Ibers, Kannewurf: Marks. et al. / Iodinated Nickel and Palladium Bisbenzoquinonedioximates
2931
Rational Synthesis of Unidimensional Mixed Valence Solids. Structure-Oxidation State-Charge Transport Relationships in Iodinated Nickel and Palladium Bisbenzoquinonedioximates Leo D. Brown,la Davida Webster Kalina,Ia Malcolm S. McClure,Ib Steven Schultz,lr Stanley L. Ruby,lCJames A. Ibers,*la Carl R. Kannewurf,*lband Tobin J. Marks*laJ Contribution f r o m the Department of Chemistry, the Department of Electrical Engineering, and the Materials Research Center, Northwestern Unicersity, Ecanston, Illinois 60201, and the Physics Division, Argonne National Laboratory, Argonne, Illinois 60439. Received August 23, 1978
Abstract: This paper presents a detailed study of crystal structure, stoichiometry, oxidation state, and electron transport in the materials Ni(bqd)2, Pd(bqd)z, Ni(bqd)zlo,olB, Ni(bqd)2lo,~.S,and Pd(bqd)2lo,s.S, where bqd = o-benzoquinonedioximato and S = an aromatic solvent. The compound Pd(bqd)2lo,so.O.52o-C~H4Cl2 has been shown by single-crystal X-ray diffraction to crystallize in the tetragonal space group D4h2-P4/rncc, with four formula units in a cell of dimensions a = 16.048 (7) and c = 6.367 (3) A. Full-matrix least-squares refinement gave a final value of the conventional R index (on F ) of 0.052 for 1278 reflections having Fo2> 3u(FO2).The crystal structure consists of stacked Pd(bqd)z units, each staggered by 65' with respect to its nearest neighbors, and disordered chains of iodine atoms extending i n the c direction. The solvent molecules are disordered throughout tunnels which extend parallel to c. The Pd-Pd distance is 3.184 (3) A, Pd-N = 1.996 (7) A, and the Pd(bqd)2 units are rigorously planar. Resonance Raman studies ( V O 4880-647 I A) of Pd(bqd)210,5.S and Ni(bqd)2lo,s.S indicate that the predominant form of the iodine present is 13- (Vfundamental 107 cm-I), hence that the formal charge on the M(bqd)z units is +O. I7 (2). Iodine-I29 Mossbauer studies are also consistent with the 13- formulation. Optical spectra of these complexes exhibit a strong, broad transition at 600 nm which is largely, if not exclusively, due to the polyiodide chains. Crystallization of Ni(bqd)2 from benzene containing traces of iodine produces the new orthorhombic phase Si(bqd)zlo,olB. Singlecrystal X-ray studies have shown it to crystallize in the space group D:i-lbam with four formula units in a unit cell of dirnensions a = 16.438 (2), b = 14.759 (4), and c = 6.360 (2) A. Full-matrix least-squares refinement gave a final value of the conventional R index (on F ) of 0.1 1 for 1026 reflections having Fo2 > 3u(FO2).The structure contains rigorously planar Si(bqd)2 units stacked along the c axis with each molecule staggered by 68' with respect to its nearest neighbors. The Ni-Ni distance is 3.180 (2) 8, and Ni-N = 1.88 ( I O ) A. Structural relationships are discussed for all M(bqd)2 and M(bqd)zl, compounds; partial oxidation results in a small contraction of the interplanar spacings of 0.019 A (Pd) to 0.027 A (Ni). Single-crystal electrical conductivity measurements (dc and 100-Hz ac) in the stacking direction show an increase in conductivity upon partial oxidation of > I O 3 ( S i ) and > I O 4 (Pd). Maximum conductivities a t 300 K are Ni(bqd)210.5~.0.32C6HsCH3 = 1 . 1 X 10-5 (R cm)-' and Pd(bqd)210.5.0.52o-C6H&l2 = 8.1 X I 0-3 ( Q cm)-'. Variable-temperature studies show that the electrical conductivity follows, over the entire range investigated, an exponential temperature dependence with a single activation energy: 0.54 f 0.08 (Ni) and 0.22 f 0.03 eV (Pd).
I n an accompanying article3 we discuss the properties of stacked, partially oxidized bisdiphenylglyoximates of nickel and palladium, M(dpg)zI, A . It was found that the iodine in these materials was present predominantly, if not exclusively, as IS-, hence that the M(dpg)2 units possess formal frac-
M = Ni, Pd. The nickel complex was reported to possess a tetragonal ( P 4 / m c c )crystal structure with stacks of partially staggered Ni(bqd)z units (Ni-Ni = 3.153 ( 3 ) A) and disor-
B A M = Ni, Pd tional oxidation states representable approximately as [ M(dpg)z]s+I~-.Though the iodine oxidation produces a 107-108 increase in d c electrical conductivity, the facility of electron transport in these materials is still less than that of K2Pt(CN)4Br~.3.3H204and several other classes of partially oxidized metallomacrocycles that we have recently synthesized.5 It was thus of interest to explore the effect of chemical functionalization on the metal bisglyoximate core. A means to decrease stacking distances and to elaborate conjugation was evident in the planar nickel and palladium complexes of benzoquinonedioxime, M(bqd)2, B.6 The earlier work of Endres and c o - w o r k e r ~established ~~~ the existence of quasi-onedimensional materials of reported stoichiometry M(bqd)zIo,s, 0002-7863/79/1501-2937$01 .OO/O
M = Ni, Pd dered chains of iodine-containing species running parallel to the c directiom8 It was proposed that iodine was present as l 3 - , though this conclusion could not be derived from the Bragg diffraction pattern. The crystal structure of the uniodinated precursor, Ni(bqd)z, was found to be monoclinic ( P 2 1 / n ) by Leichert and Weiss' and to consist of canted bis(benzoquinonedioximato)nickel units. In contrast, the structure of Pd(bqd)z is orthorhombic (Irncb) with stacked Pd(bqd)z moieties extending along the c axis.Io Though the aforementioned work provided an important initial glimpse of the range of bisbenzoquinonedioximate structures and compositions obtainable, several important questions remained unanswered. First, the nature of the iodine in the M(bqd)zIo,5 species was undetermined. Thus, it was impossible to say with certainty whether the iodinated nickel
0 1979 American Chemical Society
2938
Journal of the American Chemical Society
and palladium bisbenzoquinonedioximates were actually mixed valence (partially oxidized) materials or not. Second, the available structural data did not provide a clear picture as to what geometrical changes, if any (e.g., in the metal-metal stacking distances), accompanied iodination. The canted monoclinic Ni(bqd)z and stacked tetragonal Ni(bqd)zlo,5 structures could not be meaningfully compared in the sense that the stacked Ni(dpg)z and Ni(dpg)zl structures could.3 In addition, structural data on Pd(bqd)zlo.s were not available for comparison with the existing orthorhombic Pd(bqd)z structure. Finally, little was known about the charge transport properties of M(bqd)zlo,s single crystals vis-a-vis those of M(bqd)z." In a preliminary communication12 we reported a resonance Raman and iodine-I 29 Mossbauer study of Ni(bqd)zlo,s which showed the iodine to be present predominantly as 13-, hence that the charge distribution could be represented by formal fractional oxidation states as depicted by [Ni(bqd)z]h+l3-. Independent of this work, analysisi3of the diffuse X-ray scattering pattern arising from the disordered iodine chain structure in Ni(bqd)&s reached exactly the same conclusion concerning the form of the iodine: 13-. In this paper we present a full exposition of our chemical, spectral, structural, and charge transport investigations within the nickel and palladium bisbenzoquinonedioximate series. This discussion includes a reformulation of the actual composition of the M(bqd)zlo,s materials, the structural characterization of P d ( b q d ) ~ I o , ~ - 0 . 5 2 o - C ~ H &the l ~ , synthesis and structure elucidation of a new, orthorhombic Ni(bqd)110.018 compound, comments on M(bqd)2I, optical spectra,I4 and a comparison of the geometrical, partial oxidation state, and charge transport characteristics in all of the aforementioned materials.
