One-dimensional silver(I) coordination polymers containing cyclodiphosphazane, cis-{(o-MeOC6H4O)P(-N tBu)}2

Article abstract of DOI:10.1039/b704303a

The 1: 1 reaction between the cyclodiphosphazane cis-{(o-MeOC ₆H₄O)P(-N^tBu)}₂ (1) and AgOTf afforded one-dimensional Ag^I coordination polymer [Ag{-OTf-κO,κO}{-(o-MeOC₆H₄O)P(-N ^tBu)-κP,κP}₂]_∞ (2) containing bridging cyclodiphosphazane and trifluoromethanesulfonate (OTf) ligands. The 2: 1 reaction of 1 and AgOTf leads to the formation of simple mononuclear complex [Ag{OTf-κO,κO}({(o-MeOC₆H₄O)P(-N ^tBu)-κP}₂)₂] (3) in quantitative yield. Reaction of 1 with AgCN produces a strain-free zig-zag coordination polymer [({(o-MeOC₆H₄O)P(-N^tBu)-κP,κP} ₂)₂Ag(NCAgCN)]_∞ (4) irrespective of reaction stoichiometry and conditions. In complexes 3 and 4 cyclodiphosphazanes coordinate to Ag^I centers in a monodentate fashion. Single crystal structures were established for the Ag^I polymers 2 and 4. The Royal Society of Chemistry.

Full text of DOI:10.1039/b704303a

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PAPER
www.rsc.org/dalton | Dalton Transactions
One-dimensional silver(I) coordination polymers containing
cyclodiphosphazane, cis-{(o-MeOC6H4O)P(l-NtBu)}2
P. Chandrasekaran,a Joel T. Magueb and Maravanji S. Balakrishna*a
Received 21st March 2007, Accepted 11th May 2007
First published as an Advance Article on the web 30th May 2007
DOI: 10.1039/b704303a
The 1 : 1 reaction between the cyclodiphosphazane cis-{(o-MeOC6H4O)P(l-NtBu)}2 (1) and AgOTf
afforded one-dimensional AgI coordination polymer [Ag{l-OTf-jO,jO}{l-(o-MeOC6H4O)P(l-
NtBu)-jP,jP}2]∞ (2) containing bridging cyclodiphosphazane and trifluoromethanesulfonate (OTf)
ligands. The 2 : 1 reaction of 1 and AgOTf leads to the formation of simple mononuclear complex
[Ag{OTf-jO,jO}({(o-MeOC6H4O)P(l-NtBu)-jP}2)2] (3) in quantitative yield. Reaction of 1 with
AgCN produces a strain-free zig-zag coordination polymer [({(o-MeOC6H4O)P(l-NtBu)-
jP,jP}2)2Ag(NCAgCN)]∞ (4) irrespective of reaction stoichiometry and conditions. In complexes 3
and 4 cyclodiphosphazanes coordinate to AgI centers in a monodentate fashion. Single crystal
structures were established for the AgI polymers 2 and 4.
Introduction
Results and discussion
Rigid bridging multidentate ligands have been extensively used
for the construction of 1-D to 3-D metallopolymers and other
interesting self assemblies.1 These supramolecular complexes show
applications in catalysis, sensors, gas storage, as well as in
nanoscience.2 A variety of rigid multidentate ligands containing
nitrogen and/or sulfur donors have been designed and used in
supramolecular coordination chemistry,3 one significant example
being 4,4ꢀ-bipyridine and related systems.4 Although phosphorus-
donor ligands can stabilize a wide range of soft metal centers,
their utility for the construction of supramolecular and polymeric
structures is limited due to the non-availability of rigid ligand
frameworks with donor centers in favorable orientations.5
Synthesis and characterization
Reaction of cis-{(o-MeOC6H4O)P(l-NtBu)}2 (1) with AgOTf in
a 1 : 1 stoichiometry in dichloromethane at room temperature
affords the AgI coordination polymer [Ag{l-OTf-jO,jO}{l-
(o-MeOC6H4O)P(l-NtBu)-jP,jP}2]∞ (2) in 73% yield. Under
similar reaction conditions 2 : 1 reaction between 1 and AgOTf
produces mononuclear silver(I) complex [Ag{OTf-jO,jO}({(o-
MeOC6H4O)P(l-NtBu)-jP}2)2] (3) as shown in Scheme 1. The
31P NMR spectrum of 2 exhibits a broad signal at 116.6 ppm,
whereas compound 3 exhibits two broad signals at 139.9 ppm
and 112.8 ppm, respectively, for uncoordinated and coordinated
P centers of cyclodiphosphazane. The IR spectrum of each of
We have recently been exploring the reactivity and the
transition metal chemistry of cyclodiphosphazanes with donor
functionalities.6 The ability of these rigid four-membered P2N2
rings to act as 2e, 4e, 6e or 8e donors through various coordination
modes has resulted in the formation of species ranging from simple
mononuclear complexes to multinuclear clusters and coordination
polymers. These interesting results prompted us to use these four-
membered P2N2 ring systems with Group 11 metals which exhibit
attractive coordination architectures ranging from simple com-
plexes to multinuclear cages and coordination polymers. Although
AgI coordination polymers containing rigid sulfur and nitrogen
donor ligands are known,7 analogous compounds containing
phosphorus donors are less extensive. In this article, we report two
novel AgI coordination polymers with the cyclodiphosphazane cis-
{(o-MeOC6H4O)P(l-NtBu)}2 (1) showing both the monodentate
and the bridged bidentate coordination modes.
