Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 3, pp. 149-152, 2005

Phenoxo-Bridged Dimeric Structure of Technetium(I) Tricarbonyl Complex with Schiff
Base Ligand
Tsutomu Takayama,* Arinori Harano, Tsutomu Sekine, and Hiroshi Kudo
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Received: July 31, 2005; In Final Form: September 30, 2005
Technetium(I) carbonyl complexes such as [Tc(CO)3 (salbut)] 2 (salbut = 2-(1-butylnitrilomethylidyne)phenolato),
Tc(CO)3(salbut)(CH3CN) and Tc(CO)3(salbut)(py) (py = pridine) with Schiff base ligands were synthesized. The
dinuclear complex [Tc(CO) 3 (salbut)] 2 is the first phenoxo-bridged dinuclear technetium complex. From X-ray
crystallography, this dinuclear complex was revealed to be a “dimer” composed of two Tc(CO)3 (salbut) subunits
bridged by two oxygen atoms of the salbut ligand. The two Tc(CO)3 (salbut) subunits are in inversion symmetryeach other. Schiff base Hsalbut loses a phenol proton through the ligand exchange reaction and coordinates to thetechnetium atom as a bidentate ligand with nitrogen and oxygen atoms. Three carbonyl ligands coordinate to thetechnetium atom in a facial configuration. Structures of [Tc(CO)3(salbut)] 2 in solvents were investigated by NMR
and UV-vis spectroscopy. The mononuclear complex Tc(CO)3(salbut)(solv) (solv = solvent molecule) was formed
in strong Lewis base solvents like acetonitrile and pyridine. In weak Lewis base solvents like dichloromethaneand benzene, on the other hand, the dinuclear [Tc(CO)3(salbut)] 2 complex was stable.

1. Introduction
The complex (Et4N)2 [Tc(CO)3Cl3] is a useful starting material for synthesis of technetium(I) carbonyl complexes. Afterthe synthesis of (Et4N)2 [Tc(CO)3Cl3] under a mild condition (1atm and 65 ˚C),1 the coordination chemistry of technetium complexes in a +1 oxidation state with carbonyl ligands haveattracted considerable interest.2 Technetium(I) tricarbonyl complexes are generally six-coordinated in octahedral geometry.
The fac-[Tc(CO) 3 ] + core is stable toward ligand substitution
reactions, whereas the three Cl ligands are easily substituted byother ligands. In recent years, reactions of [99 Tc(CO) 3Cl 3 ] 2−with bidentate ligands are extensively studied to provide a basic
insight into fac-99mTc(CO)3 radiopharmaceuticals with bidentate
ligands. 3 Technetium(I) carbonyl complexes with various
bidentate ligands with N, O and S donor atoms were synthesized by ligand substitution reactions of (Et4N)2[Tc(CO)3Cl3].4−6
Schiff base ligands with N donor atoms of the imine group
and O donor atoms of the phenol group afford stable complexes
with various transition metals.7−12 Although a number of technetium complexes with a Schiff base imine-phenol ligand in
higher oxidation states (+3 to +6) have been reported in the literature,13−18 little is known about technetium(I) carbonyl complexes with this ligand.
We have synthesized technetium(I) carbonyl complexes with
Hsalbut of a Schiff base imine-phenol bidentate ligand for the
first time, and their structures are characterized in this paper.
In terms of radiopharmaceutical application, the structure oftechnetium complexes in solution is to be elucidated, and weinvestigate further the structure of technetium(I) carbonyl
complexes with a salbut ligand also in solution.19
2. Experimental
2.1. Materials. A potassium salt of pertechnetate (99Tc) purchased from Radiochemical Center Amersham was dissolved in
0.8 M aqueous ammonia solution. Hsalbut [2-(1-butylnitrilomet
hylidyne)phenol] was synthesized from the reaction of salicylal*Corresponding author. E-mail: takayama@mail.tains.tohoku.
ac.jp. FAX: +81-22-795-6596.

