Synthesis, crystal structure and luminescent behaviour of coordination complexes of copper with bi- and tridentate amines and phosphonic acids

Article abstract of DOI:10.1016/j.ica.2008.09.010

The synthesis and crystal structure of four new copper(I) and copper(II) supramolecular amine, and amine phosphonate, complexes is reported. Reaction of copper(I) with 2-,9-dimethyl-1-10-phenanthroline (dmp) produced a stable 4-coordinate Cu(I) species, [

Full text of DOI:10.1016/j.ica.2008.09.010

Inorganica Chimica Acta 362 (2009) 1872–1886
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Inorganica Chimica Acta
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Synthesis, crystal structure and luminescent behaviour of coordination complexes
of copper with bi- and tridentate amines and phosphonic acids
a
a
a
b
Kay Latham a, , Keith F. White , Katherine B. Szpakolski , Colin J. Rix , Jonathan M. White
*
a School of Applied Sciences, RMIT University, Melbourne, VIC 3001, Australia
b School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 July 2008
Received in revised form 29 August 2008
Accepted 2 September 2008
Available online 13 September 2008
The synthesis and crystal structure of four new copper(I) and copper(II) supramolecular amine, and
amine phosphonate, complexes is reported. Reaction of copper(I) with 2-,9-dimethyl-1-10-phenanthro-
line (dmp) produced a stable 4-coordinate Cu(I) species, [Cu(I)(dmp)2]Cl ꢀ MeOH ꢀ 5H2O (2), i.e., the
increased steric hindrance in the ‘bite’ area of dmp did not prevent interaction with the metal and pro-
vided protection against oxidation which was not possible for the phen analogue [R. Clarke, K. Latham,
C. Rix, M. Hobday, J. White, CrystEngCommun. 7(3) (2005), 28–36]. Subsequent addition of phenylphos-
phonic acid to (2) produced two structures from alternative synthetic routes. An ‘in situ’ process yielded
red block Cu(I) crystals, [Cu(I)(dmp)2] ꢀ [C6H5PO3H2 ꢀ C6H5PO3H] (4), whilst recrystallisation of (2) prior to
Keywords:
Copper
Phosphonic acids
Dpk
Dmp
Structure
Luminescence
addition of the acid (‘stepwise’ process) produced
a
green, needle-like Cu(II) complex,
[Cu(II)(dmp) ꢀ (H2O)2 ꢀ C6H5PO2(OH)] [C6H5PO2(OH)] (3). However, addition of excess dmp during the ‘step-
wise’ process forced the equilibrium towards product (4) and resulted in an optimum yield (99%). The
structure of (4) was similar to the phen analogue, [Cu(II)Cl(phen)2] ꢀ [C6H5PO2(OH) ꢀ C6H5PO(OH)2] (1) [R.
Clarke, K. Latham, C. Rix, M. Hobday, J. White, CrystEngCommun. 7(3) (2005), 28–36], but the presence
of dmp exerted some influence on global packing, whilst (3) exists as a polymeric layered material. In con-
trast, reaction of copper(I) with di-2-pyridyl ketone (dpk), followed by phenylphosphonic acid produced
purple/blue Cu(II) species, [Cu(II)(dpk ꢀ H2O)2] Cl2 ꢀ 4H2O (5), and [Cu(II)(dpk ꢀ H2O)2] ꢀ [C6H5PO2(OH)2
ꢀ
C6H5PO(OH)2] (6), respectively, i.e., in both cases oxidation of copper occurred. Solid-state luminescence
was observed in (2) and (4). The latter showing a 5-fold enhancement in intensity.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
Structural studies on phosphonate groups, with the aim of
designing organic solids, have only recently been reported in the
One of the lesser studied functionalities in crystal engineering is
the phosphonate group (R–P(O)(OH)2). Like sulphonic acids, phos-
phonic acids are strong acids, with the first pKa ꢁ 1–2, and so they
remain ionised over a wide pH range in aqueous media. Each phos-
phonic acid group can provide one-, two- or three-oxygen atoms to
coordinate metal ions, and thus the principal uses of these acids in-
clude chelation, e.g., to remove heavy metals from bleaching solu-
tions in the paper, pulp and textile industry, and also scale
inhibition [1]. Another fertile area of research has been the devel-
opment of metal phosphonates, a class of organic–inorganic hybrid
materials with a wide range of applications encompassing ion-ex-
change, intercalation, catalysis, light-harvesting, and molecular
magnetic devices [2]. Phosphonic acids also form extremely strong
hydrogen bonds. However, the rapid growth of metal phospho-
nates has overshadowed the potential of phosphonic acids to form
supramolecular arrays.
literature. These studies have examined only a small selection of
acids, principally phenylphosphonic acid [C6H5PO(OH)2] [3–5],
and those acids that have multiple functionalities and may form
zwitterions, e.g., N-nitrilotri(methylphosphonic) acid, NTMP [6–
8]. Some work has also been carried out on diphosphonic acids
[9]. Deprotonation of organophosphonic acids, by amines (e.g., ani-
line, phenanthrolines, etc.) [3–7] or metal(II) salts (e.g., Mn, Co, Cu,
Ni, Zn, Cd and mixtures of these ions) [3,4,8], appears to trigger a
self-assembly process and lead to the formation of structurally ro-
bust and predictable aggregates.
We have reported a number of studies on the synthesis of cop-
per(II)amine arylphosphonates with supramolecular architecture.
These materials have the general formula: [CuII(phen)2X][((O-
H)2OPC6H5)((OH)O2PC6H5)] (where X = I, Br, Cl (1), NCS), and con-
tain
a 5-coordinate copper(II) cation, counterbalanced by a
hydrogen-bonded phenylphosphonic acid dimer anion [4]. The
complexes are associated through hydrogen bonding interactions
between the phosphonic acids, and
phen–phen, phen–acid, and acid–acid aromatic rings. The supramo-
p–p interactions between
* Corresponding author. Tel.: +61 3 9925 2117; fax: +61 3 9639 3747.
E-mail address: kay.latham@rmit.edu.au (K. Latham).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.09.010

