15 T h e Ferromagnetic Ordering of Ferrous Chloride Extended Interactions between Metal Ions Downloaded from pubs.acs.org by UNIV OF TEXAS AT DALLAS on 02/15/19. For personal use only.
Polymers of Diimine Ligands W.
M.
REIFF*,
B.
DOCKUM,
and C.
TORARDI
Northeastern U n i v e r s i t y , Boston, Mass. 02115 S.
FONER,
R. B .
FRANKEL,
a n d M. A .
WEBER
F r a n c i s B i t t e r N a t i o n a l M a g n e t L a b o r a t o r y , Massachusetts Institute of Technology, C a m b r i d g e , Mass. 02139
ABSTRACT Magnetization and Mössbauer studies show that F e ( b i p y r i d i n e ) C l and Fe(phenanthroline)Cl order ferromagnetically at Tc ~ 5 K . Methyl substituted bipyridine derivatives appear to be slowly relaxing paramagnets in the range of 12 to 2 K. These results are correlated with near— and f a r - i n f r a r e d and x-ray spectroscopic data which suggest six-coordinate chloro-bridged polymeric structures for the unsubstituted d i imine systems, and five-coordinate dimeric structures for the methyl substituted compounds. 2
2
Introduction In recent years there have been extensive studies of magnetic behavior of simple dimeric o r s m a l l multimetal cluster compounds containing a variety of organic ligands. The driving force for such studies i s the hope of gaining a better understanding of exchange interactions i n magnetically condensed inorganic salts such as anhydrous and hydrated metal halides which exhibit extended cooperative magnetic behavior. F o r instance, anhydrous ferrous chloride has the cadmium chloride structure with i n t r a - and inter-chain chloro-bridging. The intra-chain interaction for this compound i s ferromagnetic (J>O) where as the inter-chain interaction i s weaker and antiferromagnetic. A s a consequence, anhydrous ferrous chloride exhibits(1,2) "meta-magnetic" phase transition f r o m an antiferromagnetic to paramagnetic state in an external field of about 11 kG. Extended (lattice) ferromagnetic interaction in transition metalorganic ligand systems i s much less common than for simple inorganic a
* Please address correspondence to this author. 205
206
EXTENDED
INTERACTIONS
BETWEEN
METAL
IONS
salts. In this article we present a M6ssbauer and magnetic susceptibility study of such behavior in polymeric octahedral complexes of the type F e ( d i - i m i n e ) C l where the di-imine i s either 2,2'-bipyridine, hereafter bipyridine o r 1,10-phenanthroline and substituted derivatives. We also present x-ray and spectroscopic data bearing on the molecular structure of these compounds. It i s of interest to see if there are any significant magnetic dilution effects on placing organic ligands " i n " ferrous chloride and at the same time maintaining a polymeric structure. The weakening of inter-chain interaction by the ligand dilution allows the possibility of lower dimensionality magnetic interaction and weak metamagnetic behavior. In this connection we make comparisons of the mag netic behavior of Fe(bipyridine)Cl2 and Fe(phenanthroline)Cl2 to our preliminary results for F e ( p y r i d i n e ) C l . The latter system i s also a chloro-bridged p o l y m e r ^ ) but contains the trans-FeN2Cl4 chromophore rather than the analogous c i s chromophore as in Fe(bipyridine)Cl2. The effects of preparative technique are also considered in the discussion of Fe(5,5'-(U-CH3-bipyridine )C1 prepared by high vacuum thermolysis. 2
2
2
2
Chemical Preparation Analytical data f o r the compounds studied are given i n Table I. A l l of the complexes were studied as powders as the preparations do not yield appropriate single crystals. The synthetic methods used con sisted of rapid precipitation f r o m aqueous-hydrochloric acid solution o r vacuum thermolysis of [Fe(di-imine)^ C l yielding fine dust-like powders. Attempts at conductivity or molecular weight measurements by the usual solution methods results in disproportionation to the thermodynamically more stable Fe(di-imine>3 . 2
Table I: Analytical Data Compound
Calculated C
Η
Ν
Fe 18.20
Fe (phenanthroline )C1
2
46.95 2.63
9.12
Zn (phenanthroline )C1
2
45. 50 2.55
Fe(bipyridine)Cl ,
Fe(4,4 -di-CH bipyridine)Cl 3
2
Observed C
Η
Ν
46.77 2.66
9.34
8.85
45. 55 2.41
8.79
42.42 2.86
9.91
42.26 2.86
10.10
46.31
3.90
9.01
46.36 3.86
8.69
46.31
3.90
9.01
45.81
3.87
8.35
2
,
Fe(5,5 -di-CH bipyridine )C1 3
2
Fe 18.60
15.
