Isomerism of a series of octahedrally coordinated transition metal carboxylate-phosphinates with 1,10-phenanthroline as a coligand: Discrete dimers or double-chains constructed by various dimeric ring motifs

Article abstract of DOI:10.1016/j.poly.2012.11.051

Six octahedrally coordinated transition metal carboxylate-phosphinates with 1,10-phenanthroline (phen) as a coligand, namely [Mn(L)(phen)(H ₂O)]·2(H₂O) (1), [Mn(L)(phen)(H₂O)] (2), [Cu(L)(phen)(H₂O)]·3(H₂O) (3), [Cd(L)(phen)] (4), [Cd(L)(phen)]·3(H₂O) (5) and [Cd(L)(phen)]·13/6(H ₂O) (6) (L^2- = (2-carboxyethyl)(phenyl)phosphinate) are presented here, of which 1 and 3 show discrete dimer structures while 2, 4, 5 and 6 feature different double-chain arrays. Compounds 1 and 2, as well as 4, 5 and 6, can be regarded as isomers, and 3 bears a strong structural analogy to 1, although the metal species in them are different.

Full text of DOI:10.1016/j.poly.2012.11.051

Polyhedron 51 (2013) 18–26
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Polyhedron
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Isomerism of a series of octahedrally coordinated transition metal
carboxylate–phosphinates with 1,10-phenanthroline as a coligand: Discrete
dimers or double-chains constructed by various dimeric ring motifs
Cui-Cui Zhao a, Zhong-Gao Zhou a, Xiang Xu b, Li-Jie Dong a, Guo-Hai Xu a, Zi-Yi Du a,b,
⇑
a College of Chemistry and Chemical Engineering, Gannan Normal University, Ganzhou 341000, PR China
b State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Six octahedrally coordinated transition metal carboxylate–phosphinates with 1,10-phenanthroline
(phen) as a coligand, namely [Mn(L)(phen)(H2O)]ꢀ2(H2O) (1), [Mn(L)(phen)(H2O)] (2), [Cu(L)(phen)(H2-
O)]ꢀ3(H2O) (3), [Cd(L)(phen)] (4), [Cd(L)(phen)]ꢀ3(H2O) (5) and [Cd(L)(phen)]ꢀ13/6(H2O) (6) (L2ꢁ = (2-car-
boxyethyl)(phenyl)phosphinate) are presented here, of which 1 and 3 show discrete dimer structures
while 2, 4, 5 and 6 feature different double-chain arrays. Compounds 1 and 2, as well as 4, 5 and 6,
can be regarded as isomers, and 3 bears a strong structural analogy to 1, although the metal species in
them are different.
Received 6 August 2012
Accepted 27 November 2012
Available online 26 December 2012
Keywords:
Metal phosphinate
Crystal structures
Isomerism
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
structural diversity required for the construction of coordination
polymers, among which supramolecular isomerism [7], an inter-
During the past few decades, the chemistry of metal–organic
coordination polymers has attracted extraordinary attention, ow-
ing to their vast range of structure types and potential applications
in areas such as gas storage, ion exchange, intercalation chemistry,
catalysis, photochemistry and magnetic materials [1,2]. Among the
broad family of metal–organic coordination polymers, carboxylate,
phosphonate and/or aza-aromatic compounds are the most widely
used ligands for moderate or strong ligation, whereas phosphinate
(R1R2PO2ꢁ) has rarely been employed for the construction of coor-
dination polymers [3–5]. However, phosphinate may be an espe-
cially interesting ligand in metal–organic hybrid engineering.
Compared with the mono-organic-group-attached carboxylate or
phosphonate moieties, the phosphinate group is further bonded
to an additional organic group, which can allow a better modula-
tion of the structure of the resultant metal complexes.
Recently, we have undertaken research work on the coordina-
tion and supramolecular chemistry of an asymmetric bifunctional
ligand, (2-carboxyethyl)(phenyl)phosphinic acid (H2L), which fea-
tures two formally analogous carboxylate and phosphinate moie-
ties (i.e., both contain two potential O donors) separated by a
flexible –CH2CH2– spacer, with the latter being further bonded to
a phenyl group [6]. It is anticipated that the use of such a conform-
ationally flexible ligand with multiple donor sites would bring the
esting phenomenon wherein more than one supramolecular struc-
ture are obtained from the same building blocks in an identical
ratio, may be observed.
Up until now, although a number of metal phosphinates have
been documented [3–6], supramolecular isomerism involving me-
tal phosphinates has been less encountered and studied
[3d,3f,4a,4d]. Considering that such systems may provide opportu-
nities to probe the conditions of their formation and to gain a greater
understanding of the factors leading to this structural variety, here
we present some examples of supramolecular isomerism based on
the above mentioned carboxylate–phosphinate ligand, with 1,10-
phenanthroline (phen) as coligand, namely [Mn(L)(phen)(H2-
O)]ꢀ2(H2O) (1), [Mn(L)(phen)(H2O)] (2), [Cu(L)(phen)(H2O)]ꢀ3(H2O)
(3),
[Cd(L)(phen)]
(4),
[Cd(L)(phen)]ꢀ3(H2O)
(5)
and
[Cd(L)(phen)]ꢀ13/6(H2O) (6), of which 1 and 2, as well as 4, 5 and
6, can be regarded as isomers, and 3 bears a strong structural anal-
ogy to 1, although the metal species in them are different. Herein,
we report their syntheses, crystal structures, supramolecular isom-
erism and properties.