dehyde and 1-butanamine. Hsalbut was identified by 1H NMR
spectroscopy. The satarting material (Et4N) 2 [99 Tc(CO) 3Cl3]
was synthesized in a manner described in the literature.1 Otherchemicals and solvents were of reagent grade, and used without
further purification.
2.2. Instruments. The elemental analysis was performed
by a Yanaco MT-3 CHN recorder. The composition of technetium was determined radiometrically with a liquid scintillation
counter (Aloka, LSC-5100). IR spectra were recorded with a
KBr pellet method on SHIMADZU FTIR-8600PC. 1H NMR
spectra were recorded on JEOL G5X270 (270 MHz) at room
temperature. UV-vis spectra were recorded in acetonitrile ordichloromethane on SHIMADZU Multi Spec-1500 at room
temperature.
2.3. X-ray crystallographic data collection and refinementof structure. A single crystal of [Tc(CO)3 (salbut)] 2 was subjected to X-ray crystallography. The diffraction data were collected at 173 K using a Rigaku Mercury CCD diffractometerwith MoKα graphite monochromator radiation (λ = 0.71070 Å).
The structure was solved by direct methods20 and expanded using
Fourier techniques.21 The non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were refined using the riding
model. The final discrepancy factors: R1 = 0.044, wR2 = 0.141
for all reflections. All of the calculations were made using theCrystalStructure crystallographic software package.22, 23 Moreinformation on crystal data and structure refinement is summarized in Table 1.
2.4. Synthesis of [2-(1-butylnitrilomethylidyne)phenolato]acetonitriletricarbonyltechnetium(I), Tc(CO)3(salbut)(CH3CN).
The starting material (Et4N)2 [Tc(CO)3Cl3] (100 µmol) was dissolved in acetonitrile (10 mL). To the solution, Hsalbut (100µmol) in acetonitrile and triethylamine (50 µL) were added.
The yellow reaction mixture was stirred for 12 h at room temperature. The solution was condensed to 3 mL and then subjected to silicagel column chromatography (20 mmΦ × 150
mm, Wakogel C-200). By elution with acetonitrile, the yellow
fraction containing Tc(CO) 3 (salbut)(CH3CN) was collected.
Evaporation of the solution gave yellow precipitate ofTc(CO) 3 (salbut)(CH 3CN) (60 µmol, 60%). Anal. Calcd for
C16H17N2O4Tc: C, 48.00; H, 4.28; N, 7.00; Tc, 24.73. Found: C,
47.44; H, 4.08; N, 6.83; Tc, 24.60%. IR (cm−1, KBr): ν(CO)© 2005 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/28/2005

150 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005
TABLE 1: The Crystallographic Data of [Tc(CO) 3 (salbut)] 2
FormulaC28H28N2O8Tc2

Formula weight
Crystal size / mm3
Crystal system
Space group
a/Å
b/Å
c/Å

714.540.15 × 0.10 × 0.10
triclinic
P-1 (No. 2)
7.897(4)9.263(4)11.547(5)104.441(5)106.708(5)105.647(5)728.4(6)
1
1.626
9.90
MoKα (0.71070 Å)
173
6.2 – 55.0
13110
3305
0.044
0.141
1.010

α / degree
β / degree
γ / degree
V / Å3Z valueD(calc) / g cm−3
µ / cm−1
Radiation
Temp / K2θ range / degree
Reﬂections measured
Reﬂections observations
R1awR2b
Goodness of ﬁt indicator
Max shift / error in ﬁnal cycle
a
b

