Preparation, chemical characterization and structural studies of 3-aminopyridinium salts of dithiooxalate ligand complexes, [M(S2C2O2)2]2− (M = NiII, PdII or PtII

Polyhedron Vol. II, No. 15, pp. 18834890, Printed

in Great

1992 0

Britain

0277-5387/92 %S.oO+.OO 1992 Pergamon Press Ltd

PREPARATION, CHEMICAL CHARACTERIZATION AND STRUCTURAL STUDIES OF ~~OPYR~~ SALTS OF DITHIOOXALATE LIGAND COMPLEXES, [M(S2CzOz)z]2- (M = Ni”, Pd” or pt”[) PASCUAL Departamento

ROMAN,? ANTONIO LUQUE, JAVIER I. BEITIA and C. GUZMAN-MIRALLES

de Quimica Inorganica, Universidad de1 Pais Vasco, Apartado 644, 48080 Bilbao, Spain (Received 27 January 1992 ; accepted 19 March 1992)

Abstract-The synthesis conditions, solid-state characterization and crystal structures of three 3-aminopyridinium salts of planar inorganic dithiooxalato complexes, (HC5H6N& l?WW@31 (0, IHC,H,N2),[Pd(S,C20,)J (2) and (HC,H,N,),[Pt(S,C2O,>J (3), are described. The compounds have been characterized by elemental analysis and thermal, spectroscopic and X-ray diffraction methods. These complexes show a high thermal stability and the surrounding atmosphere is an important factor which significantly influences the course of the thermal decompositions as well as the final products. The IR and UV-vis spectra confirm the presence of the 3-aminopyridinium cations and the complex anions. Xray diffraction analyses show that the compounds are isostructural and crystallize in the monoclinic space group P2&2 with two molecules in the unit cell. The crystal and molecular structure of 2 was determined by single-crystal X-ray diffraction. The crystal structnre consists of mixed layers of quasi-planar complex [Pd(S,C,O,)$anions and 3-aminopyridinium cations linked by strong N-H. **0 hydrogen bonds and anion-cation rc-rc interactions.

The coordination chemistry of metal complexes with sulphur donor ligands has excited great interest among chemists for many years because of the applications of these compounds in analytical chemistry, catalysis and their relevance to bioinorganic systems.’ One of these sulphur donor ligands is the dithiooxalate dianion which is a multifunctional ligand with unique coordination properties due to the presence of four donor atoms and the possibilities of charge delocalization on its atoms.’ X-ray structure determinations demonstrate the ability of the dithiooxalate ligand to coordinate to the central metal ion by two sulphur or two oxygen donor atoms, respectively ; fmthermore, dithiooxalate may coordinate simultaneously to more than one metal ion in polynuclear complexes3 Studies on compounds containing [M(S,C,O,),]‘anions4*5 have demonstrated that the nature and size of the counter7 Author to whom wrrespondence should be addressed.

ions play an important role in the crystal packing of this kind of compound. The almost planarity of the most inorganic dithiooxalato anion complexes leads to a more compact crystal packing in compounds containing organic planar cations than those observed for compounds of large and bulky cations.’ On the other hand, oxidative thermal decompositions of various nickel, palladium and platinum complexes are used for the production of metal and metal oxides which are extensively applied as catalysts in a variety of important chemical processes. 6 In view of this wide interest, and as a part of our research on complexes of the dithiooxalate ligand, we have studied the reaction between aromatic organoammonium molecules and several squareplanar inorganic metal 1,2-~~ooxalato-S,S’ anions, in order to obtain a deeper insight into the cation and metal effects on the crystal packing and the strength of the intermolecular interactions in this type of compound. This paper describes the