2. Experimental
2.1. Materials and instrumentation
2-Carboxyethyl(phenyl)phosphinic acid was synthesized using
a published procedure [8]. All other chemicals were obtained from
commercial sources and used without further purification.
⇑
Corresponding author at: College of Chemistry and Chemical Engineering,
Gannan Normal University, Ganzhou 341000, PR China. Tel./fax: +86 0797 8393670.
E-mail address: ziyidu@gmail.com (Z.-Y. Du).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.11.051

C.-C. Zhao et al. / Polyhedron 51 (2013) 18–26
19
Elemental analyses were performed on a German Elementary Vario
EL III instrument. FT-IR spectra were recorded on a Nicolet Magna
750 FT-IR spectrometer using KBr pellets in the range 4000–
400 cmꢁ1. Thermogravimetric analyses were carried out on a Dia-
mond TG/DTA 6000 unit at a heating rate of 15 °C/min under a
nitrogen atmosphere. Photoluminescence analysis was performed
on a Perkin–Elmer LS55 fluorescence spectrometer. The measure-
ments of the powder frequency-doubling effects were carried out
by means of the method of Kurtz and Perry [9]. Radiation
(1064 nm) generated by a Q-switched Nd: YAG solid-state laser
was used as the fundamental frequency light. The crystal sample
was ground and sieved into particle sizes in a range of about
1427(s), 1414(m), 1315(m), 1205(m), 1147(s), 1139(s), 1101(m),
1062(s), 1033(m), 949(m), 862(m), 846(s), 812(s), 752(m), 729(s),
696(m), 636(m), 541(s), 520(m).
2.1.5. Synthesis of [Cd(L)(phen)]ꢀ3(H2O) (5)
A mixture of Cd(NO3)2ꢀ4H2O (0.30 mmol), H2L (0.30 mmol) and
phen (0.40 mmol) in 12 mL distilled water was sealed in a Parr Tef-
lon-lined autoclave (23 mL) and heated at 150 °C for 3 days, then
the resultant clear yellow solution was left to stand at room tem-
perature. Yellow block-shaped crystals of 5 were obtained 2 days
later in ca. 61% yield based on Cd. The final pH value of the solution
was ꢂ4. Anal. Calc. for C21H23N2O7P1Cd1 (Mr = 558.78): C, 45.14; H,
4.15; N, 5.01. Found: C, 45.05; H, 4.30; N, 4.92%. IR data (KBr,
cmꢁ1): 3408(s), 3048(m), 2967(m), 1633(s), 1581(s), 1425(m),
1348(m), 1309(m), 1144(s), 1309(m), 1273(m), 1221(m), 1144(s),
1126(s), 1039(m), 1022(m), 998(m), 860(s), 730(m), 700(m),
635(m), 540(m).
150–210 lm. The sieved sample was packed in round glass boxes
with a uniform diameter of 8.0 mm and then exposed to the laser
radiation. Second harmonic radiation generated by the randomly
oriented microcrystals was detected by a photomultiplier tube
and displayed on an oscilloscope. A sample of KDP of the same par-
ticle sizes was prepared as a reference material in an identical fash-
ion to assume the SHG effect.
2.1.6. Synthesis of [Cd(L)(phen)]ꢀ13/6(H2O) (6)
A
mixture of Cd(CH3CO2)2ꢀ2H2O (0.30 mmol) with H2L
2.1.1. Synthesis of [Mn(L)(phen)(H2O)]ꢀ2(H2O) (1)
(0.30 mmol) and phen (0.30 mmol) in 15 mL distilled water was
evaporated in air at ca. 80–90 °C until colorless plate-shaped crys-
tals precipitated. These crystals were collected in approximately
72% yield based on Cd, and the final pH value of the solution was
ꢂ5. Anal. Calc. for C63H64N6O18.5P3Cd3 (Mr = 1631.31): C, 46.38;
H, 3.95; N, 5.15. Found: C, 46.29; H, 4.09; N, 5.07%. IR data (KBr,
cmꢁ1): 3524(m), 3377(m), 3070(s), 2916(m), 1621(m), 1564(s),
1515(m), 1428(s), 1305(m), 1152(s), 1127(s), 1037(m), 1024(m),
939(m), 854(m), 798(m), 730 (m), 697(m), 639(m), 541(m),
520(m).
A
mixture of Mn(CH3CO2)2ꢀ4H2O (0.30 mmol) with H2L
(0.30 mmol) and phen (0.30 mmol) in 10 mL distilled water was
stirred for half an hour and then stood at room temperature. Pale
yellow brick-shaped crystals of 1 were obtained after one day, in
approximately 56% yield based on Mn, and the final pH value of
the solution was ꢂ5. Anal. Calc. for
C21H23N2O7P1Mn1
(Mr = 501.32): C, 50.31; H, 4.62; N, 5.59. Found: C, 50.25; H, 4.73;
N, 5.53%. IR data (KBr, cmꢁ1): 3394(s), 3051(m), 2922(m),
2856(m), 1558(s), 1512(m), 1427(s), 1398(m), 1311(m), 1205(m),
1178(s), 1136(s), 1078(m), 1048(m), 1027(m), 931(m), 852(m),
756(m), 735(m), 638(m), 555(m), 513(m).
