Preparation, Characterization, Thermal Degradation, and Crystal Structures of Hydrazinium and Ammonium Salts of Ethylenediaminetetraacetic Acid and Seven Coordinated N2H5[Cd(Hedta)(H2O)].H2O

Article abstract of DOI:10.1080/15533174.2013.862654

Dihydrazinium, hydrazinium, hydrazinium ammonium, and ammonium salts of ethylenediaminetetraacetic acid (H₄edta) such as (N₂H₅)₂H₂edta, N₂H₆H₂edta, N₂H₅NH₄H₂edta and (NH₄)₂H₂edta have been prepared and characterized by elemental analyses, hydrazine analysis, conductivity measurements, and infrared spectra. The thermal degradation studies reveal that these compounds undergo complete and multi step decomposition with or without melting. The IR spectra show that in all the cases the acidic protons are attached to the tertiary nitrogen atoms of edta and all the salts exist as zwitterions. The X-ray single-crystal data and the corresponding ORTEP diagram of the dihydrazinium and hydrazonium salts clearly support and confirm the data. Hydrazinium hydrogenethylenediaminetetraacetato aquo cadmium(II) monohydrate, N₂H₅[Cd(Hedta)(H₂O)].H₂O, has been synthesized and structurally characterized. The crystal belongs to orthorhombic crystal system and the space group Pbca. The crystal data are the following: a = 9.423 ?, b = 4.406 ?, c = 23.838 ?, α = β = γ = 90°, V = 3236 ?³, Z = 8, D_c = 1.932 Mg/m³, μ = 1.412 mm^-1, F(000) = 1904, the final R = 0.0190, and wR = 0.0562 for 3707 observed reflection with I>2σ(I).

Full text of DOI:10.1080/15533174.2013.862654

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2015) 45, 1069–1079
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.862654
Preparation, Characterization, Thermal Degradation,
and Crystal Structures of Hydrazinium and Ammonium Salts
of Ethylenediaminetetraacetic Acid and Seven Coordinated
N2H5[Cd(Hedta)(H2O)].H2O
R. RAGUL, L. VIKRAM and B. N. SIVASANKAR
Department of Chemistry, Government Arts College, Udhagamandalam, The Nilgiris, Tamilnadu, India
Received 31 July 2013; accepted 2 November 2013
Dihydrazinium, hydrazinium, hydrazinium ammonium, and ammonium salts of ethylenediaminetetraacetic acid (H4edta) such as
(N2H5)2H2edta, N2H6H2edta, N2H5NH4H2edta and (NH4)2H2edta have been prepared and characterized by elemental analyses,
hydrazine analysis, conductivity measurements, and infrared spectra. The thermal degradation studies reveal that these compounds
undergo complete and multi step decomposition with or without melting. The IR spectra show that in all the cases the acidic protons
are attached to the tertiary nitrogen atoms of edta and all the salts exist as zwitterions. The X-ray single-crystal data and the
corresponding ORTEP diagram of the dihydrazinium and hydrazonium salts clearly support and confirm the data. Hydrazinium
hydrogenethylenediaminetetraacetato aquo cadmium(II) monohydrate, N2H5[Cd(Hedta)(H2O)].H2O, has been synthesized and
structurally characterized. The crystal belongs to orthorhombic crystal system and the space group Pbca. The crystal data are the
