Syntheses and chemical, spectroscopic and structural study of 4-aminopyridinium salts of dithiooxalate ligand complexes, [M(S2C2O2)2]2− (M = NiII, PdII or PtII)

Mat. Res. Bull., Vol. 27, p p . 339-347, 1992. Printed in the USA. 0025-5408/92 $5.00 + .00 C o p y r i g h t (c) 1992 Pergamon P r e s s plc.

SYNTHESES AND C H E M I C A L , S P E C T R O S C O P I C AND S T R U C T U R A L STUDY OF 4 - A M I N O P Y R I D I N I U M SALTS OF D I T H I O O X A L A T E LIGAND COMPLEXES,

[M(S2C202)2] 2" (M = Ni II, Pd II or Pt II)

P. ROMAN*, J. I. BEITIA, A. LUQUE and J. M. GUTIi~RREZ-ZORRILLA Departamento de Qufmica Inorg~inica, Universidad del Pafs Vasco, Apartado 644, 48080 Bilbao, Spain. (Received October 25, 1991; Communicated b y J.M. Garela-Ruiz)

ABSTRACT The synthesis conditions, the solid state characterization and the crystal structures of three 4-aminopyridinium salts of planar inorganic dithiooxalato anions, (CsHTN2)2[M(S2C202)2].2H20 where M = Ni(II), Pd(II) and Pt(II) (hereafter abbreviated as NIDT4AP, PDDT4AP, and PTDT4AP, respectively), are described. The compounds have been prepared by reaction of 4-aminopyridinium hydrochloride and the corresponding K2[M(S2C202)2] in aqueous solution, and then recrystaUized in N,N-dimethylformamide. The compounds have been identified by using IR, thermoanalytical, and X-ray diffraction techniques. X-ray diffraction analyses of these compounds show that all of them are isostructural and crystallize in monoclinic system, space group C2/m, Z = 2. The crystal and molecular structure of compound PDDT4AP was determined: a = 10.462(1), b = 12.020(4), c = 9.207(1)/~, [~ = 114.44(5) °, V = 1054.1(6)/~3, Z = 2, F(000) = 576, tt = 12.866 cm -1, M = 572.98, Do = 1.80(1), Dx = 1.81 Mg.m -3, and 7.(MoKct) = 0.71069 A. Final refinement led to R = 0.025 and wR = 0.030 for 1542 observed reflections with I > 3a(I). The unit cell is made up of bis(dithiooxalato)palladate(II) anions and 4-aminopyridinium cations forming layers, and the water molecules occupy the space among them. In the crystal structure there are some significant n - n interactions between the aromatic cations and also dz2-~ interactions between the metal ion of the complex anion and the planar cations. There is also an extensive hydrogen bond network. All these types of interactions ensure the lattice cohesiveness and give to the compound a tridimensional character. MATERIALS INDEX: 4-aminopyridinium, dithiooxalate, nickel, palladium, platinum Introduction The coordination chemistry and chemical characterization of the dithiooxalate ligand complexes have excited great interest among chemists for the last years (1-9). The presence of four donor atoms in the dithiooxalate dianion and the possibilities of charge delocalization on its atoms result in a multifunctional ligand with unique coordination properties (10). 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; furthermore dithiooxalate may coordinate simultaneously to more than one metal ion in polynuclear complexes (2, 3). 339

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Previous X-ray reports on the structures containing [M($2C202)2] 2- anions (8, 9) have demonstrated that the nature and size of the counterions play an important role in the crystal packing of this kind of compound. The almost planadty of the most inorganic dithiooxalato anions leads to a more compact crystal packing in compounds containing organic planar cations than those observed for compounds of large and bulky cations (9). In this context, we decided to study the reaction between aromatic organoammonium molecules and several square-planar inorganic metal(ID 1,2-dithiooxalato-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 intramolecular interactions in this type of compound. 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 (11). The present paper reports the syntheses, the chemical characterization and the thermal behaviour of 4-aminopyridinium salts of 1,2-dithiooxalate-S,S' metalate anions, [M($2C202)2] 2-, where M is Ni(II), Pd(II) or Pt(II), as well as the crystal and molecular structure of the compound, 4-aminopyridinium bis(dithiooxalato)palladate(II) dihydrate. Exrgcimental Synthesis The dithiooxalate ligand was used as purchased from Eastman Kodak. The complex anions, [M($2C202)2] 2-, were prepared following the procedure described by Cox (12) as potassium bis(dithiooxalato)metalate(II) and the purity checked by elemental analysis. The reaction between the potassium salts and 4-aminopyridinium hydrochloride in aqueous solutions with stirring at room temperature yielded immediately insoluble microcrystalline powders which were recrystallized in DMF solution. After three weeks crystals of the three compounds were collected by suction filtration, washed with H20, EtOH and Me20 and finally dried in air. Only suitable single crystals for X-ray diffraction measurements were obtained for compounds PDDT4AP and PTDT4AP. Unfortunately, all our attempts to obtain suitable crystals of NIDT4AP by recrystallization were unsuccessful. Table 1 lists formulas and calculated and experimental content for C, H, N and M(II). TABLE 1 Formulas and Content of C, H, N, and M(II) (%) of the Compounds. Formula

