A. H . MAKI,N . EDELSTEIN, A. DAVISON, AND R. H. HOLM
4580
Vol. 86
_ _ _ _ resolved Cotton effeci LHis +
CuCI2 (I:I)
H
,P\,
Complex

200
,
220
240o
260
200 o
300
l
Xhp)
Fig. 10.Rotatory dispersion curve of the Lhistidinecopper complex resolved into a simple Cotton effect and a Cotton effect similar to those of the cobalt, nickel, and zinc complexes.
the manyelectron model to this chromophoric electron. Looking a t complex I (imidazole plane), it would be reasonable to take the most polarizable zdirection in the direction of charge transfer. The ydirection would be in the imidazole plane and the xdirection would be perpendicular to t h a t plane. All of the groups lie in
[CONTRIBUTIOS FROM
THE
I
( i m i d a z o l e plane)
or very near a plane except the carboxylate anion which is clearly the principal perturbation of the "chrornophoric ellipsoid." As i t is a negative group, the product ,Ixyz would be positive in this direction, that is, the static charge effect is assumed to be dominant, and as xyz is negative, .4 must be negative, ;.e., a negative Cotton effect might be expected. Figure 10 shows that the curve for the I>histidinocopper(11) can be resolved intoa curve similar to those of the other transitionmetals and a negative Cotton effect curve. Acknowledgment.The authors express appreciation to the National Science Foundation under Grant G P 415 for financial support of this research and to Dr. D. J . Caldwell for helpful discussions on theoretical aspects oi optical rotation.
DEPARTMENT O F CHEMISTRY, HARVARD USIVERSITY, CAMBRIDGE, MASSACHUSETTS]
Electron Paramagnetic Resonance Studies of the Electronic Structures of Bis(maleonitriledithio1ato)copper (11), nickel(III) , cobalt (11), and rhodium (11) Complexes BY 4. H . MAKI,N . EDELSTEIN, ,I.DAVISON,A N D R. H. HOLM' RECEIVED J C N E 1, 1964 The electron paramagnetic resoriance spectra of the low spin ( S = ' / 2 ) planar complexes [CuSaC4(CS)rl 2, 2, and [SiSdC4(CN)4] have been obtained a t room temperature in mag[COS~C~(CN z, ) ~[RhS4C4(C9)4] ] netically dilute single crystals of diamagnetic ( ~  B U ~ S ) ~ [ S ~ S ~ C and ~ ( (Cn SB) u~r ]s )[CuSaC4(C S ) r ] , respectively, whose crystal structures are known. I t wa5 found t h a t the principal axes of the tensors g and A lie along the symmetry axes of the complex in the crystal, within experimental error. Calculations of g and A are made for several possible groundstate configuratiocs of the metal ion in the complex and are cornpared with the experimental spinHamiltonian. The following probable groundstate hole configurations are deduced: [RhS4C4(CS)a],l e 2 0 > ( e = d,,, y = d,,, [ C O S ~ C ~ ( C N ) [NiSaC4(CN)4], ~]~, le">; [ C U S ~ C ~ ( C +, N ) j ~e]> ; 0 E da22,z,where the zaxis is perpendicular to the molecular plane and the yaxis bisects each ligand). Configurational excitation energies estimated from the spinHamiltonians are compared with the optical spectra, and assignments of certain observed electronic transitions are made.
We have recently reported on the synthesis and characterization of a series of planar fourcoordinate comParamagnetic resonance spectroscopy has been explexes of transition metal ions of the 3d, 4d, and 5d tensively utilized in the study of planar chelates of groups which readily undergo oxidationreduction C u ( I I ) , which have a dgelectron c o n f i g ~ r a t i o n . ~  ~reactions. lo These complexes are remarkable in t h a t the geometry oi the complex is unaffected by oxidation(1) Alfred P . Sloan Foundation Fellow. ( 2 ) B. R McGarvey, J . P h y s . C h e m . , 6 0 , 71 (1956). reduction reactions, and one can obtain planar com(3) A . H. hlaki a n d B. K . McGarvey, J . Chem. P h y s . , 2 9 , 31, 35 (1958) plexes containing the transition metal ions in a series (4) J . F. Gibson. D . J . E . Ingram, and D. Schonland, Discussions F a v a i i a r Soc., 2 6 , 7 2 (19:s). of formal oxidation states. The object of this paper i.5) K S e i m a n and D . Kivelson. J Chew?. P h y s . , 36,136, 162 (1961). 16) D . Kivelson and R. S e i m a n , i b i d , 36, 149 (1961). is to report on the results of paramagnetic resonance
Introduction
( 7 ) I < . Petteisson and T. '\'inngird, Arkzz' Kern;. 17, 219 (1961). ( 8 ) E >f Roberts and W. S Koski. J . A m r h e i n . SOC., 8 2 , ROOfi (1960). ( 9 ) H K.Gersrnann and J D. Swalen, J . C h f m . P h y s . , 36,3221 (1962).
