Applications of manganocene in the synthesis of Mn(II) amide and imide cages

Article abstract of DOI:10.1039/b303727b

The reactions of manganocene, Cp₂Mn (Cp = C₅H ₅), with 2-aminopyrimidines give similar, octameric amido/imido cage complexesof general formulae[{CpMnNHR}{MnNR}]₄[R=4,6-Me₂pm (1a), 4-MeO-6-Mepm(1b),4,6

Full text of DOI:10.1039/b303727b

View Article Online / Journal Homepage / Table of Contents for this issue
Applications of manganocene in the synthesis of Mn(II) amide and
imide cages
Carmen Soria Alvarez,a Alan Bashall,b Andrew D. Bond,a Dale Cave,a Eilís A. Harron,a
Richard A. Layfield,a Marta E. G. Mosquera,c Mary McPartlin,b Jeremy M. Rawson,a
Paul T. Wooda and Dominic S. Wright*a
a Chemistry Department, Cambridge University, Lensfield Road, Cambridge, UK CB2 1EW.
E-mail: dsw1000@cus.cam.ac.uk.
b Department of Health and Biological Science, London Metropolitan University, London,
UK N7 8DB
c Departmento de Quimica Organica e Inorganica, Facultad de Quimica, Universidad de Oviedo,
33071 Oviedo, Spain
Received 3rd April 2003, Accepted 6th June 2003
First published as an Advance Article on the web 26th June 2003
The reactions of manganocene, Cp2Mn (Cp = C5H5), with 2-aminopyrimidines give similar, octameric amido/imido
cage complexes of general formulae [{CpMnNHR}{MnNR}]4 [R = 4,6-Me2pm (1a), 4-MeO-6-Mepm (1b), 4,6-(MeO)2-
pm (1c); pm = pyrimidinyl]. The structures of these complexes can be visualised as being composed of central Mn4N4
imido cubane units that are coordinated at their peripheries by four [CpMnNHpm] monomers. In contrast, less
acidic 2-aminopyridine (2-NH2py) and 8-aminoquinoline (8-NH2quin) are only singly deprotonated under
similar conditions, giving the unusual hexanuclear amido complex [Cp2Mn3(NHpy)4]2 (2) and the dimer [CpMn-
(µ-8-HNquin)]2 (3). N,NЈ-Dibenzylethylenediamine [(BnNHCH2)2] only forms the simple adduct [(η1-Cp)(η5-Cp)-
Mn{(BnNHCH2)2}] (4) (Bn = CH2Ph) with Cp2Mn, in which no deprotonation of the organic acid has occurred. The
X-ray structures of the new complexes 1b–c, 3 and 4 are reported (1a and 2 having been communicated previously).
work (Scheme 1, Fig. 1a), providing a potentially widely appli-
Introduction
cable route to high-nuclearity Mn() imido cage compounds.10
The potential applications of manganese carboxylate cluster
This reactivity pattern contrasts with that of the less acidic
compounds as precursors to molecule-based magnetic
2-aminopyridine (2-NH2py) with Cp2Mn, which gives the
materials, or as molecular magnets in their own right, has
hexanuclear complex [Cp2Mn3(NHpy)4]2 (2) in which the NH2
attracted considerable interest in the past two decades.1 Despite
this, the chemistry and magnetic properties of related nitrogen-
based manganese cluster compounds have been less explored,
and so far only a handful of imido manganese cluster com-
pounds (containing RN2Ϫ ligands) have been structurally
characterised.2 The majority of these species contain Mn in the
 to  oxidation states,2a the cationic species [Mn6(µ3-NPh)4-
(thf )4]4ϩ 2b being the only structurally chatacterised Mn()
imido complex. This situation contrasts with that for the amido
Mn complexes (containing R2NϪ ligands) for which the solid-
Scheme 1
state structures of a relatively large number of Mn() com-
plexes have been reported.3 Our interest in this area has arisen
from a general interest in the applications of main group and
transition metal metallocenes as precursors in the synthesis of
amido and imido compounds.4 Although the lability and bas-
icity of the C–metal bonds in stannocene (Cp2Sn) and related
p-block metallocenes has long been appreciated,5 the use of
transition metal metallocenes as soluble sources of low-
oxidation state metals has been investigated far less extensively.
There is, nonetheless, ample evidence for the emergence of
polarity in the C–metal bonds of many transition metal
metallocenes (particularly those of the transition metal series).
Thus, substitution of the Cp ligands by a range of organic
nucleophiles is a characteristic of, for example, Cp2Ni, Cp2Mn6
and [CpMؒPR3] (M = Cu, Ag).7 In addition, the deprotonation
of weaker, oxygen- and nitrogen-based organic acids using
Cp2Mn has also been reported.3a,8 Although this application of
Cp2Mn as a base has only been explored in a few limited
studies, this reagent provides a more convenient precursor
for metallo-organic Mn() derivatives than the use of highly
air-sensitive compounds such as [Mn{N(SiMe3)}2].9
In a recent communication we showed for the first time that
Cp2Mn is capable of doubly-deprotonating the NH2 group of
the moderately acidic 2-amino-4,6-dimethylpyrimidine frame-
Fig. 1 Molecular structure of 1a.
D a l t o n T r a n s . , 2 0 0 3 , 3 0 0 2 – 3 0 0 8
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
3002

View Article Online
group of the amine has only been singly deprotonated (Scheme
2, Fig. 2).11 We report here a full account of this work, includ-
ing new studies of the reactions of a more extensive range of
primary and bifunctional amines with Cp2Mn. In addition to
the synthesis and structure of [{CpMnNH(4,6-Me2pm)}{MnN-
(4,6-Me2pm)}]4 (1a)10 (pm = pyrimidinyl) and [Cp2Mn3-
(NHpy)4]2 (2),11 which we have described previously, the
syntheses and structures of the new Mn8 cage complexes
[{CpMnNH(4-MeO-6-Mepm)}{MnN(4-MeO-6-Mepm)}]4
(1b) and [{CpMnNH(4,6-(MeO)2pm)}{MnN(4,6-(MeO)2-
pm)}]4 (1c) (having similar structures to 1a), the dimer
[CpMn(µ-8-Nquin)]2 (3) (8-NH2quin = 8-aminoquinoline) and
the adduct [(η1-Cp)(η5-Cp)Mn(BnNHCH2)2] (4) (Bn = benzyl)
are reported. The characterisation of 1–4 allows an overall
assessment of the scope (and limitations) of the use of Cp2Mn
in the preparation of Mn() imido and amido complexes.
such a strong donor solvent, making it unlikely that the solu-
tion structures of the complexes are representative of those in
the solid state. Significantly, however, the IR spectra of 1b and
1c reveal the presence of both N–H and Cp functionalities and
therefore indicate that the deprotonation of the NH2 group
of the aminopyrimidines is incomplete, i.e., that amido groups
(RNH) are present in their structures. Similar spectroscopic
features were reported for the related complex [{CpMnNH(4,6-
Me2pm)}{MnN(4,6-Me2pm)}]4 (1a).10 The structural character-
isation of 1b and 1c (discussed in detail later) showed that both
RNHϪ (singly-deprotonated) and RN2Ϫ (doubly-deprotonated)
groups are present in the solid state and that the structural
arrangements of 1b and 1c are similar to that of 1a.
