Comparison of fast atom bombardment and field desorption mass

Sullivan, Maurice M. Bursey, and Thomas J. Meyer .... Ronald L. Cerny , Maurice M. Bursey , Donald L. Jameson , Mitchell R. Malachowski ... Jack Marti...
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1954

Anal. Chem. 1983, 55,1954-1958

76025-15-5; 5-nitroquinoline,607-34-1; 8-nitroquinoline,607-35-2; nitropyrene-3,6-quinone, 86689-94-3;l-hydroxy-3-nitropyrene, 86674-49-9;l-hydroxy-6-nitropyrene,1767-28-8;l-hydroxy-8nitropyrene, 1732-29-2;dinitroacridine, 50764-83-5.

LITERATURE CITED Pitts, J. N., Jr.; Cauwenberghe, K. A.; Grosjean, D.; Schmid, J. T.; Fitz, D. R.; Belser, W. L., Jr.; Knudson, G. 6.; Hynds, P. M. Science 1978, 202,515-519. Pederson, T. C.; Siak, J.4. J . Appl. Toxicol. 1981, 7 , 54-66. Mermelsteln, R.; Klriazides, D. K.; Butler, M.; McCoy, E. C.; Rosenkranz, H. S. Mutat. Res. 1981, 89, 167. Schuetzle, D.; Riley, T.; Prater, T. J.; Harvey, T. M.; Hunt, D. Anal. Chem. 1982, 5 4 , 265-271. Xu, X. 6.; Nachtman, J. P.; Jin, Z. L.; Wei, E. T.; Rappaport, S. W. Anal. Chim. Acta 1982, 736,163-174. Newton, D. L; Erickson, M. D.; Tomer, K. 8.; Pellizzarl, E. D.; Gentry, P. Environ. Scl. Technol. 1982, 16, 206-213. Jager, J. J . Chromatogr. 1978, 752, 575-578. W m . C. Y.; Lee. M. S.;Kina, C. M.; Warner, P. 0. ChemosDhere 1980; 9 , 83-87. Ramdahi, T.; Becher, G.; Bjorseth, A. Environ. Sci. Technol. 1982, 76, 861-865. Schuetzle, D.; Lee, F. S.-C.; Prater, T. L.; TeJada, S. B. I n t . J . Environ. Anal. Chem. 1981, 9, 93-144. Tejada, S. 8.; Zweidinger, R. 6.; Slgsby, J. E.; Paper 820775 presented at SAE Passenger Car Meetlng, Troy, MI, June 7-11, 1982, and references cited therein. Schuetzle, D. EHP, Environ. Health Perspect. 1963, 47,65-80. Oehme, M.; Mano, S.;Stray, H. HRC CC J . High Resolut. Chromatogr. Chromatogr. Commun. 1982, 5 , 417.

(14) (15) (16) (17)