( I O ) A . Davison, S. Edelstein, R . H. Holm, and A . H. Maki, I n o v g C h r m . , 3, 814 (1964), and papers referred t o therein
E.P.R.STUDIES OF
Nov. 5 , 1964
measurements of magnetically dilute single crystals containing certain of the paramagnetic complexes described earlier'O' l 1 as solutes. The compounds in
vestigated here are the paramagnetic tetranbutylammonium salts of the planar complexes I in which 111 = Cu. Co, Rh, z =  2 , and M = Ni, z = 1. The diamagnetic host crystals employed in this investigation were A 1 = Ni, z =  2 , for the paramagnetic z =  2 complexes, and 91 = Cu, z = 1 for the paramagnetic z =  1 complex. Preliminary paramagnetic resonance data have been reported for several complexeslO~ll b u t up to now these data have been obtained either in liquid solutions, frozen glasses, polycrystalline solids, or magnetically dilute single crystals without the benefit of a crystal structure. Although data obtained from disoriented samples may be used to obtain the spinHamiltonian'* parameters of the complex, they suffer from the very important defect t h a t the magnetic principal axis system cannot be related to a moleculefixed coordinate system by purely experimental means. The usefulness of the spinHamiltonian for the assignment of the electronic configurations of complexes is largely lost without this information. Complete structure determinations of (nBu4N)[ CuS4C4(CN) ] and (nRuhN) 2 [ CoS4C4(CN)4 ] (isomorphous with the corresponding nickel ~ o m p l e x ' ~ ) have recently been completed by Forrester, et a1.,I4 and reveal that the ligands form a planar array about the central metal atoni. From the crystallographic structures of the z =  2 and z =  1 host complexes, we obtain the orientation of the principal axis systems of A, the hyperfine tensor, and g. the gvalue tensor in a moleculefixed coordinate system. Conclusions are then drawn about the probable delectron groundstate configurations of the central metal ions by comparison of the observed A and g with those calculated from various configurations. Estimates of configurational excitation energies are obtained and discussed. Experimental Single crystals containing 1 t o 5 mole Yc of the paramagnetic complex were grown by solvent evaporation from solutions of the z =  1 crystals in dichloromethanechloroform, and from solutions of the z =  2 crystals in acetone2butanol. Faces of the doped ( B U ~ S ) ~ [ S ~ S ~ C Iand ( C S(BurN)[CuSaCd(CS)d] )~] crystals were identified by optical goniometry. Crystals were mounted on a polystyrene wedge with a n identified face attached with Apiezon S to one of the surfaces. T h e wedge was attached t o a polystyrene post with an indicator which could be rotated against a fixed angular scale. By means of this arrangement, the crystals were each rotated inside the microwave cavity of the paramagnetic resonance spectrometer through 180", (11) E;. Billig, S. I . Shupack, J . H. Watels, R . Williams, and H. B. G r a y , J . A m Chew. Soc., 8 6 , 926 11964). (12) 3f. H . L. Piyce, Proc. P h y s . Soc. (London), 863, 25 (1950). ( 1 3 ) A . Davison, N. Edelstein. R. H. Holm, and A . H. Maki, I n o r g . r h f m .a, , 1227 (1964). ( 1 4 ) J . D . Foirester, A . Zalkin, and El H . Templeton, ibiii., 3, 1.500, la07 (1964).
PL.4NAR
4581
COMPLEXES
measurements being made either a t 20 or 15" intervals. Crystals were remounted, and rotations made about two axes orthogonal to the first. The rotation axis was perpendicular to the magnetic field, T h e paramagnetic resonance measurements were made on a conventional spectrometer operating a t about 9.8 Gc./sec. employing 30 kc./sec. magnetic field modulation. T h e klystron frequency was measured with a transfer oscillator and frequency counter for each crystal orientation. T h e magnetic field was measured by means of a proton gaussmeter monitored by the same frequency counter.
Analysis of Data and Experimental Results The observed gvalues and hyperfine splittings for each rotation were averaged by a leastsquares analysis and the resulting parameters were treated according to the procedure of Sch0n1and.l~ We have assumed that g and A have the same principal axis system (discussed below) and write the spinHamiltonian**as 2
X