REiFF E T A L .
Ferwus
Chloride
Polymers
207
Susceptibility and Magnetization Studies A p r e l i m i n a r y study of the magnetic susceptibility^) showed that a solution preparation of Fe(phenanthroline)Cl2 orders ferromagnetically with T = 8 ± 2 K. F i t s with a Curie-Weiss law correspond to a p a r a magnetic C u r i e temperature θ = 12 ± 4 Κ and the Curie-Weiss constant C = 3.81 emu/mole. In this section we present magnetic data for Fe(bipyridine)Cl2 also prepared in solution and the substituted derivative Fe(5, S'-di-CHg-bipyridineX^ obtained by vacuum thermolysis. Fe (bipyr idine )Cl2 clearly i s s i m i l a r to Fe (phenanthroline )Cl2 but has a stronger ferromagnetic interaction. Evidence f o r a ferromagnetic inter action i s seen (Fig. 1) i n the X g vs Τ plot f o r which the intercept i s large 20 K) and positive. The plot of X g vs Τ i s linear from ~60 Κ to 200 Κ and a fit with the Curie-Weiss law yields θ = +25 Κ and C = 5.26 emu/mole. The temperature dependence of the dc magnetiza tion σ at low field (Fig. 2) shows the expected rapid r i s e in the vicinity of T which i s estimated to be ^ 8 K. A m o r e precise estimation of T will be discussed in connection with the Mtfssbauer data. Between 0 and ~ 1 0 k G at 4.2 Κ there i s a rapid r i s e i n the magnetic moment per gram, σ. However, above ~ 1 0 k G there i s a gradual increase in σ and the compound i s clearly not saturated for applied field B as large as 200 kG, F i g . 3. It i s interesting to point out that the sharp r i s e in σ vâ Τ seen i n F i g . 2 i s quite s i m i l a r to that found(^) for the linear chain polymer Co (pyridine )2 CI2 · In the latter compound the sharp r i s e in σ i s attributed to strong one-dimensional ferromagnetic intra-chain interaction (corre lation) above the Néel temperature at which the complex undergoes three-dimensional antiferromagnetic ordering. A s i m i l a r positive intrachain correlation may well be o c c u r r i n g in Fe(bipyridine)Cl2 and Môssbauer data bearing on this possibility will be discussed subsequentc
1
1
c
c
0
iy. The field and temperature dependence of the magnetic properties for Fe(5,5 -di-CH3-bipyridine) CI2 are somewhat different from those of Fe(bipyridine)Cl2. A plot of Xg* vs Τ (Fig. 4) appears to have a near zero o r s m a l l negative temperature intercept. A fit of the data yields 6 OK o r slightly negative with C = 4.3 emu/mole. Thus this material appears to exhibit very weak, possibly antiferromagnetic interactions. A weak exchange interaction i s also indicated by the gradual r i s e in σ vs B for this compound. The difference in magnetic behavior f o r the two bipyridine systems i s related to a difference i n molecular structure. f
Q
Magnetic Moments. Effective magnetic moments in Bohr mag netons (fig) are calculated using the relation μ
= Λ/357ΝΟ Ά
Μ
(Τ-β)
=
2.828
Je
208
EXTENDED
INTERACTIONS
BETWEEN
METAL
200
Figure
1. χ,," vs. Τ for Fe(bipyridine)Cl>, applied field B 1.14 kG for Ί80K 1
u
Fe(Bipyridine)CI
2
Η = 1.14 kilo-gauss
-ημη-Ο-ηίη-
20
30
40
50
60
70
T(°K)
Figure
2.