K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
1873
lecular motifs observed in these systems are quite robust, and rel-
atively unaffected by changes in X and the nature and position (oꢂ,
mꢂ or pꢂ) of substituents on the aromatic ring of the acid [10].
The aims of the present study were to synthesise analogues of
[Cu(II)(phen)2Cl][((OH)2OPC6H5) ((OH)O2P6H5)] (1), containing dif-
ferent amine species, and to explore the impact of this change on
the oxidation state and coordination of the copper atom. Their af-
fect upon local and global structure was also of considerable inter-
est. The synthesis of the phen analogue (1) proceeds via a Cu(I)
intermediate. However on addition of phenylphosphonic acid to
[Cu(I)(phen)2]X (X = Clꢂ, Brꢂ) spontaneous oxidation to Cu(II), to
produce [Cu(II)(phen)2Cl][((OH)2OPC6H5) ((OH)O2P6H5)] (1) occurs
[4]. This change in oxidation state has a number of chemical and
physical consequences. For example, Cu(II) d9 typically exhibits
5- or 6-coordinate geometry, whilst Cu(I) d10 prefers 4-coordinate
geometry [11] and when coordinated with two phen ligands, a
square planar structure is observed [11]. The filled d10 orbital shell
present in Cu(I) also participates in metal-to-ligand charge-trans-
fer (MLCT), and on excitation, Cu(I) donates electrons to ligands,
such as phen and its derivatives, and photoluminescence can be ob-
served [12–14]. For example, Blaskie and McMillin [12] observed
photoluminescence lasting 54 ns at ambient temperatures for
[Cu(I)(dmp)2]+ in dichloroethane. Hence, it would be beneficial to
have some control on the oxidation state and geometry exhibited
by these species, in order to exploit potential applications in sensor
design and/or redox capability. The amines used in this study are
shown in Fig. 1.
tate character, and functional groups (C@O/C–OH) that may engage
in additional H-bonding interactions.
2. Experimental
2.1. Materials
Copper(I) chloride was prepared according to published proce-
dures [18]. Phenylphosphonic acid (98%), 2,9-dimethyl-1,10-phe-
nanthroline (dmp) (98%), and di-2-pyridylketone (dpk) (99%)
were all obtained from Aldrich Chemicals, and used without fur-
ther purification.
2.2. Physical measurements
Fourier transform infrared spectra (4000–400 cmꢂ1) of the com-
plexes were recorded on a Perkin Elmer 1725X spectrometer as KBr
disks. Powder xrd spectra, of the powdered, homogeneous bulk
material, were collected on a Bruker D8 ADVANCE diffractometer
using graphite-monochromated Cu Ka radiation (k = 1.5406 Å):
scan range 3–60° 2h, step size 0.02°, count rate 2 s. Spectra were
compared to powder spectra generated from single crystal data
using Mercury software [22]. Elemental analysis for C, H, N, P
and Cl was performed by the Campbell Microanalytical Laboratory
at the University of Otago, New Zealand.
Fluorescence measurements were carried out using a Fluorolog-
3 fluorescence spectrometer from Jobin–Yvon–Horiba fitted with a
450 W Xe lamp. The powdered samples were loaded evenly into
the sample cavity of the solid sample holder and the fluorescence
emission spectra were collected between 450 and 750 nm, at an
angle 45° to the incident beam, using an excitation wavelength
of 400 nm, and a slit width of 1 nm. All spectra were collected at
room temperature.
The phen ligand, as a planar and rigid amine with aromatic
p-
electrons, is an excellent candidate for the engineering of struc-
tures, but does leave the Cu(I) centre exposed to oxidation. Thus,
2,9-dimethyl-1,10-phenanthroline (dmp), with slightly bulky sub-
stituents in the 2- and 9-positions, was selected since this ligand
may protect the Cu(I) centre from oxidation, or at least enforce a
tetrahedral geometry on the metal – a geometry generally much
more favourable for Cu(I) than Cu(II). However, it should not be
too large to prevent intercalation into the voids between the phen-
ylphosphonate layers, although it may alter some of the packing
characteristics.
The related ligand, di-2-pyridylketone (dpk), is an excellent can-
didate for metal-complex extended-structure systems [15], and
can behave as either a bidentate or tridentate ligand [15], com-
monly chelating through N,N or N,O coordination [15–17]. How-
ever, it is also capable of N,N,O chelation after hydration of the
ketocarbonyl group, to form a gem-diol, represented as (dpk ꢀ H2O),
which may ionise to yield a monoanionic ligand (Fig. 2) – a reaction
which is known to be promoted by metal ion coordination [15].
Dpk has not been investigated in a crystal engineering capacity
when coordinated with copper and phenylphosphonic acid.
In this work, studies were performed to compare the stability,
coordination and crystal structure of the Cu(I)/Cu(II) complexes
of dpk, with those of phen and dmp analogues, to gain insight into
the effect of using a sterically ‘open’ ligand with potential triden-
2.3. Synthesis of the complexes
2.3.1. [Cu(I)(dmp)2]Cl ꢀ MeOH ꢀ 5H2O (2)
A degassed suspension of 2,9-dimethyl-1,10-phenanthroline
(dmp) (0.915 g, 0.0051 mol, 30 mL ethanol) was added to cop-
per(I)chloride (0.2 g, 0.0020 mol, 20 mL ethanol) giving a dark-
red solution. This solution was stirred for 3 h at room temperature
in a two-neck round-bottomed flask, fitted with a condenser and
N2 gas flush. The reaction mixture was filtered to remove any solid
impurities, and the solvent removed from the red/orange filtrate
using a rotary evaporator. The remaining solid was recrystallised
from a 1:1 aqueous methanol solution. Crystals were collected
and washed with a few drops of cold Milli-Q water, giving red/or-
ange, fine needle crystals, which slowly became brown as the crys-
tals desolvated. Suitable X-ray diffraction quality single crystals
were isolated mechanically from the bulk material. Yield 55%. Anal.
Calc. for [C28H24N4CuCl]: C, 65.24; H, 4.69; N, 10.87; Cl, 6.88.
Found: C, 63.04, H, 5.04, N, 10.57, Cl, 6.79%.
5
6
R'
R'
O
4
7
R
H
Me
Me
R’
H
8
3
phen
dmp
bcp
2
H
9
N 1
10 N
Ph
N
N
R
R
Fig. 1. (a) 1,10-Phenanthroline and its derivatives and (b) di-2-pyridyl ketone (dpk).