0.064

R1 = ∑ ||Fo| – |Fc|| / ∑ |Fo|wR2 = [∑ (w(Fo2 – Fc2)2) / ∑ w(Fo2)2]1/2

2025, 1923, 1899. 1H NMR (δ, CD3CN): 0.96 (t, 3H; CH 3 ),1.35 (sext, 2H; CH2), 1.85 (quint, 2H; CH2), 3.87 (br, 2H; CH2),
6.47 (ddd, 1H; phenyl), 6.63 (dd, 1H; phenyl), 7.12 (dd, 1H;
phenyl), 7.18 (ddd, 1H; phenyl), 8.13 (s, 1H; N=CH).
2.5. Synthesis of bis[µ-{2-(1-butylnitrilomethylidyne) phenolato-1:2κ2O}]-hexacarbonylditechnetium(I), [Tc(CO)3(salbut)]2.
The reaction product Tc(CO)3 (salbut)(CH3CN) (80 µmol) was
dissolved in benzene (3 mL). Slow evaporation of the solution
gave pale yellow crystals of [Tc(CO)3(salbut)]2 (68 µmol, 85%).
Anal. Calcd for C28H28N2O8Tc2: C, 46.36; H, 3.83; N, 4.07; Tc,
27.55. Found: C, 46.76; H, 3.90; N, 3.90; Tc, 27.30%. IR (cm−1,
KBr): ν(CO) 2024, 1920, 1885. 1H NMR (δ , CD2Cl2): 0.99 (t,6H; CH3), 1.42 (sext, 4H; CH2), 1.73 (quint, 4H; CH2), 4.10 (br,4H; CH2), 6.88 (m, 4H; phenyl), 7.36 (m, 4H; phenyl), 8.36 (s,2H; N=CH).
2.6. Synthesis of [2-(1-butylnitrilomethylidyne)phenolato]pyridinetricarbonyltechnetium(I), Tc(CO)3 (salbut)(py). The
reaction product [Tc(CO)3(salbut)] 2 (60 µmol) was dissolved inpyridine (1 mL). The solution was stirred for 12 h at room temperature. Evaporation of the solution gave Tc(CO)3 (salbut)(py)(57 µmol, 95%). Anal. Calcd for C19H19N2O4Tc: C, 52.06; H,
4.37; N, 6.39; Tc, 22.58. Found: C, 51.66; H, 4.28; N, 6.53; Tc,
22.30%. IR (cm−1, KBr): ν(CO) 2018, 1914, 1880. 1H NMR (δ ,CD3CN): 0.98 (t, 3H; CH3), 1.38 (sext, 2H; CH2), 1.78 (quint,
2H; CH2), 3.95 (br, 2H; CH2), 6.43 (ddd, 1H; phenyl), 6.74 (dd,1H; phenyl), 7.12 (dd, 1H; phenyl), 7.16 (ddd, 1H; phenyl), 7.41(m, 3H; py), 8.13 (s, 1H; N=CH), 8.62 (m, 2H; py).
3. Results and Discussion
The reaction of (Et4N)2 [Tc(CO)3Cl3] and Hsalbut in acetonitrile gave a complex Tc(CO) 3 (salbut)(CH 3 CN) as shown in
Scheme 1 (a). When triethylamine was absent in the reaction

Takayama
(a)
2+

CO
OC

OC

+

Tc

CO

HO

Cl

Cl

N

CH3CN

OC

Et3N

OC

H3C

Tc

NCCH3
O

N

Cl
H3C

(b)
CH3

CO

OC
OC

Tc

N

H3C

NCCH3
O

benzene

OC
OC

CO

Tc
N

O
O

N

Tc
CO

CO
CO

+

2 CH3CN

H3C

Scheme 1. (a) Preparation of Tc(CO)3 (salbut)(CH3CN); (b) formation of [Tc(CO)3(salbut)]2 by dimerization of Tc(CO)3(salbut)(CH3CN).

mixture, this reaction hardly proceeded. The addition of a basewas necessary for dissociation of the phenol proton of Hsalbut.
In this reaction, three Cl ligands of [Tc(CO)3Cl3] 2+ are replacedby one bidentate salbut ligand and one acetonitrile molecule ofa monodentate ligand.
The structure of Tc(CO)3 (salbut)(CH3CN) was characterizedby 1H NMR and IR spectroscopy. The spin multiplicity of signalsof methylene protons at α-position of imine nitrogen was triplet
for free Hsalbut. Meanwhile, the signal was multiplet in the spectrum of Tc(CO)3(salbut)(CH3CN), as a result of the constraint ofa rotation of the methylene group through coordination of the imine
N atom to the Tc atom in the complex. A difference of spin multiplicity in 1H NMR spectra is also observed for signals of aromatichydrogens. Four aromatic hydrogens of free Hsalbut show multiple signals. In the spectrum of Tc(CO)3 (salbut)(CH3CN), two
signals of dd and two signals of ddd were observed. This result
indicates that the O atom of the phenol group coordinates to theTc atom. The salbut coordinates to the Tc atom in a fashion of thebidentate chelate through one N donor atom of the imine groupand one O donor atom of the phenol group. The IR spectrum ofTc(CO)3 (salbut)(CH3CN) showed a pattern typical of a facialarrangement of three CO ligands. Absorption peaks for stretching of carbonyl ligands were observed at 2025, 1923 and 1899
cm−1. The highest energy peak arises from symmetrical stretching of three carbonyl ligands. Peaks at lower wave numbers(1923 and 1899 cm −1) are due to unsymmetrical stretchingmodes.24 An acetonitrile molecule would coordinate to the sixth
coordination site. The central Tc atom acts as a chiral center.
Two enantiomeric forms of Tc(CO) 3 (salbut)(CH 3 CN) are
expected, although these have not been isolated here.
The dinuclear complex [Tc(CO)3 (salbut)] 2 was obtained in aquantitative yield from a benzene solution of Tc(CO)3 (salbut)(CH3CN). The dimerization of Tc(CO)3(salbut)(CH3CN) should
occur in the benzene solution (Scheme 1b). The dimeric complex[Tc(CO)3 (salbut)] 2 was also obtained from a dichloromethane
solution of Tc(CO)3(salbut)(CH3CN). In the 1H NMR spectrum
for the CD2Cl2 solution of Tc(CO)3(salbut)(CH3CN), two singlet
signals originated from the imine proton were observed at 7.93
and 8.36 ppm. This result indicates that both monomeric anddimeric complexes are present in the solution. The signal athigher chemical shift is assigned to [Tc(CO)3(salbut)] 2, and thelower one to Tc(CO)3(salbut)(CH3CN).
The structural determination of [Tc(CO)3 (salbut)] 2 by X-ray
crystallography was carried out for the pale yellow prism single
crystal obtained from a benzene solution. The ORTEP drawing of [Tc(CO)3 (salbut)] 2 is shown in Figure 1. Selected bonddistances and angels are listed in Table 2. The dinuclear complex is composed of two Tc(CO)3 (salbut) subunits bridged by
the O atoms of phenoxo groups of the salbut ligand. These subunits are enantiomeric. The inversion center is located at thecenter of the Tc2O2 ring. Each Tc atom is six-coordinated inJ. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005 151

