Synthesis and X-ray powder diffraction characterization of (OC)2RhCl2Rh(cod) (cod = cycloocta-1,4-diene)

Article abstract of DOI:10.1039/a704668e

In order to elucidate the nature and the structure of the elusive (OC)₂Rh(Ph₃SiO)₂Rh(COd) (cod) = cycloocta-1,5-diene) complex, an important model compound for surface catalysis, (OC)₂RhCl₂Rh(cod) has been synthesized, and structurally characterized by ab initio X-ray powder diffraction. Crystals of (OC)₂RhCl₂Rh(cod) are monoclinic, space group P2₁/c, a = 6.659(1), b = 12.274(1) and c = 16.096(1) A, β= 92.176(5)°, Z = 4, ρ_calc = 2.209 g cm^-3. The structure has been solved, from powder diffraction data only, by Patterson and Fourier-difference methods and has been ultimately refined, by the Rietveld method, down to R_p = 0.116 and R_wp = 0.154 for 4050 data points collected in the 12-93° (2θ) range. The molecule contains two square-planar rhodium atoms, one bearing two terminal carbonyls and the other bound to the chelating cod fragment, and two chlorine atoms bridging the Rh...Rh vector. The Rh₂Cl₂ core is markedly non-planar, the dihedral angle about the Cl...Cl hinge being 135.4(6)°.

Full text of DOI:10.1039/a704668e

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Synthesis and X-ray powder diffraction characterization of
(OC)2RhCl2Rh(cod) (cod ؍ cycloocta-1,4-diene)
Eleonora Corradi,a Norberto Masciocchi,a Gyula Pályi,*,b Renato Ugo,c Anna Vizi-Orosz,d
Claudia Zucchib and Angelo Sironi*,†,a
a Dipartimento di Chimica Strutturale e Stereochimica Inorganica and Centro CNR CSSMTBO,
Università di Milano, via Venezian 21, 20133 Milano, Italy
b Dipartimento di Chimica, Università di Modena, via Campi 183, 41100 Modena, Italy
c Dipartimento di Chimica Inorganica, Metallorganica ed Analitica and Centro CNR CSSMTBO,
Università di Milano, via Venezian 21, 20133 Milano, Italy
d Research Group for Petrolchemistry, Hungarian Academy of Sciences, Egyetem u. 8,
8200 Veszprém, Hungary
In order to elucidate the nature and the structure of the elusive (OC)2Rh(Ph3SiO)2Rh(cod) (cod) = cycloocta-1,5-
diene) complex, an important model compound for surface catalysis, (OC)2RhCl2Rh(cod) has been synthesized,
and structurally characterized by ab initio X-ray powder diffraction. Crystals of (OC)2RhCl2Rh(cod) are
monoclinic, space group P21/c, a = 6.659(1), b = 12.274(1) and c = 16.096(1) Å, β = 92.176(5)Њ, Z = 4, ρcalc = 2.209
g cmϪ3. The structure has been solved, from powder diffraction data only, by Patterson and Fourier-difference
methods and has been ultimately refined, by the Rietveld method, down to Rp = 0.116 and Rwp = 0.154 for 4050
data points collected in the 12–93Њ (2θ) range. The molecule contains two square-planar rhodium atoms, one
bearing two terminal carbonyls and the other bound to the chelating cod fragment, and two chlorine atoms
bridging the Rh ؒ ؒ ؒ Rh vector. The Rh2Cl2 core is markedly non-planar, the dihedral angle about the Cl ؒ ؒ ؒ Cl
hinge being 135.4(6)Њ.
The ‘two-dimensional chemistry’1 observed with transition-
metal complexes supported on oxides is one of the most active
sectors of research dealing with transition-metal catalysts.2 In
particular many aspects of the surface chemistry of rhodium,
one of the most effective catalysts,3 were studied, including the
synthesis of model complexes of supposed surface species4 and
the interconversion of Rh complexes on oxide surfaces.4c,5
Recently these latter studies have proved to be the basis of an
efficient cluster synthesis.6
instruments. Proton and 13C NMR spectra were obtained with
Bruker AMX and AC200 spectrometers.
Starting materials were of commercial origin, except for
(Ph3SiO)2Rh(CO)4,7
(Ph3SiO)2Rh2(cod)2,7
Cl2Rh2(CO)4,11
12
Cl2Rh2(cod)2
(from commercial RhCl3ؒxH2O) and Ph3-
SiONa,13 which were prepared according to published
procedures.