1874
K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
Cu]: C, 60.41; H, 4.69; N, 7.05; P, 7.79. Found: C, 59.85; H, 4.60 N;
6.96; P, 7.73%.
O
C
dpk
2.3.5. [Cu(II)(dpk ꢀ H2O)2 ]ꢀ 2Cl ꢀ 4H2O (5)
A
degassed solution of di-2-pyridylketone (dpk) (0.459 g,
N
N
N
0.00255 mol, 10 mL ethanol) was added to a suspension of cop-
per(I)chloride (0.1 g, 0.0010 mol, 20 mL ethanol) giving a dark
red/brown solution. This suspension was stirred for approximately
2 h at room temperature under N2. The reaction mixture, now a
brilliant blue colour, was filtered to remove any solid impurities.
The filtrate was evaporated using a rotary evaporator and the
remaining solid recrystallised from a hot 1:1 aqueous/ethanol
solution. Blue/purple block – like crystals were formed. Suitable
X-ray diffraction quality single crystals were isolated mechanically
from the bulk material. Yield 54%. Anal. Calc. for [C22H20N4O4CuCl]:
C, 52.49; H, 4.00; N, 11.13; Cl, 7.04. Found: C, 52.01; H, 3.97; N,
11.37; Cl, 6.95%.
H2O
-H2O
OH
C
dpk.H2O
N
OH
-H+
H+
OH
C
dpk.OH-
2.3.6. [Cu(II)(dpk ꢀ H2O)2] ꢀ [C6H5PO2(OH)]2 ꢀ [C6H5PO(OH)2] (6) –
‘ligand addition’-technique
O-
N
N
Crystals of [Cu(II)(dpk ꢀ H2O)2 ꢀ 2Clꢂ ꢀ 4H2O] (5) (0.11 g,
0.00021 mol) were dissolved in warm methanol (20 mL). Addi-
tional dpk (0.06 g 0.00033 mol) was added and stirred in the warm
solution for 30 min. Phenylphosphonic acid (0.07 g, 0.00044 mol)
was then added to the solution, stirred for 2 h, filtered to remove
any undissolved material, and allowed to crystallise. Purple clus-
tered crystals were obtained between 1 and 3 weeks. Suitable X-
ray diffraction quality single crystals were isolated mechanically
from the bulk material. Yield 48%. Anal. Calc. for [C40H39N4O13P3-
Cu]: C, 52.35; H, 3.87; N, 7.18; P, 7.94. Found: C, 52.04; H, 4.12;
N, 7.01; P, 7.55%.
Fig. 2. The hydration of dpk [17].
2.3.2. [Cu(II)(dmp) ꢀ (H2O)2 ꢀ C6H5PO2(OH)]+ [C6H5PO2(OH)]ꢂ (3) –
‘stepwise’ technique (Scheme 1)
Crystals of [Cu(I)(dmp)2]+Clꢂ ꢀ MeOH ꢀ 5H2O (2) were dissolved
in ethanol (0.32 g, 15 mL), and the solution added to an ethanolic
solution of phenylphosphonic acid (0.2 g, 0.0012 mol, 20 mL). The
reaction mixture was then stirred for 2 h, under N2, and filtered
to remove any solid impurities. The filtrate was then evaporated
under vacuum, with the remaining solid (a mixture of red and
green microcrystals) recrystallised twice from a 1:1 ethanol/water
solution. Green shard-like crystals were obtained. Suitable X-ray
diffraction quality single crystals were isolated mechanically from
the bulk material. Yield 29%. Anal. Calc. for [C26H28N2O8P2Cu]: C,
50.21; H, 4.54; N, 4.50; P, 9.96. Found: C, 50.53; H, 4.75; N, 4.55;
P, 9.72%.
2.3.7. [Cu(II)(dpk ꢀ H2O)2] ꢀ [C6H5PO2(OH)]2 ꢀ [C6H5PO(OH)2] (6a) –
‘in situ’ technique
A solution of dpk (0.46 g, 0.00255 mol, 15 mL ethanol) was
added to a suspension of copper(I) chloride (0.1 g, 0.0010 mol,
10 mL ethanol) giving a dark red/brown solution. This solution
was stirred in a round-bottomed flask for 1 h. Phenylphosphonic
acid (0.16 g, 0.001 mol) was then added to this solution, and the
reaction mixture stirred for a further 2 h. After 5 days a purple
powder was filtered from the reaction mixture. Yield 43%. Anal.
Calc. for [C40H39N4O13P3Cu]: C, 52.35; H, 3.87; N, 7.18; P, 7.94;
Cu, 8.15. Found: C, 51.46; H, 4.68; N, 6.81; P, 7.25; Cu, 7.99%.
2.3.3. [Cu(I)(dmp)2]+ ꢀ [C6H5PO3H2 ꢀ C6H5PO3H]ꢂ (4) – ‘in situ’
technique (Scheme 1)
A degassed suspension of dmp (2.265 g, 0.013 mol, 30 mL etha-
nol) was added to copper(I)chloride (0.495 g, 0.005 mol) giving a
dark-red solution. This solution was stirred under N2 in a two neck
flask fitted with a condenser, for 2 h at room temperature. A phe-
nylphosphonic acid solution (1.268 g, 0.004 mol, 30 mL ethanol)
was then added to the suspension and stirring continued for a fur-
ther two hours under N2. The red/orange solution was filtered to
remove any solid impurities. Red block crystals were obtained by
ether diffusion into the filtrate. Suitable X-ray diffraction quality
single crystals were isolated mechanically from the bulk material.
Yield 33%. Anal. Calc. for [C40H37N4O6P2Cu]: C, 60.41; H, 4.69; N,
7.05; P, 7.79. Found: C, 59.39; H, 4.84; N, 6.98; P, 7.51%.
2.4. Crystal structure determination
In the present study, the structures of products (2–4) and (6)
were determined and analysed for the first time by single crystal
X-ray diffraction. Products (1) and (5) have been previously re-
ported (CCDC No. 216752 [4] and BPYKTA10 [17], respectively).
Crystal data were collected at 130 K for all structures, using graph-
ite monochromated Mo Ka radiation for compounds (2–4) and Cu
Ka
radiation for (5) and (6). Data for (5) and (6) were collected and
integrated using an Oxford Enhance system, whilst for compounds
(2–4) the data were collected and integrated using a Bruker SMART
CCD area detector system. In all cases, structures were solved by
direct methods, using SHELXS-97 [19] (5) and (6) or SHELXTL [20] (2–
4), and refined using SHELXL-97 [19] (5) and (6) or SHELXTL [20] (2–
4). A mixed strategy was used for the refinement of hydrogen
atoms. Hydrogen atoms attached to carbon were placed in calcu-
lated positions with a C–H distance of 0.93 Å, whilst hydrogen
atoms attached to oxygen were located from difference Fourier
maps, and refined without constraint. Molecular graphics were
performed using ZORTEP [21], SHELXTL [20] and Mercury [22] pro-
grams. Selected crystal data are displayed in Table 1.
2.3.4. [Cu(I)(dmp)2]+ ꢀ [C6H5PO3H2 ꢀ C6H5PO3H]ꢂ (4a) – ‘ligand
addition’ technique (Scheme 1)
An excess of dmp ligand (0.1224 g, 0.0006 mol) was added to an
ethanolic solution of [Cu(I)(dmp)2]+Clꢂ ꢀ MeOH ꢀ 5H2O (2) (0.32 g,
0.0006 mol, 15 mL), and stirred for 10 min. This solution was then
added to an ethanolic solution of phenylphosphonic acid (0.2 g,
0.0012 mol, 20 mL), and the mixture stirred for 2 h under N2, and
then filtered to remove any solid impurities. The crimson coloured
filtrate was then evaporated to dryness and the remaining solid
recrystallised from a 1:1 aqueous ethanol solution. Red block crys-
tals grew within 2 weeks. Yield 99%. Anal. Calc. for [C40H37N4O6P2-