Magnetic
moment per gram, σ, vs. Τ at 1.14 kG for Fe( bipyridine )C l>
=
IONS
REiFF E T A L .
Ferrous
Chloride 1
~~Ί
100
1
Polymers 1
1
1
1
1
r
1
ο ο ο ο ο ο ο ο
Fe (Bipyridine ) C l
50
_J
ο
Figure
1
40
I
L_
80
120
σ vs. applied
3.
J
I
160
field, B dine)Cl
2
L Ι
200
at 4.2 Κ for
0>
Fe(bipyri-
2
Fe(5,5'-Di-CH -Bipy)CI 3
2
20
15
X 10
OK
Figure 6
L_
4.
y„~ vs. Τ for l
100
Τ (Κ)
FefrS'-di-CHs-bipyridinefih, 16.8 kG
200
B
0
=
210
EXTENDED
INTERACTIONS
BETWEEN
METAL
IONS
where k i s the Boltzmann constant, N Avogadro's number and X ^ j i s the corrected m o l a r susceptibility. The values of M f f obtained f o r the preceding values of C are: Fe(phenanthroline)Cl2 (5. 5 μ ) , Fe(bipyridine)Cl (6.4 μ ) and Fe(5,5*-οϋ-αΗ3-Μρ^(ΐ1ηβ)αΐ2 (5.8 μ ) . Since the spin-only value of the magnetic moment f o r high-spin ferrous i s 4.9 μ g, the foregoing values of μ ^ represent i n part unusually large orbital contributions to the moment,in particular f o r the last two com pounds. There i s no evidence of any high-spin f e r r i c o r other impurity that could account f o r the magnetic moment values we observe. F o r instance, an high-spin iron III impurity of ~ 3 0 % would be required to increase the room temperature moment from 5.1 to 5.4 μ . Such an impurity content would be readily observed in both the analytical data and Mflssbauer spectra (Fig. 5). No evidence f o r iron III i s detected. The Mo'ssbauer spectrum corresponds to a pure material containing a single iron II environment. Furthermore, for i r o n III complexes of d i imine ligands, there i s generally instability and a strong tendency f o r reduction of f e r r i c to diamagnetic ferrous even on exposure to ordinary light. It i s interesting to note that in a study of Fe(bipyridine)Cl and Fe(phenanthroline)Cl at 300 K, Dwyer et al(6) also observed large moments, 5.79 μ and 5.72 μ respectively. Thus we believe that the observed large effective moments are " r e a l " and probably reflect;in part, an orbital contribution. Difficulty i n saturating the compounds at low temperatures (Fig. 3) suggests a large magnetic anisotropy consistent with large, anisotropic orbital contributions to the moment. F o r instance, the moment μ c a l culated using the relation: Q
e
Β
2
Β
Β
Θ
Β
2
2
Β
Β
where M i s the molecular weight and σ the magnetization i n emu/gram are given in Table II. It i s evident that with increasing B the moments of a l l three systems are increasing. However, the high field behavior shown in F i g . 3 and a s i m i l a r data for Fe(phenanthroline)Cl2 indicate that these systems are not saturated even at 200 kG. The spin-only value of μ i s given by 0
When g = 2 and S = 2 for high-spin ferrous, μ = 4 μ , the expected saturation moment. T h e r e i s , thus, substantial enhancement of the moment for Fe(bipyridine)Cl2 and this i s reflected in its high μ ^ and μ . The somewhat l a r g e r value f o r the moment (Table II) of Fe(bipyridine)Cl than f o r F e (phenanthroline)Cl2 i s consistent with the Β
2
REiFF E T A L .
15.
