New Route to Polynuclear Ni(II) and Cu(II) Complexes with Bridging Oxime Groups That Are Inaccessible by Conventional Preparations

Article abstract of DOI:10.1021/acs.cgd.8b01262

A series of new polynuclear complexes of divalent Ni and Cu with 2-cyano-2-oximino-acetic acid (later AACO²-) were obtained as the result of the ligand modification reaction in the process of complexation, using 2-cyano-2-oximino-acetates such as methyl- (later as MeCO), and ethyl- (as ECO later on). Synthesized compounds were characterized by spectroscopic methods, thermal analysis, magnetochemistry, and X-ray crystallography. Crystal data revealed the formation of the dimeric [Ni(AACO)(H₂O)₃]₂·H₂O (1), trimeric K₂[Ni₃(AACO)₄(H₂O)₄]·4H₂O (2), and K₂[Cu₃(AACO)₄(H₂O)₄]·4H₂O (3) complexes, with bridging NO-groups cyanoxime dianions. In the latter two compounds, the AACO^2- anions adopt cis-arrangements around metal centers. One mononuclear complex of K₂[Cu(AACO)₂(H₂O)]·2H₂O (4) composition was isolated and characterized as well, where the cyanoxime forms the trans-complex 4. There is moderate-to-strong antiferromagnetic coupling between metal centers in polynuclear complexes. Data of thermal analysis studies revealed high-energy properties for dehydrated complexes 3 and 4, which violently decompose at ～200 °C. These compounds may be viewed as room temperature completely safe, but heat-triggered actuators, because of their pronounced mechanical action upon leaving the system (crucible). Final products of thermal decomposition are Ni and NiO for 1, and the mixture of NiO and K₂O for 2, with metallic copper for 3 and 4.

Full text of DOI:10.1021/acs.cgd.8b01262

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Article
New Route to Polynuclear Ni(II) and Cu(II) Complexes with Bridging
Oxime Groups which are Inaccessible by Conventional Preparations.
Adedamola A. Opalade, Carlos J. Gomez-Garcia, and Nikolay Gerasimchuk
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01262 • Publication Date (Web): 08 Jan 2019
Downloaded from http://pubs.acs.org on January 15, 2019
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New Route to Polynuclear Ni(II) and Cu(II)
Complexes with Bridging Oxime Groups
which are Inaccessible by Conventional
Preparations.
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By
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Adedamola Abraham Opalade , Carlos J. Gomez-Garcia and Nikolay Gerasimchuk *
1
- Missouri State University, 901 South National Avenue, Department of Chemistry,
Temple Hall, 456, Springfield, USA.
2
- Instituto de Ciencia Molecular. Departamento de Química Inorgánica. Universidad de
Valencia, C/José Beltrán,2. 46980 Paterna (Valencia), Spain.
Keywords:
oximes, Cu and Ni complexes, X-ray analysis, magnetism, thermal analysis
Author for correspondence: phone (417) 836-5165, email NNGerasimchuk@MissouriState.edu
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ABSTRACT
A series of new polynuclear complexes of divalent Ni and Cu with 2-cyano-2-oximino-acetic
2
acid (later AACO -) was obtained as the result of the ligand modification reaction in the process
of complexation, using 2-cyano-2-oximino-acetates such as methyl- (later as MeCO), and ethyl-
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(as ECO later on). Synthesized compounds were characterized by spectroscopic methods,
thermal analysis, magnetochemistry and X-ray crystallography. Crystal data revealed the
formation of the dimeric [Ni(AACO)(H O) ] ·H O (1), trimeric K [Ni (AACO) (H O) ]·4H O
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3 2
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2
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4
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(
2), and K [Cu (AACO) (H O) ]·4H O (3) complexes, with bridging NO-groups cyanoxime
2 3 4 2 4 2
2
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dianions. In the latter two compounds, the AACO anions adopt cis-arrangements around metal
centers. One mononuclear complex of K [Cu(AACO) (H O)]·2H O (4) composition was
2
2
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2
isolated and characterized as well, where the cyanoxime forms the trans-complex 4. There is
moderate-to-strong antiferromagnetic coupling between metal centers in polynuclear complexes.
Data of thermal analysis studies revealed high-energy properties for dehydrated complexes 3 and
o
4
, which violently decompose at ~200 C. These compounds may be viewed as room temperature
completely safe, but heat-triggered actuators, because of their pronounced mechanical action
upon leaving the system (crucible). Final products of thermal decomposition are: Ni and NiO for
1, and the mixture of NiO and K O for 2, with metallic copper for 3 and 4.