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synthesis and chemical characterization of three 3aminopyridinium salts of 1,2-dithio-oxalate-S,S’ metalate anions, [M(S,C,O,),]‘- (M = Ni**,Pd” or Pt”), as well as the crystal structure and bonding of the compound 3-aminopyridinium bis(dithiooxalato)palladate(II), (HCSHsNz)z[Pd(SzCz02)Z] (2). EXPERIMENTAL General and instrumental The dithiooxalate ligand was used as purchased from Eastman Kodak. Carbon, nitrogen and hydrogen analyses were performed on a PerkinElmer 240 C, H and N analyser. Metal was determined using atomic absorption. IR spectra were recorded on an IR Beckman 4240 spectrophotometer from 4000 to 350 cm-’ using KBr pellets. U,V-vis spectra of ethanol solutions (2 x lo- 5 M) were obtained on a Bausch-Lomb Spectronic 2000 spectrophotometer in the region 650-220 nm, using 1 cm silica cells. Density values were measured by flotation in a mixture of nC,H ,&HBr3. A Setaram Tag 24 S16 thermobalance was used to obtain the differential thermal analysis (DTA) and thermogravimetric analysis (TG and DTG) curves, simultaneously, in an argon-oxygen and argon atmosphere with a heating rate of 5°C min- ‘. X-ray powder diffraction patterns of 1 and the final products from thermal decompositions of compounds l-3 were obtained on a Philips PW 1710 instrument with nickelfiltered Cu-K, radiation. Diffraction patterns of thermal decomposition residues were compared with those obtained from the ASTM powder diffraction files of the Joint Committee on Powder Diffraction Standards. Single crystal X-ray techniques were used for the characterization of compounds 2 and 3. Synthesis of complexes The potassium bis(dithiooxalato)metallate(II) complexes were prepared following the procedure described by Cox7 and the purity checked by elemental analysis. bis(dithiooxalato)nickelate 3-Aminopyridinium (II), (HC5H6N2)2iNi(S2C202)2] (1). This compound was prepared by reaction between K2mi (S,C,O,),] (0.33 g, 0.87 mmol) and 3-aminopyridinium hydrochloride (0.28 g, 2.18 mmol) in distilled water (50 cm3), with stirring at room temperature. Immediately, an insoluble black microcrystalline powder was obtained. After 2 weeks, recrystallization from DMF solution (20 cm3)

gave the product as dark purple crystals which were collected by suction filtration, washed with EtOH and Me20 and finally dried in air. Crystals were twinned, and all our attempts to obtain suitable single crystals by recrystallization were unsuccessful. Yield: 0.37 g, 0.76 mmol, 88% based on nickel. Found: C, 34.5; H, 2.8; N, 11.5; Ni, 12.0. Calc. for Ci4Hi4N4Ni04S4 : C, 34.4 ; H, 2.9 ; N, 11.5; Ni, 12.0%. Selected IR data (KBr pellets, cm-‘): 1585~s; 1540~s; 1440m [v(C-_], 1090s [v(C-C) + v(C-S)], 950m [&C-O)+ v,(C-S)], 450m [v,(C-S)], 390m [v,(Ni-S)], 360~ [v,(Ni-S)]. UV-vis [EtOH, nm (E, M- ’ cm-‘)] : 572.1 (3349), 507.3 (4593), 298.9 (35,167), 249.9 (36,028). 3-Aminopyridinium bis(dithiooxalato)palladate (II), (HCSHsN2)2[Pd(S2C202)Z] (2). This reddishyellow compound was obtained from K2[Pd(S2C2 O,),] (0.25 g, 0.58 mmol) and 3-aminopyridinium hydrochloride (0.18 g, 1.45 mmol) in water (50 cm3) following the general procedure described for 1. Suitable single crystals for X-ray diffraction measurements appeared after 5 days by recrystallization in an EtOH/DMF mixture (30 cm’) (2/l). Yield: 0.25 g, 0.47 mmol, 81% based on palladium. Found: C, 31.4; H, 2.6; N, 10.4; Pd, 19.8. Calc. for CIqHL4N404PdS4: C, 31.3; H, 2.6; N, 10.4; Pd, 19.8%. Selected IR data (KBr pellets, cm-‘) : 1580~s ; 1440s [v(C=O)], 1085~s [v(C-C)+ v(C-S)], 950s [&C-o) + v,(C-S)], 570s; 430m [v,(C-S)], 410m [v,(Pd-S)], 355m [v,(Pd-S)]. UV-vis [EtOH, nm (E, M-’ cm-‘)]: 387.7 (7196), 277.5 (41,884), 241.7 (37,464). 3-Aminopyridinium bis(dithiooxalato)platinate (II), (HCSHsN2)2[Pt(S2C202)Z] (3). Red crystals of 3 were prepared from K2[Pt(S2CZ0&] (0.30 g, 0.48 mmol) and 3-aminopyridinium hydrochloride (0.18 g, 1.45 mmol) in water (50 cm3) by a similar procedure as described above. Yield: 0.24 g, 0.39 mmol, 80% based on platinum. Found: C, 26.9; H,2.3;N,8.8;Pt,31.1.Calc. forC,,H,4N404PtS4: C,26.9;H,2.3;N,9.0;Pt,31.2%.SelectedIRdata (KBr pellets, cm- ‘) : 1580~s 1430m [v(C=O)]; 1085s [v(C-C) + v(C-S)] ; 950m [&C-O) + v,(C-S)] ; 58Os,440m [v,(C-S)] ; 420~ [v,(Pt-S)] ; 400~ [v,(Pt-S)]. UV-vis [EtOH, nm (E, M-’ cm-‘)]: 465.9 (4699), 432.9 (5755) 413.5 (5095), 344.2 (3696), 298.3 (8262), 239.9 (34,870).