+ IAS
 2
=
PJg H
=
Po(gzSzHz
+ g y J u H u + gazSzHe) +
AzzIzSz
AUJUS,
+
+ AZZIZS,
A
where POis the Bohr magneton, H is the magnetic field, 2
2
and S and I are the electron and nuclear spin operators, respectively. We obtain the principal values of g (gTz,guu,gzz)and A (Azz, A,,, A2d from the analysis of the data. T h e analysis also gives the direction angles of the magnetic principal axis system in relation to the coordinate system defined by the three orthogonal crystal rotation axes. We now define a righthanded moleculefixed axis system as Y
I A s
I molecular plane and going into t h e paper
z
h S
The direction angles of x, y, and z were calculated from the crystallographic data in the crystal rotation axis system and compared with the direction angles of the principal axes of g and A. For each crystal analyzed, agreement was found to be, on the average, within 23', which indicates t h a t the magnetic axis systems in the crystal are coincident with the symmetry axes of the complex ion, within experimental error. This agreement also shows the assumption t h a t g and A have the same principal axis system is correct, within experimental error. Table I lists the crystals measured, the principal g and A values, and the calculated and experimental direction angles. (Bu4N)2[NiS4C4(CN)4] has one molecule per unit cell, while (Bu4N) [ C U S ~ C ~ ( C Nhas )~] eight molecules per unit cell, but only two magnetically unequivalent sites.I4 In the case of [NiS4C4(CN),], A for 61h'i was obtained from the glass spectrum of an isotopically enriched sample. The most significant differences between the principal values of g reported here and previously reported values from glass spectra occur in the case of the gz, for [NiS4C4(CN)4](found to be 2.140 in a CHC13dimethylformamide glass]"). There is also a significant difference in the maximum principal gvalue reported by Billig, et a2.,I1 for polycrystalline (nBudN)z [RhS,C4(CN), ] ( 2 . 3 5 ) and our (15) D. S. Schonland, PYOC. P h y s . Soc. (London), 73, 788 (1959)
3582
X H X ~ KNI ,EDELSTEIN, A. DAVISON, A N D R H HOLM
l7o1 Mi
TABLE I hlolecular axis
Crystal
_______
Ilirection angles, deg.
(BurN)SiSiCI(CN)ab x diluted in y (Bu;NlCuSC~(CS)r z
78.2 76.2 18.2
34.3 55.2 88.0
58.2 38.1 71.8
(Bu&)nCoSG(CK)r diluted in
y
22.9 71 R 77.0
67.2 43 1 55.7
89.1 52.8 37.3
2.798 0 003 2 023 i 0 003 1 . 9 7 7 I 0 008
2:j.S 73.6 73.6
66 5 46.2
y
22.9 71.5 77.0
67.2 43.1 55 7
89 1 52.8 37.3
2.026 2 023 2.086
24.8 70.2
37.2 54.2 82.1
64. 8 449
2.447 2.019 1.936
x
diluted in (BuiPi)2PiiSnCI(CS)4
z
(BuiX)gRhSKI(CN)aa
x
y
iSaCi(Cii)r
I
53.5
6 4 . .5
66.8 35.6
Fxperimenta
A , cm
Calculated direction angles, deg 2 160 2.042 1.998
741 76.9 20 8
+
31.7 5.j.Y 83.9
60.0 37.2 70.2
x
I
103
Ilirection angles, deg
l.ii0.2C 0.2Y,0lc
gr,, g,,, and g,, problem with a basis set of the d atomic orbitals. U'e '!lz21>> (A,,~,!L4vv. These results are typical of squarewill later attempt to account for delocalization of the planar Cu(I1) complexes with the electronic configurawave functions byreducing the spinorbit coupling tion d9, or a vacancy configuration d'. Previous , mean inverse cube electronparameter, j! and v 3 the paramagnetic resonance studies?, on single crystals nuclear distance, which are deduced from the elecof squareplanar Cu(I1) complexes makes it highly tronic spectra of the free ions. Our development will likely that the vacancy is in a d,, orbital in D P sym~ be similar to that of G~iffith*~ for the d" strong field metry. The polarized optical absorption spectra of complexes, except that we use a basis set of real dbis(acetylacetonato)copper( 11) were interpreted by Ferorbitals. guson,l8 who concluded t h a t the vacancy occupies a (19) (a: T. S. Piper and R . L. Belford, 4101. P h y s , 6 , 169 ( 1 0 6 2 ) , (b) J . Ferguson, R . L. Belford, and T . S. Piper, J . C h r m P h y s . , 37, 1569 (1962). d,, orbital in n 2 h symmetry. Fcrguson's analysis has,
value of g,, for the magnetically dilute single crystal. The effect on g,, of the nickel complex may be due to a solvent effect to be discussed more fully below, but there is no ready explanation for the large discrepancy in the case of the rhodium complex. Kormally, paramagnetic resonance data of magnetically concentrated crystals may be suspect because of the possible averaging of gvalues of magnetically unequivalent sites by electron spin exchange. Such averaging occurs in crystals of C u ( N H J 4 S 0 4 . H 2 0for , instance, l 6 containing two magnetically unequivalent sites in a unit cell. The crystal structure of the isomorphous (nBu4?J)2[ C O S ~ C ~ ( C Sreveals ) ~ ] ~ ~only one molecule per unit cell, so averaging of principal gvalues by spin exchange is not expected to occur, even with a considerable spinexchange rate.