Phenoxo-Bridged Dimeric Structure
C (4) ´C (2) ´O( 4 )C (9)C (10)

C(11) ´C (7) ´
Tc(1)

C (8)

O( 2 )C (14) ´

C (1) ´C (6) ´O( 1 ) ´

N(1) ´C(13) ´ε / M -1 cm-1

O( 3 )(a)

10000

C (3) ´C (5) ´

5000

C(12) ´
Tc(1) ´C (12) C (11)N(1)

C (13)

C(6)

C (1)

0

C(10) ´C (7)C (14)O( 2 ) ´

C (8) ´

O(1)

C (2)
C (5)

O( 4 ) ´

C (9) ´

400

O( 3 ) ´

(b)

10000

-1

Figure 1. ORTEP drawing of [Tc(CO)3 (salbut)] 2 (50% probability
level).

ε / M cm

-1

C (4)

500

λ / nmC (3)TABLE 2: Selected Bond Distances (Å) and Angles (degree)of [Tc(CO) 3 (salbut)] 2

5000

0

Distances300

Tc(1)-O(1)2.144(3)Tc(1)-O(1)'2.183(3)Tc(1)-N(1)2.177(4)Tc(1)-C(8)1.911(5)Tc(1)-C(9)1.919(5)Tc(1)-C(10)2.183(3)Tc(1)-Tc(1)'AnglesO(1)-Tc(1)-O(1)'Tc(1)-O(1)-C(7)76.1(1)119.9(2)N(1)-Tc(1)-O(1)C(8)-Tc(1)-O(1)81.7(1)98.4(2)

C(9)-Tc(1)-O(1)94.5(2)

C(10)-Tc(1)-O(1)172.9(2)Tc(1)-O(1)-Tc(1)'104.2(2)N(1)-Tc(1)-O(1)'83.8(1)

C(8)-Tc(1)-O(1)'173.5(2)C(9)-Tc(1)-O(1)'96.7(2)

C(10)-Tc(1)-O(1)'96.9(2)

Tc(1)-O(1)' -Tc(1)'103.9(1)C(8)-Tc(1)-N(1)92.0(2)

C(9)-Tc(1)-N(1)176.0(2)C(10)-Tc(1)-N(1)96.5(2)

Tc(1)-N(1)-C(1)123.5(3)Tc(1)-N(1)-C(11)120.9(3)N(1)-C(1)-C(2)126.4(4)O(1)-C(7)-C(2)122.0(4)O(1)-C(7)-C(6)119.3(4)400

500

λ / nm1.902(5)aO(1)-Tc(1)'

a

300

(c)

