Reactions of Cd(OAc)2·2H2O with variously substituted pyridines. Efforts to unravel the factors that determine structure/nuclearity of the products

Article abstract of DOI:10.1016/j.poly.2015.06.002

The reactions of Cd(OAc)₂·2H₂O with variously substituted pyridines in methanol afforded unique one-dimensional coordination polymers (1D CPs), [Cd₂(μ₂-κ²:κ¹-OAc)₂(μ₂-κ¹:κ¹-OAc)₂L₂] (L = NC₅H₅ (1), NC₅H₄Me-3 (2), and NC₅H₃Me₂-3,5 (3)) and [Cd₃(μ₃-κ¹:κ²-OAc)₃(μ₂-κ²-OAc)(μ₂-κ²:κ¹-OAc)₂(NC₅H₃Me₂-3,4)₂] (4), and discrete and bimolecular complexes, [(Cd(OAc)₂(NC₅H₃Me₂-3,4)₂(H₂O)₂] (5), [Cd(κ²-OAc)₂(NC₅H₄Me-4)₂(H₂O)]·[Cd(κ²-OAc)₂(H₂O)₂)] (6), [Cd(κ²-OAc)₂L₂L′]·xH₂O (x = 0, L′ = H₂O, L = NC₅H₄(OMe)-4 (7); NC₅H₄^tBu-4 (8); x = 2, L = L′ = NC₅H₄(NMe₂)-4 (9·2H₂O)). The products were characterised by elemental analysis, IR, solution NMR (¹H and ¹³C), solid-state CP-MAS ¹³C{¹H} and ¹¹³Cd NMR, TGA/DTA analyses, and single crystal X-ray diffraction. Phase purity of 1-4 was verified by powder X-ray diffraction (PXRD). Plausible mechanisms of formation of the products are proposed based on a point zero charge model. 4 represents the first cadmium containing 1D CP that possesses a tridentate bridging (μ₃-κ¹:κ²) acetate coordination mode and 6 represents the first structurally characterised bimolecular cadmium(II) complex containing two different neutral cadmium(II) coordination species per formula unit. 9·2H₂O was calcined at 500 °C to afford CdO as confirmed by PXRD and the morphology of CdO was studied by scanning electron microscopy.

Full text of DOI:10.1016/j.poly.2015.06.002

Polyhedron 98 (2015) 238–250
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Reactions of Cd(OAc)2ꢀ2H2O with variously substituted pyridines. Efforts
to unravel the factors that determine structure/nuclearity of the
products
⇑
Priya Saxena, Natesan Thirupathi
Department of Chemistry, University of Delhi, Delhi 110 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of Cd(OAc)2ꢀ2H2O with variously substituted pyridines in methanol afforded unique one-
dimensional coordination polymers (1D CPs), [Cd2(l2
-
j2
j1
:j - :j
1-OAc)2(l2 j1 1-OAc)2L2] (L = NC5H5 (1),
Received 8 April 2015
Accepted 3 June 2015
Available online 15 June 2015
NC5H4Me-3 (2), and NC5H3Me2-3,5 (3)) and [Cd3(l3
-
:j -j - :j
2-OAc)3(l2 2-OAc)(l2 j2 1-OAc)2(NC5H3
Me2-3,4)2] (4), and discrete and bimolecular complexes, [(Cd(OAc)2(NC5H3Me2-3,4)2(H2O)2] (5), [Cd(j2
-
OAc)2(NC5H4Me-4)2(H2O)]ꢀ[Cd(
j
2-OAc)2(H2O)2)] (6), [Cd(j2-OAc)2L2L0]ꢀxH2O (x = 0, L0 = H2O, L = NC5H4
t
Keywords:
(OMe)-4 (7); NC5H4 Bu-4 (8); x = 2, L = L0 = NC5H4(NMe2)-4 (9ꢀ2H2O)). The products were characterised
by elemental analysis, IR, solution NMR (1H and 13C), solid-state CP-MAS 13C{1H} and 113Cd NMR,
TGA/DTA analyses, and single crystal X-ray diffraction. Phase purity of 1–4 was verified by powder X-
ray diffraction (PXRD). Plausible mechanisms of formation of the products are proposed based on a point
zero charge model. 4 represents the first cadmium containing 1D CP that possesses a tridentate bridging
Cd(OAc)2ꢀ2H2O
Lewis base
Coordination polymers
CPMAS 113Cd NMR
Pzc species
(
l3- :j
j1 2) acetate coordination mode and 6 represents the first structurally characterised bimolecular
cadmium(II) complex containing two different neutral cadmium(II) coordination species per formula
unit. 9ꢀ2H2O was calcined at 500 °C to afford CdO as confirmed by PXRD and the morphology of CdO
was studied by scanning electron microscopy.
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
coordination modes exhibited by the carboxylate moiety. Various
coordination modes of the carboxylate moiety towards the metal
Lewis base coordinated cadmium(II) carboxylate complexes are
known to exist in a variety of forms ranging from mononuclear, din-
uclear, and multinuclear complexes to coordination polymers (CPs)
[1–4]. These complexes have been widely studied over the past few
decades due to their interesting structural aspects and photolumi-
nescent properties [1–4], as a surrogate metallo-bioprobe for the
active sites of Zn(II), Ca(II), and Mg(II) containing metalloproteins
through 113Cd NMR spectroscopy [5,6], and as pre-catalysts in
copolymerization of epoxides and CO2 [7]. Moreover, this class of
complexes are shown to be useful substrates [8] and key intermedi-
ates [9] in the formation of cadmium chalcogenide nanocrystals.
The structure and nuclearity of Lewis base coordinated group 12
metal carboxylate complexes in general and those of cadmium in
particular are difficult to predict due to the presence of a completely
filled d10 electronic configuration of the metal ion and the flexible
ion are illustrated in Fig. 1 [10–12]. We believe that steric and elec-
tronic properties of both the Lewis base and the carboxylate moiety
in Lewis base coordinated cadmium(II) carboxylate complexes dic-
tate the structure/nuclearity of the products when other experi-
mental conditions are identical.
In the past, we studied the reactions of Zn(OAc)2ꢀ2H2O with
structural isomers of lutidine in methanol at ambient condition
and from these reactions two types of lutidine coordinated trinu-
clear complexes and a 1D CP were isolated [13]. We now want to
investigate the reactions of Cd(OAc)2ꢀ2H2O with pyridine and var-
iously substituted pyridines (Ls) in methanol at ambient condition
with a view aimed at understanding how the differences in the
intrinsic properties of Ls in conjunction with the greater ionic
radius of cadmium than zinc (1.09 versus 0.88 Å) [14], and hence
propensity of the former metal ion to adopt higher coordination
numbers and a variety of geometries [1b,15,16] influence the
structures and nuclearity of the resulting products. From this
endeavour, we have isolated two types of CPs namely, [Cd2(l2
-
⇑
Corresponding author.
E-mail addresses: tnat@chemistry.du.ac.in, thirupathi_n@yahoo.com (N. Thirupathi).
j2
:j
1-OAc)2(l2 1-OAc)2L2] (L = NC5H5 (1), NC5H4Me-3 (2),
- :j
j1
http://dx.doi.org/10.1016/j.poly.2015.06.002
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
239
R
R
R
R
O
O
O
O
M
O
O
O
O
M
M
M
M
M
M
Monodentate
Bidentate
Tridentate chelating
Tetradentate chelating
(κ1)
chelating (κ2)
bridging (μ2-κ2:κ1)
bridging (μ3-κ1:κ2:κ1)
R
R
R
R
O
M
M
M
O
M
O
M
O
O
M
O
M
O
M
O
M
M
M
Monoatomic bridging
Bidentate bridging
Tridentate bridging
Tetradentate bridging
(μ2-κ2)
(μ2-κ1:κ1)
(μ3-κ1:κ2)
(μ4 κ2 κ2
-
:
)
Fig. 1. Types of carboxylate coordination modes.