(18) E . H . Carlson and R . D. Spence, J C h r m . P h y s , 2 4 , 471 (19.56). R . William
+
+ 2s,k)/$,> 2i 2
= 2
= NuI€2p+>
=
2szk)l
k

/4&2x>

(5)
iaaIe+p2>
&
= Nul€2p>
i + a1py+> + 2
l/za21€2X+>
+
h3/ep2>
(6)
We have truncated the complete firstorder wave functions to exclude configurations which do not contribute to the spinHamiltonian. With N , = 1, we find
(2)
2
= 2 
k
guu =
$a+
~
i
for the firstorder groundstate Kramers' doublet. N , is a normalization constant which is close to one if the mixing parameters, a t , are small. at = {/Ef,, where E,, is a configurational excitation energy. El, = E ( / p > )  E(ie>), E2, = E(Iy>)  E(Ie>), etc. With = 1, the following expressions are found for the spinHamiltonian parameters gzI
Applying the spinorbit coupling Hamiltonian to e2p> we obtain, in first order
1 $p+>
(1)
 a31i>
1/2azlj>
4583
OF P L A N A R C O M P L E X E S
2a1
(74
2  2az
(7b)
g ,,
= 2 
g,
=
+8a3
gzz = 2
and
P[2ai 
K

K
K

A,,
=
A,,
= P[ZU:,
A,,
=
P[8a3 
(7c)
+ f 3/7az] + + "7
'/7
"7
3/7(2.11

3/7(U1
+ az)]
(84 (8b) (8C)
3. ZeroOrder Kramers' Doublet le2 O+>, je20>. The spinorbit interaction mixes in many excited configurations in first order. Of these, we include only those which contribute to g and A in the following truncated firstorder groundstate doublet.
2  8a1 ( 3 ~ )
L
and
A,,
=
~P k
+ + 3 / ~ a 2 ](4a) 2i~
=
k
K
"7
:/7(a2
44

A
A
d
d
( 2 4 ) E . U . Condon and G. H Shortley, "Theory of Atomic Spectra," Cambridge University Press, Cambridge and New York, 1935. ( 2 5 ) The and  symbols above the orbital wave functions refer to the respectively, according t o standard eigenvalues of h's*, f ' / t , and  I / ? , usage
+
(IO)
Using this ground state, we find the spinHamiltonian parameters
a3)]
In these expressions, the summation is over the  vacancies (one in this case), and P = 2gX. electron & , P N ~  ~ , where g s and PN are the nuclear g value, and nuclear magneton, respectively, 4" is the Bohr magneton, and Y  ~is the mean inverse cube vacancymetal nucleus distance. aR = 4sk  ( I k . s k ) l k I k ( l I , . s k ) , and K is a parameter referring to the Fermi hyperfine coupling energy in units of P . 2. ZeroOrder Kramers' Doublet I++>, lt2k> .We will assume that in the d 3 configurations e remains the lowest energy orbital for the vacancies, and consequently in an S = '/2 configuration is doubly occupied. 1te will consider the four possibilities for the groundstate configuration based upon i $>. 2
b21e2x+> d3 2
3/7a31
2  6b1
(114
guu = 2  6b2
(1lb)
gzz
=
gzz = 2
and
A,,
=
P[6bl 
A,,
=
P[6b2 
A,,
=
)[K
K K

+ +
"7 "7
 3/7bsl
(12a)

(12b)
3/7bl]
+ b,)]
3/7(b~
(lac)
where we have made the approximation that Vb = 1. 4. ZeroOrder Kramers' Doublet ( e 2 y + > , \ ~ 2 y  >.We obtain the perturbed groundstate doublet wave functions
A H MAKI,N EDELSTEIN, 4 DAYISON, AXI) I< H HOLM
3584
1701

2
z
,
cz,€*x>  csI€2p+> 2 2
+
1,
2c41€+y2>
(14)
which again include only those admixed configurations which contribute to g and A. 1Vith N , = 1, the spinHamiltonian parameters obtained from eq. 13 and 13 are ,g,
=
2 
g,
=
2  2c4
(15a) (15b)
g,
=
2  2c2
(l5c)
GCl
 2c3
and
.4., :Iuv
=
P[6cl  2c3 
=
P[2c4 
K
=
P[2Cs 
K
K
 4,1 7 
+ + + f
3 i ' 7(cz
+ cJl
(]sa)
'17
3/7(c1
+ c2  cg)]
(16b)
'17
'/j(Ca

(I&)
61

C4)]
5. ZeroOrder Kramers' Doublet i E% +>, i E%>.Lye will not develop this case separately, since it can be shown readily that the spinHamiltonian obtained is of the same form as t h a t obtained from the doublet t 2 y  > , 1 2 y  > , but with interchanged magnetic xand yaxes. The coefficients, c l , must be changed to refer to different excitation energies, however. ~
Comparison with Observed SpinHamiltonians The observed g, Table I , will be compared with each of the theoretical expressions developed in the previous sections. The resulting parameters, ai, a,, bi, c,, will then be introduced into the expressions for A. The best overall agreement of the calculated A with experiment will be taken to indicate the probable groundstate configuration. 1. [ C U S ~ C ~ ( C N ) ~ ]In  * . this case we assume that the configuration is ! E > . We will also assume, neglecting the small for simplicity, that g,, = g, rhombic distortion and taking their average value as g. Substitution of g, and gl into eq. 3a, 3b, and 3c gives ai = l1,(11(15, a2 cy3 = O.(ilO5, Substituting these parameters into eq. 4ac, we obtain ,Izz .~lu, = P[O.30  K ] , > lAlzz, ! . I v v ' , the sign of each must be negative (P is positive for sn,B5Cu).The observed hyperfine parameters of Table I give P = 1.6 X cm.l, 3.5 X 102 and K = 0.55. For the free ion, Po cm,l ,?B so in this complex r3 has roughly onehalf the free ion value, indicating strongly covalent abonding. The inore accurate molecular orbital theory for planar Cu(I1) complexes3 has been applied by Pettersson and Vannggrd' to bis(N ,Ndisubstituted dithiocarbamato)Cu(II) complexes, which have spinHamiltonians similar to [ C U S ~ C ~ ( C S ) ~and ]  ? in which the metal is coordinated only by sulfur. Similar conclusions have been drawn regarding the high degree of covalency of the CuS bonds.

