Synthesis and structures of oxyanion encapsulated copper(I)-dppm complexes (dppm = bis(diphenylphosphino)methane)

Article abstract of DOI:10.1021/ic9801589

Copper(I)-dppm complexes encapsulating the oxyanions ClO₄^-, NO₃^-, CH₃C₆H₄CO₂^-, SO₄^2-, and WO₄^2- have been synthesized either by reduction of the corresponding Cu(II) salts and treatment with dppm, or by treating the complex [Cu₂(dppm)₂(dmcn)₃](BF₄)₂ (1) (dmcn = dimethyl cyanamide) with the respective anion. The isolated complexes [Cu₂(dppm)₂(dmcn)₂(ClO₄)] (ClO₄) (2), [Cu₂(dppm)₂(dmcn)₂(NO₃)] (NO₃) (3), Cu₂(dppm)₂(NO₃)₂ (4), [Cu₂(dppm)₂(CH₃C₆H ₄CO₂)₂]dmcn·2THF (5), Cu₂(dppm)₂(SO₄) (6), and [Cu₃(dppm)₃(Cl)(WO₄)] 0.5H₂O (7) have been characterized by IR, ¹H and ³¹P{¹H} NMR, UV-vis, and emission spectroscopy. The solid-state molecular structure of complexes 1, 2, 4, and 7 were determined by single-crystal X-ray diffraction. Pertinent crystal data are as follows: for 1, monoclinic P2₁/c, a = 11.376(10) A?, b = 42.503(7) A?, c = 13.530(6) A?, β= 108.08(2)°, V = 6219(3) A?³, Z = 4; for 2, monoclinic P2₁/n, a = 21.600(3) A?, b = 12.968(3) A?, c = 23.050(3) A?, β= 115.97(2)°, V = 5804(17) A?³, Z = 4; for 4, triclinic P1?, a = 10.560(4) A?, b = 10.553(3) A?, c = 22.698(3) A?, α = 96.08(2)°, β= 96.03(2)°, γ = 108.31(2)°,V= 2362(12) A?³, Z = 2; and for 7, orthorhombic P2₁2₁2₁, a = 14.407(4) A?, b = 20.573(7) A?, c = 24.176(6) A?, V = 7166(4) A?³, Z = 4. Analyses of the crystallographic and spectroscopic data of these complexes reveal the nature of interactions between the Cu¹-dppm core and oxyanion. The anchoring of the oxyanion to the Cu_n(dppm)_n unit is primarily through coordination to the metal, but the noncovalent C-H?O interactions between the methylene and phenyl protons of the dppm and oxygen atoms of the oxyanion play a significant role. The solid-state emission spectra for complexes 1-6 are very similar but different from 7. In CDCl₃ solution, addition of ClO₄^- or NO₃^- (as their tetrabutylammonium salts) to 1 establishes a rapid equilibrium between the anion-complexed and uncomplexed forms. The association constant values for ClO₄^- and NO₃^- have been estimated from the ³¹P{¹H} NMR spectra.

Full text of DOI:10.1021/ic9801589

Inorg. Chem. 1999, 38, 1725-1735
1725
Synthesis and Structures of Oxyanion Encapsulated Copper(I)-dppm Complexes (dppm )
Bis(diphenylphosphino)methane)
Jitendra K. Bera, Munirathnam Nethaji, and Ashoka G. Samuelson*
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
ReceiVed February 10, 1998
Copper(I)-dppm complexes encapsulating the oxyanions ClO4-, NO3-, CH3C6H4CO2-, SO42-, and WO42- have
been synthesized either by reduction of the corresponding Cu(II) salts and treatment with dppm, or by treating
the complex [Cu2(dppm)2(dmcn)3](BF4)2 (1) (dmcn ) dimethyl cyanamide) with the respective anion. The isolated
complexes [Cu2(dppm)2(dmcn)2(ClO4)] (ClO4) (2), [Cu2(dppm)2(dmcn)2(NO3)] (NO3) (3), Cu2(dppm)2(NO3)2 (4),
[Cu2(dppm)2(CH3C6H4CO2)2]dmcn‚2THF (5), Cu2(dppm)2(SO4) (6), and [Cu3(dppm)3(Cl)(WO4)] 0.5H2O (7) have
been characterized by IR, 1H and 31P{1H} NMR, UV-vis, and emission spectroscopy. The solid-state molecular
structure of complexes 1, 2, 4, and 7 were determined by single-crystal X-ray diffraction. Pertinent crystal data
are as follows: for 1, monoclinic P21/c, a ) 11.376(10) Å, b ) 42.503(7) Å, c ) 13.530(6) Å, â ) 108.08(2)°,
V ) 6219(3) Å3, Z ) 4; for 2, monoclinic P21/n, a ) 21.600(3) Å, b ) 12.968(3) Å, c ) 23.050(3) Å, â )
115.97(2)°, V ) 5804(17) Å3, Z ) 4; for 4, triclinic P1h, a ) 10.560(4) Å, b ) 10.553(3) Å, c ) 22.698(3) Å,
R ) 96.08(2)°, â ) 96.03(2)°, γ ) 108.31(2)°, V ) 2362(12) Å3, Z ) 2; and for 7, orthorhombic P212121, a )
14.407(4) Å, b ) 20.573(7) Å, c ) 24.176(6) Å, V ) 7166(4) Å3, Z ) 4. Analyses of the crystallographic and
spectroscopic data of these complexes reveal the nature of interactions between the CuI-dppm core and oxyanion.
The anchoring of the oxyanion to the Cun(dppm)n unit is primarily through coordination to the metal, but the
noncovalent C-H‚‚‚O interactions between the methylene and phenyl protons of the dppm and oxygen atoms of
the oxyanion play a significant role. The solid-state emission spectra for complexes 1-6 are very similar but
different from 7. In CDCl3 solution, addition of ClO4- or NO3- (as their tetrabutylammonium salts) to 1 establishes
a rapid equilibrium between the anion-complexed and uncomplexed forms. The association constant values for
ClO4 and NO3 have been estimated from the 31P{1H} NMR spectra.
-
-
Introduction
appended amide functionalities are hydrogen bond donors.
Appropriate functionalization of the metallocene results in
selective complexation of anions.3a,c Receptors for even the
elusive anion BF4- have been designed using iron(II) templates
The design and synthesis of smart molecules, able to function
as receptors and sensors of charged species, are of immense
interest. While cation-receptors have been studied extensively,
the design of anion-receptors has been taken up only recently.1
Due to their varied shapes and sizes,2 anions pose a greater
challenge than cations. The capture of oxyanions in particular,
is difficult due to their large ionic radii, high free energies of
solvation and lower Lewis basicities. However, significant
advances have been made in the past decade. Beer et al have
illustrated the use of metallocene3 and metal-bipyridyl4 com-
plexes to synthesize rigid yet modifiable frameworks. The
metallocene provides the requisite positive charge and the
and dinitrile ligands.5 Atwood et al have trapped BF4 using
-
the bowl shaped cycloveratrylene (CTV) which is activated for
receiving anions by complexation with Ru2+.6 The CTV bowl
also shows a preferred selectivity for large tetrahedral anions
-
such as MO4 (M ) Tc, Re). Surprisingly a preference for
-
-
TcO4 over ReO4 has been exhibited by this system.7 Thus,
most anion-receptors designed till date involve a cationic
receptor site with suitable hydrogen bond donors. The CTV
system is a notable exception highlighting the power of
noncovalent interactions in host-guest chemistry.
Copper(I) complexes are particularly attractive for the design
of anion sensors. The flexibility Cu(I) has in the coordination
number and geometry requirements8sdue to the absence of
CFSEsshould allow the formation of stable complexes with
and without the anion. Moreover the lability of these Cu(I)
(1) (a) Cooper, C. R.; Spencer, N.; James, T. D. Chem. Commun. 1998,
1365. (b) Falana, O. M.; Koch, H. F.; Roundhill, D. M.; Lumetta, G.
J.; Hay, B. P. Chem. Commun. 1998, 503. (c) Holman, K. T.; Steed,
J. W.; Atwood, J. L. Angew. Chem., Int. Ed. Engl. 1997, 36, 1736.
(d) Jacopozzi, P.; Dalcanale, E. Angew. Chem., Int. Ed. Engl. 1997,
36, 613. (e) Jagessar, R. C.; Burns, D. H. Chem. Commun. 1997, 1685.
(f) Munakata, M.; Wu, L. P.; Yamamoto, M.; Kuroda-Sowa, T.;
Maekawa, M. J. Am. Chem. Soc. 1996, 118, 3117. (g) Gale, P. A.;
Sessler, J. L.; Kra´l, V.; Lynch, V. J. Am. Chem. Soc. 1996, 118, 5140.
(h) Atwood, J. L.; Holman, K. T.; Steed, J. W. Chem. Commun. 1996,
1401. (i) Worm, K.; Schmidtchen, F. P. Angew. Chem., Int. Ed. Engl.
1995, 34, 65. (j) Steed, J. W.; Juneja, R. K.; Atwood, J. L. Angew.
Chem., Int. Ed. Engl. 1994, 33, 2456. (k) Dietrich, B. Pure Appl. Chem.
1993, 65, 1457.
(4) (a) Beer, P. D.; Szemes, F.; Balzani, V.; Sala`, C. M.; Drew, M. G. B.;
Dent, S. W.; Maestri, M. J. Am. Chem. Soc. 1997, 119, 11864. (b)
Beer, P. D.; Dent, S. W.; Wear, T. J. J. Chem. Soc., Dalton Trans.
1996, 2341. (c) Beer, P. D.; Chen, Z.; Goulden, A. J.; Grieve, A.;
Hesek, D.; Szemes, F.; Wear, T. J. Chem. Soc., Chem. Commun. 1994,
1269.