The reactivity pattern observed in the reactions of Cp2Mn
with 2-aminopyrimidines contrasts with that found for
2-aminopyridine (2-NH2py), the isolated product from toluene
solvent for the latter being the hexanuclear cage [Cp2Mn3-
(NHpy)4]2 (2) in which only single deprotonation of the NH2
group has occurred (Fig. 2). Full details of the synthesis and
characterisation of 2 have been reported previously, so will
not be discussed further here.11 A similar result is observed in
the reaction of Cp2Mn with 8-aminoquinoline (8-NH2quin),
the product of the 1 : 1 stoichiometric reaction in toluene being
the dimer [CpMn(µ-8-HNquin)]2 (3) (Scheme 4) (isolated in
42% yield). Despite repeated attempts, the extreme air sensitiv-
ity and apparent thermal instability of solid 3 has made satis-
factory elemental analysis on the complex impossible to obtain.
Scheme 2
1
Compound 3 was characterised by H NMR and IR spectro-
scopy and by an X-ray structure determination. Two weak
N–H stretching bands are observed in the infrared spectrum
of 3 (3394, 3380 cmϪ1). Although the C–H stretching vibration
for the Cp group in 3 could not be identified unambiguously in
the infrared spectrum, the presence of Cp ligands in the com-
plex is apparent in the 1H NMR spectrum, with a broad reson-
ance for this group being observed at 5.85 ppm. The 1H NMR
spectrum also suggests that the toluene molecules found in
the crystal lattice of 3 (by X-ray structure determination) are
removed by isolating the complex under vacuum (ca. 15 min,
10Ϫ1 atm).
Fig. 2 Structure of the hexanuclear Mn6 complex 2.
Results and discussion
Synthetic and structural studies
The reactions of 2-NH2(4-MeO-6-Mepm) and 2-NH2-(4,6-
(MeO)2pm) with Cp2Mn12 (1 : 1 molar equivalents) at Ϫ78 ЊC
in toluene, followed by storage at room temperature for 1–2
days give the new complexes [{CpMnNH(4-MeO-6-Mepm)}-
{MnN(4-MeO-6-Mepm)}]4ؒ6toluene (1bؒ6toluene) and [{Cp-
MnNH(4,6-(MeO)2pm)}{MnN(4,6-(MeO)2pm)}]4ؒ6toluene
(1cؒ6toluene). The first-batch yields of the crystalline com-
plexes were 44% for 1b and 12% for 1c (Scheme 3, see Experi-
mental section). Although it was shown by later structural
investigations of 1b and 1c that there are six toluene molecules
in the lattices of both compounds for each molecular unit, their
isolation under vacuum (ca. 15 min, 10Ϫ1 atm) resulted in loss
of toluene in both cases. Elemental analysis suggests that there
are ca. five toluene molecules remaining in isolated crystalline
samples of 1b and ca. one toluene molecule in 1c. Relatively
little information concerning the structures of the complexes
could be gained from 1H NMR spectroscopy, owing to the
paramagnetic nature of the complexes and to their low solubil-
ity even in polar organic solvents such as DMSO. A further
complication is the likely deaggregation of the complexes in
Scheme 4
The different outcomes of the reactions of the 2-amino-
pyrimidines, 2-aminopyridine and 8-aminoquinoline with
Cp2Mn can be rationalised simply from the expected relative
acidities of the organic acids, the presence of two electro-
negative N centres within the pyrimidinyl ring providing greater
stabilisation of the negative charge. It is perhaps unsurprising
then that reaction of Cp2Mn with the bifunctional second-
ary amine (BnNHCH2)2 (Bn = benzyl) does not lead to any
deprotonation of the two N–H groups. Instead, the simple
adduct [(η1-Cp)(η5-Cp)Mn(BnNHCH2)2] (4) is isolated
(Scheme 5). The infrared spectrum of 4 shows two N–H stretch-
ing bands at 3211 and 3192 cmϪ1 as well as a doublet Cp–H
stretching vibration at 3055 cmϪ1. Despite the paramagnetic
nature of this complex (the Mn() centre having a formal
electron count of 17 e), the resonances observed in the 1H
NMR spectrum are relatively sharp. Resonances due to the
benzylic (PhCH2–) (δ 2.55) and –CH2–CH2– methylene groups
(δ 2.04 and 1.73, respectively) are easily identified in DMSO,
although the line-widths of these resonances result in loss of
any coupling information.