Ferrous
Chloride
211
Polymers
Table II: Magnetic Moments Compound Fe(bipyridine)Cl
2
Fe(phenanthroline)Cl
2
,
Fe(5,5 -di-CH -bipyridine)Cl 3
2
T(K)
B (kG)
^
4.2
16.8
4.7
3.0 4.2
48.4 215
3.1 3.9
4.2 4.2 3.0
14.7 16.8 48.4
1.9 2.1 3.4
Q
f
l a r g e r ferromagnetic interaction of the former; a ratio of 6 s f o r these complexes is ~2:1. To conclude this section it i s important to mention that the second o r d e r Zeeman effect and spin-orbit coupling can also contribute to the enhancement of magnetic moments to values greater than the spin-only. However, this problem has been studied^) i n some detail for simple tetrahedral iron complexes such as [ ( C H 5 > N ] F e C l ^ whose effective moments (~5.4 to 5.6 μ%) are high. It i s found that the combination of the foregoing effects increases the moment to only ~5.2 Mg. F o r the rather distorted systems of this investigation these effects are expected to be less important. Thus the effective moments for the present com pounds are unusually high and we have no simple explanation f o r their origin. It is difficult to envision a large direct orbital contribution. A small amount of configuration interaction of the ground 3d^ with a nearby 4s*3d having a much higher spin-only moment could greatly enhance the moments but this would be difficult to demonstrate. 2
4
2
Mflssbauer Studies The Mëssbauer spectra of Fe (bipyridine )C1 and Fe(phenanthroline)Cl made in solution are v e r y s i m i l a r . The onset of magnetic order i s easily seen in the Môssbauer spectra, as illustrated in F i g . 6 f o r Fe(phenanthroline)Cl . The C u r i e points of Fe(bipyridine)Cl and Fe(phenanthroline)Cl are T = 3.8 Κ and T = 5.0 Κ respectively. Magnetization data previously reported f o r the Fe (phenanthroline )C1 suggested a transition temperature of about ~8 K. The higher apparent T observed by the magnetization measurements 2
2
2
2
2
c
2
c
c
212
EXTENDED
INTERACTIONS
BETWEEN METAL
Figure 5. Mossbauer spectrum of Fe(5,5'-di-CH bipyridine)Cl at 78 s
2
-2.00
0
2.00
K,B =0 o
4.00
VELOCITY (mm/sec) RELATIVE TO IRON
(a)
'
Figure 6. Mossbauer spectra of Fe(phenanthroline)Cl at (a) 9.0 K, (b) 5.3 K, (c) 5.0 K, and (d) 3.9 Κ g
-2
0
2
VELOCITY (mm/sec)
IONS
15.
REiFF E T A L .
Ferrous
Chloride
Polymers
213
may be ascribed to the difficulty in defining the magnetic transition f o r the i r r e g u l a r l y shaped powder sample. The large susceptibility above T i s illustrated i n F i g . 7 where spectra of Fe(bipyridine)Cl2 ( T = 3.8 K) at 4.2 Κ are shown at zero magnetic field and in longitudinal magnetic fields of 4 and 35 kG. It i s seen that the small external field of 4 kG induces a hyperfine field without polarizing the moment along the ex ternal field direction. T h i s i s indicated by the presence of Am = 0 lines in the spectrum and by the fact that the angle 3 between the principal component of the electric field gradient and the magnetic hyperfine field as deduced from the spectrum i s unique,and close to that observed i n the ordered state below T in zero external field. At B = 35 kG, the appearance of the spectrum i s considerably altered due to the polariza tion of the ferromagnetic moment by the external magnetic field, with a consequent randomization of 6 Below their respective C u r i e temperatures Fe (bipyridine )Cl2 and Fe(phenanthroline)Cl have essentially s i m i l a r spectra. F o r the f o r m e r at 1.5 K, = -60 kG, Δ Ε = +1.70mm/sec and & « 60° while f o r the lat ter 1% » - 75 kG, Δ Ε = +2.03 mm/sec and 8 « 60°. A s discussed previously the temperature and field dependence of magnetization of Fe(5,5 -di - C H3 -bipyridine )C1 (prepared by thermoly sis) suggests weak,possibly negative,magnetic exchange interactions. The temperature dependence φη zero field) of the Mo'ssbauer spectra f o r this material also suggests weak magnetic interactions. Instead of a sharp ferromagnetic transition over a s m a l l (^ 0.5 K) interval as in F i g . 6, Fe(5,5 -di-CH3-bipyridine)Cl exhibits gradual changes of the magnetic hyperfine splitting over a much l a r g e r temperature range. The transitions of the quadrupole doublet start broadening at ~12 Κ and a fully resolved Zeeman spectrum i s not observed until ~2 Κ indicating slow paramagnetic relaxation rather than a cooperative ordering p r o c e s s It will be shown that this compound contains high-spin iron II in a highly distorted 5-coordination environment. F o r such a low symmetry, longer spin-lattice relaxation times and slow paramagnetic relaxation are not unexpected. The observation of this phenomenon is f a r less common f o r high-spin ferrous than f o r f e r r i c complexes. c