+
+



(26) A . A h r a g a m a n d hZ. H I, Pryce. P r o c . R o y . SOC.(London!, A206, 161 f1g:l'I.
SG
2. [NiS4C4(CN)4].The configuration le2p> leads to a1 = (1.079, a::= O,(J2ll, and u3 0.lKJ1, by solving eq. Tac with the observed g values. The hyperfine interaction is then given from eq. Sac by .Iz, = 1'[0,&3  K ] , . l u y = P[IJ.%I)  K ] , and . I z 2 = f'(1.53  K ] . The observed 1..1,,~ ' a l z x : ,contrary to observation. The configuration 1f2O> is thus also unlikely. 1i:e next examine the configuration i e 2 y > . We find 3cl c3 = (l.(li9, and c4 = (1,020 by solution of eq. l5a and b. The theory is not suficiently accurate to enable the determination of c2 from eq. 13c, but it is probably small, and we shall ignore it in eq. 16. I t will be shown below that with < 1, as is required for normalization, g,, can be reduced below 2.11028. By substitution of the ci into eq. IGac, we find .l,, = P[0.11 K ] . . 1 v u = P[0.33  K ] , and:!,, = P [ o . 2 9 K ] , where we have made the approximation c1 = c : ~= 0.02 when these coetiicierits appear in the smaller terms. If it is assumed t h a t 4,. and . l p v are of the same sign, the experimental values may be fit with K = 0.51, and P = 1.6 X c m  I ; whereas, a fit is obtained with K = 11.21, and P = 2.5 X l(JPsc m  l if they are of opposite signs. The predicted values of ,Iz, are 0.35 X cm.l, and 0.20 X l ( 1 F c m  ' , respectively. The "'si hyperfine interaction in solution, (a)= 4.3 + 1 gauss, favors the assignment of &l,. and < l U vwith opposite signs. The sign of lzz is predicted to be negative. If we use the most recent value (l.0J$s,27 of the nuclear moment of "Xi, p = 0.711 we can estimate Po for the free ion. l y e use an equation given by Trees,?8derived from formulas of Goud~ m i t ,which '~ relates j to for the free ion. l i r e take j = 715 cm.] for Ni(III),""and find Po = 0.010 c m  l . Reduction of rri for the ion in the complex might be expected to reduce P to about A X 1Ou3 cm.], but not much lower. However, the order of magnitude is correct, and we accept the 1e2y> configuration as consistent with the observed spinHamiltonian. Inspection quickly shows that the Configuration e'x> is inconsistent with the spinHarniltonian. so t?y> is the probable groundstate configuration of [NiS4CI(CN4 1 . 3. [C~S~C~(CN)~]~.Beginniiig with the assumed groundstate configuration 1 e 2 p > , we find al =  l I , 4 ) 0 , u2 =  l l , O l l ~ a3 = 0.003. These parameters yield the principal hyperfine couplings .I,= = Pj1.08  K ] , ..I,, = P [ 0 . 1 4  K ] , and . I z , = P[o.t2  t i ] . The observed values of A l z r , . I v u , and .1,,
+
*
ri3
1
E.P.R. STUDIES OF PLANAR COMPLEXES
Nov. 5 , 1964
can be fit approximately with K = 1.4, P = 2 X l o p 3 cm.', provided these parameters are all positive. Po for the Co(I1) free ion has been deduced to be 0.022 cm.l by Abragam and P r y ~ e . ~It ' seems unlikely t h a t P could be reduced by an order of magnitude in this complex, so we conclude t h a t je2p> is an unlikely groundstate configuration. We next assume t h a t the groundstate configuration is 1e20>, and obtain bl = 0.133, b2 = 0.004 We will not be concerned a t this point that g, is less than 2. I t will be shown below t h a t if terms in b1* are retained in the development of the spinHamiltonian, g, = 2  3b12 is obtained which yields gzz 1.95, a value in tolerable agreement with the experimental one. Substitution of bl and b2 into eq. 12ac gives A,, = P [ o . j l  K ] , .4,u = P [  0 . 2 1  K ] , and .g,, = P [ 0 . 5 1  K ] . These values predict t h a t 1.. ilZ2 for any value of K and P and thus cannot be reconciled with the observed hyperfine tensor. These expressions are not changed significantly by retaining terms of order b12. T h e groundstate configuration 1 c20> is thus considered an unlikely one. If the groundstate configuration is Ie2y>, we find c1 = 0.13 and c4 = 0.011, where we have assumed (c31 < Icll. We shall examine this configuration using a more accurate theory below. For now, we will assume that cz and c3 are small and can be ignored. From eq. 16ac, we find A,, = P[0.23  K ] , .dyv = P[0.25 K ] , A,, = P[0.35  K ] . Taking P = 0.018cm.', K = 0.48, we find A,, = 4.5 X low3, A , , = 4.1 X cm.', values which are in and A,, = 2.3 X tolerable agreement with experiment, considering the crudeness of the theory a t this stage. T h e value of P required for this fit is reasonable in comparison with the free ion value.31 T h e agreement can be improved considerably by retaining terms in c12 in the development of the spinHamiltonian. We will justify the assumption t h a t c3 is small in comparison with cl, below. The equivalents of eq. 1lac and 12ac are found to be


g ,,
=
2  6 ~ 1 2C3
(17a)
g,
=
2  2C4 
3ClZ
(17b)
g,
=
2  2cz  3612
(1 7 4
we obtain the equation
= P [  6 ~ 1  2C3 
K
+
'/7(
 4 f
3/zC12
+ cd)]
~ ( C Z
A,,
= p[2C4

