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Distortional Isomers of [LWOCl2]+ in the Solid State and in Solution; Crystal Structures of the Blue and Green Forms of [LWOCl2]PF6.

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Distortional Isomers of [LW0Cl21 in the Solid
State and in Solution; Crystal Structures of the
Blue and Green Forms of ILWOC121PF6**
+
By Karl Wieghardt, * Gabriele Backes-Dahmann,
Bernhard Nuber. and Johannes Weiss
The blue and green crystals of the diamagnetic neutral
complex cis-mer-[MoOCI,(PMe2Ph),lI'l exhibit so-called
distortional isomerism. In each case, the Mo'" center is
surrounded octahedrally by the monodentate ligands in
identical spatial arrangement (cis-mer); in the solid state,
the two forms differ only in the lengths of the Mo=O bond
and the Mo-CI bond trans to the 0x0 group (Mo=O:
167.6(7) (blue), 180.3(11) pm (green); Mo-CI 255.1(3) and
242.6(6) pm, respectively). In solution, the green form is
transformed irreversibly into the blue form. Wilkinson et
al. have described analogous blue and green crystals of
[MoOC12(PMe&], but did not characterize these as distortional isomers.'21 Recently, we were able to confirm the existence of this type of isomerism in the complex
anions [PPh4],[MoO(CN),(H20)].4 H 2 0 (green) and
[AsPh,],[MoO(CN),(H,O)]~ 4 H 2 0 (blue) by X-ray analysis.
In this case, too, the blue form exhibits a shorter Mo=O
bond than the green form. Salts of [MoO(CN),]~- ions
also exist in blue and green forms.131Common to all of
these compounds is a Mo'"=O group, their diamagnetism,
and the fact that, in solution, only one form prevails.
This type of distortional isomerism is not well understood as yet due to the limited number of firmly established examples. Is it restricted to diamagnetic Mo'"=O
complexes or is it a solid-state effect (packing effect, etc.)?
We report here the characterization of distortional isomers, both in the solid, state and in solution, of the paramagnetic cation [LW0Cl2]+ ( L = N,N',N"-trimethyl-l,4,7triazacyclononane), the hexafluorophosphate salt of which
has been crystallized in a blue form 1 and a green form
2.141
The infrared spectra of 1 and 2 (KBr) are very similar.
Only in the region of the W=O stretching vibrations are
significant differences apparent: 1 exhibits the v(W=O) vibration at 980 cm-', whereas for 2 it is observed at 960
cm-'. 1 and 2 are stable in the solid state and d o not undergo a change in color over several months; even at temperatures u p to 450 K, they are not transformed into each
other.
The crystal structure determinations show that 1 and 2
crystallize in the same space group with very similar unit
cell parameters.'" The packing of the [LWOCI,]+ ions and
of the disordered PF, ions is also identical in the two
salts. In both cases, the geometry of the ligands around the
Wv center is identical (Fig. 1): the tridentate ligand
N,N',N"-trimethyl-l,4,7-triazacyclononane
occupies three
facial coordination sites of a distorted octahedron; two
chloro ligands in cis positions with respect to each other
and an 0x0 group occupy the remaining three coordination
sites. The only significant differences between the complex
cations in 1 and 2 are the lengths of the W=O bond and
[*I
probably of the W-Nl bond trans to it. In the blue form, a
shorter W=O distance (172(2) pm) and a longer W-Nl
distance (237(2) pm) are observed; in the green form, these
distances are 189(2) and 232(2) pm, respectively. Because
of the relatively large error limits, however, the significance of the difference in bond lengths of the two W-NI
bonds is experimentally unresolved.
CL
Fig. I . Structure of the cation [LWOClJ ' in 1 and 2 . The atoms W, < ' I , N l ,
and 0 lie on a crystallographic mirror plane. Selected bond lengths [pm] and
bond angles ["I in I (corresponding values for 2 in parentheses): W - 0
171.9(18) (189.3(20)), W-CII 2?2.2(5) (229.5(6)), W-NI 2?7.0( 17) (232.1(20)),
W-N2 223.9(1?) (224.7(16)); CII-W-CIIA 91.7(?) (9?.5(4)), CII-W-0 102,X(X)
(l01.4(8)), CIIA-W-N2 16?.7(8) (164.5(8)), N2-W-N2A 78.3(6) (76.9(8)), CIIW-N2 93.1(5) (9?.3(7)), 0 - W - N 2 Y l . l ( X ) (90.9(8)). NI-W-NZ 75.4(6)
(75.8(8)).
Crystals of 1 and 2 dissolve in dry acetonitrile, affording blue and green solutions, respectively. Such solutions
are stable for several days; in no case is a color change
from green to blue or vice versa observed.
