Mono and dinuclear group 12 phosphonates derived from a sterically encumbered phosphonic acid: Observation of esterification

Article abstract of DOI:10.1016/j.ica.2013.05.011

Metal phosphonates [Zn₂(dtbhp)₂(TMEDA) ₂(H₂O)₂]·0.5CH₃CN (1), Cd₂(dtbhp)₂(TMEDA)₂(H₂O) ₂]·0.5CH₃CN (2), [Cd2(mdtbhp)2(1,10-

Full text of DOI:10.1016/j.ica.2013.05.011

Inorganica Chimica Acta 405 (2013) 147–154
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Inorganica Chimica Acta
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Mono and dinuclear group 12 phosphonates derived from a sterically
encumbered phosphonic acid: Observation of esterification
⇑
Rana Howlader, Mrinalini G. Walawalkar, Ramaswamy Murugavel
Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai 400076, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2012
Received in revised form 6 May 2013
Accepted 15 May 2013
Available online 24 May 2013
Metal phosphonates [Zn2(dtbhp)2(TMEDA)2(H2O)2]ꢀ0.5CH3CN (1), Cd2(dtbhp)2(TMEDA)2(H2O)2]ꢀ0.5CH3-
CN (2), [Cd2(mdtbhp)2(1,10-phenanthroline)4]ꢀ(ClO4)2(CH3OH)2 (3), and [Cd(dtbhp-H)2(2,20-bpy)2](-
dtbhp-H2) (4) have been synthesized at room temperature from a reaction between a suitable metal
precursor, 3,5-di-tert-butyl-2-hydroxybenzylphosphonic acid (dtbhp-H2) and an ancillary ligand, tetram-
ethylenethylene diamine (TMEDA), 1,10-phenanthroline and 2,20-bipyridine; Single crystal X-ray struc-
ture determination reveals that compound 1 crystallizes in the orthorhombic Fdd2 space group, while
Keywords:
ꢀ
compounds 3 and 4 crystallize in the triclinic P1 space group. A rare P–O–H bond esterification is
Organic–inorganic hybrids
Metal phosphonates
Lamellar
Sterically hindered
Liphophilic phosphonic acids
observed in compound 3, presumably catalyzed by perchloric acid formed in the reaction. Compounds
1–3 are discrete dinuclear complexes while monomeric complex 4 forms a 1D polymeric chain through
extended intermolecular hydrogen bonding, aided by free P–OH and P@O groups of the coordinated as
well as the lattice phosphonic acid.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
characterized by single-crystal diffraction techniques or by ab ini-
tio structure solution from X-ray powder diffraction data. These in-
Organic–inorganic hybrid materials constitute an important
class of compounds within the area of materials chemistry. Mixed
organic–inorganic materials, where the organic and inorganic com-
ponents complement each other in structure and function, lead to
solid-state materials with composite or even new properties [1–4].
Metal phosphonates are amongst the most suited candidates for
the design of organic–inorganic hybrid materials [5–8]. In recent
years, increased attention has been paid to the exploration of novel
metal phosphonate compounds because such materials potentially
have applications as sorbents and catalysts as seen in traditional
zeotype materials, with the added benefit that the nature of the
internal surface of phosphonate materials may be altered by
changing the organic functional group of the starting phosphonic
acid [5]. It has often been observed that the phosphonate materials
containing divalent transition metal cations form lamellar struc-
tures, where the metal ions are bridged by the phosphonate
groups, and the remaining organic part of the acid is hanging in
the interlayer region [5,9–11].The divalent transition metal phos-
phonates are of particular interest because they are soluble in acid
solution and, therefore, are more easily crystallized compared to
those containing tetravalent metal ions [12]. Among the transition
metal phosphonates a number of zinc phosphonate compounds
have been prepared, most of which have been structurally
clude monophosphonates [13,14], diphosphonates [14–16], and
functionalized phosphonates [16–20]. Structures of these com-
pounds range from one-dimensional chain, two dimensional layer
to three-dimensional pillared layers or open framework solids.
Very recently Zheng and co-workers has reported a number of
functionalized phosphonates [Zn2(4-cppH)2(L1)], [Zn3(4-cpp)2
(L2)2]ꢀ2.5H2O, and [Zn3(4-cpp)2(L3)]ꢀsH2O where L1 = 1,4-bis(imi-
dazol-1-ylmethyl)benzene, L2 = 1,3-bis(imidazol-1-ylmethyl)-
benzene, L3 = 1,2-bis(imidazol-1-ylmethyl)benzene and 4-cppH3 =
4-carboxyphenylphosphonic acid [21]. In contrast to zinc phospho-
nate compounds, those involving cadmium phosphonates are
relatively few, albeit exhibiting similar structural features to those
of zinc phosphonates. The recently structurally characterized cad-
mium phosphonates includes [Cd(3-pyridylphosphonate)2]DMSO,
Cd(4-pyridylphosphonate)2, Cd(ethyl-4-pyridylphosphonate)2 [22],
Na2[Cd2(H2O)3(O3PCH(OH)CO2)2]ꢀ2H2O [23], [Cd(
l-Cl)2(2pypo)]n
[24], and [Cd3(H2O)3((O3PCH2)2NH–CH2C6H4–COOH)2]ꢀ11H2O [25].
Recently our group has reported on the alkali metal derivative of
a bis-functionalized phosphinic acid forming a 3D network struc-
ture [26].
The use of sterically hindered and liphophilic phosphonic acids
possessing additional functional groups has led to the isolation of
soluble functional metal phosphonates. Another strategy that has
also been successful in synthesizing discrete phosphonate clusters
is the use of an ancillary N-donor ligands in conjunction with a
phosphonic acid. Our group has recently focused on a variety of
⇑
Corresponding author. Tel.: +91 22 2576 7163.
