58) 362(68) -35(53) 146(58) 13(48) C(11) 844(39) 1169(27) 4932(39) 624(132) 634(125) 632(150) 46(106) -70(102) -426(106) N(12) 2164(25) 652(22) 3980(27) 324(91) 296(95) 706(113) 181(87) 275(77) 63(72) CI 8(11) 5670(9) -8(10) 352(13) 459(14) 446(12) 5(10) 19(9) -18(10)

which were refined with an overall isotropic temperature fac- tor. The final R was 0.057 (Rw = 0.070) for all reflections. Final atomic coordinates and temperature coefficients are given in Table 2.

Results and Discussion

Molecular structure of (en-H2)[CrF4(en)]Cl

The chromium(I/I) ion is surrounded by four fluorine atoms and two nitrogen atoms of an ethylenediamine ligand in an octahedron (Figure 1). The bond distances and angles are within the range of observed values given in the literature (8' 18) (Table 3). The main differences axe found in the Cr-F dis- tances. A comparison with the literature values may indicate that the Cr-F distance is related to the trans-atom (average Cr-F values according to the trans-atom are: 1.845 (OH2)08); 1.872 (OH)~S); 1.872 (NH3)(~9); 1.889 (F) and 1.91 (N-ethyl- enediamine) (this work).

The different ions of crystal structure are linked by hydro- gen bonds (Table 4). Each protonated amine C2H10N~ + ion is hydrogen bonded to three fluorine atoms belong to two [CrF4(en)]- ions and chlorine ion.

Table 3. Bond distances and angles.

I

q

H(ali Ft21 cr

N[121 Fg4J

CI~O~ HiS)

N[gj FI31 ',

C(61

Figure 1. Crystal Structure of (en-H2)[CrF4(en)]Cl.

cjll/HF/aa ratio and the new compounds

In the synthesis of fluoro-diamine complexes of chromium(III), the crIn)/amine/HF ratio is very important. Compounds such as [CrF2(en)2] +, [CrF(OH)(en)2] + or [CrF4(aa)]- or mixtures of them appear when this ratio was changed(13, 20).

F(1)-Cr 1.893(8) F(1)-Cr-F(2) F(3)-Cr 1.885(10) F(1)-Cr-F(4) F(2)-Cr 1.930(4) F(1)-Cr-N(5) F(a)-Cr 1.889(4) F(1)-Cr-N(8) N(5) - Cr 2.081 (6) F(4) - Cr-F(2) N(S)-Cr 2.078(7) F(2)-Cr-N(8) C(6)-N(5) 1.48(1) C(6)-N(5)-Cr C(7)-N(8) 1.50(1) C(7)-C(6)-N(5) C(6)-C(7) 1.36(1) N(9)-C(10)-C(ll) N(9)-C(10) 1.45(2) C(10)-C(ll) 1.53(1) C(11)-N(12) 1.410)

Average This Work Lit.

F-Cr 1.90(2) 1.86 N-Cr 2.079(1) 2.08 N-Cr-N 82.4(3) 82.6 Cr-N-C 109(1) 108.7 F~-Cr-N 90(1) 90.0 F~-Cr-F~q 89.5(3)

89.3(4) F(3)-Cr-F(2) 90.0(5) 89.5(5) F(3)-Cr-F(4) 89.3(5) 91.5(6) F(3)-Cr-N(5) 89.3(6) 89.2(5) F(3)-Cr-N(8) 92.0(5) 93.0(2) N(5)-Cr-N(8) 82.4(3) 92.5(2) F(4)-Cr-N(5) 92.2(3)

109(1) C(7)-N(S)-Cr 109(1) 118(1) C(6)-C(7)-N(8) 117(1) 1 1 3 ( 1 ) N(12)-C(11)-C(10) 110(1)

472 C. Dfaz, A. Segui, J. Ribas, X. Solans, M. Font-Altaba, A. Solans and J. Casab6 Transition Met. Chem. 9, 469-473 (1984)

Table 4. Hydrogen bonds linking the crystal structure.