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INTRODUCTION
General classification of polymetallic coordination compounds is displayed in Scheme 1.
Thus, regardless of their size – as big as homometallic (isopolyacids, for example), or
heterometallic Keggin and Dawson heteropolyacids and their salts – compounds of A-type have
distinct molecular structures with bridging oxo/hydroxo groups. This category of polymetallic
compounds includes numerous Werner-type complexes and also organometallic clusters with
metal-metal bonds. Polymers of B-type are predominantly homometallic compounds of different
dimensionality.
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purpose / applications:
M-O-M
M-M
oxo-metallates:
clusters:
homometallic
heterometallic
homometallic
heterometallic
single molecules magnets,
catalysts
non-polymeric
A
B
polymetallic
metal compounds
polymeric
electric conductors
(
metal "wires")
magnetically coupled
systems:
(ferro- / antiferro-, etc.)
1
D
2D
3D
dimensionality
Scheme 1. Classification of polymetallic complexes with their most commonly thought areas of practical
application shown on the right. A variety of bridging groups, as well as metallophilic interactions in 1D
solids connect units into polymers.
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Most polynuclear transition metals complexes demonstrate interesting magnetic
properties, such as magnetic ordering; the most common antiferro- and ferro-magnetic type. It
was discovered that some large polymetallic systems, such as Mn – complexes, exhibit single-
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molecule magnets (SMMs) behavior, by slow relaxation of the magnetization at low
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temperatures. These SMMs can potentially be used as materials for quantum bits (qubits),
because they exhibit quantum tunneling of magnetization, due to their small size and quantum
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phase interference. In such cases, the size of electronic devices and components will undergo
desirable, and rather dramatic, miniaturization. However, the SMM systems have not been able
to find applications in everyday electronics yet mainly due to their low operational
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temperatures. In those systems, the key organic ligand connecting metal centers was determined
to be an oxime moiety acting as bridging groups. Several analogous oximes were employed to
expand this class of interesting bridging ligands.4-18
The synthesis and characterization of polynuclear oximate bridged metal complexes has
been reported, using various preparative methods and ligand systems.7,19-21 The versatility in the
coordination modes of oximes, coupled with conformational flexibility made them very suitable
anionic bridging groups in polynuclear coordination compounds which exhibit magnetic
interaction.22-28 Some interesting peculiarities regarding structures of polymetallic oxime-based
complexes and their magnetic behavior were found. Thus, in the work by Das,28 the β-
aminoketoxime ligand of Ni(II) and Cu(II) ions complexes have been shown to be dimeric, with
out-of-plane oximate bridging between the metal centers. The Ni(II) complex showed weak
antiferromagnetic coupling between the dimeric nickel centers, and the Cu(II) complex showed
weak ferromagnetic coupling between the Cu(II) dimeric centers. Also, the bond distances of the
bridging oxime groups were reported to have a significant effect on the magnetism of Ni(II)
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27
polynuclear complexes of pyrazine-2-amidoxime, which displayed antiferromagnetic coupling.
The antiferromagnetic exchange is occurring via the N – O bridging group of the oxime ligand.
The N – O bond lengths of these complexes are shorter than 1.394 Å established critical bond
lengths for effective exchange, and the Ni–N–O–Ni torsion angles are less than the determined
critical angle of 75°, at which the antiferromagnetic coupling switches to the ferromagnetic
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one. The polydentate character of the oxime/nitroso groups, capable of a variety of binding
modes to metal centers, is an essential feature for the formation of polynuclear complexes which
demonstrate intense magnetic interactions. Several oximes-based ligands, which were found to
support realization of multimetallic-core compounds, are shown in Scheme 2.
Cyanoximes represent a new subclass of low molecular weight oximes which have the
general formula NC-C(N=OH)-R, with R being an electron withdrawing group.30,31 Contrary to
3
2
-
-
-
-
-
classic ambidentate ligands, such as linear pseudohalogenides CN , N , NCO , NCS , NCTe
3
-
30
and nitrite anion NO , cyanoximes exemplify versatile ampolydentate ligands that have
2
received intense development.36-38 There were only a few reported complexes of Cu and Ni with
cyanoximes in general, with most of them being mononuclear compounds.39-43 With the
4
1
44
45
exception of one di-copper, one stereospecific di-nickel, and one octa-iron complex, no
other homometallic or heterometallic complexes containing cyanoximes are reported.