2.2. Crystal structure determination for 1–6
2.1.2. Synthesis of [Mn(L)(phen)(H2O)] (2)
Data collection for 1–6 were performed on a Smart ApexII CCD
A mixture of Mn(CH3CO2)2ꢀ4H2O (0.30 mmol), H2L (0.30 mmol),
phen (0.30 mmol) and urea (0.30 mmol) in 12 mL of distilled water
was sealed in a Parr Teflon-lined autoclave (23 mL) and heated at
110 °C for 3 days. The final pH value was ꢂ6 and yellow column-
shaped crystals of 2 were collected in ca. 70% yield based on Mn.
Anal. Calc. for C21H19N2O5P1Mn1 (Mr = 465.29): C, 54.21; H, 4.12;
N, 6.02. Found: C, 54.12; H, 4.21; N, 5.96%. IR data (KBr, cmꢁ1):
3073(s), 2921(m), 1564(s), 1514(m), 1425(s), 1306(m), 1198(m),
1157(s), 1128(m), 1043(s), 1028(m), 937(m), 856(m), 798(m),
735(m), 638(m), 543(m), 521(m).
diffractometer equipped with graphite-monochromated Mo K
a
radiation (k = 0.71073 Å) at temperature of 296 K. The data sets
were corrected for Lorentz and polarization factors as well as for
absorption by the SADABS program [10]. All structures were solved
by the direct method using SHELXS-97 and refined by full-matrix
least-squares fitting on F2 by SHELXL-97 [11]. All non-hydrogen
atoms, except the lattice water molecules of 5, were refined with
anisotropic thermal parameters. All hydrogen atoms except those
of the water molecules were generated geometrically and refined
isotropically. Hydrogen atoms of the water molecules in 1–3 were
located in a difference map and refined with Uiso(H) values set at
1.5Ueq(O), while those in 5 and 6 were not included in the refine-
ments. The occupancy factors of the lattice water molecules
O(2W)–O(5W) in 5 and O(4W)–O(10W) in 6 were reduced to
50% because of their larger thermal parameters. Crystallographic
data and structural refinements for 1–6 are summarized in Table 1.
Important bond lengths are listed in Table 2.
2.1.3. Synthesis of [Cu(L)(phen)(H2O)]ꢀ3(H2O) (3)
A
mixture of Cu(CH3CO2)2ꢀH2O (0.30 mmol) with H2L
(0.35 mmol) and phen (0.30 mmol) in 15 mL distilled water was
evaporated in air at ca. 80–90 °C until green plate-shaped crystals
precipitated. These crystals were collected in approximately 78%
yield based on Cu, and the final pH value of the solution was ꢂ4.
Anal. Calc. for C21H25N2O8P1Cu1 (Mr = 527.94): C, 47.77; H, 4.77;
N, 5.31. Found: C, 44.81; H, 4.68; N, 5.35%. IR data (KBr, cmꢁ1):
3334(s), 3060(m), 2921(m), 1560(s), 1512(m), 1425(s), 1383(m),
1297(m), 1155(s), 1137(m), 1045(s), 1028(m), 949(m), 854(m),
802(m), 723(m), 700(m), 648(m), 538(m), 523(m).
3. Results and discussion
3.1. Syntheses
2.1.4. Synthesis of [Cd(L)(phen)] (4)
Since compounds 1 and 2, as well as 4, 5 and 6, can be regarded
as isomers, a comparison of their reaction conditions is worthy of
attention. While 1 was obtained under ambient conditions without
the addition of urea, the synthesis of 2 was carried out as a hydro-
thermal process in the presence of urea, which slowly hydrolyses
at the temperature of the reaction, releasing ammonia and slowly
raising the pH of the solution. The addition of urea as a slow-re-
lease, in situ alkaline regulator was also applied for the preparation
of 4. When a hydrothermal process similarly to that for 4 was
A mixture of Cd(NO3)2ꢀ4H2O (0.30 mmol), H2L (0.30 mmol),
phen (0.30 mmol) and urea (0.30 mmol) in 12 mL distilled water
was sealed in a Parr Teflon-lined autoclave (23 mL) and heated at
150 °C for 3 days. The final pH value was ꢂ7 and pale yellow
club-shaped crystals of 4 were obtained in ca. 81% yield based on
Cd. Anal. Calc. for C21H17N2O4P1Cd1 (Mr = 504.74): C, 49.97; H,
3.39; N, 5.55. Found: C, 49.85; H, 3.51; N, 5.46%. IR data (KBr,
cmꢁ1): 3059(m), 2952(m), 2919(m), 1623(m), 1564(s), 1512(m),

20
C.-C. Zhao et al. / Polyhedron 51 (2013) 18–26
Table 1
Summary of crystal data and structural refinement for 1–6.