Ramdahl, T.; Urdall, K. Anal. Chem. 1982, 54, 2256-2260. Nielsen, T. Anal. Chem. 1983, 55, 286-290. Gibson, T. Atmos. Environ. 1982, 76,2037-2040. PMs, J. N., Jr.; Lokensgard, D. M.; Harger, W.; Fisher, T. S.;Mejia, V.; Schuler, J. J.; Scorziell, G. M.; Katzenstein, Y. A. Mutat. Res. 1982, 703,241-249. (18) Rappaport, S. M.; Jin, Z. L.; Xu, X. B.; J . Chromatogr. 1980, 240, 140-154. (19) Yergey, J. A.; Risby, T. H.; Lestz, S. S. Anal. Chem. 1982, 54, 354-357. (20) Ramdahl, T.; Kveseth, K.; Becher, G. HRC CC J . High Resolut. Chromatogr. Chromatogr. Commun. 1982, 5 , 19-26. (21) Lee, F. S.-C.; Schuetzle, D. I n "Handbook of Poiycyclic Aromatic Hydrocarbons"; Bjorseth, A., Ed.; Marcel Dekker: New York, 1983: Chapter 11. (22) Campbell, N.; Wilshire, J. F. K. J . Chem. SOC. 1954, 867-669. (23) Kioetzel, M. C.; King, W.; Menkes, J. H. J . A m . Chem. SOC. 1956, 78,1165-1168. (24) Streitweser, A.; Fahey, R. C. J . Org. Chem. 1962, 27, 2352-2355. (25) Bolton, R. J . Chem. SOC. 1964, 4637-4638. (26) Bavln, P. M. G. Can. J . Chem. 1959, 37, 1614-1615. (27) Looker, J. J. J . Org. Chem. 1972, 37,3379-3361. (28) Vollman, H.; Becker, H.; Correll, M.; Streeck, H. Justus LiebQs Ann. Chem. 1937, 53, 1-159. (29) Sweetman, J.; Karasek, F. W.; Schuetzle, D. J . Chromatogr. 1982, 247,245-254. (30) Schuetzle, D.; Riley, T. L.; Prater, T. J.; Saimeen, I.; Harvey, T. M. I n "Analytlcal Techniques I n Environmental Chemistry 2"; Albaiges, J., Ed.: Pergamon Press: New York, 1982; pp 259-280.

RECEIVEDfor review March 21,1983. Accepted July 1,1983.

Comparison of Fast Atom Bombardment and Field Desorption Mass Spectrometry of Coordination Complexes Ronald L. Cerny, B. Patrick Sullivan, Maurice M. Bursey,* and Thomas J. Meyer

William Rand Kenan, Jr. Laboratories of Chemistry, T h e University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27514

Fast atom bombardment (FAB) and fleld desorption (FD) mass spectrometry of neutral, 1+, and 2+ catlonlc transltlon metal complexes suggest that FAB Is preferable for I+complexes, produclng both parent and useful fragment Ions. For neutral complexes FD Is better for molecular weight determination while FAB can provlde fragment Ion Information. Both technlques yleld a mlnlmum of lnformatlon when applled to dlcationlc complexes although some knowledge of the major fragmentation pathways can be obtalned. Llgand loss and ease of reductlon In FAB parallel ground state solutlon substitutional and redox chemlstry for complexes where the latter data are avallable. The hypothesls of Ion formatlon In FAB In the condensed phase where the matrlx could play a slgnlflcant role Is conslstent wlth these observatlons. The experlrnental results Indicate FAB fragmentations may be useful in predlctlng solutlon chemlstry of complex Ions.

The general interest in design of oxidation and reduction catalysts (1, Z), the stoichiometric reactions of coordinated ligands ( 3 , 4 ) ,and the design of new types of molecular and polymeric excited states ( 5 ) require increased sophistication in the complete characterization of cationic or involatile neutral metal complexes containing a wide variety of ligand environments. The mass spectrometric analysis of involatile or thermally labile inorganic complexes has generally proved so difficult

that mass spectrometry is an uncommon structural tool of the transition-metal coordination chemist. This is not to say, however, that its use is unknown. Field desorption (FD) (6) has been developed as a technique for involatile materials which has led to its application to inorganic complexes (7-9). Fast atom bombardment (FAB) (IO, 11) has been developed for large polar molecules, but there have been fewer applications to coordination complexes of transition metals (12-14). The combination of FD and FAB mass spectrometry applied to coordination complexes should provide information concerning the parent ion molecular weight, an indication of structural complexity though fragmentation patterns, and perhaps a prediction of chemical reactivity. Such information is particularly important for complexes containing, for example, paramagnetic sites where NMR spectral studies may be of limited value. In this paper we compare the two techniques of FAB and FD for a series of neutral, 1+ cationic, and 2+ cationic complexes of transition metals. These include many different metals in various formal oxidation states and a diverse group of ligands, including polypyridyl, phosphine, and oxo ligands.