E-mail address: rmv@chem.iitb.ac.in (R. Murugavel).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.05.011

148
R. Howlader et al. / Inorganica Chimica Acta 405 (2013) 147–154
coordination modes leading to the formation of a number of metal
cluster compounds especially in the presence of a secondary N-do-
nor and/or O-donor auxiliary ligands such as TMEDA, 2,20-bipy and
1,10-phenanthroline. Building up on our studies on phosphonic
acids and phosphate esters as ligands [27–43], we have explored
the coordination chemistry of a benzyl phosphonic acid with phe-
nol side group towards zinc and cadmium ions in the presence of
N-donor ligands with that objective to generate metalphospho-
nates that possess phenolic –OH functionalities. The results of this
investigation, reporting the isolation of mono and dinuclear metal
phosphonates, are described herein.
by elemental analysis, FT-IR and 31P NMR spectroscopy. The ob-
tained elemental percentages are supportive of the fact that com-
pound 2 is similar in composition to 1. In the IR spectrum, the
presence of broad
ence of water molecule and unreacted phenolic –OH group on the
ligand. The characteristic absorptions for masy(C–H) (P–O–O) and mM–
m
O–H absorption at 3424 cmꢁ1 indicates the pres-
,
m
-
vibration are observed at 2953, 1131 and 1034 cmꢁ1, respec-
O–P
tively. The 31P NMR spectrum of compound 2 shows two peaks
(as in 1) indicating the presence two phosphorus centres (d 28.8
and d 25.9 ppm) in the molecule in solution.
2.3. Synthesis and characterization of [Cd2(mdtbhp)2(1,10-
phenanthroline)4]ꢀ(ClO4)2(CH3OH)2 (3)
2. Results and discussion
Compound 3 has been obtained as X-ray quality single crystals
by the slow evaporation of methanol from a 1:2:2 reaction mixture
of Cd(ClO4)2ꢀH2O, dtbhp-H2 and 1,10-phenethroline (Scheme 3).
Complex 3, soluble in solvents like methanol, chloroform, acetoni-
trile, etc. has been characterized by elemental analysis, FT-IR and
multinuclear (1H and 31P) NMR spectroscopy. The obtained ele-
mental percentages are supportive to the chemical composition
of 3. In the IR spectrum, the presence of broad mO–H absorption at
3430 cmꢁ1 indicates the presence unreacted phenolic O–H group.
2.1. Synthesis of 3,5-di-tert-butyl-2-hydroxybenzylphosphonic acid (L)
The phosphonic acid ligand [44]used in this work has been pre-
pared in three steps using the Michaelis–Arbuzove’s reaction start-
ing from 2,4-di-tertbutyl phenol as shown in Scheme 1.
2.2. Synthesis and characterization of
[M2(dtbhp)2(TMEDA)2(H2O)2]ꢀ0.5CH3CN (M = Zn(1); Cd (2))
The characteristic peaks for masy(C–H)
, masy(P–O–O), mM–O–P, m
asy(Cl–O),
Compound 1 has been prepared from the reaction of Zn(CH3-
COO)2ꢀ2H2O with dtbhp-H2 in presence of N-donor ancillary ligand,
TMEDA in 1:1:1 stoichiometric ratio using CH3CN–H2O mixture
(1:1) as solvent at room temperature (Scheme 2). Analytical and
spectroscopic purity of the compound has been established by ele-
mental analysis, FT-IR and NMR (1H and 31P) spectroscopic studies
(Table 1). The obtained elemental percentages are supportive to
the formulation of 1 (Table 1). In the IR spectrum, the presence
of broad mO–H absorption at 3424 cmꢁ1 indicates the presence of
water molecule, either in the coordination sphere of the metal or
m
are observed at 2957, 1143, 1103, 1091, and
asy bending(Cl–O),
624 cmꢁ1, respectively. In the 1H NMR spectrum, the methyl pro-
tons of the two C(CH3)3 groups in the aromatic ring appear as
two well resolved singlets of equal intensity at d 0.92 and
1.14 ppm while the methylene protons are observed as a doublet
at d 3.16 ppm. The –OMe protons on phosphorus resonate at d
3.49 ppm. Aromatic protons along with py-H proton are found to
be resonating in the range d6.75–9.50 ppm. The 31P NMR of com-
pound 3 shows a single peak indicating the presence of one type
phosphorus in the compound which resonates at d 25.50 ppm.
in the lattice. The characteristic absorptions for masy(C–H), m(P–O–O)
and mM–O–P vibrations are observed at 2953, 1118 and 1065 cmꢁ1
respectively. In the 1H NMR spectrum, the methyl protons of the
two C(CH3)3 groups on the aromatic ring and the N(Me)2 group ap-
pear as three well resolved singlets in the range of d 1.23–1.35 ppm
while the methylene protons of –N(CH2)2N– are observed as mul-
tiplets in the ranged2.00–2.40 ppm. A doublet is observed at
3.01 ppm for the Ar–CH2 protons (2JP–H = 18 Hz). Aromatic protons
resonate in the range d 6.95–7.01 ppm. For the phenolic O–H pro-
tons, two singlets are observed at d 8.50 and 8.60 ppm. The 31P
NMR spectrum of compound 1 shows two peaks indicating the
presence of two kinds of phosphorus in the compound which res-
onate at d 28.6 and 26.6 ppm, probably indicating a different solu-
tion structure from that of the solid state (vide infra).
The TG-DTA trace of compound 1 shows the first weight loss of
17% in the temperature range from 25 to 125 °C corresponding to
the loss of acetonitrile and water molecules. The second major
weight loss occurs in the range 150–530 °C corresponding to the
loss of two TMEDA and the organic part of the ligand.
