J. Phys. Chem. 1994, 98, 9894-9899
9894
Chloro and Bromo Complexation of the Manganese(I1) Ion and Solvation Structure of the Manganese(II), Iron(II), Cobalt(II), Nickel@), Copper(II), and Zinc(I1) Ions in Hexamethylphosphoric Triamide Kazuhiko Ozutsumi* Department of Chemistry, University of Tsukuba, Tsukuba 305, Japan
Yuriko Abe Department of Chemistry, Faculty of Science, Nara Women's University, Nara 630, Japan
Ryouta Takahashi and Shin-ichi Ishigurot Department of Electronic Chemistly, Tokyo Institute of Technology at Nagatsuta, Midori-ku, Yokohama 227, Japan Received: May 30, 1994; In Final Form: July 20, 1994@
The complexation of the manganese(I1) ion with chloride and bromide ions has been studied by calorimetry in hexamethylphosphoric triamide (HMPA) containing 0.1 mol dm-3 (n-C&€9)4NC104as a constant ionic medium at 25 "C. The formation of binary [MnX,](2-n)+ ( n = 1-3 for X = C1; n = 1, 2 for X = Br) and of ternary [MnClBr] and [MnClzBrI- is revealed, and their formation constants, reaction enthalpies, and entropies were determined. These thermodynamic data, especially reaction entropies, suggest that the manganese(I1) ion has a solvation number larger than four in HMPA, though transition metal(I1) ions are usually thought to be four-coordinated due to bulkiness of an HMPA molecule. Indeed, our fluorescent EXAFS (extended X-ray absorption fine structure) study showed that the manganese(I1) ion is five-coordinated in HMPA. On the other hand, it is revealed that the other divalent transition metal ions such as iron(II), cobalt(II), nickel(II), copper(II), and zinc(I1) are all four-coordinated.
Introduction Hexamethylphosphoric triamide (HMPA) is an aprotic solvent with a strong electron-pair donating ability (e.g., the Gutmann's donor number DN = 38.8) and a medium dielectric constant ( E = 30).122 As HMPA is a bulky solvent molecule, divalent transition metal ions cannot accommodate six HMPA molecules in the first coordination sphere. In fact, four-coordinate [M(hmpa)4](C104)2 has been isolated for M = MnZf, Fez', Co2+, Ni2+, Cu2+,Zn2+, and Cd2f.3.4 The same coordination structure as in the crystal is suggested for a cobalt(I1) perchlorate HMPA solution, the deep blue color of which is typical of tetrahedral coordination around the metal ion. Recently, our EXAFS (extended X-ray absorption fine structure) study has established the solvation number of four, ie., the presence of [Co(hmpa)4I2+with the Co-0 (HMPA) bond length of 194 pm in neat HMPA,5 as well as in the crystal. Despite the strong electron-pair-donating ability of HMPA relative to N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), the metal complexation is much enhanced in HMPA over DMF and DMS0.6-9 This is ascribed to the different solvation structure of metal ions in these solvents, e.g., the cobalt(I1) ion has an octahedral structure in DMF and DMSO, while a tetrahedral one in HMPA. From a thermodynamic point of view, the zinc(I1) ion behaves as the cobalt(I1) ion in HMPA with respect to their halogeno complexation,l0 while the cadmium(I1) ion does behave in a different manner." Our EXAFS study revealed that the cadmium(I1) ion is five-
' Present address: Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 821, Japan. Abstract published in Advance ACS Absrrucrs, September 1, 1994. @
0022-365419412098-9894$04.50/0
coordinated to form [Cd(hmpa)5l2+in HMPA," indicating that the coordination structure of metal ions in solution is not always the same as that in the crystalline state. Note that the cadmium(II) ion has an ionic radius of 92 pm of four coordination, which is significantly larger than that of the cobalt(I1) and zinc(I1) ions (72 and 74 pm, respectively)."The manganese(I1) ion is a member of divalent 3d transition metal ions, and its ionic radius, 81 pm,12 of four coordination is appreciably larger than that of the cobalt(I1) and zinc(I1) ions, though smaller than that of the cadmium(I1) ion. Therefore, the manganese(I1) ion is supposed to form five-coordinate solvate species like the cadmium(I1) ion. To establish the solution chemistry of the manganese(I1) ion in HMPA, we then examined the halogeno complexation of the manganese(I1) ion in HMPA. With regard to solvation structure of transition metal(I1) ions in HMPA, no direct evidence has been obtained thus far, except for the cobalt(I1) ion5 In the present work, we therefore determined the solvation structure of manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(I1) ions in neat HMPA. Since the solubility of these metal@) perchlorate salts is only a few tens of m o l dm-3, not high enough to apply the transmission EXAFS method, we employed the fluorescence detection. Here, we show evidence that, with manganese(II), the coordination number in HMPA is increased compared with that in crystal, while with other metal ions examined, it is practically the same as that in crystal. Experimental Section Reagents. All chemicals used were of reagent grade. HMPA solvates of metal(I1) perchlorate were prepared and dried 0 1994 American Chemical Society
J. Phys. Chem., Vol. 98, No. 39, 1994 9895
Complexation and Structure of Metal Ions in HMPA according to the literat~re.~ Tetra-n-butylammonium perchlorate, tetra-n-butylammonium chloride, and tetra-n-butylammonium bromide were recrystallized once from a methanol-ether mixture and dried in vacuum over P2O5 at room temperature. Hexamethylphosphoric triamide was purified as described e1~ewhere.l~All test solutions were treated in a dry box over p205.
