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Absorption spectrum of manganese (II) diethylenetriamine complexes
313 Contribution from the Cyariamid European Research Institute Cologny (Geneva), 1223, Switzerland
Absorption Spectrum of Manganese( II) Diethylenetriamine
Complexes
C. K. JZrgensen Received December
18, 1968
The octahedral chromophore Mn1’N6 is studied in the reflection spectrum of the solid perchlorate of the bis-diethylenetriamine cation and in aqueous solution of this complex as well as the tris-ethylenediamine analogue, in both cases protected against oxidation by hydrazine.
The absorption spectra of diethylenetriamine complexes have recently attracted considerable interesP4 and in many cases, quite normal octahedral complexes are formed with two molecules of the tridentate ligand, as also suggested by the formation constants.5 Ligand field theory has successfully explained the alternating broad and narrow absorption bands of manganese(H) complexes having the ten excited quartet levels of 3d5 in octahedral symmetry.6-8 However, it is an experimental difficulty to measure the very weak, spin-forbidden bands mostly having E between 0.01 and 0.1, because the alkaline solutions produced by many ligands are extremely apt to oxidize to brown suspensions. Sometimes, traces of ascorbic acid’ have been used to protect the solutions. It is now found that small amounts of hydrazine hydrate are even more effective to conserve limpid solutions under reasonably anaerobic conditions. In Table I, the solution marked Mn(den)? was made from 10 g MnC12,4HzO (0.05 mole) and 16 ml redistilled 6.5 molar diethylenetriamine diluted to 50 ml with water and added a few drops of hydrazine until a clear, pale violet solution was formed. This was measured in 5 cm cells on a Cary MS 14 recordA similar solution was made, ing spectrophotometer. 1 molar in Mn(en)?+ and 1 molar jn excess ethylenediamine. The essentially white crystals of Mn(den)l(ClO& were precipitated from the former solution with 5 M NaC104, but it was extremely difficult to keep them slightly wet with small amounts of NJ%. After several experiments, we succeeded in measuring the reflection spectrum with a Beckman DU spectrophotometer. (1) C. (2) H. (3) H. (1968). (4) L. (5) H. bohm, f. (6) L. (7) C. (8) L. sot., 80,
K. Jorgensen, H. Schmidtke, H. Schmidtke
Acta Chem. Stand., IO, 887 (19%). Z. anorg. ollg. Chemie, 339, 103 (1965). and D. Garthoff, Inorg. China. Acta, 2, 357
Rasmussen and C. K. Jorgensen, Inorg. Chim. AC&, in press. B. Jonassen, G. G. Hurst, R. B. LeBlanc, and A. W. MeiPhys. Chem., 56, 16 (1952). E. Orgel, 1. Chem. Phys., 23, 1824 (1955). K. Jorgensen, Acfn Chem. Stand., 11, 53 (1957). J. Heidt, G. F. Koster, and A. M. Johnson, \. Am. Chem. 6471 (1958).
The results are in many ways an anticlimax. The solution spectra of Mn”N6 chromophores are quite characteristic and not at all reminiscent of the fivecoordinated complexes formed by heavily alkyl-substituted diethylenetriamine.g The spectra obtained here are far better resolved than the previously reported7 solution spectrum of Mn(en)Z+ (maxima at 15.9, 20.3, 23.7 and 26.9 kK) and in particular, the band group centered around 23.7 kK in this ion and around 23.5 kK in the slightly more covalent diethylenetriamine complex has several components. There has not been found definite evidence for co-excited vibrational lines close to 27 kK as may be the case for the hexa-aqua ion8 at 26.54 kK (if it is not a doubly-spinforbidden intra-sub-shell transition to a doublet level) and positively is the case” for OsCl& in various solvents. From a theoretical point of view, the most interesting conclusion is the nephelauxetic ratios fl35=0.883 and 0.875 for the two complexes derived by comparison of the first narrow band”,” with 26.85 kK for gaseous Mn*+. The sub-shell energy difference A seems to be slightly smaller for Mn(den)?+ than for Mn( en)?+ in contrast to the usual position of the two Thus, the amines in the spectrochemical series.l second-order expression from the strong-field determinants are [dT,J
= [*A,,]-A+4B-26B’/A
assuming C=4B. In solution, are in this approximation Mn(H20)Z+ Mn(en)l’+ Mn(den)t+
(1)
the A values in kK 7.0 9.5 8.8
(2)
but one should not ascribe too literal a significance to the absolute values. Recently, Foster and GillI discussed the spectra of a variety of tetrahedral and octahedral manganese( I I) complexes and concluded in A=7.6 kK for the hexa-aqua ion and lower values for six halide ligands. However, the values (2) are somewhat below those for nickel(I1) as one would (9) M. Ciampolini, Structure and Bonding, 6, 52 (1969). (10) C. K. Jorgensen, Acta Chem. Stand., 26, 793 (1962). (11) C. K. Jorgensen, Discuss. Faraday Sot., 26, 110 (1958). (12) C. K. Jorgensen, s Oxidation Numbers and Oxidation States z+, Springer-Verlag. Berlin, 1969. (13) J. J. Foster and N. S. Gill, 1. Chem. Sot. (A), 2625 (1968).