Compound 2 has been prepared from the reaction of Cd(ClO4)2-
ꢀH2O with dtbhp-H2 in presence of N-donor ancillary ligand, TMEDA
in 1:1:1 stoichiometric ratio using CH3CN–H2O mixture (1:1) as sol-
vent at room temperature (Scheme 2) and has been characterized
2.4. Synthesis and characterization of [Cd(dtbhp-H)2(2,20-
bpy)2](dtbhp-H2) (4)
As shown in Scheme 4, compound 4 has been obtained in a good
yield at room temperature by slow evaporation of methanol from a
1:2:2 reaction mixture of Cd(ClO4)2ꢀH2O, dtbhp-H2 and 2,20-bipyr-
idine respectively and characterized by elemental analysis, FT-IR
and multinuclear (1H and 31P) NMR spectroscopy. The methyl pro-
tons of the two C(CH3)3 group on the aromatic ring appear as single
peaks at d 1.3 ppm and d 1.34 ppm. The characteristic peaks in FT-
IR spectrum, for masy(C–H), masy(P–O–O) and mM–O–P are observed at
2956, 1128 and 1059 cmꢁ1, respectively. The broad peak observed
at 2318 cmꢁ1 is due to the presence of unreacted P–O–H bond of
the lattice dtbhp-H2 moiety. In the 1H NMR spectrum, the methy-
lene protons appear as two doublets at d 3.00 and 3.45 ppm. Aro-
matic protons along with 2,2’-bpy protons are found to be
resonating in the range between d 6.95–8.61 ppm. The 31P NMR
spectrum of compound 4 shows two peaks indicating the presence
of two type phosphorus in the compound which resonates at d 27.4
and 28.3 ppm, corresponding to the dtbhp-H unit and free dtbhp-
H2.
OH
OH
OH
OH
HO
HO
EtO
EtO
HO
P
P
c
a
b
O
O
70.2%
90 %
65 %
L
Scheme 1. Synthesis of ligand L. (a) LiOH, HCHO, MeOH, 65 °C; (b) P(OEt)3, Xylene, 110 °C; (c)HCl/H2O, 100 °C.

R. Howlader et al. / Inorganica Chimica Acta 405 (2013) 147–154
149
N
N
H2O
M
HO
OH
O
O
H2O3P
O
Cd(ClO4)2.H2O/Zn(OAc)2.2H2O
CH3CN, TMEDA
(0.5 CH3CN)
P
P
O
O
O
M
N
HO
H2O
N
M = Zn (1); Cd (2)
Scheme 2. Synthesis of 1 and 2.
2.5. Molecular structure of 1
comparable to the corresponding distances observed in several
cadmium phosphates and phosphonates in the literature [46,47].
Since the phosphonate ligand coordinates through two of the oxy-
gen atoms of P–O and P@O, a charge delocalization is observed
within this moiety and thus no formal P–O and P@O bonds are
found. The observed P–O distances for P(1)–O(1) 1.515 and P(1)–
O(4) 1.495 are considerably shorter than a formal P–O bond
(1.59–1.60 Å) but significantly longer then formal P@O bond
(1.45–1.46 Å). The Cd–O (2.233–2.853 Å) and Cd–N (2.324–
2.390 Å) bond distances are comparable to those reported in other
cadmium(II) phosphonates [48–50].
A list of intramolecular hydrogen bonding interactions present
in 3 is depicted in Table 2. There are two other methanol molecules
which are present in the lattice are involved in intermolecular
hydrogen bonding through C(26)–H(26)ꢀ ꢀ ꢀO(5): 3.283 Å, 161.64°
(Fig. 4).
Colourless cubic crystals suitable for X-ray measurements were
obtained from a acetonitrile and water mixture at ꢁ5 °C after
3 days. Single crystal X-ray measurements show that compound
1 crystallizes in the orthorhombic space group Fdd2. A perspective
view of the molecular structure of compound 1 is shown in Fig. 1a.
ꢁ2
The two zinc atoms and two ArP(O)O2 ligands form an Zn2O4P2
eight membered ring that is similar to most commonly found
S4R SBU of zeolities and other dinuclear zinc phosphonates [45].
The two zinc atoms in the dinuclear complex exhibit a distorted
trigonal pyramidal geometry as revealed by the observed bond an-
gles around the central metal atom Zn(1) and Zn(2). In this struc-
ture each zinc atom is coordinated with one TMEDA, two
phosphonate oxygen atoms and a water molecule as clearly shown
in the core structure (Fig. 1b). The distance between the two zinc
centres is Znꢀ ꢀ ꢀZn 4.097 Å. The molecular structure of 1 is further
stabilized in the solid state through two intramolecular hydrogen
bonding interactions O(4)–H(4W)ꢀ ꢀ ꢀO(1): 2.636 Å, 170.06° and
O(8)–H(8W)ꢀ ꢀ ꢀO(5): 2.681 Å, 175.73° (Table 2) involving phos-
phoryl P@O groups and phenolic –OH groups (donor) as shown
in Fig. 1. Key structural parameters of 1 along with those of other
crystal structure reported in this article are summarized in Table 3.
Interestingly one of the P–O–H bonds in the compound 3 under-
goes an esterification process [51] by the solvent methanol, which
may be due to the presence HClO4 produced during the course of
reaction. It is likely that HClO4 which protonates the phosphonic
acid and the subsequent attack of an alkoxide –OCH3 on the phos-
phorus atom results in the esterification of the acid.