aPhosphorus Laboratory, Department of Chemistry, Indian Institute of Tech-
nology Bombay, Mumbai, 400076, India. E-mail: krishna@chem.iitb.ac.in;
Fax: +91 22 2572 3480; Tel: +91 22 2576 7181
bDepartment of Chemistry, Tulane University, New Orleans, Louisiana, LA,
70118, USA
Scheme 1 Synthesis of silver(I) complex of cyclodiphosphazane.
Dalton Trans., 2007, 2957–2962 | 2957
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complexes 2 and 3 show m(SO3) around 1256 cm−1 and 1028 cm−1
which clearly indicates the bidentate(O,O) mode of coordination
of the triflate anion.8 The mass spectrum of 3 shows a peak at m/z
1009.00, which corresponds to the (M − OTf) ion.
IR spectrum of the AgI polymer 3 shows a strong m(CN) band at
2143 cm−1 which is at a slightly lower frequency as compared to the
same in free AgCN (m(CN) = 2164 cm−1)10 due to the p-acceptor
nature of the cyclodiphosphazane. Complexes 2–4 are sensitive to
light and they decompose on exposure to light for a week to give
black metallic powder. The molecular structures of 2 and 4 are
confirmed by single-crystal X-ray diffraction studies, whereas the
proposed structure of 3 is based on NMR spectroscopy, elemental
analysis and mass spectrometry.
Reaction of
1
with AgCN in acetonitrile produces
a strain-free zig-zag polymer, [({l-(o-MeOC6H4O)P(l-NtBu)-
jP}2)2Ag(NCAgCN)]∞ (4), irrespective of the stoichiometry of
the reactants and the reaction conditions. In complex 2, the cy-
clodiphosphazane exhibits a bridging coordination mode whereas
the monodentate mode of coordination was observed in complexes
3 and 4. Complex 4 is stable in both solid and solution states and
is soluble in CH3CN, CH3COCH3, DMSO and partially soluble
in THF and CH2Cl2. The 31P NMR spectrum of 4 shows a single
resonance at 137.2 ppm even at −50 ◦C. Two different 31P signals
are expected for complex 4 due to the presence of coordinated
and free P centers in the cyclodiphosphazane ligand. Further, no
Ag–P coupling was observed even at −50 ◦C, which may be due to
the fluxional behavior in solution. Similar complexes show both
1J(107Ag–P) and (109Ag–P) values on the order of 500–600 Hz.9 The
Molecular structures of 2 and 4
Molecular structures of complexes 2 and 4 with atom numbering
schemes are shown in Fig. 1 and 2, respectively. Crystallographic
information and the details of the structure determination are
summarized in Table 1. The important bond distances and bond
angles for 2 and 4 are listed in Tables 2 and 3, respectively.
Crystals of complex 2 were obtained by slow diffusion of Et2O
into the dichloromethane solution of 2 at room temperature. In
Fig. 1 Section of the polymeric structure of 2. Thermal ellipsoids are at 50% probability. For clarity all substituents on phosphorus and nitrogen have
been omitted. View axes: 90.60X, 35.31Y, 95.23Z. Symmetry operation i = 3/2 − x, 1 − y, 1/2 + z, ii = 3/2 − x, −1 − y, −1/2 + z.