ꢀ
ꢀ
ꢀ
ꢀ
following: a D 9.423 A, b D 4.406 A, c D 23.838 A, a D b D g D 90ꢀ, V D 3236 A3, Z D 8, Dc D 1.932 Mg/m3, m D 1.412 mm¡1
,
F(000) D 1904, the final R D 0.0190, and wR D 0.0562 for 3707 observed reflection with I›2s(I).
Keywords: hydrazinium, hydrazonium, ammonium, ethylenediaminetetraacetic acid, X-ray single crystal
Introduction
H4edta and its homologues are neutral acids and are
known as complexones. They are also weak acids and there-
Ethylenediaminetetraacetic acid (H4edta) is a versatile amino fore dissociate one or more protons in aqueous solution,
polycarboxylic acid, which as the ability to form salts with depending on the pH of the solution. The pKa values of
both stronger and weaker bases.[1] When acidic protons of H4edta are 1.99, 2.67, 6.61, and 10.26 for the four protons,
H4edta are replaced by alkali metal ions such as sodium and which clearly indicates that two of the four protons with
potassium, usually gives di-, tri-, and tetrasubstituted salts. lower pKa values can be easily replaced with even a weak
The type of salts formed depends on the extent of neutraliza- base while a strong base can replace all the protons. Though
tion with the respective bases. However, when neutralized it is not surprising that many alkali metals form salts with
with weaker base such as ammonia, H4edta forms only dia- H4edta, even a weaker base such as ammonia forms diammo-
mmonium salt. These salts are highly soluble in water and nium salt.
gives respective deprotonated acids like H2edta2¡, Hedta3¡
or edta4¡, which depends on the type of such salts.
Hydrazine is a weaker base, weaker than ammonia, and is
also capable of replacing two of the four protons from the
The mono-, di-, or deprotonated ion of H4edta are find H4edta and hence capable of forming mono- and dihydrazi-
applications in several areas and are the best candidates for nium salts with hydrazine. Hydrazine though has two nitro-
removing excess metal ions present in the human body as gen atoms with lone pairs, generally it was observed that only
water soluble complexes. Almost all the metal ions form che- one lone pair was used during the salt formation and the
lates with the above and (Hnedta)(4–n)¡ ions.
other lone pair is available over the second nitrogen atom,
which is exploited for coordination of hydrazinium cation
with several metal ions in the presence of anions such as fluo-
ride, chloride, thiocyanates, sulfite, and simple and substi-
tuted carboxylates and dicarboxylates. Hydrazinium salts of
inorganic anions[2,3] and some aliphatic and aromatic carbox-
ylic acids[4–8] have been reported in the literature. The spec-
tral and thermal properties of the above salts were
Address correspondence to B. N. Sivasankar, Department of
Chemistry, Government Arts College, Udhagamandalam, The
Nilgiris, Tamilnadu, India. E-mail: sivabickol@yahoo.com
Color versions of one or more of the figures in the article can be
found online at www.tandfonline.com/lsrt.