Preparation of Cl2Rh2(CO)2(cod) 5 by reaction (i)
In the course of our earlier efforts in preparing models of
surface species of rhodium, we observed7 that the complexes
(OC)2Rh(Ph3SiO)2Rh(CO)2 and (cod)Rh(Ph3SiO)2Rh(cod)
(cod = cycloocta-1,5-diene) are easily interconvertible. Now we
report on the formation of an intermediate of this reaction,
(OC)2Rh(Ph3SiO)2Rh(cod), which is fairly unstable in solution
and cannot be satisfactorily characterized by spectroscopic
methods. We were unable to grow suitable single crystals (for
X-ray diffraction) of such an important intermediate; therefore,
as indirect evidence of its nature, we decided to synthesize and
structurally characterize its dichloro-bridged analogue, i.e.
(OC)2RhCl2Rh(cod). Unfortunately, this latter compound did
not afford crystals of suitable quality but, given its lower com-
plexity, it was decided to attempt its complete structural analy-
sis on the basis of ab initio powder diffraction analysis, which
has been recently shown to be a powerful technique for assess-
ing the crystal and molecular structures of molecular and/or
polymeric co-ordination compounds.8,9
The complex Cl2Rh2(cod)2 (100 mg, 0.20 mmol) was dissolved
in dry n-hexane (50 cm3) while being stirred under an Ar
atmosphere at 50 ЊC in a Schlenk vessel, which was then left to
cool to room temperature (r.t.). To this stirring solution was
added at once a solution of Cl2Rh2(CO)4 (78 mg, 0.20 mmol)
in n-hexane (10 cm3). The color of the initial yellow solution
immediately turns orange and the IR ν(CO) spectrum of a
sample shows almost exclusively the emergence of a new, two-
component band system and some remaining (<10%) signals of
Cl2Rh2(CO)4.14 The solution was then cooled to Ϫ80 ЊC for 4 h.
Orange-yellow microcrystals were obtained. They were sub-
sequently recrystallized from n-pentane (two to three times) to
yield pure crystalline Cl2Rh2(CO)2(cod). Yield 160–170 mg (90–
96%) for the crude and 140-150 mg (79–84%) for the recrystal-
lized product (Found: C, 28.1; H, 2.9; Cl, 15.7; Rh, 46.5. Calc.
for C10H12Cl2O2Rh2: C, 27.24; H, 2.74; Cl, 16.08; Rh, 46.68%).
IR [ν(CO), n-hexane] 2089vs, 2022vs cmϪ1. 1H NMR (C6D6, vs.
SiMe4): δ 4.2 (s, br, 4 H, CH), 2.0 (m, 4 H, CHH), 1.3 (m, 4 H,
CHH). 13C-{1H} NMR (C6D6, vs. SiMe4): δ 179.0 (CO, JC᎐Rh 73),
79.2 (CH, JC᎐Rh 11 Hz), 30.2 (CH2).
Experimental
All operations10 were carried out under a carefully dried,
deoxygenated and CO2-free Ar or CO atmosphere, using dried,
deoxygenated solvents. Infrared spectra were recorded on IR-75
(Carl Zeiss, Jena, Germany) and Bruker FT-IR IFS 113V
Preparation of (Ph3SiO)2Rh2(CO)2(cod) 6 by reaction (i)
The complex (Ph3SiO)2Rh2(CO)2(cod) 6 was prepared similarly
to 5 from 0.2 mmol quantities of (Ph3SiO)2Rh2(cod)2 and
(Ph3SiO)2Rh2(CO)4. Yields >90% for the crude and 75–80% for
the recrystallized product (Found: C, 60.3; H, 4.8; Rh 22.3.
† E-Mail: angelo@csmtbo.mi.cnr.it
J. Chem. Soc., Dalton Trans., 1997, Pages 4651–4655
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Fig. 1 Rietveld refinement plot for polycrystalline (OC)2RhCl2Rh(cod) in the 12 < 2θ < 93Њ range. Reflection markers and difference plot are also
included. The insert shows the full raw data
Calc. for C46H42O4Rh2Si2: C, 60.00; H, 4.60; Rh, 22.35%). IR
this solution, while stirred at r.t. Ph3SiONa (66 mg, 0.22 mmol)
was added in two to three portions during 15–20 min. The solu-
tion was analysed by infrared ν(CO) spectroscopy after 20, 40
and 60 min. After 40 min, the spectra showed the formation of
ca. 80% of 6 which did not change after 60 min. Reaction (iv)
1
[ν(CO), n-hexane] 2078vs, 2015vs cmϪ1. H NMR (C6D6, vs.
