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Molecular and Crystal Structure, and EPR Studies of Tetraphenylarsonium [Bis-(l,3-dithia-2-one-4,5-dithiolato)-nickelate], (AsPh4)[Ni(dmid)2]

R. Vicente, J. Ribas Departament de Quimica Inorganica. Faeultat de Q u i m i c a , Universität de Barcelona, Diagonal 647, 08028 Barcelona, Spain

C. Zanchini, D. Gatteschi Dipartimento di Chimica, Universitä degli Studi di Firenze. Via Maragliano 75/77, 50144 Firenze, Italy

J.-P. Legros, C. Faulmann, and P. Cassoux* Laboratoire de Chimie de Coordination du CNRS, Unite 8241 associee ä l'Universite Paul-Sabatier, 205 route de Narbonne, 31077 Toulouse Cedex, France

Z. Naturforsch. 43b, 1137-1143 (1988); received January 25, 1988

Crystal Structure, EPR Studies, Tetraphenylarsonium [Bis-( 1,3-dithia-2-one-4,5-dithiolato)-nickelate]

The crystal structure of (AsPh4)[Ni(dmid)2] (dmid :~ = 1,3-dithia-2-one-4,5-dithiolato) has been determined by X-ray diffraction studies: crystals are monoclinic, space group P2,//i, a = 14.724(2), b = 14.305(5), c = 15.570(3) k , ß = 92.20(1)°, V = 3277 Ä3, ov = 1.63 gem 3 for Z = 4, final conventional agreement indices R = 0.038 and Rw = 0.049 for 2115 unique, observed reflections and 211 variable parameters. The asymmetric unit contains one (AsPh4)+ cation and one [Ni(dmid)2] anion, both in general positions. The anions are isolated from each other by the bulky cations. The [Ni(dmid)2]~ ion deviates strongly from planarity: the dihedral angle between the two Ni(dmid) moieties is 10.7°; one of the dmid ligand is almost planar, while the second one is severely puckered. Polycristalline powder and single crystal EPR spectra have been recorded at room temperature. Only one signal was observed in all crystal orientations. The angular depend-ences of the linewidth and of the g values have been determined, as well as the principal g values and directions. These results have been compared to those previously obtained for the analogue (Aj-Bu4N)[Ni(dmit)2] (drnit2" = 1,3-dithia-2-thione-4,5-dithiolato), and discussed in terms of the localization of the unpaired electron on the ligands. leading to a formal (III) and actual (II) nickel oxidation state.

Introduction

Salts with fractional oxidation state and JZ donor-acceptor compounds derived from the [M(dmit)2]"~ complexes (M = Ni, Pd, Pt; dmit2 - = 1,3-dithia-2-thione-4,5-dithiolato) exhibit electrical properties that are out of the ordinary [1, 6]. In particular two of such compounds, TTF[Ni(dmit)2]2 [3] and (Me4N)[Ni(dmit)2]2 [5], undergo a superconducting transition under pressure. It was thus interesting to extend such investigations to other similar polysul-fur-ligand complexes and we have recently shown that the oxygen-derived [M(dmid)2]"_ systems (M = Ni, Cu, Pd, Pt; dmid2 - = l,3-dithia-2-one-4,5-di-thiolato; Fig. 1) also are a source of conductive salts with fractional oxidation state and JZ donor-acceptor compounds [7, 8].

* Reprint requests to Dr. Patrick Cassoux.

Verlag der Zeitschrift für Naturforschung. D-7400 Tübingen 0932 - 0776/88/0900 -1137 /$ 01.00/0

We report here the X-ray structure determination and EPR studies of the (AsPh4)[Ni(dmid)2] precur-sor complex. These results have been compared to those obtained from similar studies of the (Ai-Bu4N)[M(dmit)2] sulfur-analogue complexes [9, 10].

Experimental

Synthesis and crystal growth (AsPh4)[Ni(dmid)2] has been prepared as previ-

ously described [7]. Good-quality single crystals have been obtained by dissolving the brown microcrystal-line raw product in a mixture of methanol: DMF (7:1) and cooling the resulting solution at —35 °C.