K
+
'/7{
2
=
P[2Cz

K
+ '/7{2 
' / Z C ~ ~ 361 64)
(19)
J
~I


(18a)
+
(18b) 3(C3

)I (W
We may now obtain a crude estimate of c3, and verify that it is smaller than cl. Neglecting interelectronic repulsion terms, c3 refers to the excitation Iy> t lp> for a vacancy; whereas, c4 refers to the excitation It> Iy>. In the Cu(I1) complex, a1 refers to the / p > directly. Assuming vacancy excitation l e > little change in the quantity (It>  ( p > ) the one electron energy level difference between Cu(I1) and Co(II),

 11I
Lalico
2  6b1
g ,,
=
g,
= 2  6bz
g,
= 2
(204
 3bi2
 3bi2
(204
and
cz  c a ) ) ]
A,,
c 4p 4__ iC"
A value of c4 is obtained from eq. 17b and the experi0.13. T h e ratio rcu/Sc0 mental g,,, assuming c1 is taken from the free ion values. 3o We find c3 =  0.01 from eq. 19, and from eq. 17ac we obtain c1 = 0.13, c2 = 0.013, and c4 = 0.037. Substitution of these values into eq. 18ac gives A,, = P[0.25  K ] , A,, = P[0.30  K ] , and A,, = P[0.37  K ] . With P = 0.020 cm.' and K = 0.47, we obtain A,, = 4.4 X lW3, A,, = 3.4 X and A , , = 2.0 X cm.l. It is noteworthy t h a t reasonable quantitative agreement is obtained with P near the free ion value. By similar arguments i t is found t h a t no reasonable agreement with experiment is obtained with the groundstate configuration 1 &>. We conclude t h a t t h e probable groundstate configuration of [ C O S ~ C ~ ( C 2 N)~] is j t2y> . 4. /RhS4C4(CN)4] 2.Assuming the configuration / e 2 p > , we find ul = 0.223, uz = 0.009, u3 = 0.008, from which are obtained &4,, = P [ 0 . 7 3  K ] , A,, = P[O.21  K ] , and A,, = P[O.54  K ] . For any value of K , either positive or negative, IA,,i or IA,,I is larger than lAv,l. Since these possibilities are in qualitative disagreement with the experimental observa, discard le2k> as untion 14,,1 > lA,,I, ~ A , , ~we likely. If we next assume t h a t the configuration is 1e20>, we find, using eq. llac, bl = 0.074, bz = 0.003, whereupon, from eq. 12ac, we find A,, = P[0.16 K], A,, = P [  0 . 2 4  K ] , and A,, = P[0.54  K ] . It iS consistent with these expressions t h a t lAuv1 > lA,,l, lAzz1. We may estimate Po for the free ion R h ( I I ) , as outlined previously, and we find Po  3.2 x 103 cm.l. If we assume t h a t F3 is reduced to about onehalf the free ion value in this complex, and use the experimentally determined lAyyl = 0.74 + 0.1 X cm.l, we find K = 0.22 + 0.06, A,, = +0.1 f 0.1 X and A,, = 0.51 f 0.1 X ern.'. A,, is predicted to be positive. A more accurate set of equations can be developed for this configuration which retain terms of order biz. These are