(5) Mann, S.; Huttner, G.; Zsolnai, L.; Heinze, K. Angew. Chem., Int.
Ed. Engl. 1996, 35, 2808.
(6) Steed, J. W.; Junk, P. C.; Atwood, J. L.; Barnes, M. J.; Raston, C. L.;
Burkhalter, R. S. J. Am. Chem. Soc. 1994, 116, 10346.
(7) Holman, K. T.; Halihan, M. M.; Steed, J. W.; Jurisson, S. S.; Atwood,
J. L. J. Am. Chem. Soc. 1995, 117, 7848.
(2) Gadre, S. R.; Ko¨lmel, C.; Shrivastava, I. Inorg. Chem. 1992, 31, 2279.
(3) (a) Beer, P. D. Chem. Commun. 1996, 689. (b) Beer, P. D.; Drew, M.
G. B.; Hesek, D.; Shade, M.; Szemes, F. Chem. Commun. 1996, 2161.
(c) Beer, P. D.; Chen, Z.; Goulden, A. J.; Graydon, A.; Stokes, S. E.;
Wear, T. J. Chem. Soc., Chem. Commun. 1993, 1834.
10.1021/ic9801589 CCC: $18.00 © 1999 American Chemical Society
Published on Web 03/25/1999

1726 Inorganic Chemistry, Vol. 38, No. 8, 1999
Bera et al.
for Cu2P4C56H56N6O6: C, 57.97 (58.13); H, 4.88 (5.09); N, 7.25 (7.46).
systems make them particularly suited for sensor design. Loss
of the ligand and reactivation of the receptor site should be
readily possible. We report in this study a set of CuI-dppm
complexes which bind oxyanions through coordination to the
metal and weak nonbonding interactions. Our work comple-
ments a recent report by Kitagawa et al. on CuI-diphosphine
complexes.9 The dimeric structure of Cu2(dppm)2 complex with
closely spaced copper centers flanked by the phenyl rings of
the dppm ligands creates a cavity. The presence of oxyanionss
with different charges, sizes, and shapessin this cavity affects
molecular parameters of the Cu2(dppm)2 core. A variety of
techniques, such as IR stretching frequencies, NMR, and solid-
state fluorescence spectra can be used to detect anion complex-
ation.
IR data (cm-1): for dppm, 3051 (w), 1484 (m), 1435 (m), 1096 (m),
-
763 (m), 694 (m), 517 (m), 477 (m); for dmcn, 2229 (s); for NO3
1359 (vs, br), 791 (m).
,
Synthesis of Cu2(dppm)2(NO3)2 (4). Tetrabutylammonium nitrate
(0.150 g, 0.49 mmol) was added to a solution of 1 (0.190 g, 0.15 mmol)
in CH2Cl2 (20 mL.) and stirred for 2 h. The solvent was removed under
reduced pressure, and the residue was washed with petroleum ether. It
was redissolved in 5 mL of CH2Cl2, layered with petroleum ether, and
kept at 4 °C for 7 days. White crystals of 4 separated out from the
solution (yield: 44%). Anal. Found (calcd) for Cu2P4C50H44N2O6: C,
58.88 (58.86); H, 4.36 (4.44); N, 2.75 (2.78). IR data (cm-1): for dppm,
3051 (w), 1484 (m), 1437 (m), 1096 (m), 763 (m), 694 (m), 516 (m),
477 (m); for NO3-, 1359 (vs, br), 791 (m).
Synthesis of [Cu2(dppm)2(CH3C6H4CO2)2]dmcn‚2THF. (5). Potas-
sium p-methyl benzoate (0.130 g, 0.75 mmol) was stirred with complex
1 (0.180 g, 0.14 mmol) in 1:1 mixture of CH2Cl2/THF (2 × 10 mL)
for 12 h. It was then filtered, and the solvent was removed under
reduced pressure, resulting in an oily residue. Addition of petroleum
ether gave a solid residue which was washed with the same solvent. It
was redissolved in dry CH2Cl2 (5 mL), filtered, and crystallized by
layering with petroleum ether (yield: 51%). Anal. Found (calcd) for
Cu2C77P4N2H80O6: C, 66.98 (67.31); H, 5.85 (5.51); N, 2.03 (2.31).
IR data (cm-1): for dppm, 3048 (w), 1482 (m), 1435 (m), 771 (m),
736 (s), 695 (s), 513 (m), 479 (m); for dmcn, 2216; for benzoate, 1592
(m) (ring C-C stretch), 1551 (m), 1372 (m) (asymmetric and symmetric
Experimental Section
Materials. Dichloromethane, petroleum ether (bp 60-80 °C) and
acetonitrile were purified and dried by conventional methods, distilled
under nitrogen, and deoxygenated before use. Methanol and tetrahy-
drofuran were distilled and used as such. [Cu(CH3CN)4]BF4 and
[Cu(CH3CN)4]ClO4 were freshly prepared before use. (Caution!
Perchlorate salts of metal complexes with organic ligands are
potentially explosiVe. While we haVe encountered no untoward incident
in their preparation and studies, it is preferable that only small amounts
are prepared at a time and handled with great caution). Bis-
(diphenylphosphino)methane, tetrabutylammonium perchlorate, and
tetrabutylammonium nitrate were purchased from Aldrich. Dimethyl
cyanamide was bought from Fluka. Sodium tungstate and p-methyl
benzoic acid were obtained from Sisco-Chem (India).
-
CO2 stretching, respectively), 906 (w).
Synthesis of Cu2(dppm)2(SO4) (6). CuSO4‚5H2O (0.120 g, 0.48
mmol) dissolved in CH3CN with minimum amount of water was
refluxed with Cu powder for 10 h. The pale blue colored solution
obtained was filtered, and the filtrate was added to dppm (0.370 g,
0.96 mmol) dissolved in CH3CN (5 mL) and stirred for 2 h. Solvent
was removed completely under reduced pressure. The solid residue
obtained was redissolved in CH2Cl2 (25 mL) and dmcn (0.12 mL, 1.44
mmol) was added to it. After stirring for 30 min, the solution was
filtered and concentrated to 2-3 mL. The complex 6 was precipitated
by the addition of petroleum ether, filtered, and washed thrice with
same solvent (3 × 5 mL). It was then dried under vacuum. Analytically
pure material was obtained by recrystallization from a mixture of CH2-
Cl2 and petroleum ether (yield: 45%). Anal. Found (calcd) for
Cu2C50P4H44SO4: C, 60.54 (60.31); H, 4.48 (4.46). IR data (cm-1):
for dppm, 3051 (w), 1585 (w), 1481 (m), 1434 (m), 773 (m), 736 (m),
693 (s), 515 (m), 482 (m); for SO42-, 1180, 1140, 1095, 612 (m).
Synthesis of [Cu3(dppm)3(Cl)(WO4)]‚0.5H2O (7). Complex 1
(0.203 g, 0.16 mmol) and sodium tungstate (0.300 g, 0.91 mmol) were
stirred in 1:1 CH2Cl2/CH3OH (2 × 15 mL) for 2 h. The reaction mixture
was filtered, and the colorless filtrate was concentrated under reduced
pressure. The residue was redissolved in CH2Cl2 and filtered, and the
solvent was removed under vacuum to obtain complex 7. Crystals of
7 were obtained using the procedure employed for preparing crystalline
6 (yield: 34%). Anal. Found (calcd) for Cu3C75P6H66ClWO4.5: C, 55.08
(55.23); H, 4.08 (4.02). IR data (cm-1): for dppm, 3051 (w), 1585
(w), 1481 (m), 1434 (m), 773 (m), 736 (m), 693 (s), 515 (m), 482 (m);
Complexes Cu2(dppm)2(CH3CN)4(ClO4)2 (8)10 and Cu3(dppm)3(OH)-
Syntheses. All reactions were carried out in an atmosphere of dried
N2 using standard Schlenk and vacuum line techniques.
Synthesis of [Cu2(dppm)2(dmcn)3](BF4)2 (1). To a CH2Cl2 (20 mL)
solution containing dppm (0.200 g; 0.52 mmol) was added Cu(CH3-
CN)4BF4 (0.160 g; 0.51 mmol) and stirred at room temperature until it
formed a clear solution. It was then treated with dmcn (0.15 mL; 1.85
mmol). After stirring for another 30 min, the solvent was removed under
reduced pressure resulting in an oily residue. Trituration with petroleum
ether resulted in precipitation of 1 which was filtered and washed with
petroleum ether (3 × 5 mL). It was dried under vacuum. Crystallization
to get analytically pure material was effected by layering a CH2Cl2
solution of the compound with petroleum ether (yield: 94%). Anal.
Found (calcd) for Cu2P4F8N6C59B2H62: C, 55.36 (55.38); N, 6.57 (6.67);
H, 4.89 (4.91). IR data (cm-1): for dppm, 3059 (w), 1579 (w), 1481
(m), 1430 (m), 771 (w), 740 (m), 695 (s), 516 (m), 475 (m); for dmcn,
2235, 2210; for BF4-, 1056 (vs, br).
Synthesis of [Cu2(dppm)2(dmcn)2(ClO4)] (ClO4) (2). Synthesis of
2 was carried out using a procedure identical to the synthesis of 1
starting with [Cu(CH3CN)4](ClO4) instead of [Cu(CH3CN)4](BF4)
(yield: 94%). Anal. Found (calcd) for Cu2C56P4N4H56Cl2O8: C, 54.46
(54.55); N, 4.54 (4.81); H, 4.58 (4.62). IR data (cm-1): for dppm, 3051
(w), 1583 (w),1482 (m), 1432 (m), 889 (w), 796 (w), 769 (w), 743
(m), 695 (s), 513 (m), 474 (m); for dmcn, 2237 (s); for ClO4-, 1091
(vs, br), 622 (m).