The 2-Cyano-2-hydroxyimino-ethylacetate, which is commercially known as ‘Oxyma’
(
HECO), and its analogous compound 2-Cyano-2-hydroxyimino-methylacetate (HMeCO)
represent inexpensive and easily accessible compounds. We report the synthesis and properties
of unusual Ni(II) and Cu(II) complexes that contain the 2-hydroxyimino-2-cyano-acetate dianion
2
-
(
AACO ), which originates via selective base-catalyzed hydrolysis of ester-cyanoximes HECO
and HMeCO by divalent transition metal ions. Presented in this paper are the polynuclear
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complexes of the latter two transition metal ions, which are inaccessible from the AACO2-
dianion, but can be readily available from starting cyanoxime esters.
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H
Me
OH
N
N
N
N
OH
2
-pyridinealdoxime (paoH)11
Methyl 2-pyridyl ketone oxime (mpkoH)12
OH
N
OH
NC
N
NH2
HO
O
Carbamoylcyanonitrosomethanide (as Ag-salt)45
(1-hydroxycyclohexyl)-phenyl ketone oxime13
OH
N
NH
NH
N
N
N
NH2
OH
OH
N
Pyrazine-2-amidoxime10
aminoketoxime ligand28

4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dioxime
Scheme 2. Chemical formulas of oximes used for preparation of polynuclear transition metal complexes.
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EXPERIMENTAL PART
SYNTHESIS
Two modified and optimized procedures for the synthesis of ligands are presented below, while
two-step method of synthesis of metal complexes is shown in Scheme 3.
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Preparation of HMeCO and HECO cyanoxime ligands. The 2-Cyano-2-(hydroxyimino)
methylacetate (later HMeCO) was obtained according to the reaction below:
o
~
50 C
NC-CH -C(O)OCH + CH COOH + NaNO  NC-C(=N-OH)-C(O)OCH + CH COONa
2
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3
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HMeCO
Glacial acetic acid (100 mL) and NaOH pellets (12 g) were placed in a 500 mL three-neck round
bottom flask equipped with a mechanical stirrer and a long stem funnel, under intense stirring.
Within ~10 minutes, pellets of hydroxide dissolved, evolving heat and bringing the mixture to
reflux. Methyl cyanoacetate (50.0 g, 0.50 mol) was added to this hot solution, and slow dropwise
addition of a solution of NaNO (80 g, 1.16 mol) in water (100 mL) began immediately. The
2
addition was complete within 1 – 1.5 hours, but the stirring continued until the reaction mixture
o
temperature dropped to ~ +25 C, and then continued for an additional three hours, until the
precipitate of the cyanoxime began to form. Then the mixture was diluted with water (100 mL)
and allowed to stand at +4°C for another three hours. Bulk solid precipitate was collected by
vacuum filtration, and dried in air to give microcrystalline off-white product. Yield: ~90%.
The 2-Cyano-2-(hydroxyimino) ethylacetate (later HECO) was obtained according to the
reaction below:
R.T.
NC-CH -C(O)OC H + H PO + NaNO

NC-C(=N-OH)-C(O)OCH + CH COONa
3 3
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3
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2
HECO
Target cyanoxime ligand was prepared by reacting 5.700 g (82.6 mM) of NaNO dissolved in 75
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mL of H O with 10.000 g (88.4 mM) of ethyl cyanoacetate in a round-bottom flask, according to
2
the reaction in Scheme 3. The 3.6 mL of 1 M H PO was added to the reaction mixture, dropwise
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over 45 minutes, and the temperature was kept at +3 – 4°C using an ice bath. After the addition
of the 1 M H PO was completed, the temperature was raised to +40°C, and the reaction was
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quenched with 7.3 mL of fuming HCl at +65°C. The mixture was left to cool to room
temperature. The reaction mixture was then kept in the refrigerator for a period of approximately
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1 hours. The mixture was filtered using filter paper and gravity filtration. The precipitate was
dried in vacuum. The filtrate was extracted with ethyl acetate after the mixture was treated with
solid NaCl to facilitate extraction. The solution was off-yellow, and the colour was maintained in
the organic phase, while the aqueous phase was colourless. The dried precipitate was 7.153 g. An
additional amount of 3.042 g was obtained after the extraction. The total yield of HECO was
10.195 g (81 %); m.p = 129.4–132.4 °C.
IR data (KBr): ν = 3600, 3248 (O-H), 3008, 2851 (C-H), 2239 (CN), 1732 (C=O), 1636, 1594,
452, 1319, 1062, 820, 763, 513 cm-1.
1
1
NMR data (300 MHz, CDCl ), H (ppm): δ = 1.407 (t, 3H, J = 6.84 Hz, CH CH ), 4.436 (q, 2H,
3
2
3
1
3
J = 6.84 Hz, CH CH ), 4.833 (br, 1H, OH). C (75 MHz, CDCl ), ppm: δ = 13.909 (CH CH ),
2
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3
2
3
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3.58 (CH CH ), 109.25, 109.46(CN), 126.46, 128.71 (C=N), 161.83 (C=O).
