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High Mass Resolution Plasma Desorption and Secondary Ion Mass Spectrometry of Neutral Nickel Thiolate Complexes. Crystal Structure of [Ni6(SC3H7)12] H erbert Feld, Angelika Leute, Derk Rading, and Alfred Benninghoven Physikalisches Institut der U niversität Münster, W ilhelm-Klemm-Straße 10, D-W-4400 Münster G. Henkel Fachgebiet Festkörperchemie der Universität Duisburg, Lotharstraße 1, D-W-4100 D uisburg 1 Thom as K rüger and Bernt Krebs* Anorganisch-Chemisches Institut der Universität Münster, W ilhelm-Klemm-Straße 8, D-W-4400 M ünster Z. N aturforsch. 47b, 929-936 (1992); received January 23, 1992 Plasma D esorption Mass Spectrometry, Secondary Ion Mass Spectrometry, Nickel Thiolate Complexes, Crystal Structure The use o f mass spectrometry for the analysis of transition metal complexes is dem onstrated by combined high resolution Plasma Desorption Mass Spectrometry (PDM S) and Secondary Ion Mass Spectrometry (SIMS) investigations of the neutral nickel thiolate complexes [Ni4(SC3H 7)8] (1 ), [Ni4(SC6H n)8] (2 ), [Ni8(SCH2CO O Et)16] (3 ) and [Ni6(SC3H 7) ,J (4 ). The posi tive spectra are dominated by three kinds of SI-species: (a) molecular ions, (b) fragment ions and (c) m olecular ions with one or more substrate atoms attached. The negative spectra show mainly nickel sulfur cluster ions of the composition ( N i ^ ) - . In contrast to many Fast Atom Bom bardm ent (FAB) spectra o f neutral metal complexes, SIMS and PDM S spectra provide molecular weight as well as fragment ion information. Both techniques are m ost powerful tools for the investigation of coordination compounds because the samples are easy to prepare and the spectra are independent of matrix conditions. Additionally crystallographic studies have been carried out for 4 . The hexanuclear complex 4 with square planar N i- S coordination sites crystallizes in the trigonal space group R 3 with Z = 3 and a = 18.537(5), c = 13.966(3)Ä. 1. Introduction Mass spectrom etry has proven to be a useful tool for the investigation of coordination com pounds. As is well known the mass spectra provide not only inform ation about the molecular weight of parent ions but also structural inform ation by the observation o f fragmentation patterns. The predom inant part o f investigations concerning metal complexes was done by fast atom bom bard ment (FAB) or field desorption (FD) mass spec trom etry [1-3]. On the other hand, little work has been carried out with plasma desorption (PDMS) [4] or secondary ion (SIMS) [5] mass spectrometry. The former PD M S and SIMS investigations are limited regarding mass resolution, mass range, or * Reprint requests to Prof. Dr. B. Krebs. Verlag der Zeitschrift für Naturforschung, D-W-7400 Tübingen 0932-0776/92/0700-0929/$ 01.00/0 transmission o f the analyzers used (quadrupole, magnetic sector field). To assess the analytical po tential of these desorption m ethods in com bina tion with a time-of-flight (TOF) mass analyzer we have now perform ed for the first time a combined PDM S/SIM S investigation of coordination com pounds. PDM S and SIMS spectra have been ob tained for a series o f different kinds of metal com plexes. According to their different behavior in the desorption process the investigated complexes can be divided into three groups: firstly neutral transi tion metal complexes, secondly 1 + and 2 + cation ic complexes and thirdly ligand stabilized metal clusters. The results concerning the latter two groups are described elsewhere [6, 7] whereas this paper focusses on neutral transition metal com plexes. In order to investigate the secondary ion (SI) emission o f neutral metal complexes we measured PDM S and SIMS spectra o f a series of group VIII (Ni, Pd, Pt) coordination com pounds. In the last Unauthenticated Download Date | 6/17/17 1:33 PM 930 three decades a great num ber of complexes has been synthesized with sulfur containing ligands. These com pounds have found an increasing inter est due to the impressive variety o f different struc tural principles [8] and their significance for bio logical systems [9—11]. Here we want to dem on strate the basic results of the mass spectrometric investigation for a representative and typical selec tion of nickel thiolate complexes. As the neutral complexes of this group are cyclic, the num ber of metal centers can be changed without changing the basic structure principle. Thus it is possible to ob serve the SI emission in dependence on the m o lecular size. We report on four complexes with a nuclearity of four, six and eight. One o f the com pounds investigated has been synthesized for the first time. An X-ray structure determ ination was carried out to assure both the empirical formula and the structure o f the com pound. 2. Experimental Section Instrumental The mass spectra were obtained with a new com bination PDM S/SIM S time-of-flight mass spectrometer (T O F -M S ) developed in M ünster [12]. In this instrum ent the sample can be bom barded consecutively with prim ary ions in the keV (SIMS) or MeV (PDM S) energy range. In the SIMS mode, a continuous beam o f 10 keV X e+ions is chopped by a 90°-deflection unit resulting in m ass-separated prim ary ion pulses. The pulse width is about 1 ns with an intensity of 5000 ions/ pulse and a repetition rate o f 5 kHz. F or the PDM S mode, fission fragments are delivered from a retractable annular 252Cf-source that can be placed between the target and the SI extractor. A source activity o f 15 //Ci leads to about 300 single desorption events per second in a sample area of 2 mm2. The beam diam eter in SIMS is adjusted to this area. In both cases the prim ary ions hit the same tar get area from the same side, thus allowing a direct com parison o f both desorption m ethods in the same instrum ent w ithout breaking the vacuum. Secondary ions generated at the target surface are extracted through the same secondary ion optics and mass separated by the same analyzer. D epend ing on the special analytical problem, the TO F-analyzer can be operated as a linear-type or reflectron-type analyzer. Due to the initial kinetic ener gy distribution the mass resolution (R = m/zfm) of H. Feld et al. • Mass Spectrometry of Nickel Thiolates the instrum ent is small for the linear operation mode (R ~ 500 1000), but high mass resolution (R ~ 8000) can be achieved by energy focussing with the reflectron-type analyzer. F urther details are described elsewhere [12, 13]. Two ways of sample preparation were used. Ei ther the sample material was dissolved in C H 2C12 and some //I of this solution (about 10~3 m ol/ 1) were deposited onto a substrate area o f about 0.4 cm2, or small crystals (crystal dimension < 0.1 mm) taken from the reaction recipient were direct ly put onto the substrate (crude sample). The sub strate was a thin aluminum foil (2 //m) with a silver suspension on the sample side. By this suspension the irradiated target is drastically enlarged. U sual ly thick samples (> 100 monolayer equivalents) were investigated. The prim ary ion dose density (PID D ) was var ied between IO10- - 1013 X e+ ions/cm 2 in SIMS and 106--10 9 fission fragments/cm 2 in PDM S, respec tively. Thus typical spectra accumulation times are 1 h for PDM S and 1 min for SIMS. Negative and positive SIMS as well as PDM S spectra were taken for all samples; the mass spectra in Figs. 2, 3, and 4 were carried out in the reflection mode. A ddition ally spectra were accumulated for different flight paths of the secondary ions (linear and reflection mode) to determine the stability of the SI. From these measurements the rate constant for fragm en tation of the SI and their half life times are calculat ed [14]. The SI-yield is determined by dividing Fig. 1. Structure of the [Ni6(SC3H 7)12] molecule in the crystal (H-atoms omitted). Unauthenticated Download Date | 6/17/17 1:33 PM H. Feld et al. ■Mass Spectrometry of Nickel Thiolates (M - S 3Ci 2H28)+ CV ° ^ 563.56 8 6°o - 5 6 3 .7 7 - u ^ 400 (563.66) D O U 565.66 (565.66) i-— 5 6 7 .5 5 -5 6 7 .7 6 (567.66) 1-— 569.65 (569.65) -j? 200 0 550 (c a lc u la ted ) 0.1 ? < Nc i'll. 600 0.2 iso to p ic d istrib u tio n c\ .N( A /c 7c sN A ,s cN C Nix ^Ni C -C 931 650 | It iso to p ic d