X-ray structure determination Crystal data are reported in Table I together with

relevant details of the intensity data collection. The intensity of three standard reflections was monitored throughout the data collection; no significant fluctua-tion was noticed. The usual Lorentz-polarization fac-

1138 R. Vicente et al. • Crystal Structure and EPR Studies of (AsPh4)[Ni(dmid)2]

C34 Fig. 1. Numbering scheme of atoms in (AsPh4)[Ni(dmid)2],

Formula weight: 802.6 Space group: P2,//t V = 3277 A3

Z = 4 F(000) = 1620 //(MoKa) = 21.1 cm"1

Crystal data Formula: C30H20AsNiO2S8 Crystal system: Monoclinic a = 14.724(2) Ä b = 14.305(5) Ä ß = 92.20(1)° c = 15.570(3) Ä £>exP = 1.61(2) g e m - 3 gx = 1.63 gem" Crystal size: 0.5x0.17x0.025 mm3

Elongation axis: [010] Data collection T = 293 K Diffractometer: CAD 4 Enraf-Nonius Radiation: MoKa, X = 0.71069 Ä, graphite monochromator Crystal-detector distance = 207 mm Detector window: height = 4 mm, width - 4 mm Take-off angle = 4° Scan mode: a>-26, maximum Bragg angle = 22° Scan width = (0.8 + 0.35 tg 0)° for w angle Parameters determining the scan speed*:

SIGPRE - 0.5 SIGMA = 0.015 VPRE = 10° min"1 TMAX = 90 s

Refinement Number of reflections for the refinement of cell dimensions: 25 Number of recorded reflections: 5731 (excluding standards) Number of utilized reflections (NO): 2115 [ I>2a( I ) ] Number of variable parameters (NV): 211

Final reliability factors R = Zlk|Fol — IFcl|/2k|Fo| = 0.038 Rw = [Zw(k|Fo| —|Fc|)2/Zwk2Fo2]"2 = 0.049 S = [2 w(k|Fo| —|Fc|)2/(NO—NV)]1'2 = 1.44 where w = U S / f o ^ F o ) + 0.001 Fo2]

Table I. Crystallographic data for (AsPh4)[Ni(dmid)2].

As defined by A. Mosset, J. J. Bonnet, and J. Galy, Acta Crystallogr. B33, 2639 (1977).

1139 R. Vicente et al. • Crystal Structure and E P R Studies of (AsPh4)[Ni(dmid)2]

t o r s w e r e app l i ed to t h e ne t in tens i t ies . A b s o r p t i o n c o r r e c t i o n s w e r e ca l cu l a t ed by t he G a u s s i a n in tegra -t ion m e t h o d [11], us ing a 3 2 x 4 x 4 g r id ; m a x i m u m a n d m i n i m u m t r ansmi s s ion coe f f i c i en t s w e r e 0 .951 a n d 0 .714 respec t ive ly a n d t h e a v e r a g e t r ansmis s ion coe f f i c i en t was 0 .905.

T h e s t ruc tu r e was so lved by di rect m e t h o d s . Leas t -s q u a r e s r e f i n e m e n t was c o n d u c t e d us ing t he b lock-d i a g o n a l a p p r o x i m a t i o n in t h e first s t ages a n d full-ma t r i x in t he f ina l s t ages . Sca t t e r ing f a c t o r s w e r e t a k e n f r o m [12] a n d a n o m a l o u s d i spe r s ion cor rec -t ions w e r e app l i ed to n o n - h y d r o g e n a t o m s . Pheny l

Table II. Non-hydrogen atom fractional coordinates and isotropic or equivalent temperature factors ( Ä 2 x l 0 0 ) with e.s.d. 's in parentheses.