Synthesis of [Cu2(dppm)2(dmcn)2(NO3)] (NO3) (3). Cu(NO3)2
(0.050 g, 0.27 mmol) was refluxed with copper powder in CH3CN for
4 h. The colorless solution obtained was filtered to a flask containing
dppm (0.200 g, 0.52 mmol) in CH3CN (5 mL) and stirred for 1 h. The
solvent was completely removed under reduced pressure. The white
residue was redissolved in CH2Cl2 (20 mL), and dmcn (0.15 mL, 1.85
mmol) was added to it. After stirring for 30 min, the solution was
concentrated to 2-3 mL. The compound was precipitated by addition
of petroleum ether, filtered, and washed with the same solvent (3 × 5
mL). It was then dried under vacuum (yield: 69%). Anal. Found (calcd)
11
(BF4)2 were synthesized following literature procedures.
1
Instruments and Measurements. H NMR spectra were recorded
with a Bruker ACF 200 MHz spectrometer operating at 81.1 MHz,
and 31P{1H} NMR spectra, on a Bruker AMX 400 MHz spectrometer
operating at 162 MHz. Chemical shifts were calibrated to tetrameth-
1
ylsilane and 85% H3PO4 as external references for H and 31P{1H}
NMR, respectively. All the 1H and 31P{1H} NMR spectra were recorded
in CDCl3 solution with the exception of 4 and 6. NMR spectrum of 4
was obtained in acetone-d6 while the 31P{1H} NMR of 6 was recorded
1
in DMSO-d6. H NMR spectrum of complex 6 was recorded from its
saturated solution in CDCl3. Infrared spectra were measured on a Bio-
Rad FTS-7 spectrophotometer. Elemental analyses were done with a
Carlo Erba model 1106 elemental analyzer. UV-visible and emission
(8) Hathaway, B. J. ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. G., McCleverty, J. A., Eds.; Pergamon Press: Oxford,
1987; Vol. 5.
(9) Kitagawa, S.; Kondo, M.; Kawata, S.; Wada, S.; Maekawa, M.;
Munakata, M. Inorg. Chem. 1995, 34, 1455.
(10) Diez, J.; Gamasa, M. P.; Gimeno, J.; Tiripicchio, A.; Camellini, M.
T. J. Chem. Soc., Dalton Trans. 1987, 1275.
(11) Ho, D.; Bau, R. Inorg. Chem. 1983, 22, 4079.

Oxyanion-Encapsulated CuI-dppm Complexes
Inorganic Chemistry, Vol. 38, No. 8, 1999 1727
Table 1. Crystallographic Data for [Cu2(dppm)2(dmcn)3](BF4)2 (1), [Cu2(dppm)2(dmcn)2(ClO4)]ClO4 (2), Cu2(dppm)2(NO3)2 (4), and
[Cu3(dppm)3(Cl)(WO4)]‚0.5H2O (7)
1
2
4
7
empirical formula
fw
crystal system
temp (K)
λ (Å)
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C59H62B2Cu2F8N6P4
1279.73
monoclinic
293
0.7107
P21/c
11.3760(10)
42.503(7)
13.530(6)
C58H56Cl2Cu2N4O8P4
1258.93
monoclinic
293
0.7107
P21/n
21.60(3)
12.97(3)
23.05(3)
C50H44Cu2N2O6P4
1019.83
triclinic
293
0.7107
P1h
10.56(4)
10.55(3)
22.70(3)
96.08(2)
96.03(2)
108.31(2)
2362 (12)
2
C75H66ClCu3O4P6W
1627.02
orthorhombic
293
0.7107
P212121
14.407(4)
20.573(7)
24.176(6)
108.08(2)
115.97(2)
6219(3)
4
1.367
5804(17)
4
1.441
7166(4)
4
1.508
Z
F
calcd (g/cm3)
1.434
10.87
abs coeff (cm-1
)
8.53
9.92
26.97
F(000)
no. of indep reflcns
2632
10 916
2592
10 212
1048
8309
3264
6894
no. of data/restraints/parameters
final R1,a wR2b [I > 2σ(I)]
final R1,a wR2b (all data)
GOFc
10748/0/678
0.0742, 0.1866
0.1102, 0.2886
1.073
10212/0/701
0.0778, 0.1731
0.1549, 0.1927
1.035
8306/0/607
0.0361, 0.0953
0.0429, 0.1018
1.086
6894/0/286
0.1075, 0.2613
0.2176, 0.2903
1.015
2
2
2
2
a R1 ) (Σ||Fo| - |Fc||)/(Σ|Fo|). b wR2 ) [Σw(|Fo| - |Fc| )2/Σw|Fo| )2]1/2
. .
c GOF ) [w(Fo - Fc2)2]/(n - p)1/2
-
spectra were recorded on Hitachi U-3400 and Hitachi F-2000 spectro-
photometers, respectively. Crystals of the complexes were freshly
prepared for the emission study.
of the oxygen atoms of the isolated ClO4 unit were found to be
disordered over two positions and could be refined with an occupancy
-
factor of 0.5. On the contrary, a very well behaved ClO4 anion is
X-ray Data Collection, Structure Solution, and Refinement.
General. Crystals of 1, 2, 4, and 7 suitable for diffraction studies were
glued to the tip of glass fibers and transferred to a computer controlled
Enraf-Nonius CAD4 diffractometer with graphite-monochromatized Mo
KR radiation. Accurate unit cell parameters and orientation matrixes
were determined by least-squares refinement of 25 well-centered
reflections in the range 10° e θ e 18°. Three periodically measured
reference reflections showed no significant decay (<5%) during the
time of data collection. Crystal data and the relevant experimental details
on data collection and refinement for 1, 2, 4, and 7 are given in Table
1. Data collected at 20 °C were corrected for Lorentz and polarization
effects. The position of the heavy atoms were determined by Patterson
methods using SHELXS86.12 The remaining atoms were found from
difference Fourier analyses using SHELXL-93.13
located inside the metal coordination sphere. All the atoms of the
complexed ClO4 were refined anisotropically with normal thermal
-
parameters. Hydrogen atoms were included in the final stage of the
refinement on calculated positions bonded on their carrier atoms. An
empirical absorption correction was applied to the data. The highest
peak in the final difference map not exceeding 1.0 e Å-3 was located
near the disordered C41 atom. Convergence was reached at R ) 0.0778.
Cu2(dppm)2(NO3)2 (4). A hexagonal block-shaped crystal was cut
to measure 0.7 × 0.5 × 0.7 mm and used for the data collection. A
total of 8867 reflections were collected in the range 1.65° e θ e 24.97°.
All non-hydrogen atoms were refined with anisotropic thermal param-
eters. Hydrogen atoms were included in the final stage of the refinement
on calculated positions bonded on their carrier atoms. The final
difference map was flat showing the highest peak of 0.66 e Å-3 near
Cu1. Convergence was reached at R ) 0.0361.
[Cu3(dppm)3(Cl)(WO4)]‚0.5H2O (7). A very fragile, stick-shaped
crystal was chosen from several crystals mixed with amorphous
material. The amorphous material wrapped around the crystal was
carefully removed by washing with petroleum ether. Intensity data of
6959 reflections were collected in the range 1.30° e θ e 24.96°. The
carbon atoms of the phenyl rings of the dppm ligands were located
from the difference Fourier maps and refined as rigid groups. Only the
tungsten, coppers and the phosphorus atoms were refined anisotropi-
cally. An empirical absorption correction was applied to the data.
Hydrogen atoms were included in the final stage of the refinement on
calculated positions bonded on their carrier atoms. An isolated partially
occupied water molecule was found from the difference Fourier maps.
The highest remaining peak in the final difference Fourier was 1.22 e
Å-3 and located at a distance of 0.659 Å from the Cu2 center. The
final R value obtained was 0.1075.
[Cu2(dppm)2(dmcn)3] (BF4)2 (1). A colorless rectangular crystal (0.5
× 0.5 × 0.7 mm) was used for the data collection. A total of 11 784
reflections were collected in the range 1.65° < θ < 24.97°. All non-
hydrogen atoms were refined with anisotropic thermal parameters except
the carbon atoms of methyl groups on the dmcn ligand and two isolated
BF4- anion fragments. The carbon atom of a methyl group attached to
N6 and the fluorine atoms of the anions were found to be severely
disordered and they were refined with partial occupancies. Hydrogen
atoms were included in the final stage of the refinement on calculated
positions bonded on their carrier atoms. An empirical absorption
correction was applied to the data.14 The final difference map shows
the highest peak of 0.82 e Å-3 located in the vicinity of one of the
-
BF4 anion. Convergence was reached at R ) 0.0742.
[Cu2(dppm)2(dmcn)2(ClO4)] (ClO4) (2). A colorless needle-shaped
crystal (0.2 × 0.3 × 0.8 mm) was selected for the X-ray diffraction
study. Intensity data of 11096 reflections were collected in the range
1.08° e θ e 24.99°. The structure was found to contain an isolated,
-
disordered ClO4 along with a complexed anion. All non-hydrogen
atoms were refined with anisotropic thermal parameters except the
carbon atoms of the methyl groups attached to N4 and atoms of the
isolated ClO4 fragment. The C41 atom was found to be disordered
Results and Discussion
-
Synthesis and Analysis. CuI-dppm complexes encapsulating
various oxyanions were prepared starting from the corresponding
Cu(II) salt or by treating 1 with the respective anion. The
procedures employed in this study have been illustrated in
Scheme 1. Complexes 1, 2, 3 and 6 were prepared from the
corresponding Cu(II) salt. Reduction was carried out by reflux-
and hence refined with partial occupancies. The electron occupancies
(12) Sheldrick, G. M. SHELXS-86: Program for Crystal Structure Deter-
mination; University of Cambridge: Cambridge, England, 1986.
