Synthesis, spectroscopic studies and structural systematics of phosphine oxide complexes with Group II metal (beryllium-barium) nitrates

Article abstract of DOI:10.1039/b600301j

Complexes of the nitrates of beryllium, magnesium, calcium, strontium and barium with the phosphine oxides OPPh₃, Ph₂P(O)CH ₂P(O)Ph₂, and o-C₆H₄(P(O)Ph ₂)₂ have been prepared and characterised by analysis and IR spectroscopy and the structures of [Be(OPPh₃)₂(NO ₃)₂], [Mg(OPPh₃)₂(NO ₃)₂], [Ca{Ph₂P(O)CH₂P(O)Ph ₂}₂(NO₃)₂] and [Ca{o-C ₆H₄(P(O)Ph₂)₂}₂(NO ₃)₂] have been determined. The solution speciation has been probed by a combination of ¹H, ³¹P{¹H} and ⁹Be NMR spectroscopy and conductance measurements. The variation in speciation and stability from Be-Ba is interpreted in terms of changes in the charge/radius ratio of the cations - thus whilst Be and Mg interact strongly with the phosphinoyl ligands, strontium and especially barium have very limited affinity for these ligands, and the complexes are extensively dissociated in solution. the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006.

Full text of DOI:10.1039/b600301j

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www.rsc.org/njc | New Journal of Chemistry
Synthesis, spectroscopic studies and structural systematics of phosphine
oxide complexes with Group II metal (beryllium–barium) nitrates
Martin F. Davis,a William Levason,*a Raju Ratnani,*b Gillian Reid*a and
Michael Webstera
Received (in Durham, UK) 10th January 2006, Accepted 23rd February 2006
First published as an Advance Article on the web 21st March 2006
DOI: 10.1039/b600301j
Complexes of the nitrates of beryllium, magnesium, calcium, strontium and barium with the
phosphine oxides OPPh3, Ph2P(O)CH2P(O)Ph2, and o-C6H4(P(O)Ph2)2 have been prepared and
characterised by analysis and IR spectroscopy and the structures of [Be(OPPh3)2(NO3)2],
[Mg(OPPh3)2(NO3)2], [Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2] and [Ca{o-C6H4(P(O)Ph2)2}2(NO3)2]
1
have been determined. The solution speciation has been probed by a combination of H, 31P{1H}
9
and Be NMR spectroscopy and conductance measurements. The variation in speciation and
stability from Be–Ba is interpreted in terms of changes in the charge/radius ratio of the
cations—thus whilst Be and Mg interact strongly with the phosphinoyl ligands, strontium and
especially barium have very limited affinity for these ligands, and the complexes are extensively
dissociated in solution.
of Be–Ba. Nitrate coordinates readily to hard metal ions and a
Introduction
rich chemistry of Sc, Y and lanthanide nitrates with phosphine
oxides has been described8–11 which also provide comparison
The coordination chemistry of the heavier alkaline earth metal
cations Ca21, Sr21 and Ba21 remains relatively little explored,
data for the present study.
and the complexes with neutral ligands are mostly with crown
ethers, cryptands and podands,1–4 whilst there has been recent
Results and discussion
interest in charged bi- and poly-dentates such as diketonates
and poly-ether-alkoxides as CVD (chemical vapour deposi-
tion) precursors.2 Magnesium has attracted rather more atten-
Beryllium complexes
Beryllium (Be21 r = 34 pm) is much smaller even than Mg
tion, with particular emphasis on complexes with nitrogen
(Mg21 r = 78 pm) and usually has a coordination number of
r4. It is also the only metal in this group suited to NMR
studies with 9Be (I = 3/2, 100%, X = 14.05 MHz, Q = 5.2 ꢀ
10ꢁ30 m2, Dc = 78) readily observed.12 The reaction of
aqueous Be(NO3)2 with OPPh3 in a 1 : 2–4 ratio in methanol
in the presence of 2,2-dimethoxypropane as dehydrating
agent, followed by recrystallisation from acetone afforded
colourless crystals of [Be(OPPh3)2(NO3)2]. The complex was
previously described by de Bolster,6 although only analytical
and IR/Raman data were reported. The structure consists of
discrete molecules with Be in a four-coordinate environment
formed from two phosphine oxides and two monodentate
nitrate ligands (Table 1 and Fig. 1). The molecule has no
crystallographic symmetry. The angles at Be1 (103–1171) are
close to tetrahedral and the NO3 ligands are clearly mono-
dentate (Be–O–N 1221) with the N–Obridging distances ca. 0.08
A longer than the N–Oterminal. The Be–O–P angles (174, 1571)
are both large and different, presumably reflecting packing
requirements around the Be. The complex has a small molar
conductance LM = 7 Oꢁ1 cm2 molꢁ1 in 10ꢁ3 mol dmꢁ3
CH2Cl2 solutionw and the 31P{1H} NMR spectrum shows
two species present both 1 : 1 : 1 : 1 quartets at d = 38.2
(major) and 39.5 (minor) (2JBeP = 4 Hz) (Fig. 2b). The
polydentates as chlorophyll models.1,2 Beryllium, although
forming the bonds with the highest covalent character in this
group, also attracts little work, probably due to its perceived
high toxicity. As with related closed shell metal ions such as
those of Groups I and III and the lanthanides, the chemistries
in Group II are largely influenced by the charge/radius ratios
and the balance between maximising M–L interaction whilst
minimising inter-ligand repulsions. Often the most informative
studies result from examining how these factors influence the
chemistry down the group whilst the ligands are kept constant.
We recently reported studies of a series of homoleptic cations
with phosphine oxides and diphosphine dioxides,5 including
the four-coordinate [M(OPPh3)4]21(M = Mg, Ca, Sr or Ba),
five-coordinate [Mg{Ph2P(O)CH2P(O)Ph2}2(H2O)]21, six-co-
ordinate [M{Ph2P(O)CH2P(O)Ph2}3]21 (M = Ca or Sr) and
[M{o-C6H4(P(O)Ph2)2}3]21 (M = Ca, Sr or Ba) and seven-
coordinate [Sr{Ph2P(O)CH2P(O)Ph2}3(EtOH)]21. Only three
beryllium complexes, [Be(OPPh3)4]Y (Y = BF4 or ClO4) and
[Be(OPPh3)2(NO3)2] have been reported with limited charac-
terisation.6,7 In the present paper we extend these studies to
the complexes of the three phosphine oxides OPPh3,
Ph2P(O)CH2P(O)Ph2, and o-C6H4(P(O)Ph2)2 with the nitrates
a School of Chemistry, University of Southampton, Southampton,
UK SO17 1BJ
w 1 : 1 Electrolytes in CH2Cl2 have LM = 20–25 Oꢁ1 cm2 molꢁ1 and
2 : 1 electrolyes LM = ca. 35–45 Oꢁ1 cm2 molꢁ1 although lower values
are found with very large ions.