Scheme 3
Scheme 5
D a l t o n T r a n s . , 2 0 0 3 , 3 0 0 2 – 3 0 0 8
3003

View Article Online
Table
1
Crystal data for [{CpMnNH(4-MeO-6-Mepm)}{MnN(4-MeO-6-Me-pm)}]4ؒ6toluene (1bؒ6toluene), [{CpMnNH(4,6-(MeO)2pm)}-
{MnN(4,6-(MeO)2pm)}]4ؒ6toluene (1cؒ6toluene), [CpMn(µ-8-HNquin)]2ؒ2toluene (3ؒ2toluene) and [(η1-Cp)(η5-Cp)Mn(BnNHCH2)2] (4)
Compounda
1bؒ6toluene
1cؒ6toluene
3ؒ2toluene
4
Empirical formula
Formula weight
C110H128Mn8N24O8
2353.88
C110H128Mn8N24O16
2481.88
C42H40Mn2N4
710.66
C26H30MnN2
425.46
Crystal system
Space group
Tetragonal
I41/a
Tetragonal
I41/a
Monoclinic
P21/c
Monoclinic
P21/c
a/Å
b/Å
23.6528(8)
–
24.3007(12)
–
14.237 (3)
10.815 (3)
8.2142(4)
14.7038(5)
c/Å
α/Њ
20.7070(6)
–
20.5467(11)
–
11.813 (2)
–
18.9720(11)
–
β/Њ
γ/Њ
–
–
–
–
93.639 (14)
–
1815.2 (6)
2
100.466(2)
–
2253.3(2)
4
Cell volume/Å3
Z
11584.6(6)
4
1.347
12133.3(11)
4
1.359
ρ/Mg mϪ3
1.300
1.254
Independent reflections (Rint
R indices [I>2σ(I )]
R indices (all data)
)
5674 (0.063)
R1 = 0.057, wR2 = 0.149
R1 = 0.099, wR2 = 0.199
3934 (0.105)
R1 = 0.059, wR2 = 0.140
R1 = 0.107, wR2 = 0.201
2522 (0.022)
R1 = 0.040, wR2 = 0.092
R1 = 0.0552, wR2 = 0.0999
3970 (0.056)
R1 = 0.046, wR2 = 0.101
R1 = 0.081, wR2 = 0.156
a Data in common; λ = 0.71069 Å; for 1b, 1c and 4 T = 180(2) K; for 3 T = 223(2) K.
Crystallographic studies
Low-temperature crystallographic studies were undertaken on
complexes 1b, 1c, 3 and 4. The structures of 1a (Fig. 1) and 2
(Fig. 2) have been reported by us previously and it will not be
appropriate to give a full account here. Details of the crystal
data, data collections and refinements of the new complexes 1b,
1c, 3 and 4 are provided in Table 1. Key bond lengths and
angles for the closely related Mn8 cage compounds 1a, 1b and
1c are listed in Table 2, for comparison. Selected bond lengths
and angles for 3 and 4 are given in Tables 3 and 4, respectively.
The low-temperature X-ray studies of complexes 1b (Fig. 3)
and 1c (Fig. 4) show that they both have similar octameric, Mn8
cage structures in the solid state of formulae [(η-Cp)Mn(2-
NHR)ؒMn(2-NR)]4 [R = 4-MeO-6-Mepm (1b), 4,6-(MeO)2pm
(1c)] possessing exact Ϫ4 symmetry. This arrangement is the
same as that observed previously in the Mn8 cage of 1a (Fig. 1).
However, unlike 1a where there are five thf molecules in the
lattice per molecule, in 1b and 1c six toluene molecules reside in
the lattice for each molecule of the complexes. The structures of
1a–c are best regarded as co-complexes of four Mn() imido
[Mn{2-NR}] and four organo/amido [(η-Cp)Mn{2-NHR}]
monomer units. The common core arrangements and number-
Fig. 4 Molecular structure of [{CpMnNH(4,6-(MeO)2pm)}{MnN-
(4,6-(MeO)2pm)}]4 (1c). H-atoms, except those attached to N, and
lattice toluene molecules have been omitted for clarity.
ing schemes for 1a, 1b and 1c are shown in Fig. 5a and 5b,
respectively. The central cores of the molecules are formed from
the association of four [Mn{2-NR}] units, giving similar dis-
torted tetrahedral arrangements of the Mn centres [in 1a
Mn(1) ؒ ؒ ؒ Mn(1A,1B) 3.1594(8), Mn(1) ؒ ؒ ؒ Mn(1C) 3.543(1)
Å; in 1b Mn(1) ؒ ؒ ؒ Mn(1A, 1B) 3.219(1), Mn(1) ؒ ؒ ؒ Mn(1C)
3.689(1) Å; in 1c Mn(1) ؒ ؒ ؒ Mn(1A,1B) 3.223(1), Mn(1) ؒ ؒ ؒ
Mn(1C) 3.724(1) Å]. This central fragment can be visualised as
a highly distorted Mn4N4 cubane unit, in which four oppo-
site edges [defined by Mn(1) ؒ ؒ ؒ N(1C), Mn(1A) ؒ ؒ ؒ N(1B),
Mn(1B) ؒ ؒ ؒ N(1A) and Mn(1C) ؒ ؒ ؒ N(1)] have been broken.
The anionic imido-N centres of the 2-NR ligands in these units
bridge the symmetry-related Mn atoms of the core [in 1a
Mn(1)–N(1) 2.085(3), Mn(1)–N(1B) 2.110(3) Å; in 1b Mn(1)–
N(1) 2.075(3), Mn(1)–N(1B) 2.097(3) Å; in 1c Mn(1)–N(1)
2.088(5), Mn(1)–N(1B) 2.101(5) Å], with one of the neutral N
centres of each pm ring spanning the four broken edges of the
Mn4N4 core via longer donor interactions [in 1a Mn(1)–N(6C)
2.160(3) Å; in 1b Mn(1)–N(6C) 2.150(3) Å; in 1c Mn(1)–N(6C)
2.144(5) Å]. As a result, the Mn centres of the core attain
a highly distorted tetrahedral geometry. The [(η-Cp)Mn-
{2-NHR}] units in 1a–c are located at the periphery of the
cages [in 1a Mn(1) ؒ ؒ ؒ Mn(2) 3.2335(7) Å; in 1b Mn(1) ؒ ؒ ؒ
Mn(2) 3.2609(8) Å; in 1c Mn(1) ؒ ؒ ؒ Mn(2) 3.300(1) Å]. The
Fig. 3 Molecular structure of [{CpMnNH(4-MeO-6-Mepm)}{MnN-
(4-MeO-6-Mepm)}]4 (1b). H-atoms, except those attached to N, and
lattice toluene molecules have been omitted for clarity.