Compound
1
2
3
4
5
6
Empirical formula
Formula weight
C
21H23N2O7P1Mn1
C21H19N2O5P1Mn1
465.29
Cc
C21H25N2O8P1Cu1
527.94
P21/c
C21H17N2O4P1Cd1
504.74
P21/n
C21H23N2O7P1Cd1
558.78
C2/c
C63H64N6O18.5P3Cd3
1631.31
P1
11.8321(4)
12.7583(4)
26.1784(10)
501.32
P21/c
9.0861(2)
ꢀ
Space group
0
18.8228(6)
13.1610(2)
5.8507(2)
23.4405(4)
a (AÅ)
0
21.4697(4)
11.2202(2)
12.6905(3)
8.6601(2)
22.5341(3)
8.1504(1)
24.1420(8)
13.5286(6)
12.0253(2)
19.3466(3)
b (AÅ)
0
c (AÅ)
a
b (°)
(°)
90
96.264(1)
90
2175.72(7)
4
1.530
0.727
1.006
0.0471, 0.0896
0.0966, 0.1070
90
94.646(2)
90
2061.85(9)
4
1.499
0.754
1.027
0.0469, 0.0821
0.0805, 0.0946
90
96.267(1)
90
2402.73(6)
4
1.459
1.023
1.001
0.0373, 0.0820
0.0648, 0.0939
90
92.269(3)
90
1909.38(12)
4
1.756
1.259
1.121
0.0644, 0.1611
0.0834, 0.1693
90
100.353(2)
92.399(2)
113.730(2)
3530.1(2)
2
1.535
1.034
0.965
0.0613, 0.1489
0.1273, 0.1828
104.370(1)
90
5282.78(15)
8
1.405
0.926
1.054
0.0542, 0.1800
0.0749, 0.2016
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
Goodness-of-fit on F2
R1, wR2 [I > 2 (I)]
R1, wR2 (all data)
r
R1
=
R
||F0| ꢁ |Fc||/
R
|F0|, wR2 = {
R
w[(F0)2 ꢁ (Fc)2]2/
R
w[(F0)2]2}1/2
.
3.2. Description of structure 1
Table 2
Selected bond lengths (Å) for 1–6.
Compound 1 features a discrete dimer structure. The asymmet-
ric unit contains one Mn2+ ion, one L2ꢁ anion, one phen ligand and
an aqua ligand as well as two lattice water molecules. The Mn(1)
ion has a distorted octahedral environment (see ESI, Fig. S1); three
of its six coordination sites are filled by one phosphinate O atom
and one bidentate chelating carboxylate group of two L2ꢁ ligands,
and the remaining three sites are occupied by one bidentate che-
lating phen ligand and a terminal aqua ligand. The L2ꢁ ligand in
1 bridges two Mn2+ ions via its one phosphinate O atom and one
bidentate chelating carboxylate group (Scheme 1b). A pair of the
Mn(1) ions are bridged by such two L2ꢁ ligands into a simple cen-
trosymmetric dimer (Fig. 1), which features a G-type ring, as
shown in Chart 1.
1
Mn(1)–O(2)#1
Mn(1)–N(1)
Mn(1)–O(4)
2.104(2)
2.257(2)
2.302(2)
Mn(1)–O(1W)
Mn(1)–O(3)
Mn(1)–N(2)
2.131(2)
2.258(2)
2.308(2)
2
Mn(1)–O(1)
Mn(1)–O(3)#2
Mn(1)–N(2)
2.057(3)
2.170(3)
2.302(4)
Mn(1)–O(2)#1
Mn(1)–O(1W)
Mn(1)–N(1)
2.086(3)
2.294(4)
2.328(4)
3
Cu(1)–O(1)#1
Cu(1)–N(2)
Cu(1)–O(1W)
1.945(2)
2.020(2)
2.297(2)
Cu(1)–O(3)
Cu(1)–N(1)
Cu(1)–O(4)
1.989(2)
2.023(2)
2.633(2)
4
Cd(1)–O(4)#1
Cd(1)–O(1)
Cd(1)–N(2)
2.196(6)
2.210(5)
2.385(6)
Cd(1)–O(2)#2
Cd(1)–N(1)
Cd(1)–O(3)#1
2.205(5)
2.357(6)
2.686(8)
The dimers in 1 are assembled through
pꢀ ꢀ ꢀp interactions be-
tween the phen ligands of adjacent dimers, in an interlocking fash-
ion, to form a two-dimensional supramolecular layer along the ac-
plane (Fig. 2). Furthermore, such layers stack along the b-axis, leav-
ing medium-sized channels parallel to the c-axis that can accom-
modate some solvent water molecules (Fig. S2). A closer analysis
reveals that a large number of hydrogen bonds are formed between
the L2ꢁ anions and water molecules, which stabilize the overall
three-dimensional supramolecular structure (Table S1).
5
Cd(1)–O(1)
Cd(1)–O(4)#2
Cd(1)–N(1)
2.225(4)
2.280(4)
2.365(5)
Cd(1)–O(2)#1
Cd(1)–N(2)
Cd(1)–O(3)#2
2.237(3)
2.295(5)
2.576(4)
6
Cd(1)–O(5)#1
Cd(1)–N(1)
Cd(1)–O(5)
Cd(2)–O(1)
Cd(2)–O(8)
Cd(2)–N(3)
Cd(3)–O(9)
Cd(3)–O(12)#2
Cd(3)–N(5)
2.260(4)
2.317(5)
2.378(4)
2.235(4)
2.329(5)
2.376(6)
2.216(5)
2.290(5)
2.343(7)
Cd(1)–O(4)
Cd(1)–N(2)
Cd(1)–O(3)
Cd(2)–O(10)
Cd(2)–N(4)
Cd(2)–O(7)
Cd(3)–O(2)
Cd(3)–N(6)
Cd(3)–O(11)#2
2.288(5)
2.368(5)
2.474(5)
2.247(4)
2.334(6)
2.433(5)
2.233(5)
2.306(7)
2.536(5)
3.3. Description of structure 2
Compound 2, exhibiting a double-chain structure, can be
viewed as an isomer of 1, but it contains no guest water compo-
nent. The Mn(1) center in 2 also adopts a distorted octahedral
geometry (Fig. S3); three of its six coordination sites are filled by
one carboxylate and two phosphinate O atoms from three L2ꢁ li-
gands, and the remaining three sites are occupied by one bidentate
chelating phen ligand and a terminal aqua ligand.