b Department of Pure and Applied Chemistry, M. D. S. University,
Ajmer, 305009, India
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Table 1 Selected bond lengths (A) and angles (1) for [Be(OPPh3)2
(NO3)2]
Be1–O1
Be1–O4
O1–N1
O4–N2
O2–N1
O3–N1
P–C
1.644(6)
1.648(6)
1.298(4)
1.298(4)
1.223(4)
1.215(4)
Be1–O7
Be1–O8
O7–P1
O8–P1
O5–N2
O6–N2
1.571(6)
1.609(6)
1.490(3)
1.495(3)
1.210(4)
1.224(4)
1.341(6)–1.396(7)
1.774(5)–1.788(5) C–C
O1–Be1–O4 105.7(3)
O1–Be1–O7 117.2(3)
O1–Be1–O8 107.5(4)
Be1–O1–N1 122.3(4)
Be1–O4–N2 121.5(3)
O1–N1–O2 118.1(5)
O1–N1–O3 117.7(5)
O2–N1–O3 124.2(5)
O4–N2–O5 118.4(4)
O4–N2–O6 118.8(4)
O5–N2–O6 122.8(5)
O4–Be1–O7 110.2(4)
O4–Be1–O8 103.4(3)
O7–Be1–O8 111.8(4)
Be1–O7–P1 173.6(3)
Be1–O8–P2 156.8(3)
O7–P1–C1 110.83(19)
O7–P1–C7 110.7(2)
O7–P1–C13 110.5(2)
O8–P2–C19 112.39(19)
O8–P2–C25 109.38(18)
O8–P2–C31 110.6(2)
C–P–C
107.0(2)–109.2(2)
Fig. 1 The structure of [Be(OPPh3)2(NO3)2] determined at 300 K,
showing the atom numbering scheme. Ellipsoids are drawn at the 35%
probability level and H atoms omitted for clarity.
corresponding 9Be NMR spectrum (Fig. 2a) shows a 1 : 2 : 1
triplet at d = þ0.68 and a weaker quartet (1 : 3 : 3 : 1) at
þ0.34 showing the two species are [Be(OPPh3)2(NO3)2] and
[Be(OPPh3)3(NO3)]1. On addition of excess OPPh3 to this
solution, the 31P{1H} NMR spectrum shows three resonances
with d = 28.0 (OPPh3), 38.2 ([Be(OPPh3)2(NO3)2]) and 39.5
([Be(OPPh3)3(NO3)]1), with the last now the major beryllium
containing species, and the solution has a significant conduc-
tance (LM = ca. 18 Oꢁ1 cm2 molꢁ1). Mass balance requires
range it could be obscured by the resonances of the phosphine
oxide complexes. Even with a large excess of OPPh3 some
[Be(OPPh3)2(NO3)2] was still present. Notably, exchange be-
tween OPPh3 and the complexes is slow even at room tem-
perature, which contrasts with the behaviour observed for the
other metal ions in this study. The known complex7
[Be(OPPh3)4][ClO4]2 has d(P) = 42.4 (2JBeP = 4 Hz) and the
tetrakis(ligand) cation did not appear to form in the nitrate
systems even with a large excess of ligand present. The
9
another beryllium species, but none was observed in the Be
spectrum (Fig. 2a), although given the small chemical-shift
Fig. 2 (a) The 9Be NMR and (b) 31P{1H} NMR spectra of [Be(OPPh3)2(NO3)2] in CH2Cl2 solution at 295 K; (c) 9Be NMR spectrum of
[Be(OPPh3)2(NO3)2] with excess OPPh3 in CH2Cl2 at 295 K.
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progressive shift of the 31P NMR resonance to high frequency
along the series [Be(OPPh3)2(NO3)2] o [Be(OPPh3)3(NO3)]1
o [Be(OPPh3)4]21 is consistent with increasing O-Be dona-
tion as the charge on the beryllium increases.
Table 2 Selected bond lengths (A) and angles (1) for [Mg(OPPh3)2
(NO3)2]
Mg1–O1
Mg1–O2
Mg1–O3
N1–O2
N1–O3
O1–Mg1–O1a
O1–Mg1–O2
O1–Mg1–O3
Mg1–O1–P1
C1–P1–C7
C1–P1–C13
C7–P1–C13
O2–N1–O4
1.9397(17)
2.0863(16)
2.1822(18)
1.275(2)
1.268(2)
99.47(11)
95.56(6)
155.05(6)
167.75(11)
108.68(11)
108.95(10)
108.77(10)
121.6(2)
P1–O1
P1–C1
P1–C7
P1–C13
N1–O4
O2–Mg1–O3
O2–Mg1–O2a
O3–Mg1–O3a
O1–P1–C1
O1–P1–C7
O1–P1–C13
O2–N1–O3
O3–N1–O4
1.4972(16)
1.802(2)
1.795(2)
1.798(2)
1.216(3)
60.42(6)
155.98(11)
86.79(10)
109.33(11)
111.07(10)
110.00(10)
115.42(18)
122.9(2)
The two diphosphine dioxide complexes [Be{Ph2P(O)CH2
P(O)Ph2}(NO3)2] and [Be{o-C6H4(P(O)Ph2)2}(NO3)2] were
obtained as cream powders from methanol solutions of the
constituents. The IR spectra (Experimental section) show only
coordinated phosphine oxide groups, and the bands assigned
as nitrate modes are generally similar to those in
[Be(OPPh3)2(NO3)2] indicating monodentate nitrato coordina-
tion and hence four-coordinate beryllium. In solution both are
non-conductors and show broad singlet 31P{1H} NMR reso-
nances, with larger coordination shifts than observed for the
1
2
Symmetry operation: a = ꢁx, y, ꢁ z.
heavier metals, consistent with the high charge/radius of Be21
.
bonded to a good approximation (ca. 5% difference in
Mg–O) and the Mg–O(P) agrees well with that found13 in
[MgCl2(Ph3PO)2] (1.9401(8) A) but is longer than the Mg–O
found in the homoleptic cation5 [Mg(OPPh3)4]21
(1.890(2)–1.919(2) A). The Mg–O–P (167.75(11)1) is some
101 larger than in the chloro-complex [MgCl2(Ph3PO)2] re-
flecting perhaps the larger steric bulk of the nitrate.
The absence of resolved beryllium coupling is probably attri-
butable to a combination of a very distorted tetrahedral
environment produced by these chelates on the very small
beryllium centre resulting in faster Be quadrupolar relaxation,
and the small coupling constants expected. The 9Be NMR
spectra are similarly singlets (W1/2 ca. 12 Hz) and the spectra
do not sharpen on cooling the solutions to 223 K.
In dry CH2Cl2 the 31P{1H} NMR spectrum at 295 K is a
broad singlet at d = 36.0 which sharpens on cooling and o233
K shows two resonances at d 36.2 and 33.9 (ratio ca. 10 : 1);
the values may be compared with the chemical shift observed5
in [Mg(OPPh3)4]21 of 41.6, showing that as expected, coordi-
nation of the nitrate anions results in a less electron-poor
magnesium centre and a corresponding shielding of the phos-
phorus. Addition of OPPh3 to the solution at 295 K produces
a broad feature whose chemical shift varies with the amount of
added phosphine oxide consistent with fast exchange. On
cooling to o210 K two resonances are resolved at d = 28.0
(OPPh3) and 34.0, the effects reversing on warming. The
species responsible for the d = 34.0 resonance is presumably
[Mg(OPPh3)x(NO3)2] (x = 3 or 4) since the solution remains
non-conducting (six-coordination could still be maintained by
switching the nitrate group(s) from bi- to mono-dentate
coordination). In spite of this, only [Mg(OPPh3)2(NO3)2] has
been isolated in the solid state. Different speciation between
the isolated solids and solutions in non-coordinating solvents
is also commonly found in Group 3 and lanthanide nitrate
complexes with phosphinoyl ligands.8–11
Magnesium complexes
In contrast to the tetrakis species formed by the heavier
alkaline earth nitrates (below), the reaction of magnesium
nitrate and four equivalents of OPPh3 in ethanol yields only
[Mg(OPPh3)2(NO3)2]. This species shows features due to co-
ordinated nitrate groups and OPPh3 in its IR spectrum
(Experimental section), and is a non-conductor in CH2Cl2
solution. Colourless crystals of the complex were obtained
from CH2Cl2/Et2O and the structure (Fig. 3 and Table 2)
consists of discrete molecules with Mg in a six-coordinate
environment formed from two phosphine oxides and two
bidentate nitrate ligands. The molecule has 2-fold crystallo-
graphic symmetry. The nitrate ligands are symmetrically
The complex [Mg{o-C6H4(P(O)Ph2)2}(NO3)2] was readily
isolated from reaction of either a 1 : 1 or 1 : 2 mol ratio of
Mg : ligand in ethanol, and the spectroscopic data (Experi-
mental section) are consistent with a neutral six-coordinate
magnesium centre. The 31P{1H} NMR spectrum of this com-
plex in CH2Cl2 is a singlet at d = 38.5 and is unchanged
on cooling the solution to 190 K. On adding excess
o-C6H4(P(O)Ph2)2 to the solution a new species with d =
35.7 is formed and the conductivity of the solution increases.