K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
1875
Table 1
Summary single crystal xrd data for compounds (1) to (6)
(1) [4]
(2)
(3)
(4)
(5)
(6)
Empirical formula
Molecular weight
Crystal class
C36H29ClCuN4O6P2
774.56
monoclinic
C2/c
C29H38ClCuN4O6
637.62
C26H28CuN2O8P2
621.98
monoclinic
P2(1)/c
C40H37CuN4O6P2
795.22
C22H28Cl2CuN4O8
610.92
monoclinic
C2/c
C40H42CuN4O13
940.20
monoclinic
C2/c
triclinic
triclinic
ꢀ
ꢀ
Space group
P1
P1
0
a (ÅA)
25.057(3)
8.3700(10)
16.546(3)
90.00
103.370(10)
90.00
6.996 (2)
15.307 (5)
15.667(5)
65.22
83.03
87.65
13.5560(12)
10.5757(10)
18.7833(17)
90.00
107.155(2)
90.00
10.8687(8)
13.3371(10)
13.9517(11)
107.5840(10)
102.0590(10)
97.5280(10)
1844.0(2)
14.46510(10)
12.19030 (10)
14.53140(10)
90.00
90.8620(10)
90.00
37.7383
0
b (ÅA)
11.4540(9)
23.3422(17)
90.00
125.325(1)
90.00
0
c (AÅ)
a
(°)
b (°)
c
0 (°)
V (ÅA3)
3376.1(8)
4
1511.86
2
2573.0(4)
4
2562.09(3)
4
8232.0(11)
8
Z
2
Crystal, colour
Crystal size (mm)
Temperature (K)
Rad wavelength (ÅA)
Radiation type
block, blue
0.65 ꢃ 0.54 ꢃ 0.25
293(2)
rod, red
0.1 ꢃ 0.15 ꢃ 0.45
130 (2)
0.71073
slab, green
0.1 ꢃ 0.40 ꢃ 0.40
130(2)
block, red
0.25 ꢃ 0.40 ꢃ 0.45
130(2)
block, purple
0.35 ꢃ 0.33 ꢃ 0.26
130(2)
block, purple
0.35 ꢃ 0.40 ꢃ 0.40
130(2)
1.54184
Cu Ka
0
0.71069
0.71073
0.71073
1.54184
Mo K
a
Mo Ka
Mo K
a
Mo K
a
Cu Ka
h minimum–maximum (°)
Index ranges
2.53–24.98
0 6 h P 29
0 6 k P 9
ꢂ19 6 l P 19
2947
0.0375
0.1028
1.074
1.57–25.00
ꢂ8 6 h P 8
ꢂ17 6 k P 18
ꢂ14 6 l P 18
5233
0.0626
0.1833
1.019
1.57–27.53
ꢂ16 6 h P 17
ꢂ13 6 k P 12
ꢂ17 6 l P 24
5844
0.0425
0.0992
1.028
1.59–27.52
ꢂ12 6 h P 14
ꢂ17 6 k P 17
ꢂ15 6 l P 18
8083
0.0475
0.1179
1.043
5.61–66.00
ꢂ17 6 h P 17
ꢂ14 6 k P 13
ꢂ17 6 l P 17
2109
0.0374
0.0978
1.177
1.75–25.00
ꢂ44 6 h P 43
ꢂ13 6 k P 7
ꢂ27 6 l P 27
7260
0.0612
0.01662
1.053
Number of reflections
R1 (F2 > 2
wR (F2)
S
r
(F2))
or, alternatively, a deficit of dmp in the reaction mixture, and there-
fore this displacement may be prevented if the excess was coun-
tered. A one mole excess of dmp was added to the isolated
intermediate (2) prior to reaction with phenylphosphonic acid (‘li-
gand addition route’ – Scheme 1). Red block-shaped crystals (4a),
similar in appearance and composition to (4) were obtained. Fur-
thermore, the addition of excess dmp pushed the reaction almost
to completion, and resulted in a 99% yield.
3. Results and discussion
3.1. Phenanthroline derivatives
The reaction of copper(I) chloride with a methanolic solution of
dmp, using the method of Pallenberg et al. [14] produced red, nee-
dle-like crystals. Elemental analysis indicated a 1:2:1 molar ratio of
Cu:dmp:Cl, in agreement with the empirical formula,
[Cu(I)(dmp)2]Cl ꢀ MeOH ꢀ 5H2O (2). Addition of phenylphosphonic
acid to an ethanolic solution of recrystallised (2), henceforth
known as the ‘stepwise route’ (Scheme 1), yielded a mixture of
red (Cu(I)) and green (Cu(II)) crystals. The green, needle-like crys-
tals (3), were separated from the red crystals by aqueous extrac-
tion, and were found to contain a copper:phosphorus:water:dmp
ratio of 1:2:2:1 and an empirical formula, [Cu(II)(dmp) ꢀ
(H2O)2 ꢀ (C6H5PO2(OH))2] (3). No chloride was present, and the 5-
coordinate Cu(II) species was bonded to a single dmp ligand, i.e. a
composition rather different to the phen analogue (1) [4]. There-
fore, using this ‘stepwise’ approach – isolation of (2) prior to the
addition of acid – the Cu(I) state was not retained, and addition
of acid resulted in both oxidation of the metal and cleavage of a
dmp ligand. Due to the poor yield and quality of the red crystalline
product, precise structural identification was not possible. How-
ever, preliminary analysis suggested that this could be starting
material (2).
An alternative, ‘in situ’ route (Scheme 1): direct addition of phe-
nylphosphonic acid to a copper(I) chloride – dmp reaction mixture
without isolation and purification of (2), produced red block-crys-
tals with a Cu:P:dmp ratio of 1:2:2. The red colour indicated that
the +1 oxidation state of copper had been retained on addition of
the acid, and that the crowding effect of the methyl groups on
the dmp could prevent oxidation of the metal centre, if this route
was followed. Thus, displacement of one of the dmp ligands did
not occur using the ‘in situ’ technique, and a composition very sim-
ilar to (1) [4], except for the absence of chloride and the presence of
monovalent copper, was obtained.
3.2. FT-IR spectroscopy
The solid-state Fourier transform infrared spectra of all com-
plexes were fully consistent with their single crystal structures –
with the structural differences between the ‘stepwise’ (3) and ‘
in situ’ (4) compounds readily observed (Table 1). The most obvious
variation, a broad band at approximately 3424 cmꢂ1 in the ‘step-
wise’ complex, [Cu(dmp) ꢀ (H2O)2 ꢀ C6H5PO2(OH)]+[C6H5PO2(OH)]ꢂ
(3) was attributed to the m(O–H) stretch of the coordinated water
molecules. The ‘in situ’ [Cu(dmp)2]+ ꢀ [C6H5PO3H2 ꢀ C6H5PO3H]ꢂ
product (4) does not possess water molecules and therefore does
not show this feature in its IR spectrum. The IR spectra also support
the presence of phenylphosphonate anions and dmp. Correspond-
ing m
(PO–H) stretches at approximately 2400 cmꢂ1 are present in
the spectra of both (3) and (4), together with the classic PO3 vibra-
tions at 1138, 1080, 1040 and 926 cmꢂ1 (typically 1200–
900 cmꢂ1). The presence of dmp was revealed by bands at around
1625, 1590 and 860 cmꢂ1, which are consistent with amine ligands
coordinated to a copper ion. Bands observed in both the IR spectra
of the ‘in situ’ and ‘ligand addition’ complexes, are almost identical
in frequency and in relative intensity, thus confirming that these
two products are very similar. For spectra and tables of FTIR data
please see Supplementary material.
3.3. Powder XRD
All experimental powder spectra (2–4a) show excellent pattern
matching to the powder spectra generated from the single crystal
data using Mercury [22]. Thus we can conclude that the composi-
tion and structure of the bulk are the same as the isolated single
It was hypothesised that cleavage of one of the bidentate dmp
ligands, which occurs in the ‘stepwise’ route during reaction with
phenylphosphonic acid, may be due to the presence of excess acid