Calorimetric Measurements. Calorimetric measurements were carried out by using a fully automatic on-line calorimetry system14 at 25 "C. All manganese(I1) perchlorate HMPA solutions contained 0.1 mol dm-3 (n-C4H9)aC104 as a constant ionic medium. Two Teflon-coated stainless steel vessels were inserted into an aluminum block thermostated at 25 "C within 0.0001 "C in an air bath. A test solution (40 cm3) was placed in the vessel and was titrated with a titrant solution by using an APB-118 autoburet (Kyoto Electronics) under dry argon atmosphere. In the binary Mn(I1)-C1 or Mn(I1)-Br system, a manganese(I1) perchlorate solution was titrated with a 0.1 mol dm-3 (n-C4H9)4NX (X = C1, Br) solution. In the ternary Mn(11)-Cl-Br system, an initial solution containing both manganese(I1) and bromide ions was titrated with a 0.1 mol dm-3 (n-C4H9)4NCl solution. Heats of complexation at each titration point were corrected for heat of dilution of titrants, which had been determined in advance by separate experiments and was found to be small. Calorimetric titration data were analyzed by considering the formation of the mononuclear ternary [MXpY9](2-P-9)+complex as follows:
The total concentrations, CM,;,CX,~, and CY,^, at an ith titration point are expressed with their respective free concentrations, [M2+]i,[X-];, and [Y-li, according to the mass-balance equations
(4) (5) The heat of complexation at the ith titration point calculated by using the overall formation constant enthalpy AH",glpq:
is and
qj,calcd
Plp9
where Vi denotes the volume of the test solution. Formation constants and enthalpies were determined by minimizing (qi,cdcd - qi,obsd)' by a nonlinear least-squares program MQCAL.15 EXAFS Measurement. Sample solutions for EXAFS measurements were prepared by dissolving powders of metal(I1) perchlorate HMPA solvate and hydrate in HMPA and water, respectively. The concentration of metal ions used was around 20 mmol dm-3. EXAFS spectra were measured around the K edge of interest using the BL6B station at the Photon Factory of the National Laboratory for High Energy Physics.16 Monochromatized X-rays were obtained by an Si( 111) double crystal. Sample solutions were sealed in a Mylar bag in order to prevent
: :I /"------~ (cl
0 6.0
6.5
7.0
7.5
Energy/keV
Figure 1. (a) The typical raw EXAFS spectrum for a manganese(I1) perchlorate HMPA solution. (b) The solvent (HMPA) background measured in the same energy region. (c) The resulting spectrum after subtraction of the curve (b) from (a).