2.8. Molecular structure of 4
2.6. Molecular structure of 2
ꢀ
Compound 4 crystallizes in triclinic P1 space group. A perspec-
Compound 2 could be crystallized as single crystals from aceto-
nitrile–methanol mixture. The crystals obtained were subjected to
a single crystal X-ray diffraction study. The poor quality diffraction
data obtained however did not allow a satisfactory refinement of
the structure. The refinement for example converged at a high R
value of 18%, although all the atoms of the two halves of crystallo-
graphically independent molecules were located from the different
Fourier maps. The structure of the molecule obtained at the end of
the refinement is shown in Fig. 2, indicating that the structure of 2
is similar to that of the zinc derivative 1. The high R value does not
allow a more detailed discussion of the metric parameters.
tive view of the final refined molecular structure is shown in Fig. 5.
The central cadmium ion adopts a distorted octahedral geometry.
The monomeric cadmium complex is composed of a cadmium
ion and two dtbhp-H moieties and two 2,20-bpy units. Interestingly
a free dtbhp-H2 ligand occupies in the lattice with no formal coor-
dination to the metal. The cadmium ion is bound to two chelating
2,20-bpy molecules in cis position while the two phosphonate oxy-
gen atoms of two different dtbhp-H2 units which are cis to each
other. The average Cd–O (phos) and Cd–N distances (2.420 and
2.330 Å, respectively) are comparable with the corresponding dis-
tances often found in cadmiun phosphates and phosphonates re-
ported already in the literature [22,23]. The observed P–O
distances for P(1)–O(3) 1.552(3), P(1)–O(4) 1.493(2), and P(2)–
O(8) 1.506(3) P(2)–O(6) 1.555(2), are shorter than a formal P–O
bond (1.59–1.60 Å) while the observed P@O distances for P(1)–
O(2) 1.494(3) and P(2)–O(7) 1.522(3), are little bit longer then a
formal P@O bond (1.45–1.46 Å).
2.7. Molecular structure of 3
ꢀ
Compound 3 crystallizes in triclinic P1 space group. A perspec-
tive view of the final refined molecular structure is shown in
Fig. 3a. The dimeric cadmium complex is composed of two cad-
mium atoms and two PO3 moieties with four bridging
l
-oxygen
A list of strong possible intra and intermolecular hydrogen
bonding interactions for compound 4 is listed in Table 2. As it
can be deduced from this table, almost without exception the
O–H–O bridges always involve one phosphonate and one water
oxygen atom. The O–H–O angles are very large (close to 180°)
and the distances are short indicating strong interactions. The
compound exhibits a 1D polymeric structure with the tertiary
atoms forming a central eight membered Cd2O4P2 ring. The central
cadmium ion adopts a distorted octahedral geometry (Fig. 3b).
Each octahedral cadmium atom is bound to two chelating 1,10-
phenanthroline molecule in cis position while the two phospho-
nate oxygen atoms are also cis to each other. The average Cd–O
(phos) and Cd–N distances (2.231 and 2.370 Å, respectively) are

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R. Howlader et al. / Inorganica Chimica Acta 405 (2013) 147–154
Table 1
Characterization data for complexes 1–4.
Formula
Yield
(%)
Elemental analysis found (calculated), % 31P NMR
(ppm)
UV–Vis (nm) Fluorescence
(nm)
C
H
N
[Zn2(dtbhp)2(TMEDA)2(H2O)2]ꢀ0.5CH3CN (1)
[Cd2(dtbhp)2(TMEDA)2(H2O)2]ꢀ0.5CH3CN (2)
35
35
87
85
50.35
(50.81)
46.22
(46.51)
53.18
(53.66)
58.45
8.14
(8.28)
7.35
(7.58)
5.21
(5.05)
6.45
6.17
(6.20)
5.82
(5.68)
6.10
(6.11)
4.09
26.62, 28.66
25.90, 28.80
25.50
a
a
a
a
[[Cd2(mdtbhp)2(1,10-phenanthroline)4]ꢀ(ClO4)2(CH3OH)2
205, 222,
279
205, 230,
282
365
324
(3)
[Cd(dtbhp-H)2(2,20-bpy)2](dtbhp-H2) (4)
27.40, 28.20
(58.98)
(6.78)
(4.23)
a
Poor solubility.
N
N
N
N
O
HO
Cd
OH
O
Cd(ClO4)2.H2O
O
H2O3P
P
P
1,10- phenanthroline
(ClO4)2(CH3OH)2
O
O
O
N
HO
Cd
N
N
N
3
Scheme 3. Synthesis of 3.
N
N
N
OH
P
HO
O
HO
HO
Cd
HO
N
OH
H2O3P
O
Cd(ClO4)2.H2O
2,2'-bypyridine
P
O
O
O
.
P
OH
OH
4
Scheme 4. Synthesis of 4.
butyl substituted aromatic ring pointing out on both side of the
inorganic back-bone with extensive inter and intramolecular
hydrogen bonding interactions when viewed along a axis (b axis
down) and viewed along a axis (c axis down)(Fig. 6).
the standard are assigned positive values. Infrared spectra were
obtained from a Perkin Elmer FT-IR spectrometer model Spectrum
One as KBr dilute discs. Microanalyses were performed on a Ther-
mo Finnigan (FLASH EA 1112) elemental analyser. TG analyses
were obtained on a Perkin Elmer thermal analysis system, under
a stream of nitrogen gas at the heating rate of 10 °C/min.