c
c
Q
2
1
2
,,
,,
,
2
Molecular Structure Studies F a r Infrared Spectra and X - r a y Data. The difference in the mag netic behavior of Fe(bipyridine)Cl and Fe(5, S ' - d i - C ^ - b i p y r i d i n e J C ^ i s probably due to the preparative method and a difference of basic molecular structure resulting therefrom, rather than from just simply a substituent effect. Figure 8 shows the far-infrared spectra of Fe (phenanthroline )Cl2 (prepared in solution) and Zn(phenanthroline )C1 . The latter zinc complex i s known by a single crystal x-ray study^) to be a pseudo-tetrahedral monomer. We have compared the x-ray powder 2
2
214
EXTENDED
Figure
8.
INTERACTIONS
BETWEEN
METAL
WAVENUMBER Far-infrared spectra of Fe and Zn (phenanthroline)C^-min eral oil mull on polyethylene at 300 Κ
IONS
15.
REiFF E T A L .
Ferrous
Chloride
215
Polymers
patterns of Fe(phenanthroline)Cl2 and the zinc analogue and they are not s i m i l a r , indicating these systems are not isomorphous. T h i s i s reflected in the f a r - i n f r a r e d spectrum of Zn(phenanthroline)Cl2. The two strong terminal Z n - C l stretching vibrations expected for a monomer having approximate 0 γ symmetry are seen as a broad band centered ~325 cm"*. In the i r o n analogue these vibrations are shifted to con siderably lower energy (~255 cm" ); this is also true f o r the zinc and i r o n bipyridine complexes. These results are consistent with chlorobridging(9> 10) as shown i n F i g . 9. A s i m i l a r polymer structure has been proposed as part of a recent study(H) of Sn(bipyridine)Cl2, i . e . , an infinite linear polymer chain with chloro-bridging. 2
1
The f a r infrared spectrum of Fe(5,5'-CU-CH3-bipyridine)C1 is shown in F i g . 10. Strong bands at 322 and 240 c m ~ l indicate the pres ence of both terminal and bridging chloro groups and hence a structure involving five-coordinate i r o n II. Fe(4,4*-di-CH3-bipyridine)Cl2 ex hibits a s i m i l a r spectrum and the 0 U - C H 3 substituted systems probably have a dimeric structure as shown in the structure of F i g . 11. That i s , a combination of steric effects f r o m the methyl substituents and high vacuum thermolysis preparation results i n dimeric rather than the extended polymeric structure proposed for the solution preparation of Fe (bipyridine )C1 . A dimeric structure s i m i l a r to that presented in F i g . 11 has been found in a single crystal x-ray s t u d y ( ^ ) of [Ni(2,9-di-CH -phenanthroline)0 ]9· R e c e n t ^ ) magnetic studies of other s i m i l a r chloro-bridged nickel II dimers suggest weak (intradimer) antiferromagnetic exchange and i s consistent with our results for the methyl substituted derivative. 2
2
13
2
3
Near Infrared Spectra. The near-infrared spectrum of Fe(phenanthroline)Cl2 given in F i g . 12 i s t y p i c a l ^ * ) of a pseudooctahedral FeN2Cl4 chromophore and strongly supports the proposed structure. Fe(pyridine) Cl2 i s an octahedral p o l y m e r ^ ) containing the same chromophore but with trans-nitrogens. As expected, it ex hibits a near-infrared spectrum quite s i m i l a r to that of Fe(phenanthroline)Cl2 and F e ( b i p y r i d i n e ) C l . The sign of the quadrupole interaction for these systems i s positive and consistent with a d^y ground orbital. We thus tentatively assign the transitions observed at 6000 and 10,300 c m " as ^ ( c L ^ ) - Β ι ( ά ) 2< xy) - ^ l ^ z ) respectively. ^ F o r a five-coordinate F e ^ C L j chromophore as suggested for the methyl substituted complexes, one expects the d-d transition at some what lower energies. We observe a ligand-field band for Fe(4,4*-di-CH3-bipyridine)C1 at 9100 and 5000 cm" . 4
1 5
2
2
1
5
a
χ 2 -
n
d
5B
d
2
2
x
1
2
Mflssbauer Isomer Shifts.