D a l t o n T r a n s . , 2 0 0 3 , 3 0 0 2 – 3 0 0 8
3004

View Article Online
Table 2 Selected bond lengths (Å) and bond angles (Њ) for [{CpMn-
NH(4-MeO-6-Mepm)}{MnN(4-MeO-6-Mepm)}]4ؒ6toluene (1bؒ
6toluene), and [{CpMnNH(4,6-(MeO)2pm)}{MnN(4,6-(MeO)2pm)}]4ؒ
6toluene (1cؒ6toluene) compared with those reported for 1aؒ5thf
1a
1b
1c
Mn(1)–N(1)
Mn(1)–N(1B)
Mn(1)–N(2)
Mn(1)–N(6C)
Mn(2)–N(1)
Mn(2)–N(3)
2.085(3)
2.110(3)
2.117(3)
2.160(3)
2.208(3)
2.200(3)
2.262(3)
2.23
2.075(3)
2.097(3)
2.095(3)
2.150(3)
2.183(3)
2.195(4)
2.300(3)
2.19
2.088(5)
2.101(5)
2.095(5)
2.144(5)
2.154(5)
2.190(5)
2.347(5)
2.20
Mn(2)–N(5)
Mn(2) ؒ ؒ ؒ Cpcentroid
Mn(1) ؒ ؒ ؒ Mn(1A)
Mn(1) ؒ ؒ ؒ Mn(2)
Mn(1) ؒ ؒ ؒ Mn(1C)
3.1594(8)
3.2335(7)
3.543(1)
3.2187(9)
3.2609(8)
3.689(1)
3.223(1)
3.300(1)
3.724(1)
N(1)–Mn(1)–N(1B)
N(1)–Mn(1)–N(2)
N(1)–Mn(1)–N(6C)
Mn(1)–N(1)–Mn(1A)
N(2)–Mn(1)–N(1B)
N(1B)–Mn(1)–N(6C)
N(1)–Mn(2)–N(3)
N(1)–Mn(2)–N(5)
N(3)–Mn(2)–N(5)
106.1(1)
100.3(1)
122.7(1)
97.7(1)
102.3(1)
109.8(1)
104.7(1)
61.9(1)
108.9(1)
100.1(1)
118.3(1)
101.0(1)
103.0(1)
106.3(1)
106.2(1)
61.5(1)
111.4(2)
101.4(2)
116.8(2)
100.6(2)
100.5(2)
105.2(2)
103.9(2)
61.2(2)
102.6(1)
103.1(1)
102.9(2)
The atom labels refer to the following symmetry operations: A Ϫ0.25
Ϫ y, Ϫ0.25 ϩ x, Ϫ0.25 Ϫz; B 0.25 ϩ y, Ϫ0.25 Ϫ x, Ϫ.25 Ϫ z; C Ϫx,
Ϫy Ϫ 0.5, z.
Table 3 Selected bond lengths (Å) and bond angles (Њ) for [CpMn-
(µ-8-HNquin)]2 (3)
Mn(1)–N(2)
Mn(1)–N(2A)
Mn(1)–N(1)
2.143(3)
2.197(3)
2.219(2)
Mn(1) ؒ ؒ ؒ Cpcentroid
Mn(1) ؒ ؒ ؒ Mn(1A)
2.18
2.944(1)
N(2)–Mn(1)–N(2A) 94.6(1)
N(2)–Mn(1)–N(1) 76.28(9)
N(2A)–Mn(1)–N(1)
Mn(1)–N(2)–Mn(1A) 85.4(1)
96.60(9)
The atom labels refer to the following symmetry operations: A 1 Ϫ x,
2 Ϫ y, Ϫz.
MnCp fragments of these monomer units are chelated by the
imido N centre [in 1a Mn(2)–N(1) 2.208(3) Å; in 1b Mn(2)–
N(1) 2.183(3) Å; in 1c Mn(2)–N(1) 2.154(5) Å] and the second
N centre [in 1a Mn(2)–N(5) 2.262(3) Å; in 1b Mn(2)–N(5)
2.300(3) Å; in 1c Mn(2)–N(5) 2.347(5) Å] of each of the 2-NR
ligands of the central Mn4N4 core. The 2-NHR groups of the
[(η-Cp)Mn{2-NHR}] units adopt a similar chelating bonding
mode to that found for the 2-NR groups within the Mn4N4
cores of 1a–c, with the anionic N(H) centres and one of the pm
ring N centres being involved in bridging the core Mn and
Mn(Cp) atoms [in 1a Mn(1)–N(2) 2.117(3), Mn(2)–N(3)
2.200(3) Å; in 1b Mn(1)–N(2) 2.095(3), Mn(2)–N(3) 2.195(4) Å;
in 1c Mn(1)–N(2) 2.095(5), Mn(2)–N(3) 2.190(5) Å]. The Mn
atoms within each [(η-Cp)Mn{2-NHR}] monomer therefore
obtain a ‘piano-stool’ coordination geometry similar to that
found in metal carbonyls such as [CpMn(CO)3].13 However, the
Mn centres in 1a–c are clearly high-spin (formally 17 e) in 1a–c
at 180 K. This conclusion is supported by the long C–Mn
distances involved [in 1a range 2.408(5)–2.616(5) Å; in 1b
2.455(6)–2.508(4) Å; in 1c 2.464(8)–2.515(9) Å; cf. 2.33–2.65 Å
Fig. 5 Core structure of 1a–c (a) showing connectivity of guanidide
units, (b) the Mn8 arrangement and shortest Mn ؒ ؒ ؒ Mn contacts.
for high spin14,15], within the range of 2.33–2.65 Å observed for
high spin and significantly greater than the values expected for
low-spin Mn() (ca. 2.11–2.14 Å).14,15
A noticeable trend can be discerned in the core Mn ؒ ؒ ؒ Mn
distances on going from 1a to 1b and 1c. There is a large expan-
sion in the key Mn ؒ ؒ ؒ Mn distances defining the cores of the
complexes as one moves from 1a to 1c. Within the central
Mn4N4 cubane units the nearest neighbouring distance expands
from Mn(1) ؒ ؒ ؒ Mn(1A) 3.1594(8) Å in 1a to Mn(1) ؒ ؒ ؒ
Mn(1A) 3.2187(9) Å in 1b, to Mn(1) ؒ ؒ ؒ Mn(1A) 3.223(1) Å in
1c,16 at the same time the Mn ؒ ؒ ؒ Mn separation across this
unit increases from Mn(1) ؒ ؒ ؒ Mn(1C) 3.543(1) Å in 1a, to
Mn(1) ؒ ؒ ؒ Mn(1C) 3.689(1) Å in 1b, to Mn(1) ؒ ؒ ؒ Mn(1C)
3.724(1) Å in 1c. In addition, the Mn ؒ ؒ ؒ Mn separation
between the independent Mn centres in the asymmetric units
[Mn(1) and Mn(2)] increases from Mn(1) ؒ ؒ ؒ Mn(2) 3.2335(7)
Table 4 Selected bond lengths (Å) and angles (Њ) for [(η1-Cp)(η5-Cp)Mn(BnNHCH2)2] (4)
Mn(1)–N(1)
Mn(1)–N(2)
Mn(1)–C(1)
2.226(2)
2.261(2)
2.331(2)
Mn(1)–C(6–11)
Cpcentroid. . .Mn(1)
2.450(2)–2.555(2)
2.21
N(1)–Mn(1)–N(2)
C(1)–Mn(1)–Cpcentroid
79.22(7)
121.8(1)
N(1)–Mn(1)–Cpcentroid
N(2)–Mn(1)–Cpcentroid
121.0(1)
114.3(1)
D a l t o n T r a n s . , 2 0 0 3 , 3 0 0 2 – 3 0 0 8
3005

View Article Online
Å in 1a, to Mn(1) ؒ ؒ ؒ Mn(2) 3.2609(8) Å in 1b, to Mn(1) ؒ ؒ ؒ
Mn(2) 3.300(1) Å in 1c. The origin of this trend may, in part, be
due to increased steric crowding resulting from the presence of
more demanding MeO groups around the core. The presence of
electron-releasing MeO substituents in the 4- and 6-positions of
the pm framework should also have an impact on the hybridis-
ation and/or charge at the ring-N and anionic 2-N atoms of the
pmNHϪ and pmN2Ϫ ligands. Although it is difficult to delineate
the potential steric and electronic contributions by a simple
comparison of the key Mn–N bond lengths and angles found in
1a–c (presented in Table 2), the major effect of changing the
substituents appears to be felt by the imido pmN2Ϫ ligands.