evaporation of solvents and to avoid moisture. The incident X-ray intensity IO was measured with an ion chamber filled with nitrogen gas. The fluorescent intensity I was measured with a fluorescent ion chamber detector (The EXAFS Co., USA)" filled with argon gas. Suitable filters with a p t value of three were used in order to reduce elastically and inelastically scattered X-rays.18 An example of the observed spectrum p (=NO) for the Mn(C104)2HMPA solution is shown in Figure la. The background curve is very distorted as seen in the figure and fitting by using any polynomial function failed to reproduce the curve. The background was measured separately with pure solvent and is shown in Figure lb. The solvent background was then subtracted from the observed spectrum and the resulting one is shown in Figure IC. The smooth background b was evaluated by fitting a smooth curve to the observed spectrum using a sixthorder polynomial function. The EXAFS oscillation ~ ( kwas ) extracted and normalized as {p(k) - b ( k ) } / m ( k ) , where k (={2m(E - E~)}"~/fi)is the photoelectron wave vector. The symbol E represents the energy of the incident X-rays and EO is the threshold energy of a K-shell electron. Other symbols are of usual meaning. The EO value was selected as the position of the half-height of the edge jump in each sample. The radial structure function F(r) was obtained by the Fourier transformation of the ~ ( kvalues ) weighted by k3 as
cW(k) is a window function of the Hanning type.19 The structure parameters were optimized by comparing the observed EXAFS spectra and the model function X(k)calcd given by the single-electron and single-scattering theory as20-23
sin(2krj
+ a,@))(8)
where F,(n,k) is the backscattering amplitude from each of n, scatterersj at distances rj from the central atom. The parameter
9896 J. Phys. Chem., Vol. 98, No. 39, 1994
Ozutsumi et al. TABLE 1: Thermodynamic Parameters, log(Kn/mol-l dm3), AH",,/kJ mol-', and AS'JJ K-' mol-', for the Stepwise Formation of [MnXn](z-n)+(X = C1, Br) in HMPA at 25 OCab
0 -2
E 7 Y \
-6 -
-
-8
-
3
-10
03
\ 0-
-12 -
-141
0
cMn, i n i t %r, i n i tlmM 0 20.67 0.00 0 25.75 0.00 29.86 0.00 a 22.25 12.38 e 20.41 22.96 0 20.02 29.38 21.71 41.30 0 20.77 56.84
I
2
-
,
1
4
6
cC I ICMn (II)-Cl-Br systems. The concentrations of manganese(II) and bromide ions in initial solutions are given. The solid lines are calculated using constants in Tables 1 and 2. 141
I
1 I
cMn.init/mM 0 7.33 0 11.27 a 14.52 15.25 e 22.54
8 1
;'1
i
i
0
2
4.1(0.5) 2.4(0.1) 12.2(0.3) 13.6(0.7) 120(9) 9W)
TABLE 2: Thermodynamic Parameters, log(Klmol-l dm3), AH'/kJ mol-', and AS"/J K-' mol-', for the Stepwise Formation of Ternary Halogeno Complexes of Manganese(I1) in HMPA at 25 'Cub reaction
\
- 0
5.8(0.5) 4.4(0.1) 2.6(0.1) - 1.7(0.2) 0.3(0.3) - ll.O(O.3) 105(10) 832) 12(2) 0.0264
1
2 10l 2 I -t-
Mn(1IkBr
The values in parentheses refer to three standard deviations. The number of calorimetric data points is 184. Hamilton R factor.
Figure 2. Calorimetric titration curves of the Mn(I1)-Cl and Mn-
--
Mn(II)-Cl
4
6
cBr/cMn Figure 3. Calorimetric titration curves of the Mn(II)-Br systems. The concentrations of manganese(I1) ion in initial solutions are given. The solid lines are calculated using constants in Table 1.