10000

Interatomic distanceoctahedral geometry. The three carbonyl ligands are arranged ina facial configuration. An anionic salbut ligand coordinates to
the Tc atom as a bidentate chelate through the N and O atoms.
The oxygen atom of the bridging phenoxo group coordinates tothe sixth coordination site. The proton dissociation makes thephenoxo group a very strong donor, and the O atom of thephenoxo group coordinates to two Tc atoms forming a bridge
between them.
The central unit of the dinuclear complex [Tc(CO)3(salbut)] 2
is a four-membered Tc2O2 ring with the Tc(1)-O(1)-Tc(1)' angleof 103.9 degree and the O(1)-Tc(1)-O(1)' angle of 76.1 degree.
The two Tc atoms and the two O atoms are fairly in the sameplane. The distance of the Tc(1)-O(1) bond (2.144 Å) is shorter
than that of the Tc(1)-O(1)' bond (2.183 Å). The distance between
the two Tc atoms is as long as 3.404 Å, and the Tc-Tc bonddoes not exist in this dinuclear complex. A typical metal-metalbond distance in dinuclear technetium complexes with Tc2O2
units is known to be in the range from 2.331 to 2.401 Å.25−28
The structure of Tc(I) complex with the salbut ligand were
investigated in a variety of solvents. The UV-vis spectrum of-1

ε / M cm

-13.408(2)

5000

0
300

400

500

λ / nmFigure 2. UV-vis spectra of (a) [Tc(CO)3(salbut)]2 in dichloromethane,(b) [Tc(CO)3(salbut)] 2 in acetonitrile and (c) Tc(CO)3(salbut)(CH3CN)
in acetonitrile.

[Tc(CO)3 (salbut)] 2 in dichloromethane is shown in Figure 2a.
The dinuclear structure is retained in dichloromethane solution.
When [Tc(CO)3 (salbut)] 2 is dissolved in acetonitrile, the UVvis spectrum (Figure 2b) is different from that in dichloromethane. The metal-to-ligand charge transfer (MLCT) absorption
peak appeared at 393 nm. The spectrum of [Tc(CO)3(salbut)] 2
in acetonitrile resembles that of Tc(CO) 3 (salbut)(CH3CN) in
acetonitrile quite well (Figure 2c). Furthermore, the 1H NMR
spectrum of [Tc(CO)3(salbut)] 2 in CD3CN was the same as thatof Tc(CO)3 (salbut)(CH3CN) observed in CD3CN. The result
indicates that Tc(CO)3(salbut)(CH3CN) is formed in the acetonitrile solution of [Tc(CO)3(salbut)] 2 as a result of substitutionof the bridging phenoxo group by the CH3CN ligand. Only themonomeric Tc(CO)3(salbut)(CH3CN) complex is present in theacetnitrile solution.
When [Tc (CO) 3 (salbut)] 2 was dissolved in pyridine,
Tc(CO) 3 (salbut)(py) was formed. In the 1H NMR spectrum ofTc(CO)3(salbut)(py), signals of pyridine coordinating to Tc areobserved at 7.21 ppm and 8.42 ppm. The other signals are similar to that of Tc(CO)3(salbut)(CH3CN) with the six-coordinatedmonomeric structure.
Strong Lewis bases such as acetonitrile and pyridine act as a

152 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005
CH3

OC

OC

CO

Tc

N

O

O

H3C

N
Tc

CO

TakayamaCO

2 solv

OC
2

CO

OC

solv

Tc
O
N

CO
H3C

solv = CH3CN, py

Scheme 2. Reaction of [Tc(CO)3(salbut)] 2 in acetonitrile or pyridine.

monodentate ligand, and substitute the bridging O atom of the
Tc(CO)3 (salbut) subunit. In these solvents, mononuclear complexes with neutral charge were formed (Scheme 2). The
molecular formula of these mononuclear complexes can be
written as Tc(CO)3(salbut)(solv).
On the contrary, no structural change of [Tc(CO)3 (salbut)] 2
was observed in dichloromethane and benzene solvents. Thesesolvents are a very weak Lewis base and should be irrelevant to
the ligand substitution reaction.
4. Conclusions
Three technetium(I) carbonyl complexes, Tc(CO) 3 (salbut)(CH3CN), Tc(CO) 3 (salbut)(py) and [Tc(CO) 3 (salbut)] 2 , weresynthesized in the present work. The phenoxo-bridged dinuclear complex [Tc(CO) 3 (salbut)] 2 is revealed to be composedof two enantiomeric Tc(CO) 3 (salbut) subunits bridged by aphenoxo group.
In solution, the Lewis basicity of the solvents is a key factor
in determining the structure of technetium(I) carbonyl complexes with salbut. In strong Lewis base solvents like acetonitrile and pyridine, dinuclear [Tc(CO) 3 (salbut)] 2 changes its
structure to a mononuclear Tc(CO) 3 (salbut)(solv). In weak
Lewis base solvents like dichloromethane or benzene, on theother hand, dinuclear [Tc(CO)3(salbut)] 2 is stable.
References(1) R. Alberto, R. Schibli, and P. A. Schubiger, Polyhedron 15,1079 (1996).
(2) R. Alberto, R. Schibli, R. Waibel, U. Abram, and A. P.
Schubiger, Coord. Chem. Rev. 192, 901 (1999).
(3) S. Mundwiler, M. Kündig, K. Ortner, and R. Alberto, Dalton
Trans. 1320 (2004).
(4) R. Alberto, R. Schibli, A. P. Schubiger, U. Abram, H.-J.
Pietzsch, and B. Johannsen, J. Am. Chem. Soc. 121, 6076
(1999).
(5) W. Wang, B. Spingler, and R. Alberto, Inorg. Chim. Acta
355, 386 (2003).
(6) H. Braband, and U. Abram, J. Organomet. Chem. 689,