istrib u tio n (from spectrum ) _______ J 700 750 800 850 mass / u — — Fig. 2. Positive PDM S spectrum (high-mass range, PID D = 2.3- 108/cm2) of [Ni4(SC3H 7)g] and calculated isotopic peak distribution. The fragment ion peak is shown with measured and calculated (in brackets) mass values. Fig. 3. Positive SIMS spectrum of [Ni6(SC3H 7)12], (highmass range, PID D = 4- 10'°/cm2). Fig. 4. Negative SIMS spectrum o f [Ni4(SC3H 7)g], (PID D = 6.9- 10n/cm2). the background corrected integrated peak area by the prim ary ion dose, whereas the yield ratio Y' is defined by the ratio of SI-yields in PDM S and SIMS: Y' = Y(PDM S)/Y(SIM S). com pounds are often formed as the main products besides cyclic complexes. The num ber of metal centers in the ring probably depends on the size of the ligands and the packing forces in the crystal lattice. The com pounds [Ni4(SC 3H 7)8] (1), [Ni4(SC 6H n )8] (2) and [Ni8(SCH 2C O O Et)16] (3) were prepared as reported in the literature [15-17]. Materials Nickel(II)chloride and 1-propanethiol used as commercially available compounds. were Preparation o f [ Ni 6(S C 3H 7) 12] (4) Synthesis Due to the high affinity of Ni(II) ions to sulfur generally high reaction rates occur with sulfur con taining ligands. During the synthesis of nickel thiolate com pounds insoluble polymeric chain 1-Propanethiol (1.52 g, 20 mmol) was added u n der a stream o f nitrogen to a solution of sodium methylate obtained from sodium (0.46 g, 20 mmol) in 40 ml of methanol. NiCl 2 (0.65 g, 5 mmol) was added and the resulting solution was filtered after Unauthenticated Download Date | 6/17/17 1:33 PM 932 H. Feld et al. • Mass Spectrometry of Nickel Thiolates stirring for 1 d. The dark precipitate was washed with m ethanol and dissolved in 20 ml of C H 2C12. After stirring for 3 h, the dark red solution was fil tered and evaporated to a volume o f 10 ml. At -2 0 °C black crystals suitable for X-ray diffrac tion were formed within 3 d. All operations were carried out in degassed solvents under a pure ni trogen atmosphere. Elemental analysis gave satis factory results. gram package SHELXTL PLUS. An empirical ab sorption correction was carried out. All non-hydrogen atoms were treated anisotropically, where as the hydrogen atoms were calculated at idealized positions ( C - H 0.96 Ä) assuming an isotropic tem perature factor coefficient of 0.08 Ä2. The final coordinates together with the equivalent isotropic tem perature factors are given in Table II [28]. 3. Results Collection and reduction o f X-ray data Crystal and molecular structure o f [ Ni 6(SC 3H 7) I2] Crystals of 4 were obtained from the reaction mixture. X-ray diffraction data were collected at room tem perature on a Siemens R 3 four-circle dif fractom eter equipped with a M oK a source, a graphite m onochrom ator and a scintillation counter. Details o f data collection are given in Table I. Table I. [Ni6(SC3H 7)12]: Details o f data collection and structure refinement. Form ula Mol. wt. a[M c[Aj ^"36^84^*6^12 V[A3] Crystal system Z dcalc>[g Cm“3] Space group Crystal dimensions // [cm"1] (M oK a) Scan speed [deg/min] in 2 6 Scan mode 20max,[deg.] No. of unique data measd. No. of obsd. data (I > 1.96er(I)) No. of variables R/R w 1253.99 18.537(5) 13.966(3) 4156.0 trigonal 3 1.50 R3 0.4x0.4x0.3 24.7 4 -2 9 6126 scan 54 2021 (+h, +k, ± 0 1829 82 0.027/0.034 Solution and refinement o f the structure The structure was solved by direct methods and refined by full m atrix least squares using the p ro Atom X Ni S(l) S(2) C (l) C(2) C(3) C(4) C(5) C(6) 0.18136(1) 0.17204(3) 0.17028(3) 0.12683(15) 0.13498(17) 0.09884(21) 0.26270(14) 0.34337(15) 0.37669(16) y 0.07934(1) -0.01486(3) -0.01420(3) -0.01071(14) -0.06579(17) -0.06121(20) -0.02573(15) 0.05204(17) 0.12097(19) z 0.00053(2) 0.10250(3) -0.10473(4) 0.21703(14) 0.29093(16) 0.38647(18) -0.09141(18) -0.12228(18) -0.05104(21) According to the X-ray structure determ ination the unit cell contains three cyclic [Ni6(SC 3H 7)12] molecules (point symmetry 3) which are composed of nearly perfect hexagons of nickel atom s with two doubly bridging thiolate ligands between each