cal.

c

H

exp.

N

cal.

M01)

cal.

exp.

NIDT4AP CCsH7NT,)~[Ni(S~CgO2)2].2H2G 32.01 31.76

3.45

3.45 10.67 10.60 11.17 11.22

PDDT4AP CC~H7N~)~[Pd(S~C20~2].2H~C 29.35 29.69

3.17

3 . 1 0 9 . 7 8 9.77 18.57 18.35

PTDT4AP (CsH7N2)2[Pt(S2C202)2].2H2O 25.41 25.63

2.74

2 . 6 3 8 . 4 7 8.46 29.48 29.62

Compound

exp.

cal.

exp.

Infrared stmrtroscoov Infrared spectra were recorded in the 4000 - 350 cm-1 range on an IR BECKMAN 4240 spectrometer, and the solid compounds were mixed with fused potassium bromide and pressed into transparent dishes.

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Thermal inv¢~0gations A SETARAM TAG 24 S 16 thermobalance was used to obtain the differential thermal analysis (DTA) and thermogravimetric analysis (TG and DTG) curves, simultaneously, in an argonoxygen atmosphere with a heating rate of 5°/min. X-rav diffraction data and rmwdCr 0iffr~ion Following preliminary oscillation and Weissenberg photographs, accurate unit-cell parameters of compounds PDDT4AP and PTDT4AP were determined by least-squares fit from 20 values of 25 reflexions measured at 295 K on an Enraf-Nonius CAD4 four-circle diffractometer with graphite monocromated radiation MoKa (7. = 0.71069 ]k). TABLE 2 Crystal Data for the Compounds. NIDT4AP

fw 525.25 Sl:mcegroup C2/m a, A 10.447(7)

PDDT4AP

PTDT4AP

572.98 C2/m 10.462(1)

661.64 C2/m 10.481(2)

b

12.009(4)

12.020(4)

12.003(5)

c i~' o V, A 3

9.275(4) 114.06(3) 1063(1)

9.207(I) 114.44(5) 1054.1(6)

9.201(2) 114.50(3) 1054(4)

2 1.80(1) 1.81

2 2.08(1) 2.09

z 2 Do, Mg.m"3 1.68(1) Dx 1.64

The compound NIDT4AP crystallizes in insufficient quality to be studied as single crystals, but its cell parameters have been obtained by powder diffraction data. Powder diffraction pattern was recorded on a Phillips PW 1710 diffractometer, 20 values were corrected using the GUINIER program (13) with an a-SiO2 standard pattern. Accurate cell parameters obtained by least squares refinement using the LSUCRE program (14) indexed powder diffraction data for a monoclinic space group C2/m unit cell. Table 2 summarizes the crystal data for the three compounds and shows that all of them are isostructural.

Crvstal structure determination A prismatic single crystal of dimensions 0.40 x 0.26 x 0.23 mm was used for the structure determination of the compound PDDT4AP. Details of the intensity data collection and structure determination are summarized in Table 3. During data collection, three reference reflexions (4 2 6), (4 -2 -6) and (-4 2 6) were monitored after every 100 reflexions and every 7200 s to check for drifts in electronics, radiation damage, variations in X-ray tube intensity, crystal stability and counter response. No crystal decay was observed. Data were corrected for Lorentz and polarization effects. The atomic scattering factors and anomalous dispersion corrections were taken from the literature (15). TABLE 3 Data Collection and Refinement for the PDDT4AP Compound. Instnmlcnt Radiation (MoKct),/~ Temperature, K Scan limits, o Scan width Scan technique hkl range