Fig. 2 (a) Structure of the asymmetric unit in 4. Thermal ellipsoids are at 50% probability. (b) Polymeric structure of 4. Thermal ellipsoids are at 50%
probability. For clarity all substituents on phosphorus and nitrogen have been omitted. View axes: 146.89X, −37.80Y, −110.49Z. Symmetry operation
i = 1/2 − x, −1/2 + y, 1/2 − z, ii = 1/2 − x, 1/2 + y, 1/2 − z, iii = 1/2 − x, 3/2 + y, 1/2 − z.
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Table 1 Crystal data and details of the structure determination for 2 and 4
2
4
Formula
fw
C46H64Ag2F6N4O14P4S2
C46H64Ag2N6O8P4
1168.65
Monoclinic
P21/n
16.482(1)
16.069(1)
22.312(2)
90
105.269(1)
90
5700.8(6)
8
1414.75
Orthorhombic
P212121
14.127(1)
19.570(2)
21.228(2)
90
90
90
5869(1)
4
1.601
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
qcalc/g cm−3
1.362
0.849
2400
l(MoKa)/mm−1
F(000)
0.929
2880
Crystal size/mm3
T/K
0.03 × 0.06 × 0.12
0.19 × 0.21 × 0.26
100
100
2h range/deg
1.7–24.8
23836
23838
−0.01(3)
0.0805 (F2 > 4r(F2))
0.1520
2.2–28.4
99847
14182
Total no. reflns
No. of indep. reflns [Rint = 0.036]
Flack parameter
a
R1
0.0427 (F2 > 4r(F2))
0.1129
1.03
b
wR2
GOF (F2)
1.09
a R = RꢁFo| − |Fcꢁ/R|Fo|. b wR2 = {[Rw(Fo − Fc2)/Rw(Fo2)2]}1/2; w = 1/[r2(Fo2) + (xP)2] where P = (Fo + 2Fc2)/3.
2
2
Table 2 Selected bond distances and bond angles for 2
Table 3 Selected bond distances and bond angles for 4
Bond angles/◦
Bond distances/A
Bond angles/◦
˚
˚
Bond distances/A
Ag1–P1
Ag1–P2
Ag2–P3
Ag2–P4
Ag1–O11
Ag1–O12
Ag2–O9
Ag2–O14
S1–O9
S1–O10
S1–O11
S1–C45
S2–O12
S2–O13
S2–O14
S2–C46
P1–N3
P1–N4
P2–N1
P2–N2
P3–N1
P3–N2
P4–N3
P4–N4
2.430(3)
2.447(3)
2.437(3)
2.442(3)
2.596(5)
2.390(5)
2.390(5)
2.546(5)
1.457(5)
1.417(5)
1.428(4)
1.793(8)
1.443(5)
1.417(5)
1.431(5)
1.796(9)
1.713(5)
1.692(5)
1.690(6)
1.692(5)
1.703(5)
1.695(6)
1.687(6)
1.686(5)
P1–Ag1–P2
P1–Ag1–O11
P1–Ag1–O12
P2–Ag1–O11
P2–Ag1–O12
O11–Ag1–O12
P3–Ag2–P4
P3–Ag2–O9
P3–Ag2–O14
P4–Ag2–O9
P4–Ag2–O14
O9–Ag2–O14
O9–S1–O11
O12–S2–O14
Ag1–O11–S1
Ag1–O12–S2
Ag2–O9–S1
Ag2–O14–S2
P1–N3–P4
136.85(6)
126.15(10)
97.81(11)
76.90(10)
118.72(11)
92.98(14)
141.09(6)
106.75(11)
109.81(10)
108.63(11)
88.56(10)
85.76(14)
113.6(3)
114.3(3)
142.8(3)
146.0(3)
130.2(2)
163.7(3)
96.6(3)
Ag1–P1
Ag1–P3
Ag1–N5
Ag1–N6
N5–C45
Ag2–C45
Ag2–C46
C46–N6
P1–N1
P1–N2
P2–N1
P2–N2
P3–N3
2.418(1)
2.423(1)
2.301(3)
2.340(3)
1.129(5)
2.042(3)
2.054(3)
1.124(4)
1.693(2)
1.682(2)
1.709(2)
1.712(2)
1.689(2)
1.687(2)
1.754(3)
1.694(2)
P1–Ag1–P3
P1–Ag1–N5
P3–Ag1–N6
N5–Ag1–N6
Ag1–N5–C45
N5–C45–Ag2
C45–Ag2–C46
Ag2–C46i–N6i
P1–N1–P2
134.06(2)
101.09(7)
95.35(7)
96.03(11)
152.0(3)
174.8(3)
173.86(13)
79.67(12)
96.92(11)
97.20(11)
82.46(11)
81.12(11)
96.30(13)
98.70(12)
81.75(11)
79.67(12)
P1–N2–P2
N1–P1–N2
N1–P2–N2
P3–N3–P4
P3–N4–P4
N3–P3–N4
N3–P4–N4
P3–N4
P4–N3
P4–N4
the type V (complex 2) containing two AgI ions bridged by both
the bisphosphines and anionic ligands are not known, whereas the
other structures of the type I–IV are routinely observed. In the
case of 2, the cyclodiphosphazane (1) and the triflate anions
form eight-membered rings [Ag(X-jO,jO)(1-jP,jP)Ag], which
are connected linearly to give a polymeric structure (2). The
majority of tetra-coordinated silver(I) polymers consist of two
different cyclic building blocks ([Ag(X-jO,jO)2Ag] and [Ag(P–
P-jP,jP)2Ag]), which are arranged alternate to give polymeric
complexes of the type I–IV. The silver(I) centers present in 2 are
four-coordinated (AgP2O2) with distorted tetrahedral geometry.