adjacent pair (Fig. 1). The resulting metal coordi nation is approximately square planar (Table III). The N i-N i distances of 2.919Ä, excluding strong m etal-m etal interactions, and the N i-S bond lengths with a mean of 2.201 Ä are com parable to the corresponding values in other known cyclic hexanuclear nickel thiolate complexes [18- 23]. S I emission Since both dried sample solutions and crystals of all investigated compounds lead to the same spectra no distinction between both preparation methods is necessary. The PDM S and SIMS spec tra do not show any significant differences. In gen eral the positive mass spectra can be divided into two parts: the mass region below and above m ~ 300 u. The low mass region is dom inated by sec ondary ions originating from the ligands and hydrocarbon contamination. In the mass range > 300 u mainly three types of SI species are found: (a) molecular ions, (b) fragment ions and (c) m o lecular ions with one or more substrate atom s a t tached. U eq * 0.03064(12) 0.03557(22) 0.03579(22) 0.0459(11) 0.0588(13) 0.0852(18) 0.0501(11) 0.0587(13) 0.0752(15) Table II. [Ni6(SC3H 7)12]: Positional param eters and equivalent isotropic thermal pa rameters. * The isotropic equivalent tem perature factor is defined as one-third of the trace of the orthogonalized tensor. Unauthenticated Download Date | 6/17/17 1:33 PM 933 H. Feld et al. • M ass Spectrometry of Nickel Thiolates Table III. [Ni6(SC3H 7)12]: Selected distances and angles3. Distances (Ä) N i- N i' N i- S ( l) N i-S (2 ) 2.919(1) 2.192(1) 2.203(1) N i'- N i- N i" S ( l) - N i—S(l') S (l) - N i-S (2 ) S ( l) - N i—S(2') N i - S ( l) - N i' 120.0( 1) N i- S ( l') N i-S (2 ') 2.204(1) 2.206(1) Angles (deg) 178.4(1) 82.4(1) 98.1(1) 83.2(1) S (2 ) -N i- S (l') S (2 )-N i-S (2 ') S (2 ')- N i- S ( l') N i-S (2 )-N i' 97.3(1) 176.6(1) 82.0(1) 82.9(1) a Symmetry transform ation: ('): +x-y, +x, -z; ("): +y, -x+ y, -z. (a) and (b) The first and m ost im portant SI species is the m olecular ion o f the metal complex, observed from all samples with the exception o f 3. The sec ond SI species is a relatively heavy fragment ion that is formed by a rearrangem ent under ion bom bardm ent. Both SI species are shown in the PDMS spectrum of 1 (Fig. 2), which is dom inated by two peaks at 565 u and 836 u. Besides the molecular ion peak at higher mass, the lower mass ion is probably due to a fragm entation of the complex and subsequent rearrangem ent o f the molecular structure. From a chemical point of view several suggestions for this fragment ion are possible. By the high mass resolution and accuracy of the ob tained mass spectrum the num ber of possible ex planations for this previously unknown rearrange ment product is drastically reduced. The com pari son o f calculated and measured isotopic peak pattern suggests a ( M - S 3C 12H 28)+ secondary ion as shown in Fig. 2. This ion can be formed by the splitting o f three complete ligands and the alkyl group o f a fourth ligand. The remaining sulfur atom may be situated above the center of the nickel ring bridging all adjacent Ni atoms. This suggestion is supported by the fact that the same rearrangem ent principle is observed in the mass spectra of [Ni4(SC 6H n)8] and [Ni8(SCH 2C O O Et)16], (c) The third type o f secondary ions observed in the positive mass spectra are molecular ions with one or m ore substrate atom s (Ag) attached. This secondary ion kind is only observed in the spectra of 1 and 4. Fig. 3 shows the peaks of the molecular and quasim olecular ions in the positive SIMS spectrum o f com pound 4. Due to the high mass re solution and accuracy o f the corresponding signal, the peak centered at about 1360 u was unam big uously derived to correspond to (M + A g)+ with M = [Ni6(SC 3H 7) 12] by com paring the calculated and measured isotopic peak distribution. The very rare case of an attachm ent of eight silver atom s to the molecular ion is only obtained by keV ion bom bardm ent of 1. The corresponding peak is centered at 1699.1 u. O ther substrate materials do not show any attachm ents to the molecular ion so that in some cases an enhancement