Thus, whereas the majority of the bond lengths and angles
associated with Mn–N cores in 1a–c remain largely unaltered
(within the crystallographic errors), there are significant
changes occurring in Mn(2)–N(5) (ca. 0.08 Å increase) and
N(1)–Mn(1)–N(6C) (ca. 6Њ decrease), N(1B)–Mn(1)–N(6C) (ca.
4Њ decrease) in going from 1a to 1b to 1c.
bonds to the N centres within the quinoline ligands [N(1)–
Mn(1) 2.219(2) Å]. The Mn–C bond lengths [range 2.429(4)–
2.515(4) Å] are indicative of high-spin Mn() [normally in the
range 2.33–2.65 Å14,15] and the Mn() centres have a formal
electron count of 17 e. The Mn ؒ ؒ ؒ Mn separation across the
dimer unit appears to be short [Mn(1) ؒ ؒ ؒ Mn(1A) 2.9440(10)
Å]; cf. Mn2(CO)10 ca. 2.90 Å.16 However, a search of the
Cambridge Crystallographic Data Base (CCDC) reveals that
Mn ؒ ؒ ؒ Mn separations within related Mn2N2 dimers (ca. 2.39–
2.64 Å) are generally significantly shorter than in 3.18 Thus, it is
unlikely that there is any degree of Mn ؒ ؒ ؒ Mn bonding in the
complex. The previously reported complex 2 and the new
species 3 are rare examples of a primary-amido Mn() complex
(containing RNHϪ ligands), the trinuclear, heteroleptic com-
plex [{(Me3Si)2NMn(µ-NHDipp)2}2Mn] (Dipp = 4,6-iPr2C6H3)
being one of the few simple primary-amido Mn() complexes
to be reported prior to our studies.19 Most other structurally
characterised examples contain secondary-amido ligands
(R1R2NϪ).3
As noted in the introduction to this paper, although amido
Mn() compounds (containing R2NϪ anions) are more com-
mon, very few Mn imido compounds like 1a–c have been struc-
turally characterised.2 Of these the majority are Mn(–)
complexes such as the nitrido anion [MnVII(N)(NtBu)3]2Ϫ and
the dimers [MnV(R)(NtBu)(µ-NtBu)]2 (R = CH2CMe3, CH2Ph),
prepared by transmetallation reactions of [Mn(NtBu)3Cl].2a
The only previously structurally authenticated example of a
Mn() imido compound is the hexanuclear adamantane-like
cation [Mn6(µ3-NPh)4(thf )4]4ϩ, obtained by the transmetal-
lation reaction of [Mg(NPh)(thf )]6 with MnBr2 in thf.2b Inter-
estingly, the Mn–N(imido) bond lengths [2.035(9)–2.080(9) Å]
in [Mn6(µ3-NPh)4(thf )4]4ϩ are at the lower end of those found in
the Mn4N4 cores of 1a–c 2.075(3)–2.110(3) Å,2b probably result-
ing from the overall positive charge of the [Mn6(µ3-NPh)4-
(thf )4]4ϩ cation. The common structure adopted by 1a–c
contains many novel features. Not least, the complexes are the
highest nuclearity imido Mn cages to be structurally character-
ised. The incorporation of four CpMn units within these cage
arrangements is also unprecedented. The most closely related
situation is found in [(CpMn)3(µ2-NO)3(µ3-NO)], containing
three CpMn fragments.17
The solid-state structure of [CpMn(µ-8-HNquin)]2 (3) (Fig. 6)
is that of a centrosymmetric dimer in which each Mn centre is
bonded to a terminal η5-Cp ligand [Mn() ؒ ؒ ؒ Cpcentroid 2.18 Å]
and is further bonded to a µ-NH centre within the central
Mn2N2 ring unit [Mn(1)–N(2) 2.143(3) Å, Mn(1)–N(2A)
2.197(3) Å]. There are two toluene molecules present in the
lattice of the complex. The Mn2N2 core of 3 is diamond shaped,
with angles of 94.6(1)Њ for N(2)–Mn(1)–N(2A) and 85.4(1)Њ for
Mn(1)–N(2)–Mn(1A). Each Mn centre then forms longer
The result of the attempted reaction of (BnNHCH2)2 with
Cp2Mn is simple complexation of the Mn() centre (without
deprotonation of the NH functionality). The composition of
the product [(η1-Cp)(η5-Cp)Mn(BnNHCH2)2] (4) (Fig. 7) is
similar to that of other donor complexes of Cp2Mn with vari-
ous mono- and bi-dentate O, N and P ligands.20 Similar η1- and
η5- bonding of the Cp ligands to that in 4 occurs in the only
other N-donor adduct of manganocene, [(η1-Cp)(η5-Cp)Mn-
(TMEDA)].20a The Mn–N bond lengths in the latter [2.338(5)
and 2.354(5) Å] are similar to those in 4 [2.226(2) and 2.261(2)
Å]. In contrast to 4 and [(η1-Cp)(η5-Cp)Mn(TMEDA)], the Cp
ligands in [Cp2Mnؒthf],20d [Cp2MnؒPR3]20b,c and [Cp2MnؒMe2-
PCH2CH2PMe2]20c all adopt η5-Cp coordination modes.