Experimental Section All solvents and chemicals were reagent grade. Benzene, toluene, and hexane were freshly distilled from sodium-potassium alloy under nitrogen; o-dichlorobenzene was dried over Davison 4A molecular hievcs. The ligand o-benzoquinonedioxime (bqdH) was synthesized by the reduction of o-dinitrosobenzene with sodium borohLdridc as described e1~ewhere.l~ Elemental analyses were by Ms. H . Beck, Northwestern Analytical Services Laboratory, Micro-Tech Laboratories. Galbraith Laboratories, or Alfred Bernhardt Microanalytical Laboratories. Analysis of Ni and I by neutron activation was performed by General Activation Analysis, Inc. Mass spectra were recorded on a Hewlett-Packard 5930 instrument by Dr. D. Hung. lodinated materials were routinely stored at -20 "C in the dark. Bis(benzoquinonedioximato)nickel(ll), Ni(bqdl2. This complex was prepared by the room temperature reaction of NiC12.6H20 with bqdH in ethanol-water. The reaction is complete within O S h. The crude, dark-brown Ni(bdq)? was collected by suction filtration, washed with distilled water, washed with methanol, and then dried for several hours at I I O "C. The crude product was finally Soxhlet extracted (twice) uith benzene to yield a dark-brown, microcrystalline solid. Yields of Ni(bqd)2 from this procedure were typically about 80%. Large crystals (clongated platelets) for transport studies were grown by very slow cooling of hot toluene solutions. Anal. Calcd for C12HIoN4O41\ji:C , 43.28; H, 3.03; N , 16.83. Found: C , 43.21: H, 2.96; N , 16.74. Infrared data (Nujol mull. cm-l): 3090 w, 1600s. 1500 s, 1265 s, I I40 m, IO80 s, 950 (br), 820 w. 740 vs, 610 m. Bis(benzoquinonedioximato)palladium(II),Pd(bqd)2. The procedure for the synthesis and purification of this compound was analogous to that described above for Ni(bqd)2 except that the PdCl2 starting material was solubilized by treatment with a small amount of hydrochloric acid. The final product, Pd(bqd)2, is a dark-green, microcrystalline solid. Larger crystals can be grown by slow cooling of hot toluene solutions. Anal. Calcd for C I ~ H I O N ~ O C, ~37.86; P ~ : H , 2.65; N , 14.72. Found: C , 37.78; H , 2.60; N , 14.68. Infrared data (Nujol mull, cm-l): 16OOs, 1520vw, 1490s, 1415 s, 1355 s, I285 vs, 1 1 8 5 m, I I65 m, I 1 30 w, 1060 vs, 965 w, 880 m, 790 m, 740 s, 730 s, 6 I5 m. Bis(benzoquinonedioximato)palladium~O.50iodine-0.520-dichlo-
/ I 0 I : I I / M a y 23, I979
robenzene, Pd(bqd)~I~.5*0.52o-C~H~C12. Solutions of Pd(bqd)2 i n odichlorobenzene (4.5 X 10-3M) were heated to 90 "C and were then made 4.0 X IO-' M in triply sublimed iodine. The resulting mixture was next filtered while hot, and the filtrate rewarmed to 90 "C. The hot solution was then allowed to cool to ambient temperature over a period of 3-5 days. At this time the cooled solution was suction filtered. and the solid product was washed repeatedly with cold hexane and then dried in air. Dark, needle-like crystals of the desired product possessed a golden luster and were typically 3-1 5 mm in length. These crystals were mechanically separated from the noncrystalline and microcrystalline material. The yield of golden crystals obtained in this manner was ca. 400% On the basis of the elemental analysis of the bulk material, thc stoichiometry Pd( bqd)210.5.0.520-CnH4C12 is assigned. Anal. Calcd for C I ~ . I ~ H ~ ~ . ~ ~ C N, ~34.91; O ~ H, P~ 2.34; I~.~CI~. N. 10.78; I, 12.13; CI. 7.06. Found: 34.56; H, 2.34; N , 10.82; I, 12.19; CI, 7.09. Analyses (C,H,N, Bernhardt) on each of three single crystals weighing 0.372, 0.500, and 0.675 mg indicated an average incorporation of o-dichlorobenzene corresponding to Pd(C6H5NzOz)z-
Io.sz(z)(o-ChH4Clz)o.41(2,.
Mass spectra of the above crystals ( I O - or 70-eV ionizing voltage) recorded with source and probe temperatures of 200 and 100 'C, respectively, revealed the parent ions and fragmentation patterns characteristic of iodine and o-dichIorobenzene.l6a Infrared data (Nujol mull, cm-I): 1600 s, 1520 vw, 149Os, 1415 s,1355s,128Ovs, 1185m,1160m,1130w,1065vs,970w,880w,790 w, 740 s, 730 s, 61 5 m. When the above synthetic procedure was carried out with increased iodine concentrations (4.9, 5.9.6.9, 7.9 X IO-* M) the yield ofgolden crystals decreased and the appearance of a dark, shiny, rather flaky material was noted. For the above four experiments, the product analyzed as Pd(bqd)zl,, where x = 1.5-2.0. As an example, the product M) in hot o-diobtained when a solution of Pd(bqd)z (4.5 X chlorobenzene was made 7.9 X IO-2 M in iodine analyzed as Pd(bqdlz11 8 . Anal. Calcd for C I ~ H I ~ N 4 0 4 P 8:d IC,I 23.66; H, 1.65; N , 9.20: I , 37.50. Found: C, 24.03; H, 1.05; N , 9.08; I, 36.72. The infrared spectrum was identical with those of the other Pd(bqd)zl, materials. The resonance Raman spectrum ( V O 5145 A) displayed prominent scattering at IO7 m, 174 vs, 21 5 w, and 360 m cm-'. Bis(benzoquinonedioximato)nickel~0.52iodine~0.32toluene,
M) and Ni(bqd)2Io.52*0.32C.IHs.Solutions of Ni(bqd)2 (6.0 X triply sublimed iodine (4.0 X 1 0-2 to 4.4 X IO-' M) in toluene at 90 " C were treated in a manner analogous to the previously described procedure involving Pd(bqd)* in o-dichlorobenzene. Large, needle-like crystals exhibiting a golden luster could be isolated from the toluene solutions in ca. 20% yield. Anal. Calcd for C14.24H12.56N404Ni10.52: C , 39.92; H, 2.96; N , 13.08; I , 15.40. Found: C, 37.60; H , 2.74; N , 13.07; I . 15.49. The mass spectrum of the above crystals ( I O or 70 eV, 200 "C source, 100 "C probe) exhibited a pattern characteristic of iodine and toluene.Ihb Infrared data (Nujol mull, cm-I): 3090 w, I600 s, 1500 s, 1265 s, 1160 m, IO80 vs, 980 w (br), 830 m, 740 vs, 615 rn. Bis(benzoquinonedioximato)nickel*0.018iodine. Ni(bqd)zIo.o~s.A solution of Ni(bqd)2 (6.2 X I 0-3 M ) and triply sublimed iodine ( I .4 X IO-* M) in benzene was heated to 78 "C and filtered while hot, and the filtrate was allowed to cool slowly to ambient temperature. The resulting dark crystals were collected by suction filtration, washed repeatedly with hexane, and dried in air. The crystals of this material are dark needles, exhibiting no golden luster. The C, H, N elemental analysis is experimentally indistinguishable from that of Ni(bqd)z. Anal. Calcd for CI~H~0N404Nil0.018: C, 43.00; H, 3.01; N, 16.72. Found: C, 43.45; H, 3.25; N, 16.23. Calcd for C 1 2 H ~ 0 N 4 0 4 N c, i: 43.28; H, 3.03; N , 16.83. A determination of the ratio of nickel to iodine in a single crystal (the X-ray data crystal) by neutron activation analysis gave Ni:I = 1 .00:0.018(7). Infrared data (Nujol mull, cm-I): 3090 w, 1600 s, I500 s, 1265 s, 1140 m, 1080 s, 950 s (br), 820 w, 740 vs, 610 m. Spectral Measurements. Infrared, resonance Raman, and electronic spectra were recorded in the same manner and with the same apparatus as described p r e v i ~ u s l y . ~ Iodine Mossbauer Studies. The apparatus and data acquisition/ analysis procedures employed were as described p r e v i ~ u s l ySamples .~
Ibers, Kannewurf. Marks, et al.