Atom x/a y/b z/c I_Jeq/LJjso

As 0.78625(6) 0.46310(6) 0.40765(5) 4.08(5) Ni 0.55641(7) 0.80798(7) 0.42844(7) 4.59(7) S( l ) 0.6966(2) 0.8015(2) 0.3923(1) 5.4(2) S(2) 0.5852(1) 0.9061(2) 0.5299(1) 5.7(2) S(3) 0.8638(2) 0.9049(2) 0.4614(2) 6.3(2) S(4) 0.7575(2) 1.0031(2) 0.5897(2) 5.9(2) S(6) 0.5271(2) 0.7055(2) 0.3305(2) 7.2(2) S(7) 0.4154(2) 0.8266(2) 0.4565(2) 5.9(2) S(8) 0.3508(2) 0.6340(2) 0.2522(2) 7.6(2) S(9) 0.2441(2) 0.7479(2) 0.3707(2) 6.8(2) 0 ( 5 ) 0.9330(4) 1.0229(5) 0.5767(4) 7.7(5) O(10) 0.1718(5) 0.6544(5) 0.2403(4) 8.4(5) C( l ) 0.7478(5) 0.8792(6) 0.4633(5) 4.2(5) C(2) 0.6997(5) 0.9247(6) 0.5221(5) 4.7(5) C(3) 0.8658(6) 0.9837(6) 0.5490(6) 5.8(6) C(4) 0.4111(6) 0.7009(6) 0.3279(6) 5.7(6) C(5) 0.3621(6) 0.7523(6) 0.3829(5) 5.3(6) C(6) 0.2418(7) 0.6726(7) 0.2785(6) 6.4(7) C ( l l ) 0.6620(3) 0.4527(4) 0.3768(3) 4.3(2) C(12) 0.6016(3) 0.4236(4) 0.4383(3) 6.1(3) C(13) 0.5108(3) 0.4069(4) 0.4146(3) 7.4(3) C(14) 0.4803(3) 0.4192(4) 0.3294(3) 7.2(3) C(15) 0.5407(3) 0.4482(4) 0.2679(3) 6.7(3) C(16) 0.6316(3) 0.4650(4) 0.2916(3) 5.6(2) C(21) 0.8491(3) 0.5387(4) 0.3303(3) 4.1(2) C(22) 0.8672(3) 0.5033(4) 0.2492(3) 5.4(2) C(23) 0.9133(3) 0.5581(4) 0.1909(3) 6.5(3) C(24) 0.9412(3) 0.6482(4) 0.2136(3) 6.7(3) C(25) 0.9231(3) 0.6836(4) 0.2947(3) 7.7(3) C(26) 0.8771(3) 0.6288(4) 0.3530(3) 6.3(3) C(31) 0.7992(4) 0.5161(4) 0.5184(3) 4.7(2) C(32) 0.8605(4) 0.4800(4) 0.5804(3) 5.3(2) C(33) 0.8732(4) 0.5252(4) 0.6594(3) 6.8(3) C(34) 0.8247(4) 0.6065(4) 0.6763(3) 7.5(3) C(35) 0.7635(4) 0.6426(4) 0.6142(3) 7.6(3) C(36) 0.7507(4) 0.5974(4) 0.5353(3) 5.9(3) C(41) 0.8380(4) 0.3421(3) 0.4047(4) 4.3(2) C(42) 0.9323(4) 0.3323(3) 0.4106(4) 6.3(3) C(43) 0.9713(4) 0.2434(3) 0.4089(4) 7.5(3) C(44) 0.9160(4) 0.1645(3) 0.4013(4) 7.5(3) C(45) 0.8217(4) 0.1743(3) 0.3954(4) 6.8(3) C(46) 0.7827(4) 0.2631(3) 0.3971(4) 5.6(2)

Table III. Selected bond lengths (Ä) and bond angles (°) with estimated standard deviations in parentheses.

