Inorganic-organic hybrids formed by p,p′- diphenylmethylenediphosphinate, pcp2-, with the Cu2+ ion. x-ray crystal structures of [Cu(pcp)H2O2]·H 2O and [Cu(pcp)bipy(H2O)]

Article abstract of DOI:10.1021/ic050171a

Weakly coordinated [Cu(pcp)(H₂O)_n] complexes are formed in aqueous solution, at room temperature, by interaction of P,P′-diphenylmethylene diphosphinic acid (H₂pcp) with copper(II) ions. However, heating of the solutions g

Full text of DOI:10.1021/ic050171a

Inorg. Chem. 2005, 44, 4008−4016
Inorganic
P,P
Crystal Structures of [Cu(pcp)(H2O)2]
−Organic Hybrids Formed by
-
+
′
-Diphenylmethylenediphosphinate, pcp2 , with the Cu2 Ion. X-ray
‚
H2O and [Cu(pcp)(bipy)(H2O)]
Samuele Ciattini,† Ferdinando Costantino,‡ Pablo Lorenzo-Luis,§ Stefano Midollini,*,|
Annabella Orlandini,| and Alberto Vacca
Istituto di Chimica dei Composti Organometallici, Consiglio Nazionale delle Ricerche, Via
Madonna del Piano, 50019 Sesto Fiorentino, Firenze, Italy, Centro di Cristallografia e
Dipartimento di Chimica, UniVersita` di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino,
Firenze, Italy, Dipartimento di Chimica, UniVersita` di Perugia, Via Elce di Sotto 8, 06123
Perugia, Italy, and Departamento de Quimica Inorganica, UniVersidad de La Laguna, E-38200
Tenerife, Canary Islands, Spain
Received February 1, 2005
Weakly coordinated [Cu(pcp)(H2O)n] complexes are formed in aqueous solution, at room temperature, by interaction
of P,P -diphenylmethylene diphosphinic acid (H2pcp) with copper(II) ions. However, heating of the solutions gives
rise to the formation of two extended metal oxygen networks of formulas [Cu(pcp)(H2O)2] H2O, 1, and [Cu(pcp)-
(H2O)2], 2. In the presence of 2,2 -bipyridyl (bipy) the diamine derivative [Cu(pcp)(bipy)(H2O)], 4, has been isolated.
Complex 1 easily loses water to form a monohydrated derivative [Cu(pcp)H2O], 3, whereas 2 is completely dehydrated
after prolonged heating at 150 C, under vacuum. The compounds 1 and 2 have substantially different solid-state
′
−
‚
′
°
structures as shown by X-ray powder diffraction spectra, IR spectra, and thermogravimetric analyses. Consistently,
the two complexes cannot be directly interconverted and present different dehydration pathways. Rehydration of
these materials in both cases allows quantitative formation of 1. X-ray analysis established that the structure of 1
consists of a corrugated two-dimensional layered polymeric array, where infinite zigzag chains of Cu centers and
bridging phenylphosphinate ligands are linked together through strong hydrogen-bonding interactions; the structure
of 4 consists of monodimensional polymers, where the hydrogen-bonding interactions play an essential bridging
role in the extended architecture. In both structures the metal center displays a five-coordinate environment with
approximate square pyramidal geometry, with the pcp ligand acting as bidentate and monodentate in 1 and solely
as bidentate in 4. In 1 the coordination sphere is completed through water molecules; in 4, through water and
diamine ligands. The thermogravimetric analyses of the complexes are compared with those of the related hybrids
[M(pcp)(H2O)3]
‚H2O, where M ) Mn, Co, or Ni, confirming that noncoordinated water molecules also play a basic
role in determining the molecular packing.
Introduction
characteristics, catalytic activity, relevant magnetism, and
nonlinear optical behavior.1,2
Inorganic-organic hybrids are materials of intense interest
in the field of contemporary material chemistry, as these
materials could exhibit attractive properties such as zeolite
A large variety of ligands containing bridging function-
alities such as carboxylates [see examples in refs 3-5] and/
or phosphonates [see examples in refs 6-9] have been
(1) Hagrman, P. J.; Hagrman, D.; Zubieta, J. Angew. Chem., Int. Ed. 1999,
38, 2639.
(2) Allcock, H. R. AdV. Mater. 1994, 6, 106.
(3) Pan, L.; Lin H.; Lei, X.; Huang, X.; Olson, D. H.; Turro, N. J.; Li, J.
Angew. Chem., Int. Ed. 2003, 42, 542.
(4) Livage, C.; Egger, C.; Ferey, G. Chem. Mater. 2001, 13, 410.
(5) Forster, P. M.; Thomas, P. M.; Cheetham, A. K. Chem. Mater. 2002,
14, 17.
* To whom correspondence should be addressed. E-mail:
stefano.midollini@iccom.cnr.it.
† Centro di Cristallografia, Universita` di Firenze.
‡ Universita` di Perugia.
§ Universidad de La Laguna.
| CNR.
Dipartimento di Chimica, Universita` di Firenze.
4008 Inorganic Chemistry, Vol. 44, No. 11, 2005
10.1021/ic050171a CCC: $30.25
© 2005 American Chemical Society
Published on Web 04/21/2005

Inorganic-Organic Hybrids Formed by pcp2- with Cu2+ Ion
Chart 1
intricate hydrogen-bonding networks and are able to cement
molecules and chains in more extended structures. The
importance of the building role of the water molecules is
well exemplified in the recently reported Be(pcp)(H2O)2
derivative.13 Here the pcp2- ligand acts as bidentate, whereas
the cement of the extended network is constituted by the
hydrogen bonding between the coordinated water molecules
and the PO2 oxygen atoms not involved in direct bonding to
the beryllium ion. The architecture is different in the pcp
hybrids with Zn(II)15 and Pb(II),16 where the water molecules
are absent and the polymeric arrangement [one-dimensional
(1D) for Pb and 2D for Zn] is reached through bridging
oxygen atoms of the phosphinate ligand.