In Table ΠΙ we present some isomer
216
EXTENDED
INTERACTIONS
BETWEEN
METAL
IONS
REiFF E T A L .
Ferrous
Chloride
Polymers
218
EXTENDED
INTERACTIONS
BETWEEN
METAL
IONS
shift (δ) and quadrupole splitting (ΔΕ) data f o r compounds (1,2,3,4) investigated in this
work and compare these data to those for other
compounds (5 through 8) of known structure. Table ΠΙ: Mtfssbauer Data Compound T(K)
Structure - Chromophore
Reference
ΔΕ
300 78
1.04
1.45 2.17
*
1.16
78
1.13
1.98
*
300 78
0.92 1.04
3.55 3.73
*
3
0.93 1.06
3.51 3.72
*
3
300 78 300 78
1.07
0.56 1.28
15
1.20
300 78
1.05
3.15
15
1.14
3.35
300 78
0.86 0.98
2.76 3.07
16
300
0.80
78
2.66 2.77
*
0.91
1. Fe (phenanthroline )C1 polymeric - o c t a h e d r a l - c i s - F e N C l ^ 2
2
2. Fe(phenanthroline)Br polymeric -octahedral -cis - F e N
_,_ 6+
*
2
3. Fe(4,4'-di-CH -bipyridine)C1 3
2
Cl
4
2
dimer-five-coordinate F e N C l 2
,
4. Fe(5,5 -di-CH -bipyridine)Cl9 dimer-five-coordinate F e N C l 3
2
5· F e ( p y r i d i n e ) C l polymeric -octahedral -trans - F e N C l ^ 2
2
2
6. F e ( p y r i d i n e ) C l monomeric-octahedral-trans-Fe 4
2
7. F e (quinoline ) C l monomeric -tetrahedral - F e N C l 2
2
2
2
8.
C1 N
2
Fe(2,9-di-CH -phenanthroline)C1 3
monomeric -tetrahedral - F e N C l 2
2
2
4
*
*
* This work *
mm/sec, relative to iron f o i l , source at 300 K.
It i s seen that f o r the six-coordinate FeClo-imine nitrogen systems a more positive isomer shift i s observed.(I*) With decreasing coordination number the isomer shift generally d e c r e a s e s ^ a s evidenced by table entries 7 and 8 f o r known tetrahedral complexes. (-^) The intermediate i s o m e r shift^O) and large quadrupole interaction of compounds 3 and 4 are reasonable f o r the proposed five-coordinate structure. Magnetic Behavior and Structure In view of the proposed structure (Fig. 9) and considerable support ing data, the observation of ferromagnetism f o r Fe (bipyridine)C1 and Fe(phenanthroline)Cl i s not unreasonable. Various m o d e l a i » ) p r e dict ferromagnetic interaction f o r such a structure when (a) the metal and bridging atoms l i e in the same plane; (b) bridge angles are ~ 9 0 ° ; (c) the exchange involves bridge atom p- and metal d-orbitals; 2
21
2
22
15.