and NC5H3Me2-3,5 (3)) and [Cd3(l3
-
j1
:j
2-OAc)3(l2
-j
2-OAc)(l2
-
2.2. Preparation of [Cd2(l2
3)2] (2)
-
:j - :j
j2 1-OAc)2(l2 j1 1-OAc)2(NC5H4Me-
j2
:j
1-OAc)2(NC5H3Me2-3,4)2] (4) and discrete and bimolecular
complexes namely, [(Cd(OAc)2(NC5H3Me2-3,4)2(H2O)2] (5),
[Cd(
(
j
2-OAc)2(NC5H4Me-4)2(H2O)]ꢀ[Cd(
j
2-OAc)2(H2O)2)] (6), [Cd
CP 2 was prepared from Cd(OAc)2ꢀ2H2O (500 mg, 1.88 mmol)
and 3-picoline (175 mg, 1.88 mmol)/(350 mg, 3.76 mmol) in
methanol (30 mL + 5 mL) following the procedure outlined for CP
1. Yield: 89% (540 mg, 1.67 mmol)/92% (560 mg, 1.73 mmol).
Anal. Calc. for C10H13NO4Cd (323.63) (2): C, 37.11; H, 4.05; N,
4.33. Found: C, 36.85/36.86; H, 4.35/4.35; N, 4.26/4.23%. m.p.
j2-OAc)2L2L0]ꢀxH2O (x = 0, L0 = H2O, L = NC5H4(OMe)-4 (7);
t
NC5H4 Bu-4 (8); x = 2, L = L0 = NC5H4(NMe2)-4 (9ꢀ2H2O)) in
moderate to good yields. The products have been characterised
by elemental analysis, IR, solution NMR (1H and 13C), solid-state
CP-MAS 13C{1H} and 113Cd NMR, TGA/DTA analyses, and single
crystal X-ray diffraction. Plausible mechanisms of formation of
products prepared in the present investigation are proposed
based on a point zero charge (pzc) model [17]. To the best of our
(DSC) 143.59 °C. IR (KBr, cmꢁ1):
1576 (br, vs), s(OC(O) + ( (C@C),
(D2O, 400 MHz) d: 1.91 (s, 2 ꢂ 3 H, CH3), 2.30 (s,
NC5H4(CH3)-3), 7.39 (apparent t, JHH = 6.6 Hz, 1 H, NC5H4(CH3)-3),
7.76 (d, JHH = 8.1 Hz, H, NC5H4(CH3)-3), 8.27 (br, H,
m
a(OC(O) + (
(C@N))L 1421 (br, vs). 1H NMR
H,
m(C@C), m(C@N))L
m
m
m
3
knowledge,
cadmium(II) carboxylate 1D CP that contains a tridentate bridging
2) acetate coordination mode while 6 represents the first
4 represents the first structurally characterised
1
1
(l3
-
j1
:j
NC5H4(CH3)-3), 8.30 (s, 1 H, NC5H4(CH3)-3). 13C{1H} NMR (D2O,
100.5 MHz) d: 20.2 (NC5H4(CH3)-3), 24.6 (CH3), 127.3, 138.2,
142.5, 148.5, 151.6 (NC5H4(CH3)-3), 184.3 (OC(O)). Solid state CP-
MAS 13C{1H} NMR (150.9 MHz) d: 17.0, 18.2 (NC5H4(CH3)-3),
21.8, 22.5, 24.2, 25.5 (CH3), 124.7, 125.4, 136.1, 140.0, 147.4,
151.3 (NC5H4(CH3)-3), 177.1, 180.2 (OC(O)).
structurally characterised bimolecular cadmium(II) complex con-
taining two different neutral cadmium(II) coordination species
per formula unit to be reported in the literature.
2. Experimental
2.3. Preparation of [Cd2(l2
3,5)2] (3)
- :j - :j
j2 1-OAc)2(l2 j1 1-OAc)2(NC5H3Me2-
2.1. Preparation of [Cd2(l2- :j - :j
j2 1-OAc)2(l2 j1 1-OAc)2(NC5H5)2] (1)
CP 3 was prepared from Cd(OAc)2ꢀ2H2O (500 mg, 1.88 mmol)
and 3,5-lutidine (202 mg, 1.88 mmol)/(405 mg, 3.76 mmol) in
methanol (30 mL + 5 mL) following the procedure outlined for CP
1. Yield: 70% (445 mg, 1.32 mmol). Anal. Calc. for C11H15NO4Cd
(337.66) (3): C, 39.13; H, 4.48; N 4.15. Found: C, 39.22; H, 4.31;
Cd(OAc)2ꢀ2H2O (500 mg, 1.88 mmol) was dissolved in methanol
(30 mL) and stirred. To this solution, methanolic (5 mL) solution of
pyridine (149 mg, 1.88 mmol)/(300 mg, 3.76 mmol) was separately
added and the resulting solution stirred at ambient temperature
for 24 h, filtered and the filtrate concentrated under vacuum to
about 5 mL. The solution was stored at ambient temperature for
several days to afford 1 as colourless crystals. The crystals were
separated, washed with n-hexane and dried under vacuum to
afford 1 in 94% (548 mg, 1.67 mmol)/90% (555 mg, 1.69 mmol)
yields. CP 1 is a hygroscopic solid and therefore elemental analysis
results were obtained as its monohydrate. Anal. Calc. for
C9H11NO4CdꢀH2O (309.61 + 18.02) (1.H2O): C, 33.00; H, 4.00; N,
4.28. Found: C, 33.04; H, 3.83; N, 3.98%. m.p. (DSC) 152.18 °C. IR
N,
4.22%.
m.p.
(DSC)
189.97 °C.
IR
cmꢁ1):
s(OC(O)) + (m(C@C),
(KBr,
m
m
a(OC(O)) + (
m
(C@C),
m
(C@N))L 1584 (br, vs);
m
(C@N))L 1420 (br, vs). 1H NMR (D2O, 400 MHz) d: 1.92 (s, 2 ꢂ 3
H, CH3), 2.29 (s, 2 ꢂ 3 H, NC5H3(CH3)2-3,5), 7.62 (s,
1 H,
NC5H3(CH3)2-3,5), 8.13 (br, 2 H, NC5H3(CH3)2-3,5). 13C{1H} NMR
(D2O, 100.5 MHz) d: 20.0 (NC5H3(CH3)2-3,5), 24.6 (CH3), 137.5,
142.9, 148.6 (NC5H3(CH3)2-3,5), 184.3 (OC(O)). Solid state CP-
MAS 13C{1H} NMR (100.6 MHz) d: 18.5, 19.3 (NC5H3(CH3)2-3,5),
22.5, 25.2, 25.5 (CH3), 134.3, 135.0, 139.5, 146.8, 148.0
(NC5H3(CH3)2-3,5), 178.0, 179.4, 180.0 (OC(O)).
(KBr, cmꢁ1):
s(OC(O) + ( (C@C), m
ma(OC(O) + (
m(C@C),
m(C@N))L 1560 (br, vs),
m
m
(C@N))L 1420 (br, vs). 1H NMR (D2O,
400 MHz) d: 1.91 (s, 2 ꢂ 3 H, CH3), 7.50 (t, JHH = 6.6 Hz, 2 H,
NC5H5), 7.93 (t, JHH = 7.7 Hz, 1 H, NC5H5), 8.50 (br, 2 H, NC5H5).
13C{1H} NMR (D2O, 100.5 MHz) d: 24.6 (CH3), 127.8, 141.9, 151.4
(NC5H5), 184.3 (OC(O)). Solid state CP-MAS 13C{1H} NMR
(150.9 MHz) d: 21.4, 24.2 (CH3), 125.5, 136.5, 140.9, 150.5
(NC5H5), 179.0, 179.8, 182.8 (OC(O)).
2.4. Preparation of [Cd3(l3
OAc)2(NC5H3Me2-3,4)2] (4)
- :j -j - : -
j1 2-OAc)3(l2 2-OAc)(l2 j2 j1
Cd(OAc)2ꢀ2H2O (500 mg, 1.88 mmol) was dissolved in methanol
and stirred. To this solution, methanolic (5 mL) solution of 3,4-

240
P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
lutidine (202 mg, 1.88 mmol) was added and the resulting solution
stirred at ambient temperature for 24 h, filtered and the filtrate
concentrated under vacuum to about 5 mL. The solution was
stored at ambient temperature for several days to afford 4 as
colourless crystals. The crystals were separated, washed with n-
NMR (150.9 MHz) d: 21.2 (NC5H4(CH3)-4), 22.1 (CH3), 126.2 (br),
148.8, 149.9 (NC5H4(CH3)-4), 179.0, 179.8, 182.8 (OC(O)).
2.7. Preparation of [Cd(
j
2-OAc)2(NC5H4(OMe)-4)2H2O] (7)
hexane and dried under vacuum to afford
4 in 62% yield
(353 mg, 0.39 mmol). CP 4 is a hygroscopic solid and therefore ele-
mental analysis results were obtained as its monohydrate. Anal.