Jorgensen 1 Diethylenetriamine Complexes
314 Table I. Wavelengths 6( +), wavenumbers.
h, wavenumbers v, molar extinction coefficients E and The excited levels are given in Mulliken notation.
half-widths
toward
Ww)
v(kK)
- 600 495 425 -385 360
16.7 20.2 23.5 26.0 27.8
-
dJT:8,
623 489 426.4 (422.5) (419.9) (383) 357
16.05 20.5 23.45 23.67 23.82 26.1 28.0
0.072 0.097 0.188 0.125 0.085 0.07 (0.23)
‘A,=, a%
y2 Mn(en):+ aq. a’Tr, a”T,,
638 498 423.2 421.5
15.7 20.1 23.63 23.72 23.87 23.96 26.63 25.92 28.2
0.066 0.072 0.118 0.116 0.096 0.082 0.12 0.12 (0.24)
‘A,,, dE,
1
419.0
(417.3)
b*Tzg
( :::.: (354:5)
b’E,
expect. It may be noted that Watt and Manhasr4 prepared white [Mn(der&]Brz. Quite recently, Larkworthy et aLI demonstrated that A= 15.0 kK for V( den)z2+ is smaller than 15.6 kK for V(en)x2+. It may be that the central atoms V” and Mn” are too (14) G. W. Watt
(1966). (15) Comm.,
and
L. F. Larkworthy, 1667 (1968).
B.
S. K.
Manhas, C.
I.
Pate1
Inor& and
Nucl. D.
lnorganica Chimica Acta 1 3:2 1 ]une, 1969
J.
Chem., 28, 1945 Phillips,
Chem.
6(-),
E
Mn(cJc;),(C)CU $T:: “A,,, $E, b’Tz, b’E, Mn(de;)r’+ aq.
smaller,
large to exploit stress.16
the
and
larger,
6(-)(kK)
broad broad narrow shotdder narrow S(:i’l.6 0.17 -
0.7 6(+) 1.5 1.2 0.11
-
-
tridentate
amine
0.75
without
steric
Acknowledgment. I would like to thank Mr. Georges Casaro for competent and helpful assistance with the spectral measurements. (16) (1969).
P.
Paoletti,
S.
Biagini
and
M.
Cannas,
Chem.
Comm.,
513
Absorption Spectrum of Manganese( II) Diethylenetriamine
Complexes
C. K. JZrgensen Received December
18, 1968
The octahedral chromophore Mn1’N6 is studied in the reflection spectrum of the solid perchlorate of the bis-diethylenetriamine cation and in aqueous solution of this complex as well as the tris-ethylenediamine analogue, in both cases protected against oxidation by hydrazine.
The absorption spectra of diethylenetriamine complexes have recently attracted considerable interesP4 and in many cases, quite normal octahedral complexes are formed with two molecules of the tridentate ligand, as also suggested by the formation constants.5 Ligand field theory has successfully explained the alternating broad and narrow absorption bands of manganese(H) complexes having the ten excited quartet levels of 3d5 in octahedral symmetry.6-8 However, it is an experimental difficulty to measure the very weak, spin-forbidden bands mostly having E between 0.01 and 0.1, because the alkaline solutions produced by many ligands are extremely apt to oxidize to brown suspensions. Sometimes, traces of ascorbic acid’ have been used to protect the solutions. It is now found that small amounts of hydrazine hydrate are even more effective to conserve limpid solutions under reasonably anaerobic conditions. In Table I, the solution marked Mn(den)? was made from 10 g MnC12,4HzO (0.05 mole) and 16 ml redistilled 6.5 molar diethylenetriamine diluted to 50 ml with water and added a few drops of hydrazine until a clear, pale violet solution was formed. This was measured in 5 cm cells on a Cary MS 14 recordA similar solution was made, ing spectrophotometer. 1 molar in Mn(en)?+ and 1 molar jn excess ethylenediamine. The essentially white crystals of Mn(den)l(ClO& were precipitated from the former solution with 5 M NaC104, but it was extremely difficult to keep them slightly wet with small amounts of NJ%. After several experiments, we succeeded in measuring the reflection spectrum with a Beckman DU spectrophotometer. (1) C. (2) H. (3) H. (1968). (4) L. (5) H. bohm, f. (6) L. (7) C. (8) L. sot., 80,
K. Jorgensen, H. Schmidtke, H. Schmidtke
Acta Chem. Stand., IO, 887 (19%). Z. anorg. ollg. Chemie, 339, 103 (1965). and D. Garthoff, Inorg. China. Acta, 2, 357
Rasmussen and C. K. Jorgensen, Inorg. Chim. AC&, in press. B. Jonassen, G. G. Hurst, R. B. LeBlanc, and A. W. MeiPhys. Chem., 56, 16 (1952). E. Orgel, 1. Chem. Phys., 23, 1824 (1955). K. Jorgensen, Acfn Chem. Stand., 11, 53 (1957). J. Heidt, G. F. Koster, and A. M. Johnson, \. Am. Chem. 6471 (1958).