3. Experimental
3.1. General
3.2. Synthesis of [Zn2(dtbhp)2(H2O)2(TMEDA)2]ꢀ0.5CH3CN (1)
Commercially available starting materials such as Zn(CH3-
COOH)2ꢀ2H2O (E.Merck), TMEDA (S.d.fine), 1,10-phenanthroline
(Aldrich), 2,20-bpy (Aldrich), Cd(ClO4)2ꢀH2O (Aldrich), Zn(ClO4)ꢀ6H2-
O (Aldrich) and 2,4-di-tert-butylphenol (Aldrich) were used as re-
ceived. Solvents were purified and dried by conventional
procedures and freshly distilled before use. The 1H (Me4Si internal
standard) and 31P NMR (85% H3PO4) spectra were recorded on a
Varian VXR 400S spectrometer. The chemical shifts downfield from
To a 15 mL acetonitrile–water (1:1) solution of dtbhp-H2
(0.075 g, 0.25 mmol), Zn(CH3COO)2ꢀ2H2O (0.0545 g, 0.25 mmol)
and TMEDA (tetramethylenthylenediamine) (0.029 g, 0.25 mmol)
were added and stirred for 1 h. The resulting solution was filtered
and the clear solution was left for crystallization at ꢁ5 °C. After
3 days white single crystals of complex
1 were obtained.
Mp > 250 °C, Yield 0.087 g (35% based on dtbhp-H2), IR data (as
KBr discs): 3418(br), 2952(s), 1640(br), 1464(s), 1425(m),

R. Howlader et al. / Inorganica Chimica Acta 405 (2013) 147–154
151
1304(w), 1359(w), 1239(m), 1166(w), 1118(s), 1104(vs),
1065(vs),1029(m), 987(s), 951(w), 800(w), 751(w). Anal. Calc. for
C
43H83.5N4.5O10P2Zn2 (mol. wt: 1016): C, 50.81; H, 8.28; N, 6.20.
Found: C, 50.35; H, 8.14; N, 6.17%. 1H NMR (CDCl3, 400 MHz): d
1.23 (s, 18H, o-Ar–But), 1.25 (s, 18H, p-Ar–But), 1.30 (s, 12H,
N(Me)2), 1.35 (s, 12H, N(Me)2), d 2.00–2.40 (m, 8H, N(CH2)2), d
1
3.01–3.11 (d, 4H, Ar–CH2, JP–H = 18 Hz), d 6.95–7.01 (m, 4H, Ar–
H), d 8.50 (s, 1H, Ar–OH), d8.60 (s, 1H, Ar–OH) ppm. 31P NMR
(CDCl3, 160 MHz): d 26.62. 28.66 ppm.
3.3. Synthesis of [Cd2(dtbhp)2(H2O)2(TMEDA)2]ꢀ0.5CH3CN (2)
To
a 15 mL acetonitrile–water (1:1) solution of dtbhp-H2
(0.060 g, 0.2 mmol), Cd(ClO4)2ꢀH2O(0.0311 g, 0.1 mmol) and TME-
DA (tetramethylenthylenediamine) (0.030 g, 0.25 mmol) was
added and stirred for 1 h. The resulting solution was filtered and
left for crystallization at room temperature. After 24 h white single
crystals of complex 2 were isolated from the solution. Mp > 250 °C,
Yield 0.079 g (35% based on dtbhp-H2), IR data (as KBr dics):
3411(br), 2953(s), 2895(s), 1638(br), 1468(s), 1432(m), 1304(w),
1359(w), 1293(m), 1239(m), 1131(s), 1034(s), 967(s). Anal. Calc.
for C43H83.5N4.5O10P2Cd2 (mol. wt: 1110): C, 46.51; H, 7.58; N,
5.68. Found: C, 46.22; H, 7.35; N, 5.82%. 31P NMR (CDCl3,
160 MHz): d 25.90, d28.80 ppm.
Fig. 1. (a) The molecular and (b) core structure of 1.Selected bond lengths (Å):
Zn(1)–O(3), 1.919(2); Zn(1)–O(6), 1.923(2); Zn(1)–N(1), 2.102(3); Zn(1)–N(2),
2.192(3); Zn(1)–O(10), 2.342(3); Zn(2)–O(7), 1.906(2); Zn(2)–O(2), 1.913(2);
Zn(2)–N(3), 2.062(3); Zn(2)–N(4), 2.191(3); P(1)–O(3), 1.514(2); P(1)–O(1),
1.524(3); P(1)–O(2), 1.527(2); P(1)–C(15), 1.812(3); P(2)–O(7), 1.517(2); P(2)–
O(5), 1.528(2); P(2)–O(6), 1.529(2); P(2)–C(36), 1.798(3). Selected bond angles
(°):O(3)–Zn(1)–O(6), 129.80(10); O(3)–Zn(1)–N(1), 110.30(11); O(6)–Zn(1)–N(1),
119.20(11); O(3)–Zn(1)–N(2), 95.56(11); O(6)–Zn(1)–N(2), 96.55(11); N(1)–Zn(1)–
N(2), 84.82(16); O(3)–Zn(1)–O(10), 92.59(10); O(6)–Zn(1)–O(10), 83.59(10); N(1)–
Zn(1)–O(10), 85.67(14); N(2)–Zn(1)–O(10), 169.17(11); O(7)–Zn(2)–O(2),
124.90(10); O(7)–Zn(2)–N(3), 116.75(10); O(2)–Zn(2)–N(3), 116.27(11); O(7)–
Zn(2)–N(4), 100.06(12); O(2)–Zn(2)–N(4), 98.42(13); N(3)–Zn(2)–N(4), 84.86(13);
O(3)–P(1)–O(1), 112.50(15); O(3)–P(1)–O(2), 111.93(14); O(1)–P(1)–O(2),
112.66(15); O(3)–P(1)–C(15), 107.30(15); O(1)–P(1)–C(15), 106.85(15); O(2)–
P(1)–C(15), 105.04(14); O(7)–P(2)–O(5), 113.00(14); O(7)–P(2)–O(6), 110.63(13);
O(5)–P(2)–O(6), 112.06(14).