2 3
GC-MS data: t = 7.20 minutes.
R
+
•
Mass-spectrometry data: m/z = 142 (M ), 125 (M-OH), 114 (M-CH CH ), 97 (M-OCH CH ),
2
2
2
3
6
9 (M-CO CH CH ).
2 2 3
Preparation of Ni(II) and Cu(II) complexes from the HMeCO ligand. Two solutions of
HMeCO were prepared separately in two 25 mL beakers by dissolving 0.300 g (2.34 mM) of the
HMeCO ligand in 5 mL of H O. Then 2.34 mL (2.34 mM) of 1M KOH solution was added to
2
each of the HMeCO solutions in the beakers for the deprotonation of the HMeCO ligand
(Scheme 3). The colour of the solution changed to deep yellow. The solutions were stirred
continuously using magnetic stirrers. Then 0.341 g (1.17 mM) of Ni(NO ) ·6H O and 0.1870g
3
2
2
(
1.17 mM) of CuSO ·5H O were dissolved in 5ml of deionized water in another two separate
4 2
beakers, and these solutions were added in, dropwise, to the separate beakers containing the
-
deprotonated MECO ligand solutions, using a Pasteur pipette. Clear, deep brown solution was
formed in the beaker to which the Ni(II) salt was added, and clear green solution was formed in
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the beaker to which the Cu(II) salt was added. The solutions were allowed to stand for ca. two
hours, under continuous stirring, at room temperature. The clear deep brown solution and green
solutions were filtered, through a Pasteur pipette packed with glass wools, into clear
polyethylene tubes. The filtrates were kept in a desiccator charged with concentrated H SO for
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almost two months, to provide slow growth of colored crystals suitable for the X-ray analysis
quality. In this way, complexes K [Ni (AACO) ·(H O) ]·4H O (2) and K [Cu(AACO) ·H O]
2
3
4
2
4
2
2
2
2
·
2H O (4) were obtained. Also, a rather significant amount of colorless large crystals (around
2
~
20 %!), which turned out to be of oxamide [H NC(O)] , was collected and analyzed. Both metal
2 2
complexes and organic diamide are products of hydrolysis of the initial HMeCO ester.
step I
step II
K [Cu(AACO) ·H O]·2H O
2
2
2
2
RO
CN
N
or
+
+
H O
+ M
2
.
[Ni(AACO)(H O) ] H O
C
C
2
3 2
2
base
2+
2+
or
M = Ni , Cu
O
OH
.
K [M (AACO) .4H O] 4H O
2
3
4
2
2
(M = Ni, Cu)
R = CH , C H
2 5
3
H N
2
O
HMeCO when R = CH3
C
C
+
HECO when R = C H5
2
O
NH2
oxamide
2-
Scheme 3. Preparation of Ni(II) and Cu(II) AACO complexes from HMeCO and HECO. Red and blue
atoms in the initial compounds indicate the core for the formation of oxamide as a product of incomplete
hydrolysis of cyanoxime esters.
2
-
Preparation of Ni(II) and Cu(II) AACO dianion complex using the HECO ligand. Two
separate solutions of HECO were prepared separately, in two 25 mL beakers, by dissolving
0
.300 g (2.11 mM) of the HECO ligand in 5 mL of H O. Then 2.11 mL (2.11 mM) of 1 M KOH
2
solution was added to each of the HECO solutions in the beakers for the deprotonation of the
HECO ligand (Scheme 3). The colour of the solution changed to deep yellow. The solutions
were stirred continuously using magnetic stirrers. Then 0.3069 g (1.06 mM) of Ni(NO ) ·6H O,
3
2
2
and 0.1685 g (1.06 mM) of CuSO ·5H O, were dissolved in 5 mL of deionized water in another
4
2
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two separate beakers, and these solutions were added in, dropwise, separately to the beakers
-
containing the deprotonated ECO ligand solutions. Clear deep brown solution was formed in the
beaker to which the Ni(II) salt was added, and green solution was formed in the beaker to which
the Cu(II) salt was added. The solutions were allowed to stand for ~2 hours, under continuous
stirring at room temperature. No precipitates were formed. The clear deep brown solution and
green solutions were filtered through a tight glass wool plug into clear 10 mL capacity
polyethylene test tubes where crystals eventually appeared in abundance. For future convenient
identification and use of the obtained metal complexes, we refer to Table 1, which contains
compounds’ abbreviations employed in this paper. We did not feel the necessity of obtaining
their elemental composition data since all characterization of the obtained four metal complexes
as well as one the initial cyanoxime ligands (HECO) and the side reaction product oxamide was
done using those crystalline samples structures of which have been determined. All other
investigations – spectroscopic, magnetochemical and thermogravimetric – were conducted from
the same well-crystallized specimen (see Supplementary Information section: SI 1, 2).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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9
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4
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8
9
0
Table 1.