REIFF ET AI. Ferrous
Chloride
219
Polymers
and (d) the exchange is between metal atoms i n oxidation states c o r r e sponding to a more than half-filled t g manifold. A study of the ferromag netic behavior f o r other bridging anions ( F , B r , I ) m a y enable a s s e s s ment of the contribution of direct metal-metal exchange as opposed to "superexchange" via the bridging ligands since the metal-metal distance can be v a r i e d considerably. T h i s work i s now in progress. A l s o inter esting is the absence of meta-magnetic behavior for the systems of this investigation in studies to as low as 1.4 Κ and for fields up to 200 kG. We have observed metamagnetic behavior i n Fe(pyridine)2Cl2 and Fe (pyridine ) ( N C S ) . This work will be discussed in a forthcoming pub lication. ( ) 2
-
2
-
-
2
2 3
Literature Cited 1. Wilkinson, M.K., Cable, J.W., Wollan, E.O., and Koehler, W.C., Phys. Rev., (1959) 113,497. 2. Simkin, D.J., Phys. Rev., (1968) 177, 1008. 3. Dunitz, J.D., Acta Cryst. (1957) 10, 307. 4. Reiff, W.M.,and Foner, S., J. Amer. Chem. Soc., (1973) 95, 260. 5. Takeda, K., Matsukawa, S., and Haseda, T., J. Phys. Soc.Japan, (1971) 30, 1330. 6. Broomhead, J.A., Dwyer, F.P., Austr.J. Chem., (1961) 14,250. 7. Clark, R.J.H., Nyholm, R.S. and T a y l o r , F.B., J. Chem. Soc., (A) (1967) 1802. 8. Reimann, C. W., Block, S., Perloff, A., Inorg. Chem., (1966) 5, 1185. 9. Postmus, C., F e r r a r o , J.R., and Wozniak, W. (1967) 6, 2030.
Inorg. Chem.,
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EXTENDED INTERACTIONS BETWEEN METAL IONS
220 15.
Long, G.J., Whitney, D.L.,
and Kennedy, J.E., Inorg. Chem.,
(1971) 10, 1406. 16.
Long, G.J., and Whitney, D.L., 33, 1196.
J. Inorg. Nucl. Chem., (1971)
17.
Burbridge, C . D . , Goodgame, D.M.L., Goodgame, Μ . , J. Chem. Soc. (A) (1967), 349.
18.
E r i c k s o n , Ν . E. i n , "The Mössbauer Effect and Its Application i n Chemistry", Advances in Chemistry Series, No. 88, American Chemical Society, Washington, D.C. (1967).
19.
Edwards, P. R., Johnson, C.E., Phys., (1967) 47, 2074.
20.
Reiff, W.M., E r i c k s o n , N.E., (1969) 8, 2019.
21.
Anderson, P.W., "Magnetism", (1963) Volume 1, Ch. 2, Rado, G. Τ., and Suhl, Η., Ed., Academic Press, New York, Ν. Y.
22.
Goodenough, J.B., "Magnetism and the Chemical Bond", Interscience, New Y o r k (1963), pp. 165-185.
23.
Reiff, W.M., Long, G.J., Little, B.F., in preparation.
and Williams, R.J., J. Chem.
and Baker, W.A.,
Inorg. Chem.,
Foner, S., Frankel,
R.B.,
Acknowledgements W. M. Reiff i s pleased to acknowledge the partial support of the Research Corporation and the Petroleum Research Fund administered by the American Chemical Society. He thanks the National Science Foundation (NSF Grant No. G H 39010) for the major support of the investigation. Finally, he thanks Dr. Graham Hunt of A F C R L for use of the Perkin-Elmer 180 IR-spectrometer. M. A. Weber was supported by an Organization of American States Fellowship. The F r a n c i s Bitter National Magnet Laboratory i s supported by the National Science Foundation.