C.AIM 0.71069 295(1) 2 _<20_< 60 t~0 = 1.0 + 0.35 tan 0 c0-20 h: 0-14; k: 0-16; 1:5:12

Recorded reflexions Observed reflexions Refined parameters (~/O)max (Ap)max, e.A 3 GOF R wR

1605 1542, ti>36(I)] 92 0.014 1.40 1.32 0.025 0.030

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The Pd and S positions were determined by Patterson techniques. A succession of difference Fourier syntheses and least-squares refinement revealed the positions of all atoms including hydrogen. A n empirical absorption correction (Ix = 12.866 cm "l) following the DIFABS procedure (16) was applied to the data refined with isotropic displacements parameters. All nonhydrogen atoms were refined anisotropically. The positional parameter o f all hydrogen atoms were refined with isotropic thermal parameters.The final full-matrix least-squares refinement, leads to the discrepancy indices R = 0.025 and wR = 0.030. A convenient weighting scheme (17) was used to obtain flat dependence in vs and . Most calculations were carded out using the XRAY76 system (18) running on a microVAX II computer. Results and discussion Infrared socctroscoov Infrared assignments of the constituent species have been made previously and a comparison of these results with the observed spectra of the reported compounds leads to the belowed assignment. The infrared spectra certify the presence of the 4-aminopyfidinium cations, giving evidence of this point the corresponding bands about 3300 and 3000 cm -1 for the N-H involved in hydrogen bonds and C-H groups, respectively, and 2700 cm -1 for N-H + groups. The characteristic and very strong bands of 4-aminopyridinium cations were obtained between 1650 and 600 cm -1. A strong band near 3500 cm -1 certifies the existence of the O-H bonds from the water molecules. The bis(dithiooxalato)metalate(II) anions have been characterized in the 1600-350 cm -1 region. Table 4 lists the infrared bands for the anions in the three compounds with the corresponding assignments. TABLE 4 Infrared Bands and Assignments for the [M($2C202)2] 2- Anions in NIDT4AP, PDDT4AP and PTDT4AP Compounds. NIDT4AP

PDDT4AP

PTDT4AP

1595 vs 1557 vs 1434s 1087 vs 948 s 578 s 419 w 358 m vs = very strong s = stron~

1592 vs

1592 s

Assignment

~C---O 1435 s 1086 vs 944 s 573 s 415 w 355 w m = medium w = weak

1429w 1084 vs 950 w 575 w 429 w 390 w ~ = stretching tension 6 = deformationmode

~ C-C + a) C-S 6 C-O + t~asC-S "sy C-S ~as M-S ~as M-S sy = symmetric as = asymmetric

There are only slight differences among the IR spectra of the three studied compounds and their vibrational spectra are very similar to those previously described in bibliography (7, 10). Thermal b~havio~ Thermal decompositions of the three compounds, NIDT4AP, PDDT4AP and PTDT4AP in an argon - oxygen atmosphere, show that all of them are dihydrated. The water molecules are lost between 80 and 140 °C during a first endothermic step. The anhydrous compounds obtained after these dehydration steps are quite stable and they have been identified by elemental analysis and infrared spectroscopy.

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The thermal decompositions are quite similar, but the final residue at 600 °C depends on the starting compound. For NIDT4AP the final solid residue is a mixture of nickel sulfurs and nickel oxides. The thermal decomposition of PDDT4AP compound (Figure 1) yields a final product of palladium and palladium(II) oxide (Pd/PdO = 36/64), whereas the final residue of the PTDT4AP decomposition is platinum(0). All last observed solid products were identified by their X-ray powder diffraction patterns. These results suggest that the present compounds may be used as precursor catalysts.

0

PDDT4AP

DTG (x/,-4-)

DTG

-10 [...,

,5o

I

-20

I

.J

100 !

['~ - s

-30

/

-40

)!o

50

L,

V-.-".~.