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K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
Scheme 1.
crystals in each case. Spectra were in general of a high quality,
showing well-resolved peaks, with the exception of the powder
XRD pattern of the ‘stepwise’ product (3) which contains some
amorphous material, as indicated by the broad peak in the region
9–15° 2h. The spectra of the ‘in situ’ (4) and the ‘ligand addition’
(4a) crystal products are very similar, see Supplementary material
for spectra and tables of xrd data.
Thus from FT-IR and powder xrd data we can confirm that prod-
ucts (4) and (4a) are indeed the same, and that both oxidation of
the copper(I) centre, and cleavage of one of the dmp ligands, can
be prevented by addition of excess dmp during the ‘stepwise’ route.
with the colour providing convincing evidence of a Cu(II) species.
Thus, like the phen analogue (1) [4], the open nature of the ligand
does not inhibit oxidation of the copper centre. Elemental analysis
indicated a 1:2:2 molar ratio of Cu:dpk:Cl, in agreement with the
empirical formula, [Cu(II)(dpk)2]Cl2 ꢀ 4H2O (5).
As in the dmp experiments, addition of phenylphosphonic acid
to (5) was attempted via both the ‘in situ’ and ‘ligand addition’ syn-
thetic procedures (Scheme 1). The ‘ligand addition’ synthesis pro-
duced purple, rod-like crystals (6) with a Cu:P:dpk ratio of 1:3:2,
whilst the ‘in situ’ synthesis yielded a purple powder (6a). In the
latter case, the product was not of sufficient quality to perform sin-
gle crystal X-ray diffraction analysis, but elemental analysis was
consistent with the presence of two dpk ligands, as well as the exis-
tence of phenylphosphonate acid in the complex, i.e., (6a) has a
similar molecular composition to (6).
3.4. Solid-state luminescence in phenanthroline derivatives
The solid-state luminescence spectrum of bis(dmp)copper(I)
chloride (2) showed a single (FWHM ꢄ 150 nm) strong emission
band at ꢄ730 nm when excited at 400 nm. The copper(I) dmp
phenylphosphonate derivative (4) exhibited a similar emission
band at ꢄ730 nm, with a similar FWHM, but with a 5-fold
enhancement in intensity, which was attributed to the extended
3.5.2. FT-IR Spectroscopy
A significant feature in the infra-red spectrum of (5), (6) and
(6a) is that the strong carbonyl band at 1683 cmꢂ1 present in the
free dpk ligand has been replaced by a strong band at around
p-system present in the phosphonate supramolecular assembly.
3172 cmꢂ1 corresponding to an
m(O–H) stretch. This is attributed
to the well established hydration of the dpk ligand. Relevant liter-
ature [15,16] also indicates that the bands at 1469 cmꢂ1 and
1444 cmꢂ1 in (5) are also characteristic of [M(dpk ꢀ H2O)2]2+ cat-
ions. Therefore all three complexes contain dpk in the gem-diol
form.
3.5. Di-2-pyridylketone (dpk) derivatives
3.5.1. Synthesis of copper–dpk intermediate (5)
The isolation of a copper–dpk intermediate was attempted
using the same molar ratio (1:2.5) of copper:dpk as used in the
dmp synthesis (2). Blue/purple block crystals of (5) were obtained,
The same vibrations occur in the spectrum of (6), but are
slightly shifted (3435 cmꢂ1
(m , ,
(O–H)), 1607 cmꢂ1 1469 cmꢂ1

K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
1877
1446 cmꢂ1), together with a group at 671–628 cmꢂ1 also present in
the spectrum of (5). Characteristic stretches of phenylphosphonate,
are also observed, most notably the distinguishing series of PO3
bands in the range of 1200–900 cmꢂ1. The FTIR spectra of (6) and
(6a) are very similar, thus the ‘ligand addition’ and ‘in situ’ routes
have resulted in materials with very similar compositions and
structures.
dinate [Cu(I)(dmp)2]+ cation, counter-balanced by a chloride anion,
with one methanol and five water molecules completing the unit
([Cu(I)(dmp)2]Cl ꢀ MeOH ꢀ 5H2O (2)). The closest relative to this
structure is the perchlorate analogue, [Cu(I)(dmp)2]ClO4, reported
by Dessy and Fares [23], though the former is monoclinic, space
ꢀ
group P21/n, whilst (2) is triclinic P1.
As illustrated, the copper bonds to four nitrogen atoms of two
dmp molecules. These Cu–N bonds (Tables 2 and 3) are unsymmet-
rical, as is the case in the perchlorate [23] and other copper–dmp
complexes [26], resulting in a distorted tetrahedral structure with
the two dmp ligands on different planes in order to minimise steric
repulsion between the methyl groups (74° angle between planes).
The charge-balancing chloride anion is disordered over two posi-
tions (occupancies Cl and Cl0, 0.522 and 0.478, respectively).
The complex exists as chains of copper cations associated
through a combination of offset-face-to-face (OFF) and edge-to-
3.5.3. Powder XRD
The powder X-ray diffraction spectrum of the ‘in situ’ product
(6a) is similar to the powder spectrum generated by Mercury
[22] from the single crystal data of (6), but there are some discrep-
ancies. Thus (6) and (6a) may not be identical, and the structure of
the latter cannot be completely solved at present.
3.6. Crystal description
face (EF) p–p interactions, which run in the a-direction, separated
3.6.1. Structures of compounds (2–4) – phenanthroline derivatives
The structure of the copper–dmp intermediate was confirmed
by single crystal xrd (Fig. 3a). The molecular unit contains a 4-coor-
by layers of water/methanol molecules and chloride anions held
together by a network of hydrogen bonds (Fig. 4). The copper cat-
ions are also associated with water, methanol and chloride through
Fig. 3. ORTEP diagrams of the molecular units of (a) [Cu(I)(dmp)2]Cl ꢀ MeOH ꢀ 5H2O (2), (b) molecular unit of the [Cu(II)(dmp) ꢀ (H2O)2 ꢀ C6H5PO2(OH)] ꢀ [C6H5PO2(OH)] (3), (c)
[Cu(I)(dmp)2] ꢀ [C6H5PO3H2 ꢀ C6H5PO3H] (4), and (d) [Cu(II)(dpk ꢀ H2O)2] ꢀ ½C6H5PO2ðOHÞꢅꢂ2 ꢀ [C6H5PO(OH)2] (6).