The [Mg{o-C6H4(P(O)Ph2)2}3]21 has5 d = 40.1 and is
therefore not the product; and the new species is possibly
[Mg{o-C6H4(P(O)Ph2)2}2(NO3)]NO3.
The reaction of a 1 : 2 molar ratio of Mg(NO3)2 ꢃ 6H2O :
Ph2P(O)CH2P(O)Ph2 in ethanol–CH2Cl2 gave a white powder
[Mg{Ph2P(O)CH2P(O)Ph2}2(NO3)2] ꢃ CH2Cl2. The solid state
structure is uncertain since repeated attempts from a variety of
Fig. 3 The structure of [Mg(OPPh3)2(NO3)2] showing the atom
numbering scheme. Ellipsoids are drawn at the 40% probability level
and H atoms omitted for clarity. Mg1 is located on a 2-fold axis.
1
2
Symmetry operation: a = ꢁx, y, ꢁ z.
ꢂc
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solvents failed to produce crystals suitable for an X-ray study.
The IR spectrum shows n(PO) at 1171(vs), 1165(sh) cmꢁ1 and
hence all PO groups are coordinated (Ph2P(O)CH2P(O)Ph2
has n(PO) at 1187 cmꢁ1), and there is no evidence for ‘free’
nitrate ions. The IR spectrum differs in detail, particularly in
the nitrate regions, from those of [M{Ph2P(O)CH2P(O)Ph2}2
(NO3)2] (M = Ca–Ba), but it is difficult to draw conclusions
due to the very different size and mass of the cations. Eight-
coordination as found for the heavier elements can be ruled
out due to the small size of the magnesium, and the most
Table 3 Selected bond lengths (A) and angles (1) for [Ca{Ph2P(O)
CH2P(O)Ph2}2(NO3)2]
Ca1–O1
Ca1–O2
Ca1–O3
Ca1–O4
P1–O1
2.313(7)
2.453(8)
2.358(8)
2.359(7)
1.487(7)
1.479(8)
Ca1–O5
Ca1–O6
Ca1–O8
Ca1–O9
P3–O3
2.496(10)
2.505(11)
2.560(10)
2.521(9)
1.483(9)
1.484(8)
P2–O2
P4–O4
P1–C13
P2–C13
N1–O5
N1–O6
N1–O7
O1ꢃ ꢃ ꢃO2
P–C (Ph)
1.814(10)
1.795(10)
1.242(15)
1.211(15)
1.215(14)
2.997(10)
1.757(11)–1.828(11)
P3–C38
P4–C38
N2–O8
N2–O9
N2–O10
O3ꢃ ꢃ ꢃO4
1.850(13)
1.798(11)
1.287(14)
1.223(14)
1.189(15)
3.041(10)
probable
formulation
is
[Mg{Ph2P(O)CH2P(O)Ph2}2
(k1-NO3)2]. The 31P{1H} NMR spectrum of this complex in
CH2Cl2 is a singlet at d = 34.1 and is unchanged on cooling
the solution to 190 K, and in contrast to most of the complexes
in this work, addition of Ph2P(O)CH2P(O)Ph2 to the solution
produces a spectrum with resonances at d = 34.1 and 25.0,
indicating exchange is slow on the NMR timescale. In 10ꢁ3
mol dmꢁ3 solution in CH2Cl2 the complex has a molar
conductivity of LM = 6 Oꢁ1 cm2 molꢁ1 consistent with a
non-electrolyte.
O1–Ca1–O2 77.9(2)
O3–Ca1–O4 80.3(3)
O1–Ca1–O4 156.2(3)
O2–Ca1–O3 78.1(3)
Ca1–O1–P1 139.5(4)
Ca1–O2–P2 135.7(4)
P1–C13–P2 114.0(5)
O–P–C(H2) 112.6(5)–113.2(5)
O5–Ca1–O6 47.7(4)
O8–Ca1–O9 49.8(3)
O6–Ca1–O8 75.5(4)
O5–Ca1–O9 110.0(5)
Ca1–O3–P3 136.5(5)
Ca1–O4–P4 138.7(4)
P3–C38–P4 115.2(7)
O–P–C (Ph) 109.7(5)–112.9(5)
powder [Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2]. The correspond-
ing strontium salt was made similarly except that the metal
nitrate was dissolved in the minimum of hot water and then
reacted with the diphosphine dioxide in ethanol. The com-
plexes are poorly soluble in alcohols but dissolve easily in
CH2Cl2 in which they are non-electrolytes. Crystals of
[Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2] were obtained from
CH2Cl2 layered with diethyl ether. The structure consists of
discrete molecules with Ca in an eight-coordinate environment
formed from two bidentate chelating phosphine oxides and
two bidentate nitrate ligands (Table 3 and Fig. 4). The
phosphine oxide ligand’s bite is ca. 791 in the six-membered
chelate ring. Conceptually replacing the nitrates by monoden-
tate ligands, the geometry can be described as a very distorted
octahedron with cis nitrates: for example the N1ꢃ ꢃ ꢃCa1ꢃ ꢃ ꢃN2
is 99.6(4)1. The nitrates are symmetrically bonded to Ca. The
Calcium, strontium and barium complexes
The reaction of calcium, strontium or barium nitrate with
OPPh3 in ethanol with a M(NO3)2 : OPPh3 ratio of 1 : Z 4
results, on concentration of the solutions, in white, air-stable
powders of composition [M(OPPh3)4(NO3)2]. The IR spectra
are very similar, showing broad strong features ca. 1180 cmꢁ1
assigned as n(PO) of the coordinated phosphine oxide (com-
pared to 1196 cmꢁ1 in OPPh3) and weaker features near 1300
and 815 cmꢁ1 attributed to coordinated nitrate groups9–11
(other expected bands from the nitrates are difficult to identify
due to the strong absorptions of the phosphine oxides). There
is no evidence for nitrate ions in the IR spectra. The 31P{1H}
NMR spectra of the complexes in dryz CH2Cl2 solution show
rather broad singlets with only small coordination shifts from
OPPh3, and the shifts are markedly less positive than in the
homoleptic cations previously reported.5 Addition of excess
OPPh3 to the solutions results in broad singlet resonances
indicative of fast exchange and these resonances remain un-
changed (apart from a small temperature drift) on cooling to
180 K in the case of M = Sr or Ba. However for M = Ca, two
resonances can be resolved o200 K attributed (from their
chemical shifts) to OPPh3 and [Ca(OPPh3)4(NO3)2], showing
that the nitrates are not displaced by the phosphine oxide, and
that no other complexes form in significant amounts. Consis-
tent with this, the complexes are non-electrolytes in dry
CH2Cl2 solution and the conductances do not increase on
adding OPPh3. Whilst the distinction of mono- and bi-dentate
nitrate coordination by IR spectroscopy is uncertain, it seems
likely that the three complexes have eight-coordinate geome-
tries with bidentate nitrate (cf. the preference for bidentate
nitrate in the lanthanides and Y complexes, except where steric
factors promote k1-NO3 binding).9–11
The reaction of Ca(NO3)2 ꢃ 4H2O with bis(diphenylphosphi-
noyl)methane in a 1 : 2.2 molar ratio in ethanol gave a white
Fig. 4 Structure of [Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2] showing the
atom numbering scheme. Ellipsoids are drawn at the 40% probability
level. To aid clarity, H atoms are omitted and C atoms are shown as
boundary ellipsoids.
