Syntheses and coordination chemistry of methylpyridylphosphine oxide ligands with copper(II)

Article abstract of DOI:10.1016/j.poly.2010.02.019

The coordination properties of three heterofunctional phosphine oxide ligands, 2-methylpyridyldiphenylphosphine oxide (L1), phenylphosphino-bis-2-methylpyridine oxide (L2) and phenylphosphino-bis-2-methylpyridine N,N′,P-trioxide (L3) with Cu(II) is descri

Full text of DOI:10.1016/j.poly.2010.02.019

Polyhedron 29 (2010) 1676–1686
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses and coordination chemistry of methylpyridylphosphine oxide
ligands with copper(II)
*
Fernando Hung-Low, Kevin K. Klausmeyer
Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The coordination properties of three heterofunctional phosphine oxide ligands, 2-methylpyridyldiphe-
nylphosphine oxide (L1), phenylphosphino-bis-2-methylpyridine oxide (L2) and phenylphosphino-bis-
2-methylpyridine N,N0,P-trioxide (L3) with Cu(II) is described. The X-ray crystal structures of the com-
pounds display a distorted octahedral geometry, which exhibit Jahn–Teller distortions. In compounds
1 and 2, the L1 and L2 ligands react with Cu(BF4)2 in a 2:1 ligand to metal ratio, respectively, with the
BF4 anions interacting with the metal center. L3 reacts with Cu(BF4)2 in 1:1 and 2:1 ligand/metal ratios
to form compounds 3 and 4, respectively. Addition of either 2,20-bipyridine or 4,40-bipyridine to reaction
solutions containing Cu(BF4)2 and L3 produces a discrete molecule (5) and a polymeric structure (7),
respectively. The reaction of both bipyridines in the presence of Cu(BF4)2 and L3 gives rise to a discrete
molecule (6) characterized by two octahedral coppers interconnected by the 4,40-bipyridine. The electro-
chemical and photophysical properties of all compounds were investigated by cyclic voltammetry (CV)
and UV–Vis, as they exhibited no emission or excitation in fluorimetric experiments.
Received 21 December 2009
Accepted 11 February 2010
Available online 16 February 2010
Keywords:
Copper
Jahn–Teller effect
Coordination modes
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
oxide (L3), the latter being a trifunctional ligand that contains both
a phosphoryl (P–O) and nitrosyl (N–O) set of donors. Herein we re-
The design and study of new functional ligands is a topic of
interest that applies in particular to phosphines, which have been
widely used in coordination and organometallic chemistry [1–5].
Accordingly, an extensive family of so-called hemilabile ligands
have been synthesized over the last few decades, many containing
either a P,N or P,O set of donors which combine a soft phosphine
moiety with a harder functionality [6–10]. These ligands have been
cited to either chelate or bridge metal centers. Among the P,N
ligands, special attention has been devoted to pyridylphosphines
[11], whereas much less investigated is the behavior of the corre-
sponding pyridylphosphine oxides [12–16]. From the multidentate
2-methylpyridylphosphines of the type PPhxCH2py3ꢀx (x = 1,2), two
oxidized products are possible; (1) the P@O moiety, obtained un-
der mild oxidation conditions, and (2) the fully oxidized form of
the ligand, which contains both the P@O and one or more N–O
moieties. To date, only the 2-methylpyridyldiphenylphosphine
oxide [17,18] and 2-(diphenylphosphino-methyl)-pyridine N,P-
dioxide [17,19,20] have been reported, while the corresponding
oxides of phenylphosphino-bis-2-methylpyridine have not. In con-
tinuation of the development of hemilabile phosphine ligands, we
have synthesized the phenylphosphino-bis-2-methylpyridine
oxide (L2) and phenylphosphino-bis-2-methylpyridine N,N0,P-tri-
port investigations of the coordinative properties of L1, L2, and L3
(Fig. 1) towards copper(II) tetrafluoroborate, and both electro-
chemical and photophysical properties of the resulting metal com-
plexes. Previous studies in our group on the coordination
chemistry of the classical pyridylphosphine ligands 2-(diphenyl-
phosphino-methyl)-pyridine [6], 4-(diphenylphosphino-methyl)-
pyridine [9], and phenylphosphino-bis-(2-methylpyridine) [21]
contrasts to the rather different binding abilities of the correspond-
ing oxides, especially as observed for L3.
The preparation and study of new copper complexes, as re-
ported here, is motivated by their potential as catalysts for the oxi-
dation of organic substrates which continues to be an area of high
interest [22–26]. Previous examples of structures containing pyr-
idylphosphine oxide ligands have been associated with a few tran-
sition metals such as Pd [10], Pt [10], Ni [27] and Rh [18], in
addition to the 4f-block element ions known for their affinity with
oxygen donating ligands [17,19,28,29]. In this paper, the use of N,P-
dioxide and N,N0,P-trioxide phosphine species instead of the classi-
cal phosphines, has made it possible to prepare a family of copper
based complexes, which exhibit the well-known Jahn–Teller (JT)
distortion [30,31]. Herein, we demonstrate the presence of the JT
effect in some complexes associated with L3 by use of the X-ray
crystallographic data.
Additionally reported, is the study and use of bipyridine ligands
* Corresponding author. Tel.: +1 254 710 2665; fax: +1 254 710 4272.
E-mail address: Kevin_Klausmeyer@baylor.edu (K.K. Klausmeyer).
(2,20-bipyridine and 4,40-bipyridine) with Cu(BF4)2:L3 adducts,
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.02.019

F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
1677
P
P
P
O
O
O
N
N
N
N
N
O
O
a
b
c
Fig. 1. Structure of (a) 2-methylpyridyldiphenylphosphine oxide (L1), (b) phenylphosphino-bis-2-methylpyridine oxide (L2) and (c) phenylphosphino-bis-2-methylpyridine
N,N0,P-trioxide (L3). Copper compounds synthesized: Cu(BF4)2(L1)2 (1), Cu(BF4)2(L2)2 (2), [Cu(BF4)2(L3)]2 (3), [Cu(BF4)2(L3)2]2 (4), Cu(BF4)2(L3)(2,20-bipy)(MeOH) (5),
Cu(BF4)2(L3)(2,20-bipy)(4,40-bipy) (6), and [Cu(BF4)2(L3)(4,40-bipy)]1 (7).
which has lead to the formation of designed and constructed coor-
dinative structures. The compounds described in this paper were
obtained on the basis of controlling ligand/metal ratio [32–35]
and functionality of the corresponding bipyridine ligand [36–42].
We also describe the changes that are brought about in the coordi-
nation sphere of the copper(II) cation by the functionalization of
the bipyridine ligand to the corresponding Cu(BF4)2:L3 complex,
and the results from CV and UV–vis studies performed on each of
the compounds.
heating L2 with H2O2/acetic acid at 70 °C. The desired ligand is
obtained as a yellow oil in good yield after purification through a
silica–gel column, using also a 9:1 mixture of CH2Cl2:MeOH. L2.
Yield: 78%. 1H NMR ((CD3)2CO, 298 K) d: 3,59 (s, 4H), 6.89 (t, 2H),
7.13 (m, 4H), 7.23 (d, 1H), 7.33 (t, 2H), 7.45 (t, 2H), 8.25 (d, 2H).
31P NMR (CDCl3, 298 K) d: 35.85 (s). IR (KBr, cmꢀ1): 1184 (mPO
,
br). +ESI-HRMS for [L2]+ calcd. 309.1151 m/z; found: 309.1152 m/
z. L3. Yield: 75%. 1H NMR (CD3CN, 298 K) d: 4.13 (m, 4H), 7.23
(m, 3H), 7.43 (m, 5H), 7.72 (m, 3H), 8.21 (d, 2H). 31P NMR (CDCl3,
298 K) d: 37.38 (s). IR (KBr, cmꢀ1): 1234 (
mNO, s), 1122 (mPO, m).