ajis the Debye-Waller factor, and ilis the mean free path of the photoelectron. The parameter aj(k)is the total scattering phase shift due to central and scattering atoms. The values of Fj(z,k) and aj(k)were taken from the 1iteratu1-e.~~ In the fitting procedure the EOand 1 values were determined in advance from the standard samples of known structure (an aqueous metal(I1) perchlorate solution containing [M(Hz0)6l2+). The parameters EOand ilwere then kept constant in the course of the structural analysis of unknown samples, while the r, u, and n values were optimized. Results Calorimetry. Calorimetric titration curves obtained are shown in Figures 2 and 3. The -q/(BvCx,ti,) values are plotted against the ratio of the total concentrations of ligand to metal ions, CXICM,where q. BY, and Cx,tit denote the measured heat of reaction, the volume of an aliquot of the added titrant, and the concentration of the titrant solution, respectively. Calorimetric data were analyzed by assuming the formation of a set of complexes, and various sets were examined and compared. In the binary Mn(II)-Cl system (three titrations), a set assuming the formation of [MnCl]+, [MnClz], and [MnCh- is the most plausible. Also, in the binary Mn(II)-Br system (five titrations), a set assuming the formation of [MnBr]+ and [MnBrz] is the most plausible. However, the parameter values of the mono-
+ C1- = [MnClz] + C1- = [MnClBr] + Br- = [MnClBr]
[MnCl]+ [MnBr]+ [MnCl]+ [MnBr]+ [MnC12] [MnClBr] [MnC12] f
+ Br- = [MnBrz] + C1- = [MnC13]+ C1- = [MnClzBrIBr- = [MnClzBrI-
log K
m
AS'
4.4(0.1) 4.3(0.5) 2.6(0.1) 2.4(0.1) 2.6(0.1) 2.7(0.4) l.O(O.3)
0.3(0.3) 0.6(0.7) 14.5(0.7) 13.6(0.7) -1 l.O(O.3) -15.3(2.0) 1.7(4.0)
85(2) 84(10) 99(2) 92(2) 12(2) lO(15) 24(14)
The values in parentheses refer to three standard deviations. The number of calorimetric data points is 184. (I
and dichloro complexes involved rather large uncertainties due to their small heats of complexation. To ascertain their parameter values, we also examined the ternary Mn(I1)-C1Br system (5 titrations), and both binary and ternary data (13 titrations) were simultaneously analyzed by taking into account the formation of ternary complexes. The whole titration curves were well explained in terms of the formation of ternary [MnClBr] and [MnClnBrI-, along with binary [MnC1,](2-n)+(n = 1-3) and [MnBr,J(2-fl)+(n = 1, 2). The thermodynamic parameters thus obtained are shown in Tables 1 and 2 . The solid lines in Figures 2 and 3, calculated using the parameter values in Tables 1 and 2 , well reproduce the experimental points. The species distribution is shown in Figure 4. EXAFS. The extracted EXAFS spectra ~ ( kweighted ) by k3 are depicted in Figure 5. The phase of the curves of metal(I1) perchlorate HMPA solutions is different from that of corresponding aqueous solutions, indicating that the coordination structure around the metal(I1) ions is different in these solvents. The Fourier transforms IF(r)l of all sample solutions examined, uncorrected for the phase shift, are shown in Figure 6. As both HMPA and water are oxygen-donor solvents, the first intense peaks observed in the IF(r)l curves are expected t o b e ascribed to the M-0 interaction. In all the metal(I1) systems, the peak position is appreciably shorter by 5-10 pm in HMPA than in water. This suggests a smaller coordination number than six for the metal(I1) ions in HMPA, considering that the metal(I1) ions in water are six-coordinated25~26 and the M-0 bond lengths become shorter with decreasing coordination number.12 The structure parameters were finally determined by using the Fourier filtered k 3 ~ ( kvalues ) in the k range of 4.0 x 11.5 x lop2 pm-'. The inverse Fourier transformation of the F(r) values was carried out over the r range including the main peak in Figure 6 for each sample. The EO and il values were obtained in advance from EXAFS of an aqueous metal(I1)
J. Phys. Chem., Vol. 98, No. 39, 1994 9897
Complexation and Structure of Metal Ions in HMPA
I
- 0.8
I
I
I
C
.o 0.4 + 2
0
0.8
+-
a~ 0.4 0
-E
O 0.8
C 0
.- 0.4 -P 3
0
0 0.8
.-
I -P
cn .- 0.4
Figure 6. Fourier transforms F(r)of the k3x(k)curves shown in Figure 5, uncorrected for the phase shift.
U
0
0 .-P) 0.8
TABLE 3: Structure Parameters, the Bond Length r, the Debye-Waller Factor 0, and the Number of Interactions n, for the Solvated Divalent Metal Ions in HMPA and WateP metal ion interaction parameter HMPA water
0 P)
a 0.4
cn
0
2
4
- I og (
8
6
[X-I /mo I
dm-3
MnZf
rlpm
ulpm
Figure 4. Species distribution in the binary Mn(I1)-C1 and Mn(I1)Br and ternary Mn(I1)-Cl-Br systems in HMPA. The R, value represents the concentration ratio of bromide to manganese(II) ions in solution. The number n and symbol [lpq] represent the [MIIX,](~-"'+ and [MnBrpC1,](2-p-'?)+ complexes, respectively.