Calc. for C26H36N2O12Cd3ꢀH2O (905.80 + 18.02) (4ꢀH2O): C, 33.80;
H, 4.15; N, 3.03. Found: C, 33.84; H, 4.16; N, 3.01%. m.p. (DSC)
Complex
7
was prepared from Cd(OAc)2ꢀ2H2O (500 mg,
1.88 mmol) and 4-methoxypyridine (410 mg, 3.76 mmol)/(205 mg,
1.88 mmol) in methanol (30 mL + 5 mL) following the procedure
outlined for CP 1. Yield: 91% (800 mg, 1.71 mmol)/40% (350 mg,
0.75 mmol). Anal. Calc. for C16H22N2O7Cd (466.77) (7): C, 41.17;
H, 4.75; N, 6.00. Found: C, 40.83; H, 4.90; N, 5.84%. m.p. (DSC)
91.67 °C. IR (KBr, cmꢁ1):
vs); s(OC(O)) + ( (C@C),
m
m
a(OC(O)) + (
m(C@C), m(C@N))L 1570 (br,
m
m
(C@N))L 1420 (br, vs). 1H NMR (D2O,
400 MHz) d: 1.90 (s, 6 ꢂ 3 H, CH3), 2.24, 2.30 (each s, 2 ꢂ 2 ꢂ 3 H,
NC5H3(CH3)2-3,4), 7.30 (d, JHH = 5.1 Hz, 2 ꢂ 1 H, NC5H3(CH3)2-3,4),
8.15 (d, JHH = 4.8 Hz, 2 ꢂ 1 H, NC5H3(CH3)2-3,4), 8.18 (s, 2 ꢂ 1 H,
NC5H3(CH3)2-3,4). 13C{1H} NMR (D2O, 100.5 MHz) d: 18.3, 21.2
(NC5H3(CH3)2-3,4), 24.7 (CH3), 128.4, 137.2, 148.6, 150.9, 153.2
(NC5H3(CH3)2-3,4), 184.3 (OC(O)). Solid state CP-MAS 13C{1H}
NMR (150.9 MHz) d: 14.7, 15.8, 17.1, 19.1 (NC5H3(CH3)2-3,4),
22.1, 24.3, 25.0 (CH3), 126.7, 132.7, 148.7, 150.8 (NC5H3(CH3)2-
3,4), 179.7, 181.2, 182.3, 183.8 (OC(O)).
90.31 °C. IR (KBr, cmꢁ1):
(O)) + ( (C@C), (C@N))L 1573 (br, vs); m
m
a(H2O) 3402 (br, s);
ma(OC
m
m
s(OC(O)) 1412 (s). 1H
NMR (D2O, 400 MHz) d: 1.92 (s, 2 ꢂ 3 H, CH3), 3.90 (s, 2 ꢂ 3 H,
NC5H4(OCH3)-4), 7.06 (d, JHH = 6.4 Hz, 2 ꢂ 2 H, NC5H4(OCH3)-4),
8.32 (d, JHH = 6.0 Hz, 2 ꢂ 2 H, NC5H4(OCH3)-4). 13C{1H} NMR (D2O,
100.5 MHz) d: 25.0 (CH3), 58.2 (NC5H4(OCH3)-4), 113.6, 152.8,
169.7 (NC5H4(OCH3)-4), 184.3 (OC(O)). Solid state CP-MAS
13C{1H} NMR (150.9 MHz) d: 20.9, 21.3 (CH3), 55.4, 57.4
(NC5H4(OCH3)-4),
109.5,
113.1,
152.6,
166.8,
167.7
(NC5H4(OCH3)-4), 179.5 (OC(O)).
2.5. Preparation of [(Cd(OAc)2(NC5H3Me2-3,4)2(H2O)2] (5)
2.8. Preparation of [Cd(
j
2-OAc)2(NC5H4t Bu-4)2H2O] (8)
Cd(OAc)2ꢀ2H2O (500 mg, 1.88 mmol) was dissolved in methanol
and stirred. To this solution, methanolic (5 mL) solution of
3,4-lutidine (405 mg, 3.78 mmol) was added and the resulting
solution stirred at ambient temperature for 24 h, filtered and the
filtrate concentrated under vacuum to about 5 mL. The solution
was stored at ambient temperature for several days to afford 5 as
colourless crystals. The crystals were separated, washed with n-
hexane and dried under vacuum to afford 5 in 90% yield (813 mg,
1.69 mmol). Anal. Calc. for C18H28N2O6Cd (480.84) (5): C, 44.96;
H, 5.87; N, 5.82. Found: C, 45.28; H, 5.60 N, 5.80%. m.p. (DSC)
Complex
8
was prepared from Cd(OAc)2ꢀ2H2O (500 mg,
1.88 mmol) and 4-tert-butylpyridine (510 mg, 3.77 mmol)/
(255 mg, 1.88 mmol) in methanol (30 mL + 5 mL) following the
procedure outlined for CP 1. Yield: 95% (900 mg, 1.79 mmol)/42%
(440 mg, 0.79 mmol). Complex 8 is a hygroscopic solid and there-
fore the elemental analysis results were obtained as its dihydrate.
Anal. Calc. for C22H34N2O5Cdꢀ2H2O (518.93 + 36.03) (8ꢀ2H2O): C,
47.61; H, 6.90; N, 5.05. Found: C, 47.67/47.57; H, 7.19/7.24; N,
4.95/4.98%. m.p. (DSC) 80.46 °C. IR (KBr, cmꢁ1):
m); a(OC(O)) + ( (C@C), (C@N))L 1578 (br, vs); m
ma(H2O) 3404 (br,
78.76 °C. IR (KBr, cmꢁ1):
(C@N))L 1574 (br, vs);
m
(H2O) 3402 (br, s); a(OC(O)) + (
m
m(C@C),
m
m
m
s(OC(O)) 1420
m
m
s(OC(O)) + ( (C@C), m(C@N))L 1419 (br,
m
(br, vs). 1H NMR (D2O, 400 MHz) d: 1.29 (s, 2 ꢂ 9 H,
NC5H4(C(CH3)3)-4), 1.91 (s, 2 ꢂ 3 H, CH3), 7.54 (d, JHH = 5.6 Hz,
2 ꢂ 2 H, NC5H4(C(CH3)3)-4), 8.39 (d, JHH = 5.8 Hz, 2 ꢂ 2 H,
NC5H4(C(CH3)3)-4). 13C{1H} NMR (D2O, 100.5 MHz) d: 24.5 (CH3),
32.0 (NC5H4(C(CH3)3)-4), 37.2 (NC5H4(C(CH3)3)-4), 125.0, 151.2,
166.9 (NC5H4(C(CH3)3)-4), 184.3 (OC(O)). Solid state CP-MAS
13C{1H} NMR (75.5 MHz) d: 19.6, 20.0 (CH3), 30.0 (NC5H4
(C(CH3)3)-4), 34.1, 34.8 (NC5H4(C(CH3)3)-4), 119.3, 150.5, 159.1,
160.8 (NC5H4(C(CH3)3)-4), 177.7, 178.8 (OC(O)).
vs). 1H NMR (D2O, 400 MHz) d: 1.91 (s, 2 ꢂ 3 H, CH3), 2.22, 2.29
(each s, 2 ꢂ 2 ꢂ 3 H, NC5H3(CH3)2-3,4), 7.27 (d, JHH = 5.1 Hz, 2 ꢂ 1
H, NC5H3(CH3)2-3,4), 8.15 (d, JHH = 5.1 Hz, 2 ꢂ 1 H, NC5H3(CH3)2-
3,4), 8.17 (s, 2 ꢂ 1 H, NC5H3(CH3)2-3,4). 13C{1H} NMR (D2O,
100.5 MHz) d: 18.2, 21.1 (NC5H3(CH3)2-3,4), 24.7 (CH3), 128.3,
137.0, 148.6, 150.8, 152.8 (NC5H3(CH3)2-3,4), 184.2 (OC(O)). Solid
state CP-MAS 13C{1H} NMR (150.9 MHz) d: 14.7, 17.0, 19.0, 20.5
(NC5H3(CH3)2-3,4), 21.4, 22.5 (CH3), 124.9, 125.6, 133.1, 148.6,
152.3 (NC5H3(CH3)2-3,4), 178.6 (OC(O)). Note: Four d values are
observed for 3,4-lutidine CH3 carbons and two d values are
observed for acetate CH3 carbon as two molecules are present in
an asymmetric unit.
2.9. Preparation of [Cd(
j
2-OAc)2(NC5H4(NMe2)-4)3]ꢀ2H2O (9ꢀ2H2O)
Complex 9ꢀ2H2O was prepared from Cd(OAc)2ꢀ2H2O (500 mg,
1.88 mmol) and 4-dimethylaminopyridine, DMAP (690 mg,
5.64 mmol)/(230 mg, 1.88 mmol)/(460 mg, 3.76 mmol) in metha-
nol (30 mL + 5 mL) following the procedure outlined for CP 1.