3.4. Synthesis of [Cd2(mdtbhp)2(1,10-phenanthroline)4]ꢀ(ClO4)2
(CH3OH)2 (3)
To a 15 mL methanol solution of dtbhp-H2 (0.060 g, 0.2 mmol)
and Cd(ClO4)2ꢀH2O (0.0311 g, 0.1 mmol), 1,10-phenethroline
(0.036 g, 0.2 mmol) was added and stirred for 1 h. The resulting
solution was filtered and left for crystallization at room tempera-
ture. After 24 h white single crystals of complex 3 were observed.
Compound 3 was found to be soluble solvents like methanol, chlo-
roform, acetonitrile, etc. Mp 244–246 °C, Yield 0.29 g (87% based
on dtbhp-H2), IR data (KBr, cmꢁ1): 3430(br), 2957(w), 2866(w),
1623(w), 1517(w), 1427 (s), 1143(m), 1103(vs), 1091(vs),
Table 2
Intra- and intermolecular hydrogen bonds in 1, 3 and 4.
Compound
H-bonds
D–H (Å)
Dꢀ ꢀ ꢀA (Å)
Hꢀ ꢀ ꢀA (Å)
<D–Hꢀ ꢀ ꢀA (°)
1
O(4)–H(4W)ꢀ ꢀ ꢀO(1)a
O(8)–H(8W)ꢀ ꢀ ꢀO(5)a
O(3)–H(3W)ꢀ ꢀ ꢀO(1)a
C(26)–H(26)ꢀ ꢀ ꢀO(5)b
O(5)–H(5W)ꢀ ꢀ ꢀO(8)a
O(6)–H(6W)ꢀ ꢀ ꢀO(2)a
O(9)–H(9W)ꢀ ꢀ ꢀO(10)a
O(1A)–H(1A)ꢀ ꢀ ꢀO(4)
O(1B)–H1Bꢀ ꢀ ꢀO(2)
1.007(2)
0.939(2)
0.715(2)
0.930(3)
1.047(2)
0.902(3)
1.043(3)
0.820(5)
0.820(6)
1.212(3)
1.036(2)
0.959(2)
2.636(3)
2.681(3)
2.732(3)
3.283(5)
2.675(4)
2.588(4)
2.670(4)
2.906(5)
3.081(7)
2.425(4)
2.646(3)
2.550(3)
1.639(2)
1.744(2)
2.021(2)
2.387(4)
1.738(3)
1.767(3)
1.649(2)
2.132(3)
2.269(3)
1.212(3)
1.612(2)
1.605(2)
170.06(16)
175.73(16)
172.87(16)
161.64(19)
146.65(15)
149.98(19)
165.11(16)
157.38(33)
170.92(41)
180.00(17)
174.67(17)
167.71(18)
3
4
O(11)–H(10W)ꢀ ꢀ ꢀO(11)c
O(12)–H(12W)ꢀ ꢀ ꢀO(2)d
O(3)–H(3W)ꢀ ꢀ ꢀO(10)d
a
b
c
Equivalent positions: x, y, z.
ꢁx + 1, ꢁy + 1, ꢁz + 1.
ꢁx + 1, ꢁy + 1, ꢁz + 2.
ꢁx + 2, ꢁy + 1, ꢁz + 2.
d
Table 3
A comparison of structural features in compounds 1, 3 and 4.
Complex
Nuclearity Metal ion coordination
number
Coordination geometry around Role of
Denticity and Harris
notation [55]
metal ion
phosphonate ion
[Zn2(dtbhp)2(TMEDA)2(H2O)2]ꢀ0.5CH3CN (1) dimer
five
six
trigonal bipyramidal
octahedral
bidentate
bidentate
[2.110]
[2.110]
[Cd2(mdtbhp)2(1,10-
dimer
phenanthroline)4]ꢀ(ClO4)2(CH3OH)2 (3)
[Cd(dtbhp-H)2(2,20-bpy)2](dtbhp-H2) (4)
monomer
six
octahedral
monodentate
[1.100]

152
R. Howlader et al. / Inorganica Chimica Acta 405 (2013) 147–154
Fig. 2. The molecular structure of 2 (hydrogen atoms and acetonitrile molecules are
omitted for clarity of the picture).
Fig. 4. Structure of 3 with possible intermolecular and intramolecular hydrogen
bonding (a part of hydrogen atoms and perchlorate molecule are omitted for clarity
of the picture).
Fig. 5. Molecular structure of 4 (hydrogen atoms are omitted for clarity of the
picture) Selected bond lengths (Å): Cd(1)–O(4), 2.12(2); Cd(1)–O(8), 2.56(2); Cd(1)–
N(2), 2.296(3); Cd(1)–N(3), 2.319(3); Cd(1)–N(1), 2.337(3); Cd(1)–N(4), 2.357(3);
P(1)–O(4), 1.493(2); P(1)–O(2), 1.494(3); P(1)–O(3), 1.552(3); P(1)–C(15), 1.783(4);
P(2)–O(8), 1.506(3); P(2)–O(7), 1.522(3); P(2)–O(6), 1.555(2); P(2)–C(30), 1.792(4);
P(3)–O(10), 1.506(3); P(3)–O(11), 1.509(2); P(3)–O(12), 1.560(3). Selected bond
angles (°):O(4)–Cd(1)–O(8), 97.72(9); O(4)–Cd(1)–N(2), 98.18(10); O(8)–Cd(1)–
N(2), 88.94(10); O(4)–Cd(1)–N(3), 87.15(10); O(8)–Cd(1)–N(3), 99.56(10); N(2)–
Cd(1)–N(3), 169.31(10); O(4)–Cd(1)–N(1), 93.94(10); O(8)–Cd(1)–N(1), 158.69(11);
N(2)–Cd(1)–N(1), 71.73(10); N(3)–Cd(1)–N(1), 98.78(10); O(4)–Cd(1)–N(4),
157.27(11); O(8)–Cd(1)–N(4), 89.49(9); N(2)–Cd(1)–N(4), 103.50(11); N(3)–
Cd(1)–N(4), 70.36(11); N(1)–Cd(1)–N(4), 86.52(10); O(4)–P(1)–O(2), 115.40(16);
O(4)–P(1)–O(3), 109.48(15); O(2)–P(1)–O(3), 109.48(15); O(8)–P(2)–O(7),
112.14(14).