SiMe4): δ 7.97, 7.66, 7.24 (m, 30, CH, Ph), 4.18 (br s, 4 H, CH),
1.97 (br m, 4 H, CHH), 1.24 (br m, 4 H, CHH). 13C-{1H} NMR
(C6D6, vs. SiMe4): δ 180.1 (CO, JC᎐Rh 76), 138.0, 136.8, 136.1,
130.8 (CH, Ph), 79.8 (CH, JC᎐Rh 13 Hz), 31.3 (CH2).
1
was also followed by H NMR spectroscopy, using C6D6 as
solvent.
Preparation of (Ph3SiO)2Rh2(CO)2(cod) 6 by reaction (ii)
X-ray powder diffraction of (OC)2RhCl2Rh(cod)
The complex (Ph3SiO)2Rh2(CO)4 4 (4 mg, 0.05 mmol) was dis-
solved in dry n-hexane (10 cm3). To this solution, while stirring
at r.t. under an Ar atmosphere, cycloocta-1,5-diene C8H12 (52.0
µl, 45.9 mg, 0.085 mmol, 1.7 equivalents with respect to Rh2)
was added in three to four portions during 10 min periods. The
reaction mixture was then stirred for an additional 15–20 min.
A sample taken for spectroscopic analysis [IR, ν(CO) region]
showed almost complete disappearance of the absorption
bands of 4, while the ν(CO) bands of 6 were practically those of
the sole metal carbonyl species observed. The (spectroscopic)
yield was calculated to be higher than 90%. Complex 5 could
be prepared analogously from 3 and 1.5–1.7 molar excess of
cod, yield >95%.
The orange powder was deposited, with the aid of silicon
grease, on a silicon monocrystal cut normal to 511, minimizing
the scattering from the substrate. Given the limited amount of
the available material, the ‘infinitely thick’ limit, which allows
absorption corrections in Bragg–Brentano geometry to be neg-
lected, could not be reached; therefore, the average isotropic
‘thermal’ parameter, which is known to absorb most θ-
dependent systematic errors, may be slightly overestimated. The
sample was rotated at about 60 rpm about the scattering vector
in order to minimize preferred orientation effects. The spectrum
was collected under a nitrogen atmosphere to prevent sample
decomposition. X-Ray powder diffraction (XRPD) data were
taken with Cu-Kα radiation (λ = 1.5418 Å) on a Rigaku D III/
MAX horizontal scan powder diffractometer equipped with
parallel Soller slits and a graphite monochromator in the dif-
fracted beam. Data were collected in the 3 < 2θ < 93Њ range,
in the θ–2θ mode and step scan with ∆2θ = 0.02Њ and t = 12 s.
Slits used: DS, 1.0Њ; AS, 1.0Њ; RS, 0.15Њ. Standard peak-search
methods were used to locate the diffraction maxima.
Preparation of Cl2Rh2(CO)4 3 by reaction (iii)
The complex Cl2Rh2(CO)2(cod) 5 (44 mg, 0.1 mmol) was dis-
solved in dry n-hexane (10 cm3) under an Ar atmosphere. Over
this solution, while stirring at r.t., the atmosphere was changed
to a 1:1 mixture of Ar ϩ CO. An immediate color change to
orange was observed. The infrared spectroscopic analysis of the
reaction mixture showed complete conversion of 5 into 3 after
10 min. The same method for transforming 6 into 4 yielded 30–
40% of complex 6, accompanied by the formation of 20–30%
of Rh6(CO)16.15 We observed that if the gases were not perfectly
dry, humidity caused the formation of even higher quantities of
Rh6(CO)16. Using non-diluted CO also favoured the formation
of the latter compound.