Crystallographic reJnement of 2

data collection

and structural

Cell parameters for 1 were obtained from the Xray powder diffraction method since the crystals were twinned. Following preliminary oscillation and Weissenberg photographs, accurate unit cell

Preparation,

characterization

and structural studies of [M(S2C202)J-

1885

Table 1. Crystal data for compounds 1,2 and 3 Compound Formula Formula weight Space group a (A) b (A) c (A) B (“) v (A’) Z D, (g cm- 3, R (g cm-3)

1”

Cd14N4Ni04S4 489.22 P2,ln 10.616(4) 7.372(6) 13.475(4) 109.10(3) 996( 1) 2 1.64 1.66(l)

26 CLdH, J’WJ’dS4 536.95 J%ln 10.724(l) 7.338(2) 13.364(2) 110.04( 1) 987.9(7) 2 1.81 1.80(l)

36 C,,H,&OQtS, 625.61 p2,ln 10.749(3) 7.378(4) 13.391(4) 109.83(2) 999.1(8)

“X-ray powder diffraction data. bX-ray single crystal diffraction data.

parameters of 2 and 3 were determined by a leastsquares fit from 28 values of 25 reflections (10 < 13< 22”), measured at 295 K on an EnrafNonius CAD4 four-circle diffractometer with

radiation, MO-K, graphite monochromated (A = 0.71069 A). Table 1 summarizes the crystal data for the three compounds and shows that all of them are isostructural. Only the crystal structure of 2 was determined due to the bad quality of crystals of 1 and since all compounds are isostructural. For intensity data collection, a prismatic single crystal of 2 with dimensions 0.28 x 0.30 x 0.13 mm was selected. Intensity data were collected in the range 2<8<35” (O, 30(I), were used in the structure refinement. The positions of the non-hydrogen atoms were located by Patterson and Fourier methods. An empirical absorption (p = 13.599 cm- ‘) correction following the DIFABS procedure’ was applied to data refined with isotropic displacement parameters (minimum and maximum correction factors : 0.678 and 1.330). Anisotropic refinement was carried out by the fullmatrix least-squares analysis. A unit weighting scheme was used. All hydrogen atoms were clearly visible in a difference-Fourier synthesis and were refined isotropically. Last cycles of refinement gave the discrepancy indices R = 0.028 and R, = 0.027 for 152 parameters ; goodness 1.05 ; maximum shift/error in the final

of fit = cycle =

0.10 and the largest positive and negative peaks on a final Fourier difference synthesis were 1.0 and -0.7 e Ae3, respectively. Most calculations were carried out using the X-ray 76 system” running on a MicroVAX II computer. Final atomic positional and thermal parameters, together with observed and calculated structure factors, have been deposited as supplementary material with the Editor, from whom copies are available on request. Atomic coordinates have also been submitted to the Cambridge Crystallographic Data Centre.