Although the steric demands of the Me2PCH2CH2PMe2 ligand
are greater than that of the (BnNHCH2)2 ligand, making a
change in the hapticity of the Cp ligands more likely, the
decisive factor is the shortness of Mn–N bonds compared to
Mn–P bonds. Thus, the resulting closer approach of the
(BnNHCH2)2 ligand to the Cp2Mn monomer unit in fact pro-
duces a greater disruption of the Cp–Mn bonding than the
Me2PCH2CH2PMe2 ligand. Despite the shortness of the Mn–O
bond in [Cp2Mnؒthf], the coordinated ligand has low steric
demands so that the η5-Cp coordination is retained. Further
evidence of steric congestion within the structure of 4 is seen
in the asymmetry of the coordination of the two N centres
of the (BnNHCH2)2 ligand [the Mn(1)–N bonds differing by ca.
0.35 Å]. The observation that Cp2Mn does not deprotonate
(BnNHCH2)2 can be compared to the formation of the complex
[{Dipp(N)CH2CH2N(H)Dipp}2Mn] (Dipp = 4,6-iPr2C6H3) in
the reaction of Mn{N(SiMe3)2}2 with DippN(H)CH2CH2N-
(H)Dipp (the product resulting from deprotonation of just one
of the N–H groups of the organic acid).21 Apart from the obvi-
ous difference in the Mn() base employed in this reaction, the
major difference is the likely greater acidity of DippN(H)CH2-
CH2N(H)Dipp compared to that of (BnNHCH2)2.
Fig. 6 Structure of the dimer [CpMn(µ-8-HNquin)]2 (3). H atoms,
except those attached to N, have been omitted for clarity.
Fig. 7 Structure of the adduct [(η1-Cp)(η5-Cp)Mn(BnNHCH2)2] (4).
H atoms, except those attached to N, have been omitted for clarity.
D a l t o n T r a n s . , 2 0 0 3 , 3 0 0 2 – 3 0 0 8
3006

View Article Online
NMR (400.16 MHz, ϩ25 ЊC, D6-DMSO, δ/ppm = 7.19 (s, aryl
Conclusions
C–H), 6.93 (s, br, Cp–H) 2.47 (s, MeO), 2.24 (s, Me). Elemental
analysis; found C 54.8, H 5.5, N 14.6; cald. for 1bؒ5toluene C
54.7, H 5.4, N 14.6%.
The results presented in this paper show that the reactions of
aromatic primary amines with Cp2Mn can be used in the prep-
aration of imido and amido Mn() cage compounds. In order
for complete deprotonation of the NH2 functionality to occur,
however, organic aromatic substituents possessing more than
one ring N atom are required in order to stabilise the negative
charge within an imido group. The more acidic 2-amino-
pyrimidines can be doubly deprotonated even in the presence of
electron-donating MeO and Me substituents, while only single
deprotonation of 2-aminopyridines and related aromatic
amines occurs under the reaction conditions employed. So far
studies have only investigated room-temperature reactions of
these species. Future studies will investigate higher temperature
reactions of primary amines, in an attempt to effect complete
deprotonation, and the reactions of primary phosphines with
Cp2Mn. Although limited, magnetic studies of 1a and 2 have
been reported in preliminary publications,10,11 the studies pre-
sented in this paper have focused only on the synthetic scope of
the use of manganocene as a base. Detailed magnetic and elec-
tronic measurements of the new complexes will be the subject
of a future paper.
[(ꢀ5-Cp)Mn{2-NH(4,6-(MeO)2pm)}Mn{2-N(4,6-(MeO)2pm)}]4
(1c). A solution of 2-amino-4,6-dimethoxypyrimidine (0.155 g,
1.0 mmol) in toluene (40 ml) was added dropwise to a solution of
Cp2Mn (0.185 g, 1.0 mmol) in toluene (20 ml) at Ϫ78 ЊC. The
solution became dark brown. It was stirred at Ϫ78 ЊC for five
minutes then allowed to warm to 5 ЊC, turning light brown. The
solution was stored at room temperature for 2 days. Light brown
crystals of 1c were produced. Although later X-ray structure
determination shows that there are six toluene molecules in the
lattice of 1c, isolation of crystalline samples under vacuum (10Ϫ1
atm, 15 min) gives material in which there is only one toluene per
molecule of 1c. The following data refer to this material. Yield
0.03 g (12%). Decomp 178 ЊC to black solid. IR (Nujol, NaCl
windows), ν/cmϪ1 = 3347, 3298 (w, N–H str.), ca. 3060 (vw, Cp–H
1
str.), 1589 (w, C᎐N str.). H NMR (400.16 MHz, ϩ25 ЊC, D -
᎐
6
DMSO) δ/ppm = 7.08 (s, aryl C–H), 5.25 (s, Cp), 2.23 (s, MeO).
Elemental analysis; found C 43.5, H 4.5, N 15.4; cald. for 1cؒ
toluene C 44.6, H 4.4, N 16.6%.
[CpMn(ꢁ-8-HNquin)]2 (3). A solution of 8-aminoquinoline
(0.14 g, 1.0 mmol) in toluene (10 ml) was added dropwise to a
solution of Cp2Mn (0.19 g, 1.0 mmol) in toluene (15 ml) at
Ϫ78 ЊC. The mixture turned orange and a precipitate was
formed. It was stirred (5 min) and warmed to room temper-
ature. A dark orange solution was obtained on brief, gentle
heating and stored at room temperature (24 h), resulting in the
formation of brown crystals of 3 (0.14 g, 42%). Decomp. 90 ЊC,
Experimental
General
Manganocene and the new compounds 1b, 1c, 3 and 4 are
highly air- and moisture-sensitive. They were handled on a
vacuum line using standard inert-atmosphere techniques and
under dry/oxygen-free argon.22 The pyrimidine and pyridine
starting materials were used as supplied (Aldrich). Toluene, thf
and hexane were dried by distillation over sodium/benzo-
phenone prior to the reactions. Manganocene was prepared
using the method of Wilkinson et al.12 Complexes 1–5 were
isolated and characterised with the aid of a nitrogen-filled
glove box fitted with a Belle Technology O2 and H2O internal
recirculation system and equipped with an O2 meter (reading
ca. 1–10 ppm while in use). Melting points (uncorrected) were
determined by using a conventional apparatus and sealing
samples in capillaries under argon. IR spectra were recorded as
Nujol mulls using NaCl plates and were run on a Perkin-Elmer
Paragon 1000 FTIR spectrophotometer. Elemental analyses
were performed by first sealing the samples under argon in air-
tight aluminium boats (1–2 mg) and C, H and N content was
analysed using an Exeter Analytical CE-440. 1H NMR spectra
were recorded on a Bruker AM400 MHz spectrometer in dry
deuterated D6-DMSO (using the solvent resonances as the
internal reference).