EXPERIMENTAL SECTION Instrumentation. Field Desorption. A Du Pont 21-492B mass spectrometer modified for field desorption was operated at 3 kV accelerating potential and the cathode was at -7 kV. Samples were dissolved in methylene chloride and placed on the emitter by the dipping technique. Cobalt dendrites were used with heating currents of 15-30 mA. Their preparation has been described

0003-2700/83/0355-1954$01.50/00 1963 American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 55, NO. 12, OCTOBER 1983

19ti5

Table I. Comparison of FD and FAB Spectra of [Ag(2,2'-bpy),](C104) technique

'''A~(~PY ;1 m/z 419 re1 intens, %

10'Ag(bPY)+ m/z 263 re1 intens, %

FD FAB

100 4

31 21

other peaks m/z (re1 intens) 313 (17), 315 (13), 317 ( 6 ) 355 (3), 337 (2), 2911 ( l o ) , 293 (8), 199 (28), 201 (24), 107 (20), 109 (18), 157 (100)

elsewhere (15). 'The source was held at ambient temperature. Fast Atom Bombardment. A VG 7070 mass spectrometer equipped with a standard VG data system was fitted with a modified saddle-field ion source (Ion Tech. Ltd.) as the atoim beam gun. Xenon was used for the primary beam (1 mA, 4-8 keV). Spectra were obtained at an accelerating voltage of 4 kV over a ao mass range from 50 to 700. A stainlesssteel probe tip was covered ._ with a small piece of aluminum foil and the sample was placed on the foil as either a solution or a suspension in glycerol. This technique proved an easy way to eliminate "memory effects'' from prior samples. It also eliminated the need for tedious and time-consuming probe clieaning described by others (16). w a The complexes t ru ns ,c i s - [Re(bpy ) S a m p l e s, (PMe2Ph)2C12] (PF,) and trum,cis-[Re(bpy)(PMe2Ph)2(CO)~I(PFd were synthesized according to procedures described elsewhere (1a). The preparation of Re(bpy)(PMe2Ph)2C03will be described in a forthcoming paper (18). Samples of mer-Re(bpy)(CO)&l (19) 300 400 500 600 700 and rner-O~(PMe~Ph)~Cl:~ (20),were prepared by literature prom/z cedures. [ o ~ ( t r p y ) , ] ( P Fwas ~ ) ~ prepared and purified by the Figure 1. FAB mass spectrum of trans ,cis-[Re"'(bpy)general methods detailed in ref 5. The complexes Rh(L)(CQ(PMe2Ph)2C121 (PFd D)(PF,), where IAis either a substituted bipyridine or lphenanthroline ligand, were prepared by the general procedure of Camus Both eq 1 and 2 have reasonable precedents in the solution et al. (21) using NH4PF6instead of perchlorate salts. chemistry of [Re1n(bpy)(PMe2Ph)zClz]+. Thus the homolytic The complex [Ag(bpy]12](C104)was prepared by reacting pucleavage in eq 1 is consistent with cyclic voltammetry studies rified bpy with AgC104 (Alfa) in a 2:l stoichiometry in acetone (17,28,29)which indicate a relatively facile metal reductlion solution at room temperature for 30 min followed by addition of of Rem to Ren for this and related complexes. The phosphine Et20. The yellow-white precipitate was washed with dry EtzO loss shown in eq 2 is a dominant pathway in the solution and air-dried. The complex should be kept in the darlk as it is substitutional chemistry of complexes of this type (28, 5!9). quite light sensitive. Phosphine loss in the FAB mass spectrum has the highest The oxo complexes cis-Os(bpy),O?+ (22) and M O ( S ~ C ~ \ T E ~ ) ~ O ~ (23), recently characterized, were gifts. relative intensity, three times that of (M - Cl)'. The FAB positive ion spectrum of the related complex RESULTS AND DISCUSSION [Rell'(bpy)(PMezPh)COB]+peaks a t m/z 619 which correStudies on Monocationic Complexes. Derivatives of sponds to the reduction of Re(II1) to a formally four-coorRe(II1) and Re(1). Figure 1 shows the FAB positive ion dinate Re(1) (eq 4). The peak at m/z 541 corresponds to (M spectrum of tr~ns,cis-[Ite~~'(bpy)(PMe~Ph)~Cl,] (PF6)(bpy = [Re"'(bpy)(PMezI'h)~C0~]+* 2,2'-bipyridine), The molecular cation occurs a t m / z 689 (principal isotope ls7Re), (M - C1)+ a t m/z 654, (M [Re'(b~y)(PMe~Ph)~ +l COS + (4) PMe2Ph)+a t m / z 551, (M - PMe2PhCl)+ at m / z 516, (M - PMe2Ph)+;m/z 3'73 corresponds to an unknown ion without 2PMezPh)+at m/z 413, and (M - PMe,Ph(bpy))+ at m / z 391. Re. The informative peaks in the spectrum rise well above the Several Re(1) complexes were analyzed for comparison with noise and background due to glycerol. the Re(II1) species discussed above. The complex tru,rts,The two highest m / z fragment ion peaks, (M - PIMe,Ph)+ ~ ~ - [ ~ ' ( b p y ) ( P M e ~ ~ h ) ~ ( Cyielded 0 ) ~ ] (the P FFAB ~ ) spectrum and (M -- Cl)', are formally related to the parent ion by the shown in Figure 2, which consists of two major peaks; the base simple dissociations (eq 1 and 2). In these equations and those peak for the complete cation occurs at m / z 675 (lE7Re)and described below, the asterisks on the precursor complexes the fragment (M - PMezPh)+ at m / z 537 (formally by ea1 5). signify a thermally excited vibrational state. v)