z Addition of oxygen donor solvents including alcohols and water lead
to partial displacement of the OPPh3 and the formation of a mixture of
species.
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IR spectra of the Ca and Sr complexes are very similar and
almost certainly both have similar structures. The 31P{1H}
NMR spectrum of [Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2] in
CH2Cl2 solution at 295 K is a singlet at d = 29.9 (compare
Ph2P(O)CH2P(O)Ph2, d = 25.0). The spectrum is unchanged
down to 210 K, but below this temperature other features
appear and at 190 K, weak peaks at d 25.0 and 32.4 are present
in addition to the major feature at d 29.9. The minor species
are assigned to Ph2P(O)CH2P(O)Ph2 and [Ca{Ph2P(O)
CH2P(O)Ph2}3]21 (lit.5 32.6 at 295 K), respectively (mass
balance also requires some phosphinoyl ligand-free calcium
species). Addition of Ph2P(O)CH2P(O)Ph2 to the solution
results in a very broad resonance d ca. 27 at 295 K, but on
cooling to 190 K, the spectrum shows only features at d 25.0
and 32.4 suggesting that excess ligand converts the sample to
[Ca{Ph2P(O)CH2P(O)Ph2}3]21. The conductance of a solution
of [Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2] in CH2Cl2 is LM = 8
Oꢁ1 cm2 molꢁ1 and increases on adding excess diphosphine
dioxide to ca. 28 Oꢁ1 cm2 molꢁ1 consistent with the inferences
from the NMR study. The 31P{1H} NMR spectrum of
[Sr{Ph2P(O)CH2P(O)Ph2}2(NO3)2] in CH2Cl2 solution at 295
K is a singlet at d = 27.6 and this is little changed on cooling
to 190 K. Addition of Ph2P(O)CH2P(O)Ph2 to the solution
results in a very broad resonance d ca. 26 at 295 K, but on
cooling to 190 K broad features at d 25.0 and 28.0 are present.
The resonance5 of [Sr{Ph2P(O)CH2P(O)Ph2}3]21 is d 31.5,
suggesting that in contrast to calcium, the homoleptic cation
does not form.
Fig.
5
Structure of the Ca1 centred molecule of [Ca{o-C6H4
(P(O)Ph2)2}2(NO3)2] showing the atom numbering scheme. The other
(Ca2) molecule has a similar geometry. Ellipsoids are drawn at the
40% probability level and H atoms omitted for clarity. Ca1 (and
Ca2) is positioned on a 2-fold axis. Symmetry operation: a = 3/2 ꢁ x,
1
y, ꢁ z.
2
symmetry. The bidentate phosphine oxide has
a
(P)O–Ca–O(P) ligand bite of ca. 741, smaller than in the
previous example above, despite the larger seven-membered
ring. Conceptually replacing the nitrates by monodentate
ligands, the geometry can be described as a very distorted
octahedron with trans nitrates; for example the
N1ꢃ ꢃ ꢃCa1ꢃ ꢃ ꢃN1a is 155.10(1)1. The differences between the
two diphosphine dioxide structures presumably result from the
lack of any geometric preference from the closed shell calcium
ion and the different steric requirements of the two ligands.
The solution behaviour is similar to that described above for
the Ph2P(O)CH2P(O)Ph2 complexes, but differs in detail. The
calcium complex is a non-electrolyte in CH2Cl2 solution
(LM = 10 Oꢁ1 cm2 molꢁ1 and at 295 K the 31P{1H} NMR
spectrum is a singlet at d 35.0. At 190 K the major resonance
now at d 33.3 is accompanied by minor features at d 36.2, 34.2
and 31.0. Addition of o-C6H4(P(O)Ph2)2 to the solution shows
only a broad resonance, consistent with fast exchange at room
temperature, but at 190 K, four resonances are again present,
although those with d 36.2 and 31.0 are relatively much more
intense. Comparison with literature data5 allows assignments
The [M{o-C6H4(P(O)Ph2)2}2(NO3)2] (M = Ca, Sr) were
obtained similarly to the Ph2P(O)CH2P(O)Ph2 complexes. A
crystal structure of [Ca{o-C6H4(P(O)Ph2)2}2(NO3)2] estab-
lished that the structure consists of discrete molecules with
Ca in an eight-coordinate environment formed from two
bidentate chelating phosphine oxides and two bidentate ni-
trate ligands (Table 4 and Fig. 5). There are two chemically
similar but crystallographically distinct molecules in the asym-
metric unit and each molecule has 2-fold crystallographic
Table 4 Selected bond lengths (A) and angles (1) for [Ca{o-C6H4
(P(O)Ph2)2}2(NO3)2]
Ca1–O1
2.3208(18)
2.3866(19)
2.580(2)
Ca2–O6
2.3119(19)
2.4079(19)
2.563(2)
Ca1–O2
Ca2–O7
Ca1–O3
Ca2–O8
Ca1–O4
2.493(2)
Ca2–O9
2.460(2)
P1–O1
1.486(2)
P3–O6
1.486(2)
P2–O2
1.485(2)
P4–O7
1.489(2)
of the
d
36.2 and 31.0 resonances as [Ca{o-C6H4
N1–O3
1.262(3)
N2–O8
1.254(3)
N1–O4
1.262(3)
N2–O9
1.250(3)
(P(O)Ph2)2}3]21 and o-C6H4(P(O)Ph2)2, respectively, and the
resonance at d 33.3 is probably [Ca{o-C6H4(P(O)Ph2)2}2
(NO3)2]. The solution shows a marked increase in conductivity
in the presence of excess ligand (LM = 30 Oꢁ1 cm2 molꢁ1).