Yield: 94% (1.12 g, 1.77 mmol)/30% (355 mg, 0.56 mmol)/62%
2.6. Preparation of [Cd(
(H2O)2)] (6)
j
2-OAc)2(NC5H4Me-4)2(H2O)]ꢀ[Cd(
j
2-OAc)2
Complex
6
was prepared from Cd(OAc)2ꢀ2H2O (500 mg,
1.88 mmol) and 4-picoline (175 mg, 1.88 mmol)/(350 mg,
3.76 mmol) in methanol (30 mL + 5 mL) following the procedure
outlined for CP 1. Yield: 92% (606 mg, 0.86 mmol). Anal. Calc. for
(738 mg, 1.17 mmol). Anal. Calc. for
(597.01 + 36.03) (9ꢀ2H2O): C, 47.43; H, 6.37; N, 13.28. Found: C.
C
25H36N6O4Cdꢀ2H2O
47.36; H, 6.63; N, 13.31%. m.p. (DSC) 135.72 °C. IR (KBr, cmꢁ1):
C
20H32N2O11Cd2 (701.29) (6): C, 34.25; H, 4.60; N, 3.99. Found: C,
34.18; H, 4.86; N, 3.96%. m.p. (DSC) 98.65 °C. IR (KBr, cmꢁ1):
a(H2O) 3402 (br, s); a(OC(O)) + ( (C@C), (C@N))L 1574 (br, vs),
1505 (sh, m); s(OC(O)) + ( (C@C),
(C@N))L 1422 (br, vs). 1H
m
a(H2O) 3369 (br, m), 3300 (sh, m);
ma(OC(O)) 1566 (s);
ms(OC(O)) + ( (C@C),
m
m
(C@N))L 1411. 1H NMR (D2O, 400 MHz) d:
m
m
m
m
1.89 (s, 2 ꢂ 3 H, CH3), 3.10 (s, 3 ꢂ 6 H, NC5H4(N(CH3)2)-4), 6.78
(d, JHH = 7.3 Hz, 3 ꢂ 2 H, NC5H4(N(CH3)2-4), 8.00 (d, JHH = 6.6 Hz,
3 ꢂ 2 H, NC5H4(N(CH3)2-4). 13C{1H} NMR (CDCl3, 100.5 MHz) d:
21.8 (CH3), 39.1 (NC5H4(N(CH3)2)-4), 106.8, 149.4, 154.8
(NC5H4(N(CH3)2-4)), 180.2 (OC(O)). Solid state CP-MAS 13C{1H}
NMR (75.5 MHz) d: 24.0 (CH3), 37.6 (NC5H4(N(CH3)2)-4), 108.0,
149.0, 154.2 (NC5H4(N(CH3)2-4)), 176.8 (OC(O)).
m
m
m
NMR (D2O, 400 MHz) d: 1.91 (s, 4 ꢂ 3 H, CH3), 2.39 (s, 2 ꢂ 3 H,
NC5H4(CH3)-4), 7.36 (d, JHH = 5.8 Hz, 2 ꢂ 2 H, NC5H4(CH3)-4), 8.33
(d, JHH = 4.8 Hz, 2 ꢂ 2 H, NC5H4(CH3)-4). 13C{1H} NMR (D2O,
100.5 MHz) d: 23.0 (NC5H4(CH3)-4), 24.7 (CH3), 128.6, 150.9,
154.5 (NC5H4(CH3)-4), 184.3 (OC(O)). Solid state CP-MAS 13C{1H}

P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
241
listed in Fig. 2 [18,19]. Cd(OAc)2ꢀ2H2O was separately treated with
one equiv of pyridine, 3-picoline, and 3,5-lutidine in methanol at
ambient condition for 24 h to afford 1D CPs, 1–3 in 94%, 89%, and
70% yields, respectively while the aforementioned reactions car-
ried out with two equiv. of the respective Ls afforded 1–3 in com-
parable yields. Cd(OAc)2ꢀ2H2O was separately treated with one and
two equiv. of 3,4-lutidine in methanol at ambient condition for
24 h to afford a 1D CP, 4 in 62% yield and a mononuclear complex,
3. Results and discussion
3.1. Syntheses
Cd(OAc)2ꢀ2H2O was treated with various Ls in methanol at
ambient condition in 1:1, 1:2, and 1:3 Cd:L ratios that led to the
formation of a variety of products as outlined in Scheme 1. The
Ls employed in the present investigation and their pKa values are
NMe2
N
O
O
O
Cd
N
NMe2
R
O
O
O
O
L
O
O
L
O
O
O
O
O
N
O
Cd
Cd
Cd
Cd
Cd
O
N
Cd
N
O
O
O
O
O
O
O
O
O
L
O
L
O
O
O
NMe2
O
H2
O
9
⋅2H2O
N
N
L
=
x = 1, 2 or 3
N
R
x = 1 or 2
7 R = OMe
8 R = tBu
x = 1 or 2
1
2
3
xL
Cd(OAc)2⋅2H2O
MeOH, 24 h
L = Pyridine and substituted
pyridines
x = 1
x = 1 or 2
x = 2
O
N
N
O
O
O
O
O
Cd
Cd
Cd
O
N
O
O
O
O
O
O
H2O
O
O
O
O
O
O
O
N
Cd
N
Cd
N
O
O
Cd
N
O
O
Cd
N
O
OH2
O
O
H2
O
Cd
O
O
O
O
O
O
H2
O
O
H2
4
6
5
Scheme 1. Synthesis of CPs/complexes.
Lewis base
N
N
N
N
N
N
6.65
6.57
6.99
pKa
6.46
5.23
6.15
NMe2
OMe
Lewis base
N
N
N
N
N
N
6.04
9.55
6.58
6.00
pKa
5.70
5.99
Fig. 2. Lewis bases employed in the present investigation and their pKa values.

242
P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
5 in 90% yield, respectively. Cd(OAc)2ꢀ2H2O was separately treated
with one and two equiv. of 4-picoline in methanol at ambient con-
dition for 24 h to afford a bimolecular complex, 6 in 92% yield from
both the reactions. Cd(OAc)2ꢀ2H2O was separately treated with two
equiv. of 4-methoxypyridine and 4-tert-butylpyridine in methanol
at ambient condition to afford mononuclear complexes, 7 and 8 in
91% and 95% yields, respectively. Complexes 7 and 8 were also
obtained as the exclusive products albeit in lower yields of 40%
and 42%, respectively even when one equiv of L per cadmium
was used. Similarly, the reactions of Cd(OAc)2ꢀ2H2O with one,
two, and three equiv of 4-dimethylaminopyridine (DMAP) in
methanol at ambient condition afforded a mononuclear complex,
9ꢀ2H2O in 30%, 62%, and 94% yields, respectively. Thus, the level
of aggregation of the products depends upon Cd:L ratio in the for-
mation of 4 and 5 and does not depend upon Cd:L ratio in the for-
mation of other products.
a
b
c
Fig. 3. ORTEP representations of 1 (a), 2 (b) and 3 (c) at the 50% probability level. Hydrogen atoms are removed for clarity. Symmetry transformations: (1) a = b = c = x, y, z;
d = 1 ꢁ x, 1 ꢁ y, 1 ꢁ z; e = ꢁ1 + x, ꢁ1 + y, 1 + z. (2) a = b = c = x, y, z; d = 1 ꢁ x, 1 ꢁ y, 1 ꢁ z; e = ꢁ1 + x, y, z. (3) a = b = c = x, y, z; d = ꢁ1 ꢁ x, ꢁy, ꢁz; e = ꢁ1 + x, y, z.

P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
243
Fig. 4. The ORTEP representation of 4 at the 30% probability level. Hydrogen atoms are removed for clarity. Symmetry transformations: a = b = c = x, y, z; d = x, ꢁ1 + y, z;
e = f = x, 1 + y, z.
Fig. 5. Spacefill models illustrating two different types of the growing units in 3 (a) and 4 (b).

244
P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
distinct cadmium atoms, Cd1 and Cd3 are surrounded by a pair
of oxygen atoms from a pair of bidentate bridging (l2
1) acet-
ate moieties, a pair of oxygen atoms from a pair of tridentate
chelating bridging (l2
1) acetate moieties and the nitrogen
-
j1
:j
-
j2
:j
atom from a pair of Lewis bases and thus attain a coordination
number of six. The two pairs of oxygen atoms and the pair of nitro-
gen atoms are centrosymmetrically related. On the other hand, the
central cadmium atom, Cd2 is surrounded by a pair of oxygen
atoms from a pair of bidentate bridging acetate moieties, and
two pairs of oxygen atoms from a pair of tridentate chelating
bridging acetate moieties and thus attains a coordination number
of six. The cadmium atoms Cd1 and Cd3 revealed a distorted octa-
hedral geometry while the cadmium, Cd2 revealed a distorted trig-
onal prismatic geometry. Thus, two adjacent cadmium atoms in a
repeat unit are linked by one bidentate bridging and one tridentate
chelating bridging acetate moieties and thus lead to the growth of
a 1D CP. The N1–Cd1–N1 and N2–Cd3–N2 units are non-coplanar
with the angle between these units being 76.46(4)°, 78.39(3)°,
and 77.22(4)° in 1–3, respectively.
