INORG. NUCL. CHEM. LETTERS Vol. 2, pp. 403-M17. 1966. Pergamon P.... Ltd. Printed In Great Britain.

MASS SPECTRA OF METAL ACETYLACETONATES

by John Macklin and Gerald Dudek

Departments of Chemistry: Cornell University, Ithaca, N. Y.

and Harvard University, Cambridge 38, Mass.

(Rece/vetl 13 Octob.. 1966)

Bonding and structure in metal acetylacetonates is an

extremely active and even somewhat controversial field.1-3

We

wish to report here the information which we have gathered from

an analysis of the mass spectra of some particular complexes of

this kind.4

Acetylacetonates of the metal ions Al (III), Be(II),

Cd (II), Cr (III), Cu (II), Mn (II), and Zn (II) yield mass

5spectra similar to that of the Cr(III) chelate which has been

4apreviously reported. A well-defined molecular ion with frag-

ments involving the loss of ligand(s) is observed. An interest-

ing process, which is strongly dependent upon the metal present,

is the loss of a fragment of mass 15 (CH3)

from the parent ion;

in the berylium chelate it is the base peak. However the spectra

of the chelates of Sr (II), Ca (II), Mg (II), and Na (I) are

unusual, and hence are the special subject of this communication.

The spectra of these Na, Mg, Ca, and Sr compounds contain

intense mass peaks corresponding to polymeric species. Such ions

of high mass are most evident in the spectrum of the strontium

complex, where fragments are observed well above m/e = 1500. The

6base peak is at m/e = 473 and corresponds to a conglomerate of

+2 strontium ions and 3 ligands (L3M2 ), while the highest mass403

MASS SPECTRA OF METAL ACETYLACETOHATES Vol. 2, Ho• 12

fragment with reasonable intensity is at rn/e = 1045 (28% of the

base) and consists of 7 ligands and 4 strontium ions (L7M2+).

+The fragments above 1045 appear only at temperatures just below

the irrevers ible decomposition of the chelate (~2700 C). Intense

metastable ions interrelate all the major ionic species and in-

dicate that the polymer can decompose by cleavage of small frag-

ments such as ligand or ligand--metal combinations. Other

smaller fragments can also result from the loss of a fragment of

mass 58 (CH3COCH3~' For example, rn/e = 473 eliminates 58 mass

units to form 425+ (intensity 29"), of the base peak) .

In the spectrum of the calcium chelate (Figure 1) , the base

+peak occurs at rn/e = 377 (L3M2 ), while the highest prominent ion

+has an rn/e = 853 (L7M4

). Weaker fragments are found beyond

rn/e = 1090. The largest fragment observed in the spectrum of the

+magnesium acetylaectonate complex is at rn/e = 344 (L3M2

) , how-

+ever the most abundant 'i on is at rn/e = 128 (LM ). In the

spectrum of the sodium complex, the largest mass fragment is at

+rn/e = 389 (L3M4 ).

It is interesting to note that in the spectra of the tris-

acetylacetonato complexes , the most abundant fragments are always

at the mass corresponding to the loss of one acetylacetone

ligand. Likewise the most abundant mass peaks observed f or the

polymeric gaseous ions are those which correspond to the loss of

one acetylacetone ligand from the species which would r ep r e s ent

a neutral polymeric structure (In Figure 1 note the weakness of

+ + +238 , 476 , and 714 ). This suggests that the most stable

Vol. 2, No. 12 MASS SPECTRA OF METAL ACETYLACETONATES 405

oeno

0~0

E 0::l CD It)

.~ ,...4-l U

~----0 MIIIU

;> I(J)

0 0I"- -IJ

-l IIIJ::

(J) E 0l-I ::l .~

::l H '00'> +J (l)

.~ U J::r.. (J) III 0 0

0.. +J 0 ,... 0CIl J:: en ..... ~

(l)en 0.. 1'0en I ~III <:I' 1'0::E: ..

10Nal

lJl.~ Q)fIl <,

E

0 00 0al 10

-al1'0N

ooI'-

10

CD

o oQ

o~-......_--"----"-----IO

o______'' ....-_......._ ......._....I.go

406 MASS SPECTRA OF METAL ACETYLACETONATES Vol. 2, No. 12

gaseous species are those where the charge resides primarily on

the metal. The nature of the distribution of the charge may be

the primary cause of the differences in the fragmentation between

the various metal chelates.

Several acetylacetonates (such as that of nickel) are poly-

meric in solution, but the state of association of the majority

is not well known.l

However, it should be remembered that the

nature of the association in the solid state and the gaseous

state need not be identical. It may be that the polymeric ma-

terials result from the decomposition of the crystalline solid

upon heating. The metastable ions indicate that they can also

result from fragmentation after ionization, but the compounds

yielding polymeric ions are those with the higher melting or

decomposition points.

From both the mass spectrometric data and from information

previously discussed,l bridging structures for the polymeric

species appear plausible:

- -• • - -(. .-(. .- -- • - - - - -. .)-In the later full report on this work, many of the points

alluded to here will be discussed in greater detail.

References

1. For a recent review see: J. P. Fackler, Jr. in "Progress in

Inorganic Chemistry," Vol. 7, F. Cotton, Editor, Interscience,

New York, 1966, pg. 361 ff.

2. H. Musso and H. Jange, Tetrahedron Letters, 1966, 4003.

3. E. C. Lingafelter and R. L. Brown, ~. Am. Chem. Soc., 88,

V.I. 2. N•• 12 MASS SPECTRA OF METAL ACETYLACETONATES 407

2951 (1966).

4a. F. McLafferty, ~. Spectroscopy, 11, 148 (1957).

b. S. H. H. Chaston, S. E. Livingston, T. N. Lockyer and J. S.

Shannon, Aust. ~. Chern., 18, 1539 (1965).

c. S. J. Lippard, ~. bill. Chern. Soc., 88, 4300 (1966).

5. Mass spectra were taken on an A. E. I. MS - 9 Double Focus­

ing Mass Spectrometer using direct insertion of the sample.

The source temperature was the lowest required to obtain

sufficient ion intensity. The spectra of the polymeric

species in particular were very temperature dependent.

6. In assigning the base peak, m(e ~ 43 and 58 are ignored.