Now here we report the synthesis and characterization of
the hydrated copper(II) complexes [Cu(pcp)(H2O)2]‚H2O (1),
[Cu(pcp)(H2O)2] (2), and [Cu(pcp)(H2O)] (3) and also of the
diamine derivative [Cu(pcp)(bipy)H2O] (4). The molecular
structures of 1 and 4 have been determined by single-crystal
diffraction analyses, whereas no suitable crystals were
available for compounds 2 and 3. The thermogravimetric
analyses of these copper pcp complexes have been compared
with those of the previously reported manganese, cobalt, and
nickel derivatives.
successfully employed in recent years to synthesize extended
networks with metal ions. Differently related phosphinate
ligands have been comparatively less investigated,10,11 and
these have been generally found to favor the formation of
monodimensional polymers. However, phosphinates appear
to be interesting ligands in inorganic-organic hybrids
engineering. Even if the phosphinate group contains only
two oxygen donor atoms, the presence of two organic
moieties should allow a better modulation of the structure
of the resulting metal complexes than in the case of the
related phosphonate.
Recently we have found that the bifunctional dianion of
the P,P′-diphenylmethylene diphosphinic acid (H2pcp)12
(Chart 1) possesses interesting coordinating characteristics
to give extended networks. Indeed, pcp2- can bridge metal
ions with formation of six-membered chelate rings, each
oxygen atom in turn being able to bridge two metal centers.
Moreover, the diphosphinate can balance the charge of a
bivalent metal cation, avoiding the presence of counteranions.
When the phosphinate oxygen atoms are not capable of
saturating the metal center, water molecules are in turn
coordinated, potentially causing the formation of a net of
hydrogen bonds. Actually extended networks of Be(II),13
Mn(II), Co(II), Ni(II),14 Zn(II),15 and Pb(II)16 with this ligand
have been reported.
Experimental Section
Materials and Methods. All chemicals were used as purchased
without purification. H2(pcp) was prepared as previously described12
and then purified by recrystallization from ethanol.
IR spectra were recorded, as Nujol mulls, on a Perkin-Elmer
1600 series FTIR spectrometer. Thermal analyses (TG-DTA) were
carried out on a Perkin-Elmer Diamond TG-DTA system (SEGAI
Service of the University of La Laguna), under a nitrogen
atmosphere (flow rate 80 cm3‚min-1) in the range from ambient
temperature to 550 °C. Small needlelike crystals of the samples
(between 6.258 and 3.039 mg) were heated in an aluminum crucible
(45 µL) at a rate of 10 °C‚min-1. The TG curves were analyzed as
mass loss (milligrams) as a function of temperature. The numbers
of decomposition steps were identified by use of derivative
thermogravimetric curves (DTG). The DTA curves were analyzed
by differential thermal analysis [∆T (microvolts)]. X-ray powder
diffraction patterns were collected by the step scanning procedure
with Cu KR radiation on a Philips X’PERT APD diffractometer,
PW3020 goniometer equipped with a bent graphite monochromator
on the diffracted beam. Divergence and scatter slits (0.5°) and a
0.1 mm receiving slit were used. The LFF ceramic tube operated
at 40 kV and 30 mA. To minimize preferred orientations, the sample
was carefully side-loaded onto an aluminum sample holder with
an oriented quartz monocrystal underneath. The effective magnetic
moments were measured, at room temperature, on a Cryogenics
S600 SQUID magnetometer. The determination of the equilibrium
constants was performed from pHmetric titrations at 298 K at an
ionic strength of 0.5 mol dm-3 in Me4NCl by use of the
HYPERQUAD program.17 The emf apparatus and the experimental
technique have been described previously.18 The titrations were
carried out by adding a 0.1 mol dm-3 Me4NOH solution to acid
solutions containing either the ligand (deprotonation experiments)
The [M(pcp)(H2O)3]‚H2O (M ) Mn, Co, and Ni14)
hybrids, containing ions octahedrally coordinated, represent
an isomorphous series, where the overall structure is arranged
in the form of corrugated two-dimensional (2D) layers. As
a consequence, in such a series the metal can be replaced
by another metal without changing the primary structure, and
mixed-metal pcp complexes could be isolated. Remarkable
in these networks is the role of the water molecules, both of
coordination and of crystallization, which are involved in
(6) Bakhmutova, E. V.; Ouyang, X.; Medvedev, D. G.; Clearfield, A.
Inorg. Chem. 2003, 42, 7046.
(7) Kong, D.; Li, Y.;. Ross Jr., J. H.; Clearfield, A. Chem. Commun. 2003,
1720.
(8) Stock, N.; Frey, S. A.; Stucky, G. D.; Cheetham, A. K. J. Chem. Soc.,
Dalton Trans. 2000, 4292.
(9) Burlholder E.; Golub, V. O.; O’Connor, C. J.; Zubieta, J. Inorg. Chim.
Acta 2002, 340, 127.
(10) Grohol, D.; Ginge, F.; Clearfield, A. Inorg. Chem. 1999, 38, 751.
(11) Oliver, K. W.; Rettig, S. J.; Thomson, R. C.; Trotter, J.; Xuia, S. Inorg.
Chem. 1997, 36, 2465.
(12) Garst, M. E. Synth. Commun. 1979, 9, 261.
(13) Cecconi, F.; Dominguez, S.; Masciocchi, N.; Midollini, S.; Sironi,
A.; Vacca, A. Inorg. Chem. 2003, 42, 2350.
(14) Berti, E.; Cecconi, F.; Ghilardi, C. A.; Midollini, S.; Orlandini, A.;
Pitzalis, E. Inorg. Chem. Commun. 2002, 5, 1041.
(15) Cecconi, F.; Dakternieks, D.; Duthie, A.; Ghilardi, C. A.; Gili, P.;
Lorenzo-Luis, P. A.; Midollini, S.; Orlandini, A. J. Solid State Chem.