-50

-60 TG -70

-20

-60

-80 I

0

,

I

100

,

I

,

I

200

,

I

I

300

400

500

,

i

,

-100

800

T ("C) FIG. 1 Thermal Decomposition of the Compound PDDT4AP in an Argon - Oxygen Atmosphere. Crystal structure Atomic coordinates and equivalent isotropic temperature factors are listed in Table 5. The crystal structure solution of the 4-aminopyridinium bis(dithiooxalato)palladate(II) dihydrate reveals that its crystals are composed of complex anions, [Pd($2C202)2] 2-, 4-aminopyridinium cations and water molecules in a ratio 1/2/2. The anion, with the Pd atom lying on an inversion center, has a 2/m symmetry and it is almost planar, the S atom is moving away from the best plane by 0.03 A. The dihedral angle between the strictly planar PdS4 group and the $2C202 ligand mean plane is of 2.28(7) °. This angle is in the lower end of the range previously observed for similar bis(dithiooxalato)metalate(II) anions in compounds also containing aromatic cations (4, 7), and is considerably lower than those observed in analogous complexes containing large and bulky cations (8, 9). The value of this angle is affected upon a combination of some factors including the hydrogen contacts between the oxygen atoms and the hydrogen atoms of cations or the water molecules, as well as the g-g interactions between the aromatic cations and the dithiooxalate groups where a significant degree of electronic delocalization is present. Both of them may produce a displacement of the ligand atoms and a higher value of the dihedral angle between the MS4 and the dithiooxalate groups.

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TABLE 5 Coordinates and Equivalent Thermal Parameters for PDDT4AP. Atom

x

y

z

Ueq/U s

Atom

x

y

z

Pd 0.00000(-) 0.00000(-) 0.00000(-) 318(2) C(1) 0.1306(2) 0.0642(1) 0.3724(2) S 0.07126(5) 0.13426(3) 0.19497(4) 426(3) O(1) 0.1735(2) 0.1106(1) 0.5018(2) N(1) 0.7311(2) 0.0000(-) 0.1951(3) 44(1) C ( 4 ) 0.6223(2) 0.0000(-) -0.1328(3) C(2) 0.7052(2) -0.0971(2) 0.1166(2) 46(1) N(5) 0.5690(3) 0.0000(-) -0.2917(3) C(3) 0.6514(2) -0.]001(]) -0.0456(2) 43(1) O(2)w 0.50000 0,1970(2) 0.5000(-) H(I) 0.761(7) 0.000(-) 0.297(7) 59(9) H ( 5 ) 0.552(4) -0.059(3) -0.340(5) H(2) 0.727(3) -0.158(3) 0.181(4) 39(7) H(2)w 0.436(4) 0.239(4) 0.496(5) H(3) 0.633(4) -0.168(4) -0.102(4) 46(8) aNon-hydrogen atoms: Ueq = ~ Z[Uij.ai .aj .ai.aj.cos(ai,aj)] x 103A2 (x 104 for Pd, S).

Ueq/U a

40(1) 60(1) 36(1) 49(2) 61(2) 43(8) 59(11)

Hydrogen atoms: U = exp[-81t2U(sin 0/X)2] x 103A2 The cation 4-aminopyridinium is planar and is placed in a mirror plane passing through the N(1), C(4) and N(5) atoms. There are no strong differences between this cation and those found in the bibliography (19). Perspective drawings of the anion and cation are shown in Figure 2 together with the atom labelling. Selected interatomic distances and bond angles are listed in Table 6.

~.s

o(1)

H(1)

H(3) C(4)~ _%2j<~ /T%

~7

H(5)

FIG. 2 Bis(dithiooxalato)palladate(H) Anion and 4-Aminopyridiniurn Cation with Atom Labelling The PDDT4AP compound has a laminar structure and is built up by parallel columns of ions stacked along the a axis, following a sequence ...acca... (a = anion and c = cation). These columns are located in two different y levels, y = 0 and y = 1/2, and stepped by a/2. Best planes of anion and cation are almost parallel to each other, with a dihedral angle of 1.3(1) ° and are tilted by c a . 23 ° respect to the bc plane. Figure 3 shows a stereoscopic view of the complex PDDT4AP crystal structure, together with the network of hydrogen contacts (dotted lines).

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FIG. 3 Stereoscopic View of the PDDT4AP Unit Cell It is interesting to note the interstack distances among anions and cations. Each anion is placed between two 4-arninopyridinium cations which lie up and down the PdS4 plane [interplanar separation, 3.50 A]. The Pd atom is distant from the aromatic planes by 3.49 A and its dz2 orbital forms an angle of 87.6(8) °. This arrangement suggests the existence of a significant interaction between the dz2 orbital of the metal and the ~-systems of the aromatic cations. Figure 4a shows the overlap between one anion and two neighbour cations, projected on the PdS4 plane. However, the palladium atom is displaced towards C(4) atom [Pd..-C(4): 3.62 A, Pd...C(3): 3.69 ]k, Pd-.-C(2): 3.84/~, Pd.-.N(1): 3.92/~] due to the influence of amine group on the electron distribution of the aromatic ring. On the other hand, the two neighbour cations in the same column, related by an inversion center, are parallel to each other and their mean planes are separated by 3.47 A (Figu~ 4b). This value is comparable to interplanar distances found in aromatic ~-systems (ca. 3.4 A) with strong x-n interactions (20).