+ESI-HRMS for [L3]+ calcd. 341.1049 m/z; found: 341.1050 m/z.
2. Experimental
2.2.2. Synthesis of Cu(BF4)2(L1)2 (1)
2.1. General remarks
This reaction used 2 equiv. of L1 (0.117 g, 0.399 mmol) in
CH3CN (5 mL) added to 1 equiv. of Cu(BF4)2ꢁxH2O (0.047 g,
0.198 mmol) in CH3CN (5 mL). The solution was stirred for 1 h,
and the resulting dark-blue solution was dried in vacuo to leave
a blue powder isolated in 71% (0.116 g, 0.141 mmol) yield. Crystal-
lization formed blue blocks obtained by slow diffusion of ether into
a CH3CN solution of 1 at 5 °C. Anal. Calc. for C36H32B2CuF8N2O2P2
(823.76): C, 52.49; H, 3.92; N, 3.40. Found: C, 52.31; H, 3.82; N,
All reactions were carried out under nitrogen atmosphere using
standard Schlenk-vessels and Schlenk-line techniques. All phos-
phine reagents were stored in an inert-atmosphere glovebox; sol-
vents were distilled either under nitrogen from the appropriate
drying agent or with a low pressure solvent distiller immediately
before use. Copper(II) tetrafluoroborate hydrate and n-butyl lith-
ium were purchased from VWR and used as received. Chlorodi-
phenylphosphine, dichlorophenylphosphine, 2,20-bipyridine, and
4,40-bipyridine were purchased from Aldrich Chemical and used
as received. 1H and 31P NMR spectra were recorded at
360.13 MHz with a Bruker Spectrospin 300 MHz spectrometer.
Infrared spectra were recorded on a Thermo Mattson IR300 spec-
trometer (4 cmꢀ1 resolution). Cyclic voltammetry was performed
using a CH Instruments 1140 Electrochemical Analyzer. The mea-
surements were done using a glassy carbon working electrode, Pt
wire auxiliary electrode, and Ag/AgCl reference electrode. All
potentials are expressed relative to the formal potential of the fer-
rocenium–ferrocene couple (Fc+/Fc). UV–Vis absorption data were
acquired on a Varian Cary Bio spectrophotometer. Solutions were
prepared in CH3CN and charged into quartz cuvettes. Elemental
analyses were performed by Atlantic Microlabs Inc. in Norcross,
Georgia. High resolution mass spectra (HRMS) were obtained in
the Baylor University Mass Spectrometry Core Facility on a Thermo
Scientific LTQ Orbitrap Discovery using +ESI. Percent yield of metal
complexes is based on amount of ligand used.
3.42%. IR (KBr, cmꢀ1): 1065 (
mPO, br).
2.2.3. Synthesis of Cu(BF4)2(L2)2 (2)
To a stirred solution of Cu(BF4)2ꢁxH2O (0.047 g, 0.198 mmol) in
CH3CN (5 mL) was added L2 (0.122 g, 0.396 mmol) in CH3CN
(5 mL). The resulting solution was allowed to stir for 1 h and then
dried in vacuo to leave a blue solid isolated in 65% (0.109 g,
0.128 mmol) yield. Blue blocks were obtained by slow diffusion
of ether into a CH3CN solution of 2 at 5 °C. Anal. Calc. for
C36H34B2CuF8N4O2P2 (853.79): C, 50.64; H, 4.01; N, 6.56. Found:
C, 50.49; H, 4.13; N, 6.45%. IR (KBr, cmꢀ1): 1060 (
mPO, br).
2.2.4. Synthesis of Cu(BF4)2(L3)(CH3CN)2 (3)
A solution of L3 (0.069 g, 0.203 mmol) in CH3CN (5 mL) was
added to Cu(BF4)2ꢁxH2O (0.048 g, 0.202 mmol) in CH3CN (5 mL).
The initial blue solution of Cu(BF4)2 immediately turned green
upon addition of the ligand. The solution was then stirred for 1 h,
and upon evaporation,
a green solid was obtained in 79%
(0.053 g, 0.161 mmol) yield. Crystallization formed green blocks
obtained by slow diffusion of ether into a CH3CN solution of 3 at
5 °C. Anal. Calc. for C44H46B4Cu2F16N8O6P2 (659.58): C, 38.84; H,
3.26; N, 6.79. Found: C, 38.87; H, 3.34; N, 6.77%. IR (KBr, cmꢀ1):
2.2. Synthesis
2.2.1. Synthesis of the ligands
1201(mNO), 1052 (mPO, br).
Literature methods were used to prepare L1 [6,17] and phen-
ylphosphino-bis-(2-methylpyridine) [21]. L2 was synthesized by
a procedure similar to that reported for L1, where phenylphosphi-
no-bis-(2-methylpyridine) is oxidized with H2O2/acetone for 1 h. A
yellow oil is isolated by evaporating the solvent. The ligand is then
2.2.5. Synthesis of Cu(BF4)2(L3)2 (4)
The reaction was done in a 2:1 ratio of L3 (0.136 g, 0.400 mmol)
in CH3CN (5 mL) to Cu(BF4)2ꢁxH2O (0.046 g, 0.193 mmol) dissolved
in 5 mL of CH3CN. The resulting apple-green solution was allowed
to stir for 1 h and then dried in vacuo to leave a green solid isolated
purified on
a silica–gel column using a 9:1 mixture of
CH2Cl2:MeOH. Preparation of L3 requires forcing conditions by

1678
F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
in 60% (0.109 g, 0.119 mmol) yield. Crystallization formed green
blocks obtained by slow diffusion of ether into a MeOH solution
of 4 at 5 °C. Anal. Calc. for C72H68B4Cu2F16N8O12P4 (1835.59): C,
47.11; H, 3.73; N, 6.10. Found: C, 46.97; H, 3.69; N, 6.16%. IR
0.138 mmol) yield. Green crystals were obtained by slow diffusion
of ether into a MeOH solution of 5 at 5 °C. Anal. Calc. C29H29B2CuF8-
N4O4P (765.70): C, 45.49; H, 3.82; N, 7.32. Found: C, 45.47; H, 3.60;
N, 7.56%. IR (KBr, cmꢀ1): 1231 (
mNO), 1211 (mNO), 1059 (mPO, br).
(KBr, cmꢀ1): 1204 (
mNO, br), 1129 (mPO), 1061 (mPO, br).
2.2.7. Synthesis of Cu(BF4)2(L3)(2,20-bipyridine)(4,40-bipyridine) (6)
A solution of L3 (0.068 g, 0.200 mmol) in CH3CN (5 mL) was
added to Cu(BF4)2ꢁxH2O (0.048 g, 0.202 mmol) dissolved in CH3CN
(5 mL). This was stirred for 1 h, and then a solution of 2,20-bipyri-
dine (0.031 g, 0.201 mmol) in CH3CN (5 mL) was added to the solu-
tion. After stirring for 15 min, 4,40-bipyridine (0.031 g, 0.198 mmol)
in CH3CN (5 mL) was added to the olive-green solution, and allowed
to stir for 2 h without observing any further color change of the
2.2.6. Synthesis of Cu(BF4)2(L3)(2,20-bipyridine)(CH3OH) (5)
To a stirred solution of Cu(BF4)2ꢁxH2O (0.049 g, 0.206 mmol) in
CH3CN (5 mL) was added L3 (0.067 g, 0.197 mmol) in CH3CN
(5 mL). After stirring for 1 h, a solution of 2,20-bipyridine (0.031 g,
0.198 mmol) in CH3CN (5 mL) was added to the reaction mixture.