o f the molecu lar ion peak is observed. The negative SIMS and PDM S spectra of all com pounds are dom inated by nickel sulfur cluster ions o f the com position (Ni^S^)- . F or most of these ions an excess of metal atom s is observed: i.e. x > y. The distribution o f these cluster ions ranges from x, y = 4 up to x, y « 30. The highest intensity is observed for the peaks o f the symmetric cluster ions (Ni 4S4)~ and (Ni 4S4)2_. Fig. 4 shows the nega tive SIMS spectrum o f 1. The whole series o f sig nals is due to ions of the com position N ixS;c_2, NiA - i and N ixSx. All spectra show a similar mass resolution for peaks resulting from the same SI species. High mass resolution is obtained for the molecular ion peaks whereas the fragm ent ion peaks are not well resolved. F or all complexes investigated the yields Y o f all characteristic secondary ions are signifi cantly higher in PDM S than in SIMS. The abso lute yields range from 0.01 to 0.4% in PDM S and between 0.001 and 0.08% in SIMS. The exact val ue depends on the special complex and the consid ered SI species. The yield o f molecular ions de creases with increasing diam eter o f the metal thiolate ring, whereas the yields o f fragm ent ions increase. The yield ratio Y' = Y(PDM S)/Y(SIM S), however, is mainly determined by the kind o f SI species. Y' varies between four (fragment ions) and eight (molecular ions). The stabilities of the generated secondary ions are estimated by m easuring their half life times. Values from about 100 //s (fragment ions) up to one ms (molecular ions) are found. Generally the stabilities o f these ions are only slightly higher in PDM S than in SIMS. Especially the molecular ion Unauthenticated Download Date | 6/17/17 1:33 PM 934 of 4 with one silver atom attached, (M + Ag)+, has a very high stability, even as com pared to the m o lecular ion itself. The half life times t 1/2 of these SI species in SIMS are 190 //s for M + and 640 ^s for (M + A g )\ 4. Discussion The yield ratio Y' (Y' ~ 5) and the dependence of the absolute SI-yield Y on the mass (respectively size) is relatively small for this group of metal com plexes com pared to other classes o f com pounds, e.g. cationic metal complexes [7], peptides [24] or poly mers [25] (Y' ~ 20 " 100). This behavior is typical for substances with a low interm olecular binding energy. Due to the fact that the desorption-active area is distinctly higher in PDM S than in SIMS, the molecular size o f strongly bonded molecules has a stronger effect on the decrease o f the SI-yield in SIMS than in PDM S. By contrast, this phenom enon is not observed for molecular solids with low binding energies. As the sample material was de posited in thick layers or small crystallites onto the target, completely neutral complexes occupy lat tice points and therefore the binding energy is dom inated by the weak van der W aals interaction. In this way both the relative independence of the absolute yield o f m olecular ions in PDM S and SIMS and the small value o f Y' can be explained. Our results fit very well to observations on poly mers where the yield relation can be determ ined for a broad spectrum o f binding energies [25], e.g. Y ' is about 10 for the fragment ions of the thoroughly fluorinated polymer polytetrafluorethylene over a large mass range whereas for the secondary ions of polymers that build hydrogen bonds (higher bind ing energies) Y' is about 100. Possible explanations for the observation o f sil ver atom attachm ent (although thick layers have been used) are: the solvent C H 2C12 dissolves the sil ver suspension resulting in a m ixture o f complex molecules and silver particles or simply inhom o geneities in the target coverage. The stability of the secondary ion (M + Ag)+, only observed in the mass spectrum of 4, can be well explained from the interatomic distances o f the metal atoms, if a posi tion of the attached substrate atom in the center of the ring is assumed. Calculation o f the hypotheti cal N i-A g distances gives: 1.9Ä for 1 and 2, 2.9 Ä for 4 and 4.1 Ä for 3. Only the size of the hexanu- H. Feld et al. • Mass Spectrometry