2004, 177, 786.
(16) Cecconi, F.; Ghilardi, C. A.; Midollini, S.; Orlandini, A. Inorg. Chem.
Commun. 2003, 6, 546.
(17) Gans, P.; Sabatini, A.; Vacca, A. Talanta 1996, 43, 1739.
(18) Alderighi, L.; Vacca, A.; Cecconi, F.; Midollini, S.; Chinea, E.;
Dominguez, S.; Valle, A.; Dakternieks D.; Duthie, A. Inorg. Chim.
Acta 1999, 285, 39.
Inorganic Chemistry, Vol. 44, No. 11, 2005 4009

Ciattini et al.
Table 1. Crystal Data and Structure Refinement for 1 and 4
1
4
empirical formula
formula weight
temperature (K)
wavelength (Å)
crystal system, space group
unit cell dimensions
a (Å)
C13H18Cu1O7P2
411.75
293(2)
1.541 80
C23H22Cu1N2O5P2
531.91
293(2)
0.710 69
triclinic, P-1
monoclinic, P2/c
19.490(8)
9.443(3)
9.434(3)
90
110.37(3)
90
1627.7(10)
4, 1.680
4.064
7.135(9)
10.870(2)
16.271(5)
99.26(2)
99.94(6)
102.10(5)
1189.7(16)
2, 1.485
1.089
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z, calcd density (g cm-3
)
absorption coefficient (mm-1
F(000)
)
844
546
crystal size (mm)
θ range for data collection (deg)
limiting indices
reflections collected/unique
refinement method
0.45 × 0.40 × 0.012
0.40 × 0.125 × 0.05
4.68-55.07
2.56-22.97
-20 e h e 19, 0 e k e 10, 0 e l e 10
2347/1904
-7 e h e 7, -11 e k e 11, 0 e l e 17
3490/3288
full-matrix least-squares on F2
1904/0/208
full-matrix least-squares on F2
3288/0/386
data/restraints/parameters
goodness-of-fit on F2
0.990
1.023
final R indices [I > 2σ(I)]
R1 ) 0.0660,
R1 ) 0.0414,
wR2 ) 0.1562
wR2 ) 0.0954
R indices (all data)
R1 ) 0.0877,
R1 ) 0.0710,
wR2 ) 0.1689
wR2 ) 0.1063
largest diff. peak, hole (e‚Å-3
)
0.744, -0.466
0.385, -0.511
or a metal chloride (CoCl2, NiCl2, and CuCl2 in the complex
formation experiments). Concentrations of metal and ligand were
in the range 1-3 mmol dm-3. The ligand-to-metal ratios were 1:1
and 2:1 (two titrations, 60-90 data points in the pH range 2.5-
5.5). At higher pH regions, precipitation of metal-containing species
(presumably metal hydroxides) occurred and this precluded further
collection of data. The electrode system was calibrated in terms of
hydrogen ion concentration [H+], by the method of Gran.19
Synthesis of [Cu(pcp)(H2O)2]‚H2O, 1. H2pcp (0.1 g, 0.34 mmol)
was dissolved in water (65 mL) at room temperature under stirring
(ca. 1 h). A solution of copper(II) acetate monohydrate (0.068 g,
0.34 mmol) in 10 mL of water was added. The resulting solution
was evaporated at ca. 70 °C till pale sky-blue crystals precipitated.
The complex was filtered, washed with water, and dried in air at
room temperature. Yield 0.120 g, 86%. Anal. Calcd for C13H18-
by further heating at 150 °C, under vacuum (5 × 10-2 Torr). Anal.
Calcd for C13H14Cu1O5P2: C, 41.55; H, 3.76. Found: C, 41.47; H,
3.61.
Synthesis of [Cu(pcp)(bipy)(H2O)], 4. [Cu(pcp)(H2O)2]‚(H2O)
(0.050 g, 0.12 mmol) was suspended in 50 mL of boiling water,
then solid 2,2′-bipyridyl (0.019 g, 0.12 mmol) was added. The
complex dissolved to give a blue solution, which was filtered and
concentrated at 70-80 °C till blue crystals precipitated. The
complex was filtered, washed with water, and dried in air at room
temperature. Yield 0.051 g, 80%. Alternatively, the complex can
be obtained by reacting in water equimolar amounts of H2pcp, Cu-
(acetate)2‚H2O, and bipy at 70-80 °C. Anal. Calcd. for C23H22-
Cu1N2O5P2: C, 51.93; H, 4.17; N, 5.27. Found: C, 51.68; H, 4.12;
N, 5.24. µeff ) 1.90µB at 295 K.
X-ray Data Collection and Structure Solution. Diffraction data
for 1 and 4 derivatives were collected at room temperature on a
Philips PW1100 and on an Enraf Nonius CAD4 automatic diffrac-
tometer, respectively. Unit cell parameters for both compounds were
determined by least-squares refinement of the setting angles of 25
carefully centered reflections. Crystal data and data collection details
of 1 and 4 are given in Table 1. The intensities I were assigned the
standard deviations σ(I) calculated by using a value of 0.03 for the
instability factor k.20 They were corrected for Lorentz polarization
effects and for absorption.21 Atomic scattering factors for neutral
atoms were taken from ref 22. Both ∆f′ and ∆f′′ components of
anomalous dispersion were included for all non-hydrogen atoms.23
The structures were solved by direct methods and refined by full-
matrix F2 refinement, with anisotropic thermal parameters assigned
to all non-hydrogen atoms. Whereas in 1 the hydrogen atoms were
introduced in their calculated positions riding on their carbon atoms,
Cu1O7P2: C, 37.92; H, 4.41. Found: C, 37.63; H, 4.20. µeff
1.93µB at 295 K.