1070
Ragul et al.
C
investigated in detail. Though several hydrazinium (N2H5
)
were recorded on a STA 1500 thermal analyzer using about
salts are known to the literature, only a few hydrazonium 3 mg of the samples with the heating rate of 10ꢀC per min
(N2H62C) salts such as hydrazonium nitrate, sulfate,[9] chlo- and the platinum cups as sample holders. X-ray intensity
ride, fluoride,[10] and perchlorate[11] have been reported so data were collected on a Kappa-Apex II CCD diffractometer
far. Further, though several hydrazinium salts of simple system wꢀith graphite monochromated Mo-Ka radiation (λ D
mono- and dicarboxylic acids are known these salts of substi- 0.71073 A).
tuted carboxylic acids especially amino poly carboxylic acids
The structure was solved by direct methods using SIR-92
have not been studies so far. The formation of hydrazinium program and completed using Fourier techniques and refined
salts with amino acids is prevented due to their zwitterion applying full-matrix least square techniques. Refinement was
character, which makes the acidic protons not available for carried out using SHELXL-97 program.[19,20]
salt formation especially with the weaker bases. Furthermore,
hydrazonium salts are scarce in the literature and as for as we
are aware of the literature no such salt with any carboxylic
Preparation of (N2H5)2H2edta
acid has been reported so far. The interests in these salts are
The dihydrazinium dihydrogenethylenediaminetetraacetate
due to their utility as ligand in the preparation of hydrazi-
was prepared by adding an aqueous solution of hydrazine
nium metal complexes that are in turn used as precursors for
hydrate (10 mL, 0.2 mol) to an aqueous suspension of
pure metal oxides. Metal(II) chelates with versatile ethylene-
H4edta (29.24 g, 0.1 mol) in 100 mL of distilled water with
stirring. The resulting solution was filtered through a What-
man filter paper and the clear solution after concentration on
a water bath to 50 mL was stood at room temperature. The
colorless crystals formed after 2–3 days were filtered, washed
with 1:1 water-alcohol mixture and dried in air. The crystals
were further purified by recrystallization in distilled water.
diaminetetraacetic acid have been exhaustively investigated
with respect to their infrared spectra and coordination behav-
ior.[1,12] The X-ray structures of few such complexes have
been reported in the literature. A number of metal(II) and
metal(III) edta chelates containing charge neutralizing cati-
ons such as NaC, RbC, KC, and NH4 have been character-
C
ized by IR and XRD studies.[13–17] However, corresponding
metal(II) edta complexes with N2H5 ions are scarce[6] and
C
Preparation of N2H6H2edta
so for X-ray single-crystal analysis they have not been done
with hydrazinium complexes. Hence, in this article we wish
to report the preparation, characterization, and spectral and
thermal studies of hydrazine and ammonium salts of H4edta
and hydrazinium cadmium(II) ethylenediaminetetraacetates
hydrate. The crystal and molecular structure of dihydrazi-
nium and hydrazonium dihydrogen ethylenediaminetetraace-
tates have also have been presented in this paper to prove the
existence of zwitterions in these salts in solid state. Hitherto,
we also report the structure of hither to unknown cadmium
complex, which shows some salient features that are not
observed in any of the metal-edta complexes reported so far.
This rare hydrazonium salt was prepared by adding with stir-
ring an aqueous solution (20 mL) of hydrazine hydrate
(7.5 mL, 0.15 mol) to an aqueous suspension of H4edta
(29.24 g, 0.1 mol) in 100 mL of distilled water. The resulting
solution was heated on a water bath for about two hours to
get the clear solution. This solution was evaporated for con-
centration to 50 mL. The resultant solution was allowed to
crystallize at room temperature to yield the hydrazonium salt.
Preparation of N2H5 NH4 H2edta and (NH4)2H2edta
These salts were prepared by the same method adopted for
the preparation of the dihydrazinium dihydrogenethylenedia-
minetetraacetate using a mixture of hydrazine hydrate
(5 mL, 0.1 mol) and aqueous ammonia (0.1 mol) in the case
of hydrazinium ammonium dihydrogenethylenediaminete-
traacetate and aqueous ammonia (0.2 mol) in the case of dia-
mmonium dihydrogenethylenediaminetetraacetate instead of
hydrazine hydrate.
Experimental
Materials and Methods
The chemicals used are of AR grade and hydrazine hydrate
(99–100%) was used as received from S. D. Fine chemicals.
The solvents were distilled before use. For the preparation
and hydrazine analysis, distilled water was used.
The hydrazine content was determined volumetrically
using a standard KIO3 solution (0.025 mol) under Andrew’s
conditions.[18] The cadmium content was determined by com-
plexometric titrations. A Perkin Elmer CHN analyzer (model
1240) was used for C, H, and N analyses.
All the salts are colorless crystals, stable, nonhygroscopic,
soluble in water, and insoluble in ethyl alcohol. All the salts
were recrystallized from distilled water.
Preparation of N2H5[Cd(Hedta)(H2O)].H2O
The molar conductance of the 0.001 M solutions of the To an aqueous solution (50 mL) of Cd(NO3)2.4H2O (6.16 g,
compounds in conductivity water was measured with a Cen- 0.02 mol), the ligand (14.24 g, 0.04 mol) in water (50 mL)
tury Digital Conductivity meter (model cc 601) and a dip was added slowly with constant stirring. The resultant solution
type cell with a smooth platinum electrode. The infrared was allowed to stand for 2 h. The free H4edta precipitated was
spectra of the solid samples were recorded using KBr pellets filtered and the clear solution was kept at room temperature.
on a Perkin Elmer 597/1650 spectrophotometer in the range Colorless transparent cubical crystals formed after two
4000–500 cm¡1. The simultaneous TG-DTA data of the salts months were collected, filtered, washed with ice-cold water