The formation of a 1D CP, 3 as against the formation of a dis-
crete open framework trinuclear complex, [Zn3(OAc)2(l2
- : -
j2 j1
OAc)2(l2
-
j1
:j
1-OAc)2(H2O)2(NC5H3Me2-3,5)2] reported earlier by
one of us [13] from the reactions of M(OAc)2ꢀ2H2O (M = Cd and
Zn) with 3,5-lutidine under identical condition confirms the find-
ings that cadmium(II) salts are prone to form polymeric complexes
while the respective zinc(II) salts are prone to form discrete com-
plexes. It is to be noted that both Zn(OAc)2€ꢀ2H2O [20] and
(Imidazole)2Zn(OAc)2 [21] are monomers while Cd(OAc)2ꢀ2H2O
[16] and (Imidazole)2Cd(OAc)2 [2] are 1D CPs aggregated through
the acetate moiety.
Fig. 6. The ORTEP representation of 5 at the 50% probability level. Hydrogen atoms
are removed for clarity. There are two molecules in an asymmetric unit in the
crystal lattice but the structural parameters (Å and deg) of only one molecule are
given below: Cd(1)–O(1) = 2.253(2), Cd(1)–O(3) = 2.368(2), C(8)–O(1) = 1.256(3),
C(8)–O(2) = 1.252(3), Cd(1)–N(1) = 2.345(2), O(1)–Cd(1)–O(3) = 91.41(7)/88.59(7),
O(1)–Cd(1)–N(1) = 92.01(8)/87.99(8), N(1)–Cd(1)–O(3) = 93.47(8)/86.53(8).
The molecular structure of 4 is illustrated in Fig. 4 and selected
bond distances and bond angles are listed in Table S2 in the
Supplementary material. 4 is a 1D CP consisting of three distinct
cadmium atoms namely, Cd1, Cd2, and Cd3. A pair of tridentate
bridging (l3- :j
j1 2) acetate moieties simultaneously bridges not
only the Cd1/Cd3 pair through two pairs of oxygen atoms, O3, O4
and O9, O10 but also two adjacent Cd1/Cd2 and Cd2/Cd3 pairs of
atoms through the oxygen atoms, O4 and O9, respectively. A tri-
dentate bridging acetate moiety simultaneously bridges not only
the Cd2/Cd3 pair through the oxygen atoms O7 and O8 but also
the Cd1/Cd2 pair through the oxygen atom, O7. Each of the afore-
mentioned pairs of cadmium atoms is also bridged by a tridentate
Remarkably, the reactions of Cd(OAc)2ꢀ2H2O with one or two
equiv. of sterically more hindered Ls namely, 2-picoline, 2,3-, 2,4-
and 2,6-lutidines in methanol at ambient condition did not afford
any new products. The pKa value of 2-picoline is comparable with
that of 4-picoline but greater than that of 3-picoline (Fig. 2).
Analogously, pKa values of 2,3-, 2,4- and 2,6-lutidines are greater
than those of 3,4- and 3,5-lutidines. Hence, steric factor rather than
basicity/nucleophilicity appears to be the reason for the non-reac-
tive nature of sterically more hindered Ls towards Cd(OAc)2ꢀ2H2O.
The reactions of Zn(OAc)2ꢀ2H2O with 2,3- and 2,4-lutidine carried
out separately in methanol at ambient condition resulted in the
chelating bridging (l2- :j
j2 1) acetate moiety. One 3,4-lutidine is
coordinated to each Cd1 and Cd3 and thus only two lutidines are
present in a repeat unit. 3,4-lutidine bound to Cd1 and that bound
to Cd3 are significantly twisted by forming an angle of 64.40(6)°
between the two Cd-L planes. The Cd–O distances pertaining to
the acetate that contains O1, O2, C8, and C9 atoms around Cd1 in
4 differ greatly (2.262(4) and 2.733(6) Å) and this pattern is remi-
niscent to that observed for the acetate moiety in a 1D CP,
[Cd(OC(O)Me)(OC(O)Ph)(H2O)2] (2.279(4) and 2.728(5) Å [22]).
The acetate moiety in [Cd(OC(O)Me)(OC(O)Ph)(H2O)2] was sug-
formation of trinuclear complexes, [Zn3(l2- :j - -
j1 1-OAc)4(l2 j2
OAc)2L2] (L = 2,3-lutidine and 2,4-lutidine) [13]. Thus, the differ-
ence in reactivity pattern of M(OAc)2ꢀ2H2O (M = Zn and Cd) pair
towards 2,3- and 2,4-lutidines is attributed to greater ionic radius
of cadmium than zinc in conjunction with the greater steric bulk of
these lutidines. Due to greater ionic radius, cadmium tends to
adopt higher coordination numbers in its complexes but such com-
plexes would be destabilised when the L is sterically more
hindered.
gested to possess a tridentate chelating bridging (l2- :j
j2 1) coordi-
nation mode with the coordination number of the cadmium being
seven. However, the acetate containing O1, O2, C8, and C9 atoms in
4 is assigned as monoatomic bridging (l2-j
2) as one of the d(113Cd)
values for 4 supports 5O,1 N environment for the cadmium atoms
ligated by 3,4-lutidine (see later). The cadmium atom which is
devoid of lutidine (i.e. Cd2) possesses 7O environment.
3.2. X-ray diffraction studies
The presence of a total of three types of acetate coordination
modes in 4 as against two in 1–3 is likely ascribed to the fact that
the L in the former CP is more basic than the Ls present in the latter
CPs. It has been shown that syn lone pair of the carboxylate moiety
in metal carboxylate complexes is more basic than anti lone pair
[23] and the presence of more basic 3,4-lutidine in 4 than the Ls
in 1–3 is anticipated to increase the basicity of even anti lone pair
ORTEP representations of 1–3 are illustrated in Fig. 3 and
selected bond distances and bond angles are listed in Table S1 in
the Supplementary material. 1–3 possess an identical 1D CP frame-
work. There are two types of chemically distinct cadmium atoms in
a repeat unit and in one of these units, there are two crystallo-
graphically distinct cadmium atoms. The crystallographically

P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
245
Fig. 7. The ORTEP representation of
6 at the 50% probability level. Hydrogen atoms are removed for clarity. Selected bond distances and angles (Å and deg):
Cd(1)–O(1) = 2.408(3), Cd(1)–O(2) = 2.454(3), Cd(1)–O(3) = 2.415(3), Cd(1)–O(4) = 2.450(3), Cd(1)–O(5) = 2.331(3), Cd(1)–N(1) = 2.326(4), Cd(1)–N(2) = 2.336(4),
N(1)ꢁCd(1)ꢁO(1) = 91.8(1), N(1)ꢁCd(1)ꢁO(2) = 89.6(1), N(1)ꢁCd(1)ꢁO(3) = 88.3(1), N(1)ꢁCd(1)ꢁO(4) = 90.0(1), N(1)ꢁCd(1)ꢁO(5) = 91.6(2), N(2)ꢁCd(1)ꢁO(1) = 88.9(1),
N(2)ꢁCd(1)ꢁO(2) = 88.6(1), N(2)ꢁCd(1)ꢁO(3) = 89.5(1), N(2)ꢁCd(1)ꢁO(4) = 90.0(1), N(2)ꢁCd(1)ꢁO(5) = 91.3(2), N(1)–Cd(1)–N(2) = 177.1(1), O(2)ꢁCd(1)ꢁO(3) = 89.0(1),
O(1)ꢁCd(1)ꢁO(5) = 83.0(1), O(4)ꢁCd(1)ꢁO(5) = 81.5(1) (Unit 1); Cd(2)–O(6) = 2.383(3), Cd(2)–O(7) = 2.302(3), Cd(2)–O(8) = 2.358(3), Cd(2)–O(9) = 2.305(3),
Cd(2)–O(10) = 2.206(4), Cd(2)–O(11) = 2.218(4), O(6)–Cd(2)–O(10) = 93.1(2), O(7)–Cd(2)–O(10) = 102.5(2), O(8)–Cd(2)–O(10) = 148.3(1), O(9)–Cd(2)–O(10) = 92.6(2),
O(6)–Cd(2)–O(11) = 148.6(1), O(7)–Cd(2)–O(11) = 93.3(2), O(8)–Cd(2)–O(11) = 92.6(1), O(9)–Cd(2)–O(11) = 101.9(2), O(10)–Cd(2)–O(11) = 94.3(1), (Unit 2).
in the former and thus appears to encourage aggregation through
the tridentate bridging acetate coordination mode. Cadmium(II)
acetate CPs wherein the two adjacent cadmium atoms are linked
exclusively by the acetate moiety or the Lewis base or both the
acetate moiety and the Lewis base are known in the literature
[2–4]. However, cadmium(II) acetate CPs aggregated exclusively
through the acetate moiety [2,3] are rarer than those aggregated
exclusively through the Lewis base or both the acetate moiety
and the Lewis base. Hence, molecular structures of 1–4 add to
the rare class of CPs aggregated exclusively through the acetate
moiety. One dimensional (1D) CPs are an important class of com-
pounds due to their interesting magnetic, electrical, mechanical,
and optical properties [24].