The resulting olive-green solution was stirred for 1 h, and then
dried in vacuo to leave a green solid isolated in 70% (0.106 g,
Table 1
Crystallographic data for compounds 1–4.
1
2
3
4
Empirical formula
Formula mass
a (Å)
b (Å)
c (Å)
C40H38B2CuF8N4OP2
905.84
C40H40B2CuF8N6O2P2
935.88
C50H55B4Cu2F16N11O6P2
1442.31
21.4096(7)
15.4207(5)
21.3967(10)
90
119.897(2)
90
6124.1(4)
4
C75H80B4Cu2F16N8O15P4
1931.67
8.9350(6)
10.0014(6)
12.4270(8)
105.892(3)
105.681(4)
94.441(3)
1014.47(11)
1
9.986(5)
10.509(5)
11.568(6)
110.79(3)
91.24(3)
107.96(2)
1067.9(9)
1
14.2249(6)
16.6896(7)
18.7480(9)
96.299(2)
104.2700(10)
96.350(2)
4243.5(3)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Crystal system
Space group
T (K)
triclinic
P1
110(2)
1.483
0.695
triclinic
P1
110(2)
1.455
0.664
monoclinic
C2/c
110(2)
1.564
0.852
25.67
43 003
5783(0.0317)
0/482
0.0335
triclinic
P1
110(2)
1.512
0.679
25.70
15 801
15 801(0.0289)
10/1136
0.0381
0.1066
0.0436
ꢀ
ꢀ
ꢀ
Dcalcd. (g cmꢀ3
)
l
(mmꢀ1
2hmax (°)
Reflections measured
)
26.71
24.86
14 232
4219(0.0389)
0/269
0.0429
0.1212
0.0497
19 151
3543(0.0323)
0/278
0.0368
0.1015
0.0483
Reflections used (Rint
Restraints/parameters
)
R1 [I > 2
wR2 [I > 2
r
(I)]
(I)]
r
0.0877
0.0378
RðF2oÞ (all data)
RwðF2oÞ (all data)
0.1264
1.051
0.1096
1.059
0.0909
1.033
0.1093
1.102
Goodness-of-fit (GOF) on F2
Table 2
Crystallographic data for compounds 5–7.
5
6
7
Empirical formula
Formula mass
a (Å)
b (Å)
c (Å)
C30H33B2CuF8N4O5P
797.73
C66H58B4Cu2F16N10O6P2
1623.48
C57H56B4Cu2F16N8O8P2
1517.36
18.7186(8)
22.3796(9)
17.0595(8)
90
112.811(2)
90
6587.5(5)
4
10.9368(4)
13.0358(5)
13.7056(5) A
69.534(2)
79.810(2)
66.935(2)
1682.52(11)
2
9.7711(11)
13.360(2)
14.0711(19)
99.138(4)
101.343(6)
106.913(4)
1676.8(4)
1
a
(°)
b (°)
c
(°)
V (Å3)
Z
Crystal system
Space group
T (K)
triclinic
triclinic
monoclinic
P2(1)/c
110(2)
1.530
0.798
25.69
12 527
12 527(0.0554)
20/914
0.0568
ꢀ
ꢀ
P1
P1
110(2)
1.575
0.787
110(2)
1.608
0.788
Dcalcd. (g cmꢀ3
)
l
(mmꢀ1
2hmax (°)
Reflections measured
)
25.72
25.67
26 419
6306(0.0262)
0/470
0.0318
0.0830
0.0380
29 605
6309(0.0266)
10/543
0.0534
0.1408
0.0615
Reflections used (Rint
Restraints/parameters
)
R1 [I > 2
wR2 [I > 2
r
(I)]
(I)]
r
0.1497
0.0899
RðF2oÞ (all data)
RwðF2oÞ (all data)
0.0863
1.043
0.1483
1.048
0.1630
1.105
Goodness-of-fit (GOF) on F2

F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
1679
Fig. 2. Thermal ellipsoid of 1 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms and a CH3CN molecule have been removed for clarity.
mixture. The solution was then evaporated to dryness to obtain a
green solid isolated in 62% (0.201 g, 0.124 mmol) yield. Crystalliza-
tion formed green blocks obtained by slow diffusion of ether into a
CH3CN solution of 6 at 5 °C. Anal. Calc. for C33H29B2Cu1F8N5O3P1
(1623.48): C, 47.80; H, 3.71; N, 8.45. Found: C, 47.80; H, 3.71; N,
unless specified. The phenyl ring of the L3 ligand in 3 is disordered
over two positions with a 15:85 occupancy ratio, and hence re-
strained to have similar bond lengths and angles (Fig. S1). The
structures of 4 and 7 contain one and two disordered BF4 anions,
respectively, which were modeled over two positions. Additionally
in compounds 4 and 7 we were unable to satisfactorily model sol-
vent methanol and H2O molecules (32 and 76 eꢀ, respectively) and
therefore they were removed from the structure using the
SQUEEZE procedure implemented in PLATON [46]. In 6 one pyridyl
ring of the 2,20-bipyridine ligand is disordered over two positions
8.45%. IR (KBr, cmꢀ1): 1230 (
mNO), 1067 (mPO, br).
2.2.8. Synthesis of Cu(BF4)2(L3)(4,40-bipyridine) (7)
This reaction used 1 equiv. of 4,40-bipyridine (0.031 g,
0.198 mmol) in CH3CN (5 mL) added to 1 equiv. of Cu(BF4)2ꢁxH2O
(0.047 g, 0.198 mmol) in CH3CN (5 mL). After stirring for 15 min,
a solution of L3 (0.068 g, 0.200 mmol) in CH3CN (5 mL) was added
to the reaction mixture. The resulting cloudy spring-green solution
was stirred for 1 h, and then dried in vacuo to leave a solid isolated
in 68% (0.103 g, 0.068 mmol) yield. Green crystals were obtained
by slow diffusion of ether into a CH3CN/H2O solution of 7 at 5 °C.
Anal. Calc. for C57H56B4Cu2F16N8O8P2 (1517.36): C, 45.28; H, 3.53;
N, 7.54. Found: C, 45.36; H, 3.57; N, 7.65%. IR (KBr, cmꢀ1): 1226
(mNO), 1078 (mPO, br).
2.3. X-ray crystallography
Single X-ray diffraction data were collected on crystals with
approximate dimensions of 0.325 ꢂ 0.224 ꢂ 0.166 mm for 1,
0.310 ꢂ 0.300 ꢂ 0.280 mm for 2, 0.310 ꢂ 0.280 ꢂ 0.260 mm for 3,
0.300 ꢂ 0.300 ꢂ 0.220 mm for 4, 0.270 ꢂ 0.250 ꢂ 0.200 mm for 5,
0.280 ꢂ 0.230 ꢂ 0.190 mm for 6, and 0.270 ꢂ 0.220 ꢂ 0.190 mm
for 7. Data were collected at 110 K on a Bruker X8 Apex using
Mo Ka radiation (k = 0.71073 Å). All structures were solved by di-
rect methods after correction of the data using SADABS [43,44]. De-
tails of the crystal parameters, data collection, and refinement
are summarized in Tables 1 and 2. The molecular structure of the
compounds is displayed in Figs. 2–8. Summary of selected bond
lengths, angles, and interatomic distances are given in Tables 3
and 4. All data were processed using the Bruker AXS SHELXTL soft-
ware, version 6.10 [45]. Hydrogen atoms were placed in calculated
positions and all non-hydrogen atoms were refined anisotropically,
Fig. 3. Thermal ellipsoid of 2 with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms and a CH3CN molecule have been removed
for clarity.