The 31P{1H} NMR data on solutions of [Sr{o-C6H4
(P(O)Ph2)2}2(NO3)2] show similar behaviour with a room
temperature resonance d = 32.9, splitting at o200 K into
four resonances at d 31.0, 32.2, 33.0, 36.3 in the approximate
ratio 1 : 2 : 2 : 4. The first is ‘free’ ligand and the last the
homoleptic cation [Sr{o-C6H4(P(O)Ph2)2}3]21, one of the in-
termediate shifts will be due to [Sr{o-C6H4(P(O)Ph2)2}2
(NO3)2]. Addition of o-C6H4(P(O)Ph2)2 to the solution results
in fast exchange, and even at 190 K, broad lines are still
N1–O5
1.226(3)
N2–O10
1.245(4)
P–C
1.791(3)–1.827(3)
2.866(3)
P–C
1.795(3)–1.835(3)
2.819(3)
O1ꢃ ꢃ ꢃO2
O6ꢃ ꢃ ꢃO7
O1–Ca1–O2
O1–Ca1–O3
O1–Ca1–O4
O2–Ca1–O3
O2–Ca1–O4
O3–Ca1–O4
Ca1–O1–P1
Ca1–O2–P2
O3–N1–O4
O3–N1–O5
O4–N1–O5
O–P–C
75.00(6)
O6–Ca2–O7
O6–Ca2–O8
O6–Ca2–O9
O7–Ca2–O8
O7–Ca2–O9
O8–Ca2–O9
Ca2–O6–P3
Ca2–O7–P4
O8–N2–O9
O8–N2–O10
O9–N2–O10
C–P–C
73.32(7)
83.82(7)
86.08(7)
130.26(7)
71.67(7)
131.97(7)
72.07(7)
73.11(6)
73.81(7)
50.31(6)
50.73(7)
149.88(13)
139.02(11)
117.6(3)
151.64(12)
137.77(12)
118.7(3)
121.7(3)
121.7(3)
120.7(2)
119.5(3)
108.45(12)–116.61(12)
102.75(13)–108.48(13)
ꢂc
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present indicating the low temperature limit has not been
reached.
(see also ref. 5), these are extensively dissociated in solution
and can only be isolated in the presence of an excess of
phosphine oxide in the solutions. Due to greater lability and
the unsuitability of the metal nuclei for NMR studies, the
solution behaviour of the Mg–Ba compounds is less easily
probed than that of beryllium, but the combination of low
temperature 31P NMR spectroscopy with molar conductance
measurements, and the effects of added excess phosphine
oxide, has led to a reasonably clear picture of the behaviour
in these systems. The occurrence of a mixture of species in
solution and a smaller number isolable as pure solids is also a
characteristic of other closed shell metal ions including Sc, Y
and the lanthanides.9–11
The affinity of barium nitrate for the diphosphine dioxides is
small. The reaction of Ba(NO3)2 with Z 3 equivalents of
Ph2P(O)CH2P(O)Ph2 in aqueous ethanol, followed by recrys-
tallisation of the product from methanol/CH2Cl2/diethyl ether
containing added Ph2P(O)CH2P(O)Ph2 (Ba : added ligand ca.
1 : 2) gave [Ba{Ph2P(O)CH2P(O)Ph2}2(NO3)2], although it
was difficult to obtain an analytically pure sample. Recrystal-
lisation in the absence of excess ligand, gave materials with low
and variable C, H content, which appeared to be mixtures of
this complex and barium nitrate. The 31P{1H} NMR spectrum
of [Ba{Ph2P(O)CH2P(O)Ph2}2(NO3)2] in CH2Cl2 solution at
295 K is a singlet at d = 25.2, only slightly shifted from that of
the diphosphine dioxide and little change occurred on low-
ering the temperature to 195 K, so that no conclusions about
solution speciation can be drawn. Repeated attempts to isolate
pure products from reaction of o-C6H4(P(O)Ph2)2 with
Ba(NO3)2 in a variety of solvents and using molar ratios of
Ba : ligand of up to 1 : 4 failed. The white powders isolated
had variable composition, and on dissolution in organic
solvents left a residue of Ba(NO3)2. Barium is substantially
larger than the other metals in this group (Ba21 r = 143 pm),
and the low charge/radius ratio will be diminished further by
coordination of the nitrate ions, leading to little affinity for the
neutral phosphinoyl ligands. Complexation with o-C6H4
(P(O)Ph2)2 clearly occurs since the impure solids show no
evidence of uncoordinated diphosphine dioxide in the IR
spectra, but in solution the complex appears to be extensively
dissociated, for example the 31P{1H} NMR spectrum shows a
singlet resonance little shifted from that of the ligand even at
190 K, and under such conditions whether a pure complex can
by crystallised from the solution will depend upon the relative
solubilities of the constituents.
Experimental
The metal nitrates, Ba(NO3)2, Sr(NO3)2, Ca(NO3)2 ꢃ 4H2O and
Mg(NO3)2 ꢃ 6H2O and Ph3PO were obtained from Aldrich and
used as received. Aqueous beryllium nitrate (35 wt%) was also
obtained from Aldrich. The o-C6H4(P(O)Ph2)2 and
Ph2P(O)CH2P(O)Ph2 were made by SnI4 catalysed air-oxida-
tion of the corresponding diphosphines.14 IR spectra were
recorded as Nujol mulls on a Perkin Elmer PE 983G spectro-
meter, 1H NMR spectra in CDCl3 solutions on a Bruker
9
AV300, 31P{1H} and Be NMR were obtained from CH2Cl2/
5%CD2Cl2 solutions referenced, respectively to external 85%
H3PO4 and aqueous [Be(H2O)4]21 15 on a Bruker DPX400.
Microanalytical measurements were performed by the micro-
analysis service of Strathclyde University. Conductance mea-
surements were made as described previously,9 using CH2Cl2
distilled from CaH2.
CAUTION: Beryllium compounds are carcinogenic and
particularly hazardous as dust or aerosols. Appropriate pre-
cautions should be observed.
Conclusions
[Be(OPPh3)2(NO3)2]
The greatest variable in this series of compounds is the size of
the metal centres—taking the metal ionic radii as illustrating
this effect—the values1 range from 34 pm at Be21 to 143 pm at
Ba21, and hence the charge/radius ratio falls dramatically
down the group. The data above show that Be is exclusively
four-coordinate, has a high affinity for the neutral ligands, and
that ligand exchange is slow on the NMR timescale in solu-
tion. The combination of 9Be and 31P NMR with conductance
measurements also provided a clear picture of solution specia-
tion. The larger Mg (Mg21 r = 78 pm) prefers six-coordina-
tion, but still binds both the neutral ligands and the nitrates
strongly, although the OPPh3/Mg(NO3)2 system shows fast
exchange on the NMR timescale at room temperature. The
larger Ca (Ca21 r = 106 pm) and Sr (Sr21 r = 127 pm)
produce labile complexes which are undergoing fast exchange
in solution except at very low temperatures, and the mixture of
species present in solution shows reduced discrimination be-
tween the neutral phosphine oxide and charged nitrate ligands.
Notably, despite the mixture of species in the solution, only
the neutral eight-coordinate complexes have been isolated in
the solid state. The very large Ba has little affinity for the
phosphine oxides and although some examples were isolated
An aliquot (0.5 mmol) of the commercial Be(NO3)2 aqueous
solution (35 wt%) was diluted with water (2 mL) and added to
a solution of OPPh3 (0.28 g, 1.0 mmol) in ethanol (20 mL) and
2,2-dimethoxypropane (5 mL). The clear solution was heated
to reflux for 20 min and then the solvent removed in vacuo.