2066 (2004).
(7) P. G. Cozzi, Chem. Soc. Rev. 33, 410 (2004).
(8) T. Katsuki, Chem. Soc. Rev. 33, 437 (2004).
(9) J. D. Bois, J. Hong, E. M. Carreira, and M. W. Day, J. Am.
Chem. Soc. 118, 915 (1996).
(10) W. A. Herrmann, M. U. Rauch, and G. R. J. Artus, Inorg.
Chem. 35, 1988 (1996).
(11) A. Hori, T. Ozawa, H. Yoshida, Y. Imori, Y. Kuribayashi, E.
Nakano, and N. Azuma, Inorg. Chim. Acta 281, 207 (1998).
(12) A. Duatti, A. Marchi, S. A. Luna, G. Bandoli, U. Mazzi,
and F. Tisato, J. Chem. Soc. Dalton Trans. 867 (1987).
(13) S. Jurisson, K. Dancey, M. McPartlin, P. Tasker, and E.
Deutsch, Inorg. Chem. 23, 4743 (1984).
(14) T. Takayama, R. Koudo, T. Sekine, and H. Kudo, J. Nucl.
Radiochem. Sci. 4, 1 (2003).
(15) T. Takayama, T. Sekine, and H. Kudo, J. Radioanal. Nucl.
Chem. 255, 97 (2003).
(16) H. J. Pietzsch, U. Abram, R. Kirmase, and K. Kohler, Z.
Chem. 27, 265 (1987).
(17) J. R. Dilworth, P. Jobanputra, R. M. Thompson, D. C. Povey,
C. M Archer, and J. D. Kelly, J. Chem. Soc. Dalton Trans.
8, 1251 (1994).
(18) T. Takayama, Y. Abe, T. Sekine, and H. Kudo, Radiochim.
Acta 92, 265 (2004).
(19) S. S. Jurisson and J. D. Lydon, Chem. Rev. 99. 2205
(1999).
(20) SIR92: A. Altomare, G. Cascarano, C. Giacovazzo, A.
Guagliardi, M. Burla, G. Polidori, and M. J. Camalli, Appl.
Cryst. 27, 435 (1994).
(21) DIRDIF99: P. T. Beurskens, G. Admiraal, G. Beurskens,
W. P. Bosman, R. de Gelder, R. Israel, and J. M. M. Smits(1999). The DIRDIF-99 program system, Technical Reportof the Crystallography Laboratory, University of Nijmegen,
The Netherlands.
(22) CrystalStructure 3.6.0: Crystal Structure Analysis Package,
Rigaku and Rigaku/MSC (2000-2004). 9009 New Trails
Dr. The Woodlands TX 77381 USA.
(23) CRYSTALS Issue 10: D. J. Watkin, C. K. Prout, J. R. Carruthers, and P. W. Betteridge, Chemical Crystallography
Laboratory, Oxford, UK, 1996.
(24) T. P. Ortiz, J. A. Marshall, L. A. Emmert, J. Yang, W. Choi, A.
L. Costello, and J. A. Brozik, Inorg. Chem. 43, 132 (2004).
(25) K. E. Linder, J. C. Dewan, and A. Davison, Inorg. Chem. 28,3820 (1989).
(26) G. Anderegg, E. Müller, K. Zollinger, and H. B. Burgi, Helv.
Chim. Acta 66, 1593 (1983).
(27) H. B. Burgi, G. Anderegg, and P. Blauenstein, Inorg. Chem.
20, 3829 (1981).
(28) R. Alberto, G. Anderegg, and A. Albinati, Inorg. Chim.
Acta 178, 125 (1990).