)
Synthesis of [Cu(pcp)(H2O)2], 2. H2pcp (0.1 g, 0.34 mmol) was
dissolved in 65 mL of boiling water, and then a solution of copper-
(II) acetate monohydrate (0.068 g, 0.34 mmol) in 10 mL of water
was added. The resulting solution was concentrated by boiling till
thin pale-blue crystals precipitated. The resulting mixture was cooled
at room temperature; then the compound was filtered, washed with
water, and dried in air. Yield 0.108 g, 81%. Anal. Calcd for C13H16-
Cu1O6P2: C, 39.65; H, 4.09. Found: C, 39.28; H, 4.04. The
complex, held under vacuum (5 × 10-2 Torr) at 150 °C for 3 days,
loses water to yield an amorphous material analyzing as Cu(pcp).
Anal. Calcd for C13H12CuO4P2: C, 43.65; H, 3.38. Found: C, 43.50;
H, 3.45.
Synthesis of [Cu(pcp)(H2O)], 3. The solid complex 1, at room
temperature, slowly loses water till after ca. 20 days it analyzes as
Cu(pcp)(H2O). This compounds can be obtained more rapidly
(hours) by heating 1, in air, at temperatures > 70 °C. Alternatively,
the monohydrated derivative can be obtained by washing 1 with
ethanol. The composition of monohydrated solid does not change
(20) Corfield, P. W. R.; Doedens, R. J.; Ibers, J. A. Inorg. Chem.1967, 6,
197.
(21) Parkin, S.; Moezzi, B.; Hope, H. J. Appl. Crystallogr. 1995, 28, 53.
(22) International Tables for X-ray Crystallography; Kluwer: Dordrecht,
The Netherlands, 1992; Vol. C, p 500.
(23) International Tables for X-ray Crystallography; Kluwer: Dordrecht,
The Netherlands, 1992; Vol. C, p 219.
(19) Gran, G. Analyst 1952, 77, 661.
4010 Inorganic Chemistry, Vol. 44, No. 11, 2005

Inorganic-Organic Hybrids Formed by pcp2- with Cu2+ Ion
Table 2. Decimal Logarithm Values of the Equilibrium Constants for
the Reactions of pcp2- with H+, Co2+, Ni2+, and Cu2+ in Aqueous
Solutiona
reaction
log K
H+ + pcp2- a Hpcp-
H+ + Hpcp- a H2pcp
Co2+ + pcp2- a Copcp
Ni2+ + pcp2- a Nipcp
Cu2+ + pcp2- a Cupcp
3.33(1)
1.35(9)
2.9(1)
3.43(6)
4.25(9)
a T ) 298 K and I ) 0.5 mol dm-3, Me4NCl. Values in parentheses are
standard deviations on the last significant figure.
with thermal parameters 20% larger, in 4 it was possible to locate
the hydrogen atoms from a difference Fourier map and refine them.
The function minimized during the refinement was Σw(Fo2 - Fc2)2,
with w ) 1/[σ2(Fo ) + (0.0876P)2 + 11.24P] and w ) 1/[σ2(Fo )
2
2
+ (0.0636P)2] [P ) (max(Fo , 0) + 2Fc2)/3] for 1 and 4,
2
respectively. All the calculations were performed on a Pentium
processor, using the package WINGX24 (SIR97,25 SHELX97,26
ORTEP-III27).
Results and Discussion
Interaction of Copper(II) Ions with H2pcp in Aqueous
Solution and Synthesis of Solid Networks. The interaction
of H2pcp with copper(II) ions in aqueous solution has been
investigated by potentiometric measurements. The results of
the experimental data are shown in Table 2 together with
those of the related cobalt(II) and nickel(II) complexes for
comparison purposes. The two basicity constants of pcp2-
were in excellent agreement with a recent determination
under the same experimental conditions (log K ) 3.34 and
1.3, respectively).13 The complex formation experiments were
all satisfactorily fitted with the assumption that only one
complex species (namely ML) is present at the equilibrium.
The characterized complexes appear to be relatively weak
at room temperature. This is probably the reason complex
species with higher ligand-to-metal ratios were not detected
under the experimental conditions of this study; in any case,
the trend of the stability Co(II) < Ni(II) < Cu(II) is that
expected according to the Irving-Williams order.
However, we have found that, in agreement with previous
reports,28 the increasing temperature favors the elimination
of coordinated water and the formation of infinite metal-
oxygen networks. As a matter of fact, heating of the aqueous
solution of copper(II) acetate [the complexes can be prepared
also from copper(II) nitrate with similar yields] and H2pcp
allows the preparation of two polymeric complexes. At ca.
70 °C, pale blue crystals of formula Cu(pcp)(H2O)3 were
isolated, whereas from a boiling solution, thin crystals of
the same color but analyzing as Cu(pcp)(H2O)2 precipitated.
The IR spectra of the two compounds (Figure 1) appear to
be rather similar, even if the spectrum of Cu(pcp)(H2O)3
Figure 1. IR spectra of the complexes (A) Cu(pcp)(H2O)3, (B) Cu(pcp)-
(H2O), (C) Cu(pcp)(H2O)2, and (D) Cu(pcp) [material from Cu(pcp)(H2O)2
at 150 °C under vacuum].
shows three O-H stretching bands of H2O at 3540 (m), 3391
(s), and 3206 (s, br), whereas that of Cu(pcp)(H2O)2 shows
in the same region two bands at 3394 (m) and 3339 (s). It is
noteworthy that this latter complex, even if treated with water
for days at room temperature, remains absolutely unchanged.