HMPA
Mn-0
I
Water
n
Fez+
Fe-0
co2+
co-0
Ni2+
Ni-0
rlpm ulpm n
rlpm ulpm n rlpm
ulpm n
cu2+
cu-0
0
cu-0 (
3
I
0
Zn2+
a I
Zn-0
0
rlpm ulpm rlpm ulpm n
0
-
n n
E
a
rlpm ulpm
207( 1) 7.7(1) 4.9(1) 198(1) 4.3(1) 4.0(1) 195(1) 3.3(1) 3.9(1) 197(1) 6.8(1) 4.2(1) 192(1) 4.8(1) 3.7(1)
193(1) 4.8(1) 4.1(1)
218(1) 6.9(1) 6b 212(1) 7.9(1) 66 209(1) 7.2(1) 6b 205(1) 6.4( 1) 6b 198(1)' 6.5(1)' 4b.c 227(2)' 11(1)d 2b.d 207( 1) 8.2(1) 6b
F
Standard deviations of curve fits are given in parentheses. The values were kept constant during the calculations. For the equatorial site in a distorted octahedron. For the axial site in a distorted octahedron.
\
2
0
x
(3
a
0
previously determined with a laboratory EXAFS ~pectrometer.~ In Figure 7, we show the comparison between the experimental and calculated k3x(k) curves.
0
Discussion
-10
2
6
IO
2
6
10
14
k/10-2 pm-' Figure 5. The extracted EXAFS spectra in the form of k3x(k) for sample solutions. perchlorate solution containing the [M(HZO)~]~+ ion. The M-0 bond lengths within [M(HZO)~]~+ were also allowed to vary in order to check the reproducibility of the values. The best fit values are given in Table 3. The M - 0 bond lengths thus obtained are in good agreement with the literature value^,^^.*^ and thus the EOand A values are well approximated in the present study. The interatomic distance, the Debye-Waller factor, and the solvation number for the metal(I1) ions in HMPA were then optimized, based on the EO and A values evaluated above. The parameter values thus obtained are also given in Table 3. The Co-0 (HMPA) bond length thus obtained agrees well with that
Binary Halogeno Complexation of Manganese(I1). In DMF the transition metal(I1) ions are all ~ix-coordinated.~~ In the course of chloro complexation of these metal ions, ligating solvent molecules are successively replaced with chloride ions to finally form tetrahedral [MC14I2-. An octahedral-totetrahedral geometry change thus takes place at a certain step of complexation. As the geometry change is accompanied by an extensive liberation of solvent molecules, an irregular variation of stepwise thermodynamic parameters is expected. Indeed, relative large reaction enthalpy and entropy values were found at the second step for the manganese(II), cobalt(II), and zinc(I1) indicating that the following reaction takes place: [MCl(dmf),]+
+ C1- = [MCl,(dmf),l + 3dmf
(9)
Ozutsumi et al.
9898 J. Phys. Chem., Vol. 98, No. 39, 1994
HMPA
Water
(3
I
E
a co 1
0 c
\
-x
a (3
a
4
6
8
IO
4
6
8
1 0 1 2
w 1 0 - 2 pm-' Figure 7. Fourier filtered k3x(k) curves for sample solutions. The observed values are shown by dots and calculated ones using parameter values in Table 3 by solid lines.