Fig. 3. (a)Molecular structure of 3 (hydrogen atoms, methanol and perchlorate
molecules are omitted for clarity of the picture). (b) The core structure of 3. Selected
bond lengths (Å): Cd(1)–O(4), 2.233(17); Cd(1)–O(1), 2.285(16); Cd(1)–N(4),
2.324(2); Cd(1)–N(2), 2.367(2); Cd(1)–N(1), 2.376(2); Cd(1)–N(3), 2.390(2); P(1)–
O(4)#1,1.495(16); P(1)–O(1), 1.515(17); P(1)–O(2), 1.584(19); P(1)–C(15), 1.803(2);
O(4)–P(1)#1, 1.495(16). Selected bond angles (°): O(4)–Cd(1)–O(1), 90.44(6); O(4)–
Cd(1)–N(4), 110.19(7); O(1)–Cd(1)–N(4), 89.30(7); O(4)–Cd(1)–N(2), 83.00(7);
O(1)–Cd(1)–N(2), 107.97(7); N(4)–Cd(1)–N(2), 158.53(7); O(4)–Cd(1)–N(1),
85.16(6); N(4)–Cd(1)–N(1), 99.43(7); N(2)–Cd(1)–N(1), 70.33(7); O(4)–Cd(1)–
N(3), 96.19(6); O(1)–Cd(1)–N(3), 160.35(7); N(4)–Cd(1)–N(3), 71.04(7); N(2)–
Cd(1)–N(3), 91.23(7); N(1)–Cd(1)–N(3), 97.82(7); O(4)#1–P(1)–O(1), 117.06(9);
O(4)#1–P(1)–O(2), 107.26(10); O(1)–P(1)–O(2), 110.38(10); O(4)#1–P(1)–C(15),
108.66(10); O(1)–P(1)–C(15), 107.36(11); O(2)–P(1)–C(15), 105.52(11); P(1)–O(1)–
Cd(1), 125.80(9). [Symmetry transformations used to generate equivalent atoms:
#1 ꢁ x + 1, ꢁy + 1, ꢁz + 1].
3
3
(dd, 4H, CgH, Cg0H (phen), JH–H = 8.00 Hz, JH–H = 5.1 Hz), d 7.90
3
{s, 4H, CeH, Ce0H(phen)}, d 8.10 (dd, 4H, CfH, C0f H (phen), JH–
-
-
3
3
0
H = 8.2 Hz, JH–H = 3.8 Hz,) d 9.50 (dd, 4H, CxH, Cx H (phen), JH–
3
H = 8.2 Hz, JH–H = 1.8 Hz) ppm. 31P NMR (CDCl3, 160 MHz, ppm):
d 25.50. TGA [temp range, °C (% weight loss)]; 230–280 (17, –
2ClO4 and –2CH3O); 125–530 (57, -2 TMEDA, -2 dtbhp-H).
1041(s), 848(m), 729(s), 624(m). Anal. Calc. for C82H92Cl2N8O18P2-
Cd2 (mol. wt: 1835): C, 53.66; H, 5.05; N, 6.11 Found: C, 53.18;
H, 5.21; N, 6.10%. 1H NMR (CDCl3, 400 MHz): d 0.92 (s, 18H,
3.5. Synthesis [Cd(dtbhp-H)2(2,20-bpy)2]ꢀ(dtbhp-H2)(4)
o-Ar–But), 1.14 (s, 18H, p-Ar–But),
d
3.16 (d, 4H, Ar–CH2,
To a 15 mL methanol solution of dtbhp-H2 (0.060 g, 0.2 mmol)
1JP–H = 18 Hz), d 3.49 (s, 6H, OCH3), d 6.75 (m, 4H, Ar–H), d 6.90
and Cd(ClO4)2ꢀH2O (0.0311 g, 0.1 mmol), 2,20-bpy (0.032 g,

R. Howlader et al. / Inorganica Chimica Acta 405 (2013) 147–154
153
Fig. 6. Structure of 4 with possible intermolecular and intramolecular hydrogen bonding (a part of hydrogen atoms are omitted for clarity of the picture); (a) view along b
axis, a axis down (b) view along a axis, c axis down).
Table 4
Crystallographic cell parameters and experimental details of X-ray intensity data collection for metal complexes.