Hydrazinium and Ammonium Salts
1071
and dried in air. The complex formed was stable, soluble in
water, and insoluble in alcohol.
The results of hydrazine and elemental data are well in
accordance with the calculated values. The molar conductivi-
ties of the salts in aqueous solutions are observed in the range
240–260 Ohm¡1 cm2 mol¡1. This indicates in aqueous solu-
tion these salts behave as 2:1 electrolytes. In the case of
hydrazonium salt, though 1:1 electrolyte nature is expected
Results and Discussion
Hydrazine hydrate in aqueous medium when reacts with
H4edta, neutralization reaction takes place and water soluble
salts are formed in solution. The solution when evaporated to
saturated conditions yielded a colorless crystalline hydrazi-
nium salts. When hydrazine hydrate and H4edta were mixed
in 1:1 ratio, only a portion of the acid dissolved indicating
the possibility of formation of only a dihydrazinium salt.
However, the addition of hydrazine hydrate resulted in a
clear solution, which gave the dihydrazinium salt quantita-
tively. This salt is colorless, crystalline in nature, soluble in
water, and insoluble in alcohol. The composition of the salt
was found to be (N2H5)2H2edta on the basis of the hydrazine
analysis by Andrew’s method and elemental analyses.
2C
due to the instability (second ionization constant of N2H6
ion is 8.9 £ 10¡16), the N2H62C ion in aqueous solution disso-
ciates into N2H5 and HC ions so that it also behaves as 2:1
C
electrolyte. Also due to the higher mobility of the HC ion this
compound shows relatively higher conductance than the
other salts. The conductivity of 0.001 mol of aqueous solu-
tion of this complex in distilled water is 120 Ohm¡1 cm2
mol¡1, which suggests that it is 1:1 type of electrolyte. The
analytical and conductance data of the salts and complex are
summarized in Table 1.
The purity of this salt was further improved by recrystalli-
zation in water. The salt was dissolved in warm water to give
nearly a saturated solution yielded pure colorless needles. In
the present investigation, under controlled and suitable con-
ditions we were able to isolate the hydrazonium dihydrogen
ethylenediaminetetraacetate. H4edta (1 mol) was neutralized
with 1.5 mol of hydrazine hydrate, and undissolved portion
of the acid was dissolved by heating the solution over water
bath for about 2 h. The resulting dilute solution was allowed
to crystallize, which yielded the hydrazonium salt as hexago-
nal crystals. This salt was water soluble and pure.
Further, we are interested in preparing a mixed salt, the
hydrazinium ammonium dihydrogenethylenediaminetetraa-
cetate, by neutralizing H4edta with a mixture of 1 mol of
hydrazine hydrate and 1 mol of ammonia. The resulted solu-
tion after evaporation, crystallization and recrystallization
yielded pure crystals of N2H5NH4H2edta. The corresponding
diammonium dihydrogenethylenediaminetetraacetate was
prepared by neutralizing 1 mol H4edta with two moles of
ammonia. Hydrazinium hydrogenethylenediaminetetraaceta-
toaquocadmium(II) monohydrate has been prepared by the
aqueous reaction between dihydrazinium dihydrogenethyle-
nediaminetetraacetate and cadmium nitrate tetra hydrate in
1:2 molar ratio. The excess H4edta precipitated was removed
and the clear solution left for two months at room tempera-
ture yielded colorless crystals suitable for X-ray crystallo-
graphic studies. The chemical reaction involved may be
represented as follows.
Infrared Spectra
All the salts show three or four bands in the region 2850–
3450 cm¡1 due to the N-H stretching as expected. How-
ever, the region 1680–1720 cm¡1 is important in deciding
the presence or absence of the free carboxylic acid. As
both hydrazine and ammonia are capable of removing
only two protons, the location of other two protons is
quite interesting. The amino acids are known to exist as
zwitterions and the higher pKa values for the third and
fourth protons are attributed to the attachments of two
protons with the tertiary nitrogen’s of H2edta. Hence, no
bands are expected in the region 1680–1720 cm¡1. Indeed
the absence of any bands at the above frequency confirms
the absence of free carboxylic acid.[21] The nasy and nsym
stretching of carboxylate ions observed in the range 1630–
1650 cm¡1 and 13C90–1400 cm¡1, respectively. The N-N
stretching of N2H5 ions are observed at 970 cm¡1 in the
case of dihydrazinium and hydrazinium ammonium salts.
In the case of hydrazonium salt the band at 1000 cm¡1 is
2C
attributed to the N-N stretching of N2H6 ion.[22] Dia-
mmonium salt does not show any band in this region indi-
cating the absence of N-N stretching.
Though based on the infrared spectral studies it is proposed
that the salts are behaving as zwitterions, it is not the conclu-
sive evidence. Fortunately, we were able to obtain a single
crystal of the rare hydrazonium salt suitable for X-ray single-
crystal study and the structure of this salt clearly indicates the
existence of zwitterion in the solid state.
H4edta C 2N2H4:H2O ! ðN2H5Þ2H2edta C 2H2O
H4edta C N2H4:H2O ! N2H6H2edta C H2O
H4edta C NH4OH C N2H4:H2O ! N2H5NH4H2edta C 2H2O
The infrared spectra of Cd complex suggest that the car-
boxylate oxygens are coordinated to cadmium in monoden-
tate fashion and one free carboxylic acid group present in the
H4edta molecule. The nasy and nsym stretchings of COO¡ are
observed at 1640 cm¡1 and 1400 cm¡1 respectively. The car-
H4edta C 2NH4OH ! ðNH4Þ2H2edta C 2H2O
CdðNO3Þ2:xH2O C 2ðN2H5Þ2H2edta
! N2H5½CdðHedtaÞðH2OÞꢁ:H2O
bonyl stretching of free carboxylic acid is seen at 1720 cm¡1
.
In the region, 2900- 3400 cm¡1 number of sharp bands are
observed which are attributed to the N-H and O-H stretching
of hydrazine and water (coordinated and noncoordinated)
C H4edta C 2N2H5NO3 C N2H4