/ Iodinated Nickel and Palladium Bisbenzoquinonedioximates
were prepared by weighing ca. 70 nig of Ni(bqd)2 into a small vial, adding the desired amount of IZ9l2-' in 1-2 mL of benzene or o-dichlorobenzene, capping the vial, heating the mixture to ca. 80 "C, and then allowing it to cool slowly overnight. The solid product was next collected by centrifugation. washed several times with 1-2 mL of hexane, and then dried under a stream of dry nitrogen. Several samples were prepared which elemental analysis showed to have a Ni:I ratio grcater than 1 .O. Single-Crystal Electron Transport Measurements. The procedures and apparatus for four-probe conductivity measurements were those described for the M(dpg)zl work.3 Contact materials were colloidal graphite suspended in I ,3-butylene glycol or Demetron M8001 cold-setting conductive gold contact paint. Results with these two contact preparations were indistinguishable. Typical crystalline samples of the bisbenzoquinonedioximates were approximately tetragonal needles with lengths of 2.0-4.0 mm and widths of 0.1-0.3 tiim. All measurements were conducted with current flow along the necdlc axis, i.e., along the molecular stacking direction. Variabletemperature studies employed measurements taken with both increasing and decreasing temperature to check for possible hysteresis; none was observed. Room temperature conductivity measurements wcre always made after high-temperature studies to ascertain i f sample decomposition was taking place. X-ray Diffraction Study of Ni(bqdl2Io.ols.Preliminary film data were consistent with Laue symmetry mmm. Systematic extinctions are indicative of space groups /bani or lbn2. Based on the setting angles of 14 manually centered reflections (40" I 28 5 60', Cu Kal) the cell constants presented in Table I were obtained. Data were collected at room temperature on a Picker FACS- I diffractometer using methods general i n this laboratory.'' Important features of the data collection are summarized i n Table I. The structure was solved and refined in a facile manner, using procedures and computer programs described before.17 The centrosymmetric space group Ibam was assumed on the basis of excellent agreement among Friedel pairs. The positions of the atoms of the Ni(bqd)2 species were obvious from a three-dimensional, originrcmoved, sharpened Patterson function. Included in the final cycle of least-squares refinement were the contributions from hydrogen atoms on the carbon atoms. The positions of these hydrogen atoms wcre calculated, assuming C-H = 0.95 A. The hydrogen atom position in the O( I)-H-0(2) hydrogen bond was not included. This final refincment converged to R indices and an error in an observation of unit weight given in Table I. Examination of the final agreement between IFo/ and IFc/reveals some disturbing features: ( I ) The highest residual peak of I .36 e/A3 is located at I/:OO, but there is a general level of density along the I/20z line. (2) There are some outstanding differences between IF,( and IFc( especially for hkO reflections (e.g., 510 ( 8 . 7 , 25.0); 330 (12.3, 1.9 e-)). O n the basis of the neutron activation analysis of the data crystal (see above) there appears to be approximately 0.02 iodine atoms per nickel atom in the material. Presumably, the iodine atoms are positioned along the '/*Oz row, since there are large channels there that could accommodate iodine. Although a number of attempts were made to approximate the iodine scattering, none was especially successful. However, these calculations did establish that the overall structural parameters of the Ni(bqd)2 portion of the structure are insensitive to models for the iodine scattering. Ultimately we chose as the final model one that ignores the presence of iodine. Table I I presents the final parameters from this model. Tdble 111 presents the final listing of I O IFo/vs. 10IFcI for those reflections used in therefinement.'s X-ray Diffraction Study of Pd(bqd)210.g0.52C6H4CI~. Preliminary film data indicated Laue symmetry 4/mmm, and systematic extinctions are consistent with space groups P4/mcc and P4cc. The cell constants (Table I)were obtained from the setting angles of 15 reflections manually centered on a FACS-I diffractometer (30 < 28 < 40'. MO Kal).Other features of the crystal and data collection are given in Table I. The structure was solved and refined as described above. Examination of Friedel pairs strongly suggested that the centrosymmetric space group P4/mcc is the correct one. The Pd(bqd)zl, portion of the structure was located from a Patterson function and subsequent difference Fourier maps. In the final refinement of this portion of the structure variable occupancy of the iodine atom was included. The resultant formula was Pd(bqd)210.444 and the final values of R , w R , and an error in an observation of unit weight were 0.070,O.102, and
2939
Table I. Crystal Data and Details of Data Collection and Structure Refinement ~
~~
compd
Ni(bqd)zlo 0 1 s
formula
C I ~ 1010 H 01sN4Ni04
formula weight, amu a, A b, A
355. I6
16.438 (5) 14.759 (4) C, A 6.360 (2) v,A3 1543.2 space group 0::- Ibam Z 4 Pcd,cd*g/Cm3 1.443 Cu Ka rad Iat ton crystal shape (001111 I O ) faces, needle axis [00 I ] crystal dimensions, 0.8 X 0.1 X 0.1 mm crystal volume, 0.0062 mm3 g>cm-' 21.9 transmission 0.703-0.864 factors takeoff angle, deg 4.2 aperture, mm 5.5 X 4.8 32 cm from crystal scan speed, deg/ 2.0 min 0.85 below K a l to scan range, deg 0.85 above Ka2 20 s with rescan background counting times option 28 range 3- 160" data collected h, k , f I