A-H B dAB dB~

N(9)-H(N9)..- F(2) ~) 2.75(1) 2.2(2) N(9)-H(N9)... F(3) a) 2.84(1) 2.3(2) N(9)-H(N9) F(4) b/ 2.84(1) 2.0(2) N(9)-H(N9)... el b) 3.24(1) N(12)-H(N12)... F(2) e) 2.79(1) 1.8(2) N(12)-H(N12)... F(3) a~ 2.76(1) 2.4(2) N(12)-H(N12)... F(4) 8/ 2.85(1) 2.2(2) N(12)-H(N12)... CF / 3.14(1) 2.1(2)

Symmetry code:

a ) = x - l , y , z b) = -x, y - 1/2, 1- z c) = l - x , y - 1/2, 1 - z d ) = x , y , z e) = - x, y - 1/2, - z

In the present investigation when an attempt was made to prepare (en-H2)[CrF4(en)]Cl by Dahme's method, the results were not satisfactory. For this reason the reaction was studied under slightly different conditions. We concluded that the most important factor in improving the yield of [CrF4(en)]- is the increase in the HF ratio, undoubtly due to the increase of the acid character that prevents the secondary reactions of formation of ~t-OH or ~t-oxo polymers. We also conclude that a slight excess in the en ratio was preferable.

In short, in the extensive study that we have carried out the syntheses for the en, chxn and pn compounds are found to be optimum under the following conditions: CrC13.6H20 (1 mol)/HF (5.47 mo0/amine (3.97 tool). The CrC13 �9 6 HaO was dissolved in the minimum amount of water and the corres- ponding diamine was added dropwise (see Experimental).

Conductivity measurements

The molar conductivities of (1), (2) and (3) in H20 at a concentration of 10 -~M are 187, 192 and 220 ohm -1 tool -~ cm 2, respectively. These values are expected for species giving three ions in solution. On the other hand, the conductivity of (4), (6) and (8) are 130, 103 and 110 ohm -1 tool -1 cm 2, respectively. These values are the expected for 1 : 1 electrolytes.

Electronic spectra

The electronic spectra are given in Table 5. All the com- pounds of the [CrF4(aa)]- and [CrF~Br(H20)(aa)] series show the same spectral characteristics which are consistent with a distorted octahedral environment. The spectra consist of two well-defined bands in the visible zone, assigned to the transi- tions: 4T2g(F ) <---4A28 and 4T~g(F)<--4A28. The complexes [CrFzBr(H~O)(aa)] show splitting of the band corresponding to the second electronic transition. Since the structure has not been stablished it is difficult to define precisely the origin of this splitting.

I.r. spectra

All the compounds show the band frequencies assigned to the vibrational modes of H:O, aa and Cr-F (21'22). A well

Table 5. Electronic absorption spectra.

Complex X~ (nm) k- h(~h) X~

(en-Hz)iCrF4(en)]Cl 572(37.5) 478(13.4) - 407(26.1) (chxn-H2)[CrF4(chxn)]C1 571(33.6) 474(6.8) - 407(19.1) (pn-Hz)[CrF4(pn)]C1 570(31.5) 472(7.9) - 406(17.5) [CrF2(H20)2(en)]Br 570(31.5) 472(7.9) - 406(17.5) [CrF2(H20)z(chxn)]Br 546(35.0) 451(5.5) 415 377(10.3) [CrFz(HzO)z(pn)]Br 546(34.7) 452(8.4) 415 375(12.9) [CrF2Br(HzO)(en)] "/ 544(35.7) 450(6.3) 415 373(11.3) [CrF2Br(HzO)(chxn)] a) 565 480 - 414 [CrFzBr(HzO)(pn)] ) 581 480 - 401

577 480 - 403

a) Solid state with KBr pellet.

defined band assigned to the v(Cr-F) appears in the 500--450cm "I region, the Cr-Br vibration appears in the 300-200 cm -1 region, according to the literature (22).