Symmetry codes: For 1: #1 ꢁx + 1, ꢁy + 1, ꢁz + 1. For 2: #1 x, ꢁy, z + 1/2; #2 x, y,
z + 1. For 3: #1 ꢁx + 1, ꢁy + 1, ꢁz + 1. For 4: #1 ꢁx + 2, ꢁy, ꢁz + 2; #2 x ꢁ 1, y, z. For
5: #1 ꢁx + 1, y, ꢁz + 1/2; #2 ꢁx + 1, ꢁy + 1, ꢁz. For 6: #1 ꢁx + 1, ꢁy + 2, ꢁz; #2
ꢁx + 2, ꢁy + 3, ꢁz + 1.
The L2ꢁ ligand in 2 bridges three Mn2+ ions via its one carboxyl-
ate and two phosphinate O atoms (Scheme 1a). The interconnec-
tion of the Mn2+ centers by the bridging L2ꢁ ligands leads to a
non-centrosymmetric double-chain array, which is related by the
symmetry of the c glide plane (Fig. 3). Such a double-chain features
another type of dimeric ring motif (Ring E, see Chart 1) that is
edge-shared with two neighboring ones through its two Mn–O–P
borders and is further stabilized by intra-chain hydrogen bonds be-
tween the non-coordinated carboxylate O atom and terminal aqua
ligand (Table S1). These non-centrosymmetric chains stack along
implemented with a slight excess of the phen ligand, but without
the addition of urea, the resultant product manifested as a clear
yellow solution; however, yellow crystals of 5 were precipitated
2 days later. Compared with 4 and 5, the isomeric 6 was obtained
without a hydrothermal process, but instead by evaporation of the
reaction mixture at a temperature of 80–90 °C, and the metal
source of cadmium nitrate was replaced by cadmium acetate. We
note that the final pH values of the reaction solutions of 4, 5 and
6 were about 7, 4 and 5, respectively.
the bc-plane by C–Hꢀ ꢀ ꢀ
p interactions to form a non-centrosymmet-

C.-C. Zhao et al. / Polyhedron 51 (2013) 18–26
21
M
M
O
P
O
O
P
O
O
P
O
O
P
O
M
O
M
M
O
M
M
O
O
O
M
Cd
O
M
O
M
O
(c)
(a)
(d)
(b)
Scheme 1. The coordination modes of the L2ꢁ ligands in 1–6.
torted octahedral environment and possesses one weak coordina-
tion bond [Cu(1)–O(4): 2.633(2) Å)], although its surrounding
coordination atoms are similar to those in 1 (Fig. S4). Another obvi-
ous difference is that a pair of intra-molecular hydrogen bonds
involving the terminal aqua ligands can be observed in the dimer
unit of 3 (Table S1), while such a phenomenon is not present in 1.
The dimers in 3 are also assembled through
pꢀ ꢀ ꢀp interactions
between the phen ligands of adjacent dimers, forming a two-
dimensional supramolecular layer along the bc-plane (Fig. 7). Fur-
thermore, such layers stack along the a-axis, with guest water mol-
ecules between the layers; and a large number of hydrogen bonds
are also formed amongst the L2ꢁ anions and water molecules,
which stabilize the overall three-dimensional supramolecular
structure (Fig. S5 and Table S1).
Fig. 1. View of the dimer structure of 1. The phen ligands and phenyl groups of the
L2ꢁ ligands have been omitted for clarity. Mn, P, O and C atoms are represented by
yellow, purple, red and black circles, respectively. (Color online.)
C
O
P
P
O
O
O
O
O
P
O
3.5. Description of structure 4
M
M
M
M
M
M
M
O
O
O
Compound 4 exhibits another type of double-chain array, which
is different to that in 2. The asymmetric unit contains one Cd2+ ion,
one L2ꢁ anion and one phen ligand. The Cd(1) ion adopts a severely
distorted octahedral geometry (Fig. S6): four of its six coordination
sites are filled by two phosphinate O atoms and one bidentate che-
lating carboxylate group from three L2ꢁ ligands, and the remaining
two sites are occupied by a bidentate chelating phen ligand. The
Cd–O and Cd–N distances are in the normal range, with the excep-
tion of one somewhat longer Cd–O distance [2.686(8) Å].
O
M
P
O
(CA)
P
(B)
(C)
(D)
P
P
O
O
O
O
O
P
O
M
M
M
M
M
O
The L2ꢁ ligand in 4 bridges three Cd2+ centers via its two phosph-
inate O atoms and one bidentate chelating carboxylate group
(Scheme 1d). The interconnection of the Cd2+ centers by the bridg-
ing L2ꢁ ligands results in the formation of a double-chain, which is
related by 21 symmetry parallel to the a-axis (Fig. 8). Different to
the double-chain of 2 which contains an E-type ring motif, the dou-
ble-chain in 4 features a centrosymmetric G-type ring motif unit
that is edge-shared with two neighboring ones via its two Cd–
O
O
O
O
O
O
M
P
O
P
P
(E)
(F)
(G)
Chart 1. Various dimeric ring motifs in 1–6 and three other cadmium(II)
compounds previously reported (see Ref. [6c]).