RESULTS AND DISCUSSION Spectroscopic

characterization

IR assignments of the constituent species have been made previously and a comparison of these results with the observed spectra of the reported compounds *J leads to the assignments described in the Experimental. There are only slight differences among the IR spectra of the three studied compounds. The vibrational frequencies of the 3aminopyridinium cations and bis(dithiooxalato)metallate(I1) anions have been characterized in the 4000-800 cm- ’ and 1600-350 cm-’ regions, respectively. ’ ’ The W-vis spectra of the compounds exhibit two strong absorption bands in the W range, at ca 240 and 290 nm, which may be due to the rc* t n and II* t x transitions of the aromatic cations and the dithiooxalate ligands. The less intensive bands in the visible region, which do not appear in the cation spectra, are attributable to metal-ligand charge transfer absorptions and they are shifted as a function of the metal nature. 2*‘2

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ROMAN et al. 490°C for compounds

1, 2 and 3, respectively. At 6OO”C,the final solid residue from 1 was identified as a mixture of nickel sulphide and nickel oxide. The thermal decomposition of 2 yields a mixture of palladium and palladium(I1) oxide, whereas the final residue from 3 is platinum. Due to the influence of the surrounding atmosphere and experimental conditions on the thermal decompositions of thiocomplexes, ’ 3 the thermal bzhaviour of the three compounds in an argon atmosphere has been studied (Fig. 2). All processes are endothermic in this atmosphere. At 650°C only a constant mass was achieved for the nickel complex, the final residue being NiS. No other peaks belonging to nickel or nickel sulphide were found in the X-ray powder diffraction patterns. However, for 2 and 3 the decompositions are not completed at 650°C and the elemental analyses of the residues revealed the presence of high amounts of carbon. For this reason, the thermal decompositions were continued up to 850°C where constant mass was reached. The final residues were identified as PdS and platinum for 2 and 3, respectively.

Thermal analyses

Table 2 lists the thermoanalytical results of the thermal decomposition of the compounds in argonoxygen and argon atmospheres. In both atmospheres, the thermogravimetric curves indicate that the decompositions are not simple, and stable intermediate products were not found because most of the stages were not resolved. Attempts to correlate the results with theoretical weight losses were not successful, except for the final solid products which were identified by X-ray powder diffraction methods. The simultaneous TG-DTA curves for the compounds in the oxidative atmosphere are shown in Fig. 1. Compounds are anhydrous and stable up to approximately 200°C beyond which a first abrupt weight loss takes place corresponding to an exothermic peak in the DTA curve. This first decomposition step is followed by a progressive mass loss with poorly resolved peaks in the DTG curves and no clear peaks in the DTA curves. Then, several exothermic processes take place and the thermal decomposition finishes above 590,360 and

Table 2. Thermal analysis data for compounds l-3

Step

T,

1 2 3 4 5

1 2 3 4

Ar+O,

Ar

Tf

T,,,”

Amb

210 260 301 393 518

260 301 393 518 600

245( +)

38.05 8.55 8.90 23.73 1.42 (80.65)

200 260 325 360

260 325 360 600

Step

z

Tr

T,,,”

Am’

1 2” 3 4 5

210 265 331 447 650

265 331 447 650 850

247( -)

255 290 340 400 850

230( -)

3

200 255 290 340 400

28.54 14.97 15.27 5.24 10.31 (74.33)

1 2 3

180 260 430

260 430 850

230( -)

24.59 20.45 23.91 (68.95)

1

470( +) 543(+)

358( -)

33.06 13.25 31.64 2.78 0.01 (80.74)

2 230( +) 351( +)

37.63 20.86 19.33 0.27 (78.09)

:d

3 1 2’ 3 4

200 260 375 490

-

260 375 490 600

230(f) 440(+)

22.18 16.10 29.01 0.05 (67.34)

-

“Endothermic (-) or exothermic (+) process. bTotal mass losses are shown between parentheses. ‘Progressive mass loss without clear peaks in DTG and/or DTA curves. dOverlapped processes.