1680
F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
Fig. 4. Thermal ellipsoid of the cationic portion of 3 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Anions, hydrogen atoms and two CH3CN
molecules have been removed for clarity.
Fig. 5. Thermal ellipsoid of the cationic portion of 4 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Anions, hydrogen atoms and three CH3OH
molecules have been removed for clarity.
with a 50:50 occupancy ratio, and one BF4ꢀ molecule is disordered
about the B position (Fig. S2). Corresponding bonds and anisotropic
displacements parameters were restrained to be similar.
perature, followed by oxidation in a H2O2/acetone mixture. The
first step produces phenylphosphino-bis-2-methylpyridine in high
yield as previously reported [21]. If this air-sensitive compound is
not purified prior to the next step, pure L2 can be obtained by pas-
sage through
a silica gel column using a 9:1 mixture of
3. Results and discussion
CH2Cl2:MeOH. Subsequent oxidation of L2 in a H2O2/acetic acid
mixture at 70 °C affords L3 in high yield and purity. Pure L3 can
be further purified by using the same purification procedure for
L2. As expected, the oxidized form of the phosphine ligands can
be indefinitely stored at room temperatures and in air. The 1H
and 31P NMR spectra of L2 and L3 confirm the formation of the li-
gands with a phosphorus singlet centered at 35.85 and 37.38 ppm,
respectively, which are in the region expected for phosphine oxi-
des. HRMS and IR spectra of the ligands are also consistent with
the corresponding structures, with an infrared band at
3.1. General characterizations
3.1.1. Syntheses and characterization
The novel set of ligands obtained from the oxidation of phen-
ylphosphino-bis-2-methylpyridine can be prepared in high yield
and separated, if necessary, from other oxidation products by col-
umn chromatography. L2 is prepared stepwise from the reaction of
the corresponding 2-lithiomethylpyridine with PhPCl2 at low tem-

F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
1681
Fig. 6. Thermal ellipsoid of the cationic portion of 5 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Anions, hydrogen atoms and one CH3OH
molecule have been removed for clarity.
Fig. 7. Thermal ellipsoid of the cationic portion of 6 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Anions, hydrogen atoms have been removed for
clarity.
1188 cmꢀ1 assigned to the P@O stretch of L2, the same as reported
for L1 [17]; and the infrared bands at 1234 and 1122 cmꢀ1 for the
corresponding N–O and P@O stretching frequencies of L3.
tively. Under the same conditions, reaction of 1 equiv. of 2,20-
bipyridine with a reaction mixture containing Cu(BF4)2ꢁxH2O and
L3 yields compound 5, and further addition of 1/2 equiv. of 4,40-
bipyridine affords the three mixed-ligand complex 6. On the other
hand, compound 7 is prepared by reaction of the Cu(BF4)2/4,40-
bipyridine adduct with L3. No further reaction of either
Cu(BF4)2(L1)2 or Cu(BF4)2(L2)2 with any of the bipyridine ligands
was observed. Upon coordination, all of the copper compounds re-
ported herein are stable in air and room temperature, and obtain-
able in analytical purity by precipitation with ether from the
corresponding solutions in CH3CN. The IR spectra of all compounds
are consistent with the structures reported herein, with infrared
bands that range between 1052 and 1078 cmꢀ1 for the P@O
stretch, and from 1201 to 1230 cmꢀ1 for the N–O vibration.
Compounds 1–7 were synthesized by the direct reaction of the
corresponding phosphine oxide ligand with Cu(BF4)2ꢁxH2O. The L1
and L2 complexes are isolable as blue solids, while all of the com-
pounds containing L3 are obtained as green powders of varying
shades. The reaction under ambient conditions of Cu(BF4)2ꢁxH2O
with L1 and L2 affords compounds 1 and 2, respectively in a 2:1 li-
gand to metal ratio. The coordination chemistry of L3 was also
investigated with Cu(BF4)2ꢁxH2O, studying the effect of varying
the ligand/metal ratio and by using additional electron donating
ligands to form mixed-ligand complexes. Compounds 3 and 4 are
obtained in ligand:metal stoichiometries of 1:1 and 2:1, respec-

1682
F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
Fig. 8. (a) Expanded view of the two-dimensional growth of the cationic polymer of 7. (b) Thermal ellipsoid of the cationic portion of 7 with an atomic numbering scheme.
Ellipsoids are shown at the 50% level. Anions, hydrogen atoms and two MeOH molecules have been removed for clarity.
3.2. Description of the crystal structures
due to its flexible nature. This variability in binding modes allows
the formation of metal complexes with L3 acting as a face capping
ligand in discrete molecules (5 and 6) and a polymeric array (7), a
bridging connector across two metal centers in a dimeric copper
complex (3), and a cross-linking ligand in a bimetallic compound
(4). Although numerous pyridyl rings are observed to form part
The X-ray crystal structures of compounds 1–7 show the copper
centers in distorted octahedral environments, where both the cis
and trans angles cover a range of values that depends upon the ste-
ric constrains present in the molecule. As expected, all of the cop-
per(II) centers are six coordinate but with a variety of structural
motifs that are demonstrative of several variables that are involved
of the core structure of the molecules, no
p-stacking effects are
present in the packing structures of the metal complexes.[6,47]
ꢀ
ꢀ
in the formation of the complexes: anion dependence, as the BF4
All restraints are applied to disordered BF4 ions.
ion can take part in the coordination sphere of the metal center, ra-
tio dependence of structural features as 1:1 and 2:1 ligand/metal
proportions were observed, and functionality of the corresponding
ligands as mixed-ligand complexes were prepared by using bipyr-
idine molecules that either chelate or bridge the metal centers.
Both L1 and L2 are seen to act as bidentate ligands, while L3, being
formally a tridentate ligand, displays multiple coordination modes
3.2.1. Structure of compounds 1 and 2
The structures of compounds 1 and 2, obtained by reaction of
Cu(BF4)2 with L1 and L2, are shown in Figs. 2 and 3, respectively.