N i - S ( l ) 2.162(2) S( l ) - N i - S(2) 93.2(1 Ni —S(2) 2.143(2) S( l ) - N i - S(6) 87.3(1 Ni —S(6) 2.147(3) S(2) - N i - S(7) 86.3(1 Ni —S(7) 2.155(2) S(6) - N i - S(7) 93.4(1 S ( l ) - C ( l ) 1.721(8) N i - S ( l ) - C( l ) 101.8(3 S (2 ) -C(2 ) 1.715(8) Ni —S(2) — C(2) 102.5(3 S ( 3 ) - C ( l ) 1.748(8) C( l ) — S(3 - C ( 3 ) 96.2(4 S (3 ) -C(3 ) 1.769(10) C(2) - S ( 4 - C ( 3 ) 96.2(4 S (4 ) -C(2 ) 1.738(8) Ni—S(6) — C(4) 102.5(3 S (4 ) -C(3 ) 1.760(9) Ni —S(7) — C(5) 101.9(3 0 ( 5 ) - C ( 3 ) 1.204(9) C(4) — S(8 - C ( 6 ) 96.7(5 S (6 ) -C(4 ) 1.708(9) C(5) — S(9 - C ( 6 ) 95.6(4 S (7 ) -C(5 ) 1.729(9) S( l ) - C ( l - S ( 3 ) 122.0(5 S (8 ) -C(4 ) 1.735(9) S( l ) - C ( l - C ( 2 ) 121.3(6 S (8 ) -C(6 ) 1.760(10) S(3) - C ( l - C ( 2 ) 116.7(6 S (9 ) -C(5 ) 1.740(9) S(2)-- C ( 2 - S ( 4 ) 121.1(5 S (9 ) -C(6 ) 1.795(10) S(2) - C ( 2 - C ( l ) 121.1(6 0 (10) —C(6) 1.199(9) S(4) - C ( 2 - C ( 1 ) 117.8(6 C ( l ) - C ( 2 ) 1.347(10) S(3) - C ( 3 - S ( 4 ) 113.0(5 C ( 4 ) - C ( 5 ) 1.358(11) S(3) - C ( 3 - 0 ( 5 ) 124.2(7

S(4) - C ( 3 - 0 ( 5 ) 122.8(8 A s - C ( l l ) 1.879(4) S(6) - C ( 4 - S ( 8 ) 121.5(6 As—C(21) 1.887(4) S(6) - C ( 4 - C ( 5 ) 121.3(7 As—C(31) 1.887(4) S(8) - C ( 4 - C ( 5 ) 117.1(7 As—C(41) 1.892(4) S(7) - C ( 5 - S ( 9 ) 121.3(6

S(7)-- C ( 5 - C ( 4 ) 120.8(7 S(9)-- C ( 5 - C ( 4 ) 117.7(7 S(8)-- C ( 6 - S ( 9 ) 112.6(5 S(8)-- C ( 6 — 0(10) 126.2(8 S(9)-- C ( 6 - 0 ( 1 0 ) 121.2(8

r ings w e r e t r e a t e d as idea l ized rigid g r o u p s ( C — C = 1.395 Ä a n d C - C - C = 120.0°), wi th an ind iv idua l i so t rop ic t e m p e r a t u r e f a c t o r fo r each c a r b o n a t o m a n d a f ixed a rb i t r a ry t e m p e r a t u r e f a c t o r ( U = 0 .07 Ä 2 ) f o r h y d r o g e n a t o m s . Al l o t h e r a t o m s w e r e given an i so t rop ic t h e r m a l p a r a m e t e r s . F ina l a g r e e -m e n t f a c t o r va lues f igure in T a b l e I . Pos i t iona l p a r a m e t e r s a n d e q u i v a l e n t i so t rop ic t e m p e r a t u r e fac-to r s f o r n o n - h y d r o g e n a t o m s a re given in T a b l e I I ; a t o m s a re label led a c c o r d i n g t o Fig. 1. C o m p o n e n t s of t he an i so t rop ic t e m p e r a t u r e f a c t o r s , h y d r o g e n a t o m pos i t iona l p a r a m e t e r s , o b s e r v e d a n d ca l cu l a t ed s t r u c t u r e f ac to r a m p l i t u d e s , a n d d e v i a t i o n s of a t o m s f r o m leas t - squares p l a n e s a n d d i h e d r a l ang le be -t w e e n p l a n e s have b e e n d e p o s i t e d as s u p p l e m e n t a r y m a t e r i a l * . B o n d l eng ths a n d angles a r e l is ted in T a b l e I I I . C o m p u t e r a n d p r o g r a m s u s e d a re indi-ca t ed in [13].

* Lists of structure factors and anisotropic thermal param-eters have been deposited with the Fachinformationszen-trum Energie, Physik, Mathematik, D-7514 Eggenstein-Leopoldshafen 2, FRG. Copies may be obtained by quoting the deposition number CSD 53266, the authors, and the journal reference.