Preparation,

characterization

and structural studies of [M(S2C20J2]‘-

(a)

1887

(b) I

I

I.III

0

100

200

300

400

500

.I

100

600

IL.1.I.l.l.l*l.I*

200

300

TEMPERATURE (“C) Fig. 1. (a) TG and (b) DTA curves for compounds 1-3 in an argon-oxygen

X-ray structure determination

The structural analysis reveals that the crystal structure of 2 consists of complex anions, [Pd(S2C20&]*- and 3aminopyridinium cations stacked in mixed sheets (at z = 0 and l/2) along the [210] direction following a sequence . . acca.. (where a = anion and c = cation). Anion and cation best planes are almost parallel to each other with a dihedral angle of ca 7”, while the anion normal is tilted by 19” relative to the b-axis. Figure 3 shows the structure of the complex dianion and the cation with the atomic numbering scheme. A stereoscopic view of the unit cell together with the network of hydrogen contacts are shown in Figure 4. Selected

400

500

600

TEMPERATURE (“C) atmosphere.

bond lengths, angles and the hydrogen contacts are listed in Table 3. The Pd-S bond lengths are slightly shorter than those of 2.334(l) A found in dithiooxalatobis(trimethylphosphine)palladium(II), in agreement with a lower degree of strain within the five-membered ring.14 The short average C-S bond distance of 1.70 8, and the long average (==o bond distance of 1.22 8, are consistent with the existence of a significant degree of delocalization throughout the S-C-O units in the dianion, with a single C-C bond of 1.555(3) A. The complex anion is not completely planar; an overall chair conformation is present with a dihedral angle between the PdS, central plane and the S2C202 ligand mean plane of 4.49(4)“. This angle is similar

Ibl

(a)

.-I

2 a-b\ r I\,,,,.,/'/"--\-*:\, I-\#--, ,/y,“ ;I f I II II II -60

1

-70 L -60 L 0

1 100 200 300 400 500

600

700 600

TEMPERATURE (“C)

I.I.I.,.,,I~I.I.1.I,,.,.,.,.,.,,,, 100 200 300 400 SO0 600 700 600 TEMPERATURE

Fig. 2. (a) TG and (b) DTA curves for compounds 1-3 in an argon atmosphere.

(“C)

P. ROMAN

1888

et al.

O(1)

NC

5)

C

4)

O(2)

(a)

(b)

Fig. 3. An ORTEP view of the structure of (a) the [Pd(S2Cz02)2]2- anion and (b) the 3-aminopyridinium cation, showing the atom-labelling scheme.

to those previously observed for bis(dithiooxalato)metallate(II) anions in compounds also containing aromatic cationq4” and is considerably lower than those observed in analogous complexes containing large and bulky cations.5 The value of this angle is affected by the complex system of interactions present in the crystal packing, including the hydrogen contacts between the anion oxygen atoms and the hydrogen atoms of the cations,’ or the water molecules l6 and the possible n-rc interactions between the aromatic cations and the dithiooxalate groups, where a significant degree of electronic delocalization is present, or between dithiooxalate ligands of-different anions. ’ 5 All of them produce a displacement of the ligand atoms and a higher value

of the dihedral angle between the PdS4 and the dithiooxalate groups. The 3-aminopyridinium cation is almost planar and the bond lengths and bond angles are within the normal range reported in the literature. ’ 7 An interesting structural feature is the interstacking distances among anions and cations. Each anion is placed between four 3-aminopyridinium cations of two neighbouring sheets, which are disposed above and below the dithiooxalate ligands. The interstack distances are from 3.20 to 3.60 A, and the shortest contact, between C(2) and C(14), is 3.28 A. These values are comparable to interplanar distances found in aromatic n-systems (3.2-3.6 A) with strong rc-rcinteractions’* and they may suggest

Fig. 4. A stereoscopic view of the unit cell of 2 (hydrogen contacts : dotted line).