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K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
Fig 3. (continued)
Table 2
Significant bond angles (°) for compounds (1)–(6)
(1) [4]
[Cu(phen)2]I [25]
82.27
(2)
82.90
82.67
116.58
117.10
(3)
79.69
(4)
82.61
82.84
130.00
107.48
(5)
(6)
N1–Cu–N2
N3–Cu–N4
80.85
95.14
88.05
88.35
87.63
92.35
91.94
N(2)–Cu–N(3)
N(1)–Cu–N(4)
N*–Cu–O (dpk)
N–Cu–O (H2O)
106.82
91.95
74.16–75.30
73.67–75.03
102.07
O–Cu–O (H2O)
O–Cu–O3 (phos–)
85.80
87.51
Cu–O3–P1
144.44
Cl–Cu–N1
Cl–Cu–N2
93.07
130.35
Angle between amine planes
81.86
43.30
73.47
76.18
66.02
85.65
0
weak H-bonds (3.629–3.790 ÅA) between the methyl groups (C14–
H14Aꢀ ꢀ ꢀO3, C27–H27Aꢀ ꢀ ꢀCl0, C28–H28Aꢀ ꢀ ꢀO6), and between the
heterocyclic carbons of dmp (C28–H28Bꢀ ꢀ ꢀC1, C9–H9ꢀ ꢀ ꢀO2, C2–
H2ꢀ ꢀ ꢀCl, C5–H5ꢀ ꢀ ꢀCl0, C19–H19ꢀ ꢀ ꢀCl, C20–H20ꢀ ꢀ ꢀO3, C16–
H16ꢀ ꢀ ꢀO5). The OFF interactions between the N1N2 dmp rings
and those between the N3N4 dmp rings are perfectly parallel

K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
1879
Table 3
Significant bond lengths (Å) for compounds (1)–(6)
(1) [4]
[Cu(phen)2]I [25]
(2)
(3)
(4)
(5)
(6)
Cu–Cl
2.647
1.989
2.133
Cu–N1
Cu–N2
Cu–N3
Cu–N4
Cu–O (H2O)
Cu–O
2.008
2.02
1.993
2.220
2.032
2.033
1.997
2.080
2.001
2.013
2.007
2.012
2.008
2.020
2.032
2.033
2.006
1.948–2.011
1.965
2.459
2.418–2.425
P1–O2
P1–O1
P1–O3
P2–O4/O40
P2–O5
1.522
1.501
1.564
1.505
1.513
1.571
1.505
1.510
1.574
1.488
1.525
1.564
1.521/1.665
1.538
1.503
1.512
1.570
1.507
1.516
1.568
P2–O6
1.506
Fig. 4. Packing of (2) along a-axis showing EF/OFF stacked copper ‘ribbons’ separated by layers of H-bonded water and chloride layers.
0
0
with interplanar distances of 3.388 ÅA and 3.387 AÅ, respectively,
strong, perfectly linear hydrogen-bond (d(Oꢀ ꢀ ꢀH) = 1.21(7) Å), O2–
H2a–O20 = 180.00°), with H2a lying on a centre of inversion. Adja-
cent acid dimers are connected through pairs of regular strength
H-bonds (d(H3aꢀ ꢀ ꢀO1) = 1.784 Å, O3–H3a–O1 = 169.22°). The alter-
nation of these motifs forms H-bonded acid ‘chains’, which further
associate via EF interactions of the phenyl rings (E = H14, H15), to
form acid ‘sheets’.
and the EF interaction between the N1N2 dmp ligand frame-
work and the methyl protons of the N3N4 dmp ligand (H28B0) oc-
0
curs at a distance of 2.716 AÅ (H28B0 to plane C1 ring). All
p–p
interactions observed in (2) are within recognised and reported
limits [24].
The phen analogue of (2) is too unstable to isolate and is readily
oxidised. Reaction with phenylphosphonic acid ‘in situ’ yields blue
crystals of [Cu(II)Cl(phen)2][C6H5PO2(OH) ꢀ C6H5PO(OH)2] (1). The
structure of (1) was previously solved by Clarke et al. [4], and
found to contain a molecular unit with a 5 co-ordinate [Cu-
(phen)2Cl]+ cation, counter-balanced by a phenylphosphonic ‘dimer’
anion. This ‘symmetrical’ complex is assembled into ‘ribbons’ via a
continuous OFF interaction between the outer surfaces of the phen
rings: a common motif for phenanthroline complexes [24]. The
acid dimer consists of a hydroxyl proton (H2a) shared equally (cen-
trosymmetric) between the O2 and O20 atoms, resulting in an ionic,
The reaction of [Cu(I)(dmp)2]Cl ꢀ MeOH ꢀ 5H2O (2) with phenyl-
phosphonic acid, via the ‘stepwise’ route, resulted in a green
crystalline
product
[Cu(II)(dmp) ꢀ (H2O)2 ꢀ C6H5PO2(OH)]+
[C6H5PO2(OH)]ꢂ (3). Single crystal analysis revealed a Cu(II) species
with 5-coordinate, distorted trigonal-bipyramidal geometry. The
bidentate dmp ligand and one water molecule occupy equatorial
positions, whilst the other water molecule and a phenylphospho-
nate ligand occupy the distorted axial positions (Fig. 3b and Tables
2 and 3) i.e. a composition and structure rather different to the
phen analogue (1) [4]. Strong intramolecular interactions are pres-

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K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
Fig. 5. The motifs observed in (3) (a) colour coding of molecular unit, (b) the H-bonded ‘ladders’ and (c) connection of the ‘ladders’ to form extended polymeric layers.
ent: hydrogen bonding occurs between the bound water molecules
the same free acid anion through O8 is also present. These individ-
of the cation and the O6 and O8 oxygen atoms of the counter-bal-
ual H-bonding interactions combine to produce H-bonding ‘lad-
0
ancing
161.7(1)°; O2–H2Bꢀ ꢀ ꢀO6–2.722AÅ, 170.1(2)°), forming an R2,2(8)
motif (Fig. 5); and OFF interactions between the bound acid
phenylphosphonate
anion
(O1–H1Aꢀ ꢀ ꢀO8–2.683 ÅA,
ders’ which run along the b-direction of the crystal. A
0
symmetrical H-bonding pair also forms between O4ꢀ ꢀ ꢀH5A0–H50,
0
p–p
and O5–H5Aꢀ ꢀ ꢀO40 of adjacent bound acid anions (2.612 ÅA,
169.8(2)°) (Fig. 5c), which connect the ‘ladders’ together to form ex-
tended polymeric layers.
0
anion and the dmp ring (3.342 ÅA, 173.3(4)°).
The molecular unit interacts with its inverted neighbour by
forming an R2,4(8) H-bonding motif between alternate water li-
gands and oxygen atoms of the free acid anion. An R2,2(10) motif
linking the free acid anion through O7–H7A to O40 of an adjacent
bound acid and a neighbouring bound water molecule (O2) to
Association between layers is achieved through OFF interac-
0
tions between neighbouring dmp ligands (3.275 AÅ, 180°), and EF
interactions between bound and free acids at an angle of 24.1(8)°
0
to the normal and a distance of 3.988 ÅA between C250 and the cen-