+ 3(C1 +

Cn
and
A,,
4585

(31) A . Abragam and SI. H. L. Pryce, P r o c . R o y . So is unlikely for the rhodium complex. I t is found t h a t the configuration E?C> leads to l,, = P[o.73  K ] , .Iuu = p[f),46  t i ] , and .Az2 = P[o.38  K J . X value of ti may be found such that !.+lvg1> ~  A Z z ~:A42zl , by a factor of roughly two which is the experimental criterion, but this requires K ,> 0.33. In order to fit the experimental value of &.lv,, P = 1,O X l ( J + cm.' would be required. Although a value of P this small can not be ruled out, it seems less likely than the larger value discussed in connection with the i c20> configuration above. Me conclude that the probable groundstate configuration of [RhS4C4(CN)4]2 is 1 E * < ) > .
VOl. 86
50,000 cm.  l . The paramagnetic resonance data are again consistent with a strong tetragonal field. The optical spectrum of the ion in acetone reveals a t least one band with E 5 100 near 19,000 crn.l appearing as a shoulder to a more intense band ( E 26(J(J) peaking a t 21,000 cm.'. The weak shoulders are reasonably assigned to any of the dd transitions 1 c2y> e2O>, ? p > , c y 2 > , since they are of reasonable intensity and occur in the frequency region predicted by the paramagnetic resonance data. h band with E 300 occurring as a shoulder a t ,8850 cm.' on an extremely intense band a t 11,590 cm.' ( E 8000) can not be assigned as a dd transition. [CoS4C4(CN)a]*.The Co(I1) free ion has = 515 cm.'. Using j = 310 50 cm.' for the complex, and the values c1 = 0.13, cr = i).013, c3 = 0.01, and c4 =  0 , 0 3 i , we find that the energies of the configurations E * ( ) > , 1 t2x>, I $ p > , and ty2> are 2300 + 400, 24,000 f 4000, 31,000 f 5000, and 8400 f 1400 crn.' above the groundstate configuration 1 ~ ? y > . In the visible region, transitions 1 t*y> + ty2>, ~eyO> would be predicted to occur a t approxi1200 cm.' and 10,800 + 1800 cm.  l , mately 8400 whereas all other dd transitions would be expected Comparison with Optical Spectra either in the ultraviolet or in the farinfrared range. Two weak bands are, in fact, observed in the visible Evaluation of the parameters ai,a,, etc., from the exspectrum in dimethylformamide solution and occur as pressions for g in the previous section allows an estishoulders on a strong band peaking a t 18,000 cm.' mate of configurational excitation energies to be made. ( E "3300). The weak bands have maxima a t 12,50(J N o great accuracy can be expected, since the oneelecem.' ( E 70) and I5,(NJO cm.l ( E ~ 1 0 0 ) .The tron parameter, j, is reduced from the free ion value agreement with the observed positions of the bands because of the covalency of the orbitals in the complex, may be improved considerably by using a larger value by an undetermined factor. For these complexes, i t of jfor the complex. The paramagnetic resonance is probably reasonable in general to take j to be about hyperfine structure of the cobalt complex was fit with 0.6 to 0.7 of the free ion value, to. a value of .Papproximately 90ycof the free ion value, [ C U S ~ C ~ ( C N ) ~ ]  ~ . ,C u F (OI I~) , the free ion value of and since P has the same dependence on r7< as does the spinorbit coupling parameter is To = 828 cm.l. j, a value of j about 9070 of the free ion value  O . ( J l l ) in Since it was found t h a t a I a2 ? a3 would seem more reasonable in this case. m'ith order to fit the paramagnetic resonance data, we conj0.9j,, 460 cm.', the visible transitions are preclude that the states , p > , ~.v>, and y> lie between dicted to occur a t approximately 12,400 and l.5,900 4I),O(JO and 60,000cm.' above the configuration E > . cm.'. The approximate energies of the excited conThese excitation energies arise from assuming j = figurations ' E ? ( ) > e ? ~ > , and I t2p> based upon the 0.5jo and j = (J.7ja,respectively. The energy of ;I)> larger value of j are then *36(J(J,35,O(J(l, and 46,000 cannot be obtained from the paramagnetic resonance cm.', respectively. data, since I O > is not mixed with the ground state, 1 E > , [RhS4C4(CN)4]2.In R h ( I I ) , j,, = 1220 cm.'. by spinorbit coupling. Assuming j(0.6 f 0.1){0, and using bl = 0.Oi4 Ue find one optical transition in [ C U S ~ C ~ ( C P I ) ~ ]  ~ and bz = 0.0056, we find that the energies of the a t S330 cm.l, t = 93, which could possibly be asconfigurations It2y> and ~ E ~ . X > are 9900 f 1600 and signed to a dd transitionmost likely l e > + (O> . 130,000 f 22,000 cm.  I , respectively, above the groundSome doubt is cast upon the interpretation of this state configuration I E * ( ) > . The latter excitation energy transition as E > t IO> by our failure to observe any is probably not reliable, since i t is obtained from the transition of t 2 I O in the range 6~10lJ12,OOO cm.' rather small Ag,,, and inadequacies in the theory for in bis(S,Sdiethyldithiocarbamato)copper(II). This 4d complexes would be expected to affect conclusions complex has g8 and gL essentially the same as those drawn from the smaller Ag values to the greatest extent. ?,' and consequently the delectron of [CuS4C4(CS),] The energy of $y> is probably a better estimate since excitation energies would be expected to be similar. it is obtained from the relatively large AgrT. [NiS4C4(CN)4].ln Ni(IIl), j" = i1.7 cm.I, and The optical spectrum of [RhS4C4(CN)4]2 contains we will assume that j is reduced to 430 + TO cm.' a dd one weak band which could be assigned to in the complex. If c1 r 3 * we find c1 c3 c4 transition. The band has E 30. and a maximum at  (J.02. From the paramagnetic resonance data, 7810 cm.'. I t is reasonable to assign this transition we predict that the excited configurations i A ) > , to E'()> + $y>, lie between li;.Ol)lJ and 26,000 cm.l ; E ? K > , and Summary above the groundstate configuration E ? ? ! > . In terms of oneelectron energies, we have consistency with the From measurements of the paramagnetic resonance results for [CuSIC4(CN);]? for which the excitation spectra of the complexes [ C U S ~ C ~ ( C ? J ) ~[NiS4C4]~, 'E> t ifi> was predicted to occur in the vicinity of ( C N ) 4 ]  , [ C O S ~ C ~ I C N ) ~and ]   ~ [RhS4C1(CN)1].? , in
 

1



~
~
~

I
*
~
*
~
 
~
'

~

  