TABLE 6 Selected Bond Distances (/~), Angles (o) and Hydrogen Contacts in the Compound PDDT4AP. Angles

Distances

Pd--S 2.2968(7) C(4)-N(5) S--CO) 1.710(2) N(1)--H(1) C(1)-O(1) 1.221(2) C(2)-H(2) N(1)-C(2) 1.341(2) C(3)-H(3) i C(2)--C(3) 1.361(3) N(5)-H(5) C(3)-C(4) 1.408(2) O(2)w-H(2)w

1.333(3) 0.86(8) 0.91(4) 0.94(4) 0.82(4) 0.82(5)

Pd-S-C(1) 105.82(6) N(1)--C(2)-H(2) 114(3) S-C(1)--O(1) 123.3(1) C(2)--C(3)-H(3) 122(3) N(1)--C(2)-C(3) 120.9(2) C(4)--N(5)-H(5) 120(2) C(2)--C(3)-C(4) 119.8(2) C(4)--C(3)-H(3) 118(2) C(3)--C(4)-N(5) 121.3(1) C(3)--C(2)--H(2) 125(2) C(2)-N(1)-H(1) 119.4(1)

Hydrogen contacts X-H'"O

N(1)-H(1)-O(1) N(1)-H(1)-O(I) N(5)-H(5)-O(2)w N(5)-H(5)-O(2)w O(2)w-H(2)w-O(l)

(1) (2) (3) (4) (5)

X'"O

H ""O


2.872(3) 2.872(3) 2.943(3) 2.943(3) 2.936(3)

2.15(6) 2.15(6) 2.13(6) 2.13(6) 2.15(5)

141.7(1) 141.7(1) 170(4) 170(4) 160(5)

Symmetry codes (1) l-x,-y, 1-z

(2) l-x, y, 1-z

(3) l-x, -y, -z

(4) x, -y, z-I

(5) I/2-x, I/2-y, l-z

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In similar compounds described in the literature, x-~ interactions between the aromatic cations and the dithiooxalate ligands (4, 6) or between different anions (4, 5, 7) are observed. In our case, there is no evidence of this type of interaction.

S

0(1)

cO) C(2)

1)

(a)

(b)

FIG. 4 View of the Overlap: a) Cation-Anion-Cation and b) Cation-Cation In the crystal structure an extensive network of hydrogen bonds of type N-H...O and O-H...O is present (Table 6). The columns situated in the same y level are linked by a bifurcated hydrogen contact between the hydrogen atom of the pyridine ring nitrogen atom and two oxygen atoms of the same dithiooxalate ligand, and by one water molecule. The sheets placed in different y levels are connected by hydrogen contacts among amine group of cations, the water molecules and the anions. These hydrogen contacts stabilize the crystal structure and, together with the electrostatic attractions and the x-x and dz2-X interactions, play an important role in the crystal packing of this type of compound. It would be necessary to point out that the hydrogen contacts involving water molecules are nearly linear, and the no linear N-H..-O contacts are stablished by two parallel ions located in the same y level along the [300] direction. This latter factor and the no existence of x-x interactions between the dithiooxalate ligands and the cations, might also be responsible of the high planarity of the complex anion. Conclusions In summary, in the course of the studies on the reactions between amine bases and dithiooxalate ligand complexes, three new 4-aminopyridinium salts of square-planar inorganic metal(II) 1,2-dithiooxalato-S,S' anions, have been prepared and the crystal structure and bonding of 4-aminopyridinium bis(dithiooxalato)palladate(II) dihydrate has been solved. The oxidative thermal decomposition of these compounds may be used to the preparation of catalysts. The nature and size of cations seems to be an important factor which show a considerably influence on the type of intermolecular interactions as well as on the crystal packing in these compounds. The structural feature of these compounds is the existence of important ~-x and dz2-X interactions which permit an effective crystal packing of cations and anions.

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Ackn0wlcd~em~nts The authors would like to thank Iberdrola, No. 169.310-T155/90) for financial support.

S. A. and UPV/EHU

(Grant

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