O2C–C–P borders and is further stabilized by intra-chain
p p
ꢀ ꢀ ꢀ
ric two-dimensional supramolecular layer, with adjacent chains
also related by the symmetry of the c glide plane (Fig. 4). Further-
more, the uni-oriented stacking of such layers results in its crystal-
lization in the polar Cc space group (Fig. 5). It is worthy of note that
the two distinct structures of 1 and 2 are mainly derived from the
two different tridentate coordination modes of the L2ꢁ ligand con-
tained within them.
packing interactions between the neighboring phen ligands
(Fig. 9). It is also noted that similar G-type rings can be observed
in 1 and 3, but the lack of a second coordinated phosphinate O atom
of the L2ꢁ ligand in these complexes results in the formation of 0D
discrete dimers rather than one-dimensional extended structures.
Overall, the double-chains in 4 are assembled through van der
Waals forces to form a three-dimensional supramolecular struc-
ture and there exist no lattice water molecules between these dou-
ble-chains (Fig. S7). We note that such an assembly and stacking
pattern in the crystal structure of 4 is more compact than those
of 5 and 6 (Dcalc: 1.756 ? 1.405 or 1.535 g cmꢁ3).
3.4. Description of structure 3
Compound 3 features a discrete dimeric structure and its asym-
metric unit contains one Cu2+ ion, one L2ꢁ anion, one phen ligand
and an aqua ligand as well as three lattice water molecules. Apart
from the different metal species (Cu versus Mn), compound 3 bears
a strong structural analogy to 1, considering that they feature essen-
tially similar discrete dimers but differ in the detailed geometric
parameters (Fig. 6, Table 2). The Cu(1) center in 3 has a severely dis-
3.6. Description of structure 5
Compound 5 can be viewed as an isomer of 4, but it contains an
additional guest water component. The asymmetric unit also

22
C.-C. Zhao et al. / Polyhedron 51 (2013) 18–26
Fig. 2. The
p
ꢀ ꢀ ꢀ
p
packing interactions between the phen molecules (drawn as dashed lines) observed in 1 along the ac-plane. Mn, P, O, N and C atoms are represented by
yellow, purple, red, blue and black circles, respectively. (Color online.)
Fig. 3. View of the chain array along the c-axis in 2. The phen ligands and phenyl groups of the L2ꢁ ligands have been omitted for clarity. For display details, see the caption for
Fig. 2. Hydrogen bonds are represented by dashed lines. (Color online.)
Fig. 4. The
pꢀ ꢀ ꢀp packing interactions between the phen molecules (drawn as dashed lines) observed in 2 along the c-axis. H atoms are represented by bright green circles. For
other display details, see the caption for Fig. 2. (Color online.)
contains one Cd2+ ion, one L2ꢁ anion and one phen ligand apart
from the lattice water molecules. The Cd(1) ion has a distorted
octahedral geometry and its six surrounding coordination atoms
are similar to those of 4 (Fig. S8). The Cd–O and Cd–N distances
are in the normal range, with the exception of one slightly longer
Cd–O distance [2.576(4) Å].
the bridging L2ꢁ ligands results in the formation of a new type of
double-chain array (Fig. 10), which is very different from those in
2 and 4. Such a chain features two types of edge-sharing dimeric
ring motifs (Rings C and G, see Chart 1), in which these rings are
arranged alternately in a [(G–C)–(G–C)ꢀ ꢀ ꢀꢀ ꢀ ꢀ] fashion.
The double-chains in 5 are assembled through
pꢀ ꢀ ꢀp interac-
The L2ꢁ ligand in 5 has a same coordination mode (Scheme 1d)
as that of 4. However, the interconnection of the Cd2+ centers by
tions between the phen molecules of adjacent chains to form a
three-dimensional supramolecular structure, with intra-chain

C.-C. Zhao et al. / Polyhedron 51 (2013) 18–26
23
Fig. 8. View of the chain structure of 4 along the a-axis. The terminal phen ligands
and phenyl groups of the L2ꢁ ligands have been omitted for clarity. Cd, P, O and C
atoms are represented by cyan, purple, red and black circles, respectively. (Color
online.)
Fig. 5. View of the three-dimensional supramolecular structure of 2 down the c-
axis. Hydrogen bonds are represented by dashed lines. For display details, see the
caption for Fig. 2.
Fig. 9. The intra-chain
ligands (drawn as dashed lines) observed in 4. Cd, P, O, N and C atoms are
pꢀ ꢀ ꢀp packing interactions between the neighboring phen
represented by cyan, purple, red, blue and black circles, respectively. (Color online.)
Fig. 6. View of the dimer structure of 3. The phen ligands and phenyl groups of the
L2ꢁ ligands have been omitted for clarity. Cu, P, O and C atoms are represented by
green, purple, red and black circles, respectively. Hydrogen bonds are represented
by dashed lines. (Color online.)
p p interactions also being present between neighboring phen
ꢀ ꢀ ꢀ
and L2ꢁ ligands (Figs. 11 and S9). The lattice water molecules are
located at the voids of the structure.