P unique data with Fo2 > 3 4 F 0 2 ) no. of variables R index
16.048 (7) 16.048 (7) 6.367 (3) 1639.6 D&- P4/mcc 4 2.320 Mo K a 1001)I 1 101 faces, needle axis [OOI] 0.8 X 0.2 X 0.2 0.030 23.4 0.61 9-0.697 2.5 4.0 X 4.8 32 cm from crystal 2.0
0.04 1026
0.85 below K a l to 0.85 above Ka2 20 s with rescan option 3-80' h 2 . k , I with I odd terminated at 55 ' h 2 k , -I to 40" 0.03 1278
65 0.1 1
74 0.052
3.63 e-. Again there were some individual examples of poor agreement between IFo( and IFc(. in this instance not restricted primarily to the hkO reflections. A difference Fourier map showed as its main features ;I peak of height I .28 e/A3 at approximately 0.06,O.13.0. I5 and a ring of electron density about x = 0, J' = 0 in the z = '/4 plane. At this point it was discovered (see above) that thecrystals of this compound contain varying amounts of o-dichlorobenzene, the average amount being 0.52 solvent molecule/palladium atom. Consequently, it number ofattempts were made to account for the residual electron density as arising from a variable amount of o-ChH4C12 i n the O,O, z channel. Because of the fourfold symmetry imposed on this channel and the fact that the solvent molecule does not intrinsically possess such symmetry, the disordering of the solvent is considerable. Although a calculation of the contributions of a ChH4C12 rotor, constrained to lie i n the z = '/4 plane, led to some improvement between IFo)and l F c J .this model did not account for the main residual peak. Ultimately, a CI atom was placed at the position of this residual peak and in subsequent cycles the occupancy and isotropic thermal parameter of this CI atom were varied, along with the other variables of the Pd(bqd)2lX portion. This refinement ultimately converged to the formula Pd(bqd)210.48.0.9 I O - C ~ H ~ and C I ~agreement indices present in Table I . Because of correlation between occupancy and thermal parameter of the CI atom and because of the very approximate nature of the model for solvent scattering, the ratio of solvent to Pd(bqd)zl derived from these data is very uncertain. We will henceforth refer to this compound, based upon the elemental analysis (vide supra), as Pd(bqd)zIo,5~0.52.o-C~H4Cl2. Placement of a CI atom at this position is made chemically reasonable by the resultant CI.-CI distance of 3.05 A, a value to be expected in o-C6H4CI2. The improvement in agreement indices is considerable as is, more impor-
/ May 23, 1979
Journal ofthe American Chemical Society / 101:l I
2940
Table 11. Positional and Thermal Parameters for the Atoms of Ni(bqd)210.018 ITOM NI
0111
0121
NIII
X
1
0 01144911b31
-0.0Z7451161
C I O
0.112011621 0.029391931 0.15b71(831 O.LOO5IlOl
CI3I
0~14231151
CIbI C I O
NIZI
CllI
2
I
.LIBOR
0,.2
4.091111
2.331121
22.861791
0
5.bblbbl 9.171611
9.31168l
32.61301
4.121b91
38.11341
-0.01692168l 0.124751711
0
3.CbI331 8.651691
6.111651 4.751551
25.61291 23.61311
10.9111l 6.911761
17.21341 27.51401
-0.111641
7.01121 25.51321
35.91b91 27.71571
Zb.Ol3bl 18.01211
bl.51811 29.91b9l
0 0
0.06051111
0
0
b.331511 5.111661
0
11.+1131
0.2275123I
0.228711SI 0.22~31281
0
1h.bI19l
O.28OlllSl 0.2417llll
0.1b461291 0.06b0119#
0
5.blILl
0
5.bb1701
nic131 niccbr
0.112
0.211
0
9.6
0.253
0.286
0
14.9
H1CIII MlC16I
0.338
0.155 0.019
0
13.0
0
10.1
0.283
812
033
0
O~lb3OIlOl
CIaI
022
0 -0.09610I11l 0.11933166l
0.l3llZl 3.23(411 2.011bbI
023
011
0 0
0
0 0
0
0
0
0
-2.031621
0 1 0
-2.61101
0
0
-16.41221
0
0
-b.91161 -3.71101
0
0
0
0
0.7313bI -0.671b1l
0 0
Estimated standard deviations in the least significant figure(s) are given in parentheses in this and all subsequent tables. The form of the anisotropic thermal ellipsoid is: exp[-(BI 1 h 2 B 2 2 k 2 B331 2B12hk 2B13hl 2B23kl)l. The quantities given in the table are the thermal cofficients X IO3.
+
+
+
+
+
Table IV. Positional and Thermal Parameters for the Atoms of Pd(bqd)~l0,~~.0.9lo-C~H~Cl~ P
LTOM
I
'I
I
0
811 O R 8 . L
2
022
012
033
5.64151 3.83131 4.661261
5-66 3.65131 4.81(271
54.531631 15.441141 30.51101
a
3.951231
c
7.301301 4.251271
5.741101
35.61191 16.51151
0.6164714CI 0.553171531
C C
5.321311 5.191411
L.OS(ZLII
18.81171
5.491431
14.81171
-5.501361
0.117471541 0~:59491691
0.628951521 D.IG7901621
0
5.571411
4.161381
0
0.621641
51691491
18.CIl8l 29.113Ol
-0.51(331 -2.121451
0.24404l831 0.29217(641
0.75553192) 5.6331719bl
0 0
b.841771 4.971491
9.22(751 12.341921
0.256751531
0.558061751 0.762
0
3.931371
9.49164)
30.41331 3r.91371 25.7(251
0
6.1
0.757
0
7.9
nisi
0.274 0.152
0.644
0
0.0
HI61
0.291
0
6.1
nio-oi
0.008
0.501) 0.364
CL
0.04858196l
0.12534(771
0.14311181
I
It2
ll2
1/4
PO
s J.157501341
0121
0.98il41371 0.1231914ll
ll2 0.40910134I 0.612201351 0.4828414lI
0
0111
C.035b21441 0.167131541
H(1I N12l
Clll
CIZI C(3I C141
C151 Clbl H(3l
nisi
0.134
0
C
0
023
013
0 0 0
0
1.481231 5.761231
0
0
0
0
5.1412*1
o
0 0
O.48(41
1.191231
0 0
0 0 0
0
-5.121591 -2.901571
0
0
0
0
-1.081401
0
0
0
6.a
27.16(661
a Estimated standard deviations in the least significant figure(s) are given in parentheses in this and all subsequent tables. quantities given in the table are the thermal cofficients X IG3.