K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
1881
Fig. 6. The alternate stacking of the diagonally packed ‘stepwise’ [Cu(dmp) ꢀ (H2O)2 ꢀ C6H5PO2(OH)]+ [C6H5PO2(OH)] (3) viewed along the c-axis.
Fig. 7. The strong H-bonding interactions that occur between disordered acids and acid anions in (4).
troid of C16–21, which are typically found with M(phen)n crystal
structures [11]. The 5-coordinate Cu(II) metal ion alternates with
the phenylphosphonate counter-anion and a diagonal-type stack-
ing is observed (Fig. 6).
In the case of the ‘in situ’ compound (4), further structural anal-
ysis confirmed that it contained a 4-coordinate, distorted tetrahe-
dral [Cu(I)(dmp)2]+ cation (Tables 2 and 3 list selected bond lengths
and angles), created by the coordination of a Cu(I) ion to the two
nitrogen atoms of two bidentate dmp ligands (Fig. 3c), and that
the phenylphosphonate dimer anion of (1) [4] had been replaced
by a disordered acid molecule (occupancies of O4 and O40 0.632
and 0.368, respectively), and a phenylphosphonate anion, giving
a
molecular unit of formula [Cu(I)(dmp)2]+ ꢀ [C6H5PO3H2 ꢀ
C6H5PO3H]ꢂ (4). A very strong H-bond exists between the disor-
dered acid and acid anion which is almost linear (175.13°) and
has a length of 2.228 Å (centroid O4/O4’–H4A–O2) (Fig. 7), as com-
pared to 180° and 2.439 Å, respectively, for the O2–H2A–O2 dimer
linkage in (1) [4]. There is also an intramolecular EF interaction be-
tween the protons of the disordered acid and the aromatic ring of
the anion (H40-plane C29–C34 2.845 Å, angle between planes

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K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
Fig. 8. local interactions in (4) (a) the OFF interactions between dmp aromatic rings, (b) the EF interactions between the dmp methyl protons and the dmp ring system.
Fig. 9. The H-bonded phosphonic acid/phosphonate chains which run through the structure and interact with the [Cu(dmp)2]+ cations through EF
p–p stacking.
C29–C34 and C35–C40 = 75.99°), and between the methyl groups
and the aromatic dmp rings (Fig. 8).
disordered acid (N3N4 plane: centroid C35–C40:3.553 Å, 163.26°)
(Figs. 8 and 9).
The packing of (4) has similarities to (1) [4] in that the acids/an-
ions form extended H-bonded chains, and OFF interactions exist
between the dmp ligands, but the latter are isolated, not extended,
ribbon-like structures, and the chains of acids are not connected
directly to each other through EF interactions. Thus the substituted
methyl groups of dmp do not prevent intercalation of the com-
plexed copper(I) cation between the self-assembled phen-
ylphosphonate dimers, but they do disrupt the extended packing
motifs. In (4), the acid chains form via the aforementioned EF inter-
action and via two separate H-bonding interactions: an R2,2(8)
motif connecting the disordered acids within each molecular unit
(O5–H5A–O6:2.500 Å, 167.83°), and an R2,2(8) motif connecting
the acid anions (O1–H1A–O3: 2.533 Å, 167.83°) (Figs. 7 and 8).
The [Cu(I)(dmp)2]+ cations are connected through two separate,
perfectly parallel OFF interactions between the N1N2 rings and be-
tween the N3N4 dmp rings (N1N2:3.465 Å; N3N4:3.549 Å), and an
OFF interaction also exists between the N3N4 dmp rings and the
3.6.2. Structures of compounds (5–6) – di-2-pyridylketone derivatives
Single crystal X-ray diffraction of (5) confirmed the +2 state of
copper and revealed an asymmetric unit having a Cu(II) centre
bound to a tridentate N,N,O chelating dpk ligand that has under-
gone hydrolysis at the carbonyl group (dpk ꢀ H2O) (Fig. 10). Also
present were two water molecules and a charge-balancing chloride
anion. Therefore, the molecular unit contains a 6-coordinate (octa-
hedral) Cu(II) ion coordinated to two dpk ꢀ H2O ligands, charge-bal-
anced by two chloride ions. Four water molecules intercalate
within the lattice and add to the overall packing in the
[Cu(II)(dpk ꢀ H2O)2]Cl2 ꢀ 4H2O (5) crystal. Thus, the composition
and structure are identical to that of a material previously pub-
lished by Wang et al. [17], however the unit-cell dimensions are
marginally smaller, and the R factor is improved.
A stronger interaction is observed between the Cu(II) and N
than between Cu(II) and O, as indicated by the substantially short-

K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
1883
Fig. 10. (a) asymmetric unit of the blue/purple intermediate (5) and (b) the three planes that pass through the copper centre of [Cu(dpk ꢀ H2O)2] Cl2 ꢀ 4H2O.
Fig. 11. H-bonding motifs observed between water and chloride ions in (5).
Fig. 12. Hydrogen bonded ribbons of [Cu(II)(dpk ꢀ H2O)2] Cl2 ꢀ 4H2O (5) viewed along b-axis, with R4,2(12) motif.
0
0
er bond lengths in the former (Cu–N1 = 2.001 ÅA, Cu–O1 = 2.458 ÅA)
(Tables 2 and 3). These results concur with those of Serna et al.
[14] and Wang et al. [17] who witnessed similar structural
arrangements in other [M(dpk ꢀ H2O)2]2+ cations.
Single crystal analysis of (6) revealed the same 6-coordinate
Cu(II) cation as observed in the intermediate (5) (Fig. 3d). However,
the perfect symmetry of the [CuII(dpk ꢀ H2O)2]+ cation was not re-
tained (Tables 2 and 3). The chloride counter ions in the interme-
diate product have been displaced by two phenylphosphonate
anions, together with a highly disordered phenylphosphonic acid.
The disordered acid appears to have an equivalent void volume
of a fully-protonated phenylphosphonic acid and is intercalated
within the crystal structure, filling vacancies within the lattice
and engaging in complex hydrogen-bonding with the free phos-
phonate anions.
Packing diagrams show non-linear H-bond links occurring be-
tween oxygen atoms, attributed to the hydrated dpk ligands inter-
acting with the phenylphosphonate dimers forming the skeletal
sheets of the packing structure (Fig. 14). H-bonding interactions
also occur between O8 and O7 of the acid molecules, which
Hydrogen bonding is responsible for the predominant interac-
tion between the cations in the structure. These occur between
O4–H4A of a hydrated oxygen and O1 of a water molecule
0
(2.727 ÅA) which, in turn, forms another H-bond with another hy-
0
drated oxygen (O30–H3A0) (2.733 AÅ) in an adjacent molecule result-
ing in a repeating R4,2(12) motif and a H-bonded ribbon of
[CuII(dpk ꢀ H2O)2]Cl2 ꢀ 4H2O cations and water molecules along
the b-axis (Fig. 11). These ribbons interact via further H-bonding
0
between water molecules (O2) (2.658 ÅA) and chloride anions to
produce linked R6,4(12) and R2,4(8) motifs (Fig. 12), and through
OFF interactions between aromatic
p
-electrons in the pyridyl rings
0
(2.676 ÅA) of the cations in each layer (Fig. 13).