In HMPA, on the other hand, no geometry change is expected, because metal(I1) ions are usually four-coordinated in the solvent. Indeed, in the case of cobalt(II), no irregular variation was found for the chloro complexation, Le., K1 > K2 > K3 > K4, AH", AH"2 x AH"3 AH"4, and AS"' > AS"2 > AS"3 > AS"4.6 The same applies to the zinc(I1) ion.1° As mentioned above, the cobalt(I1) ion is coordinated with the different number of solvent molecules in DMF and HMPA. Upon formation of the monochloro complex of the metal ion, no geometry change occurs, and one solvent molecule is liberated as follows:
+ + dmf [Co(hmpa),I2+ + C1- = [CoCl(hmpa),]+ + hmpa [Co(dmQ6I2+ C1- = [CoCl(dmf),]+
(10) (1 1)
The AS"1 values for the formation of [CoCl]+ are 87 and 78 J K-' mol-' in DMF and HMPA, respectively,@ and these values are not significantly different. Also, the AS"1 values for the formation of [CoBr]+ are 95 and 98 J K-' mol-' in DMF and HMPA, respectively,6,28and these values are virtually the same. The manganese(I1) ion and the monohalogeno [MnX]+ (X = C1, Br) complexes are all six-coordinated in DMF. Therefore, if both the manganese(I1) ion and the complexes are fourcoordinated in HMPA, like cobalt@), we expect almost the same values of AS"1 for the formation of [MnX]+ in DMF and HMPA. However, the reaction entropies for the formation of [MnCl]+ and [MnBr]+ are 105 and 120 J K-' mol-', respectively, in HMPA, which are appreciably larger than the corresponding values (74 and 84 J K-' mol-') in DMF.8v28The fact suggests that the manganese(I1) ion has a larger solvation number than four and more than one coordinating HMPA molecules are liberated upon complexation. This is indeed supported by EXAFS measurements as will be shown below. Solvation Structure. As seen in Table 3, the n value for manganese(I1) is 4.9 in contrast to 4 for other metal ions, suggesting that the manganese(I1) ion is five-coordinated in HMPA, unlike in crystal. Such an unusual coordination number is not unexpected if we take into account that five coordination has been found for the relatively large cadmium(I1) ion, [Cd-
(hmpa)#+, and that the manganese(I1) ion is also large relative to other transition metal(I1) ions, though smaller than the cadmium(I1) ion. Another possibility that four- and sixcoordinate species are present in equilibrium is unlikely, because metal(I1) ions cannot accommodate simultaneously six solvent molecules of bulky HMPA. 1,1,3,3-Tetramethylurea (TMU) is also a bulky solvent molecule like HMPA, and it recently turned out by EXAFS that the manganese(I1) ion exhibits practically the same structural parameters, n = 5 and r = 209 pm, in On the other hand, the iron(II), cobalt(II), nickel(II), copper(II), and zinc(II) ions show the n values of practically four within uncertainty of f0.3, indicating that these metal ions are all fourcoordinated in HMPA as well as in crystal. In crystal, the [M(hmpa).#+ complexes of these metal ions have a tetrahedral g e ~ m e t r y . ~The . ~ observed M-0 bond lengths in solution are close to those of the tetrahedral species in crystal?O suggesting that [M(hmpa)4I2+has a tetrahedral geometry in solution. In all the metal(I1) systems examined, the r values in HMPA are smaller than those in water. This is expected because the solvation number of the metal(I1) ion is smaller in HMPA than in water. However, the decrements in r depend strongly on the metal(I1) ion, Le., 14 pm for Fe2+, Co2+,and Zn2+, 11 pm for Mn2+, 8 pm for Ni2+, and 6 pm for Cu2+. The decrement of Ni2+ is significantly smaller than the value of Fez+,Co2+,or Zn2+. Such a metal dependence is expected to be related to LFSE (ligand field stabilization energy). The LFSE's in an octahedral field (Oh) are -'/5Ao, -4/5A~,and -6/& for Fe2+, Co2+,and Ni2+,respectively, and the corresponding LFSE's in a tetrahedral field (Td) are -3/5At, 4 5 A , , and -4/5At. The LFSEs of Mn2+ and Zn2+ are zero in both fields. If we introduce an approximation, At = 4/9Ao, the LFSE differences between the octahedral and tetrahedral fields are V45A0, '2/45A0, and 38/45Aofor Fe2+, Co2+, and Ni2+, respectively. Evidently, the LFSE difference is large for Ni2+ but small for Fe2+ and Co2+. Therefore, the iron(I1) and cobalt(I1) ions are expected to behave as the zinc(I1) ion without LFSE, Le., these metal ions exhibit only weak electronic resistance for the oh to Td geometry change, leading to a large decrement of bond length. On the other hand, the nickel(I1) ion shows a strong resistance for the oh to Td geometry change, leading to a relatively small decrement of bond length. Ternary Complexation. Comparison between the following reactions is especially interesting because ternary complexation depends strongly on the ligating atoms: [MnCl]' [MnBr]'
+ X- = [MnClX] + X- = [MnBrX]
(12)
(13)
where X is C1 or Br. In both cases of X = C1 and Br, as seen in Table 2, the thermodynamic parameters for the reactions are practically the same, Le., there is no appreciable difference between [MnCl]+ and [MnBr]+. The similar enthalpies imply that the Mn-0 bond strength within [MnCl(hmpa)# and [MnBr(hmpa)# is not essentially changed or influenced by the ligating halide ion. This behavior is the same as that of the hard zinc(@ ionlo but is different from that of the soft cadmium(11) ion," indicating that the manganese(I1) ion behaves as the hard ion in HMPA. Also, the entropies for the reactions 12 and 13 are practically the same, suggesting that no steric interaction is operated between the ions and molecules bound to the manganese(I1) ion. Acknowledgment. EXAFS measurements were performed under the approval of the Photon Factory Program Advisory Committee (Proposal No. 91-005).