-

-

+* -

Re'(bpy)(PMezPh32(CO)2+*

[Re1"(bpy)(PMezPh)lC12]+*

CRe"(bpy)(PMezPh)2C1]+ -t. C1. (1) m / z = 551 [Re"'(bpy) (PMezPh)&12] [Re"'(Ibpy) (PMe2Ph)C12J m / z = 551

+

+ PMezPh (2)

The formal process nn eq 1 involves reduction of the Re"' center to Ren concomitant with formation of a chlorine radical; this process appears to be favored over chloride ion dissociation (shown in eq 3) since no peak is seen at 327, where the dicationic species would appear. [Re"'(bpy)(PMezPh) 2C12]+* Re11'(bpy)(PMezPh)zC12+t- C1- (3) -+

Re'(bpy)(PMe,Ph)(CO),+

+ PMezPh

(5)

There are no peaks for sequential losses of the carbonyl groups from M+; but m / z 509 is probably (M - PMezPh - CO)+ and m/z 481 (M - PMezPh - 2CO)+. Thus the weaker of the two possible monodentate a-acceptor ligands, Le., the tertiary phosphine, is lost in preference to CO; and CO loss occurs only from fragments. Silver-2,2'-Bipyridine Complexes. Table I compares the peaks in the FD and FAB spectra of [Ag(bpy)z](C104).'The main peaks correspond to Ag(bpy),+ at mlz 419 and Ag(bpy)+ a t m/z 263 (for lo7Ag). Fragmentation in the FD spectrum is unusual. The ratio of intensities of the mlz 419 to m/z 263 is ca. 3:l in FD; iri FAB, it is 1.5. This difference suggests that FAB deposits more energy into the analyte ion and so

1956

ANALYTICAL CHEMISTRY, VOL. 55, NO. 12, OCTOBER 1983

100

93

%?+(

1x10 II

I

1

e ._

5 60

c

-

II

(a)

FD

PF6- 1

PhMe P-R6-PMe2Ph

60

2'1

E p

OC co

:

40

20

[r

400

I

m/z

(bl

500 5b0

FAB

rn/z

Flgure 2.