1072

Hydrazinium and Ammonium Salts
1073
Fig. 1. Simultaneous TG-DTA-DTG of N2H6H2edta.
respectively. The O-H stretching of COOH group is also seen shows a broad endotherm in the temperature range 130–
in this region.[17,22]
160ꢀC for the loss of hydrazine molecule. Then the acid
undergoes decomposition in the wide temperature range
160–600ꢀC. The DTA shows a broad exotherm corre-
sponding to this degradation.
Thermal Decomposition
(N2H5)2H2edta
From this salts one hydrazine molecule is eliminated in the
temperature range 145–200ꢀC. Further, this hydrazinium
edta undergo decomposition by losing another molecule in
the higher temperatures. Then the acid formed as an interme-
diate decomposes continuously up to 580ꢀC leaving no resi-
NH4N2H5H2edta
This salt melts at 103ꢀC followed by the loss of one molecule
of ammonia in the temperature range 130–160ꢀC. Further
heating results in the loss of one molecule of hydrazine in the
temperature range 160–180ꢀC. Then the ethylenediaminete-
traacetic acid formed as an intermediate undergoes continu-
ous decomposition in the temperature range 180–625ꢀC
without leaving any residue. TG shows 100% weight loss
due. The DTA shows
decomposition of the acid.
a
broad exotherm for the
N2H6H2edta
This salt initially melts at 102ꢀC then loses a hydrazine expected. The DTA shows two exotherms for the loss of
molecule in the temperature range 120–160ꢀC. The DTA ammonia and hydrazine at 120 and 160ꢀC. Then the broad
Fig. 2. Simultaneous TG-DTA-DTG of (NH4)2H2edta.

1074
Ragul et al.
Fig. 3. Simultaneous TG-DTA of N2H5[Cd(Hedta)(H2O)].H2O.
exotherm indicates the slow and continuous decomposition of range 200–600ꢀC. The DTA shows a broad exotherm with
the intermediate.
the maximum at 560ꢀC corresponding to this degradation.
The simultaneous TG-DTA traces of hydrazonium and
diammonium salts are shown in Figures 1 and 2, respectively.
(NH4)2H2edta
This salt melts at 98ꢀC, which is shown by an endotherm in
N2H5[Cd(Hedta)(H2O)].H2O
DTA. TG does not show any weight loss and DTG is flat The complex undergoes multistep degradation when sub-
indicating no change in weight. After melting this salt loses jected to TG analysis. This decomposition involves dehydra-
two molecules of ammonia in the temperature range 180– tion and dehydrazination followed by ligand pyrolysis to
210ꢀC. Then the ethylenediaminetetraacetic acid undergoes yield the fine CdO as the end residue at 520ꢀC (Figure 3).
continues and complete decomposition in the temperature The formation of CdO is confirmed by the X-ray powder
Fig. 4. ORTEP diagram of (N2H5)2H2edta.