On the other hand, the complex Cu(pcp)(H2O)3 slowly
darkens in air, at room temperature (from pale blue to sky
blue), losing water to give, in ca. 20 days, a derivative
analyzing as Cu(pcp)(H2O). The same material can be rapidly
obtained by either heating Cu(pcp)(H2O)3 at 150 °C (0.5 h)
or washing the same with ethanol. The solid Cu(pcp)(H2O)
remains substantially unchanged after further heating, under
vacuum (5 × 10-2 Torr), at 150 °C for 3 days. Its IR
spectrum shows a new pattern in the νOH range (Figure 1)
with two bands at 3510 and 3272 cm-1. It is noteworthy
that this latter derivative, when treated with water at room
temperature, quantitatively re-forms the trihydrated com-
pound (IR and analysis). The process can be repeated without
any decomposition. By contrast, the treatment of complex
Cu(pcp)(H2O)2 at 150 °C, under vacuum (5 × 10-2 Torr),
allows a progressive dehydration as shown by the IR spectra
where the water stretching absorptions progressively dis-
appear. In Figure 1D is reported the IR spectrum of the
material Cu(pcp) resulting after heating of Cu(pcp)(H2O)2
at 150 °C under vacuum for 3 days. Also, this latter solid,
when reacted with water at room temperature, gives the
trihydrate complex Cu(pcp)(H2O)3. All these findings are
summarized in Scheme 1.
(24) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 876.
(25) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. C.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(26) Sheldrick, G. M. SHELX97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(27) Burnett, M. N.; Johnson, C. K.; ORTEP-III; Oak Ridge National
Laboratory: Oak Ridge, TN, 1996.
(28) Livage, C.; Egger, C.; Ferey, G. Chem. Mater. 2001, 13, 410.
Inorganic Chemistry, Vol. 44, No. 11, 2005 4011

Ciattini et al.
Scheme 1
Table 3. Selected Bond Lengths and Angles for 1
Bond Lengths (Å)
Cu(1)-O(3)
Cu(1)-O(1)
Cu(1)-O(2)a
Cu(1)-O(6)
Cu(1)-O(5)
P(1)-O(1)
1.933(5) P(1)-C(1)
1.962(5) P(1)-C(11)
1.986(5) P(2)-O(4)
1.991(6) P(2)-O(3)
2.215(6) P(2)-C(1)
1.507(6) P(2)-C(21)
1.529(5)
1.809(9)
1.823(10)
1.494(6)
1.516(5)
1.795(9)
1.811(9)
P(1)-O(2)
Bond Angles (deg)
O(3)-Cu(1)-O(1)
92.8(2)
O(1)-P(1)-C(11)
108.5(4)
108.8(3)
108.1(4)
115.8(3)
109.6(4)
106.9(4)
108.1(4)
108.4(4)
107.8(4)
133.4(4)
O(3)-Cu(1)-O(2)a 167.9(2)
O(2)-P(1)-C(11)
C(1)-P(1)-C(11)
O(4)-P(2)-O(3)
O(4)-P(2)-C(1)
O(3)-P(2)-C(1)
O(4)-P(2)-C(21)
O(3)-P(2)-C(21)
C(1)-P(2)-C(21)
P(1)-O(1)-Cu(1)
O(1)-Cu(1)-O(2)a
O(3)-Cu(1)-O(6)
O(1)-Cu(1)-O(6)
O(2)a-Cu(1)-O(6)
O(3)-Cu(1)-O(5)
O(1)-Cu(1)-O(5)
O(2)a-Cu(1)-O(5)
O(6)-Cu(1)-O(5)
O(1)-P(1)-O(2)
O(1)-P(1)-C(1)
O(2)-P(1)-C(1)
89.3(2)
85.8(2)
165.6(3)
89.2(2)
96.9(2)
96.8(2)
94.7(2)
97.7(3)
113.9(3)
108.2(4)
109.1(4)
The X-ray powder diffraction spectra of Cu(pcp)(H2O)3
and Cu(pcp)(H2O)2 are shown in Figure 2. The diffraction
pattern for Cu(pcp)(H2O) is not shown because it contains
only a few weak signals, the compound being practically
amorphous. The position of the reflections for the pattern of
Cu(pcp)(H2O)3 are in agreement with the cell parameters
derived from the single-crystal X-ray analysis, but the basal
reflections (h00) are strongly enhanced, probably because
of severe orientation effects.29 The XRD pattern of 2 has
been indexed by use of the TREOR program,30 giving as
the best solution the tetragonal cell a ) 9.1887 and c )
17.2641 Å [M(10) ) 23].31 These values are very similar to
those of the trihydrate compound, showing that the structure
likely rearranges itself with higher symmetry when a water
P(1)-O(2)-Cu(1)b 119.5(3)
P(2)-O(3)-Cu(1)
P(2)-C(1)-P(1)
135.0(3)
116.2(5)
a Symmetry transformation (x, -y, z +1/2) was used to generate equivalent
atoms. b Symmetry transformation (x, -y, z -1/2) was used to generate
equivalent atoms.
molecule is lost. Unfortunately the attempts to solve this
structure failed because of the presence of several impurity
lines in the diffraction pattern. Concerning the material
resulting from dehydration of Cu(pcp)(H2O)2, the XRD
powder pattern did not show any peak, reflecting that the
crystal structure collapsed and the sample became amor-
phous. A crystalline phase of the anhydrous Cu(pcp), which
does not react with water, has been successively isolated in
hydrothermal conditions and the details of its structure,
solved ab initio by XRPD and analogous to that of the
reported 1D Pb(pcp) polymer,16 will be published.32
The solid complex [Cu(pcp)(H2O)2]‚H2O easily reacts in
water with stoichiometric amounts of bipy to give blue
solutions. Evaporation of the water at 70-80°C affords well-
shaped blue crystals of formula [Cu(pcp)(bipy)(H2O)].
The complexes 1 and 4 are paramagnetic with µeff of
1.93µB and 1.90µB, respectively, at room temperature. These
values are consistent with noninteracting five-coordinated
copper ions at room temperature.
Description of the Structures. As recently reported, all
the complexes of the isomorphous series [M(pcp)(H2O)3]‚
H2O, where M ) Ni(II), Co(II) and Mn(II) (both mono and
mixed), are isostructural, their structures being constituted
by bidimensional layers. As a matter of fact polymeric chains,
built up by an alternating array of metals centers and
phenylphosphinate ligands, are connected through strong
hydrogen-bonding linkages to form corrugated 2D layers.