(13) Sheldrick, G. M. SHELXL-93: A Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(14) Parkin, S.; Moezzi, B.; Hope, H. J. Appl. Crystallogr. 1995, 28, 53.

1728 Inorganic Chemistry, Vol. 38, No. 8, 1999
Bera et al.
Scheme 1
ing the Cu(II) salt in acetonitrile with copper powder under
nitrogen atmosphere. In the case of 1 and 2, the intermediate
Cu(I) complexes [Cu(CH3CN)4]X (X ) BF4-, ClO4-) were
isolated. Complexes 3 and 6 were prepared by adding dppm
and dmcn to the colorless Cu(I) solution obtained in situ after
filtering the copper powder. The reduction time varies with the
anion present in the reaction mixture. The SO42- salt takes the
longest and is not completely reduced even after 12 h. Reduction
of CuSO4 is hampered by its poor solubility in CH3CN. The
reduction is facilitated if CuSO4 is dissolved in a minimum
Chart 1
2-
amount of water. Partial reduction in the case of the SO4
Chart 2
complex results in a low yield of the complex. Interestingly,
although excess dmcn is used in the preparation of complex 6,
the crystalline material does not contain any of the ligand.
Complexes 3 and 6, which do not have the ancillary ligand dmcn
have poor solubility in CH2Cl2.
Complexes 4, 5, and 7 were prepared starting from 1.
Replacement of the BF4- by oxyanions during the reaction was
monitored by IR spectroscopy. Complex 1 was reacted with
tetrabutylammonium nitrate in CH2Cl2 to obtain complex 4.
Copper(I)-dppm complexes containing benzoate or substituted
benzoate anion had been synthesized earlier by the reaction of
CO2 with CuI-aryls in the presence of the diphosphine ligand.15
Recently, the acetate bridged Cu2(dppm)2 complex has been
prepared by stirring the Cu3(dppm)3(OH)(BF4)2 with sodium
with the Cu2(dppm)2 system (Chart 1). Complex 3 was prepared
in the presence of excess dmcn and the ratio of Cu(I) and NO3
-
was 1:1. Use of excess dmcn results in formation of 3 containing
two dmcn and one NO3- inside the metal coordination sphere.18
On the contrary, treatment of complex 1, which has 1.5
-
equivalent of dmcn for each Cu(I), with excess NO3 gives 4.
Complex 4 does not contain any dmcn and both NO3- ions are
-
bonded to copper. This illustrates the labile nature of both NO3
-
acetate.16 We have prepared complex 5 by replacing the BF4
and dmcn, which allows formation of either 3 or 4 depending
on the ratio of the reagents used.
in 1 with p-methyl benzoate. The time taken for complete
-
replacement of BF4 by the benzoate anion was around 12 h.
Solid-State Molecular Structure. X-ray structure determi-
nation was carried out to confirm the nuclearity and understand
the nature of the interaction between the anions and CuI-dppm
core. Single crystals suitable for X-ray diffraction study were
obtained for 1, 2, 4, and 7 and their molecular structure were
established. We discuss the common features observed in these
complexes first. The structural details unique for the individual
complexes are discussed later.
The solid-state molecular structure of complexes 1, 2, and 4
consists of a dimeric Cu2(dppm)2 core while complex 7 is a
trimeric Cu3(dppm)3 unit. In the dimeric complexes, two copper
atoms are doubly bridged by two dppm ligands to form an eight-
membered Cu2P4C2 ring. The Cu2P4C2 ring can adopt both boat
and chair conformations If the methylene carbons are cis, they
have a boat conformation and if they are trans, a chair
conformation results (Chart 2). Several structurally characterized
Cu2(dppm)2 complexes are in the boat form.16,19 Recently
Walton et al. have solved the structure of [Re2(dppm)2] units
The decrease in the intensity of BF4- bands and the development
of new peaks due to the benzoate anion were followed by IR
spectroscopy. The composition of 5 included two molecules of
1
THF and one molecule of dmcn. This was confirmed by H
NMR and chemical analysis.
Complex 7 was prepared by treating 1 with Na2WO4 in 1:1
-
CH2Cl2/CH3OH solvents. Complete replacement of BF4 was
confirmed by the IR spectra and the analytical data. Abstraction
of Cl- from the chlorinated solvent in the presence of sodium
salts is known.17 In this case also, CH2Cl2 is the probable source
of Cl-.
The composition of complexes 3 and 4 bring out some
-
interesting features regarding the interaction of dmcn and NO3
(15) Marsich, N.; Camus, A.; Nardin, G. J. Organomet. Chem. 1982, 239,
429.
(16) Harvey, P. D.; Drouin, M.; Zhang, T. Inorg. Chem. 1997, 36, 4998.
(17) (a) Pe´rez-Lourido, P. A.; Garc´ıa-Va´zquez, J. A.; Romero, J.; Louro,
M. S.; Sousa, A.; Chen, Q.; Chang, Y.; Zubieta, J. J. Chem. Soc.,
Dalton Trans. 1996, 2047. (b) Yam, V. W.-W.; Lee, W.-K.; Lai, T.-
F. Organometallics 1993, 12, 2383. (c) Diez, J.; Gamasa, M. P.;
Gimeno, J.; Lastra, E.; Aguirre, A.; Garc´ıa-Granda, S. Organometallics
1993, 12, 2213.
(18) The structure of complex 3 is inferred from the spectroscopic and
chemical analysis data. The proposed structure is analogous to complex
-
-
2 except that the anion is NO3 instead of ClO4
.

Oxyanion-Encapsulated CuI-dppm Complexes
Inorganic Chemistry, Vol. 38, No. 8, 1999 1729
Figure 1. X-ray structure of the [Cu2(dppm)2(dmcn)3]2+ unit in the
crystal of 1. Only one position of the disordered C62 atom is shown.
Hydrogen atoms are omitted for clarity.
Figure 2. X-ray structure of the [Cu2(dppm)2(dmcn)2(ClO4)2]+ unit
in 2. Only one position of the disordered C41 atom is shown. Hydrogen
atoms are omitted for clarity.
Table 2. Selected Bond Distances (Å) and Angles (deg) of
[Cu2(dppm)2(dmcn)3](BF4)2 (1)
Table 3. Selected Bond Distances (Å) and Angles (deg) of
[Cu2(dppm)2(dmcn)2(ClO4)] ClO4 (2)
Bond Distances
Cu(1)-Cu(2)
Cu(1)-N(1)
Cu(1)-N(5)
Cu(1)-P(1)
Cu(1)-P(2)
Cu(2)-N(3)
3.143(2)
2.037(8)
2.129(6)
2.245(2)
2.270(2)
2.034(7)
Cu(2)-P(3)
Cu(2)-P(4)
Cu(2)-N(5)
N(1)-C(11)
N(3)-C(31)
N(5)-C(51)
2.251(2)
2.255(2)
2.278(7)
1.126(10)
1.122(10)
1.126(9)
Bond Distances
Cu(1)-Cu(2)
Cu(1)-N(1)
Cu(1)-P(1)
Cu(1)-P(2)
Cu(1)-O(11)
Cu(2)-N(3)
Cu(2)-P(4)
3.424(5)
2.011(6)
2.247(4)
2.257(5)
2.323(5)
2.014(7)
2.241(5)
Cu(2)-P(3)
Cu(2)-O(11)
Cl(1)-O(14)
Cl(1)-O(12)
Cl(1)-O(13)
Cl(1)-O(11)
2.246(4)
2.329(5)
1.393(6)
1.402(6)
1.410(7)
1.455(5)
Bond Angles
N(1)-Cu(1)-N(5) 96.0(3)
N(1)-Cu(1)-P(1) 110.8(2)
N(5)-Cu(1)-P(1) 117.4(2)
N(1)-Cu(1)-P(2) 106.9(2)
N(5)-Cu(1)-P(2) 108.2(2)
P(1)-Cu(1)-P(2)
N(3)-Cu(2)-P(3) 105.4(2)
N(3)-Cu(2)-P(4)
P(3)-Cu(2)-P(4)
N(3)-Cu(2)-N(5)
P(3)-Cu(2)-N(5)
P(4)-Cu(2)-N(5)
114.6(2)
125.05(7)
95.5(3)
109.2(2)
102.9(2)
Bond Angles
N(1)-Cu(1)-P(1) 108.2(2)
N(3)-Cu(2)-P(3)
106.7(2)
133.47(13)
N(1)-Cu(1)-P(2) 107.2(2)
P(4)-Cu(2)-P(3)
P(1)-Cu(1)-P(2)
131.09(13) N(3)-Cu(2)-O(11) 100.7(3)
115.44(7) Cu(1)-N(5)-Cu(2) 90.9(2)
N(1)-Cu(1)-O(11) 100.8(3)
P(1)-Cu(1)-O(11) 102.7(2)
P(4)-Cu(2)-O(11) 104.27(14)
P(3)-Cu(2)-O(11) 98.93(14)
P(2)-Cu(1)-O(11) 102.73(14) Cu(1)-O(11)-Cu(2) 94.8(2)
N(3)-Cu(2)-P(4) 107.9(2)
in both the chair and boat forms.20 Complexes 1 and 4 adopt a
boat conformation with a C13-Cu1-Cu2-C24 torsional angle
of -94° and -105° respectively. Complex 2 crystallizes in a
chair form with a C13-Cu1-Cu2-C24 torsional angle 132°.