Fig. 7. The
pꢀ ꢀ ꢀp packing interactions between the phen molecules (drawn as dashed lines) observed in 3 along the bc-plane. Cu, P, O, N and C atoms are represented by green,
purple, red, blue and black circles, respectively. (Color online.)

24
C.-C. Zhao et al. / Polyhedron 51 (2013) 18–26
Fig. 10. View of the chain structure of 5 along the c-axis. The terminal phen ligands and phenyl groups of the L2ꢁ ligands have been omitted for clarity. For display details, see
the caption for Fig. 9.
3.7. Description of structure 6
of adjacent chains to form a three-dimensional supramolecular
structure, with intra-chain
p p interactions being present be-
ꢀ ꢀ ꢀ
Compound 6 can be regarded as an isomer of 4 and 5, with their
molecular formulas only differing in the numbers of the lattice
water molecules. It exhibits a more complicated double-chain
structure. The asymmetric unit contains three Cd2+ ions, three
L2ꢁ anions and three phen ligands, as well as six and a half lattice
water molecules. Similarly to the Cd2+ ions in 4 and 5, all the three
unique Cd2+ ions here are octahedrally coordinated by two phosph-
inate O atoms and one bidentate chelating carboxylate group of
three L2ꢁ ligands as well as a bidentate chelating phen ligand
(Fig. S10).
tween neighboring phen and L2ꢁ ligands (Figs. 13 and S11). The lat-
tice water molecules are located at the voids of the structure.
3.8. Comparisons of the structures of 2, 4 and 5
Since the three different double-chain arrays of 2, 4 and 5 are
assembled through L2ꢁ ligands with a very similar or even identical
coordination mode (i.e., each bridging three metal centers via its
two phosphinate
O atoms and one carboxylate group, see
Scheme 1a and d), it is meaningful to compare their structures.
As shown in Chart 2, the metal ion and the L2ꢁ ligand in these three
compounds each can be reduced to a 3-connected node, and the
linkages between them can be classified as two categories: {P–O–
M} and {P–C–CO(O)–M} linkages in a 2:1 ratio. The {P–O–M} link-
ages in 2 constitute a continuous zigzag chain (Chart 2a), while
those in 4 are divided into two parallel sub-chains (Chart 2b),
and those in 5 are enclosed as discrete four-membered rings
(Chart 2c). Furthermore, the combinations of the above three types
of {P–O–M} linkages with their corresponding discontinuous {P–C–
CO(O)–M} linkages result in the formation of the three topologi-
cally similar double-chain arrays of 2, 4 and 5.
The three unique L2ꢁ ligands in 6 all bridge three Cd2+ centers,
but adopt two types of coordination modes. The L2ꢁ ligand contain-
ing the P1 or P3 atom bridges three Cd2+ ions via two phosphinate
O atoms and one bidentate chelating carboxylate moiety, which is
similar to the L2ꢁ ligands in 4 and 5. The L2ꢁ ligands containing the
P2 atom bridges three Cd2+ ions via one phosphinate
l2-O atom
and one bidentate chelating carboxylate moiety (Scheme 1c). Thus,
the interconnection of the Cd2+ centers by these L2ꢁ ligands results
in the formation of a novel double-chain structure, which features
three types of edge-sharing dimeric ring motifs (Rings B, C and G,
see Chart 1) arranged in a complicated [(G–B–G–C–G–C)–(G–B–G–
C–G–C)ꢀ ꢀ ꢀꢀ ꢀ ꢀ] fashion (Fig. 12). The formation of such a new dou-
ble-chain array in 6 compared with its two isomers (4 and 5) is
mainly caused by the presence of an additional tetradentate L2ꢁ li-
gand in 6.
3.9. Influences of the L2ꢁ and phen ligands on the structures of 1–6
The L2ꢁ anion, as a conformationally flexible bridging ligand,
can exhibit various coordination modes via its four potential O do-
nor sites, even with the same dentate number, thus leading to
Similar to the double-chains in 5, the double-chains in 6 are also
assembled through
pꢀ ꢀ ꢀp interactions between the phen molecules
Fig. 11. The
pꢀ ꢀ ꢀp
packing interactions amongst the phen and L2ꢁ ligands (drawn as dashed lines) observed in 5. For display details, see the caption for Fig. 9.

C.-C. Zhao et al. / Polyhedron 51 (2013) 18–26
25
Fig. 12. View of the chain structure of 6. The terminal phen ligands and phenyl groups of the L2ꢁ ligands have been omitted for clarity. For display details, see the caption for
Fig. 9.
Fig. 13. The
pꢀ ꢀ ꢀp
packing interactions amongst the phen and L2ꢁ ligands (drawn as dashed lines) observed in 6. For display details, see the caption for Fig. 9.
Chart 2. Comparisons of the three different double-chain arrays of 2 (a), 4 (b) and 5 (c). Mn, Cd and P atoms are represented by yellow, cyan and purple circles, respectively.