Cd–N 2.3756(3) Å and Cd–O(acetate) 2.2814(4)) [26]. Complex 5 is
stabilised through C–Hꢀ ꢀ ꢀO and O–Hꢀ ꢀ ꢀO hydrogen bonds in the
crystal lattice that leads to the formation of a sheet like structure
(Figs. S16–S18, Supplementary material).
ORTEP representations of 6, 7, 8, and 9ꢀ2H2O with the relevant
bond parameters are shown in Figs. 7–9. Complex 6 is a bimolecu-
lar species that consists of two chemically distinct neutral species
(units 1 and 2) in an asymmetric unit. The unit 1 consists of [Cd(j2
-
OAc)2(NC5H4Me-4)2(H2O)] moiety and the unit
2 consists of
[Cd(j
2-OAc)2(H2O)2)] moiety. The unit 1 of 6, 7 and 8 are similar
with same coordination environment (5O, 2N) around the cad-
mium atom. The structure of 9ꢀ2H2O is similar to that found in unit
1 of 6, 7, and 8 with the difference being that there are three DMAP
per cadmium in the former complex without any coordinated
water molecule. The geometry of the cadmium atom in unit 1 of
6 and that in 7, 8, and 9ꢀ2H2O is best described as a distorted pen-
tagonal bipyramidal wherein the equatorial positions are occupied
by two pairs of oxygen atoms with each pair arising from a j2
chelating acetate moiety and one oxygen atom from a water mole-
cule (6 (unit 1), 7 and 8) or the nitrogen atom from DMAP (9ꢀ2H2O)
(Mean deviation of the atoms from the equatorial plane 0.0135 Å
(6 (unit 1)), 0.1341 Å (7), 0.1389 Å (8) and 0.0097 Å (9ꢀ2H2O))
while the apical positions are occupied by the nitrogen atom of
two respective Ls. The bond distances around the cadmium atom
in unit 1 of 6 are comparable with the respective bond distances
1D CPs 1–3 are linear while the CP 4 is syndiotic and as a rep-
resentative example, the space fill models of 3 and 4 are illustrated
in Fig. 5. CPs 1–4 form a 2D sheet like structures through C–Hꢀ ꢀ ꢀO,
C–Hꢀ ꢀ ꢀ
p
, and
p p interactions as illustrated in Figs. S1–S6 in the
ꢀ ꢀ ꢀ
Supplementary material. The phase purity of the bulk material of
CPs 1–4 was confirmed by powder X-ray diffraction (PXRD) of
the ground single crystals of each CP. The powder X-ray pattern
of all CPs agreed well with the respective simulated patterns gen-
erated from single crystal X-ray diffraction data [25] of each CP
(Figs. S7–S15, Supplementary material).
The ORTEP representation of 5 with the relevant bond parame-
ters is shown in Fig. 6. The cadmium atom is surrounded by the
oxygen atom of monodentate acetate, that of water and nitrogen
atom of 3,4-lutidine and their inversion related atoms. Thus, the
cadmium atom attains a distorted octahedral environment. The
Cd–O(water) 2.368(2) Å distance is greater but Cd–N 2.345(2) Å
and Cd–O(acetate) 2.253(2) distances are shorter as compared to
the respective distances reported for structurally related
[Cd(OAc)2(diethylnicotinamide)2(H2O)2] (Cd–O(water) 2.2988(4) Å,
known for the structurally related [Cd(j
2-OAc)2(2-(pyridin-4-
yl)benzo[d]thiazole)2(H2O)] [27] except the Cd-O(water) distance
which is longer in the former complex (2.331(3) versus
2.278(3) Å). The asymmetry in chelation of the acetates in 7, 8,
and 9ꢀ2H2O increases in the following order:
O) = 0.003(4), 0.024(4) Å (8) < 0.044(3), 0.072(3) Å
(7) << 0.231(4) Å (9ꢀ2H2O). This trend is ascribed to the greater
Dd(Cd–

246
P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
Fig. 8. ORTEP representations of 7 (a) and 8 (b) at the 50% probability level. Hydrogen atoms are removed for clarity. Selected bond distances and angles (Å and deg) 7/8:
Cd(1)–O(3)/Cd(1)–O(1) = 2.400(2)/2.394(3), Cd(1)–O(4)/Cd(1)–O(2) = 2.444(2)/2.397(2), Cd(1)–O(5)/Cd(1)–O(3) = 2.370(2)/2.405(3), Cd(1)–O(6)/Cd(1)–O(4) = 2.442(2)/
2.429(3), Cd(1)–O(7)/Cd(1)–O(5) = 2.305(2)/2.324(2), Cd(1)–N(1) = 2.353(2)/2.370(2), Cd(1)–N(2) = 2.348(2)/2.403(3), N(1)–Cd(1)–O(3)/N(1)–Cd(1)–O(1) = 90.46(7)/
95.51(9), N(1)–Cd(1)–O(4)/N(1)–Cd(1)–O(2) = 87.00(7)/87.60(9), N(1)–Cd(1)–O(5)/N(1)–Cd(1)–O(3) = 93.02(7)/95.97(9), N(1)–Cd(1)–O(6)/N(1)–Cd(1)–O(4) = 82.79(7)/
87.90(9), N(1)–Cd(1)–O(7)/N(1)–Cd(1)–O(5) = 90.72(8)/88.69(9), N(2)–Cd(1)–O(3)/N(2)–Cd(1)–O(1) = 86.54(7)/84.29(9), N(2)–Cd(1)–O(4)/N(2)–Cd(1)–O(2) = 88.95(7)/
95.59(9), N(2)–Cd(1)–O(5)/N(2)–Cd(1)–O(3) = 87.44(7)/86.89(9), N(2)–Cd(1)–O(6)/N(2)–Cd(1)–O(4) = 100.74(7)/91.4(1), N(2)–Cd(1)–O(7)/N(2)–Cd(1)–O(5) = 91.90(8)/
87.2(1), N(1)–Cd(1)–N(2) = 175.89(7)/175.86(9), O(3)–Cd(1)–O(7)/O(1)–Cd(1)–O(5) = 86.36(8)/84.29(9), O(6)–Cd(1)–O(7)/O(4)–Cd(1)–O(5) = 81.33(8)/83.76(9),
O(4)–Cd(1)–O(5)/O(2)–Cd(1)–O(3) = 86.49(6)/86.42(8).
basicity of L in 7 than that in 8 and greater number of more basic
DMAP in 9ꢀ2H2O. It is to be noted that the coordination mode of the
carbamate in [(N,N)Zn(OC(O)NR2)2] (N,N= tetramethylethylenedi
amine, R = Et [28] and N,N = (1,1,3,3-tetramethylguanidine)2,
R = iBu [29]) is chelating in the former complex and monodentate
in the latter, primarily due to higher basicity of the guanidine in
the latter complex. In the crystal lattice of 6–8, intermolecular
C–HꢀꢀꢀO and O–HꢀꢀꢀO hydrogen bonds result in the formation of
sheets in various planes (Figs. S19–S24, Supplementary material).
Two water molecules are present per cadmium in the crystal
lattice of 9ꢀ2H2O as solvent of crystallisation and form a cyclic tet-
ramer through an intermolecular O–HꢀꢀꢀO hydrogen bond with the
crystallographically related adjacent water molecules and this tet-
ramer is further connected to four oxygen atoms of four acetates
and four hydrogen atoms of four DMAP through O–HꢀꢀꢀO and
C–HꢀꢀꢀO hydrogen bonds, respectively (Figs. S25 and S26,
Supplementary material). An analogous water tetramer formed
through O–HꢀꢀꢀO hydrogen bond was also observed in the crystal
lattice of [Cd(OAc)2(2-aminobenzimidazole)2]ꢀ3H2O [30].
Cd(OAc)2ꢀ2H2O is a 1D CP wherein the cadmium atom is seven
coordinated and is surrounded by one j2 chelating and one
tridentate chelating bridging (l2- :j
j2 1) acetate moieties and two
water molecules [13]. The differences in Cd–O distances of two
acetate moieties in unit 2 of 6 are significantly smaller than the
corresponding difference of 0.242(4) Å observed for the j2 chelat-
ing acetate moiety in Cd(OAc)2ꢀ2H2O. Moreover, Cd–O distances of
2.206(4) and 2.218(4) Å associated with two water molecules in
unit 2 of 6 are significantly shorter than the corresponding dis-
tances of 2.325(4), and 2.299(3) Å observed in Cd(OAc)2ꢀ2H2O.