to a black solid. IR (Nujol, NaCl windows), ν/cmϪ1 = 3394,
1
3380 (w, N–H str.), 1613 (w, C᎐N str.), 1592 (m, C᎐C str.). H
᎐
᎐
NMR (400.16 MHz, ϩ25 ЊC, D6-DMSO) δ/ppm = 8.67, 8.13,
7.17 (br s, C–H aromatic), 5.85 (br s, Cp), 3.28 (br s, NH).
[(ꢀ1-Cp)(ꢀ5-Cp)Mn{(BnNHCH2)2}] (4). A solution of N,NЈ-
dibenzylethylenediamine (0.23 ml, 1.0 mmol) in thf (10 ml) was
added dropwise to a solution of Cp2Mn (0.185 g, 1.0 mmol) in
thf (10 ml) at Ϫ78 ЊC. The reaction mixture turned dark brown
and was stirred at Ϫ78 ЊC for five min then allowed to warm to
room temperature, finally becoming light brown. After briefly
bringing the reaction to reflux, it was stirred for another hour.
A white solid was formed, which dissolved on heating. Storage
at room temperature (4 days) produced colourless crystals of 4.
Yield 0.14g (33%). IR (Nujol, NaCl windows), ν/cmϪ1 = 3211,
3192 (m, N–H str.), 3082 (m), 3069 (m), 3055 (d, m; Cp–H str.),
3025 (m, aryl C–H), other major bands at 1181 (s), 1090 (s),
1080 (s), 1027 (s), 1003 (s), 965 (s), 747 (vs), 732 (vs), 696 (vs).
1H NMR (400.16 MHz, ϩ25 ЊC, D6-DMSO) δ/ppm = 7.27 (s),
7.19 (s, aromatic C–H), 3.82 (s, Cp), 2.55 (s, PhCH2), 2.04 (s),
1.73 (s) (CH2CH2). Elemental analysis; found C 71.6, H 6.8, N
7.1; cald. for 4 C 73.4, H 7.1, N 6.6%.
Syntheses
[(ꢀ5-Cp)Mn{2-NH(4-MeO-6-Mepm)}]Mn{2-N(4-MeO-6-
Mepm)}]4 (1b). A solution of 2-amino-4-methoxy-6-methyl-
pyrimidine (0.075 g, 0.54 mmol) in toluene (30 ml) was added
dropwise to a solution of Cp2Mn (0.10 g, 0.54 mmol) in toluene
(15 ml) at Ϫ78 ЊC. The reaction mixture initially became very
dark but after stirring for 5 min at Ϫ78 ЊC and then allowing the
temperature to increase to 5 ЊC, a series of colour changes
finally led to a yellow solution. A precipitate was formed which
was dissolved by addition of 10 ml of toluene and heating gen-
tly. The bright yellow solution was stored at room temperature
for 2 days. Orange crystals were produced. Although later
X-ray structure determination shows that there are six toluene
molecules in the lattice of 1b, isolation of crystalline samples
under vacuum (10Ϫ1 atm, 15 min) gives material in which there
are only five toluene molecules per molecule of 1b. The follow-
ing data refer to this material. Yield 0.07 g (44%). Decomp. 164
X-Ray crystallography
Crystals of 1b, 1c, 3 and 4 were mounted directly from the
mother solution under nitrogen at room temperature, a per-
fluorocarbon oil being used to protect them from atmospheric
air and moisture.23 Data for 1b, 1c and 4 were collected using a
Nonius Kappa CCD diffractometer, and for 3 on a Bruker P4
four-circle diffractometer. The structures were solved by direct
methods and refinement carried out using full-matrix least
squares on F 2 (SHELXL-97 1b; SHELXL-93 1c, 3 and 4).24
The crystals of 1b and 1c were isomorphous and in both crys-
tals 1.5 toluene molecules were disordered in the asymmetric
unit (i.e., per two independent manganese atoms). It was not
possible to locate the toluene methyl groups so these were
assumed to be disordered over all carbons of the ring; hydrogen
ЊC to black solid. IR (Nujol, NaCl windows), ν/cmϪ1 = 3341
(w, N–H str.), 3060 (vw, Cp–H str.), 1575 (w, C᎐N str.). H
1
᎐
D a l t o n T r a n s . , 2 0 0 3 , 3 0 0 2 – 3 0 0 8
3007

View Article Online
5
C. A. Russell, A. Steiner and D. S. Wright, Organometallics, 1996,
15, 639.
8 M. A. Beswick, M. E. G. Mosquera, J. S. Palmer, P. R. Raithby and
D. S. Wright, New J. Chem., 1999, 23, 1033.
9 See, for example: M. A. Beswick, C. N. Harmer, P. R. Raithby,
A. Steiner, K. Verhorevoort and D. S. Wright, J. Chem. Soc.,
Dalton Trans., 1997, 2029 and references therein.
10 C. Soria Alvarez, A. D. Bond, E. A. Harron, R. A. Layfield,
J. A. McAllister, C. M. Pask, J. M. Rawson and D. S. Wright,
Organometallics, 2001, 20, 4135.
11 C. Soria Alvarez, A. D. Bond, D. Cave, M. E. G. Mosquera,
E. A. Harron, R. A. Layfield, R. M. McPartlin, J. M. Rawson,
P. T. Wood and D. S. Wright, Chem. Commun., 2002, 2980.
12 G. Wilkinson, F. A. Cotton and J. M. Birmingham, J. Inorg. Nucl.
Chem., 1956, 2, 95.