The viscous oil obtained was dissolved in warm acetone (15
mL), diethyl ether added until turbidity was seen, and then
allowed to stand. Crystals separated after a few h and these
were filtered off and rinsed with diethyl ether, and dried in
vacuo. Yield 0.27 g, 78%. Calc. for C36H30BeN2O8P2 : C, 62.7;
1
H, 4.4; N, 4.1. Found: C, 61.3; H, 4.25; N, 4.4%. H NMR
(CDCl3, 300 K): d 7.3–7.7 (m). 31P{1H} NMR (CH2Cl2, 300
K): d 38.2 (1 : 1 : 1 : 1 quartet, 2J = 4 Hz), 39.5 (1 : 1 : 1 :
1, 2J = 4 Hz), see text. 9Be NMR (CH2Cl2, 300 K): d 0.68 (t,
2J = 4 Hz), 0.34 (quartet, 2J = 4 Hz). IR (Nujol/cmꢁ1):
(possible nitrate bands are italicised) 1452(vs,br), 1342(sh),
1312(s), 1215(m), 1169(br){PQO}, 1165(m){PQO}, 1121(m),
1076(m), 970(w), 843(w), 811(s), 795(s), 752(m), 691(m),
601(s), 516(vs), 438(m). LM (10ꢁ3 mol dmꢁ3 CH2Cl2) =
7 Oꢁ1 cm2 molꢁ1; with excess ligand LM (10ꢁ3 mol dmꢁ3
CH2Cl2) = 18 Oꢁ1 cm2 molꢁ1
.
ꢂc
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[Mg(OPPh3)2(NO3)2]
a solution of Ph2P(O)CH2P(O)Ph2 (0.21 g, 0.5 mmol) in
ethanol (20 mL) and 2,2-dimethoxypropane (5 mL). The clear
solution was heated to reflux for 20 min and then the solvent
removed in vacuo to leave a waxy residue. This was stirred with
diethyl ether (10 mL) for 2 h, the diethyl ether syringed off and
discarded, and the waxy solid dissolved in dichloromethane
(10 mL). The solution was decanted from any insoluble
material and taken to dryness in vacuo to yield a cream
powder. Yield 0.19 g, 69%. Calc. for C25H22BeN2O8P2 ꢃ
CH2Cl2: C, 49.2; H, 3.8; N, 4.4. Found: C, 49.2; H, 4.3; N,
4.4%. 1H NMR (CDCl3, 300 K): d 7.2–7.9 (m), 5.2 (s)
(CH2Cl2), 3.8 (m). 31P{1H} NMR (CH2Cl2, 300 K): d 40.7
Magnesium nitrate hexahydrate (0.045 g, 0.18 mmol) was
dissolved in absolute ethanol (10 mL) and a solution of OPPh3
(0.197 g, 0.74 mmol) in ethanol (10 mL) added and the mixture
gently refluxed. The solution was concentrated to ca. 5 mL and
diethyl ether added dropwise until precipitation occured, when
the mixture was left to stand for 12 h. The white solid
produced was filtered off, rinsed with diethyl ether (10 mL)
and dried in vacuo. Yield 0.10 g, 80%. Calc. for
C36H30MgN2O8P2: C, 61.3; H, 4.3; N, 4.0. Found: C, 61.6;
H, 4.1; N, 3.8%. 1H NMR (CDCl3, 300 K): d 7.2–7.7 (m).
31P{1H} NMR (CH2Cl2, 300 K): d 36.0 (s), (210 K) 36.2, 33.9
(ratio 10 : 1). IR (Nujol/cmꢁ1): 1350(sh), 1299(s), 1206(w),
1183(br){PQO}, 1153(s), 1028(m), 997(w), 817(s), 744(m),
689(m), 538(vs). LM (10ꢁ3 mol dmꢁ3 CH2Cl2) = 1.5 Oꢁ1
9
(s). Be NMR (CH2Cl2, 300 K): d 0.91 (s). IR (Nujol/cmꢁ1):
1450(s,br), 1346(m), 1308(m), 1259(m), 1168(sh){PQO},
1156(s){PQO}, 1121(m), 1022(m), 966(w), 890(m), 845(w),
806(sh), 792(s), 736(s), 670(w), 503(s). LM (10ꢁ3 mol dmꢁ3
cm2 molꢁ1
.
CH2Cl2) = 2 Oꢁ1 cm2 molꢁ1
.
[Ca(OPPh3)4(NO3)2]
[Mg{Ph2P(O)CH2P(O)Ph2}2(NO3)2]
This was made similarly from calcium nitrate tetrahydrate and
OPPh3 in absolute ethanol. White powder. Yield 65%. Calc.
for C72H60CaN2O10P4: C, 67.2; H, 4.7; N, 2.2. Found: C, 67.3;
H, 4.4; N, 2.2%. 1H NMR (CDCl3, 300 K): d 7.2–7.7 (m).
31P{1H} NMR (CH2Cl2, 300 K): d 31.0 (s). IR (Nujol/cmꢁ1):
1572(w), 1345(sh), 1315(m), 1179(s){PQO}, 1171(sh){PQO},
1120(m), 1033(w), 1032(w), 998(w), 975(m), 822(m), 740(s),
693(s), 543(vs). LM (10ꢁ3 mol dmꢁ3 CH2Cl2) = 1.0 Oꢁ1
Solutions of Mg(NO3)2 ꢃ 6H2O (0.026 g, 0.11 mmol) in ethanol
(10 mL) and Ph2P(O)CH2P(O)Ph2 (0.11 g, 0.26 mmol) in
CH2Cl2 (15 mL) were mixed and heated to reflux. The solution
was cooled, concentrated in vacuo to ca. 5 mL and diethyl
ether (5 mL) added to precipitate a white powder, which was
filtered off, rinsed with diethyl ether and dried. Yield 0.075 g,
64%. Calc. for C50H44MgN2O10P4 ꢃ CH2Cl2: C, 57.2; H, 4.3;
1
cm2 molꢁ1
.
N, 2.6. Found: C, 56.8; H, 4.6; N, 2.4%. H NMR (CDCl3,
300 K): d 7.2–7.7 (m), 5.4 (s), 3.8 (br). 31P{1H} NMR (CH2Cl2,
300 K): d 34.1 (s); (190 K) 34.6 (s). IR (Nujol/cmꢁ1): 1340(m),
1308(m), 1260(m), 1172(s){PQO}, 1165(sh){PQO}, 1119(m),
994(w), 843(w), 815(sh), 795(s), 734(s), 670(s), 543(m), 502(s).
[Sr(OPPh3)4(NO3)2]
Strontium nitrate (0.034 g, 0.16 mmol) was dissolved in the
minimum amount of hot water (ca. 2 mL) and the solution
added to a stirred solution of OPPh3 (0.17 g, 0.64 mmol) in
absolute ethanol (20 mL) which was then heated to reflux.
Concentration to ca. 5 mL resulted in the precipitation of a
white powder, which was filtered off, rinsed with diethyl ether
(5 mL) and dried in vacuo. Yield 0.12 g, 56%. Calc. for
C72H60N2O10P4Sr: C, 65.2; H, 4.6; N, 2.1%. Found: C, 64.2;
H, 4.1; N, 2.2%. 1H NMR (CDCl3, 300 K): d 7.2–7.7 (m).
31P{1H} NMR (CH2Cl2, 300 K): d 29.0(s). IR (Nujol/cmꢁ1):
1576(w), 1345(sh), 1307(m), 1183(br,s){PQO}, 1169(sh),
1120(m), 1070(w), 1035(w), 973(m), 857(w), 814(m), 740(s),
697(s), 541(vs). LM (10ꢁ3 mol dmꢁ3 CH2Cl2) = 0.5 Oꢁ1 cm2
L
M (10ꢁ3 mol dmꢁ3 CH2Cl2) = 6 Oꢁ1 cm2 molꢁ1; with excess
ligand LM (10ꢁ3 mol dmꢁ3 CH2Cl2) = 9 Oꢁ1 cm2 molꢁ1
.
[Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2]
Ca(NO3)2 ꢃ 4H2O (0.025 g, 0.11 mmol) was dissolved in etha-
nol (10 mL) and a solution of Ph2P(O)CH2P(O)Ph2 (0.11 g,
0.26 mmol) in CH2Cl2 (5 mL) added and the mixture stirred
for 2 h. Concentration to small volume (ca. 5 mL) and slow
addition of diethyl ether (5 mL) gave a white solid, which was
filtered off, rinsed with diethyl ether and dried in vacuo. Yield.
0.058 g, 49%. Calc. for C50H44CaN2O10P4 ꢃ CH2Cl2: C, 56.6;
H, 4.3; N, 2.6. Found: C, 55.1; H, 3.9; N, 2.6%. 1H NMR
(CDCl3, 300 K): d 7.2–7.7 (m), 5.4 (s) (CH2Cl2), 3.8 (t).
31P{1H} NMR (CH2Cl2, 300 K): d 29.9 (s); (190 K) 25.0,
29.9, 32.4; ratio ca. 2 : 1 : 10. IR (Nujol/cmꢁ1): 1360(sh),
1303(m), 1168(s){PQO}, 1121(m), 967(m), 935(m), 892(m),
846(w), 825(m), 774(s), 543(vs), 506(s). LM (10ꢁ3 mol dmꢁ3
CH2Cl2) = 8.0 Oꢁ1 cm2 molꢁ1; with excess ligand LM
molꢁ1
.
[Ba(OPPh3)4(NO3)2]
This was made similarly to the strontium complex as a white
powder. Yield 65%. Calc. for C72H60BaN2O10P4: C, 62.9; H,
4.4; N, 2.0. Found: C, 61.4; H, 4.1; N, 2.3%. 1H NMR
(CDCl3, 300 K): d 7.2–7.7 (m). 31P{1H} NMR (CH2Cl2, 300
K): d 30.0 (s). IR (Nujol/cmꢁ1): 1590(w), 1364(sh), 1350(sh),
1307(m), 1183(br,s){PQO}, 1120(m), 1093(w), 1072(w),
1028(w), 996(w), 970(m), 864(m), 846(m), 816(m), 756(s),
697(s), 540(vs). LM (10ꢁ3 mol dmꢁ3 CH2Cl2) = 1.0 Oꢁ1 cm2
(10ꢁ3 mol dmꢁ3 CH2Cl2) = 25.0 Oꢁ1 cm2 molꢁ1
.
[Sr{Ph2P(O)CH2P(O)Ph2}2(NO3)2]
This was made similarly to [Sr(OPPh3)4(NO3)2] using a 1 : 2.2
mol ratio of Sr(NO3)2 : Ph2P(O)CH2P(O)Ph2. Yield 58%.
Calc. for C50H44N2O10P4Sr ꢃ CH2Cl2: C, 54.2; H, 4.1; N, 2.5.
Found: C, 54.0; H, 4.0; N, 2.3%. 1H NMR (CDCl3, 300 K): d
7.2–7.7 (m), 5.4 (s) (CH2Cl2), 3.8 (t). 31P{1H} NMR (CH2Cl2,
300 K): d 27.6 (s). IR (Nujol/cmꢁ1): 1360(sh), 1311(m),
molꢁ1
.
[Be{Ph2P(O)CH2P(O)Ph2}(NO3)2]
An aliquot (0.5 mmol) of the commercial 35 wt% Be(NO3)2
aqueous solution was diluted with water (2 mL) and added to
ꢂc
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1260(w), 1192(sh){PQO}, 1168(s,br){PQO}, 1120(m),
1020(w), 935(w), 846(w), 798(m), 775(m), 737(m), 563(vs),
to reflux, cooled and stirred for 1 h. Concentration to 5 mL
and dropwise addition of diethyl ether (ca. 10 mL) produced a
white precipitate, which was filtered off, rinsed with diethyl
ether (5 mL) and dried in vacuo. Yield 0.055 g, 91%. Calc. for
C30H24MgN2O8P2.: C, 57.3; H, 4.3; N, 4.1. Found: C, 57.5; H,
3.8; N, 4.5%. 1H NMR (CDCl3, 300 K): d 7.2–7.7 (m).
31P{1H} NMR (CH2Cl2, 300 K): d 38.5 (s), unchanged to
190 K. IR (Nujol/cmꢁ1): 1342(sh), 1306(m), 1165(vs){PQO},
1115(s), 1100(w), 1030(m), 995(w), 887(m), 816(w), 746(s),
690(s), 563(m), 547(s), 530(s). LM (10ꢁ3 mol dmꢁ3 CH2Cl2)
= 4.5 Oꢁ1 cm2 molꢁ1; with excess ligand LM (10ꢁ3 mol dmꢁ3
506(s). LM (10ꢁ3 mol dmꢁ3 CH2Cl2) = 8 Oꢁ1 cm2 molꢁ1
;
with excess ligand LM = 12 Oꢁ1 cm2 molꢁ1
.
[Ba{Ph2P(O)CH2P(O)Ph2}2(NO3)2]
This was made similarly to the strontium analogue but using a
1 : 3 Ba : ligand ratio. The complex was recrystallised from
methanol/CH2Cl2/diethyl ether containing excess diphosphine
dioxide. Yield 63%. Calc. for C50H44BaN2O10P4 ꢃ CH2Cl2: C,
51.9; H, 3.9; N, 2.4. Found: C, 50.8; H, 4.3; N, 2.2%. 1H NMR
(CDCl3, 300 K): d 7.2–7.7 (m), 5.4 (s), 3.8 (br,s). 31P{1H}
NMR (CH2Cl2, 300 K): d 25.0 (s). IR (Nujol/cmꢁ1): 1330(sh),
CH2Cl2) = 18.0 Oꢁ1 cm2 molꢁ1
.
1307(m),
1260(m),
1193(s){PQO},
1168(s,br){PQO},
[Ca{o-C6H4(P(O)Ph2)2}2(NO3)2]
1120(m), 1027(m), 935(w), 812(w), 799(s), 775(m), 737(m),
565(m), 512(s). LM (10ꢁ3 mol dmꢁ3 CH2Cl2) = 4 Oꢁ1 cm2
This was made similarly. Yield 87%. Calc. for C60H48
CaN2O10P4: C, 64.3; H, 4.3 : N, 2.5. Found: C, 64.0; H, 4.0;
molꢁ1; with excess ligand LM = 8 Oꢁ1 cm2 molꢁ1
.
1
N, 2.7%. H NMR (CDCl3, 300 K) : d 7.2–7.7 (m). 31P{1H}
NMR (CH2Cl2, 300 K): d 35.0; (190 K) 36.2, 34.5, 33.4, 31.0;
ratio ca. 1 : 3 : 10 : 1. IR (Nujol/cmꢁ1) : 1350(sh), 1303(m),
1260(w), 1170(vbr,s){PQO}, 1115(s), 1100(m), 1035(m),
997(w), 820(m), 746(s), 690(m), 559(s), 542(s), 532(s). LM
(10ꢁ3 mol dmꢁ3 CH2Cl2) = 10 Oꢁ1 cm2 molꢁ1; with excess
[Be{o-C6H4(P(O)Ph2)2}(NO3)2]
This was made similarly to the Ph2P(O)CH2P(O)Ph2 analogue
as a cream powder in 65% yield. Calc. for C30H24BeN2O8P2.:
1
C, 58.9; H, 4.0. Found: C, 58.9; H, 4.4%. H NMR (CDCl3,
300 K): d 7.2–7.7 (m). 31P{1H} NMR (CH2Cl2, 300 K): d 44.2
ligand LM = 33 Oꢁ1 cm2 molꢁ1
.