1
2a
3
4
Identification code
Empirical formula
Formula weight
T (K)
newrm309_relable
newrm329_relable
C84H167N9O20P4Cd4
2014.50
newrm319_relable
C82H92Cd2Cl2N8O18P2
1835.28
newrm324_relable
C65H89CdN4O12P3
1323.71
C86H167N9O20P4Zn4
2032.65
150(2)
150(2)
150(2)
153(2)
k (Å)
0.71073
orthorhombic
Fdd2
57.7913(5)
37.7407(3)
9.77270(10)
90
0.71073
0.71073
0.71073
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
11.2858(11)
14.4394(8)
17.6252(14)
91.43(0)
96.48(1)
100.29(1)
10.6154(3)
14.6571(4)
14.7787(4)
110.342(3)
96.600(2)
101.016(2)
2074.80(10)
1
1.469
0.688
944
0.22 ꢂ 0.20 ꢂ 0.17
3.32–25.00
14469
7307
1.053
10.7838(3)
18.2473(9)
18.2922(9)
93.761(4)
103.296(3)
103.699(3)
3375.8(3)
2
1.302
0.455
1392
0.24 ꢂ 0.22 ꢂ 0.17
3.34–25.00
22284
11251
0.999
a
(°)
b (°)
90
90
c
(°)
V, (Å3)
21315.1(3)
8
1.267
1.013
8688
0.23 ꢂ 0.18 ꢂ 0.13
3.17–25.00
35978
9004
1.051
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
h
Total reflections
Unique reflections
Goodness of fit (GOF) on F2
R1 [I > 2
wR2 [I > 2
r
(I)]
(I)]
0.0347
0.0924
1.195 and ꢁ0.505
0.0293
0.0812
1.204 and ꢁ0.423
0.0481
0.1167
0.788 and ꢁ0.734
r
Largest difference in peak and hole (e Å3)
a
Poor diffraction data; refinement incomplete.
0.2 mmol) was added and stirred for 1 h. The resulting solution
was filtered and left for crystallization at room temperature. After
24 h white single crystals of complex 4 were isolated. Compound 4
was found to be soluble solvents like methanol, chloroform, aceto-
nitrile, etc. Mp. 244–246 °C, Yield 0.22 g (85% based on dtbhp-H2),
IR data (KBr, cmꢁ1): 3417(br), 2956(vs), 2866(w), 2318(br),
1600(w), 1479(s), 1441(m), 1361(w), 1305(w), 1229(m),
1201(m), 1158(m), 1128(w), 1017(m), 934(m), 878(m), 766(m),
737(w). Anal. Calc. for C65H89N4O12P3Cd (mol. wt: 1323): C,
58.98; H, 6.78; N, 4.23. Found: C, 58.45; H, 6.45; N, 4.09%. 1H
NMR (CDCl3, 400 MHz): d 1.26 (s, 18H, o-Ar–But), 1.27 (s, 18H,
Ar–But), d 1.35 (s, 18H, p-Ar–But), d 3.00 (d, 2H, Ar–CH2, 1JPH = 21 -
1
Hz), d3.45 (d, 2H, Ar–CH2, JPH = 20 Hz), d6.95 (dd, 4H, Ar–H,
4
4JHH = 3 Hz), d 7.10 (dd, 4H, Ar–H, JHH = 2 Hz), d 7.69–7.72 (dd,
4H, C3H, C03H 3JHH = 7.1 Hz), d 8.20 (dd, 4H, C4H, C04H, 3JHH = 8.3 Hz),
2
d 8.50 (dd, 4H, C5H, C05H, JHH = 9.1 Hz) ppm. 31P NMR (CDCl3,
160 MHz): d 27.40, d 28.20 ppm.
3.6. Crystal structure determination
Intensity data for all the four samples were collected on an Ox-
ford XCalibur CCD diffractometer. All calculations were carried out

154
R. Howlader et al. / Inorganica Chimica Acta 405 (2013) 147–154
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tails of its structure are not reported.
4. Conclusions
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We have reported here zinc and cadmium phosphonate com-
plexes, [Zn2(dtbhp-H)2(TMEDA)2(H2O)2]ꢀ0.5CH3CN (1), [Cd2(-
dtbhp-H)2(CH3OH)2(TMEDA)2]ꢀ0.5CH3CN (2), [Cd2(mdtbhp)2(1,10-
phenanthroline)4]ꢀ(ClO4)2(CH3OH)2 (3), and [Cd(dtbhp-H)2(2,20-
bpy)2](dtbhp-H2) (4) derived from a sterically hindered phos-
phonic acid (dtbhp-H2) and ancillary N-donors such as 2,2’-bipyir-
idine, 1,10-phenanthroline and tertraethylenehylenediamine
(TMEDA). Compounds 1–4, which represent the first examples of
the metal derivatives of dtbhp-H2, were characterized by spectro-
scopic methods and single crystal X-ray diffraction method. In
the case of 3, an unexpected esterification of P–O–H group [51]
has been observed even under the ambient conditions employed
for the synthesis of the metal phosphonate, leading to the isolation
of the only cationic complex reported in this study. However, when
2,20-bipyiridine is employed in the place of 1,10-phenanthroline no
esterification observed and the resultant neutral complex contains
two mono deprotonated phosphonate ligands. Several attempts to
synthesize similar types of complexes of zinc phosphonates with
2,20-bipyiridine and 1,10-phenanthroline were unsuccessful under
similar conditions as in each case ZnL2ꢀ2H2O was obtained as the
final product and it was confirmed from spectroscopic and elemen-
tal analysis. The presence of reactive Ar–OH and P–OH groups on
the complexes reported in this study offer further possibilities to
study their reactivity with other metal ions in order to prepare het-
erometallic phosphonates. We are currently investigating these
aspects.
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Acknowledgements
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The authors thank the SAIF, IIT-Bombay for analytical, spectral
data and National Single Crystal Diffraction facility for the X-ray
data for all complexes. This work was supported by DST, New Delhi
and DAE-BRNS, Mumbai. R. M. thanks DAE for the DAE-BRNS Out-
standing Investigator Award.
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Appendix A. Supplementary material
CCDC 881699–881701 contain the supplementary crystallo-
graphic data for compounds 1, 3 and 4, respectively. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic 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 http://dx.doi.org/10.1016/j.ica.2013.05.011.
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