FAB mass spectrum of trans ,cis -[Re'(bpy)(PMe,Ph),-

(W,l(PF,). increases fragmentation. The small peaks in the FD spectrum at m/z 313,315, and 317 are due to Ag2(C104)+clusters. The FAB spectrum also shows peaks at m/z 355 and 357 [Ag(bpy) + glycerol]', m/z 291 and 293 (Ag + 2glycerol)+,m/z 299 and 201 (Ag + glycerol)+, and m / z 107 and 109 (free Ag+) as well as protonated bipyridine ligand at m/z 157, which is the base peak in the spectrum. The extensive fragmentation observed for Ag(bpy),+ in the FD experiment, which is not observed for the other samples in this study, reflects solution ligand-exchange reactivity (24): Ag'-bipyridine bond energies are weaker than those of other metals studied here. Rapid exchange of nitrogenous ligands on AgI with solvent occurs under conditions where our other metal complexes are substitutionally inert (25). [Rh(heterocycle)(COD)]+ Complexes (COD, 1,5Cyclooctadiene). Both FD and FAB spectra were obtained for the complex [Rh(bpy)(COD)](PF,). These data and results for some substituted 2,2'-bipyridine and 1,lO-phenanthroline derivatives are shown in Table 11. The FD spectrum of [Rh(bpy)(COD)](PF6) contains only the cation. In addition to this m / z 367 peak, the FAB spectrum of the complex contains a m / z 259 peak (loss of cyclooctadiene ligand) and m / z 157 peak (protonated bipyridine). The (M - bpy)+ fragment is absent in the spectrum; if it is formed at all, it is unstable. Exchange of positive ions bound to ligands has been characterized in FD (25,26)but has not been systematically characterized in FAB yet. The substituted variations of the complexes were analyzed by FAB to confirm fragmentations in mass regions free from matrix-related peaks. All produced the expected peaks for the cationic complex, for (M - COD)+,and for the protonated ligand. In all cases (M - COD)+ from the loss of the a-bonded ligand was the largest metal-complex peak in the spectrum. An unexpected peak at m / z 471 in the spectrum of [Rh(Mezbpy)(COD)]PF6is assigned as Rh(Me,bpy),+. In general, these spectra show that the major fragmentation is loss of the olefinic ligand and not of the heterocycle. As will be demonstrated later, the emerging pattern for most complexes is that the fragments containing the metal-bipyridine unit are the most stable observed in this study. Studies on Neutral Complexes. The complex fuc-ReI(bpy)(CO),Cl is neutral in charge, and unlike most of the cationic complexes studied, the FAB spectrum contains no ion with all ligands intact. Here the base peak instead is (M - Cl)+,m/z 427, and the fragmentation corresponds formally to the process shown in eq 6. Fragmentation to (M - C1)+ [Re'(bpy)(CO3)C1]*

-

R e ' ( b ~ y ) ( C 0 ) ~++C1-

(6)

can occur in the neutral state upon impact. However, the formalism of eq 6 is better described (at least in this case, perhaps not universally) as the protonation by glycerol and

200

300 m/z

400

Figure 3. (a) FD and (b) FAB mass spectra of cis-Mo"'(S,CNEt,),O,.

loss of HCl (eq 7). The process written for other ionization methods occurring in the gas phase (eq 8) must be distinguished from eq 6. [Re1(bpy)(C0)3C1H]+

-

-+

R e * ( b ~ y ) ( C 0 )+ ~ +HC1 (7)