An X-ray structural determination of [Cu(pcp)(H2O)2]‚H2O
revealed again a 2D layered structure but differing from the
above series in the number of coordination waters (Table 3
reports selected bond distances and angles). Now the metal
center is five-coordinated, being surrounded by three phos-
(29) Zhang, Y.; Scott, K. J.; Clearfield, A. Chem Mater. 1993, 5, 495.
(30) Werner, P. E.; Eriksson, L.; Westdhal, M. J. Appl. Crystallogr. 1985,
18, 367.
(31) De Wolff, P. M. J. Appl. Crystallogr. 1968, 1, 108.
(32) Costantino, F.; Midollini, S., Orlandini, A. Unpublished results.
Figure 2. X-ray powder diffractograms for (a) [Cu(pcp)(H2O)2]‚H2O and
(b) [Cu(pcp)(H2O)2].
4012 Inorganic Chemistry, Vol. 44, No. 11, 2005

Inorganic-Organic Hybrids Formed by pcp2- with Cu2+ Ion
Figure 5. Perspective view of a portion of the polymer [Cu(pcp)(H2O)2]‚
H2O, showing the propagation of the layer in the yz plane. For the sake of
clarity, the phenyl rings are omitted and only the most important interchain
hydrogen-bonding connections are represented.
Figure 3. Perspective view of the asymmetric unit of the polymer [Cu-
(pcp)(H2O)2]‚H2O: ORTEP III drawing with 30% probability ellipsoids.
cementing of the whole architecture [O1‚‚‚O6IV 2.76 Å (IV
x, -y, -0.5 + z); O2‚‚‚O6IV 2.79 Å; O2‚‚‚O5II 2.92 Å]. The
extension of the structure in the third dimension is precluded
by the presence of the organic part of the hybrid ligand,
which through the phenyl rings shields each other from the
2D layers. The packing diagram of the above polymer with
view normal to [010] is given in Figure 6.
Bond distances and angles in the coordination polyhedron
of the copper center are as expected, the Cu-O in the basal
plane being significantly shorter [average 1.97(1) Å] than
the Cu-O in apical position [2.215(6) Å]. The values of the
P-O distance lie in a range 1.494(6)-1.529(5) Å and the
O-P-O angles are slightly larger than the tetrahedral,
probably because of the involvement of oxygen in the bridge
formation.
Figure 4. Perspective view of some symmetry-related units of [Cu(pcp)-
(H2O)2]‚H2O showing the zigzag chain propagated along the z axis. Phenyl
rings are omitted for the sake of clarity.
phinate oxygen atoms from two ligands (one of them in
bidentate and the other in monodentate fashion) and by two
water molecules. The geometry is distorted square pyramidal,
with the basal sites occupied by the phosphinate oxygen
atoms and by a water molecule, with the metal displaced
0.22 Å above the basal plane. The third water molecule is
present as a solvating moiety (see Figure 3). An alternating
array of CuO5 copper moieties and bridging phosphinate
ligands creates an infinite zigzag chain, where the Cu‚‚‚Cu
separation is 5.36 Å (see Figure 4). Very important is the
role played by the water molecules, both of coordination and
of crystallization, in the building up of the structure. As a
matter of fact an extended net of hydrogen bonding connects
the chains together, resulting in a corrugated 2D layer (see
Figure 5). The most important linkages are displayed by the
solvating water molecule (O7), which, through hydrogen-
bonding interaction with itself, creates an infinite winding
of water molecules between the chains [O7‚‚‚O7I 2.77 Å (I
1 - x, -1 - y, -z); O7‚‚‚O7II 2.81 Å (II 1 - x, y, -0.5 -
z)]. These water molecules are in turn connected through
hydrogen bonding to the water oxygen (O5) coordinated to
the metal and to the phosphinate oxygen (O4) not involved
in direct bond to the copper [O7‚‚‚O5I 2.75 Å (I 1 - x, -1
- y, -z); O7‚‚‚O4 2.69 Å]. Another very important
interchain hydrogen-bonding interaction is due to the same
phosphinate oxygen O4 with the coordinated water oxygen
O6 [O4‚‚‚O6III 2.68 Å (III x, -1 - y, -0.5 + z)]. Other
intrachain interactions < 3.0 Å, even if of minor importance,
are present in the lattice and are anyway significant in the
The structure of 4 consists of monodimensional [Cu(pcp)-
(bipy)(H2O)] hydrogen-bonding polymers. In the asymmetric
unit the copper center is surrounded in a distorted square
pyramidal geometry by two phosphinate oxygen donors, two
bipy nitrogen atoms, and one water molecule in the apical
position (see Figure 7). Table 4 reports selected bond
distances and angles of 4. The copper lies 0.26 Å above the
basal plane. Unlike the structure of 1, here the ligand
phenylphosphinate coordinates as bidentate only one metal
center, so that two phenylphosphinate oxygen atoms remain
free and available for hydrogen-bonding interactions with
the water molecule of one neighboring moiety. It results in
an infinite chain, where phenylphosphinate ligands are
bridging the metal centers through strong hydrogen bonding
[O2‚‚‚O5I 2.72 Å; O4‚‚‚O5I 2.72 Å (I 1 + x, y, z)] (see Figure
8). The inorganic part of each chain is shielded by a
hydrophobic region, namely, by the phenyl rings of the pcp
ligand and the bipyridine molecules. In the lattice the chains
are packed in pairs, so that two chains, facing each other
with the bipy ligand, create a column where the bipy planes
are stacked, with a slightly alternate sliding (the shortest
contacts between the atoms of two adjacent bipy moieties
of ca. 3.5 Å are likely indicative of some stabilizing π-π
interactions). Interestingly the open site in the coordination
sphere of the metal is directed toward one ring of the bipy
Inorganic Chemistry, Vol. 44, No. 11, 2005 4013

Ciattini et al.