The electronic absorption spectra of 1 and 2 in CH,CN
(Fig. 2) show a weak-intensity d-d transition in the visible
range ( I : L=712 nm, & = 2 0 c m - ' mol-' L; 2 : 693 (40)),
which is typical for 0x0 complexes of W". Interestingly,
the spectrum of 2 shows a relatively strong charge transfer
band (probably of the W=O group) at 419 nm (F-890 cm
mol-' L), which is responsible for the green color of 2 and
ILWvOCIzl PFs
I
Prof. Dr. K. Wieghardt, Dr. G. Backes-Dahmann
Lehrsruhl fur Anorganische Chemie I der Universitat
Postfach 102148, D-4630 Bochum (FRG)
Dr. 8. Nuber, Prof. Dr. J . Weiss
Anorganisch-chemisches Institut der Universitat
Im Nruenheimer Feld 270, D-6900 Heidelberg (FRG)
[**I
CLA
We thank Dr. W . Kaim for measurement o f the ESR spectra. This work
was supported by the Fonds der Chemischen Industrie.
Anyew. Chem
In!. Ed Engl. 24 (198.5) No. 9
- [nml
A
Fig. 2. Electronic absorption spectrum of 1 (----) (3.5
(2.0 x 1 O - l ~ )in dry acetonitrile (I-cm cuvette).
0 VCH Verlagsgesellsehaft mbH, 0-6940 Weinheim, 1985
x 10
'M)
0570-083~i85/0909-0777$ 02.50/0
and 2
(-)
777
which, for 1 , is shifted to appreciably shorter wavelengths
(286 nm). From the ESR measurements on these solutions
at 293 K, g values of 1.775(3) for 1 and 1.790(3) for 2 were
derived.
Both methods show that two species of the cation
[LWOC12]+also exist in soiuriun. When small amounts of
water are added to the green solution of 2, an immediate
color change to blue is observed. Blue 1 can be crystallized
nearly quantitatively from this solution by addition of
solid NaPF,. Electrochemically, 1 and 2 can be reversibly
reduced to [LW'"0Cl2] in dry CH3CN with 0.1 M
/Bu4NPF, as electrolyte ( E ' = - 1.14 V vs. ferrocenium/
ferrocene for 1 and 2).14.'l
Received: April 30, 1985 [Z 1283 IE]
German version: Angew. Chem. 97 (1985) 773
CAS Registry number:
I , 97879-02-2.
[ I ] a ) J. Chatt, L. ManojloviC-Muir, K. Muir, Chem. Cornmun. 1971. 655: h)
A. V. Butcher, J. Chatt, J . Chem. Soc. A 1970, 2652; c) L. ManojlovicMuir, ibid. 1971. 2797; d) L. ManojloviC-Muir, K. Muir, J . Chem. SOC.
Dalfon Trans. 1972. 686; e) the crystal structure of the green form of
[Mo0C12(PMe2Ph)3]was recently determined: B. 1. Haymore, W. A.
Goddard I l l , J. N. Allison in Abstracts ofthe International Conference on
Coordination,Chemistry, Boulder, C 0 , USA 1984, p. 535.
[2] E. Carmona, A. Galindo, 1.Sanchez, A. Nielson, G. Wilkinson, Po/yhedron 3 (1984) 347.
[3] K . Wieghardt, G. Backes-Dahmann, W. Holzbach, W. J . Swiridoff, J .
Weiss, 2. Anorg. Allg. Chem. 49Y (1983) 44.
[4] a) G. Backes-Dahmann, W. Wieghardt, Inorg. Chem., in press; b) 1 , 2 :
Air oxidation of an aqueous solution of red [LW"'C13]CI (313 K, 20 min)
resulted in a blue solution, from which blue, hydrolytically stable
[LW0CI2]PF61 crystallized after addition of solid NaPF,. If, on the other
hand, [LW(CO),] in I O M HCI is refluxed for 2 d in the presence of air and
then solid NaPF6 is added to the cooled, green solution, green
[LWOCI,]PF, 2 crystallizes. Elemental analyses of the two salts (C, H, N,
CI, W) gave nearly identical values [4a] and are in very good accord with
the composition [LWOC12]PF6.Both salts are paramagnetic; the effective
magnetic moments of the two forms are temperature independent from 98
to 293 K and correspond to the spin-only value of the d ' electronic confi(1:
pv,i(293K)=1.90pB, 2 :
guration
of
a
W"
center
fit,, (293 K ) = 1 . 8 9 ~ ~ ) .