The tetrahedral angles vary from 136.85(6)◦ to 76.90(10)◦ at
the Ag1 center, whereas at the Ag2 center the angles vary from
141.09(6)◦ to 85.76(14)◦. The distortions in the coordination
geometries around Ag1 and Ag2 decrease the strain created during
P1–N4–P4
N3–P1–N4
N3–P4–N4
P2–N1–P3
97.5(2)
82.1(2)
83.1(2)
96.7(3)
P2–N2–P3
96.9(3)
complex 2, cyclodiphosphazane and trifluoromethanesulfonate
(OTf) ligands are bridging the two different silver(I) atoms to
give a chain-like 1-D polymeric structure as shown in Fig. 1. Each
repeat unit consists of two silver atoms bridged by cyclodiphosp-
hazane and OTf (O,O) ligands to form a chain of eight-membered
rings in a spirocyclic fashion.
The possible coordination modes for tri- and tetradentate AgI
polymers containing both bisphosphines and anionic ligands are
shown in Chart 1.11 Interestingly, the coordination polymers of
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the formation of the AgCN polymer, the cyclodiphosphazane
ligands play an ancillary role to stabilize the cyanometallated link-
ers. The structure of [Ag{l-OTf-jO,jO}{l-(o-MeOC6H4O)P(l-
NtBu)-jP,jP}2]∞ (2) is a rare example of both phosphines and
anions bridging the two silver atoms simultaneously to form the
spirocyclic chains. Presently, we are investigating the coordination
behavior of cyclodiphosphazanes with various gold(I) derivatives.
Experimental
General
All manipulations were performed under rigorously anaerobic
conditions using high vacuum manifolds and Schlenk techniques.
All the solvents were purified by conventional procedures and
freshly distilled and degassed prior to use.15 The compound cis-
{(o-MeOC6H4O)P(l-NtBu)}2 (1) was prepared according to the
published procedure.6 AgOTf and AgCN were purchased from
commercial sources and used as received. The H and 31P{ H}
NMR (d in ppm) spectra were recorded using a Varian Mercury
Plus spectrometer operating at the appropriate frequencies using
TMS and 85% H3PO4 as internal and external references, respec-
tively. IR spectra were recorded on a Nicolet Impact 400 FT-
IR instrument in KBr disks. Microanalyses were performed on a
Carlo Erba Model 1112 elemental analyzer. Mass spectrometry
experiments were carried out using a Waters Q-Tof micro-YA-
105. Melting points were recorded in capillary tubes and are
uncorrected.
Chart 1 Possible coordination modes for Ag polymers.
the formation of one dimensional polymer 2. The distance between
˚
Ag1 and Ag2 is 5.723 A which is too long for any Ag · · · Ag
1
1
bonding interactions.12 This is as expected since the rigidity of the
cyclodiphosphazane ligand enforces a relatively large metal–metal
separation when it functions as a bridging ligand. The normal span
of the triflate ligand when functioning in an O,Oꢀ-bridging mode
is less. Consequently it adopts an asymmetrical bridging mode
here presumably so as to form one relatively strong bond to silver.
The exocyclic phenyl substituents on phosphorus are arranged in
endo,exo fashion.