tantly, the removal of outstanding, individual discrepancies between IF,[ and I F c [ .Table IV presents the final parameters from this model. Table V gives a listing of 101F,I vs. 101F,[ for the reflections used in the refinernent.l8
Results and Discussion Chemistry and Stoichiometry. The slow crystallization of Ni(bqd)2 and Pd(bqd)2 from certain hot aromatic solvents in the presence of an approximately tenfold molar excess of 12 produces iodinated crystalline materials with a golden luster: M(bqd)2
+ 12 + S + M(bqd)2-I,-nS
(1)
M = Ni, Pd S = aromatic solvent
In the case of Pd(bqd)2, iodination in o-dichlorobenzene yields a crystalline compound of approximate composition Pd(bqd)& 50-0.52o-C6H4C12. The presence of the solvent could be demonstrated by elemental analysis and mass spectrometry (see Experimental Section). Ni(bqd)2 was found to be too soluble in o-dichlorobenzene to give good yields of a crystalline iodination product. However in toluene, golden, lustrous crystals of approximate composition Ni(bqd)210.520.32C6H5CH3 could be isolated. The solvent incorporation was again assigned by elemental analysis and mass spectrometry. For Pd(bqd)z, the solubility in hot toluene was too small to allow isolation of crystalline iodinated materials in sufficient quantities for complete characterization. The above formu-
The
lations differ from previous iodination studies on the nickel and palladium bisbenzoquinonedioximates where solvent incorporation (o-dichlorobenzene) was apparently not d e t e ~ t e d . ' . ~ . ' ~ I n our experiments, iodination of Pd(bqd)2 in o-dichlorobenzene with a greater than tenfold excess of iodine produced a dark, flaky solid which analyzed approximately as Pd(bqd)zl,, x = 1.5-2.0. Iodination of Ni(bqd)2 in hot benzene with a twofold excess of iodine yielded a dark (not golden) crystalline material which contained little or no iodine according to standard elemental analyses. For the crystal of this material chosen for X-ray diffraction studies (vide infra), neutron activation analysis revealed a nickel/iodine ratio consistent with the stoichiometry Ni(bqd)2Io,olg. Thus, our chemical results indicate that the M(bqd)zI, stoichiometry has considerably greater variability than previously thought, both in terms of halogen content and in terms of the tendency for solvent incorporation. It will be seen that both characteristics are understandable in terms of the crystal structures of these materials. Resonance Raman and Iodine-] 29 Mossbauer Measurements. Raman spectra of the M(bqd)2I,.nS materials are presented in Figure 1 ; data are set out in Table VI. As was discussed in depth for the M(dpg)zI ~ t u d i e s different ,~ polyiodide species give rise to characteristic, resonant-enhanced Raman scattering ~ p e c t r a . Spectra ~ ~ , ~ ~ of Ni(bqd)210.520.32C6H5CH3 and Pd(bqd)2Io,50-0.52o-C6H4C12 are essentially identical; a strong emission is observed a t 107 cm-I and an overtone a t 215 cm-I. These bands are absent in the unio-
Ibers, Kannewurf, Marks, et al.
/
294 1
Iodinated Nickel and Palladium Bisbenzoquinonedioximates 1
Table VI. Raman Data for Metal BisbenzoquinonedioximatesaVb
Ni(bqd)2: none detected Ni(bqd)21o,olg:none detected Ni(bqd)210,5~0.32CsH5CH3: 322 w, 215 w, 153 w, 107 s Pd(bqd)z: none detected Pd(bqd)210,5.0.52o-C~H.&l2:322 w, 215 m, 155 w, 107 s Polycrystalline samples, 5145 A excitation. In cm-'; s = strong, m = medium. w = weak. (I
5
-
ab---,--
._,-
dinated materials. Such a Raman scattering pattern is characteristic of 13-, the 107-cm-' vibration corresponding to the /"L /" totally symmetric 1-1-1 ~ t r e t c hThere . ~ ~is ~no~evidence ~ ~ ~ for ~ free 12,weakly coordinated 12, or any more than trace amounts of IS- in these spectra. As was discussed in the M(dpg)2I work, such species are readily detected in resonance Raman spectra.3-5a-19 Unlike the diphenylglyoximate systems, no scattering from the M(bqd)2 units could be discerned in the iodinated materials. In the iodine-rich compounds of stoichiometry 500 400 300 200 I00 WNEVJNBER Pd(bqd)zI,, x = 1.5-2.0, strong scattering at ca. 180 cm-I was Figure 1. Resonance Raman spectra ( V O 5145 A) of ( A ) Pd(bqd)2observed, indicative of weakly coordinated 12, as found in the lo.s.0.520-C6H4C12.(B)Pd(bqd)z, (C) Ni(bqd)*Io,sz.0.32CsH~CH~, (D) structures and spectrasa.19 of materials containing I 2 and 13Ni(bqd)l. Weak transitions in (B) and (D)at I17 and 77 cm-' result from units in close proximity (e.g., (phena~etin)2H+I3--12,~~~~~ laser plasma emission. (cs+)2(13-)2.12,sa".9,21 (C2H~)4N+13-.212s"io~2ic). In the iodine-poor material, Ni(bqd)210.018, no Raman scattering attributable to a polyiodide species could be observed. Control stacking direction. A view of the unit cell is presented in Figure experiments indicated that this amount of iodine, present as 2. Each Ni(bqd)z moiety is staggered by approximately 6 8 O 13- or 15-, would be detectable. with respect to its nearest neighbors along the stacking axis.23 I n an effort to explore the possibility that Raman-inactive The iodine atoms, whose presence was established by neutron I- was present in the iodinated M(bqd)2 materials, iodine-129 activation analysis of the crystal used in the X-ray diffraction Mossbauer22s t ~ d i e s ~were . ~ " undertaken." In a cubic or apexperiment, are presumed, based upon analogous structures, proximately cubic environment, I- gives a characteristic singlet (6 -0.51 mm/s, e24Q = 0)22 in the iodine Mossbauer spec- to be positioned in the channel^^.^^^^.^^'^ along I/>,0, z , which exhibit residual electron density. trum. Because of the expense of iodine- 129 and the very large The Ni atoms in Ni(bqd)210.018occupy the 4c special posiexcesses of iodine necessary to prepare practical quantities of Ni(bqd)zIo,~r.O.32C6H5CH3or Pd(bqd)2Io.s0.52o-C6H~Cl2 tions in the orthorhombic space group fbam; thus, all Ni atoms are equally spaced along the stacking axis by c/2 (3.180 ( 2 ) as crystalline samples, it was necessary to study polycrystalline 8,).This Ni-Ni distance can be compared with values of 3.856 powders. Several iodinated nickel specimens were prepared (2) 8, for Ni(bqd)z (a monoclinic, slipped-stack s t r ~ c t u r e ) ~ by stirring Ni(bqd)2 compounds with a stoichiometric amount and 3.153 (3) 8, for Ni(bqd)210.50.