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K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
oxidation, which was not observed during the preparation of the
copper–phen analogues [4].
The addition of phenylphosphonic acid produced two structures
from alternative synthetic routes. An ‘in situ’ process yielded red
block Cu(I) crystals, with dimeric phenylphosphonate counter an-
ions (4) replacing the chloride ion of (2). However, if the interme-
diate (2) was isolated from solution prior to addition of the acid
(‘stepwise’ process) a green, needle-like Cu(II) complex formed,
whereby a dmp ligand was replaced by a phenylphosphonate ion
(3) and two water molecules. It was concluded that the balance be-
tween steric pressures and bond strength around the metal centre
was delicate, and that addition of an extra mole of the dmp ligand
to the ‘stepwise’ intermediate (2), before the addition of the phenyl-
phosphonic acid (ligand addition process) may force the ligand-
coordination
equilibrium
towards
the
[Cu(dmp)2]+ ꢀ
[C6H5PO3H2 ꢀ C6H5PO3H]ꢂ product (4). This hypothesis proved cor-
rect, and also resulted in an ideal synthetic route to (4) which was
isolated in maximum yield (99%). Thus, even in the presence of
acidic oxidising conditions the bulky methyl substituents of dmp
were able to protect the metal centre, and provide redox control.
The structure and composition of (4) was subtly different to the
phenanthroline
analogue,
[Cu(II)Cl(phen)2]+ ꢀ [C6H5PO3H2 ꢀ
Fig. 13.
p–p interactions between parallel pyridine rings viewed along the b-axis in
C6H5PO3H]ꢂ (1) [4], since, the slightly bulky methyl-substituents
of the dmp had some influence on global packing. Indeed the OFF
(5).
p–p stacked ribbons of copper complexes in (1) were replaced by
alternating pairs of OFF and EF stacked complexes in (4), and the
layers of H-bonded acids were replaced by isolated chains. The
structure of product (3) was very different to both (1) and (4) ow-
ing to the cleavage of an amine ligand and its replacement by
water and a coordinated acid anion. The latter enabled the forma-
tion of a polymeric layered material where the copper cations were
connected to the free acid anions via a series of intra- and inter-
molecular H-bonds.
The luminescent activity reported for copper(I) dmp salts [11–
14] was also observed in (2), with a strong emission band at
ꢄ730 nm following excitation at 400 nm. This activity was retained
and slightly enhanced, when the dmp complex was incorporated
into a phosphonate network (4), and is ascribed to the extended
pi system present in the phosphonate supramolecular assembly.
Like the unsubstituted phen and bipy ligands, the sterically open
dpk ligand did not prevent oxidation of the Cu(I) metal centre, and
a purple/blue 6-coordinate bis dpk Cu(II) species was formed,
[Cu(II)(dpk ꢀ H2O)2] Cl2 ꢀ 4H2O (5), in which the dpk ligand under-
went hydration to produce the gem-diol [15], capable of coordinat-
ing with the copper ion through tridentate N,N,O bonding. Thus, a
6-coordinate copper(II) cation, exhibiting the well-known Jahn–
Teller tetragonal distortion typical of Cu(II) complexes is observed,
in contrast to the 5-coordinate species in (1) [4], and the presence
of the two OH groups in the cation of (6/6a) provides it with im-
proved H-bonding potential. The latter resulted in the formation
of a polymeric chain of copper cations linked by the OH groups
of the diol and the intercalated water molecules. Reaction of (5)
with phenylphosphonic acid by both the ligand addition and
in situ routes produced similar products (6 and 6a). The 6-coordi-
nate geometry and composition of the cationic Cu(II) species was
retained, whilst the Clꢂ counter ions were replaced by two
phenylphosphonate anions and a highly-disordered, fully-proton-
ated phenylphosphonic acid: [Cu(II)(dpk ꢀ H2O)2] ꢀ [C6H5PO2(OH)]2 ꢀ
[C6H5PO(OH)2] (6 and 6a). The familiar H-bonding R2,2(8) motifs
were again present, this time forming between the acid anions,
and also between bound OH groups and acid anions. The disor-
dered acid being intercalated between the layers of H-bonded
Fig. 14. Non-linear alternating H-bonding between the phenylphosphonate dimers,
as well as linking towards the disordered acid layer in (6).
support the interleaved, disordered acid molecules, and build the
layers of the structure. Figs. 15 and 16 clearly show the disordered
acid interleaved between the sheets of the alternating cations and
phenylphosphonates. Adding to stability of the structural packing
are columns formed by OFF and EF
p–p interactions between the
phenyl rings. Notably, OFF contacts occur from dpk pyridine rings
0
aligned to a phenylphosphonate anion at a distance of 4.343 ÅA.
OFF interactions and EF interactions also occur from the edge of
the same phenylphosphonate molecule to the opposite dpk pyri-
dine ring on the octahedral [CuII(dpk ꢀ H2O)2 ꢀ 2Clꢂ ꢀ 4H2O] cations
(Fig. 17).
4. Conclusions
It was found that the use of 2,9-dimethyl-1-10-phenanthroline
(dmp) instead of unsubstituted phenanthroline (phen) produced a
stable, readily isolable 4-coordinate Cu(I) product (2), i.e., the in-
creased steric hindrance in the ‘bite’ area of dmp did not prevent
coordination with the metal but it did provide protection against
and p–p stacked cations and anions.
Clearly, the comparative studies described here using phen,
bipy, dpk and the substituted phen derivative (dmp), provide good
evidence for the delicate balance between steric crowding, coordi-

K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
1885
Fig. 15. Sheets of alternating H-bonding phenylphosphonate dimers and the cation in (6), with the disordered acid occupying the voids between the sheets. Viewed along the
b-axis.
Fig. 16. Packing of the ‘step wise’ product viewed along along the c-axis.

1886
K. Latham et al. / Inorganica Chimica Acta 362 (2009) 1872–1886
Fig. 17. The OFF and EF interactions forming aromatic columns in (6): a = 4.343, b = 4.190, c = 2.674 Å
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Acknowledgements
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The authors wish to thank Dr. Alan Fowless, RMIT for useful dis-
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Appendix A. Supplementary material
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CCDC 692110, 692112, 692113 and 692114 contain the supple-
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tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2008.09.010.
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