Ehtylenediamine exhibits two intense and characteristic bands due to the chain vibration at 1140 vs cm -~ and 1060 vs cm-1 (23). The chxn shows a more complicated spectrum, with bands at 1240m, 1200m, 1140vs, 1120w, 1100w, 1070vs and 1030 s cm -1 (22). The pn exhibits poorly defined bands at 1335 w cm -1 (sometimes this band appears as a shoulder), 1100s, 1047m and 1026w cm -1.

The spectra of the (aa-H2)[CrF4(aa)]C1 complexes are very complicated and exhibit partially coupled vibrations due to the presence of coordinated and protonated amine groups, so the bands can be split or broadened. For example, for all these complexes a strong splitting at 1600 cm -1 for the coordinated amine and at 1520-1530 cm -1 for the protonated amine appear in the region corresponding to the bending vibration NH2.

References

(1) j. Ribas, J. Casabt, J. M. Coronas and M. Serra, Inorg. Chim, Acta, 36, 41 (1979). - (2/j. Ribas, J. Casab6, J. M. Coronas, M. Monfort and M. L. Alvarez, J. Inorg. Nud. Chem., 42, 707 (1980). - (3) j. Ribas, M. Serra, A. Escuer and J. M. Coronas, J. Inorg. Nucl. Chem., 43, 3113 (1981). - (4/j. Ribas, J. Casab6, and M. D. Bart, Thermochim. Acta, 47, 271 (1981). - (st j. Ribas, M. Serra, J. M. Coronas and J. Casab6, An. Quire., 78B, 55 (1982). - (6) M. Serra, A. Escuer, J. Ribas, M. D. Bar6 and J. Casab6, Thermochim. Acta, 56, 183 (1982). - (7) M. Corbella, M. Serra, M. L. Martinez, and J. Ribas, Thermochim. Acta, 57, 283 (1982). - (8) X. Solans, M. Font-Altaba, M. Monfort and J. Ribas, Acta Crystallogr., 38B, 2899 (1982). - (9) M. Serra, A. Escuer, J. Ribas and M. D. Bar6, Thermochim. Acta, 64, 237 (1983). - (~o) j. Ribas, M. L. Martinez, M. Serra, A. Escuer, M. Monfort and N. Navarro, Transition Met. Chem. 8, 87 (1983).

01) j. W. Vaughn and J. Marzowski, Inorg. Chem., 12, 2346 (1973). - (12) j. W. Vaughn and G. J. Seller, Inorg. Chem., 13, 598 (1974), - (13) W. Dahme, Gmelin: Handbuch tier Anorganischen Chemic. Vol. 12, Chrom. part C, Verlag - Weinheim, 274 (1965). - 04)j. W. Vaughn and G. J. Seiler, Synth. React. Inorg. Metal-Org. Chem., 9, 1 (1979), - (15) p. Main, S. L. Fiske, 8. E. Hull, L, Lessinger, G. Get- main, J. P. Declerq and M. M. Woolfson, MULTAN, A system of computer programs for crystal structure determination from X-ray dif- fraction data. Univ. of York, England and Univ. of Louvain, Belgium (1980). - (16) G. M. Sheldrick. SHELX. A computer program for crys- tal structure determination. Univ. of Cambridge, England (1976). - (17) International Tables of Crystallography, Vol. IV. Kynoch Press, Birmingham, England. - (18)X. Solans, M. Font-Altaba, J. L. Brianst, A. Solans, J. Casab6 and J. Ribas, Crystal Struct. Comm. 11, 1199 (1982). - (19)j, W. Vaughn, Inorg. Chem., 20, 2397 (1981).-

Transition Met. Chem. 9, 473-476 (1984) Stability constants of Mg It, MnII, Co H, Ni 1~, CuII, Zn n and Cd n chelates 473

(20/j. W. Vaughn, O. J. Stvan and V. E. Magnusson, lnorg. Chem., 7, 736 (1968).

(zl) K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coor- dination Compounds, Wiley, New York, 1978. - (z2) D. M. Adams, Metal-Ligand and Related VibratiorL~, St. Martin's Press. New York,

1968.- (23) j. L. Bellamy, The Infrared Spectra of Complex Molecules, Methuen, London, 277, 1962.