~Partial oxidation typically of 12912in benzene or o-dichlorobenzene, then removing the results in a contraction in the metal-metal distance as illussupernatant and washing the solid product with hexane (see trated by the nickel metallomacrocycles Ni(dpg)2 and Experimental Section for details). The Raman spectra of these Ni(dpg)zI (3.547 8, vs. 3.271 ( I ) A),3 as well as N ~ P and c ~ ~ samples exhibited the characteristic 13- fundamental at ca. N ~ P C I , ~ ~ Pc ~ . ' J = phthalocyanine (4.79 8, for a slipped-stack 108 cm-I and no evidence of appreciable Is- or 12. Elemental structure vs. 3.244 (3) A). Nickel-nickel separations for analysis showed a Ni:I ratio greater than 1 .O. The Mossbauer stacked, unoxidized glyoximate systems are as short as 3.24 spectra of these materials were somewhat broader than norA in Ni(CHD)2,'5 C H D = 1,2-cyclohexanedionedioximato, maL3 apparently reflecting macroscopic and microscopic and 3.25 8, in Ni(dmg)2,26dmg = dimethylglyoximato. The sample inhomogeneity arising from the preparative procedure. shortest Ni-Ni distances are found in the dimeric, eclipsed, For this reason the derived polyiodide spectral parameters are not as accurate as in the M(dpg)zI ~ t u d i e s and , ~ exhaustive data refinement was not carried out. Most important, however, is the information these Mossbauer data provide on the possible presence of I- or, also, free 1 2 (6 = +0.98 mm/s, e24Q - 1586 M H Z ) . ' ~A conservative estimate of the amount of Iwhich could be present is 3 mol %: for free 12, this number is vN ca. 5 mol %. C D As already noted, an independent diffuse X-ray scattering study13 of Ni(bqd)zIo,s reached the same conclusion as our face-to-face structures of nickel macrocyclic compounds C spectral studies in regard to the form of the iodine present: 13-. (Ni-Ni = 3.063 ( I ) and D (Ni-Ni = 2.788 (2) In W e find that the diffuse scattering pattern exhibited by these complexes the nickel atoms are displaced slightly out of Pd(bqd)2lo,50.0.52~-C~H4CI2 (vide infra) is identical with that the ligand planes (as defined by the four coordinated nitrogen of Ni(bqd)210.5o,l3indicating that an identical form of iodine atoms) toward each other. Thus, the interplanar spacings are is present, namely, I3-. estimated to be 3.19 (Qz7 and 3.00 8, (D).28The metal-metal Ni(bqd)210.018 Crystal Structure. The crystal structure of separation in nickel metal is 2.49 A.29 Ni(bqd)zI0.018is composed of individual Ni(bqd)* units which The Ni(bqd)2 unit in Ni(bqd)210.018has crystallographically exhibit no unusual nonbonded contacts. The Ni(bqd)2 units imposed symmetry 2 / m and is therefore planar. Figure 3 shows are stacked along the crystallographic c axis, such that the the structure of the molecule and the atom numbering scheme. coordination planes of the Ni atoms are perpendicular to the The bond lengths and angles i n the Ni(bqd)2 unit are in good :PI-'I
'.A.
2942
Journal of the American Chemical Society
/
IOl:11
/
May 23, 1979
Figure 3. A drawing of the Ni(bqd)2 molecule in Ni(bqd)2lo,ols showing the atom numbering scheme. The vibrational ellipsoids are drawn at the 50% level.
Figure 2. View of the unit cell of Ni(bqd)2lo,o,salong the stacking direction. The a axis is vertical from botton to top, the b axis is horizontal to the right, and the c axis is toward the reader. The vibrational ellipsoids are drawn at the 50% level.
agreement with the parameters reported in Ni(bqd)29 and Ni(bqd)210.5.~These values are set out in Table VII. Pd(bqd)2Io,s*0.52o-C6H4C12 Crystal Structure. The structure of Pd(bqd)2Io.s.0.52o-C6H4C12is composed of individual Pd(bqd)2 units and I atoms exhibiting no unusual nonbonded contacts. A view of the unit cell is presented in Figure 4. The Pd(bqd)2 moieties are stacked along the crystallographic c axis, such that the coordination planes of the Pd atoms are perpendicular to the stacking direction. Each Pd(bqd);! moiety is staggered by approximately 65' with respect to its nearest neighbors along the stacking axis. The iodine atoms also stack one above the other in the c direction, filling the "tunnels" along i/21/2z created by the benzo rings of the benzoquinonedioximato ligands. The observed diffuse X-ray scattering pattern, which is identical with that reported for Ni(bqd)210.5.~~ is attributable to the disorder of the iodine atoms along the stacking direction. I n addition, the o-dichlorobenzene molecules are believed to reside, in a disordered fashion, in the tunnels of larger diameter (along OOz) created by the oxygen atoms and benzo rings of the benzoquinonedioximato ligands. The Pd atoms occupy the 4f special positions in the space group P4/mcc; thus, all Pd atoms are e ually spaced along the stacking direction by c / 2 (3.184 (3) ). This Pd-Pd distance is comparable with the Pd-Pd distances found in the partially oxidized stacked glyoximate compounds Pd(gly)zI (3.244 ( I ) A),30 gly = glyoximato, and Pd(dpg)2I (3.26 A).3ia-bThese distances are significantly shorter than the Pd-Pd distances found in the corresponding precursors P d ( g l ~ (3.558 )~ A)32 and P d ( d ~ g (3.52 ) ~ A)3icbut are only slightly shorter than the Pd-Pd distances in the unoxidized complexes Pd(bqd)z (3.202 (1) A),10Pd(dmg)2 (3.253 A),26 and Pd(CHD)2 (3.250 A).25 All of the above distances are considerably longer than the metal-metal distance in palladium metal (2.75 The Pd(bqd)2 unit has crystallographically imposed symmetry 2/m and is required to be planar. The molecular geometry is essentially that shown for Ni(bqd)210.018in Figure 3; the atom numbering scheme is the same. The bond lengths
x
Figure 4. View of the unit cell of Pd(bqd)*lo,s.0.52o-C~H~Cl2 along the stacking direction. The a and b axes are in the plane of the page, and the c axis is toward the reader. The vibrational ellipsoids are drawn at the 50% level; the dark circle depicts an iodine atom.
and angles in the Pd(bqd)z unit of the Pd(bqd)210.~.0.520C6H4C12 crystal structure are in good agreement with the parameters reported in Pd(bqd)2,Io and these values are given in Table VII. The most significant differences in the parameters of the Pd(bqd)2 units in the two structures are in the Pd-N(1)-C(1) and Pd-N(2)-C(2) bond angles, 114.0 (6) and 115.8 (6)Oin Pd(bqd)2lo.s.0.52o-C6H4CI2and122 ( I ) and 124 (1)' in Pd(bqd)2.Io Electronic Spectra. Figure 5 presents electronic spectra of the M(bqd)z and M(bqd)zI, compounds as polycrystalline speciments. Data are compiled in Table VIII. Several features are noteworthy. For both nickel and palladium systems, iodination does not produce a detectable change in the spectra at wavelengths shorter than ca. 500 nm. Considering the drastic structural change which occurs upon iodination of Ni(bqd)2 (monoclinic slipped stack structure with Ni-Ni = 3.856 (2) As tetragonal stacked structure with Ni-Ni = 3.153 (3) %,8) it seems unlikely that these bands are metalmetal3 (intramolecular nd,2 (n l)pz transitions with borrowing of intensity from metal metal charge transfer transition@) in origin. Rather, these are, in all likelihood, M(bqd)2 molecular transitions. The second noteworthy feature of the electronic spectra is the appearance of a broad transition in the 600-nm region upon iodination. We assign a major part of this absorption to the 13- chains. As discussed elsewhere, such intense optical transitions are typical of delocalized p ~ l y i o d i d e sThe . ~ ~spectrum ~~ of (benzamide)zH+13-, which
-
- -+
Ibers, Kannewurf, Marks. et al.