Both complexes display the same coordination environment
around the metal center, and exhibit a slightly distorted octahedral
geometry in a 2:1 ligand to metal ratio. The 1:1 ratio reaction of the

F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
1683
Table 3
Table 4
Selected bond lengths [Å], angles [°], and distances for the compounds Cu(BF4)2(L1)
Selected bond lengths [Å], angles [°], and distances for the compounds
Cu(BF4)2(L3)(2,20-bipyridine)(CH3OH) (5), Cu(BF4)2(L3)(2,20-bipyridine)(4,40-bipyri-
dine) (6), and Cu(BF4)2(L3)(4,40-bipyridine) (7).a
(1), Cu(BF4)2(L2) (2), Cu(BF4)2(L3)(CH3CN) (3), and Cu(BF4)2(L3)2 (4).a
1
Cu(1)–O(1)
Cu(1)–F(1)
1.9172(17)
2.5207(2)
Cu(1)–N(1)
2.0370(2)
5
Cu(1)–O(2)
Cu(1)–N(4)
Cu(1)–O(4)
1.9568(14)
1.9917(18)
2.3308(16)
Cu(1)–O(1)
Cu(1)–N(3)
Cu(1)–O(3)
1.9830(14)
2.0030(17)
2.5550(14)
O(1)#1–Cu(1)–O(1)
O(1)–Cu(1)–N(1)#1
O(1)–Cu(1)–N(1)
180.00(10)
88.24(8)
91.76(8)
O(1)#1–Cu(1)–N(1)#1
O(1)#1–Cu(1)–N(1)
N(1)#1–Cu(1)–N(1)
91.76(8)
88.24(8)
180.00(1)
O(2)–Cu(1)–O(1)
O(1)–Cu(1)–N(4)
O(1)–Cu(1)–N(3)
O(2)–Cu(1)–O(4)
N(4)–Cu(1)–O(4)
O(2)–Cu(1)–O(3)
N(4)–Cu(1)–O(3)
O(4)–Cu(1)–O(3)
O(1)–P(1)–C(1)
O(1)–P(1)–C(7)
C(1)–P(1)–C(7)
96.60(6)
173.23(6)
92.08(7)
93.79(6)
91.22(7)
83.50(5)
98.71(6)
169.67(6)
111.70(9)
115.83(9)
106.84(10)
O(2)–Cu(1)–N(4)
O(2)–Cu(1)–N(3)
N(4)–Cu(1)–N(3)
O(1)–Cu(1)–O(4)
N(3)–Cu(1)–O(4)
O(1)–Cu(1)–O(3)
N(3)–Cu(1)–O(3)
O(1)–P(1)–C(13)
C(13)–P(1)–C(1)
C(13)–P(1)–C(7)
89.63(7)
167.94(7)
81.38(7)
91.01(6)
94.42(6)
79.44(5)
89.89(6)
110.22(9)
104.25(10)
107.28(10)
2
Cu(1)–N(1)
Cu(1)–F(1)
2.0670(2)
2.5875(2)
Cu(1)–O(1)
1.9170(19)
O(1)#1–Cu(1)–O(1)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(1)#1
180.00(11)
91.09(9)
88.91(9)
O(1)#1–Cu(1)–N(1)
O(1)#1–Cu(1)–N(1)#1
N(1)–Cu(1)–N(1)#1
88.91(9)
91.09(9)
180.00(12)
3
Cu(1)–O(1)
Cu(1)–N(4)
Cu(1)–N(3)
1.9733(13)
1.9829(17)
2.2912(18)
Cu(1)–O(2)
Cu(1)–O(3)
Cu(1)–O(3)#1
1.9783(15)
2.0058(14)
2.3274(14)
6
Cu(1)–N(3)
Cu(1)–O(2)
Cu(1)–N(4)
Cu(1)–N(5)
1.8600(2)
1.9840(2)
2.0020(3)
2.2560(3)
Cu(1)–O(1)
Cu(1)–O(3)
Cu(1)–N(3A)
1.9720(2)
2.8569(4)
2.1240(15)
O(1)–Cu(1)–O(2)
O(2)–Cu(1)–N(4)
O(2)–Cu(1)–O(3)
O(1)–Cu(1)–N(3)
N(4)–Cu(1)–N(3)
O(1)–Cu(1)–O(3)#1
N(4)–Cu(1)–O(3)#1
N(3)–Cu(1)–O(3)#1
88.97(6)
85.26(6)
170.72(6)
89.64(6)
96.40(7)
82.85(5)
93.23(6)
157.57(6)
O(1)–Cu(1)–N(4)
O(1)–Cu(1)–O(3)
N(4)–Cu(1)–O(3)
O(2)–Cu(1)–N(3)
O(3)–Cu(1)–N(3)
O(2)–Cu(1)–O(3)#1
O(3)–Cu(1)–O(3)#1
172.23(6)
91.75(5)
93.11(6)
99.08(7)
90.18(6)
101.88(6)
69.06(6)
N(3)–Cu(1)–O(1)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–N(4)
N(3)–Cu(1)–N(3A)
O(2)–Cu(1)–N(3A)
N(3)–Cu(1)–N(5)
O(2)–Cu(1)–N(5)
N(3A)–Cu(1)–N(5)
96.10(7)
94.93(10)
171.73(12)
7.30(10)
164.50(7)
97.90(9)
97.36(11)
97.80(7)
N(3)–Cu(1)–O(2)
N(3)–Cu(1)–N(4)
O(2)–Cu(1)–N(4)
O(1)–Cu(1)–N(3A)
N(4)–Cu(1)–N(3A)
O(1)–Cu(1)–N(5)
N(4)–Cu(1)–N(5)
O(3)–Cu(1)–N(5)
161.50(8)
76.70(7)
91.06(11)
88.70(4)
84.00(5)
4
87.74(10)
97.16(11)
161.75(10)
Cu(1)–O(2)
Cu(1)–O(12)
Cu(1)–O(3)
Cu(2)–O(10)
Cu(2)–O(6)
Cu(2)–O(11)
1.9593(17)
1.9742(17)
2.5067(2)
1.9517(16)
1.9948(18)
2.2647(18)
Cu(1)–O(5)
Cu(1)–O(1)
Cu(1)–O(4)
Cu(2)–O(9)
Cu(2)–O(7)
Cu(2)–O(8)
1.9701(17)
1.9935(17)
2.2767(17)
1.9542(17)
2.0328(18)
2.3281(18)
7
Cu(1)–O(3)
Cu(1)–O(2)
Cu(1)–O(1)
Cu(2)–N(8)
Cu(2)–N(7)
Cu(2)–O(8)
1.9670(2)
1.988(2)
2.218(2)
1.997(3)
2.023(3)
2.5639(4)
Cu(1)–N(4)
Cu(1)–N(3)
Cu(2)–O(6)
Cu(2)–O(5)
Cu(2)–O(4)
1.988(3)
2.017(3)
1.965(3)
2.010(3)
2.287(3)
O(2)–Cu(1)–O(5)
O(5)–Cu(1)–O(12)
O(5)–Cu(1)–O(1)
O(2)–Cu(1)–O(4)
O(12)–Cu(1)–O(4)
O(10)–Cu(2)–O(9)
O(9)–Cu(2)–O(6)
O(9)–Cu(2)–O(7)
O(10)–Cu(2)–O(11)
O(6)–Cu(2)–O(11)
O(10)–Cu(2)–O(8)
O(6)–Cu(2)–O(8)
O(11)–Cu(2)–O(8)
177.12(7)
89.96(7)
87.75(7)
88.54(7)
95.72(7)
177.21(7)
91.10(7)
95.60(7)
91.25(7)
89.79(7)
94.28(7)
98.08(7)
170.64(7)
O(2)–Cu(1)–O(12)
O(2)–Cu(1)–O(1)
O(12)–Cu(1)–O(1)
O(5)–Cu(1)–O(4)
O(1)–Cu(1)–O(4)
O(10)–Cu(2)–O(6)
O(10)–Cu(2)–O(7)
O(6)–Cu(2)–O(7)
O(9)–Cu(2)–O(11)
O(7)–Cu(2)–O(11)
O(9)–Cu(2)–O(8)
O(7)–Cu(2)–O(8)
87.17(7)
95.09(7)
170.77(7)
91.74(7)
93.29(7)
86.34(7)
86.98(7)
173.26(7)
89.84(7)
89.46(7)
84.98(7)
83.31(7)
O(3)–Cu(1)–N(4)
N(4)–Cu(1)–O(2)
N(4)–Cu(1)–N(3)
O(3)–Cu(1)–O(1)
O(2)–Cu(1)–O(1)
O(6)–Cu(2)–N(8)
N(8)–Cu(2)–O(5)
N(8)–Cu(2)–N(7)
O(6)–Cu(2)–O(4)
O(5)–Cu(2)–O(4)
84.65(11)
173.23(11)
90.88(12)
92.24(10)
86.03(10)
83.84(11)
173.11(11)
91.67(12)
89.85(10)
85.28(10)
O(3)–Cu(1)–O(2)
O(3)–Cu(1)–N(3)
O(2)–Cu(1)–N(3)
N(4)–Cu(1)–O(1)
N(3)–Cu(1)–O(1)
O(6)–Cu(2)–O(5)
O(6)–Cu(2)–N(7)
O(5)–Cu(2)–N(7)
N(8)–Cu(2)–O(4)
N(7)–Cu(2)–O(4)
88.59(11)
173.62(11)
95.84(11)
94.47(11)
92.64(11)
89.39(11)
175.39(11)
95.12(11)
93.40(11)
91.44(11)
a
Symmetry transformations used to generate equivalent atoms. For 1:
#1 ꢀ x + 1, ꢀy + 2, ꢀz + 2. For 2: #1 ꢀ x + 1, ꢀy + 1, ꢀz. For 3: #1 ꢀ x, y, ꢀz + 1/2.