Indexing was performed using DICVOL 9116 [a = 6.66,
b = 12.27, c = 16.10 Å; β = 92.18Њ; M(15) = 34.4; F(15) = 71.1
(0.007, 28)]. The space group P21/c was chosen from systematic
absences and subsequently confirmed by satisfactory refine-
ment. The integrated intensities were extracted by Le Bail’s
method,17 using EXTRA;18 the Rh atoms were located from a
Patterson synthesis, while the Cl, C, O and N atoms were
located from Fourier-difference maps and model building tech-
niques. The final refinements were performed using the Rietveld
method of GSAS19 and restraining Rh᎐C᎐O and Rh᎐cod
fragments to known geometries. A single isotropic atomic dis-
placement parameter was refined from the rhodium and chlor-
ine atoms [Uiso = 0.067(2) Å2], while light(er) atoms were
Preparation of (Ph3SiO)2Rh2(CO)2(cod) 6 by ion metathesis
[reaction (iv)]
The complex Cl2Rh2(CO)2(cod) 5 (44 mg, 0.1 mmol) was dis-
solved in dry n-hexane (10 cm3) under an Ar atmosphere. To
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J. Chem. Soc., Dalton Trans., 1997, Pages 4651–4655

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Table 1 Crystal data and refinement details for (OC)2RhCl2Rh(cod)
Compound
Formula
Mr/g molϪ1
System
Space group
a/Å
(OC)2RhCl2Rh(cod)
C10H12Cl2O2Rh2
440.8
Monoclinic
P21/c
6.659(1)*
12.274(1)
16.096(1)
92.176(5)
1314.7(2)
4
b/Å
c/Å
β/Њ
U/Å3
Fig. 2 An ORTEP21 drawing of the (OC)2RhCl2Rh(cod) molecule,
Z
with partial labelling scheme. Relevant bond distances (Å) and angles (Њ):
Rh(1) ؒ ؒ ؒ Rh(2) 3.252(7), Rh(2) ؒ ؒ ؒ Rh(2Ј) 3.55(1), Rh(1)᎐Cl(1)
2.409(4), Rh(1)᎐Cl(2) 2.400(4), Rh(2)᎐Cl(1) 2.396(13), Rh(2)᎐Cl(2)
2.409(13); Rh(1)᎐Cl(1)᎐Rh(2) 85.2(4), Rh(1)᎐Cl(2)᎐Rh(2) 85.1(3)
[Rh(2Ј) is centrosymmetrically related to Rh(2)]
F(000)
840
2.209
Cu-Kα (1.5418)
12–93
θ:2θ
4050
1133
0.116
0.154
ρcalc/g cmϪ3
Radiation (λ/Å)
2θ Range/Њ
Scan mode
No. of parameters
No. of reflections
Rp
derivatives clearly indicate that compounds 5 and 6 are the
thermodynamically favoured products in the reaction mixture,
to an extent which is significantly larger than that foreseen by
purely entropic (configurational, i.e. ‘mixing’) arguments. This
implies a small enthalpic stabilization of 5 (and 6), possibly due
to the larger polarity of the mixed-ligand derivatives. The
observed ‘instability’ to moisture and/or air contamination (in
solution and in the solid state), which increases with the car-
bonyl content in the order 1 < 5 < 3 (and, similarly, for siloxy
derivatives, 2 < 6 < 4), could be related to the availability of
easy degradation paths leading to stable carbonyl clusters [e.g.
Rh6(CO)16] but not to homoleptic poly(olefinic) derivatives.
Rwp
RF
0.085
* Estimated standard deviations of lattice parameters are derived from
the whole-pattern Rietveld refinement.
X
Rh
Rh
X
1 X = Cl
2 X = OSiPh3
(i)
OC
OC
X
X
CO
Rh
Crystallography
Rh
CO
As repeated attempts to grow single crystals of 5 suitable for
conventional X-ray diffraction methods failed, affording either
very small (maximum dimensions 20 × 20 × 100 µm), thus poor-
ly diffracting and untreatable (single?) crystals or macroscopic
aggregates of polycrystalline nature, we decided to characterize
5 via XRPD. Note that, in principle, we could also have
attempted an XRPD characterization of 6; however, the fore-
seen asymmetric unit volume of its crystalline phase (1015 Å3,
obtained by averaging that of 2 and 4)7 was discouraging, while
that of 5 (328 Å3, obtained by averaging that of 1 and 3)21 was
not.