/ Iodinated Nickel and Palladium Bisbenzoquinonedioximates
2943
Table VII. Comparison of Bond Distances (A) and Angles (deg) in Nickel and Palladium Bisbenzoquinonedioximateso
M-M M-N( 1) N(1)-N(2) M-O( 1) N(2)-0(2) N(1 )-C(1) N(2)-C(2) C( 1 )-C(2) C(I)-C(6) cwc(3) C(3)-C(4) C(4)-C(5) C(5)-C(6) O( 1 ) - o m N ( 1 )-M-N( 2) O(l)-N(l)-C(l) O( 2)-N( 2)-C( 2) C( I )-C( 2)-C(3) C( 2)-C( 3)-C(4) C(3)-C(4)-C(5) C ( 4)-C( 5)-C(6) C(5)-C(6)-C( 1) C ( 6)-C( 1)-C( 2) M-N( I)-C( 1) M-N(2)-C(2)
Ni(bqd)do.o18
Ni(bqd)2W
Ni(bqd)zd
Pd(bqd)zIo.~ 0.52C6H4C12e
Pd(bqd)zf
3.180 ( I ) 1.858 ( I O ) 1.904 ( I O ) 1.288 (12) 1.335 (16) 1.341 (17) 1.199 (20) 1.510 (22) 1.545 (20) 1.440 (21) 1.402 (46) 1.460 (45) 1.297 (38) 2.372 (1 7) 83.0 ( 5 ) 123.5 ( 1 1) 121.4 (14) 115.2(16) 129.0 (23) 120.2 (23) 1 15.4 (25) 124.3 (16) 113.9 (9) 113.9 (9) 117.7 (12)
3.153 (3) 1.91 (2) 1.90 (2) 1.33 (3) 1.28 (3) 1.27 (4) 1.35 (4) 1.50 (4) 1.44 (4) 1.42 (4) 1.42 (6) 1.42 (7) 1.32 (6) 2.43 (3) 84 (1) 122 (2) 122 (2) 122 (3) 112 (2) 129 (4) 120 (4) 119 (3) 119(3) 115 (2) 1 I3 (2)
3.856 (2) 1.868 (4) 1.860 (5) 1.313 (7) 1.313 (8) 1.309 (8) 1.313 (8) 1.445 (8) 1.424 (8) 1.427 (9) 1.346 ( I O ) 1.432 (1 I ) 1.338 ( 1 1) 2.480 (6) 83.6 (2) 124.9 (4) 125.7 (4) 119.1 ( 5 ) 118.6 (6) 122. l ( 7 ) 121.5 (7) 117.0 (6) 119.8 (6) 1 1 5.4 (4) 114.7 (4)
3.183 (2) 1.996 (7) 1.955 (7) 1.305 (7) 1.356 (8) 1.331 ( I O ) 1.325 ( I O ) 1.454(11) 1.441 (12) 1.435 ( 1 2) 1.358 ( 1 5) 1.395 (18) 1.333 (15) 2.687 (9) 80.8 (3) 123.0 (7) 120.1 (7) 118.7 (8) 116.4(11) 125.2 (1 1) 121.1 ( I O ) 118.4 (10) 120.1 (8) 1 14.0 (6) 115.8 (6)
3.202 ( I ) 2.00 (2) 1.95 (2) 1.34 (2) 1.33 (3) 1.29 (3) 1.35 (3) 1.47 (3) 1.43 (3) 1.43 (3) 1.38 (4) 1.48 (4) 1.34 (4) 2.66 (4) 81 (1) 124 (2) 120 (2) 121 (2) 119 (2) 120 (3) 123 (3) 120 (2) 1 I7 (2) 122 ( I ) 124 ( 1 )
Atom numbering scheme is that in Figure 3. This work. work. 'I Reference IO.
Reference 8 and the refinement described in this work.
Reference 9. This
Table VIII. Electronic Spectral Data for Metal Bisbenzoquinonedioximatesin nm ( X IO3 cm-1)0,6 compd Ni(bqd)2
N i ( bqd)210,52. 0.32C,jH~CH3
Pd( bqd)2lo.s.0.520C6H4C12
Nuiol mull 238 318 420sh 472 590 220sh 260 315 450 540 650 br 802
(42.0) (31.4) (23.8) (21.2) (16.9) (45.5) (38.5) (31.7) (22.2) (18.5) (15.4) (12.5)
235 295sh 325sh 385 440sh 680
(42.6) (33.9) (30.8) (26.0) (22.7) (14.7)
295 sh 320sh 390 440sh 605 sh 685 br
(33.9) (31.2) (25.6) (22.7) (16.5) (14.6)
CHCI3 solution 308 417 455 553sh
(32.5) (24.0) (22.0) (18.1)
335 393 505sh 650 br
(29.8) (25.4) (19.8) (15.4)
20
4
-
e~
a
1 6,- e e r ,
__ 5 -
L
lrr
Figure 5. Electronic spectra ( N U J Omulls) ~ of polycrystalline samples
Pd(bqd)zloyO 520-CgH4C12. (B) Pd(bqd)2, (C) Ni(bdq)2105~ 0 32C&CH,, (D)Ni(bqd)z, (E) (beniamide)zH+I3of (A)
be polarized in the chain direction34cand that the presence of the 13- chains cannot be ignored in such analyses. Comparison of Metal Bisbenzoquinonedioximate Crystal sh = shoulder, br = broad. Data in parentheses given in Structures. The metrical and oxidation state information cm-'. contributed by the present investigation now allows a detailed assessment of the crystal structural consequences of partial is also a triiodide chain compound,35 is presented in Figure 5 oxidation. A comparison of unit cell data for the series is for comparison. A recent polarized single crystal reflectance compiled in Table IX; bond distances and angles are set out studyI4 of Ni(bqd)210.50 and Pd(bqd)210.50reached the conin Table VII. In the nickel system, the unoxidized material, clusion that reflectance maxima a t 1.6-1.7 eV (775-730 11131)~~ Ni(bqd)2, has a slipped-stack s t r u ~ t u r eA . ~packing diagram, in these materials, which were polarized in the chain direction, which has not previously been shown, is presented in Figure were metal-metal (d,z band pz band) in origin. Although 6. As has been noted e l ~ e w h e r e , ~this . ' ~ arrangement of the such an assignment for the M(bqd)2 stacks is reasonable, it planar molecules within the unit cell allows more efficient must be noted that the intense polyiodide transition should also packing (as judged by the density) than a stacked arrangement
-
2944
Journal of the American Chemical Society
/
101.1 I
1 May 23, 1979
Table IX. Comparison of Unit Cell Parameters for Various Metal Benzoquinonedioximates compd space group
z
a, A b, A C,
A
P
deg
3
v,A3
symmetry imposed on M(bqd)2
a
b
e
d
Ni(bqdh C$,-~2lJn 2 3.856 (3) 9.461 (6) 16.542 (1 2) 90.45 (6) -603.5 1
Ni( bqd)zIo.o18 D:f,-lbam 4 16.438 (2) 14.759 (4) 6.360 (2) 90 1543.2 2/m
Ni(bqdhIo 50 D:h-P4/mcc 4 15.553 (4) 15.553 (4) 6.307 (3) 90 1525.6 2Jm
Wbqd)2 D$,-lmeb 4 6.405 (1) 9.728 ( I ) 20.649 (2) 90 1286 2lm
Reference 9. This work.