The {P–O–M} and {P–C–CO(O)–M} linkages (M = Mn or Cd) are reduced to purple and green lines, respectively. (Color online.)
diversified structures. The isomeric complexes 1 and 2 are derived
from the different coordination modes of the tridentate L2ꢁ ligands
in them (Scheme 1a and b); and similar isomerism can be observed
in 4/5 and 6, but with different coordination modes of their tetra-
dentate L2ꢁ ligands (Scheme 1c and d). It deserves to be specially
noted that even if the L2ꢁ ligands adopt a same coordination mode,
varied structures can also be achieved, as exemplified by the above
discussed isomers 4 and 5. It is also worthy of note that these com-
pounds are apt to form various dimeric rings between two metal
centers and two L2ꢁ ligands, amongst which rings A, C, D, F and G
(see Chart 1) have been observed in previously reported three cad-
mium(II) compounds [6c], and the G-type ring was the most fre-
quently occurring form.
facilitates the formation of conformation-flexible low-dimensional
structures (such as 0D clusters or one-dimensional chain struc-
tures). Furthermore, the
p-rich aromaticity of the phen molecule
may readily induce diverse
p
ꢀ ꢀ ꢀ
p
and/or C–Hꢀ ꢀ ꢀ
p
interactions dur-
ing the self-assembly of these low-dimensional structures, as indi-
cated by the above mentioned structure descriptions of these
compounds.
3.10. Optical properties
The solid-state luminescent spectra of 4, 5 and 6 were investi-
gated at room temperature (Fig. S12). The free H2L ligand shows
only a fluorescent emission band at kmax = 293 nm under 225 nm
excitation. The phen ligand displays a broad fluorescent emission
band at kmax = 381 nm with a shoulder at 364 nm upon excitation
at 339 nm. Upon complexion of the L2ꢁ and phen ligands with
The introduction of 1,10-phenanthroline (phen), as a terminal
bidentate-chelating coligand in 1–6, can reduce the coordination
sites available for the carboxylate–phosphinate ligand, and thereby

26
C.-C. Zhao et al. / Polyhedron 51 (2013) 18–26
Cd2+ ions, 4 displays a fluorescent emission band at kmax = 370 nm
with a shoulder at 387 nm (kex = 322 nm), and 5 exhibits a very
similar fluorescent emission band to that of 4 but with somewhat
weaker intensity, while 6 shows a fluorescent emission band at
kmax = 375 nm (kex = 325 nm). These emission bands are neither
metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge
transfer (LMCT) in nature, but rather can be attributed to an intral-
igand emission state.
coordinated water molecules, which can be attributed to the tri-
dentate ? tetradentate coordination mode of the L2ꢁ ligand.
Acknowledgments
This work was supported by the NNSF of China (No. 21061001),
the NSF of Jiangxi Province (No. 20114BAB203004) and the Jiangxi
Province Young Scientists Training Program.
In view of the fact that 2 crystallizes in a non-centrosymmetric
space group (Cc), we investigated the second harmonic generation
(SHG) property of a polycrystalline sample of 2. The results indi-
cated that 2 exhibits a SHG response of about 0.1 times that of
KDP (KH2PO4).
Appendix A. Supplementary data
CCDC 859988–859992 and 870046 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.htmlg, or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033;
or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.poly.2012.11.051.
3.11. Thermogravimetric analysis
TGA curves for 1–6 are shown in Fig. S13, and all six compounds
continue to lose weight at 900 °C. For 1, the first weight loss corre-
sponding to the release of two lattice water molecules is observed
from 25 to 76 °C (obsd 7.1%, calcd 7.2%); the second weight loss
corresponding to the release of one coordinated water molecule
is observed from 130 to 160 °C (obsd 3.6%, calcd 3.6%); and further
decomposition of the residual composition occurs at 272 °C. Com-
pound 2 shows an initial 4.1% weight loss from 168 to 201 °C, cor-
responding to the loss of one coordinated water molecule (calcd
3.9%); and further decomposition of the residual composition oc-
curs at 210 °C. For 3, the first weight loss of 10.3% from 25 to
108 °C is attributed to the release of three lattice water molecules
(calcd 10.2%), the second weight loss of 3.7% from 138 to 197 °C is
ascribed to the release of one coordinated water molecule; and fur-
ther decomposition of the residual composition starts at 224 °C.
Compound 4 contains no water components and is stable up to
326 °C, whereupon a rapid decomposition of the organic ligand oc-
curs. Compound 5 shows an initial 10.9% weight loss from 25 to
88 °C, corresponding to the release of the lattice water molecules
(calcd 9.7%); and further decomposition of the residual composi-
tion occurs at 280 °C. Compound 6 undergoes dehydration in the
range 39–162 °C (obsd 8.8%, calcd 7.2%), and further decomposi-
tion of the residual composition happens at 327 °C.
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4. Conclusions
In summary, the reactions of octahedrally coordinated transi-
tion metal ions (Mn2+
,
Cu2+ or Cd2+
)
with (2-carboxy-
ethyl)(phenyl)phosphinate and 1,10-phenanthroline ligands
afforded six compounds, of which 1 and 3 show discrete dimer
structures, while 2, 4, 5 and 6 feature different double-chain arrays.
Two species of compounds that have the same host compositions,
i.e., [Mn(L)(phen)(H2O)] in 1 and 2, and [Cd(L)(phen)] in 4, 5 and 6,
can be identified and regarded as isomers. Particularly, the isola-
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the same coordination mode, varied structures can be achieved.
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metal species in them are different (Cu versus Mn). In addition, it
is worthy of note that the host compositions in 4, 5 and 6 have
the same metal-L2ꢁ-phen ratio as those in 1–3, but contain no
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