The X-ray quality single crystals of 4 were grown from CH3CN–
THF (1 : 1) solution at −30 ◦C. The molecular structure
of 4 consists of [(P2N2)2Ag]+ moieties linked by [NCAgCN]−
bridging unit in an alternating zig-zag fashion to form a one-
dimensional AgI coordination polymer (Fig. 2). The approximate
Synthesis of [Ag{l-OTf-jO,jO}{l-(o-MeOC6H4O)P(l-NtBu)-
jP,jP}2]∞ (2). A dichloromethane solution (15 cm3) of cis-{(o-
MeOC6H4O)P(l-NtBu)}2 (1) (114 mg, 0.25 mmol) was added
dropwise to a AgOTf (65.1 mg, 0.25 mmol) suspension in
dichloromethane (5 cm3) at room temperature. The colorless
reaction mixture was stirred further for 6 h with minimum light
exposure. The volume of the solution was reduced to 7 cm3, diluted
with 3 cm3 of diethyl ether and stored at −30 ◦C for a day to give a
white crystalline solid (130 mg, 73%). Mp 124–126 ◦C (decomp.).
C23H32N2O7F3P2SAg (707.4): calcd C 39.05, H 4.55, N 3.96, S 4.53;
found: C 39.17, H 4.82, N 3.76, S 4.69%. IR (KBr disk, cm−1):
1499 (s), 1456 (s), 1370 (m), 1256 (s), 1168 (s), 1028 (s), 893 (s).
1H NMR (400 MHz, CDCl3): dH = 7.32–6.86 (m, 8 H, Ph), 3.84
distances between the Ag1 · · · Ag1 and Ag1 · · · Ag1i atoms are
I
˚
˚
16.069 A and 10.087 A, respectively. Two different Ag cations
with different coordination numbers are present in molecule 4.
The Ag1 center adopts a distorted tetrahedral geometry being
coordinated by a phosphorus atom from each of two different
cyclodiphosphazane ligands and a nitrogen atom from each of
two cyanide units. The angles at silver vary from 134.06(2)◦
to 95.35(7)◦. The Ag2 center is di-coordinated being bound to
the carbon atoms of the two bridging cyanide groups with a
C45–Ag2–C46 angle of 173.86(13)◦. In a previously reported13
polymeric silver(I) complex, [(Cy3P)Ag(NCAgCN)]∞, the terminal
silver center is tri-coordinated whereas the corresponding Ag1
center in 4 is tetra-coordinated which may be due to the less bulky
nature of the cyclodiphosphazane as compared to PCy3. The Ag1–
1
(s, 6 H, OMe), 1.41 (s, 18 H, tBu) ppm. 31P{ H} NMR (121 MHz,
CDCl3): dP = 116.6 (br s) ppm.
Synthesis of [Ag{OTf-jO,jO}({(o-MeOC6H4O)P(l-NtBu)-
jP}2)2] (3). A dichloromethane (15 cm3) solution of cis-{(o-
MeOC6H4O)P(l-NtBu)}2 (1) (151 mg, 0.34 mmol) (7 cm3) was
added dropwise over a dichloromethane suspension of AgOTf
(43.2 mg, 0.17 mmol) at room temperature. The reaction mixture
was stirred for 4 h, concentrated to 10 cm3, diluted with 5 cm3
of diethyl ether and stored at −30 ◦C for a day to afford
product as a white crystalline solid (167 mg, 86%). Mp 146–
148 ◦C. C45H64N4O11F3P4SAg (1157.8): calcd C 46.68, H 5.57,
N 4.83, S 2.76; found: C 46.92, H 5.63, N 5.03, S 2.87%. IR (KBr
disk, cm−1): 1497 (vs), 1458(w), 1256 (s), 1201 (m), 1111 (m), 1026
(s), 905 (s). 1H NMR (400 MHz, CDCl3): dH = 7.30–6.85 (m, 16 H,
˚
˚
P1 and P2–Ag1 bond distances are 2.418(1) A and 2.423(1) A,
respectively, and are comparable with literature values.14 The
cyclodiphosphazane ligands in complex 4 show cis (endo,exo)
confirmation with slightly puckered P2N2 rings, as indicated by the
sum of the angles around the N center of the cyclodiphosphazane
(∼355◦).
Conclusions
In summary, we describe the synthesis and structures of two
novel AgI one-dimensional coordination polymers of cyclodiphos-
phazane. The bridging coordination mode of the rigid P2N2
ring favors the linear propagation of a polymeric chain whereas
the monodentate mode produces a zig-zag polymeric chain. In
1
Ph), 3.84 (s, 12 H, OMe), 1.42 (s, 36 H, tBu) ppm. 31P{ H} NMR
(161 MHz, CDCl3): dP = 139.9 (br s), 112.8 (br s) ppm. MS(EI):
m/z 1009.00 (M − OTf).