1140 R. Vicente et al. • Crystal Structure and EPR Studies of (AsPh4)[Ni(dmid)2]

EPR spectra EPR spectra were recorded at X- and Q-band by

using a Bruker ER 2000 and a Varian EQ spec-trometer, respectively.

Results and Discussion

Fig. 2 is a view of the unit cell content. The crystal structure consists of isolated [Ni(dmid)2]~ anions sur-rounded by the bulky (AsPh4)+ cations, in such a way that no close stacking is observed. The asymmetric unit contains one (AsPh4)+ cation and one [Ni(dmid)2]~ anion, both in general positions. The proposed stoichiometry is thus confirmed and the nickel atom could be considered to be in the formal Ni(III) oxidation state. From this point of view the title compound is analogous to (n-Bu4N)[Ni(dmit)2] described by Lindqvist et al. [9]. However, it will be shown later that the actual oxidation state of the nickel atom in both complexes is more probably II. The average Ni —S distances are quite consistent: 2.152 Ä in [Ni(dmid)2]- and 2.156 Ä in [Ni(dmit)2]"; C - S and C—C distances also agree fairly well and have values intermediate between single and double bond lengths, indicating a high degree of electron dereali-zation. The C—O distances of 1.20 Ä are close to the

double-bond value as are the terminal C—S distances in [Ni(dmit)2]-: as a matter of fact this comparison can be extended to all oxidized [Ni(dmit)2]x_ species for which detailed structural data are available [1, 2, 14]. In all these species the Ni(dmit)2 entities are planar or fairly close to planarity; the more strongly distorted Ni(dmit)2 group is observed in («-Bu4N)[Ni(dmit)2] where the dihedral angle between the two Ni(dmit) moieties is 6.1° [9]. On the opposite, the [Ni(dmid)2]~ ion in (AsPh4)[Ni(dmid)2] deviates strongly from pla-narity. Furthermore, one of the dmid ligands is al-most planar, while the second one is severely puck-ered as illustrated in Fig. 3. The dihedral angle be-tween the two Ni(dmid) mean planes is 10.7°. This distortion is similar to or even higher than those ob-served in TTF[Pt(dmit)2]3 [2], TTF[Pd(dmit)2]2 [15], or (rt-Bu4N)x[Pd(dmit)2] [16]: yet, in all these com-plexes a direct metal —metal interaction induces the formation of [M(dmit)2]2 dimers and thus the folding of the normally planar M(dmit)2 units (dihedral an-gles are 11.2°, 6.3°, and 6.2°, respectively). In the case of (AsPh4)[Ni(dmid)2] there is at this point no such evident theoretical reason for such a distortion and only packing effects could be invoked to explain this unusual structural feature.

1141 R. Vicente et al. • Crystal Structure and EPR Studies of (AsPh4)[Ni(dmid)2]

010

Fig. 3. Side view of the [Ni(dmid)2] ion, emphazising the distortion to planarity. The 0(5)- - -0(10) axis lies in the plane of the paper and the S(l)---S(2) axis is perpendicular to the plane of the paper. Ellipsoids are scaled to en-close 50% probability.

Polycristalline powder EPR spectra of (AsPh4)[Ni(dmid)2] at X- and Q-band frequency at room temperature are shown in Fig. 4. Single crystal spectra were recorded at X-band frequency at room temperature by rotating around the a*, b and c axes. Only one signal was observed in all the crystal orien-tations: the angular dependences of the linewidth and of the g values, with the calculated best fit curve, are shown in Fig. 5. The principal g values and direc-tions are shown in Table IV: one principal direction is along b, as expected for exchange narrowed sig-nals. The other two directions are in the a*c plane, rotated of ~50° from the axis. The lineshape, ana-lyzed as previously reported [17], results Lorentzian thus confirming the exchange narrowed character of the spectra.

In the monoclinic cell there are four [Ni(dmid)2]~ chromophores, two by two related by a center of symmetry or by a reflection plus a translation. From an EPR point of view, atoms related by an inversion center are magnetically equivalent, while those re-lated by a reflection are not, so we expect two non-equivalent sites in the cell with non parallel g tensors, i. e. tensors having the same principal values but dif-

1.19 121 123 125 ~ 127

Fig. 4. Polycrystalline powder EPR spectra of (AsPh4)[Ni(dmid)2] at room temperature at X-band fre-quency (top) and Q-band frequency (bottom).