1075

1076
Ragul et al.
diffraction pattern of the residue. The particle size of the
The ORTEP diagram for this salt is given in Figure 5. The
oxide was calculated by the Scherrer equation and found to structure clearly indicates it has a C2 axis of symmetry and
be 31 nm .
this salt crystallizes as triclinic system with P1 space group.
The crystal density observed (Table 2) from X-ray single
crystal study is 1.573 mg/m3, which is close to that deter-
mined experimentally (1.567 mg/m3). Figure 6 reflects that
when the molecule H2edta2¡ molecule is cut in to two equal
halves by a plane passing perpendicular to the C-C bond, the
one half is found to be exactly trans to the other. All the
atoms in the first half are exactly trans to the second half.
Structure Determination
Structure of (N2H5)2H2edta
The ORTEP diagram of this salt is given in Figure 4. This
salt crystallizes as triclinic system with P1 space group. The
crystal density observed from X-ray studies is 1.568 mg/m3,
which is very close to that determined experimental value,
1.564 mg/m3
The number of molecule per unit cell is 1. The X-ray crys-
tal data of this salt is given in Table 2 and the bond lengths
and bond angles for this salt are given in Tables 3 and 4,
respectively.
The crystal structure of this salt shows that it consists of
three discrete ions such as two hydrazinium ions and an
anion. The anion has a C2 axis of symmetry and the axis pass-
ing through C-C bond of ethylenic carbon atoms cuts the
anion into two equal halves, and one half is exactly trans to
the other. The tertiary nitrogen atoms of edta4– are proton-
ated and the salt behaves as zwitterion.
The salt consists of discrete N2H6 ions and H2edta2¡
2C
ions, which are in close packing arrangement held together
by hydrogen bonds.
An interesting result observed from the X-ray single-
crystal analysis is that though with amino carboxylic acids,
the formation of zwitterions have been observed in solution
such zwitterions in solid state have not been isolated. Inter-
estingly, in the present case the crystal structures clearly
show that all the four carboxylic acid protons have been
removed and two combined with two nitrogen atoms of
the hydrazine and the other two surprisingly attached to
the two nitrogen atoms of ethylenediamine chain. Hence,
from the structure the formation of the zwitterion in solid
state has been established.
The X-ray crystal data of this salt are given in Table 2 and
the bond lengths and bond angles for this salt are given in
Structure of N2H6H2edta
2C
Table 3 and 4, respectively. The N-N bond length in N2H6
This compound is a special hydrazonium salt with a diamino-
tetracarboxylic acid, which is a first report in carboxylic and
substituted carboxylic acids known despite a few of hydrazo-
nium salts have been reported and characterized.
ꢀ
iꢀon is 1.436(2) A. In hydrazine the N-N bond length is 1.47
A, in free hydrazinium cation the N-N bond length is 1.419
ꢀ
ꢀ
(8) A and in coordinated N2H5C ion it is 1.456(2) A. Though
ꢀ
Table 3. Bond lengths (A)
(N2H5)2H2edta
N2H6H2edta
N2H5 [Cd(Hedta)(H2O)].H2O
C1O1
C1C2
C2H2A
C3N1
C3H3
C4N1
C4H4A
C5O3
N1H1N
N2H1
N2H1A
N4H2D
C1O2
1.2417(9)
1.513(9)
0.9700
1.5004(8)
0.971(12)
1.4915(8)
0.9700
1.2366(9)
0.901(12)
0.896(15)
0.882(15)
0.887(18)
1.2535(10)
1.5000(8)
0.9700
1.5229(12)
0.958(13)
1.5254(9)
0.9700
C1O1
C1C2
C2H2A
N3C6
N3H3
C4H4A
C5O4
C6C6
C6H6B
N1AH1A1
N1AH1A3
N2AH2A2
C1O2
C2N3
C2H2B
N3C4
C4C5
C4H4B
C5O3
C6H6A
N1AN2A
N1AH1A2
N2AH2A1
N2AH2A3
1.238(2)
1.524(2)
0.9700
1.500(2)
0.9100
Cd1-O14b
Cd1-O14b
Cd1-O12b
Cd1-O24b
Cd1-O22b
Cd1-N1
2.294(2)
2.294(2)
2.343(2)
2.350(2)
2.577(2)
2.392(2)
2.407(2)
0.9700
1.243(2)
1.527(3)
0.9700
0.8900
0.8900
Cd1-N2
0.8900
1.264(2)
1.498(2)
0.9700
1.502(2)
1.522(2)
0.9700
1.252(2)
0.9700
1.436(2)
0.8900
C2N1
C2H2B
C3C32
C3H3B
C4C5
C4H4B
C5O4
N2N4
N2H1B
N4N2
N4H2F
1.2651(9)
1.4377
0.894(16)
1.4377(10)
0.83(2)
0.8900
0.8900