a
Symmetry transformations used to generate equivalent atoms. For 6: #1 ꢀ x,
ꢀy + 1, ꢀz + 1. For 7: #1 x, ꢀy + 1/2, z + 1/2; #2 x, ꢀy + 1/2, z ꢀ1/2.
reactants resulted only in the formation of the 2:1 compound. The
equatorial plane is formed by the interaction of two molecules of
the corresponding ligand through the phosphoryl oxygen and
one pyridyl group, with nearly right angles for the cis ligands at
88.24(8)° and 91.76(8)° for 1, and 88.91(9)° and 91.09(9)° for 2 (Ta-
ble 3). The axis formed by the Cu1–F1 interactions exhibit an angle
of 180°, since the copper atoms lies on a crystallographic inversion
center. Despite L2 being formally a tridentate ligand; it only binds
through the oxygen and one of the pyridyl functionalities, leaving
the second pyridyl arm free of coordination. This is likely due to
steric constraints, as the second pyridyl arm would have a difficult
time reaching back to the Cu center, as well as electronic contribu-
tions as rather than binding the coordinating acetonitrile, it has the
non-innocent BF4 anions loosely bound (F1–Cu1 2.5207(2) Å in 1
and 2.5875(2) Å in 2), to coordinatively saturate the metal center.
The P2–C1–C2 angle formed between the P and the pyridyl arm
bound to the Cu allows for an easy approach of the N-donor atom
to the metal center, with a value of 109.32(2)° in 1 and 110.29(2)°
in 2.
3.2.2. Structure of compound 3
The crystal structure of compound 3 presented in Fig. 4 was ob-
tained by reaction of Cu(BF4)2 and L3 in a 1:1 ratio. In this dimeric
molecule, L3 acts as a tridentate ligand capping the face of a dis-
torted octahedron. Accordingly, the metal is six coordinate with
one phosphine oxide ligand, two CH3CN molecules and an oxygen
from an N–O group from the L3 ligand of the other half of the di-
mer. As a result, the full molecular structure consists of two copper
centers separated by a distance of 3.5741(5) Å, but bridged by the
oxygen moiety of the nitrosyl groups, forming a diamond like binu-
clear copper center. The middle of this 4-center conformation lies
on a crystallographic inversion center. The angles around O3 range
between 110.92(6)° and 125.33(11)° and sum to 359.87° to
describe a trigonal planar geometry. All of the oxygen atoms in this
molecular structure appear to exhibit sp2 hybridization as the
angles around O1, O2, and O3 range between 115.49° and
127.15°, deviating only slightly from the ideal 120°. The flexibility
of the L3 ligand is evidenced by the free rotation of the pyridyl
functionalities around the methylene group, which allows the

1684
F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
nitrosyl oxygen atoms to adopt the proper orientation to coordi-
nate to the copper centers. As a result, the dihedral angle for P1–
C7–C8–N1 is reported to be 74.45(3)° and 154.78(2)° for P1–
C13–C14–N2. Additionally, the angle between the planes of the
pyridyl groups is 66.55(7)°. The Jahn–Teller effect is evidenced in
the N3–Cu–O3#1 axis as both the N–Cu and O–Cu bond lengths
are about 0.3 Å longer than the lengths of the corresponding N4–
Cu–O1 axis.
3.2.5. Structure of compound 6
Given the labile nature of the CH3OH molecule coordinated to
the copper center in compound 5, the crystal structure 6 was ob-
tained by addition of one equiv. of 4,40-bipyridine to a reaction
mixture containing Cu(BF4)2, L3, and 2,20-bipyridine. A thermal
ellipsoid plot of the discrete molecule of 6 is presented in Fig. 7,
and selected bond lengths and angles are given in Table 4. The
reaction product, formed by controlled and stepwise addition of
the reactants, consists of a discrete molecule composed of two cop-
per centers in an octahedral environment interconnected by a 4,40-
bipyridine molecule. The Cu–N and Cu–O bond distances fall in the
range of reported values, although they cover an important range
of values. For example, the Cu1–N3 interaction at 1.8600(2) Å is
considerably shorter than Cu1–N4 at 2.0020(3) Å, which confirms
the sterics that exists around the metal center. This geometric con-
straint is induced by the pyridyl arm that binds to Cu1 through O3,
and helps explain the deviation from planarity of the rings of the
2,20-bipyridine with an angle of 14.44(1)°, being this more pro-
nounced than the one observed in compound 5. The Jahn–Teller
distortion is found by looking at the Cu1–N5 bond at 2.2560(3) Å
and the Cu1–O3 at 2.8569(4) Å, both of these are considerably
longer than any of the other Cu–N or Cu–O bonds. Another conse-
quence of the steric constrains present in the molecule is the devi-
ation from linearity of the O3–Cu1–N5 angle with a value of
161.75(10)° to describe a rather distorted octahedral geometry.
The center of 4,40-bipyridine lies on a crystallographic inversion
center.
3.2.3. Structure of compound 4
The reaction of a second equivalent of L3 with a 1:1 ligand to
metal ratio mixture forces the core structure observed in 3 to rup-
ture into a molecular structure formed by two independent and
unique copper centers, but still interconnected by the phosphine
oxide ligands. In the crystal structure of 4, shown in Fig. 5 each
copper is bound to an L3 molecule, two oxygen atoms (P@O and
N–O) from a second phosphine oxide ligand, and a nitrosyl group
belonging to a bridging third equiv. of L3. Hence, both copper cen-
ters display a distorted octahedral geometry, where the axial Cu–O
bonds exhibit rather long distances compared to the equatorial
interactions, which can be attributed to the commonly known
Jahn–Teller distortions. This distortion is more pronounced in
Cu1, where the Cu1–O4 distance is 2.2767(17) Å, and the Cu1–O3
bond is considerably longer at 2.5067(2) Å. The rest of Cu1–O dis-
tances fall into the range of reported values with an average of
1.97 Å. For Cu2, the axial bond distances are 2.2647(18) and
2.3281(18) Å for Cu2–O11 and Cu2–O8, respectively. The equato-
rial Cu2–O interactions range between 1.9517(16) and
2.0328(18) Å. All angles around Cu1 and Cu2 are only slightly devi-
ated from the ideal values of an octahedral geometry.