Molecular Structure of 1. The solid-state structure of this
complex consists of dinuclear [Cu2(dppm)2(η1-dmcn)2(η1,µ2-
dmcn)]2+ species and two isolated BF4- anions. The molecular
structure together with the atomic numbering scheme is depicted
in Figure 1. Important bond distances and bond angles are given
in Table 2. The coordinating environments of both copper atoms
are distorted tetrahedral. Each copper atom is coordinated to
two phosphorus atoms of two different dppm ligands and two
nitrogen atoms of two dmcn ligands. One dmcn ligand is
terminally bonded to each of the copper centers while the other
dmcn is bridging the two metal centers. Though the structure
of the dimeric moiety of complex 1 looks apparently similar to
the reported structure10 of Cu2(dppm)2(CH3CN)4(ClO4)2 (8),
significant differences are present. In the latter, two acetonitrile
ligands are linearly bonded with each copper atom. On the other
hand, the solid-state structure of complex 1 has only one
terminally bonded dmcn for each copper atom. The bridging
dmcn ligand between the two metal centers completes the
tetrahedral environment around the metal center (Chart 3).
The copper-phosphorus distances are marginally shorter than
those observed in the acetonitrile complex 8 (2.283 and 2.270
Å). The Cu1-N1 and Cu2-N3 distances are similar and shorter
than the Cu-N5 distances observed for the bridging nitrogen
atom. Moreover, Cu1-N5 and Cu2-N5 distances are not equal
adding to the asymmetry around the copper centers. The
distorted tetrahedral environment around both metal centers is
evident from the angles reported in Table 2. The P1-Cu1-P2
and P3-Cu2-P4 angles are larger than the ideal tetrahedral
value of 109°. The obvious consequences are the narrowing of
the N1-Cu1-N5 and N3-Cu2-N5 angles.
Molecular Structure of 2. The solid-state structure of the
above complex can be described as a discrete cationic [Cu2-
(dppm)2(η1-dmcn)2(η1,µ2-OClO3)]+ species and an isolated
ClO4- anion. The structure together with the atomic numbering
scheme is depicted in Figure 2. Important bond distances and
bond angles are given in Table 3. The most interesting feature
of this structure is the inclusion of the perchlorate anion inside
the coordination sphere of the metals. The structure of the
dimeric cationic unit is similar to that of complex 1 except for
-
the fact that the bridging dmcn ligand is replaced by the ClO4
anion (Chart 3). The oxygen atom of the perchlorate anion forms
a bridge between two copper centers in η1,µ2 fashion. Similar
bond distance values of Cu1-O11 and Cu2-O11 indicate the
symmetrical nature of this bridge. The P1-Cu1-P2 angle is
larger than the ideal tetrahedral value forcing smaller values
for O11-Cu1-P1, O11-Cu1-N1, and O11-Cu1-P2.
(19) (a) Blagg, A.; Shaw, B. L.; Thornton-Pett, M. J. Chem. Soc., Dalton
Trans. 1987, 769. (b) The structural characterization of a dimeric
chloro-bridged complex has confirmed the boat conformation of the
Cu2P4C2 ring in Cu2(dppm)2(dmcn)(Cl)2 (ref 30).
(20) Wu, W.; Fanwick, P. E.; Walton, R. A. Chem. Commun. 1997, 755.

1730 Inorganic Chemistry, Vol. 38, No. 8, 1999
Bera et al.
Figure 3. View of the Cu2P4C2 ring showing (a) the boat conformation when dmcn is the bridging ligand in complex 1 and (b) the chair conformation
-
when ClO4 bridges the two Cu centers in complex 2. The interaction between H24A and O13 in complex 2 is shown by the solid line.
Chart 3
-
The spherical nature of ClO4 often results in a very high
degree of thermal motion even in the solid state. Although the
-
constituting oxygen atoms of the ClO4 outside the metal
coordination sphere in complex 2 are severely disordered, the
-
encapsulated ClO4 exhibits normal thermal motion. Careful
inspection of the structure reveals that the oxygen atoms of the
-
complexed ClO4 engage in weak hydrogen bonding C-H‚‚‚
O interactions21 with the methylene and the phenyl protons of
the dppm ligands. The C‚‚‚O distances are in the range of 3.426-
(9)-3.784(12) Å. These weak interactions help to anchor the
ClO4- inside the cavity generated by the Cu2(dppm)2 core which
results in normal thermal parameters for the oxygen atoms of
the included oxyanion.
Another unique feature of this structure is the chair confor-
mation of the Cu2P4C2 ring. The change in the conformation
from boat to chair on changing the bridging ligand dmcn (1) to
ClO4- (2) is remarkable. The difference in the conformation is
Figure 4. X-ray structure of Cu2(dppm)2(NO3)2 (4). The hydrogen
-
atoms are omitted for clarity.
due to the presence of ClO4 inside the cavity which is tilted
toward the methylene bridge (C24). One of the perchlorate
oxygens (O13) makes a short contact with H24A. This interac-
tion would not be possible if the complex had the boat structure
where both C13 and C24 stay on opposite sides of the bridging
ligand (Figure 3a and 3b).
Molecular Structure of 4. The solid-state structure of this
complex consists of neutral dinuclear [Cu2(dppm)2(η1-ONO2)2]
units. The molecular structure together with the atomic number-
ing scheme is depicted in Figure 4. Important bond distances
and angles are given in Table 4. The coordination environment
around the copper centers are quite similar and can be considered
as distorted trigonal with two phosphorus atoms of different
dppm units and an oxygen atom of the nitrate anion bonded to
it. Surprisingly, copper binds to dppm in an asymmetric fashion.
The Cu1-P1 and Cu2-P4 are 0.02 Å longer than the Cu1-P2
and Cu2-P3 distances. The Cu1-O11 and Cu2-O21 bond
distances are similar and significantly shorter than the Cu1-
O12 and Cu2-O22 distances. The short and long Cu-O
distances indicate that the NO3- unit is bonded to the Cu(I) in
a pseudo-bidentate fashion.22
The P1-Cu1-P2 and P3-Cu2-P4 are greater than 120°.
The other angles at Cu1 and Cu2, namely, O11-Cu1-P1 and
O21-Cu2-P4 compensate for this widening and are smaller.
A closer inspection of the structure reveals some short contacts
between the oxygen atoms of the nitrate anion and aryl
(21) (a) Jones, P. G.; Ahrens, B. Chem. Commun. 1998, 2307. (b) Steiner,
T. Chem. Commun. 1997, 727.
(22) Wells, A. F. Structural Inorganic Chemistry, 4th ed.; The ELBS and
Oxford University Press: Oxford, 1975.

Oxyanion-Encapsulated CuI-dppm Complexes
Inorganic Chemistry, Vol. 38, No. 8, 1999 1731
Table 5. Selected Bond Distances (Å) and Angles (deg) of
[Cu3(dppm)3(Cl)(WO4)]‚0.5H2O (7)
Bond Distances
Cu(1)-Cu(2)
Cu(1)-Cu(3)
Cu(2)-Cu(3)
Cu(1)-O(1)
Cu(2)-O(1)
Cu(3)-O(1)
W(1)-O(1)
W(1)-O(2)
W(1)-O(3)
W(1)-O(4)
3.032(5)
3.077(5)
3.090(5)
2.25(2)
2.16(2)
2.24(2)
1.84(2)
1.75(2)
1.77(3)
1.71(3)
Cu(1)-Cl(1)
Cu(2)-Cl(1)
Cu(3)-Cl(1)
Cu(1)-P(1)
Cu(1)-P(6)
Cu(2)-P(3)
Cu(2)-P(2)
Cu(3)-P(4)
Cu(3)-P(5)
2.563(8)
2.506(8)
2.523(8)
2.245(7)
2.269(7)
2.246(7)
2.245(7)
2.273(7)
2.278(8)
Bond Angles
110.7(13) P(3)-Cu(2)-P(2)
109(2)
O(4)-W(1)-O(2)
O(4)-W(1)-O(3)
O(2)-W(1)-O(3)
O(4)-W(1)-O(1)
O(2)-W(1)-O(1)
O(3)-W(1)-O(1)
P(1)-Cu(1)-O(1)
P(1)-Cu(1)-P(6)
O(1)-Cu(1)-P(6)
118.5(3)
84.1(5)
O(1)-Cu(2)-Cl(1)
106.3(12) P(3)-Cu(2)-Cl(1)
101.8(3)
117.7(3)
116.4(4)
107.4(4)
124.6(3)
82.1(4)
105.7(11) P(2)-Cu(2)-Cl(1)
111.4(9)
113.4(11) O(1)-Cu(3)-P(5)
O(1)-Cu(3)-P(4)
Figure 5. X-ray structure of the Cu3(dppm)3(Cl)(WO4) unit in 7. The
hydrogen atoms are omitted for clarity.