(Received April 6th, 1984) TMC 1t55

Physico-Chemical Studies on the Chelation Behaviour of Acenaphthenequinone Monothiosemicarbazone (AQTS) with some Bivalent Metal Ions

Shailendra K. Singh, Rakesh K. Sharma and Shrawan K. Sindhwani*

Department of Chemistry, University of Delhi, Delhi-ll0007, India

Summary

The stability constants of the chelates formed from acenaph- thenequinone monothiosemicarbazone and magnesium(II), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) or cadmium(II) have been determined pH-metrically in 75% v/v aqueous dioxan at various ionic strengths of NaC104 and at different temperatures. The method of Bjerrum and Cal- vin(t. 2) as modified by Irving and Rossotti 0), has been used to determine the fi and pL values. The stability constants were calculated on an IBM 360 FORTRAN-IV computer patterned after that of Sullivan et al. (4) to give [3n values using a weighted least squares method. The Sm~ values were also calculated. The thermodynamic stability constant has been determined by extrapolating the log K1 vs ~ plot at zero ionic strength. The other thermodynamic functions have been calculated from the stability constants obtained for different temperatures at con- stant ionic strength. The bivalent metal stability sequence of AQTS chelates is in agreement with reported metal orders for other chelating reagents. The order of free energies and enthalpies of chelate formation for AQTS are: Mn 2+ < Co 2+ < Ni ~+ < Cu 2+ > Zn 2+.

Introduction

Acenaphthenequinone monothiosemicarbazone (AQTS) is a potential analytical reagent because it forms characteristic coloured chelates with different metal ions. In this paper, the metal ligand stability constants and some thermodynamic functions of the chelates of magnesium(II), manganese(II), cobalt(II), nickel(U), copper(II), zinc(II) and cadmium(II) with AQTS are reported. These chelates have been studied pH-metrically by the method of Bjerrum and Calvin as mod- ified by Irving and Rossotti. Thermodynamic stability con- stants were determined at 25 ~ by conducting experiments at 0.01 M, 0.05 M, 0.1 M and 0.2 M NaC104 ionic strength. AG, AH and AS values were calculated at 0.1 M NaC104 ionic strength.

* Author to whom all correspondenc e should be directed.

Experimental

Chemicals

Acenaphthenequinone monothiosemicarbazone (AQTS) was prepared by reacting the requisite amount of acenaph- thenequinone (Fluka A.R.) dissolved in absolute EtOH with thiosemicarbazide in HzO containing glacial HOAc. The reac- tion mixture was boiled under reflux for 2 h and the AOTS so formed was filtered and recrystallized from EtOH. An AQTS solution was prepared in freshly distilled dioxan.

The solution of bivalent metal ions viz. Mg n, Mn n, Co n, Ni II, Cu n, Zn n and Cd II were standardised by conventional methods.

MegNOH (TMAH) (E. Merck, A.G., Darmstadt) in 75% dioxan (aqueous) was used as titrant. Its solution was standar- dised with (CO2H)2.

HC104 was standardised with NazCO3 and diluted to the required molarity (0.02 M) with conductivity H20. NaC104 (Riedel) was used to maintain the ionic strength.

Dioxan A.R. (B.D.H.) was purified by the method given by Vogel (5).

Apparatus

A digital pH-meter (ECIL, model PH5651) in conjunction with a glass electrode was used for pH measurements. The pH- meter was standardised with potasium hydrogen phthalate and phosphate buffers before performing the titration.

All measurements were made at a definite temperature maintained constant by using MLW (West Germany) (NBE Type) thermostat. An IBM 360 computer was used for most of the calculations.

Titration technique

Investigations were carried out at four ionic strengths viz. 0.01 M, 0.05 M, 0.1 M and 0.2 M NaC104 at 25~ With 0.1 M NaC104, studies were also performed at 30~ 40 ~ and 50 ~ temperatures. For each set of experiments, the final vol was made upto 20 cm 3, maintaining the 75% aqueous dioxan

�9 Verlag Chemic GmbH, D-6940 Weinheim, 1984 0340-4285/84/1212-0473502.50/0