3.2.6. Structure of compound 7
The crystal structure of compound 7 consists of a polymeric ar-
ray obtained by addition of 1 equiv. of L3 into a reaction mixture
containing Cu(BF4)2ꢁxH2O and 4,40-bipyridine in a 1:1 ratio. Chang-
ing the order of reaction of the reactants by adding the bipyridine
to a solution containing the copper salt and the phosphine oxide
ligand, only results in the formation of compound 3, which is indic-
ative that the bridging effect of 4,40-bipyridine is not as favored as
the chelating effect of 2,20-bipyridine to disrupt the dimeric copper
structure described for 3. The crystal structure of 7 contains two
crystallographically independent molecules (Fig. 8b) differentiated
only by the interaction of a BF4 anion and a water molecule with
Cu1 and Cu2, respectively. The extended polymeric structure of
the monomer containing Cu2 is shown in Fig. 8a and reveals an
infinite chain in a zigzag conformation as indicated by the N4–
Cu1–N3 angle of 90.88(12)°. The octahedral environment observed
in 7 is formed by one molecule of L3 capping a face of the molecule,
two 4,40-bipyridines in a cis position, and a H2O molecule trans to
the P@O–Cu interaction. The rings of the bipyridine ligand are
highly twisted with an angle of 34.38(2)°. The Jahn–Teller distor-
tion for this molecule involves the BF4ꢀ ion and phosphoryl oxygen
for Cu1 and the solvent H2O and phosphoryl oxygen for Cu2. For
Cu1 the anion to Cu distance is 2.727 and to O1 is 2.218 Å. For
Cu2 these interactions are Cu2–O8 2.5639(4) and Cu2–O4
2.287(3) Å. The angle for O4–Cu2–O8 is rather deviated from the
ideal 180° with a value of 167.92(1)°, while the equatorial plane
display a range of angles between 83.84(11)° and 95.84(11)°.
3.2.4. Structure of compound 5
Formation of compound 4 as a result of the reaction of an
additional equivalent of L3 with a 1:1 ligand to metal ratio mix-
ture provides evidence that more complex coordinative structures
could result from the addition of different electron donating li-
gands. As a first example of this series of mixed-ligand complexes
Fig. 6, shows the crystal structure of 5 obtained by reaction of the
bidentate 2,20-bipyridine with a solution containing Cu(BF4)2 and
L3 in a 1:1:1 ratio of the reactants. As expected, the bipyridine
binds the copper cation in a chelating fashion to form a discrete
molecule. The disruption of the dimeric copper motif observed
in 3 is likely due to steric effects rather than electronic factors,
as it might be expected that the 2,20-bipyridine would substitute
the CH3CN molecules in 3 but conserve the structural conforma-
tion. The copper center in 5 is in a distorted octahedral environ-
ment, where a MeOH molecule is occupying an axial position
along with the interaction between Cu1 and O3 to display an an-
gle of 169.67(6)° (Table 4). The Jahn–Teller effect is displayed
along this axis by the very long Cu–O3 distance of 2.5550(14) Å
and the Cu–O4 distance of 2.3308(16) Å. It is interesting to note
that the methanol oxygen is considerably closer to the copper
center than the nitrosyl oxygen, this may be due to some steric
crowding around the Cu center. The equatorial angles range be-
tween 81.38(7)° and 96.60(6)°, the smallest value corresponding
to the acute binding of the 2,20-bipyridine. The biggest deviation
among the reported angles for 5 with respect to the ideal values
for an octahedral geometry is exemplified by O1–Cu1–O3 with a
value of 79.44(5)°, which is evidence of the constraining effect of
the ligand coordinated to the metal center. The angles around P1
suggests a slightly distorted tetrahedral geometry, being close to
the ideal 109.5°, ranging between 104.25(10)° and 115.83(9)°. The
aromatic rings of 2,20-bipyridine are slightly twisted from planar-
ity at an angle of 9.09(1)°, a well-known characteristic of bipyri-
dine ligands.
3.3. Electrochemical properties
The electrochemical properties of compounds 1–7 were investi-
gated by cyclic voltammetry. All of the experiments were per-
formed at room temperature in CH3CN solutions. Before each
measurement, the solutions were degassed and the working elec-
trode polished with alumina powder (1.0, 0.3, and 0.05 lm). The
voltammograms were recorded under nitrogen atmosphere
containing approximately 0.1 M [Bu4N][PF6] as the supporting
electrolyte, all relative to the formal potential of the

F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
1685
ferrocenium–ferrocene couple (Fc+/Fc). Potential data for all com-
pounds are shown in Table 5, and a voltammogram model for com-
None of the compounds discussed here showed any fluorescence
even at liquid nitrogen temperatures.
pound
2 is shown in Fig. S3. For the sake of comparison,
electrochemical measurements have also been carried out with
standard solutions of each of the phosphine oxides studied in this
work.
4. Conclusions
The synthesis, characterization and study of the novel phen-
ylphosphino-bis-2-methylpyridine oxide and phenylphosphino-
bis-2-methylpyridine N,N0,P-trioxide constitute the continuation
of preceding works reported in our group, that comprise the inves-
tigation of the coordinating ability of the phenylphosphino-bis-2-
methylpyridine ligand. Several new discrete molecules and a poly-
meric structure have been characterized using X-ray crystallogra-
phy, which reveals the flexible nature of this series of phosphine
oxide ligands, being this an effective way of manipulating the
structures and properties of the resulting complexes. Reaction of
2,20-bipyridine and 4,40-bipyridine with Cu(BF4)2/L3 adducts re-
sults in the formation of mixed-ligand complexes that exhibit the
well-known JT distortion.
The complexes, according to their structures and electrophysi-
cal characteristics, are seen to be highly dependent on the bipyri-
dine ligand used in the reaction, also responsible to induce a
more constrained environment that resulted in the deviation of
bond length and angles from the ideal values. To date, we are
continuing to study the coordination properties of L3 with other
transition metals, including lanthanide starting materials, as this
novel phosphine oxide ligand demonstrates its versatility to coor-
dinate in different modes, specially in high coordination number
centers.
As expected, none of the ligands exhibit electrochemical re-
sponse, as the oxidation–reduction process observed in the com-
pounds can be assigned to the CuII/CuI redox couple. CV spectra
of compounds 1–7 show an irreversible peak in both the anodic
and cathodic region. The irreversible behavior observed in these
electrochemical experiments reflects the stability of the copper(I)
complexes with phosphine oxide ligands in solution, which is
likely to undergo fast dissociation. The reduction (Epa) and oxida-
tion potentials (Epc) of all compounds span approximately
ꢀ0.264 and ꢀ0.179 V, respectively, as there are different coordina-
tion environments present in each of the metal complexes.
3.4. Spectroscopic properties
We examined the UV–Vis spectra of compounds 1–7, and a
comparison with the parent starting material Cu(BF4)2ꢁxH2O is
shown in Table 6. Compound 4 exhibits the longest absorption
wavelength (kmax = 814 nm) followed by compound 3 (kmax
=
805 nm). For the series of L3 compounds that contain a bipyridine
unit, compound 7 is more bathochromic (kmax = 780 nm) than
compounds 5 (kmax = 675 nm) and 6 (kmax = 680 nm) which pre-
sents wavelengths on the same order of magnitude. This order re-
flects the charge transfer effect of the L3 ligand when compared to
nitrogen donor ligands. Accordingly, bipyridines will enhance a
bigger degeneracy to the d orbitals of the octahedral environment,
which results in lower wavelength absorption values. The UV–Vis
data is then in accordance with the spectroscopic series where
compound 4 is red shifted relative to the rest of compounds re-
ported herein due to the full coordination of L3 ligands to the metal
center. On the other hand, compounds 1 and 2 exhibit, as expected,
similar absorption wavelengths at 690 and 695 nm, respectively,
blue shifted when compared to Cu(BF4)2 (kmax = 785 nm), which
is more likely to be coordinated by CH3CN molecules in solution.
Acknowledgments
This research was supported by funds provided by grant from
the Robert A. Welch Foundation (AA-1508). The authors would like
to thank Dr. Alejandro Ramirez (Mass Spectrometry Core Facility,
Baylor University, Texas) for the HRMS analysis.
Appendix A. Supplementary data
CCDC 758971, 758972, 758973, 758970, 758974, 758976 and
758975 contain the supplementary crystallographic data for 1, 2,
3, 4, 5, 6 and 7, respectively. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2010.02.019.