Hydrazinium and Ammonium Salts
1077
Table 4. Bond angles (ꢀ)
(N2H5)2H2edta
N2H6H2edta
O1 C1 O2
O2 C1 C2
N3 C2 H2A
N3 C2 H2B
H2A C2 H2B
C2 N3 C4
C2 N3 H3
C4 N3 H3
N3 C4 H4A
N3 C4 H4B
H4A C4 H4B
O4 C5 C4
N3 C6 C6
C6 C6 H6A
C6 C6 H6B
N2A N1A H1A1
H1A1 N1A H1A2
H1A1 N1A H1A3
N1A N2A H2A1
H2A1 N2A H2A2
H2A1 N2A H2A3
127.58(15)
117.11(14)
109.3
109.3
107.9
112.24(13)
105.9
105.9
109.2
109.2
O1 C1 C2
N3 C2 C1
C1 C2 H2A
C1 C2 H2B
C2 N3 C6
C6 N3 C4
C6 N3 H3
N3 C4 C5
C5 C4 H4A
C5 C4 H4B
O4 C5 O3
O3 C5 C4
N3 C6 H6A
N3 C6 H6B
H6A C6 H6B
115.31(15)
111.68(13)
109.3
109.3
113.01(13)
113.18(12)
105.9
111.92(13)
109.2
109.2
107.9
126.57(16)
117.59(14)
109.2
109.2
107.9
109.5
109.5
109.5
109.5
115.82(16)
111.85(16).2
109.22
109.22
109.5
109.5
109.5
109.5
109.5
N2A N1A H1A2
N2A N1A H1A3
H1A2 N1A H1A3
N1A N2A H2A2
N1A N2A H2A3
H2A2 N2A H2A3
109.5
109.5
109.5
N2H5 [Cd(Hedta)(H2O)].H2O
O14b Cd1 O1w
O1w Cd1 O12b
O1w Cd1 O24b
O14b Cd1 N1
O12b Cd1 N1
O14b Cd1 N2
O12b Cd1 N2
N1 Cd1 N2
O1w Cd1 O22b
O24b Cd1 O22b
N2 Cd1 O22b
Cd1 O1w H2w
C13 N1 Cd1
78.46(8)
O14b Cd1 O12b
O14b Cd1 O24b
O12b Cd1 O24b
O1w Cd1 N1
O24b Cd1 N1
O1w Cd1 N2
O24b Cd1 N2
O14b Cd1 O22b
O12b Cd1 O22b
N1 Cd1 O22b
Cd1 O1w H1w
C11 N1 Cd1
110.02(8)
81.37(8)
C21 N2 Cd1
C23 N2 Cd1
C2 N2 Cd1
107.71(16)
109.71(17)
106.24(16)
95.06(8)
95.29(8)
71.19(8)
71.77(8)
129.30(8)
94.98(8)
76.38(8)
81.57(7)
94.37(8)
66.96(7)
115(2)
165.97(9)
139.50(8)
105.72(9)
143.97(8)
71.13(8)
159.07(8)
77.81(7)
129.39(7)
111(2)
105.28(17)
108.24(16)
115.99(19)
107.54(17)
116.54(18)
C1 N1 Cd1
C14 O14b Cd1
C12 O12b Cd1
hydrazine is an unsymmetrical molecule the repulsion
When this N2H5C ion is coordinated the lone pair over one
between two lone pairs is the cause for the higher bond length nitrogen is discharged towards the metal ion, which weakens
C
than that of all the other entities such as N2H5 (noncoordi- the N-N bond hence the bond length increases when com-
C
2C
nated), N2H5 (coordinated) or N2H6 ion. The N-N bond pared to the noncoordinated ion.
lengths are given below in the decreasing order as follows:
2C
The N2H6 ion, since the lone pair repulsion have been
completely removed one would expect the N-N bondClength
in range of that observed with non-coordinated N2H5 ions.
However, the slightly higher bond length could be attributed
to the repulsion between the positive charges over two nitro-
C
C
2C
Compound/ion N2H4 N2H5
N2N5
N2H5
(Coorodinated) ꢀ (Non-coordinated)
N-N bond length 1.47 A 1.456(2)A 1.419(8)A 1.436(2)
ꢀ
ꢀ
gen atoms, which is absent in N2H5C ion.
2C
Furthermore, when N2H4 and N2H6
are closely
The higher distance in hydrazine is quite understandable
and because of the lone pair-lone pair repulsion the nitrogen
atoms move away from each other. In the case of N2H5C ion
the lower bond length is due to the removal of one lone pair,
which removes the repulsion and hence the nitrogen atoms are
closer to each other. When it is noncoordinated the bond
becomes very strong and hence the lowest bond length is
observed.
observed, though in both cases repulsions are expected, the
repulsion between lone pairs is higher than the repulsion
between positive charges. In fact, the reverse is expected. This
2C
should be due to the fact that in N2H6 ion the positive
charge is partially shared by the N-H protons, while due to
the higher electronegativity of nitrogen the electron pairs can-
not be shared by protons. By closely analyzing the data it is