The results are in many ways an anticlimax. The solution spectra of Mn”N6 chromophores are quite characteristic and not at all reminiscent of the fivecoordinated complexes formed by heavily alkyl-substituted diethylenetriamine.g The spectra obtained here are far better resolved than the previously reported7 solution spectrum of Mn(en)Z+ (maxima at 15.9, 20.3, 23.7 and 26.9 kK) and in particular, the band group centered around 23.7 kK in this ion and around 23.5 kK in the slightly more covalent diethylenetriamine complex has several components. There has not been found definite evidence for co-excited vibrational lines close to 27 kK as may be the case for the hexa-aqua ion8 at 26.54 kK (if it is not a doubly-spinforbidden intra-sub-shell transition to a doublet level) and positively is the case” for OsCl& in various solvents. From a theoretical point of view, the most interesting conclusion is the nephelauxetic ratios fl35=0.883 and 0.875 for the two complexes derived by comparison of the first narrow band”,” with 26.85 kK for gaseous Mn*+. The sub-shell energy difference A seems to be slightly smaller for Mn(den)?+ than for Mn( en)?+ in contrast to the usual position of the two Thus, the amines in the spectrochemical series.l second-order expression from the strong-field determinants are [dT,J
= [*A,,]-A+4B-26B’/A
assuming C=4B. In solution, are in this approximation Mn(H20)Z+ Mn(en)l’+ Mn(den)t+
(1)
the A values in kK 7.0 9.5 8.8
(2)
but one should not ascribe too literal a significance to the absolute values. Recently, Foster and GillI discussed the spectra of a variety of tetrahedral and octahedral manganese( I I) complexes and concluded in A=7.6 kK for the hexa-aqua ion and lower values for six halide ligands. However, the values (2) are somewhat below those for nickel(I1) as one would (9) M. Ciampolini, Structure and Bonding, 6, 52 (1969). (10) C. K. Jorgensen, Acta Chem. Stand., 26, 793 (1962). (11) C. K. Jorgensen, Discuss. Faraday Sot., 26, 110 (1958). (12) C. K. Jorgensen, s Oxidation Numbers and Oxidation States z+, Springer-Verlag. Berlin, 1969. (13) J. J. Foster and N. S. Gill, 1. Chem. Sot. (A), 2625 (1968).
Jorgensen 1 Diethylenetriamine Complexes
314 Table I. Wavelengths 6( +), wavenumbers.
h, wavenumbers v, molar extinction coefficients E and The excited levels are given in Mulliken notation.
half-widths
toward
Ww)
v(kK)
- 600 495 425 -385 360
16.7 20.2 23.5 26.0 27.8
-
dJT:8,
623 489 426.4 (422.5) (419.9) (383) 357
16.05 20.5 23.45 23.67 23.82 26.1 28.0
0.072 0.097 0.188 0.125 0.085 0.07 (0.23)
‘A,=, a%
y2 Mn(en):+ aq. a’Tr, a”T,,
638 498 423.2 421.5
15.7 20.1 23.63 23.72 23.87 23.96 26.63 25.92 28.2
0.066 0.072 0.118 0.116 0.096 0.082 0.12 0.12 (0.24)
‘A,,, dE,
1
419.0
(417.3)
b*Tzg
( :::.: (354:5)
b’E,
expect. It may be noted that Watt and Manhasr4 prepared white [Mn(der&]Brz. Quite recently, Larkworthy et aLI demonstrated that A= 15.0 kK for V( den)z2+ is smaller than 15.6 kK for V(en)x2+. It may be that the central atoms V” and Mn” are too (14) G. W. Watt
(1966). (15) Comm.,
and
L. F. Larkworthy, 1667 (1968).
B.
S. K.
Manhas, C.
I.
Pate1
Inor& and
Nucl. D.
lnorganica Chimica Acta 1 3:2 1 ]une, 1969
J.
Chem., 28, 1945 Phillips,
Chem.
6(-),
E
Mn(cJc;),(C)CU $T:: “A,,, $E, b’Tz, b’E, Mn(de;)r’+ aq.
smaller,
large to exploit stress.16
the
and
larger,
6(-)(kK)
broad broad narrow shotdder narrow S(:i’l.6 0.17 -
0.7 6(+) 1.5 1.2 0.11
-
-
tridentate
amine
0.75
without
steric
Acknowledgment. I would like to thank Mr. Georges Casaro for competent and helpful assistance with the spectral measurements. (16) (1969).
P.
Paoletti,
S.
Biagini
and
M.
Cannas,
Chem.
Comm.,
513