-i i 1 r i 1 1 r

Fig. 5. Angular dependence of the linewidth (top) and of g values (bottom) of (AsPh4)[Ni(dmid)2] in three orthogonal planes. The full lines represent the best fit curves; ( ) and ( ) are the calcu-lated angular dependences of gM1 and gM2 (see text).

1142 R. Vicente et al. • Crystal Structure and EPR Studies of (AsPh4)[Ni(dmid)2]

Table IV. Experimental principal values and directions of the crystal g tensor for (AsPh4)[Ni(dmid)2] and calculated values of gM1 and gM2 molecular tensors, assuming the re-ported principal directions3.

g l g 2 g 3

2.028(2) 2.032(1) 2.082(1) 0.645(5) 0.0000 0.764(7) 0.0000 1.0000 0.0000 0.764(7) 0.0000 -0.654(5)

g M l . l gM1.2 g M 1 . 3 gM2.1 gM2.2 gM2..1

2.110 2.041 1.988 2.110 2.041 1.988 0.5129 0.8499 -0.1207 0.5129 0.8499 -0.1207

-0 .5234 0.4198 0.7414 0.5234 -0.4198 -0.7414 -0 .6803 0.3185 -0.6600 -0.6803 0.3185 -0.6600

11 The directions are given by their cosines referred to a*, b and c axes.

ferent, symmetry related, principal directions. Since only one signal is observed, the experimental g val-ues result from the average of the contributions of the molecular g tensors of the two magnetically non equivalent sites, gMi and

The minimum Ni—Ni distance between non equiv-alent molecules is 10.64 Ä, while for two equivalent sites it is 6.18 Ä. Nevertheless, the fact that the EPR signals are exchange narrowed shows that inter-molecular exchange interactions are operative. The g values are reasonably close to those previously ob-served for the analogue («-Bu4N)[Ni/Au(dmit)2] [10], However, in that case the g values are true molecular values, because they were obtained from doped crys-tals. In the present case, the largest g value is ob-served in the a*c plane, close to the projection of the bisector of the S (2 ) -N i -S (7 ) angle (^12°), thus showing that also in this case the z molecular axis is

in the molecular plane. Therefore it must be con-cluded that the unpaired electron is largely localized on the ligand. like in (/j-Bu4N)[Ni/Au(dmit)2]. This is also in agreement with previous EPR studies of electrogenerated [M(Ph2C2S2)(dppe)]+ [18] and [M(dmit)(dppe)]+ species [19]. Since the unpaired electron is mainly localized on the sulfur-ligand, all these supposedly M(III) complexes should actually be regarded as M(II) species.

In order to obtain g molecular values, we assumed the principal directions of the molecular g^n and gM2

tensors for the two non equivalent sites by analogy with (rt-Bu4N)[Ni/Au(dmit)2] [10], and, from the ex-perimental g values, we obtained the principal molecular values shown in Table IV. The agreement with (VBu4N)[Ni/Au(dmit)2] is almost perfect, show-ing that the electronic structures of the two complex-es are very similar one to each other. The calculated angular dependences of the gMi and gM2 values (Fig. 5) showed that the maximum anisotropy be-tween the two sites is —160 G at X-band and ==610 G at Q-band. Since also in the 35 GHz spectra the separate resonances of the two sites are never seen, the exchange frequency is much larger than 0.057 cm"1.

The angular dependence of the linewidth shows maxima close to b. Since the direction of minimum approach between the molecules is close to b, it may be assumed that the broadening of the lines is essen-tially due to dipolar spin-spin interactions rather than to g anisotropy effects.

We thank the Commission of the European Com-munities for support of the work at the LCC-CNRS at Toulouse through Grant 86200171FR16PUAL1 to R. V. J .R . and R.V. are grateful for financial assist-ance from C . A . I . C . Y . T . (n° 0855/84). J .P .L . is indebted to Dr. J. Galy for the facilities put at his disposal.

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1143 R. Vicente et al. • Crystal Structure and EPR Studies of (AsPh4)[Ni(dmid)2]

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