[Re1(bpy)(C0)3C1]+* R e ' ( b ~ y ) ( C 0 ) ~++C1. (8) This degradation of neutrals has been described in the FD analysis of cobalamines by Schiebel and Schulten (27). Intervention of solvating glycerol in the mechanism of ionization has analogy in the solution substitution chemistry of many of these complex ions. The fragmentation process shown in eq 6 very much resembles the known solution substitution chemistry of fucRe(bpy)(CO),Cl. For example, for a polar alcoholic solvent with an entering ligand (L), complexes of the type fuc-Re(bpy)(CO),L+ are formed. This occurs presumably by a dissociative mechanism through an intermediate coordinatively unsaturated species Re'(bpy) (CO),+. Furthermore, more forcing conditions and excess L lead predominately to carbonyl loss, not bpy loss, to form cis- or truns-Re(bpy)(CO),L,+ (17, 28, 29). Comparison of the fragmentations of f~c-Re'(bpy)(CO)~Cl with other Re' and Re'I' complexes reveals an extreme sensitivity to the nature of the metal-ligand bond. While chloro ligand loss from the parent ion is the predominant feature for fuc-Re'(bpy)(CO),Cl, it is secondary in truns,cis-Re"I(bpy)(PMe2Ph)2Clz+, where phosphine loss dominates. This relation parallels the fact that in Re'I' complexes which have a d4 electron configuration, halide ions are good net donors to the metal in both a u and a ?r sense. The ?r-typeoverlap in R e q 1 occurs from pa(Cl-)-da(Re) orbital interactions. In the Re1-halide complexes these interactions are absent and the ionic component to the bond diminishes since the metal atom has a lower formal charge. Thus in terms of relative bond energies, thermal excitation would be expected to labilize weaker donors like phosphine or CO more than halide ions in the Ren1complexes, while the reverse would be true for Re' complexes. The FAB spectrum for the neutral complex rner-0s"'(PMeZPh),Cl, shows no molecular ion; the heaviest intense osmium-containing ion is (M - 2C1)+, m/z 641 (lszOs). The (M - C1)+ ion, a small peak at m / z 676, could be produced by the formal process in eq 9, much like the analogous Re' species (eq 6). (Again, protonation may precede fragmentation, as in eq 10.)

-

O S ~ I ' ( P M ~ ~ P ~ )O ~C S '~I '~( *P M ~ ~ P ~ )+ ~C C1-~ ~ + (9)

ANALYTICAL CHEMISTRY, VOL. 55, NO. 12, OCTOBER 1983

-

O S ~ ~ ’ ( P M ~ ~ P ~ ) ~ C ~Os111(PMe2Ph)3C12+ ~C~H’’’ + HC1

Table 11. Summary of Results for the Analysis of [Rh(L)(COD)1+Complexes, m/z Values and (Relative Intensity )

(10)

Other peaks related to the structure are m/z 605 (M - 3C1)+, m/z 538 (M - PMezPh - Cl)+, and m/z 503 (M - PMezPh 2C1)+. The preferred loss from mer-Os(PMezPh)BC1,of chloro rather than the phosphine ligand parallels its solution substitutional chemistry in polar media. Thus with monodentate ligands one C1 is replaced (eq 11)while with bidentate ligands two chloro ligands are replaced (eq 12), and substitution is followed by reduction to Os” (31). r n e r - O ~ ” ’ ( P M e ~ P h ) ~t C lpy ~

l9Sif

complex

L

FD FAB

bpya bpy

Me,bpyb Me,phenc Ph,phend

(M-COD)’

367 (100) 367 (20) 395 (24) 447 (51) 543 (42)

259 287 339 435

(L t H)’ 157 (16) 185 (57)

(32) (100) (80)

237 ( 6 4 )

(82)

333 (52)

2,2’-Bipyridine. 4,4’-DimethyL2,2’-bipyridine. 3,4,7,8-Tetramethyl-1,lO-phenanthroline. 4,7Diphenyl-1,lO-phenanthroline.