3 X = Cl
4 X = OSiPh3
OC
X
X
Rh
Rh
OC
5 C = Cl
6 X = OSiPh3
OC
X
CO
Rh
Rh
(ii)
OC
X
CO
3 X = Cl
4 X = OSiPh3
(iii)
X-Ray powder diffraction methods revealed that 5 contains
two square-planar Rh atoms (see Fig. 2), one bearing two
terminal carbonyls and the other bound to the chelating cod
fragment (chelating, four-electron donors, η2,η2-cod ligands,
being idealized by two pseudo-atoms located at the midpoints
SiPh3
(iv)
OC
OC
Cl
OC
OC
O
Rh
Rh
Cl
Rh
Rh
O
SiPh3
of the C᎐C bonds), joined by two chlorine atoms bridging the
᎐
5
6
Rh ؒ ؒ ؒ Rh vector [Rh ؒ ؒ ؒ Rh 3.252(7) Å; average Rh᎐Cl 2.40(1)
Å]. The Rh2Cl2 core is markedly non-planar, the dihedral angle
about the Cl ؒ ؒ ؒ Cl hinge being 135.4(6)Њ, thus resembling much
more of the geometry of (OC)2RhCl2Rh(CO)2 [126.8(3)Њ],22a
rather than that of the (cod)RhCl2Rh(cod) (180Њ)22b analogues.
Note that L2M(µ-X)2ML2 fragments (M = Co, Rh or Ir;
X = Cl, Br, I, OR, SR or PR2; L = any two-electron donor
ligand), based on square-planar metal centers, are known to
belong to two distinct structural types, containing essentially
planar or markedly bent M2X2 cores, respectively, while inter-
mediate conformers are lacking; this bimodal distribution
shows two well separated peaks: a very sharp one for ‘planar’
conformations and a broader one for bent fragments, mainly
reflecting the variety of bridging (µ-X) and ancillary (L) lig-
ands. As a consequence, since 5 does not belong to the ‘planar’
class (for reasons which are not yet understood), it is not
surprising that it shows a dihedral angle similar to that of
(OC)2RhCl2Rh(CO)2.
Scheme 1
assigned the same value arbitrarily raised by 0.020 Å2. A more
detailed description of the ab initio XRPD methodology
applied to moderately complex molecular crystals can be found
in ref. 20. Crystal data and refinement details are reported
in Table 1. A final plot of the Rietveld refinement is shown in
Fig. 1.
CCDC reference number 186/722.
Results and Discussion
Synthesis
Scheme 1 pictorially shows the different routes and alternative
methods employed in the preparation of complexes Cl2Rh2-
(CO)2(cod) and (Ph3SiO)2Rh2(CO)2(cod), together with the
numbering scheme adopted for all reactants and products.
The high yield syntheses from symmetrically substituted
bis(diolefinic) (1 or 2) and tetracarbonyl (3 or 4, respectively)
If the presence of short Rh ؒ ؒ ؒ Rh intermolecular contacts
is taken as a criterion of similarity, 5, which packs as ‘dimers’
[Rh(2) ؒ ؒ ؒ Rh(2Ј) 3.55(1) Å], is intermediate between
J. Chem. Soc., Dalton Trans., 1997, Pages 4651–4655
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bound to cod by simple packing considerations. Such inform-
ation could be, in principle, exploited by joint Rietveld/steric
energy/packing energy refinements, but this feature has not
been implemented on currently available programs. The com-
mon use of restraints in complex Rietveld refinements (ensur-
ing chemical significance to the derived parameters), normally
obtained by introducing new observational equations of geo-
metrical nature, may be interpreted as a very rough approach of
optimization of a few intramolecular degrees of freedom. With-
in the GSAS approach, this corresponds to harmonic potential
wells for stretching modes (bond distances) with arbitrary force
constants; since bond angles and torsions cannot be restrained,
1,3 and 1,4 distances may be, in principle, included. However,
if the minima of the two cost functions (Rwp in the Rietveld
refinement and Etot in the MM program) are close, as in the
present case [compare Fig. 3(a) with the monodimensional cuts
of Rwp surface reported in Fig. 3(b) and 3(c)], even independent
Rietveld and steric energy/packing energy refinements can be
used to confirm the reliability of the proposed molecular con-
formation. A similar approach, involving only intermolecular
(i.e. packing and electrostatic) energies and very limited diffrac-
tion data sets (2θ < 30Њ, Cu-Kα radiation), has been used for
structural analysis of the monoclinic polymorph of titano-
phthalocyanine.26 Note that our computations represent only a
shortcut to the correct approach (the joint refinement) since,
even if the two minima match (which is not always true, mainly
because of the intrinsic weakness of the force field), their curv-
atures may not. Indeed, Rwp is much more sensitive to the
Rh ؒ ؒ ؒ Rh than to the Cl ؒ ؒ ؒ Cl deformation [compare Fig. 3(b)
and 3(c)], since it is more ‘expensive’ to displace high Z atoms,
contributing the most to the diffraction pattern. Conversely,
from Fig. 3(a), it is clear that the potential energy hypersurface
is softer along the Rh ؒ ؒ ؒ Rh direction rather than along the
Cl ؒ ؒ ؒ Cl.