The differences in bond parameters between unit 2 of 6 and
Cd(OAc)2ꢀ2H2O reflect the type of constraints imposed on these
units by acetate coordination mode, coordination number and
geometry of the cadmium, and intermolecular packing forces. To
the best of our knowledge, 6 represents the first crystallographi-
cally characterised bimolecular cadmium(II) complex containing
two different neutral cadmium(II) coordination species per for-
mula unit to be reported in the literature.
The cadmium atom in unit 2 of 6 is surrounded by two j2
chelating acetate moieties and two water molecules and revealed
3.3. 13C{1H} and 113Cd NMR Spectroscopy
a distorted trigonal prismatic geometry. The unit 2 in 6 is isostruc-
The CPs/complexes prepared in the present investigation
revealed simpler 1H and 13C{1H} NMR patterns in solution than
one would anticipate based on their solid-state structures. This
anomalous behaviour is ascribed to sample dissociation [13] and
proclivity of the acetate moiety to undergo a low energy ‘carboxy-
late shift’ process [32] in solution. The solid state Cross Polarisation
i
tural with [Cd(
j
2-OC(O)R)2(H2O)2] (R = CH2 Pr [31a] and
(CH2)4(CH(CH2)2S2) [31b]). However, the coordination mode of
acetate is asymmetrical in unit 2 of 6 ( d(Cd-O(acetate)) = 0.081(4)
and 0.053(4) Å) while it is symmetrical in the latter two
complexes ( d(Cd-O(acetate)) = 0.0(0) and 0.006(4) Å, respectively).
D
D

P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
247
Table 1
d(13C) values of the carbonyl carbon of the acetate moieties in 1–8 and 9ꢀ2H2O
obtained from solid state CP-MAS 13C{1H} NMR spectroscopy, acetate coordination
mode and number of anticipated OC(O) carbon signals.
CP/Complex d(13C) Acetate coordination mode Number of anticipated
OC(O) carbon signals
1
179
179.8
Chelating bridging
Chelating bridging or
bidentate bridging
Bidentate bridging
4a
182.8
2
3
177.1
180.2
Chelating bridging
Bidentate bridging
4a
4a
178
179.4
Chelating bridging
Chelating bridging or
bidentate bridging
Bidentate bridging
180
4
179.7
181.2
182.3
183.8
Monoatomic bridging
Chelating bridging or
Tridentate bridging
6
5
178.6
179
Monodentate
Chelating
2b
2c
6 (unit 1)
179.8
Chelating
6 (unit 2)
7
8
182.8
179.5
177.7
178.8
Chelating
Chelating
Chelating
Chelating
2
2c
2c
9ꢀ2H2O
176.8
Chelating
1d
a Due to the presence of two chemically identical but crystallographically distinct
cadmium (4O, 2N) atoms.
b Due to the presence of two molecules in an asymmetric unit in the crystal lattice.
c Due to the presence of two chemically identical but crystallographically distinct
acetates.
Fig. 9. The ORTEP representation of 9ꢀ2H2O at the 50% probability level.
Water molecule and hydrogen atoms are removed for clarity. Selected bond
distances and angles (Å and deg): Cd(1)–O(1) = 2.591(3), Cd(1)–O(2) = 2.360(3),
Cd(1)–N(1) = 2.333(3), Cd(1)–N(3) = 2.324(4), N(1)–Cd(1)–O(1) = 89.7(1)/90.3(1),
N(1)–Cd(1)–O(2) = 89.8(1)/91.1(1), N(1)–Cd(1)–N(3) = 89.41(8), N(1)–Cd(1)–N(1) = 178.8(2),
O(1)–Cd(1)–N(3) = 86.25(6).
d Both acetates are chemically as well as crystallographically identical.
i. The 113Cd nucleus surrounded by oxygen ligands is the most
shielded, that surrounded by nitrogen ligands is intermedi-
ate and that surrounded by sulphur ligands is the least
shielded [6b,22,36,37].
ii. In cadmium complexes containing 4-substituted pyridines
and 4,5,7-substituted 1,l0-phenanthrolines as L, d(113Cd)
shielding decreases upon increase in pKa value of the L [38].
iii. d(113Cd) shielding increases with increase in the coordina-
tion number of the cadmium atom [5,6,36a,b,38–40].
Magic Angle Spinning (CP-MAS) 13C{1H} NMR spectroscopy is an
important tool to identify the chemically and sometimes even
crystallographically distinct carboxylate moieties in metal car-
boxylate complexes as the sample remains intact during NMR
acquisition [13,15b,33–35]. Moreover, one can qualitatively assign
the coordination modes of the carboxylate moiety from the chem-
ical shift range that the carbonyl carbon of a metal carboxylate cov-
ers in its 13C{1H} NMR spectrum. The deshielding of d(13C) of the
carbonyl carbon of metal acetate complexes decreases in the order
shown below: bidentate chelating > bidentate bridging > monoa-
tomic bridging > monodentate [13,33b,34,35].
The d(113Cd) values and their assignment to a particular type of
cadmium nucleus in the CPs/complexes reported in this manu-
script are listed in Table
2
(see also Figs. S52–S60,
Using the aforementioned empirical trend, the d(13C) values of
the carbonyl carbon and the associated coordination mode of the
acetate moiety in 1–8 and 9ꢀ2H2O are listed in Table 1 (see also
Figs. S27–S51, Supplementary material). The number of signals
for the carbonyl carbon of the acetate moieties in the
CPs/complexes except for unit 1 of 6, 8 and 9ꢀ2H2O is less than
anticipated and this is ascribed to the overlapping peaks. This
argument gains support from the fact that four d(13C) signals
were observed for CH3 carbon of the acetate moiety in 2 (see
Section 2).
Supplementary material). An increase in shielding with increase
in the number of oxygen atoms and decrease in shielding with
increase in the number of nitrogen atoms for the cadmium having
identical coordination number (i.e. trend i) is followed well in 1–3
as the cadmium nucleus with 6O environment is more shielded
than that with 4O, 2N environment. The d(113Cd) values of 1 and
2 also follow the basicity trend associated with L but those of 3
do not (see empirical trend ii). The differences in bond parameters
around cadmium atoms and intermolecular interactions in the
crystal lattice in 1 and 2 on one hand and those in 3 on the other
are believed to cause the observed anomaly (see Figs. S1–S4,
Supplementary material). Ramamoorthy and co-workers invoked
hydrogen bond interactions in the solid state as one of the possible
reasons for the observed difference between calculated d(113Cd)
values and experimentally measured d(113Cd) values of inorganic
complexes [41].
113Cd NMR spectroscopy is an important technique to under-
stand the structure-chemical shift correlation of cadmium(II) com-
plexes due to the favourable magnetic properties of 113Cd nucleus
and the fact that this nucleus covers a wide chemical shift range of
about 1000 ppm [5]. The following empirical shift trends have
been identified for the cadmium nucleus surrounded by oxygen,
sulphur and nitrogen donors in cadmium complexes reported in
the literature.
The d(113Cd) values observed for 5 are more shielded than those
observed for the cadmium atom possessing 4O, 2N environment in

248
P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
1–3. This difference is attributed to the combination of the follow-
ing factors. (i) The cadmium atom in 1–3 is surrounded by two
types of oxygen atoms that arise out of tridentate chelating bridg-
observed for the analogous cadmium present in 7 (d(113Cd) ꢁ8.2)
and 8 (d(113Cd) ꢁ6.9) and this difference is attributed to the differ-
ence in bond parameters around the cadmium and the presence of
two chemically distinct species and intermolecular forces between
these species in an asymmetric unit in the crystal lattice of the for-
mer. It is to be noted that d(113Cd) ꢁ13.0 value for unit 2 of 6
wherein the cadmium possesses 6O environment is more
deshielded than that reported for Cd(OAc)2ꢀ2H2O (d(113Cd) ꢁ58.0
[6a] and ꢁ51.6 [42]) wherein the cadmium possesses 7O environ-
ment which is in line with the empirical trend iii mentioned previ-
ously. It is to be noted that even a difference of 10 ppm in the
d(113Cd) values of two compounds oddly causes only 1% error given
the fact that d(113Cd) covers a wide range of about 1000 ppm [5].