Complexation and Structure of Metal Ions in HMPA References and Notes (1) Gutmann, V., The Donor and Acceptor Approach to Molecular Interactions; Plenum: New York, 1978. (2) Riddick, J. A,; Bunger, W. B.; Sakano, T. K. Organic Solvents, 4th ed.; Wiley-Interscience: New York, 1986. (3) Donoghue, J. T.; Drago, R. S. Inorg. Chem. 1962, 1, 866. (4) Donoghue, J. T.; Drago, R. S. Inorg. Chem. 1963, 2, 1158. (5) Ozutsumi, K.; Tohji, K.; Udagawa, Y.; Abe, Y.; Ishiguro, S . Inorg. Chim. Acta 1992, I9I, 183. (6) Abe, Y.; Ozutsumi, K.; Ishiguro, S. J. Chem. SOC.,Faraday Trans. 1 1989, 85, 3747. (7) Ishiguro, S.; Ozutsumi, K.; Ohtaki, H. Bull. Chem. SOC.Jpn. 1987, 60, 531. (8) Ishiguro, S.; Ozutsumi, K.; Ohtaki, H. J. Chem. SOC.,Faraday Trans. 1 1988, 84, 2409. (9) Suzuki, H.; Ishiguro, S . J. Chem. SOC.,Faraday Trans. 1990, 86, 2179. (10) Abe, Y.; Ishiguro, S. J. Solution Chem. 1991, 20, 793. (11) Abe, Y.; Takahashi, R.; Ishiguro, S.; Ozutsumi, K. J. Chem. SOC., Faraday Trans. 1992, 88, 1997. (12) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751. (13) Abe, Y.; Morikawa, M.; Kikukawa, M. Polyhedron 1988, 7,2135. (14) Suzuki, H.; Ishiguro, S. Netsu Sokutei 1988, 15, 152. (15) Suzuki, H.; Ishiguro, S. Inorg. Chem. 1992, 31, 4178.
J. Phys. Chem., Vol. 98, No. 39, 1994 9899 (16) Nomura, M.; Koyama, A.; Sakurai, M. KEK Report 91-1;National Laboratory for High Energy Physics, Tsukuba, Japan, 1991. (17) Lytle, F. W.; Greegor, R. B.; Sandstrom, D. R.; Marques, E. C.; Wong, J.; Spiro, C. L.; Huffman, G. P.; Huggins, F. E. Nucl. Instrum. Methods 1984, 226, 542. (18) Wong, J. Nucl. Instrum. Methods 1984, 224, 303. (19) Harris, F. J. Proc. IEEE 1978, 66, 51. (20) Sayers, D. E.; Stem, E. A.; Lytle, F. W. Phys. Rev. Lett. 1971,27, 1204. (21) Stem, E. A. Phys. Rev. B 1974, 10, 3027. (22) Stem, E. A.; Sayers, D. E.; Lytle, F. W. Phys. Rev. B 1975, 11, 4836. (23) Lengeler, B.; Eisenberger, E. Phys. Rev. B 1980, 21, 4507. (24) Teo, B.-K.; Lee, P. A. J . Am. Chem. SOC.1979, 101, 2815. (25) Ohtaki, H.; Yamaguchi, T.; Maeda, M. Bull. Chem. SOC.Jpn. 1976, 49, 701. (26) Nomura, M.; Yamaguchi, T. J. Phys. Chem. 1988, 92, 6157. (27) Ozutsumi, K.; Koide, M.; Suzuki, H.; Ishiguro, S . J . Phys. Chem. 1993, 97, 500. (28) Ozutsumi, K.; Ishiguro, S. J. Chem. SOC.,Faraday Trans. 1990, 86, 271. (29) Inada, Y.; Sugimoto, K.; Ozutsumi, K.; Funahashi, S. Inorg. Chem. 1994, 33, 1875. (30) Reuter, B.; Riedel, E. Z. Anorg. Allg. Chem. 1969, 369, 306.