Reference 8.
Pd (bqd) 2 10.5 D:h- P4/mcc 4 16.048 (7) 16.048 (7) 6.367 (3) 90 1639.6 2/m
Reference 10.
Figure 6. Packing diagram of Ni(bqd)2 plotted from the data of ref 9. Vibrational ellipsoids are drawn at the 50% level.
where the molecular planes are perpendicular to the stacking direction. In contrast to the Ni(bqd)z result, the Ni(bqd)210.018 structure is a n orthorhombic stacked one. Figure 7 compares the packing of stacked M(bqd)zI, structures. The change in crystal structure on proceeding from Ni(bqd)2 to Ni(bqd)z10.0~ includes ~ a decrease in the interplanar spacing of 0.22 8, and a decrease in the metal-metal distance of 0.68 A. There is no significant alteration in metrical parameters within the Ni(bqd)2 unit (Table VII). The crystal structure of Ni(bqd)tIO 018 evidences large tunnels extending in the stacking direction which contain only a small amount of iodine, but which may have contained larger quantities of material a t some time during the crystallization process. That polyiodide species (12, l3-, etc.) were not detected in the resonance Raman examination of this material suggests the predominant presence of iodine as I- and that the solid-state charge distribution can be formally represented as Ni(bqd)2 0,0’8+(I-)o.o18. The presence of undetected polyiodides (e.g., 13-) would mean that the degree of partial oxidation was even lower. Further oxidation of Ni(bqd)z produces “Ni(bqd)210.~O”with iodine present predominantly as I3-, indicating a formal charge distribution of Ni(bqd)zo.17+(13-)o.50/3.The oxidation state change is accompanied by an additional 0.027-A contraction in the Ni-Ni distance. There is no perceptible change in the internal N i(bqd)2 dimensions. Interestingly, the angle of eclipsing between Ni(bqd)z units changes only slightly upon further oxidation (68” 65”); however, the relative orientation of the stacks changes appreciably. As can be seen in Figure 7 , the effect is to provide two sets of tunnels which are nonequivalent in size and in surrounding environment. The smaller tunnel, which contains the iodine, is of approximate cross-sectional dimensions 4.8 X 4.8 A and is lined with hydrophobic C-H residues. T h e larger tunnel is ca. 7.4 X 7.4 A in size and is surrounded by C-H groups as well as more polar oxygen atoms
-
8
Figure 7. Comparison of metal bisbenzoquinonedioximate crystal structures viewed along the stacking direction.
which are engaged in hydrogen bonding). These tunnels contain the solvent molecules. In contrast to this result, the tunnels in Ni(bqd)2Io,olg are all crystallographically equivalent, have both polar and nonpolar regions, and differ in size (ca. 5 X 6 A) from those in Ni(bqd)210.50. The structure of Pd(bqd)2 is orthorhombic with molecular planes perpendicular to the stacking direction and a 90” eclipsing angle between neighboring Pd(bqd);! units (Figure 7 ) . The degree to which this structure differs from that of
Ibers, Kannewut$ Marks, et ai.
/
-3 0
2.8
2945
Iodinated Nickel a n d Palladium Bisbenzoquinonedioximates I
1
3. I
3.4
IIT
I
I
1
1
3.7
4.0
4 3
4 6
(10~1'~)
Figure 8. Electrical conductivity (dc) of representative Ni(bdq)tIo,sr0.32CH3C6H5 crystals as a function of temperature. Data are measured i n the crystallographic c direction. I
-
1
1
I
1
1
8.0
90
-2 0
E 0 I
C -30 t
I
-4 0
I-
O 0 -5.0 2
0 0
aP
-6 0
0 -7 0 20
3.0
I
I
1
I
4.0
5.0
6.0
70
I/T
(I03/'K)
Figure 9. Electrical conductivity (dc) i n the crystallographic e direction of representative Pd(bqd)>lo&52o-ChH4C12 crystals as a function of ternperature.
monoclinic Ni(bqd)2 may not be energetically significant since there is evidenceI4 (as yet unpublished) that Pd(bqd)z can also be crystallized in the same monoclinic form observed for Ni(bqd)z. Upon partial oxidation to Pd(bqd)2O 1 7 + ( I ~ - ) o 5013, the Pd-Pd distance decreases by 0.019 8, and the eclipsing angle between the stacked metallomacrocycle moieties decreases by 25'. A spreading out of the structure in the a-b plane provides tunnels for iodine and solvent inclusion. The arrangement of groups within the unit cell of Pd(bqd)& 5 0.520-CbH4C12 is identical with that in Ni(bqd)210 5 0 , Indeed, our refinement of the published Ni(bqd)& 50 crystallographic data,8 reported for a crystal grown from o-dichlorobenzene,8 indicates residual electron density in the larger set of lattice tunnels, i.e., those which contain solvent in Pd(bqd)& 50.52o-C6HdC12. The internal structural parameters of the Pd(bqd)2 unit change insignificantly upon partial oxidation (Table VII). Electrical Conductivity. Four-probe, variable-temperature c-axis conductivity data for Ni(bqd)zIo 52-0.32C6HsCH3 and Pd(bqd)zIo 5-0.520-C6H4C12 single crystals are shown in Figures 8 and 9, respectively. These and related data are summarized in Table X. The range of conductivities observed
for the Ni(bqd)2lo 52.0.32C6H5CH3 crystals is fairly narrow for all samples examined. The wider range for the Pd(bqd)zIo ~ . O . S ~ O - C ~ H data ~ C includes I~ a single sample of particularly poor conductivity. Nearly all other values were clustered at the high conductivity end of the range. Table X also compares the dc conductivity of selected M(bqd)zIo 5.S crystals with measurements at a frequency of 100 Hz. For M = Pd, there is good agreement between the techniques. For M = Ni, there is less good agreement, which is attributed to the integrity of the electrode contacts. The nickel-containing specimens presented the greatest measurement difficulties, and a large number of crystals were rejected owing to fractures and to nonohmic electrode behavior. It can be seen i n Table X that the conductivities of the uniodinated M(bqd)2 materials are immeasurably low. As has been observed for the metal bisdiphenylglyoximates and similar macrocycles, partial oxidation such as to M(bqd)zo 1 7 + results in a large increase in electrical conductivity. The enhancement for the bisbenzoquinonedioximates is ca. 1 03-I 06. Interestingly, considerably lower conductivities are observed for the Ni(bqd)210.018 crystals than for the Ni(bqd)zlo 5 2 0.32ChH~CH3crystals. This may reflect the differences in
Journal of the American Chemical Society
2946
/
101.1 I
1 May 23, 1979
Table X. Single Crystal (c axis) Electrical Conductivity Data for Metal Bisbenzoquinonedioximates and Bisdiphenylglyoximates
material
dc conductivityC at 300 K, ( Q crn)-’
N i(bqd)2 N i(bqd 1 2 10 01 8 N i( bqd)zlo 52*S4 Pd(bqd)z Pd(bqd)zlo 5.S’ Ni(dpg)zl Pd(dpg)zl