The d(113Cd) values observed for 7 and 8 compare well with that
reported for the related 1D CP [Cd(j2-OAc)2L2(H2O)] (L = 4,40-
bipyridylethylene; d(113Cd) 58.3 with solid Cd(OAc)2ꢀ2H2O as
ing (l2
that in 5 is surrounded by two types of oxygen atoms that arise
out of monodentate (
1) acetate and water. The orientation of lone
- :j - :j
j2 1) and bidentate bridging (l2 j1 1) acetates while
j
pairs on the oxygen atoms bound to the cadmium in 1–3 is thus
different from that in 5 and this could cause a difference in
d(113Cd) values [6b], (ii) The cadmium atom is part of two six-
membered rings in 1–3 which likely induces deshielding [38,39],
and (iii) The difference in the pKa value of L [38]. It appears that
factors i and ii have a greater influence upon d(113Cd) values than
factor iii because shielding decreases upon going from 1 to 2 as
anticipated but later it increases in 3.
The d(113Cd) 34.6 value observed for unit 1 of 6 wherein the
cadmium possesses 5O, 2N environment is deshielded than that
O
O
O
H2O
L
Cd
L
H2O
O
H2O
O
L
Cd
L
O
O
O
O
Cd
O
H2O
Cd
Cd
S
O
S
O
H2O
S
O
OH2
OH2
OH2
OH2
OH2
O
O
O
S
O
O
O
S
O
A
E
A
E
A
−10 H2O, −5 S
O
O
O
L
O
O
L
O
O
O
O
O
O
Cd
O
Cd
Cd
Cd
Cd
O
O
O
O
O
O
L
O
O
L
O
O
1−3
Scheme 2. Self-Assembly process leading to the formation of CPs 1–3.
O
H2O
L
L
O
O
O
O
O
O
O
O
O
Cd
S
H2O
OH2
S
d
Cd
S
C
S
S
S
OH2
OH2
O
O
OH2
OH2
O
OH2
OH2
S
S
O
Cd
L
S
Cd
O
O
O
O
L
D
D
A
D
D
−10 H2O, −9 S
L
L
O
O
O
O
O
O
Cd
O
Cd
O
Cd
O
O
O
O
O
O
O
O
O
O
O
Cd
L
O
Cd
L
O
4
Scheme 3. Self-Assembly process leading to the formation of 4.

P. Saxena, N. Thirupathi / Polyhedron 98 (2015) 238–250
249
Table 2
functionalities in the pzc intermediates. Complex 5 may be consid-
ered as a desolvated version of E while the bimolecular complex 6
may be considered as an equilibrating mixture of desolvated A, and
B. Complexes 7 and 8 represent pzc intermediate B and 9ꢀ2H2O
represents dihydrated pzc intermediate C.
It is remarkable that the bimolecular complex 6 is the sole pro-
duct of the reaction of Cd(OAc)2ꢀ2H2O with one or two equiv. of 4-
picoline and this complex upon reflux in methanol even after two
days did not transform into any new product. This observation sug-
gests that complex 6 is stabilised so effectively through inter-
molecular forces in the solid state, that even forcing condition
such as the aforementioned one does not lead to the formation
of any new product. The fact that 9ꢀ2H2O is the sole product irre-
spective of employing one, two or three equivalent of DMAP per
cadmium suggests that the course the reaction is mainly driven
by high nucleophilicity in conjunction with high basicity of DMAP.
Solid state CP-MAS d (113Cd) values (66.6 MHz) for 1–8 and 9ꢀ2H2O.a
CP/Complex
d (113Cd)
1
2
3
4
5
6
7
8
15.8 (4O, 2N), ꢁ19.9 (br, 6O)
21.6 (4O, 2N), ꢁ14.1 (br, 6O)
2.7 (4O, 2N), ꢁ23.8 (br, 6O)
ꢁ7.8 (5O, 1N), ꢁ55.2 (7O)
ꢁ55.7, ꢁ54.2 (4O, 2N)b
34.6 (5O, 2N), ꢁ13.0 (6O)
ꢁ8.2 (5O, 2N)
ꢁ6.9 (5O, 2N)
9ꢀ2H2O
69.4 (4O, 3N)
a d(113Cd) values are externally referenced to solid Cd(ClO4)2ꢀxH2O.
b The two d(113Cd) values observed are ascribed to the presence of two crystal-
lographically distinct molecules in an asymmetric unit in the crystal lattice.
external standard [4c]). The d(113Cd) 69.4 value observed for
9ꢀ2H2O is more deshielded than that observed for 7 and 8 and
this difference is in accordance with empirical trends i and ii.
4. Conclusions
The reactions of Cd(OAc)2ꢀ2H2O with pyridine and substituted
3.3. Thermal studies
pyridines in methanol at ambient temperature allowed us to iso-
late
a series of products with distinct structures/nuclearity.
CPs/complexes were subjected to TGA/DTA analyses to under-
stand their mode of decomposition. The TGA/DTA thermograms
are illustrated in Figs. S61–S67 in the Supplementary material.
The mode of decomposition of each complex determined from
the weight loss in TGA pattern is outlined in Fig. S68 in the
Supplementary material. Decarboxylation is one of the pathways
of decomposition of metal carboxylates [43,44] and all complexes
Plausible mechanisms of formation of new CPs and complexes
were discussed with the aid of a pzc model. The product formation
was found to be independent of the Cd:L ratio in all reactions
except in those that involve 3,4-lutidine. The basicity, nucleophilic-
ity and substitution pattern of the Lewis base appear to be critical
factors in determining the nature of pzc species and hence struc-
ture/nuclearity of the products. The frameworks present in CPs
1–4 and the presence of two distinct units together in the crystal
lattice of 6 are unprecedented in the literature. The solid state
CP-MAS 13C{1H} NMR and 113Cd NMR techniques were used to
identify the coordination modes of the acetate and coordination
environment around the cadmium atom, respectively in the prod-
ucts. The outcome of the present investigation is anticipated to be
useful to those who work in the field of carboxylate based metal
complexes/CPs and metal organic frameworks (MOFs).
except
4
undergo decarboxylation in at least one step.
Decarbonylation is also observed during the thermolysis events
of 4, 8 and 9ꢀ2H2O. The TGA weight loss pattern of 1–3 is identical
with the successive loss of L, CO2 and ethane. Metallic cadmium
was the end product in the thermolyses of 1–3 and 5–7. On the
other hand, 4 decomposed to cadmium(II) methoxide while 8
and 9ꢀ2H2O decomposed to CdO. As a representative example,
9ꢀ2H2O was calcined at 500 °C for 4 h under N2 atmosphere to con-
firm the formation of CdO as the end product in the thermolysis
event. The brown coloured end product obtained from calcination
experiment was confirmed as CdO through PXRD pattern (Fig. S69,
Supplementary material). All the peaks in the pattern can be
indexed to a pure cubic phase (space group Fm3m, No. 225) of
CdO (JCPDS 65–2908). The morphology and size of the CdO were
observed through scanning electron microscopy (SEM), which
Acknowledgements
N.T. and P.S. acknowledge University of Delhi, Delhi and Council
of Scientific and Industrial Research for research grant and fellow-
ship, respectively. We acknowledge (i) University Science
Instrumentation Centre, University of Delhi, Delhi for instrumental
facilities, (ii) Jeol NMR Ltd., Tokyo, Japan for solid state CP-MAS
13C{1H} NMR spectra of 1, 2, and 4–7, (iii) NMR Research Centre,
Indian Institute of Science, Bangalore for solid state CP-MAS
13C{1H} NMR spectra for 8 and 9ꢀ2H2O and solid state CP-MAS
113Cd NMR spectra of all complexes.
revealed the presence of pyramidal particles of
Supplementary material).
lm size (Fig. S70,
3.4. Mechanistic aspects
A plausible mechanism of formation of 1–8 and 9ꢀ2H2O is sug-
gested based on a point zero charge (pzc) model proposed by
Ramanan and Whittingham for the formation of MOFs and CPs
from the metal salt and organic ligands [17]. Cd(OAc)2ꢀ2H2O upon
dissolution in methanol disassembles leading to the formation of
pzc intermediate A as shown in Scheme S1 in the Supplementary
material. The pzc species A transforms either to pzc species C via
pzc species B or pzc species E via pzc species D depending upon
the basic, nucleophilic properties, and substitution pattern of L.
CPs, 1–3 are formed through a reassembly process involving pzc
intermediates A and E through the formation of Aꢀ ꢀ ꢀEꢀ ꢀ ꢀAꢀ ꢀ ꢀEꢀ ꢀ ꢀA
ensemble as shown in Scheme 2. Analogously, the CP 4 is formed
through a reassembly process involving pzc intermediates A and
D through the formation of Dꢀ ꢀ ꢀDꢀ ꢀ ꢀAꢀ ꢀ ꢀDꢀ ꢀ ꢀD ensemble as shown
in Scheme 3. The driving force for the formation of the aforemen-
tioned ensembles is believed to be steric and electronic comple-
mentarity between hydrogen bond donor and acceptor
Appendix A. Supplementary data
CCDC 1010758–1010766 contain the supplementary crystallo-
graphic data for 1–9ꢀ2H2O. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or e-mail:
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.2015.06.002.
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