1078
Ragul et al.
Fig. 5. ORTEP diagram of N2H6H2edta.
noted that all the N-H bond lengths in N2H62C ions are equal Structure and Coordination Geometry of N2H5[Cd(Hedta)
ꢀ
(0.89 A), which are in accordance with the principle of coor- (H2O)].H2O
dinate covalent bond.
The crystal system is orthorhombic with the space group Pbca.
The N-H bond length in zwitterion structure (i.e., N3-H3
The density of the crystals observed is 1.961 mg/m3, which is
ꢀ
in ORTEP diagram) is 0.91 A, which slightly higher than the
close to that of calculated from X-ray analysis. The X-ray
N-H bond. This is the indication of the acidic nature of these
crystal data, bond lengths, and bond angles for this complex is
protons in this zwitterion structure; however, due to the
given in Tables 2, 3, and 4, respectively. The ORTEP diagram
higher pKa values, these could not be easily removed.
showing the configuration of the molecules and the atom num-
In the H2edta2¡ ion, since all the carboxylic acid protons
bering scheme with thermal ellipsoids is given in Figure 6.
were dissociated, the individual carboxylate ions are expected
One would expect stable six coordination around Cd(II) ion
to have equal C-O1 and C-O2 bond lengths due to their reso-
based on its composition. Generally Hedta is expected to
nance. However, the data shows that one of the C-O bonds is
behave as pentadentate ligand and one water molecule is
shorter than the other in all the four carboxylate ions, which
expected to satisfy the sixth coordination in an octahedral
may be due to location of these bonds with respect to the
structure. However, the crystal data clearly shows that Cd(II)
ion is bound to seven atom resulting in the seven coordination
2C
N2H6
ion, and in turn due to the hydrogen bonding
interactions.
Fig. 6. ORTEP diagram of N2H5[Cd(Hedta)(H2O)].H2O.

Hydrazinium and Ammonium Salts
1079
geometry. Though seven coordination is common with edta4¡
References
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.
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In this structure there are five chelated five membered rings
and a coordinated water molecule, as observed previously
with several hydrated metal-edta and metal-Hedta com-
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ꢀ
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C
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dihydrogenethylenediaminetetraacetate. Dihydrazinium salt
forms N2H5[Cd(Hedta)(H2O)].H2O complex when reacts
with cadmium nitrate tetra hydrate in aqueous medium. The
crystal structures of these salts reveal that they exist as zwitter-
ions in solid state. The cadmium complex show interesting
seven coordinated structure in which the cadmium(II) ion is
surrounded by two nitrogen atoms, two carboxylate oxygen
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Supplementary Material
Crystallographic data for the structures reported have been
deposited with the Cambridge Crystallographic Data Centre
(CCDC NO: (N2H5)2edta – 656246, N2H6H2edta – 656243,
N2H5[Cd(Hedta)(H2O)].H2O - 703624).
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Acknowledgement
The authors sincerely thank, Maduari Kamraj University,
Mudurai, and IIT – Madras, Chennai, for recording X-ray
diffraction data.
Funding
The authors also thank UGC-New Delhi for financial assis-
tance in the form of minor research project.

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