of Nickel Thiolates clear ring 4 results in N i-A g distances com parable to those in a metal lattice. For the (M + A g)+ quasimolecular ion of 4 a half life time more than three times higher was found as com pared to the molec ular ion. If this new complex ion (M + A g)+ is sta bilized through the silver atom in the ring center, the six nickel atoms together with the silver atom form a section of a closed packed layer, as it is pre sent in both crystal structures of Ni and Ag. A ddi tionally the correlation between the fragm ent ion yield and the diameter of the metal thiolate ring may be attributed to the lower m echanical solidity of the larger rings. Due to steric effects the attach ment of eight silver atom s to a molecular ion only occurs at complex 1. We assume these silver atom s to be built in between the sulfur functions o f the eight thiolate ligands. The nickel-sulfur cluster ions ( N i ^ ) - have been observed for the first time in the gas phase. The re lated signals are present in the negative spectra of all investigated complexes. The appearance in the mass spectra of different com pounds indicates a strong formation tendency and stability o f these ions. Since we observe all nuclearities one can as sume structures of the gas phase species based on fragments of solid state com pounds such as NiS. The observed different mass resolution for frag m ent and molecular ion peaks is not due to instru m ental conditions. The resolution of the mass ana lyzer is mainly determined by the initial kinetic en ergy distribution. Thus we postulate that the desorbed molecular ions as well as the quasimolecular ions, e.g. (M + Ag)+, have a lower kinetic energy as compared to the fragment ions. This is probably caused by the different desorption p ro cesses which are responsible for the creation of these secondary ions. The form ation o f a fragment ion requires more initial energy because it is neces sary to overcome not only the weak van der Waals forces (lattice binding energy) but also the inner molecular forces (covalent binding energy). There fore the fragment ions are probably formed in a target area where a higher energy density has been deposited by the primary ion. As this energy is divided into internal and kinetic energy of the frag m ent ions, both the lower stability and the lower mass resolution are explained. All spectra show that SIMS and PD M S are able to yield highly significant molecular as well as fragment ion inform ation of neutral metal com- Unauthenticated Download Date | 6/17/17 1:33 PM 935 H. Feld et al. • Mass Spectrometry of Nickel Thiolates plexes with high accuracy. The observed fragment ions give useful data for structural characteriza tion and additionally the stability o f different frag ment ions can be com pared by determining their half life times. The sample preparation is not criti cal and only a small am ount of m aterial is neces sary, e.g. some small crystallites (sub ng-range) are sufficient. By multilayer preparation the substrate influence is negligible or very small. Only under special conditions matrix effects, e.g. an attach ment o f substrate atoms, are observed. Neverthe less, in no case a degradation o f the complex or li gand loss due to matrix effects were observed. This is in strong contrast to F A B -M S , the mass spectrom etric technique m ost frequently used in the in vestigation of metal complexes. Here the draw backs are mainly due to the problems o f solubility and stability of the complexes in the liquid matrix [26]. Therefore one has to find out suitable matrix conditions, but the enhancement o f ion form ation without degrading the metal complex is critical [27]. Even if these conditions are found, the inten sities o f quasimolecular ions are small com pared to the matrix signal. In many cases FAB does not Support of this work by the Fonds der Che mischen Industrie and the Deutsche Forschungs gemeinschaft (D FG ) is gratefully acknowledged. [1] J. M. Miller and G. Wilson, J. Organomet. Chem. 249,299(1983). [2] R. L. Cerny, B. T. Sullivan, M. M. Bursey, and T. J. Meyer, Anal. Chem. 55, 1954 (1983). [3] J. M. Miller, Mass. Spectrom. Rev. 9, 319 (1989). [4] L. K. Panell, H. M. Fales, J. P. Scovell, D. L. Klagman, D. X. West, and R. L. Tate, Trans. Met. Chem. 10, 141 (1985). [5] J. L. Pierce, K. L. Busch, R. G. Cooks, and R. A. Walton, Inorg. Chem. 21, 2597 (1982). [6] a) H. Feld, A. Leute, D. Rading, A. Benninghoven, and G. Schmid, Z. Phys. D 17, 73 (1990); b) H. Feld, A. Leute, D. Rading, A. Benninghoven, and G. Schmid, J. Am. Chem. Soc. 112, 8166 (1990). [7] H. Feld, A. Leute, D. Rading, A. Benninghoven, G. Reusmann, and B. Krebs, Int. J. Mass. Spectrom. and Ion Proc. 110, 225 (1991). [8] B. Krebs and G. Henkel, in H. W. Roesky (ed.): Rings, Clusters and Polymers of M ain G roup and Transition Elements, S. 439, Elsevier, Amsterdam (1989). [9] J. M. Berg and R. H. Holm, in T. G. Spiro (ed.): Iron-Sulfur Proteins, S. 1, John Wiley & Sons, New York (1982). [10] B. Krebs and G. Henkel, Angew. Chem. 103, 785 (1991); Angew. Chem. Int. Ed. Engl. 30, 769 (1991). [11] J. R. Lancaster (Jr.) (ed.): The Bioinorganic Chem istry of Nickel; VCH Verlagsgesellschaft, Weinheim (1988). [12] H. Feld, D octoral Thesis, M ünster (1991). [13] H. Feld, A. Leute, R. Zurm ühlen, and A. Benning hoven, Anal. Chem. 63, 903 (1991). [14] B. Schueler, R. Beavis, G. Bolbach, W. Ens, D. E. Main, and K. G. Standing, in A. Benninghoven, R. J. Colton, D. S. Simons, and H. W. W erner (eds): Secondary Ion Mass. Spectrometry, SIMS V, S. 57, Springer Series in Chemical Physics 44, Springer-Verlag, Berlin-H eidelberg (1986). [15] T. Krüger, B. Krebs, and G. Henkel, Angew. Chem. 101, 54 (1989); Angew. Chem., Int. Ed. Engl. 28, 61 (1989). [16] M. Kriege and G. Henkel, Z. Naturforsch. 42b, 1121 (1987). [17] I. G. Dance, M. L. Scudder, and R. Secomb, Inorg. Chem. 24, 1201 (1985). [18] T. A. W ark and D. W. Stephan, Organometallics 8, 2836(1989). [19] E. W. Abel and B. C. Crosse, J. Chem. Soc. (A) 1966, 1377. [20] P. W oodward, L. F. Dahl, E. W. Abel, and B. C. Crosse, J. Am. Chem. Soc. 87, 5251 (1965). [21] R. O. G ould and M. M. H arding, J. Chem. Soc. (A) 1970, 875. [22] M. Capdevila, P. Gonzales-Duarte, J. Sola, C. Foces-Foces, F. H. Cano, and M. Martinez-Ripoll, Polyhedron 8, 1253 (1989). [23] H. Barrera, J. C. Bayon, J. Suades, C. Germain, and J. P. Declerq, Polyhedron 3, 969 (1984). [24] S. Della-Negra, J. Depauw, H. Joret, and Y. Le Beyec, J. Phys. Colloque C2, 50, 63 (1989). provide molecular ion inform ation of neutral com plexes [2]. Also signals due to fragm entation pro cesses are small so that it is difficult to get structur al inform ation. 5. Conclusion PDM S as well as SIMS are well suited for an ef ficient determ ination of molecular weight with high accuracy and establishing of the molecular form ula of unknown coordination compounds. The results do not critically depend on the sample preparation; crystallites, powder and dried solu tions can be investigated without any sample pre treatm ent. Spectra are obtained in minutes. Both desorption techniques are an appropriate tool for the analysis of neutral transition metal complexes. Because of the relatively small yield ratio Y' and the com parable results for PDM S and SIMS there is an advantage for SIMS concerning the spectra accum ulation time. Unauthenticated Download Date | 6/17/17 1:33 PM 936 [25] H. Feld, R. Zurmühlen, A. Leute, B. Hagenhoff, A. Benninghoven, in A. Benninghoven, C. A. Evans, K. D. McKeegan, H. A. Storms, and H. W. W erner (eds): Secondary Ion Mass Spectrometry, SIMS VII, S. 219, John Wiley & Sons, New York (1990). [26] J. Cleareboudt, B. De Spiegeleer, E. A. De Bruijn, R. Gigbels, and M. Cleays, J. Pharm. Biomed. Anal. 7, 1599(1989). [27] L. M. Mallis and W. J. Scott, Org. Mass Spectrom. 25,415(1990). H. Feld et al. ■Mass Spectrometry o f Nickel Thiolates [28] Further details o f the crystal structure determina tion may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft für wissenschaft lich-technische Inform ation mbH. D-W-7514 Eggenstein-Leopoldshafen 2, Germany, on quoting the depository number CSD 56407, the names of authors, and the journal citation. Unauthenticated Download Date | 6/17/17 1:33 PM