EtOH 7

rner,tr~ns-[Os~~’(PMe~Ph)~C1~py]+ + C1- (11) HO OH U

mer-Os111(PMezPh)C13f bpy

p

mer-[O~”(PMe~Ph)~(bpy)Cl]’” (12) A comparison of the FD and FAB spectra of the neutral complex c ~ ~ - M o ~ ( S ~ C N is shown E ~ ~ )in~Figure L ~ 3. The FD spectrum shows only the molecular ion of‘the complex, m/z 426 (g8M~). The P‘AB spectrum does not contain a moleculm ion. Instead, the ion of highest mass (98Mo)has m/z 410, (M - O)+. At least here, then, FD is superior to FAB in identifying the mass of a cation with a thermally labile oxo groupl. The m/z 338 ion corresponds to (M - 0 - N(CZH&)+;the m/z 278 ion corresponds to (M - S2CNEt2)+and is distorted by the 277 peak from glycerol, (gly, + H)’. The m/z 394 ion may be (M - 20)+ but ion intensities were too weak to confirm the postulate. The relative intensity of the rather weak m/z 369 peak (gly, H)+overwhLelms the spectrum of the complex and demonstrates that the overall sensitivity for this complex by FAB is very low. The peaks at m/z 207 and 223, due to (gly, + Na)+ and (gly, .t K)’, respectively, are unusually intense here and provide some historical information on the preparation of the complex. The m / z 338 peak represents a ligand fragmentation process, the only one that we observed. This fragment is probably derived from the (M - 0)+ion (MIKE experiments were unsuccessful) since m/z 344, (M - NEt2)+,is absent. Either of the formal processes shlown in eq 13 or 14 could apply. We

L?

rn/z

+

MoV(0)(S&NEt2)2+* -* Mo1V(IO)(S2CNEt2)(CSz)++ .NEC2 (13)

MeV( 0)(S&NEt2)2+* -* MoV(0)(S2CNEt2)(CS2)+ + NEt,- (14) have no way of distinguishing between the formal processes in eq 13 or 14. Both, however, require a redox event: in eq 13 a t the metal while eq 14 requires ligand reduction. Equation 13 is, of course, the process analogous to E1 and other processes in which ionization precedes dissociation, and eq 14 requires separation of charged species, perhaps in solution. If protonation precedes this fragmentation (eq 15) once again, the problem of charge separation can be avoided.

-

MoV(0)(S2CNEt2),H+ Mo”(C~)(S2CNEt2)(CSz)+ + “Etz

(15)

Studies on Dications. Examples of the application of FD and FAB to 2+ cationic complexes are shown in Figure 4. The FD spectrum of Os(trpy),2+(PF,Jz (trpy = 2,2/,2”-terpyridine) in Figure 4a demonstrates that the method is very insensitive, relative to its success for neutral and 1+ cationic complexes. The spectrum shows only m/z 658 (lgzOs),which corresponds to reduction of Os to produce a 1+ ion. By analogy to siolution this reduction event (eq 16) is apparently a ligand-localized

100

300

500

700

m/z

Flgure 4. (a) FD mass spectrum of [Os(trpy),](PF,),; (b) FAB spectrum of cis-[Os”’(t~py),O,](pF,),.

~

mass

process in contrast to the metal-localized events common for the other complexes studied. Ligand-localized reduction of

+

[O~I’(trpy),]~+* [R]

-

Os”(trpy),+

+ [O]

(16)

trpy is well documented for Os1’ complexes (31), but the mechanism of the reduction process in the FAB experiment including the nature of the reducing species [R] and the oxidizing species [O] in Equation 18 is unknown. Reduction of 2+ ions to I+ ions in FD of metal complexes has precedeint (26).

A FAB spectrum of the 2+ complex ~ i s - O s ~ ( b p y ) ~ O ~ ( P F , ) , is displayed in Figure 4b. As in the FD example, the major peaks which can be (assignedare due to reduced Os (the 1+ complex). Instead of 2 0 , the elements of H,Oz are lost ( m / z 502); Cl&l&z is lost instead of bipyridyl (C1J&N2)(m/z 3713); and, instead of a loss of bipyridyl and 0,the loss is of C l a lJU, and OH. We do not have solution analogies for these reductions of lost ligands. However, the loss of oxo ligands in preference to the chlelate ligands, as was observed above for C ~ ~ - M O ~ ’ ( O ) ~ ( Sand ~ C cNi sE- ~O~~ )( b~ p y ) ~ Ohas ~ ~precedent +, in the thermal redox chemistry of high valent oxo complexes where oxo group loss to external reagents takes place in preference to substitlution of other ligands in the coordination sphere (32). CONCLUSIONS Apparently the techniques of FD and FAB mass spectrometry are complementary for transition metal complexes. For 1+ complexes, ]?AB is in our experience the method of choice; FAB spectra give both molecular ion information and structurally useful fragments but the FD spectrum usually contains only the peak for the intact cation. The ion current