114.0(5)
122.2(3)
111.8(5)
P(4)-Cu(3)-P(5)
O(1)-Cu(3)-Cl(1)
P(4)-Cu(3)-Cl(1)
P(5)-Cu(3)-Cl(1)
Table 4. Selected Bond Distances (Å) and Angles (deg) of
Cu2(dppm)2(NO3)2 (4)
101.9(3)
116.6(3)
P(1)-Cu(1)-Cl(1) 105.5(3)
P(6)-Cu(1)-Cl(1) 114.9(3)
Cu(2)-Cl(1)-Cu(3) 75.8(2)
Cu(2)-Cl(1)-Cu(1) 73.5(2)
Cu(3)-Cl(1)-Cu(1) 74.5(2)
Bond Distances
O(1)-Cu(2)-P(3)
O(1)-Cu(2)-P(2)
117.8(5)
111.8(5)
Cu(1)-Cu(2)
Cu(1)-O(11)
Cu(1)-P(2)
Cu(1)-P(1)
Cu(1)-O(12)
Cu(2)-O(21)
Cu(2)-P(3)
Cu(2)-P(4)
3.170(4)
2.108(5)
2.239(5)
2.256(5)
2.511(6)
2.108(5)
2.239(6)
2.257(4)
Cu(2)-O(22)
N(1)-O(13)
N(1)-O(12)
N(1)-O(11)
N(2)-O(23)
N(2)-O(22)
N(2)-O(21)
2.514(7)
1.222(4)
1.252(5)
1.262(4)
1.224(5)
1.245(4)
1.262(4)
- 24
2- 25
“noncoordinating” anions such as CF3SO3
,
SO4
,
and
-
26
PF6
have been trapped inside this cavity and the anion-
binding activity of the Cu3(dppm)3 core has been highlighted
recently.27 The cationic metal centers act as soft Lewis-acid
centers and the phenyl groups of dppm anchors the anion
through noncovalent interactions. In complex 7, the O11 atom
Bond Angles
2-
is bonded to the three copper centers. The spherical WO4 is
O(11)-Cu(1)-P(2)
O(11)-Cu(1)-P(1)
P(2)-Cu(1)-P(1)
118.3(2) O(21)-Cu(2)-P(3)
109.9(2) O(21)-Cu(2)-P(4)
131.78(6) P(3)-Cu(2)-P(4)
118.3(2)
109.8(2)
131.79(5)
engaged in weak hydrogen bonding interactions with the
methylene and the phenyl protons of the dppm ligand, similar
to the oxyanions ClO4- and NO3-. The C‚‚‚O distances are in
the range of 3.118-3.737 Å.
O(11)-Cu(1)-O(12) 54.2(2)
P(2)-Cu(1)-O(12)
O(21)-Cu(2)-O(22) 54.0(2)
111.8(2) P(3)-Cu(2)-O(22)
112.0(2)
97.2(2)
P(1)-Cu(1)-O(12)
97.25(13) P(4)-Cu(2)-O(22)
(23) (a) Xiao, J.; Hao, L.; Puddephatt, R. J.; Manojlovic-Muir, L.; Muir,
K. W. J. Am. Chem. Soc. 1995, 117, 6316. (b) Hao, L.; Xiao, J.; Vittal,
J. J.; Puddephatt, R. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 346.
(c) Maekawa, M.; Munakata, M.; Kuroda-Sowa, T.; Hachiya, K. Inorg.
Chim. Acta 1995, 233, 1. (d) Xiao, J.; Kristof, E.; Vittal, J. J.;
Puddephatt, R. J. J. Organomet. Chem. 1995, 490, 1. (e) Xiao, J.;
Puddephatt, R. J.; Manojlovic-Muir, L.; Muir, K. W. J. Am. Chem.
Soc. 1994, 116, 1129. (f) Rashidi, M.; Kristof, E.; Vittal, J. J.;
Puddephatt, R. J. Inorg. Chem. 1994, 33, 1497. (g) Mirza, H. A.; Vittal,
J, J.; Puddephatt, R. J. Inorg. Chem. 1993, 32, 1327. (h) Lloyd, B. R.;
Manojlovic-Muir, L.; Muir, K. W.; Puddephatt, R. J. Organometallics
1993, 12, 1231. (i) Xiao, J.; Vittal, J. J.; Puddephatt, R. J.; Manojlovic-
Muir, L.; Muir, K. W. J. Am. Chem. Soc. 1993, 115, 7882. (j)
Manojlovic-Muir, L.; Muir, K. W.; Mirza, H. A.; Puddephatt, R. J.
Organometallics 1992, 11, 3440. (k) Jennings, M. C.; Puddephatt, R.
J.; Manojlovic-Muir, L.; Muir, K. W.; Mwariri, B. N. Organometallics
1992, 11, 4164. (l) Puddephatt, R. J.; Manojlovic-Muir, L.; Muir, K.
W. Polyhedron 1990, 9, 2767. (m) Franzoni, D.; Pelizzi, G.; Predieri,
G.; Tarasconi, P.; Vitali, F.; Pelizzi, C. J. Chem. Soc., Dalton Trans.
1989, 247. (n) Manojlovic-Muir, L.; Muir, K. W.; Lloyd, B. R.;
Puddephatt, R. J. J. Chem. Soc., Chem. Commun. 1983, 1336. (o)
Bresciani, N.; Marsich, N.; Nardin, G.; Randaccio, L. Inorg. Chim.
Acta 1974, 10, L5. The two-up-one-down conformation of the Cu2P4C2
ring also noted in the solid-state structure of the complexes Cu3-
(dppm)3(µ3-Br)2ClO4 and Cu3(dppm)3(µ3-I)2I (ref 30).
hydrogens. The short C‚‚‚O distances are in the range of 3.257-
(7)-3.476(8) Å.
Molecular Structure of 7. The solid-state structure of the
complex 7 consists of a neutral Cu3(dppm)3(Cl)2(η1,µ3-OWO3)
unit. The structure together with the atomic numbering scheme
is depicted in Figure 5. Important bond distances and bond
angles are given in Table 5. The three Cu(I) ions form an
isosceles triangle with a dppm ligand bridging each edge to form
a Cu3P6 core. The chlorine and oxygen atoms are bonded to
the three copper atoms in µ3 mode from opposite faces of the
triangle. The Cu-Cl distances are not very different and fall in
the range of 2.51-2.56 Å. In contrast, the oxygen atom of the
2-
WO4 is bonded to the three copper atoms in an asymmetric
fashion (Table 5). The copper atoms are tetracoordinate, each
being bonded to two phosphorus, one chlorine and one oxygen
atom of the WO42- unit. The Cu-P distances vary over a small
range 2.24-2.27 Å. The Cu2P2C rings adopt envelope confor-
mations with the methylene carbon atoms on the flap, one of
them folded toward one of the faces and the other two, away
from it. This two-up-one-down conformation of dppm ligands
is found in analogous trimeric M3(dppm)3 clusters.11, 23
The most interesting observation in this structure is the
location of WO42- inside the cavity formed by the phenyl rings
of the dppm ligand. Disposition of the phenyl rings of the dppm
ligands in M3(dppm)3 complexes is unique. Two phenyl rings
attached to a phosphorus center stay on opposite sides of the
plane formed by the three metal centers. Therefore, it creates
two hydrophobic cavities consisting of six phenyl rings. Several
(24) Knoepfler, A.; Wurst, K.; Peringer, P. J. Chem. Soc., Chem. Commun.
1995, 131.
(25) Ha¨mmerle, B.; Mu¨ller, E. P.; Wilkinson, D. L.; Mu¨ller, G.; Peringer,
P. J. Chem. Soc., Chem. Commun. 1989, 1527.
(26) In a recent publication, Harvey et al. have shown that even an elusive
anion PF6- can be trapped inside the cavity generated by the Pd3-
(dpam)3 core where dpam (Ph2As-CH2-AsPh2) is an arsenic analogue
of dppm (Zhang, P.; Drouin, M.; Harvey, P. D. Chem. Commun. 1996,
877). In the solid-state structure of Cu3(dppm)3(µ3-OH)(BF4)2 (ref
-
11), two BF4 anions are situated in the hydrophobic cavities above
and below the Cu3 triangle.
(27) Provencher, R.; Harvey, P. D. Inorg. Chem. 1996, 35, 2235.

1732 Inorganic Chemistry, Vol. 38, No. 8, 1999
Bera et al.
Chart 4
Chart 5
The molecular structure of complex 5 has been proposed on
1
the basis of H and 31P{1H} NMR, IR, emission spectra, and
analysis data. A similar complex containing the unsubstituted
benzoate ligand has been characterized structurally.28 The
available spectral data of this complex matches with the complex
we have synthesized and hence we assume that it adopts a
similar structure (Chart 4).
Our efforts to obtain a single-crystal of complex 6, suitable
for X-ray diffraction study were not successful. As a significant
amount of water was used during the synthesis, the likelihood
of forming a trinuclear species [Cu3(dppm)3(µ3-OH)]SO4 was
envisaged. However, this possibility was rejected on the basis
of the 31P NMR chemical shift (see discussion of NMR spectra).
The IR spectrum of complex 6 indicates the bidentate bridging
mode of the SO42- to copper. Both structures 6a and 6b, fit the
spectral and the analysis data (Chart 5). The polymeric structure
(6b) is more probable considering the fact that it has very poor
solubility in chlorinated solvents unlike other dimeric complexes
reported in this study.
Figure 6. Schematic representation of the structurally characterized
-
dimeric CuI-diphosphine complexes coordinating ClO4- (a-c), NO3
(d, e), and acetate anion (f). The corresponding Cu‚‚‚Cu and Cu-O
distances are also given. Values are taken from ref 10 (a and b), this
work (c and d), ref 29 (e), and ref 16 (f).
perchlorate. Similarly among the trimeric complexes, the Cu-O
distances in complex 7 are in the range 2.16(2)-2.25(2) Å and
much longer than that observed in Cu3(dppm)3(OH)(BF4)2
(1.996-2.026 Å).11
The Cu1-Cu2 distances in complexes 1, 2, and 4 are much
shorter compared to that observed in complex 8 (3.757 Å).10
The large reduction in the metal-metal separation (0.61 Å) in
complex 1 due to the presence of a bridging dmcn ligand
between the two copper centers is significant. The separation
increases by 0.28 Å when the bridging dmcn ligand is replaced
by the ClO4- unit. Similarly, the bridging mode of nitrate causes
a significant difference in the Cu-Cu distances (3.170(4) and
3.652(10) Å for complex 4 and the η2,µ2-bonded NO3- complex,
respectively). This is a consequence of the different modes of
Variation of Cu-O distances. The Cu-O distances in the
oxyanion-coordinated CuI-dppm complexes show a large
variation depending on the nature of oxyanion and the mode of
binding. The ClO4- ion coordinates in different modes depend-
ing on the separation between the two copper centers. The Cu-
Cu, Cu-O distances and the corresponding coordination modes
of ClO4- have been shown in Figure 6a-c. The Cu-O distances
are in the range 2.236(6)-2.435(8) Å.9 Interestingly, much
smaller Cu-O values are obtained with NO3- bonded to copper.