I
'
PIPERIDINATE COMPLEXES OF KICKELA N D COPPERMESOPORPHYRIN IX
Nov. 5 , 1964
magnetically dilute single crystals of known structure, we have concluded t h a t the probable groundstate vacancy configurations are 1 e > , I e*y>, E ? Y > , and 'C*O>, respectively. In n z h symmetry, E = d,,, y d,,, and 0 E daZ2 y z . The zaxis is perpendicular to the molecular plane, and the yaxis bisects each ligand. The configurational excitation energies predicted from spinHamiltonians have been compared with the optical spectra of solutions of the complexes, and observed weak transitions were assigned. The agreement between predicted and observed optical transition energies is satisfactory considering the uncertainty in the spinorbit coupling parameter, {, for the complex. From the value of and { required to fit the hyperfine structure, and the optical transition energies of the cobalt complex, the dorbitals are considerably less covalent in this complex than in the other three. In the other complexes, the hyperfine structure of the paramagnetic resonance and the optical spectra are best fit with r+ and { about 0,50.6 of the calculated free ion values. \Ye find that the strength of the tetragonal field of maleonitriledithiolate dianion as measured by the one,u (where u , = dZ2 v 2 ) is large, this electron energy E energy difference being estimated in the region of 40,000 cm.' for the copper, nickel, and cobalt complexes. The parameter giz is reduced in CHC13DMF glass of [?jiS1C4(CN)4]below its value in the single crystal. According to the theory this implies a reduction in the parameter cl, or in c3. Since c1 refers to the excitation le*y> 1 c 2 0 > , whereas c3 refers to ~ E * Y > ) e ? p > , i t is more reasonable that the solvent would affect the energy of the former excitation, which ap
r3



[COXTRIBETION FROM
THE
4587
pears to be increased by the order of 10% in the glass over its value in the single crystal. The common feature of our interpretation of the electronic configurations of the d3hole complexes is the proximity of the energies of the configurations j ~ ~ y > and 1 E * O > . The splitting is largest in the nickel(II1) complex, with ie?y> lower (by about 20,000 cm.l), smaller in the cobalt(I1) complex (350(1 cm.I), and the E ~ O > has become the groundstate configuration in the rhodium(I1) complex (with l k y > a t about 8000 cm.I). No reliable estimate can be obtained of the energy of the e2x> configuration from the theory, but i t may be stated that the energy of this configuration is well above that of e 2 y > , probably by > 15,000 cm.'. The large splitting of !e*y> and 1e2x> implies an extensive interaction of the metal 1y> and Ix> orbitals with rrorbitals of the ligands. Finally, molecular orbital calculations of the groundstate configurations of [KiS4C4(CN)4] and [Cos4C4(CN)d]*using the extended Huckel theory correctly predict the 1 e2y> c o n f i g ~ r a t i o n . ~ ~ Acknowledgments.Support of this work by the National Science Foundation through grants GP957 and GP596, the 4dvanced Research Projects Agency (Department of Defence) through Contract SDXS, and the Milton Fund of Harvard University is gratefully acknowledged. \Ye wish to thank Professor D . H . Templeton and his associates for informing us of the results of their crystal structure determinations prior to publication. \Ye also thank Mr. A. Kwok for engaging in many helpful discussions.
i
I
1
(32) R. Hoffmann and R. H . Holm, unpublished work.
CHEMICAL LABORATORIES OF THEJOHNS HOPKIXSCXIVERSITY, BALTIMORE, MARYLAXD2 12181
Piperidinate Complexes of Nickel and Copper Mesoporphyrin IX'
w.BAKER,LTAURICE s. BROOKHART, A N D ALSOPH H . CORWIN
BY EARL
RECEIVED FEBRUARY 15, 1964 By spectrophotometric techniques, it is shown t h a t copper and nickel mesoporphprin IX form, respectively, a mono and a dicomplex with piperidine. The thermodynamic constants for these reactions are reported The crystal field stabilization energy of the structure of the transition metal ion is correlated with the structure of metalloporphyrin ligand comple\es and a relationship of spectral shifts t o ligand number is shown
T h e formation of complexes of copper and nickel mesoporphyrin with a variety of ligands was reported by Corwin, Whitten, Baker, and Kleinspehn.2 Previously, Caughey, Deal, McLees, and Alben3 had shown that nickel porphyrins form complexes with pyridine. Miller and Dorough studied the formation of pyridine complexes of several metallo derivatives of tetraphenylporphine and reported equilibrium constants of their formation. This article reports a spectrophotometric study of the reaction of piperidine with copper and nickel meso( 1 ) Polphyiin Studies. X X X I I . Papet X X X I : E. W. Baker, hl. Iluccia, and A. H . Coiwin, A n a l . Riochem., 8, 5 1 2 (1964) This work was supported in patt b y Resealch G r a n t A2877 from the Sational Institutes of Health and in palt b y the Petroleum Resealch Fund administered by the American Chemical Society. Presented in part a t the 146th Xational hleeting of t h e American Chemical Society, Denver. Colo., 1961. 12) A H Coimin, D. G . Whitten, E. W. Baker, and G . G. Kleinspehn, J . A m . ( h e m . Soc., 86, 3621 (1963). 13) W .S. Caughey, R . 31. Deal, B . D . McLees, and J 0. Alben, ibi