[ S ] X-ray structure analysis of blue 1 and green 2 (values for 2 in parentheses): Phcm (Phcm); a=722.3(4) (726.7(5)), b= 1489.8(6) (1495(1)),
c = 1653.5(8) ( l649( 1 )) pm : Z = 4 (4); P ~ , ,=, 2.~ I9
~ (2.17) g cm ; R = 0.062
(0.073) for 1608 (1378) independent reflections ( I > 2 0 ( I ) ) ; MoK., radiation, AED-Siemens 11. Further details of the crystal structure investigation are available o n request from the Fachinformationszentrum Energie
Physik Mathematik, D-7514 Eggenstein-Leopoldshafen 2, by quoting the
depository number CSD 5 1404, the names of the authors, and the journal
citation.
-'
Fe"' complexes of this type have recently been synthesized
and characterized."] The agreement between the spectroscopic properties (electronic, resonance Raman, and Mossbauer spectra) and the magnetic susceptibilities of methemerythrin on the one hand, and those of the inorganic
model compounds on the other, is remarkable. This underscores the value and relevance of studies on low-molecular
model complexes for an understanding of metal-containing pr0teins.1~1
The active form of the protein, deoxyhemerythrin, contains dinuclear Fe" complexes with high-spin electron
configuration. The electronic spectrum and the magnetic
properties of deoxyhemerythrin have been well documented,I5l but give very little information about its structure; a crystal structure analysis has so far not been reported.
MCD-ESR measurements on deoxyhemerythrin indicate a bis(y-carboxylato)(y-hydroxo)-bridging for the diiron(ir) centers;"] the same structure was proposed by
Stenkarnp et aI.["] The coupling constant J was estimated
to be - 13 T 5 cm- I. We report here on the first low-molecular model compound for the active protein.
Reaction of Fe(C10&.6 H 2 0 in anhydrous methanol
with the cyclic triamine N,N',N"-trimethyl- 1,4,7-triazacyclononane (L) in the presence of anhydrous sodium acetate and in strict absence of oxygen led to pale greenishyellow crystals of [L2Fe:'(p-OH)(u-CH,C02)2](C104).H 2 0 ,
1 .171
The structure of 1 (Fig.
consists of a p-hydroxobridged diiron(i1) unit containing two further acetate
bridges and non-coordinatively bound, statistically disordered perchlorate ions. Two facially coordinated, tridentate amine ligands complete the distorted octahedral coordination sphere of the two Fe" centers. The structure of 1
thus corresponds to the structure proposed'"] for deoxyhemerythrin. The F e - 0 and Fe-N bonds in 1 are significantly longer than in 2, the oxidation product of 1 ; they
are consistent with a d" high-spin electron configuration of
the Fe" centers.
cI A
5
C
IL,Fe:'(~-OH)(pCH,C02)zl(C104).H20,
a Model Compound for the
Diiron Centers in Deoxyhemerythrin""
By Phalguni Chaudhuri, Karl Wieghardt,*
Bernhard Nuber, and Johannes Weiss
In the oxidized forms of the oxygen-transporting protein
hemerythrin containing dinuclear (p-oxo)bis(y-carboxylato)diiron(iri) structural units,"] the two Fe"' centers are
strongly antiferromagnetically coupled ( J = - 134 c m - ' in
metazidohemerythrin).l*i Some low-molecular, dinuclear
Fig. 1. Structure o f the [L,Fe:'(OH)(CH,CO:)z]'
cation in the crystal of 1.
Important bond lengths [pm] and angles ["I: Fe-01 198.7(8), Fe-02 214.2(9),
Fe-03 212.3(9), Fe-NI 225.7(10), Fe-N2 230(1), Fe-N3 231(1), C 8 - 0 2 120(2),
C8-03A 134(2), C7-C8 155(2), Fe-FelA 332(1); Fe-01-FelA 1 l3.2(2), 01-Fe0 2 98.2(4), 0 1 - F e - 0 3 95.6(5), 02-Fe-03 92.6(5).
[ * ] Dr. P. Chaudhuri, Prof. Dr. K. Wieghardt
Lehrstuhl fur Anorganische Chemie I der Universitit
Postfach 1021 48, D-4630 Bochum (FRG)
[**I
778
Dr. B. Nuher, Prof. Dr. J. Weiss
Anorganisch-chemisches lnstitut der Universitit
Im Neuenheimer Feld 270, 13.6900 Heidelberg (FRG)
This work was supported by the Fonds der Chemischen Industrie.
0 VCH Verlagsyesellschufi mbH, 0-6940 Weinheim, 1985
The electronic spectrum of 1 in methanol (Fig. 2, left)
[A=928 nm ( & = I 0 c m - ' mol-' L); 1100 (sh) (7)] is very
similar to that of deoxyhemerythrin.['I The magnetic susceptibility data (Faraday method) for crystalline 1 in the
0570-0833/85/0909-077~$ 02.50/0
Anyew Chem. Int. Ed. Engl. 24 (IP85I No. Y
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