-
bonding adopted by NO3 in the two complexes. The ligand-
controlled Cu-Cu distance in dimeric and trimeric CuI-dppm
complexes have been discussed in detail by us recently.30
Solid-State IR Spectra. All the complexes in the solid-state
exhibit usual infrared absorptions characteristic of the ligands
present and the associated anionic moiety. Two closely spaced
bands separated by 25 cm-1 corresponding to CtN stretching
frequencies of the terminal and bridging dmcn ligands are
observed in the IR spectra of complex 1. Such splitting is not
observed in the IR spectrum of complex 2 where both dmcn
-
In complex 4, the NO3 is η1 bonded (Figure 6d). Recently a
similar CuI-dppm complex with η2,µ2-bonded NO3- has been
structurally characterized (Figure 6e).29 The Cu-O bond
distance in this complex (2.183(5) Å) is longer than that in
complex 4 (2.108(5) Å). Short Cu-O distances are observed
in the CuI-benzoate (2.002(4) Å)28 and CuI-acetate (1.993(4)
Å)16 complexes (Figure 6f). The variation of the Cu-O distances
can be rationalized on the basis of the charge density on the
coordinating atom. The greater the charge on the coordinating
atom, the shorter the Cu-O distance and better is the interaction.
The strengths of the Cu-O interaction based on the CuI-O
distances are as follows: acetate, benzoate > nitrate >
-
ligands are terminal. Surprisingly, the ClO4 encapsulated in
the cavity of this complex could not be distinguished from that
outside using IR spectroscopy. However, a comparison of the
IR spectra of complex 2 with other Cu2(dppm)2 complexes31
(30) Bera, J. K.; Nethaji, M.; Samuelson, A. G. Inorg. Chem. 1999, 38,
218.
(31) The IR spectrum of complex 2 was compared with those of complexes
1, 4, and Cu2(dppm)2(dmcn)(Cl)2. It is to be noted that the Cu2P2C4
ring in all these complexes adopt a boat conformation with the sole
exception of complex 2 which has a chair conformation in the solid
state.
(28) Lanfredi, A. M. M.; Ugozzoli, F.; Camus, A.; Marsich, N.; Capelletti,
R. Inorg. Chim. Acta 1993, 206, 173.
(29) Ruina, Y.; Kunhua, L.; Yimin, H.; Dongmei, W.; Douman, J.
Polyhedron 1997, 16, 4033.

Oxyanion-Encapsulated CuI-dppm Complexes
Inorganic Chemistry, Vol. 38, No. 8, 1999 1733
Table 6. NMRa and Emissionb Spectral Data of Complexes 1-7
δ(31P)
δ (1H)
CH2 (dppm)
emission spectra
compound
(31P{1H})a
CH3 (dmcn)
Ph (dppm)
λ
max (emission)
λ
max (excitation)
[Cu2(dppm)2(dmcn)3] (BF4)2 (1)
[Cu2(dppm)2(dmcn)2(ClO4)](ClO4) (2)
[Cu2(dppm)2(dmcn)2(NO3)]NO3 (3)
Cu2(dppm)2(NO3)2 (4)c
-9.98
-10.89
-11.25
-11.00
-11.76
2.92
2.87
2.85
-
3.55
3.40
3.28
3.39
3.20
7.12-7.27
6.92-7.35
7.06-7.33
6.95-7.38
6.75-7.50
470
470
469
466
468
366
318
362
380
360e
[Cu2(dppm)2(CH3C6H4CO2)2]
2.82
(dmcn)‚2THF (5)d
Cu2(dppm)2(SO4) (6)
-9.13 f
-14.61
-
-
3.39
3.26
6.91-7.50
6.92-7.29
470
510
380
383
[Cu3(dppm)3(Cl)(WO4)]‚0.5H2O (7)
a Spectra recorded in CDCl3 unless otherwise stated. b Emission spectra were recorded in solid state. c Recorded in acetone-d6. d Additional peaks
are observed at 2.57 (CH3-benzoate), 7.99, 8.27 (C6H4-benzoate), and 1.85, 3.75 (THF). e See text. f Recorded in DMSO-d6.
Figure 7. UV-vis absorption spectra of 1 (solid line) and 2 (dashed
Figure 8. Emission (dashed line) and the corresponding excitation
line) in CH2Cl2 at room temperature.
(solid line) spectra of a solid sample of 1 at room temperature.
shows the presence of two new bands at 889 and 796 cm-1. As
these bands are present only in complex 2 and appear in the
region of the CH2 rocking vibration,32 it is likely that they are
caused by the unique chair conformation present in this complex.
The IR spectra of complexes 3 and 4 are identical with the
exception that 3 also exhibits a sharp absorption at 2229 cm-1
due to the dmcn ligand. Based on the difference in the symmetric
and the asymmetric stretching frequencies of the benzoate ligand
(186 cm-1),15 a monodentate binding is inferred28 for complex
5.
2 are extremely similar, the excitation maxima differ (Table
6). The excitation maximum of complex 2 was observed at 318
nm while no significant emission was noted on irradiation at
362 nm (cf. complexes 1 and 3). Complex 4 exhibits a broad
excitation spectrum with an excitation maximum around 380
nm. The emission band of complex 5 is relatively weak and
the excitation spectrum exhibits a very broad absorption ranging
from 340 to 380 nm. However, maximum emission occurs on
irradiating the sample at 360 nm. The emission spectra of
complex 7 is characteristic of trimeric Cu3(dppm)3 complexes34
and is completely different from those of the dimeric species
reported in this study.
Several assignments such as those involving a phosphine
intra-ligand excited state,35 a ligand-to-metal charge transfer
state,36 a metal-cluster-centered excited state37 or combinations
of these have been made to explain the emission spectra of
copper(I) phosphine complexes. The Cu‚‚‚Cu distances observed
in the solid-state structure of 1, 2, and 4 are different. If cluster-
The structure of complex 6 containing the sulfate anion
bridging the two copper centers in a bidentate fashion is inferred
from the IR spectra. Two closely spaced peaks were observed
at 1180 and 1140 cm-1 along with a strong band at 1095 cm-1
.
2-
A similar observation has been noted for the bidentate SO4
bridged cobalt complex.33
UV-Vis and Emission Spectra. The electronic absorption
spectra of all the complexes except 4 and 6 were measured at
room temperature in CH2Cl2. They are similar and as represen-
tative examples, the spectra of complexes 1 and 2 have been
given in Figure 7. An intense absorption around 250 nm and a
relatively weak absorption around 300 nm dominate the
electronic spectra. The luminescence spectra of all the complexes
were measured at room temperature in the solid-state. The
relevant spectral data are given in Table 6. The luminescence
spectrum of complex 1 along with the corresponding excitation
spectrum are shown in Figure 8 as representative examples.
Complexes 1-6 display emission maxima around 470 nm.
Interestingly, though the emission spectra of complexes 1 and
(34) The luminescence spectra of trimeric Cu3(dppm)3 complexes show a
common broad band centered around 510-520 nm. Examples are [Cu3-
(dppm)3(µ3-OH)](BF4)2 (ref 27), [Cu3(dppm)3(µ3-Cl)2](ClO4), [Cu3-
(dppm)3(µ3-Br)2](ClO4), and [Cu3(dppm)3(µ3-I)2](I) (ref 30).
(35) (a) Yam, V. W.-W.; Lee, W.-K.; Cheung, K.-K.; Crystall, B.; Phillips,
D. J. Chem. Soc., Dalton Trans. 1996, 3283. (b) Li, D.; Che, C.-M.;
Wong, W.-T.; Shieh, S.-J.; Peng, S.-M. J. Chem. Soc., Dalton. Trans.
1993, 653.
(36) (a) Yam, V. W.-W.; Lo, K. K.-W.; Cheung, K.-K. Inorg. Chem. 1996,
35, 3459. (b) Yam, V. W.-W.; Fung, W. K.-M.; Cheung, K.-K. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1100. (c) Yam, V. W.-W.; Lee, W.-
K.; Lai, T.-F. J. Chem. Soc., Chem. Commun. 1993, 1571.
(37) (a) Simon, J. A.; Palke, W. E.; Ford, P. C. Inorg. Chem. 1996, 35, 5,
6413. (b) Li, D.; Yip, H.-K.; Che, C.-M.; Zhou, Z.-Y.; Mak, Thomas
C. W.; Liu, S.-T.; J. Chem. Soc., Dalton Trans. 1992, 2445. (c) Barrie,
J. D.; Dunn, B.; Hollingsworth, G.; Zink, J. I. J. Phys. Chem. 1989,
93, 3958. (d) Zink, J. I.; Henary, M. J. Am. Chem. Soc. 1989, 111,
7407.
(32) Bacci, M. Spectrochim. Acta 1972, 28A, 2286.
(33) Nakamoto, K. Infrared spectra of inorganic and coordination
compounds, 3rd ed.; Wiley: New York, 1978.

1734 Inorganic Chemistry, Vol. 38, No. 8, 1999
Bera et al.
centered transitions are involved, they are likely to be effected
by Cu‚‚‚Cu interactions. The invariance of the emission
wavelength rules out the possibility of emission from such a
metal-cluster-centered excited state. We tentatively assign the
origin of these emission bands to an intra-ligand phosphine
excited state. Trimeric complexes also have this relatively weak
emission bands around 470 nm along with a strong emission at
510 nm. In fact it is possible to differentiate the dimeric and
trimeric CuI-dppm complexes on the basis of their emission
spectra.30 The photophysical properties of these complexes can
be advantageously used in the design of an oxyanion-sensor.