Table 3. Selected bond lengths (A) and bond angles (“), and hydrogen for compound 2

contacts

1889

Anion 2.2908(7) 2.2921(8) 1.701(3) 1.696(2) 1.555(3) 1.218(3) 1.225(4)

Pd-S( 1) Pd-S(2) S(l)-C(l) S(2wX2) C(l)-U2) C(lW(1) C(2W(2)

S( I)-Pd-S(2) Pd-S(l)--C(l) Pd-S(2)-C(2) S(l)--c(l)--c(2) S(2)--c(2)--c(l) S(1)_C(1)--0(1) S(2)--c(2>--0(2) C( 1)-C(2W(2) C(2)-C(lW(1)

90.17(3) 105.00(8) 104.75(9) 119.4(2) 120.3(2) 124.1(2) 123.5(2) 116.2(2) 116.5(2)

Cation N(ll)-C(12)

C(12)-N(ll)-C(16)

1.330(3) 1.381(3) 1.393(4) 1.374(4) 1.362(5) I .327(5) 1.344(3)

C(l2>--c(l3) C(l3)-+14) C(l4Vw5) C(l5tc(l6) C(16)--N(l1) C(13)-N(13)

N(1 l)-C(l2)-C(l3) C(l2)--c(l3)--c(l4) C(13)-C(14)-C(15) C(l4)--c(l5)--c(l6) C(15)-C(16bN(ll) C(12)-C(13)--N(13) C(14)-C(13FN(13) Hydrogen

N(ll)--H(ll)...O(l) N(Il)-H(I1)...0(2) N(13)-H(131)...0(1) N(13)-H(132)...0(1)(2) Symmetry (I)

3/2-x,

(1)

N-H 0.81(4) 0.81(4) 0.91(4) 0.82(4)

contacts N...O

H...O

2.916(4) 2.820(3) 2.899(3) 2.912(4)

2.30(5) 2.09(3) 2.33(3) 2.11(4)

123.7(3) 120.1(3) 117.2(2) 120.2(3) 120.2(3) 118.5(3) 120.7(3) 122.1(3)


codes 1/2+y,

1/2-z

(2)

1/2+x,

1/2-y,

1/2+z

NO

W3)

NO 1)

(a) Fig. 5. Overlapping

tb)

of anions and cations in the crystal structure of (a) compound aminopyridinium bis(dithiooxalato)palladate(II).

2 and (b) 4-

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P. ROMAN

the existence of a significant interaction

between the dithiooxalate groups and the z-systems of the aromatic cations, as found in other [Pd(S2C202)2]2salts. In our case, there is no evidence of z-z interactions between dithiooxalate groups belonging to neighbouring anions or between aromatic cations, which have also been observed in other structures of similar compounds. i5*‘6 It is possible that the nature and size of the cation play an important role in this type of interaction. Figure 5 shows the anioncation overlapping in 2 and in the 4-aminopyridinium bis(dithiooxalato)palladate(II) dihydrate crystal structure. I6 The centrosymmetric positions of the organic cations have been omitted for clarity, In the 4-aminopyridinium salt, the aromatic rings lie up and down the PdS4 plane [Pd * * . pyridine ring, 3.49 A] and their best planes form an angle of 87.6(S)’ with the palladium d,z orbital. It is interesting to note that the cation nitrogen atoms are placed over the centre of the five-membered ring of the complex anion due to possible electrostatic interactions. This arrangement suggests the existence of a significant interaction between the dzz orbital of the metal and the n-systems of the aromatic cations. A similar disposition is observed in metalloporphyrins in which the metal atom lies above the centre of the porphyrin ring.” In 3aminopyridinium salts, the position of the amine group affects the interaction between cations and anions. The cation nitrogen atoms are as far as possible from the metal position and the aromatic rings interact with the dithiooxalate groups. In the crystal structure of 2, there is an extended hydrogen-bond network of the type N-H .. .O. The hydrogen atom of the endo pyridine nitrogen forms a bifurcated hydrogen contact with the oxygen atoms of the complex anion in the same sheet. The exe amine group establishes two hydrogen contacts with two different anions placed in neighbouring sheets. The closest approach distances that are suitably orientated to permit hydrogen contacts are listed in Table 3.

Acknowledgements-Authors wish to thank Iberdrola S. A. and UPV/EHU (Grant No. 169.310-E180/91) for financial support.

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