Figure 6. Packing diagram of [Cu(pcp)(H2O)2]‚H2O, with view normal to [010].
Figure 7. Perspective view of the asymmetric unit of [Cu(pcp)(bipy)-
(H2O)]: ORTEP III drawing with 30% probability ellipsoids.
Figure 8. Perspective view of some symmetry-related units of [Cu(pcp)-
(bipy)(H2O)], showing the propagation of the chains in the x direction.
Table 4. Selected Bond Lengths and Angles for 4
Bond Lengths (Å)
Cu(1)-O(1)
Cu(1)-O(3)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-O(5)
P(1)-O(2)
P(1)-O(1)
P(1)-C(110)
P(1)-C(1)
1.931(3) P(2)-O(4)
1.939(3) P(2)-O(3)
2.010(4) P(2)-C(21)
2.016(4) P(2)-C(1)
2.174(4) N(1)-C(2)
1.484(4) N(1)-C(6)
1.511(3) N(2)-C(11)
1.800(5) N(2)-C(7)
1.803(4) C(6)-C(7)
1.495(4)
1.512(3)
1.801(4)
1.810(5)
1.341(6)
1.347(6)
1.340(6)
1.351(5)
1.479(6)
Bond Angles (deg)
O(1)-Cu(1)-O(3)
O(1)-Cu(1)-N(1)
O(3)-Cu(1)-N(1)
O(1)-Cu(1)-N(2)
O(3)-Cu(1)-N(2)
N(1)-Cu(1)-N(2)
O(1)-Cu(1)-O(5)
O(3)-Cu(1)-O(5)
N(1)-Cu(1)-O(5)
N(2)-Cu(1)-O(5)
O(2)-P(1)-O(1)
96.54(14) O(4)-P(2)-O(3)
89.51(14) O(4)-P(2)-C(21)
163.68(14) O(3)-P(2)-C(21)
161.72(14) O(4)-P(2)-C(1)
89.99(14) O(3)-P(2)-C(1)
79.98(15) C(21)-P(2)-C(1)
94.89(17) P(1)-O(1)-Cu(1)
94.20(17) P(2)-O(3)-Cu(1)
100.39(16) C(2)-N(1)-C(6)
101.66(17) C(2)-N(1)-Cu(1)
117.3(2)
109.4(2)
106.9(2)
111.6(2)
107.3(2)
103.3(2)
134.3(2)
135.2(2)
118.6(4)
125.6(3)
115.7(3)
118.8(4)
116.3(2)
C(6)-N(1)-Cu(1)
C(11)-N(2)-C(7)
O(2)-P(1)-C(110) 109.7(2)
O(1)-P(1)-C(110) 106.1(2)
C(11)-N(2)-Cu(1) 125.5(3)
O(2)-P(1)-C(1)
O(1)-P(1)-C(1)
C(110)-P(1)-C(1)
111.2(2)
107.3(2)
105.5(2)
C(7)-N(2)-Cu(1)
P(1)-C(1)-P(2)
N(1)-C(6)-C(7)
N(2)-C(7)-C(6)
115.6(3)
115.9(3)
114.4(4)
114.1(4)
Figure 9. Packing diagram of [Cu(pcp)(bipy)(H2O)] with view normal to
[100].
167.9° in 1. As in 1, the apical bond distance [2.174(4) Å]
is significantly larger than the basal ones [the Cu-O and
Cu- N linkages average 1.935(4) and 2.013(3) Å, respec-
tively].
Thermogravimetric Study. The removal of water mol-
ecules could represent an important challenge, to leave open
coordination sites on the metals for possible intercalation or
catalytic reactions. With this kept in mind, an extensive
of the neighboring chain. No important interaction involving
the metal seems anyway present. In Figure 9 the packing
diagram of 4 with view normal to [100] is reported.
From a comparison of the coordination spheres of 4 and
1, a larger distortion of 4 is evidenced by the axial angles of
the square pyramid of 161.7° and 163.7° vs 165.6° and
4014 Inorganic Chemistry, Vol. 44, No. 11, 2005

Inorganic-Organic Hybrids Formed by pcp2- with Cu2+ Ion
Figure 10. TG/DTG-DTA curves of [Cu(pcp)(H2O)2]‚H2O. (Insets) TG/
DTG-DTA curves for the isomorphous series member [Ni(pcp)(H2O)3]‚
H2O. TG ) mass loss (percent); DTA ) ∆T (microvolts) and DTG )
percent per minute (V endo and v exo).
Figure 11. TG curves of (a) [Cu(pcp)(H2O)2] 2, (b) [Cu(pcp)(H2O)] 3,
and (c) [Cu(pcp)(bipy)(H2O)] 4. TG ) mass loss (percent).
justify the step overlapping.13,14 The corresponding curves
of the Mn(II) and Co(II) derivatives, reported in the
Supporting Information, appear quite similar. On the other
hand, the first strong DTA peak temperature for the removal
of the water molecules follows the order Mn(II) (69 °C) <
Co(II) (78 °C) < Ni(II) (99 °C), indicating decreasing acidity
from Mn(II) to Ni(II).