Scheme 2
[Cu2(dppm)2(dmcn)3](BF4)2 + tBuN+X- h
[Cu2(dppm)2(dmcn)2(X)](BF4) + tBuN+BF4
data. As a significant amount of water was used to prepare
complex 6, the possibility of forming a trimeric species of the
formulas [Cu3(dppm)3(OH)](SO4) was considered. The lowest
negative value (-9.13 δ) noted for complex 6 confirms its
dimeric structure.
The methylene protons in 1H NMR (methylene) and the 31P-
{1H} signal (P) of the dppm ligand suffer a considerable shift
on coordination with Cu(I). The values for the free ligand are
2.82 and -22.68, respectively. The NMR shifts reflect the extent
of binding of the dppm ligand with the metal centers. The
interaction of an oxyanion with the metal core indirectly
influences Cu-P bonding. A stronger interaction (shorter Cu-O
distance) with the oxyanion leads to weaker bonding between
dppm and the copper (longer Cu-P distance). The chemical
shift values of the dppm ligand in solution can then be an
indirect measure of the interaction of the anion with copper.
The data shown in Table 6 indicates that oxyanions benzoate,
ClO4- and NO3- coordinate better with the metal core compared
to the dmcn ligand. The corresponding values also indicate that
the extent of interaction is maximum for benzoate and least for
1
Solution-Phase Study. The H and 31P{1H} NMR spectral
data have been summarized in Table 6. Although the solid-
state structure of complex 1 shows the presence of both bridging
and terminally bonded dmcn in 1:2 ratio, the 1H NMR spectrum
shows a single and sharp methyl signal in solution for all methyl
groups. This signal is gradually shifted to higher field when
stoichiometric amounts of dmcn is added, suggesting a rapid
exchange between the coordinated and noncoordinated dmcn
ligands at room temperature. Small but significant changes are
1
observed in the H NMR when complex 1 encapsulates the
oxyanions. The methylene protons of dppm show an upfield
shift when the bridging dmcn ligand in complex 1 is replaced
with ClO4- to give 2 and NO3- to give 3 (Table 6). The NMR
spectrum of 4 was recorded in acetone-d6 as it was insoluble in
CDCl3 and the methylene protons resonate at δ 3.39 ppm.
Complex 5 exhibits the lowest δ value for the methylene proton
of the dppm ligand while complex 6 gives a significantly higher
value. The trimeric complex 7 shows a δ value of 3.26, typical
of other trimeric structures.11,23 Phenyl protons of the dppm
ligand for all the complexes containing the oxyanions inside
the metal coordination sphere resonate over a larger frequency
range compared to complex 1. The weak C-H‚‚‚O interactions
presumably persist in solution resulting in the chemical shift
spread.
ClO4-. The NO3 complex has an intermediate value.39
Addition of tetrabutylammonium salt of ClO4 in excess to
1 causes an upfield shift of the methylene proton. Unfortunately
this signal is completely masked by the tetrabutyl protons
-
-
-
ranging from 3.25 to 3.29 when NO3 salt is added to 1.
However, the 31P{1H} NMR signal can be conveniently used
to monitor the presence of the anion in the cavity. Addition of
the tetrabutylammonium salt of PF6 to 1 does not change the
-
31P NMR values significantly. However, a gradual shift of the
signal is observed while adding stoichiometric amount of
tetrabutylammonium salt of either ClO4- or NO3- to 1 in CDCl3
indicating a rapid equilibrium between the anion-complexed and
uncomplexed forms (Scheme 2). Association constants were
calculated from the resulting titration curves using the program
Though all molecules reported in this paper contain more
than one type of (crystallographically different) phosphorus
centers, the 31P{1H} NMR spectra of these complexes show
only a single resonance. The magnetic equivalence of the
phosphorus atoms in solution is consistent with the lability of
ligands around Cu(I) and their chemical equivalence. For
complex 1, even at -70 °C, the signal does not split but
gradually shifts to a higher field. The upfield shifts noted in
-
EQNMR.40 The values obtained are 249 mol-1 dm3 for ClO4
and 154 mol-1 dm3 for NO3-. It is interesting to note that though
NO3- coordinates better with Cu(I) (causes a larger shift in 31
P
NMR), ClO4- forms a thermodynamically more stable complex
compared to the planar NO3-. The greater number of oxygen
atoms allows many more C-H‚‚‚O interactions and the
tetrahedral disposition of the oxygen atoms make a better fit of
the anion in the cavity.
1
the H NMR spectra on replacing the bridging dmcn ligand in
1 by ClO4- (2) and NO3- (3) are observed in the 31P{1H} NMR
spectra also (Table 6).
During our study, we have observed a consistently higher
negative value in the 31P NMR spectra for Cu3(dppm)3
complexes compared to Cu2(dppm)2 complexes.38 A good
comparison is provided by the dimeric 4 and the trimeric [Cu3-
(dppm)3(OH)](BF4)2. Although each copper is bonded to two
phosphorus atoms and one oxygen atom in both complexes, the
31P{1H} NMR chemical shift for the trimer is -15.26 whereas
complex 4 resonates at -11.00 ppm. Consistently, the highest
negative value in these series was recorded for the trimeric 7.
This suggests that the 31P NMR values can be reliably used to
distinguish between dimeric and trimeric structures. The dimeric
structure of complex 6 has been assigned from the 31P NMR
Encapsulation of Oxyanion. It is evident from the structural
information and spectroscopic data that Cun(dppm)n complexes
have the potential to be efficient receptors for oxyanions. The
Cu2(dppm)2 core forms a cavity generated by the phenyl rings
of the dppm ligands with two Lewis-acceptor copper centers
inside it. The entry of oxyanion to the cavity is initiated by the
coordinate-bond formation with the copper ions. Inside the
cavity, the oxyanion is locked by multiple hydrogen bonding
interactions. The low crystallographic thermal parameters of the
oxygen atoms of the encapsulated oxyanion bear testimony of
this fact. For example, a well-behaved ClO4- was located inside
the cavity formed by Cu2(dppm)2 cores in complex 2, although
(38) Consistently larger negative values in the 31P NMR spectra are noted
for trinuclear Cu3(dppm)3 complexes compared to dinuclear Cu2-
(dppm)2 complexes. The values vary over a smaller range of -9.0 to
-12.0 ppm in the case of dimers and -14.5 to -22.5 ppm in the
case of trimers. One exception among dimers is complex Cu2(dppm)2-
(dmcn)(Cl)2 which could exist as a trimer in solution and hence has
a chemical shift of -15.2 ppm. For details, see ref 30.
(39) As the NMR spectrum of complex 4 could only be recorded in acetone-
d6, the value could not be compared with others. The methylene peaks
of the CuI-dppm complexes undergo considerable downfield shift
when acetone-d6 is used as the solvent compared to CDCl3.
(40) Hynes, M. J. J. Chem. Soc., Dalton Trans. 1993, 311.

Oxyanion-Encapsulated CuI-dppm Complexes
Inorganic Chemistry, Vol. 38, No. 8, 1999 1735
-
the oxygen atoms of ClO4 outside the metal coordination
understanding the solid-state structure of the complexes and the
nature of interaction between the oxyanion and the copper-
dppm core. The anchoring of the oxyanion to the core is
predominantly through coordination to the metal. Noncovalent
C-H‚‚‚O interactions between the oxygen atoms of the oxya-
nion and the methylene and phenyl protons of the dppm also
play a significant role. The presence of the anion is reflected in
the IR spectra. The solid-state photophysical properties of these
complexes are characteristic of the anion present. This property
along with the lability of these complexes in solution suggest
the possibility of designing an anion sensor based on Cu2(dppm)2
units. Addition of the oxyanion to CDCl3 solutions of 1 results
in an equilibrium reaction favoring the anion-complexed form.
1H and 31P{1H} NMR chemical shift values can be used to
monitor the equilibrium.
sphere were severely disordered. Significant structural changes
of the host Cu2(dppm)2 core are also observed as a result of
encapsulation. The methylene and the phenyl hydrogens protons
of the dppm ligands orient themselves toward the cavity in
complex 2 in which ClO4- is located. Such an alignment is not
observed in complex 1 where the cavity is occupied by neutral
-
dmcn. The encapsulation of ClO4 inside the cavity can also
be inferred from the higher association constant values compared
-
to NO3- in solution. Due to its tetrahedral topology, the ClO4
2-
anion has greater number of interactions. Similarly, the WO4
is located inside the hydrophobic cavity consisting of six phenyl
rings of the Cu3(dppm)3 core. The coordination of the anion to
copper centers is primarily responsible for this but weak
2-
nonbonding interactions between the oxygen atoms of WO4
and methylene and phenyl hydrogens of dppm also play a very
significant role.
Acknowledgment. This work was supported by a grant from
CSIR (New Delhi).
Conclusion
Supporting Information Available: Listing of the atomic coor-
dinates and equivalent isotropic displacement parameters, all bond
lengths and angles, anisotropic displacement parameters, hydrogen
coordinates and isotropic displacement parameters, intra- and intermo-
lecular hydrogen bonding, and the emission and corresponding excita-
tion spectra of the complexes, as well as titration curves and space-
filling models of the complexes with and without the oxyanion. This
material is available free of charge via the Internet at http://pubs.acs.org.
CuI-dppm complexes are excellent hosts for anions. When
the weakly coordinating BF4 is present, the cavity generated
-
by the Cu2(dppm)2 core is occupied by a neutral guest such as
dmcn. Several CuI-dppm complexes encapsulating oxyanions
-
can be prepared by replacing the noncoordinating BF4
.
Independent synthesis of these anion-encapsulated complexes
are possible starting with the corresponding Cu(II) salts. X-ray
crystallographic characterization of the complexes helps in
IC9801589