Table 5
Electrochemical properties of compounds 1ꢀ7 determined by CV on a glassy carbon
working electrode in CH3CN + 0.1 M [Bu4N][PF6] solutions at room temperature.a
Compound
Epa
Epc
1
2
3
4
5
6
7
ꢀ1.137
ꢀ1.218
ꢀ1.102
ꢀ1.210
ꢀ1.181
ꢀ1.003
ꢀ1.267
ꢀ0.660
ꢀ0.636
ꢀ0.589
ꢀ0.659
ꢀ0.629
ꢀ0.481
ꢀ0.629
References
[1] A. Cingolani, E. Di Nicola, D. Martini, C. Pettinari, B.W. Skelton, A.H. White,
Inorg. Chim. Acta 359 (2006) 2183.
a
Values for Epa and Epc in V at a scan rate of 0.2 V sꢀ1
.
[2] E. De la Encarnacion, J. Pons, R. Yanez, J. Ros, Inorg. Chim. Acta 359 (2006) 745.
[3] A. Aeby, G. Consiglio, Inorg. Chim. Acta 296 (1999) 45.
[4] G.R. Newkome, Chem. Rev. 93 (1993) 2067.
[5] A. Murso, D. Stalke, Dalton Trans. (2004) 2563.
[6] F. Hung-Low, K.K. Klausmeyer, Inorg. Chim. Acta 361 (2008) 1298.
[7] K.K. Klausmeyer, F. Hung, Acta Crystallogr., Sect. E E62 (2006) m2415.
[8] K.K. Klausmeyer, F. Hung-Low, Acta Crystallogr., Sect. E E62 (2007) m1931.
[9] F. Hung-Low, K.K. Klausmeyer, J.B. Gary, Inorg. Chim. Acta 362 (2009) 426.
[10] G. Minghetti, S. Stoccoro, M.A. Cinellu, A. Zucca, M. Manassero, M.J. Sansoni, J.
Chem. Soc., Dalton Trans. (1998) 4119.
[11] Z.Z. Zhang, H. Cheng, Coord. Chem. Rev. 147 (1996) 1.
[12] J.A. Bertrand, Inorg. Chem. 6 (1967) 495.
[13] G. Pilloni, G. Valle, C. Corvaja, B. Longato, B. Corain, Inorg. Chem. 34 (1995)
5910.
Table 6
UV–Vis data for compounds 1–7 at room temperature and 1 ꢂ 10ꢀ4 M in CH3CN.
Compound
kmax (nm)
1
2
3
4
5
6
7
690
695
805
814
675
680
780
785
[14] P. Bhattacharyya, A.M.Z. Slawin, M.B. Smith, J.D. Woollins, Inorg. Chem. 35
(1996) 3675.
[15] M.R. Churchill, B.G. DeBoer, S.J. Mendak, Inorg. Chem. 14 (1975) 2496.
[16] T.S. Lobana, S.S. Sandhu, Coord. Chem. Rev. 47 (1982) 283.
Cu(BF4)2

1686
F. Hung-Low, K.K. Klausmeyer / Polyhedron 29 (2010) 1676–1686
[17] B.M. Rapko, E.N. Duesler, P.H. Smith, R.T. Paine, R.R. Ryan, Inorg. Chem. 32
(1993) 2164.
[18] C. Abu-Gnim, I.J. Amer, Organomet. Chem. 516 (1996) 235.
[19] R.T. Paine, E.M. Bond, S. Parveen, N. Donhart, E.N. Duesler, K.A. Smith, H. Noth,
Inorg. Chem. 41 (2002) 444.
[20] S. Pailloux, C.E. Shirima, A.D. Ray, E.N. Duesler, K.A. Smith, R.T. Paine, J.R.
Klaehn, M.E. McIlwain, B.P. Hay, Dalton Trans. (2009) 7486.
[21] F. Hung-Low, K.K. Klausmeyer, Eur. J. Inorg. Chem. (2009) 2994.
[22] J.A. Halfen, V.G.J. Young, W.B. Tolman, Angew. Chem., Int. Ed. Engl. 35 (1996)
1687.
[30] L.R. Falvello, J. Chem. Soc., Dalton Trans. (1997) 4463.
[31] R.J. Deeth, L.J.A. Hearnshaw, Dalton Trans. (2006) 1092.
[32] R.P. Feazell, C.E. Carson, K.K. Klausmeyer, Eur. J. Inorg. Chem. (2005) 3287.
[33] R.P. Feazell, C.E. Carson, K.K. Klausmeyer, Inorg. Chem. 45 (2006) 935.
[34] R.P. Feazell, C.E. Carson, K.K. Klausmeyer, Inorg. Chem. 45 (2006) 2627.
[35] R.P. Feazell, C.E. Carson, K.K. Klausmeyer, Inorg. Chem. 45 (2006) 2635.
[36] C. Kaes, A. Katz, M.W. Hosseini, Chem. Rev. 100 (2000) 3553.
[37] K. Biradha, M. Sarkar, L. Rajput, Chem. Commun. (2006) 4169.
[38] G.A. Bowmaker, Effendy, S. Marfuah, B.W. Skelton, A.H. White, Inorg. Chim.
Acta 358 (2005) 4371.
[23] N. Kitajima, K. Fujisawa, Y. Morooka, K. Toriumi, J. Am. Chem. Soc. 111 (1989)
8975.
[39] Effendy, F. Marchetti, C. Pettinari, B.W. Skelton, A.H. White, Inorg. Chim. Acta
360 (2007) 1424.
[24] E. Pidcock, H.V. Obias, M. Abe, H.C. Liang, K.D. Karlin, E.I. Solomon, J. Am. Chem.
Soc. 121 (1999) 1299.
[40] L. Cunha-Silva, R. Ahmad, M.J. Carr, A. Franken, J.D. Kennedy, M.J. Hardie, Cryst.
Growth Des. 7 (2007) 658.
[25] H.V. Obias, Y. Lin, N.N. Murthy, E. Pidcock, E.I. Solomon, M. Ralle, N.J.
Blackburn, Y.M. Neuhold, A.D. Zuberbhler, K.D. Karlin, J. Am. Chem. Soc. 120
(1998) 12960.
[26] W.E. Lynch, D.M.J. Kurtz, S. Wang, R.A. Scott, J. Am. Chem. Soc. 116 (1994)
11030.
[27] J.T. Mague, J.L. Krinsky, Inorg. Chem. 40 (2001) 1962.
[28] J.H. Matonic, M.P. Neu, A.E. Enriquez, R.T. Paine, B.L. Scott, J. Chem. Soc., Dalton
Trans. (2002) 2328.
[41] F. Hung-Low, A. Renz, K.K. Klausmeyer, J. Chem. Crystallogr. 39 (2009) 438.
[42] F. Hung-Low, A. Renz, K.K. Klausmeyer, Polyhedron 28 (2009) 407.
[43] Bruker APEX2 (Version 1. 0-28) and SAINT-Plus (Version 6. 25). (2003) Bruker
AXS Inc., Madison, Wisconsin, USA.
[44] G.M. Sheldrick, SHELXS97 and SHELXL97, University of Gottingen, Germany, 1997.
[45] G.M. Sheldrick, SHELXTL, Version 6.10, Bruker AXS, Inc., Madison, Wisconsin,
USA, 2000.
[46] A.L.P. Speck, Acta Crystallogr., Sect.
A 46 (2006) C34. A Multipurpose
[29] D.J. McCabe, A.A. Russell, S. Karthikeyan, R.T. Paine, R.R. Ryan, B. Smith, Inorg.
Chem. 26 (1987) 1230.
Crystallographic Tool, University of Utrecht, The Netherlands.
[47] C.J. Janiak, J. Chem. Soc., Dalton Trans. (2000) 3885.