9
(s). Be NMR (CH2Cl2, 300 K): d 0.98 (s). IR (Nujol/cmꢁ1):
1436(vs,br), 1363(m), 1311(m), 1259(m), 1163(vs,br){PQO},
1121(s), 1095(m), 1020(m), 990(w), 898(m), 811(sh), 798(s),
735(s), 691(s), 560(sh), 546(s), 531(s). LM (10ꢁ3 mol dmꢁ3
[Sr{o-C6H4(P(O)Ph2)2}2(NO3)2]
This was made similarly. Yield 87%. Calc. for
C60H48N2O10P4Sr: C, 61.7; H, 4.1; N, 2.4. Found: C, 62.2;
H, 4.0; N, 2.2%. 1H NMR (CDCl3, 300 K): d 7.2–7.7 (m).
31P{1H} NMR (CH2Cl2, 300 K): d 32.9; (190 K) 31.0, 32.2,
33.0, 36.3; ratio 1 : 2 : 2 : 4. IR (Nujol/cmꢁ1): 1350(sh),
1306(m), 1258(w), 1178(vbr,s){PQO}, 1115(m), 1077(m),
1035(w), 997(w), 814(s), 746(s), 691(s), 653(w), 557(s), 554(s),
CH2Cl2) = 3 Oꢁ1 cm2 molꢁ1
.
[Mg{o-C6H4(P(O)Ph2)2}(NO3)2]
Mg(NO3)2 ꢃ 6H2O (0.026 g, 0.11 mmol) was dissolved in
ethanol (10 mL) and a solution of o-C6H4(P(O)Ph2)2 (0.050
g, 0.11 mmol) in CH2Cl2 (5 mL) added and the mixture heated
Table 5 Crystal data and structure refinement detailsa
Compound
Formula
[Be(OPPh3)2(NO3)2]
C36H30BeN2O8P2
[Mg(OPPh3)2(NO3)2]
C36H30MgN2O8P2
[Ca{o-C6H4(P(O)Ph2)2}2(NO3)2]
[Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2]
C50H44CaN2O10P4
C60H48CaN2O10P4
M
689.57
704.87
1120.96
996.82
Crystal system
Monoclinic
P21/n (no. 14)
10.272(3)b
9.579(2)
34.807(7)
90
Monoclinic
C2/c (no. 15)
15.343(3)
13.705(2)
17.202(3)
90
Monoclinic
P2/n (no. 13)
21.771(4)
10.6990(10)
24.074(4)
90
Orthorhombic
Pca21 (no. 29)
20.4255(16)
11.3207(10)
22.2120(15)
90
Space group
a/A
b/A
c/A
a/1
b/1
90.868(10)
90
96.971(4)
90
104.394(5)
90
90
g/1
90
U/A3
3424.3(13)
4
3590.4(11)
4
5431.6(14)
4
5136.1(7)
4
Z
T/K
m/mmꢁ1
F(000)
300
120
120
120
0.182
0.191
0.296
0.303
1432
1464
2328
2072
Total no. of obsns. (Rint
Unique obsns.
Min, max transmission
)
31143 (0.113)
5996
14502 (0.044)
4116
60223 (0.098)
12261
15486 (0.120)
5673
0.841, 1.000
442, 0
0.819, 1.000
222, 0
0.932, 0.982
695, 0
0.897, 1.004
604, 1
No. of parameters, restraints
Goodness-of-fit on F2
Resid. electron density/e Aꢁ3
R1, wR2 (I > 2s(I))c
1.01
1.00
0.97
1.04
ꢁ0.24 to þ0.18
0.073, 0.115 (2538 ref.)
0.211, 0.152
ꢁ0.28 to þ0.37
0.049, 0.118 (2838 ref.)
0.084, 0.135
ꢁ0.50 to þ0.34
0.055, 0.116 (6807 ref.)
0.128, 0.140
ꢁ0.42 to þ1.37
0.084, 0.213 (4196 ref.)
0.116, 0.236
R1, wR2 (all data)
a
b
0.71073 A. The cell dimensions at 120
Common items: wavelength (Mo-Ka)
=
K
are:
4 1/2
] .
a
=
10.218(2),
b
=
9.508(2),
c
=
34.294(9) A,
P
P
P
P
b = 91.270(9)1, U = 3330.9(13) A3. R1 = 8 Fo| ꢁ |Fc8/ |Fo|. wR2 = [ w(Fo ꢁ Fc2)2/ wFo
c
2
ꢂc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006
New J. Chem., 2006, 30, 782–790 | 789

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531(s), 450(w). LM (10ꢁ3 mol dmꢁ3 CH2Cl2) = 6 Oꢁ1 cm2
thanks M.D.S University, Ajmer (India) for granting leave of
absence.
molꢁ1; with excess ligand LM = 10 Oꢁ1 cm2 molꢁ1
.
X-Ray crystallography
Brief details of the crystal data and refinement are given in
Table 5. Data collections were carried out using a Nonius
Kappa CCD diffractometer fitted with graphite monochro-
mated Mo-Ka radiation (l = 0.71073 A) with the crystals held
at 120 K in a gas stream (not Be). Crystals of the complexes
were made as follows: [Mg(OPPh3)2(NO3)2] vapour diffusion
References
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p. 1.
of diethyl ether into
a CH2Cl2 solution; [Ca{o-C6H4
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F. Vogtle, Elsevier, Oxford, 1996, vol. 1, p. 315.
¨
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solution, University of Gottingen, Germany, 1997.
¨
17 G. M. Sheldrick, SHELXL-97, Program for crystal structure
(P(O)Ph2)2}2(NO3)2] and [Ca{Ph2P(O)CH2P(O)Ph2}2(NO3)2]
from CH2Cl2 solutions of the complexes layered with diethyl
ether; [Be(OPPh3)2(NO3)2] crystals were obtained directly
from the preparation. Structure solution and refinement were
carried out using SHELXS16 and SHELXL17, respectively
with an empirical absorption correction.18,19 Hydrogen atoms
were introduced into the model in calculated positions. Our
usual laboratory setup with 120 K as the data collection
temperature was used, offering the low temperature advan-
tages20 and ease of handling crystals of limited room tempera-
ture stability due to loss of solvate molecules or moisture/air
sensitivity. For the Be compound this arrangement gave a
structure solution with several very elongated C atom adp
ellipsoids in three phenyl rings. Repeating the experiment gave
the same result but attempts to model the presumed disorder
were unsuccessful and the suggestion that the ellipsoids were in
some way hinting at a solid phase change on lowering the
temperature led to a room temperature (300 K) data collec-
tion. Although this was a weak data set (42% reflections with
I > 2s(I)) the ellipsoids’ anisotropy was less marked and this
is the data set reported.
CCDC reference numbers 298677–298680. For crystallo-
graphic data in CIF or other electronic format see DOI:
10.1039/b600301j.
refinement, University of Gottingen, Germany, 1997.
¨
18 G. M. Sheldrick, SADABS, Bruker-Nonius area detector scaling
and absorption correction (V 2.10), Bruker AXS Inc., Madison,
Wisconsin, USA, 2003.
Acknowledgements
19 R. H. Blessing, J. Appl. Crystallogr., 1997, 30, 421.
20 A. E. Golta and J. A. K. Howard, Chem. Soc. Rev., 2004, 33,
490.
We thank the EPSRC for support (MFD), the Royal Society,
UK (JEB/1676/India) and DST, India for funding, and R. R.
ꢂc
790 | New J. Chem., 2006, 30, 782–790 This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006