Table 5. Thermal Data of the Dehydration Process for All Samples
complexes
∆T (°C)
N°H2O losses
calcd/found (%)
[Cu(pcp)(H2O)2]‚H2O 1
[Ni(pcp)(H2O)3]‚H2O
[Mn(pcp)(H2O)3]‚H2O
[Co(pcp)(H2O)3]‚H2O
[Cu(pcp)(H2O)2] 2
25-202
27-210
33-139
29-128
27-200
26-221
30-197
2.9
4.0
4.0
4.0
2.0
1.1
1.1
13.11/12.54
16.94/17.00
16.94/17.00
16.94/17.00
9.14/9.14
[Cu(pcp)(H2O)] 3
[Cu(pcp)(bipy)(H2O)] 4
4.79/5.26
3.38/3.63
The thermal behavior for 2-4 in the water evaporation
range of temperature (<300 °C) appears comparatively
simple (Figure 11). Thus, compound 2 (curve a) shows two
overlapped weight losses; the first at 155 °C [(DTG)peak at
138 °C (one water molecule)] and the second at 200 °C
[(DTG)peak at 185 °C (one water molecule)] with endothermic
associated processes [(DTA)peak at 141 and 187 °C]. Analo-
gously, compounds 3 and 4 (curves b and c) show respec-
tively one loss of weight at 221 °C [(DTA)peak at 207 °C]
and one at 197 °C [(DTA)peak at 178 °C], each corresponding
to ca. one water molecule. Since compound 4 has been
ascertained by X-ray crystal structure (see above) to contain
one coordination water molecule, we can trustfully assign
also the water molecules in 2 and 3 as metal-coordinated.
After the dehydration steps, there is a region of constant
weight at high temperature for all the compounds. The
existence of exothermic peaks [(DTA)peak at 309, 305, and
312 °C for 1, 2, and 3, respectively] is due to a possible
phase transition followed by a strong exothermic effect,
caused by the combustion of part of the organic matter. The
IR spectrum (reported in the Supporting Information) shows
that actually the bands due to the ν(OH) vibrations of the water
molecules are not present. This behavior is closely related
to that of the recently reported, anhydrous derivatives
[M(II)(pcp)], where M(II) ) Zn or Pb.15
thermogravimetric study has been performed on the
copper derivatives [Cu(pcp)(H2O)2]‚H2O, [Cu(pcp)(H2O)2],
[Cu(pcp)(H2O)], and [Cu(pcp)(bipy)(H2O)] and on the related
compounds of the isomorphic series [M(II)(pcp)(H2O)3]‚H2O
[where M(II) ) Ni, Mn, and Co]14 for comparison purposes.
Thermal data of the dehydration process for all samples are
reported in Table 5.
The thermal behavior of [Cu(pcp)(H2O)2]‚H2O 1 (Figure
10 and Table 5) shows, from 25 to 202 °C, a complicated
first weight loss with five overlapped stages (see DTG curve),
which is likely attributable to the loss of the water molecules.
In fact, the temperature range is in agreement with previous
reports13 and the total loss of mass in this process corresponds
to ca. three water molecules (calcd 13.11% vs found
12.54%). The water loss begins at relatively low temperature
according to the preparative experiments. It is noteworthy
that, during the process, the crystallization water molecules
are not distinguished from the coordination ones. This fact
could well be justified because in the crystal structure the
water molecules are strongly involved in a complicated
hydrogen-bonding network and anchored to the structural
building. It is interesting to note that at ca. 150 °C the loss
of weight corresponds to ca. two water molecules, in
agreement with the preparative experiment.
Summary
Accordingly, the curves of the complex [Ni(II)(pcp)-
(H2O)3]‚H2O, an example of the isomorphic series (see inset
in Figure 10), substantially show that, during the heating,
the complex loses the crystallization water molecule, fol-
lowed by the coordinated ones in two overlap steps (see DTG
curve). Also in this case the involvement of the water
molecules in an extended hydrogen-bonding network can
In accord with previous reports, diphenylmethylenedi-
phosphinate is a suitable ligand to produce extended materials
with metal(II) ions.13-16,32 We have now found that the
heating of aqueous solutions of H2pcp and copper(II) ions
allows the formation of two different hydrated polymeric
compounds: [Cu(pcp)(H2O)2]‚H2O and [Cu(pcp)(H2O)2].
Inorganic Chemistry, Vol. 44, No. 11, 2005 4015

Ciattini et al.
The structure of [Cu(pcp)(H2O)2]‚H2O consists of an alter-
nating array of CuO5 copper moieties and bridging diphos-
phinates resulting in infinite zigzag chains. These are
connected together by an extended net of hydrogen bonding
to give a corrugated 2D layer. Hydrogen bonds are formed
by both the coordinating and crystallization water molecules,
and the solvating water plays a determining role in the
construction of the crystal packing. The determinant cement-
ing role of the solvating water molecules is in agreement
with the thermal analysis results, where the presence of only
one complicated dehydration step seems due to the difficulty
in distinguishing the loss of crystallization water from that
of coordinated water. Consistently the two compounds 1 and
2, despite the close formulas, have different lattices, and they
cannot be interconverted by a direct reaction. The complex
1 easily loses two water molecules to form a new derivative
of formula [Cu(pcp)(H2O]. This latter, even if not more
crystalline, retains the primary structure because it can be
quantitatively reconverted into 1 in the presence of water.
This property, typical of open-framework materials, suggests
a potential involvement of these phosphinate hybrids in the
field of the intercalation chemistry and/or catalytic processes.
The easy substitution of the water molecules in 1 is evidenced
also by the formation of the bipy derivative 4. In the latter
complex, the coordination of a diamine to the copper ion
leads the diphosphinate ligand to coordinate as bidentate only
one metal center. It ensues a hydrogen-bonding monodi-
mensional polymer, where the non-metal-bonded phenylphos-
phinate oxygens are involved in strong hydrogen-bonding
interactions with the water molecule of one neighboring
moiety.
Acknowledgment. We thank Dr. S. Costantini (Univer-
sita` di Firenze) for microanalyses and Mr. F. Cecconi
(ICCOM, CNR) for the synthesis of the ligand.
Supporting Information Available: Thermogravimetric curves
for [Mn(pcp)(H2O)3]‚H2O and [Co(pcp)(H2O)3]‚H2O and FTIR of
[Cu(pcp)(H2O)2]‚H2O at high temperatures (PDF). This information
is available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data for structures 1 and 2 in CIF format have
been deposited with the Cambridge Crystallographic Data Centre,
nos. CCDC 249822 and 249823, respectively.
IC050171A
4016 Inorganic Chemistry, Vol. 44, No. 11, 2005