Fig. 3 (a) A three-dimensional view of the potential energy hyper-
surface (kcal molϪ1, cal = 4.184 J), projected onto the Rh ؒ ؒ ؒ Rh vs.
Cl ؒ ؒ ؒ Cl plane (values in Å); (b) and (c): monodimensional cuts of
the Rwp hypersurface along the Rh ؒ ؒ ؒ Rh and Cl ؒ ؒ ؒ Cl directions,
respectively
(OC)2RhCl2Rh(CO)2 and (cod)RhCl2Rh(cod). Indeed, while
the former is a ‘polymer’ with Rh ؒ ؒ ؒ Rh contacts of 3.31 Å, no
short interactions are observed in the latter. A closer analysis
shows that short contacts invariably involve the Rh atoms
bound to carbonyls, thus suggesting that the presence of
(bulky) cod ligands requires long(er) Rh ؒ ؒ ؒ Rh contacts.
As meaningful Rietveld XRPD refinements require intro-
duction of numerous constraints on the geometrical values of
chemically known fragments, at least when working with con-
ventional instrumentation, only the packing and conformations
of the molecules, together with the heavy atom locations, can be
assessed with reasonable accuracy. The introduction of con-
straints normally drives the ‘molecular’ shape toward an ideal-
ized conformation with loss of structural details (which are
anyway unaccessible by PD) but hardly control intermolecular
contacts. For instance, at the end of the refinement we still
observe a rather short packing contact [namely, O(1) ؒ ؒ ؒ O(1Ј)
2.67(6) Å] which could be easily relaxed by small, but
unpredictable, structural changes.
For this reason, we have further checked the obtained results
by minimizing the steric energy of different molecular con-
formations in the actual crystal lattice, with a locally
developed23 version of Allinger’s MM3 program.24 On adopt-
ing the empirical force field for π-bonding ligands discussed in
ref. 25, avoiding any bias toward the planar or bent conform-
ations at the intramolecular level, all deformation paths of
the central Rh2Cl2 butterfly from the geometry determined by
XRPD substantially raised the overall (intramolecular ϩ pack-
ing) steric energy; this is pictorially shown in Fig. 3(a), which
contains a section of the potential energy hypersurface along
the Cl ؒ ؒ ؒ Cl and Rh ؒ ؒ ؒ Rh coordinates, all other degrees of
freedom being optimized at each (hyper)point. This does not
imply that the observed stereochemistry is dictated by packing
constraints but, rather, that the experimentally accessible lattice
parameters and symmetry alone may contain useful inform-
ation on the molecular stereochemistry. For instance, in the pres-
ent case, at the resolution stage where only the Rh2Cl2 core was
known, we could immediately devise which rhodium atom was
Conclusion
The preparation of complexes 5 and 6 complements our earlier
observations about the formation of dinuclear rhodium car-
bonyl complexes with two different anions in the bridging
position.4b
The existence of complexes 5, and especially 6, is of an add-
itional significance, since it shows that the greatest care should
be taken on formulating the Rh-containing surface species;
indeed, as demonstrated earlier7 and in this work, the actual
ligand environment of rhodium is found to be very sensitive to
the reaction conditions.
Once again, XRPD (from conventional laboratory equip-
ment) has been proven to be a useful tool in addressing struc-
tural problems which have no easy solution with standard tech-
niques. As a matter of fact, it is likely that new instrumentation
and sources (high brilliance synchrotrons and time of flight
neutrons) will soon raise the complexity of the organometallic
molecules which can be characterized by PD. Nevertheless,
even in the future, it will be the daily use of easily accessible
conventional instrumentation which will provide the organo-
metallic chemistry community with otherwise inaccessible
structural results,8 well beyond the conventional use of XRPD
as an ‘analytical’ tool.
Acknowledgements
Support of this work by the (Italian) Ministry of University
and Research (MURST 40%) is acknowledged. The technical
support of Mrs. G. Mezza and P. Illiano is also acknowledged.
References
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Received 2nd July 1997; Paper 7/04688E
J. Chem. Soc., Dalton Trans., 1997, Pages 4651–4655
4655