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ANALYTICAL CHEMISTRY, VOL. 55, NO. 12, OCTOBER 1983

due to the molecular ion in FAB may be weaker than that obtained by FD, but it is ample enough for measurement. The ease of the FAB experiment relative to FD also must be considered as a strong point in its favor. For neutral complexes FAB often does not provide molecular ion information. This is especially true for complexes with thermally labile ligands. Then we obtain this information by FD and use FAB for structure information. For multiply charged species, there is no clear method of choice. In both techniques the spectrum is dominated by 1+ ions from reduction of the metal species. This is not fully understood; in some cases rearrangement processes are involved. Finally, some cautious generalizations with regard to FAB fragment ions can be made. These are as follows: (1)Monodentate ligands are lost in preference to bidentate ligands; bidentate ligand loss occurs only from fragment ions. In particular, bpy and phen type ligands are tenaciously retained in fragment ions. (2) Redox processes produce many fragment peaks. Most of the fragments are formed by reduction of a higher oxidation state metal center to a lower one. Where metal reduction is highly disfavored the fragments are produced by simple ligand loss. When the metal atom has a redox accessible zero oxidation state, the redox process is observed. The extreme in redox processes is found for [Os(trpy),12+,where production of the monopositive cation, [Os(trpy),]+ (which is presumably ligand localized), occurs even in the milder FD experiment. (3) In a series of four Re complexes, chloride ion is retained in the higher mass fragment ions in preference to the a-acceptor ligands in the Re”’ (d4),while the reverse is found for Re1(d6).In Re1(d6)the better n-acceptor CO group is retained more than the weaker phosphine ligands. (4) A loose but potentially important analogy can be drawn between the solution substitution chemistry in polar organic media for many of the complexes studied here and the initially formed fragment ions observed in the FAB experiment. In every case where solution chemistry was known, it was paralleled by the FAB fragmentation. The FAB chemistry and solution chemistry are so similar that there is no evidence yet to discount a hypothesis that the energy transfer process from the primary atom beam to the metal complex-glycerol matrix produces the initially formed parent ion in excited vibrational states of the ground state which also can be populated by conventional thermolysis of the complex in a polar alcoholic solvent. Whether this mechanism obtains, or whether protonation precedes fragmentation, the utility of FAB mass spectral for prediction of the chemistry of coordination complexes is apparent.

ACKNOWLEDGMENT We thank Kenneth Takeuchi for the cis-Os(bpy)20z2+ sample and Kenneth Goldsby for the Mo(S&NEt)202. Registry No. [Ag(bpy)2](C104),86783-78-0; [Rh(bpy)(COD)](PF,), 37726-78-6; [Rh(Me2bpy)(COD)](PF6), 86727-92-6; [Rh(Me,phen)(COD)](PF6),56678-56-9; [Rh(Ph2phen](COD)] (PF,), 86727-91-5; trans,&- [Re(bpy)(PMezPh)zClzl(PF,),

86765-88-0;truns,ci~-[Re(bpy)(PMe~Ph)~(CO)~] (PF,), 86727-94-8; M o ( S ~ C N E ~ ~ 18078-69-8; )~O~, [OS(trpy)2](PF6)2,86727-96-0; ~is-[OS(bpy)zOz] (PF,),, 86727-97-1.

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RECEIVED for review March 18,1983. Accepted July 14,1983. Presented in part at the 33rd Southeastern Regional Meeting of the American Chemical Society, Lexington, KY, Nov 1981, and in part at the 184th National Meeting of the American Chemical Society, Kansas City, MO, Sept 1982. Supported in part by the National Science Foundation (Grant CHE8210801).