13 A. F. Berndt and R. E. Marsh, Acta Crystallogr., 1963, 16, 118;
P. J. Fitzpatrick, Y. Le Page, J. Sedman and I. S. Butler, Inorg. Chem.,
1981, 20, 2852; J. Cowie, E. J. M. Hamilton, J. C. V. Laurie and
A. J. Welch, J. Organomet. Chem., 1990, 394, 1.
14 (a) M. E. Switzer, R. Wang, M. F. Rettig and A. H. Maki, J. Am.
Chem. Soc., 1974, 96, 7669; (b) M. L. Hays, D. J. Burkey,
J. S. Overby, T. P. Hanusa, S. P. Sellers, G. T. Lee and V. G. Young,
Jnr., Organometallics, 1998, 17, 5521 and references therein.
15 The C–Mn interactions in 1a–c are similar to those observed
in paramagnetic [{E2(NCy)4}(MnCp)2] (E = As, Sb): A. Bashall,
M. A. Beswick, H. Ehlenberg, S. J. Kidd, M. McPartlin, J. S. Palmer,
P. R. Raithby, J. M. Rawson and D. S. Wright, Chem. Commun.,
2000, 749 [range C–Mn 2.389(10)–2.615(8) Å].
–
atoms of occupancy were assigned to the six ring carbon
6
atoms of the complete toluene solvate molecules. In 3 and 4 the
hydrogen atoms of the cyclopentadienyl groups were directly
located, and were included in the observed positions, without
refinement in 3 and refined freely in 4. In all four structures
anistropic displacement parameters were assigned to all full
occupancy non-hydrogen atoms.
CCDC reference numbers 207480–207483.
See http://www.rsc.org/suppdata/dt/b3/b303727b/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We gratefully acknowledge the EPSRC (C. S. A., A. B.,
A. D. B., D. C., E. A. H., M. McP., J. M. R., P. T. W.), Clare
College, Cambridge (Denman Baynes Fellowship for R. A. L.)
and the EU [Socrates grant for C. S. A. (University of Oviedo)]
for financial support. We thank Dr J. E. Davies for collecting
X-ray data on 1a, 1b and 4.
References and notes
1 G. Christou, Magnetism: A Supramolecular Function, ed. O. Kahn,
Nato ASI Series, Kluwer, Dordrecht, The Netherlands, 1996, 383;
G. Aromí, S. M. J. Aubin, M. A. Bolcar, G. Christou, H. J. Eppley,
K. Folting, D. N. Hendrickson, J. C. Huffman, R. C. Squire,
H.-L. Tsai, S. Wang and M. W. Wemple, Polyhedron, 1998, 17,
3005.
2 (a) A. A. Danopoulos, G. Wilkinson, T. K. N. Sweet and
M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1995, 205;
(b) W. J. Grigsby and P. P. Power, J. Chem. Soc., Dalton Trans., 1996,
4613.
3 (a) A. Belforte, F. Calderazzo, U. Englert, J. Strähle and K. Wurst,
J. Chem. Soc., Dalton Trans., 1991, 2419; (b) P. G. Eller, D. C.
Bradley, M. B. Hursthouse and D. W. Meek, Coord. Chem. Rev.,
1977, 24, 1; (c) B. D. Murray and P. P. Power, Inorg. Chem., 1984,
23, 4584; R. A. Bartlett, X. Feng, M. M. Olmstead, P. P. Power and
K. J. Weese, J. Am. Chem. Soc., 1987, 109, 4851; (d ) A. Belforte,
F. Calderazzo, U. Englert and J. Strähle, J. Chem. Soc., Chem.
Commun., 1989, 801.
4 M. A. Beswick, J. S. Palmer and D. S. Wright, Chem. Soc. Rev., 1998,
27, 225.
5 (a) P. Jutzi, Adv. Organomet. Chem., 1986, 26, 217; (b) J. W. Connolly
and C. Hoff, Adv. Organomet. Chem., 1981, 19, 123.
6 K. Jonas, Angew. Chem., Int. Ed. Engl., 1985, 24, 295.
7 M. A. Beswick, C. Brasse, M. A. Halcrow, P. R. Raithby,
C. A. Russell, A. Steiner, R. Snaith and D. S. Wright, J. Chem. Soc.,
Dalton Trans., 1996, 3793; C. Brasse, P. R. Raithby, M.-A. Rennie,
16 The Mn ؒ ؒ ؒ Mn distances can be compared to a value of 2.90 Å in
Mn2CO10 for a single Mn–Mn bond: M. R. Churchill, K. N. Amoh
and H. J. Wasserman, Inorg. Chem., 1981, 20, 1609.
17 R. C. Elder, Inorg. Chem., 1974, 13, 1037.
18 Search of the Cambridge Crystallographic Data Base, February
2003; for example, the Mn() dimer [(η5-Cp)Mn{µ-NN(SiMe3)2}]2
[Mn ؒ ؒ ؒ Mn 2.393(2) Å]: N. Wiberg, H.-W. Haring, G. Hüttner and
P. Friedrich, Chem. Ber, 1978, 111, 2708.
19 D. K. Kennanpohl, S. Brooker, G. M. Sheldrick and H. W. Roesky,
Z. Naturforsch., Teil B, 1992, 47, 9.
20 (a) J. Heck, W. Massa and P. Weinig, Angew. Chem., Int. Ed. Engl.,
1984, 23, 722; (b) G. G. Howard, G. S. Girolami, G. Wilkinson,
M. Thorton-Pett and M. B. Hursthouse, J. Am. Chem. Soc.,
1984, 106, 2033; (c) F. Bottomley, P. N. Keizer and P. S. White,
J. Am. Chem. Soc., 1988, 110, 137; (d ) J. T. Weed, M. F. Rettig and
R. M. Wing, J. Am. Chem. Soc., 1983, 105, 6510.
21 H. Chen, R. A. Bartlett, H. V. R. Dias, M. M. Olmstead and
P. P. Power, Inorg. Chem., 1991, 30, 2487.
22 D. F. Shriver and M. A. Drezdzon, The Manipulation of
Air-Sensitive Compounds, Wiley, New York, 2nd edn., 1986.
23 T. Kottke and D. Stalke, J. Appl. Crystallogr., 1993, 26, 615.
24 (a) G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Göttingen, 1997; (b) G. M. Sheldrick,
SHELXL-93, Program for Crystal Structure Refinement, University
of Göttingen, 1993.
D a l t o n T r a n s . , 2 0 0 3 , 3 0 0 2 – 3 0 0 8
3008