2960 | Dalton Trans., 2007, 2957–2962
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Synthesis of [Ag{NCAgCN}({(o-MeOC6H4O)P(l-NtBu)-
jP}2)2]∞ (4). A mixture of 1 (196 mg, 0.44 mmol) and AgCN
(58.4 mg, 0.44 mmol) in acetonitrile (25 cm3) was stirred under
reflux conditions for 6 h. The reaction mixture was cooled to
room temperature, concentrated to 10 cm3 under reduced pressure
and stored at −30 ◦C for a day to give a white crystalline product
(226 mg, 89%). Mp 110–112 ◦C. C23H32N3O4P2Ag (584.3): calcd C
47.27, H 5.51, N 7.19; found: C 47.32, H 5.47, N 7.47%. IR (KBr
Acknowledgements
We are grateful to the Department of Science and Technology
(DST), New Delhi for funding through grant SR/S1/IC-05/2003.
PC thanks CSIR for Research Fellowship. JTM thanks the
Louisiana Board of Regents through grant LEQSF(2002-03)-
ENH-TR-67 for purchase of the Bruker APEX CCD diffrac-
tometer and the Chemistry Department of Tulane University for
support of the X-ray laboratory.
1
disk, cm−1): 2143 [m(C≡N)]. H NMR (400 MHz, acetone-d6):
dH = 7.35–6.89 (m, 8 H, Ph), 3.86 (s, 6 H, OMe), 1.44 (s, 18 H,
1
tBu) ppm. 31P{ H} NMR (161 MHz, acetone-d6): dP = 137.2 (br
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X-Ray crystallography
Crystals of 2 and 4 were mounted in a Cryoloop with a drop
of Paratone oil and placed in the cold nitrogen stream of the
Kryoflex low temperature attachment of a Bruker Smart APEX
CCD diffractometer. Full spheres of intensity data were collected
as follows: for 2, three sets of 400 scans in x (0.5◦ per scan at
u = 0, 90 and 180◦) and two sets of 800 scans in u (0.45◦ per
scan at x = −30 and 210◦); for 4, three sets of 606 scans in
x (0.3◦ per scan at u = 0, 120 and 240◦). Intensity data were
collected using the SMART software package16 and these were
reduced to F2 values with the SAINT+ software17 which also
performed a global refinement of unit cell parameters using 7372
(for 2) and 8660 (for 4) reflections chosen from the full data set.
The crystal of 2 proved to be twinned and the integration of
the raw data was carried out with the two-component version
of SAINT+ using the two-component orientation file prepared
by CELL_NOW18 and with the cell parameters of the second
domain on the twin constrained to be identical to those of the
first domain. Multiple measurements of equivalent reflections
provided a basis for empirical absorption corrections (using the
programs TWINABS19 for 2 and SADABS20 for 4. In the case
of 2, the corrected F2 data were merged according to the point
group 222 but with the exclusion of those reflections for which
one or more of the symmetry equivalents was a composite. The
structures were solved by direct methods and refined by full-
matrix, least-squares procedures using the SHELXTL program
suite.21 For 2, the small size of the crystal resulted in there
being little useful diffraction data beyond 2h = 49.2◦ so with a
limited amount of high order data it was not feasible to carry
out a refinement of the light atoms with unrestricted anisotropic
displacement parameters. Instead, they were restrained to approx-
imate isotropic behavior. In the case of 4, two of the tert-butyl
groups are rotationally disordered over two resolved sites while
one of the P–O–R groups is also disordered. All three disordered
groups were refined subject to restraints that they approximate
idealized geometries. Details of the disorder are provided in the
CIF. Hydrogen atoms were placed in calculated positions (C–H =
˚
˚
0.95 A (aromatic rings) and 0.98 A (methyl groups)) and included
as riding contributions with isotropic displacement parameters
1.2 (aromatic) or 1.5 (methyl) times those of the attached carbon
atoms.
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2002, 1110–1118; (b) B. Punji, J. T. Mague and M. S. Balakrishna,
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CCDC reference numbers 641238 (2) and 641239 (4). For
crystallographic data in CIF or other electronic format see DOI:
10.1039/b704303a
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 2957–2962 | 2961
©

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2962 | Dalton Trans., 2007, 2957–2962
This journal is
The Royal Society of Chemistry 2007
©