Glossary for the obtained polymetallic complexes discussed in this work.
Compound # Molecular Formula
Used Abbreviation
F.W., g/mol
242.82
1
2
3
4
C H N NiO
[Ni(AACO)(H O) ] ·H O
3
8
2
7
2
3 2
2
C H K N Ni O
K [Ni (AACO) (H O) ]·4H O
423.33
1
2
16
2
8
3
20
2
3
4
2
4
2
C H K N Cu O
K [Cu (AACO) (H O) ]·4H O
430.57
12 16
2
8
3
20
2
3
4
2
4
2
C H CuK N O
K [Cu(AACO) (H O)]·2H O
419.89
6
6
2
4
9
2
2
2
2
Safety note: handling of copper(II) complexes in general should be careful since it is known that
in 2+ oxidation state it is a mild oxidizer of organic compounds. Moreover, we discovered in
current work that synthesized polynuclear copper(II) complexes represent high-energy
compounds after some heat activation. No shock sensitivity tests were performed! Therefore,
preparation and handling of these complexes should be done with appropriate care with the
amounts not exceeding 250 mg.
PHYSICAL METHODS, INSTRUMENTATION.
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Spectroscopy. The IR spectra of the initial compounds and complexes were recorded on a
Bruker FT-IR Vertex 70 spectrophotometer, in 13 mm diameter KBr pellets, at room
-1
temperature, using 64 repetitions with 4 cm resolution. All spectra were compensated for
background, to minimize moisture and CO appearance. The UV-visible spectra were recorded
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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2
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9
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1
2
3
4
5
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8
9
0
1
2
3
4
5
6
7
8
9
0
for solid samples of complexes using diffuse reflectance technique (SDR), with the aid of a
Labsphere accessory to Cary 100-Bio spectrophotometer, operating from 200 to 850 nm (SI 3).
A sample of fine powder of MgO was used as calibration standard.
Thermal Analysis. The TG analysis was performed on the TA Instrument Q-600, in an alumina
o
crucible, under pure nitrogen flow, in the range between 30 – 1000 C at 100 ± 2mL/min, and a
heating rate ranging from 1 to 20°C/min, depending on a sample behavior. The crucible was
calcined prior to each experiment, using the propane torch. Data of the TG analyses were
processed using the TA Universal Analysis software package.
Magnetic Studies. The magnetic susceptibility measurements were carried out in the
temperature range 2-300 K, with an applied magnetic field of 0.5 T, on polycrystalline samples
of compounds 1-4, with a Quantum Design MPMS-XL-5 SQUID susceptometer. The
susceptibility data were corrected for the sample holders previously measured, using the same
conditions, and for the diamagnetic contributions of the salt, as deduced by using Pascal´s
constant tables.
X-Ray Crystallography. The crystal structures were determined for all four compounds
presented in this work: [Ni(AACO)(H O) ] ·H O (1), K [Ni (AACO) (H O) ]·4H O (2),
2
3 2
2
2
3
4
2
4
2
K [Cu (AACO) (H O) ]·4H O (3) and K [Cu(AACO) (H O)]·2H O (4). Selected crystals of
2
3
4
2
4
2
2
2
2
2
these complexes were mounted on a thin glass fiber, or placed into the CryoLoop, and then
attached to the copper pin positioned on the goniometer head of the Bruker APEX2
diffractometer, equipped with a SMART CCD area detector. The data sets were measured at low
temperatures. The intensity data were collected in  scan mode, using the Mo tube
(K radiation  = 0.71073 Å) with a highly oriented graphite monochromator. The intensities
o
were integrated from four series’ of 364 exposures each, covering 0.5 in  at 10 to 60 seconds
of exposure time, with the total data set being a sphere for both wavelengths. The space group
determination was done with the aid of XPREP software.46 The absorption correction was
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performed, using values from face-indexed crystals and numerical values obtained from the set
of images recorded with the video-microscope (SI 4, 5), followed by the SADABS program that
was included in the Bruker AXS software package.47,48 All structures were solved by direct
2
methods, and refined by least squares on weighted F values for all reflections, using the
0
1
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0
SHELXTL program. The structures reported herein metal complexes did not have apparent
errors and are well refined with their checkCIF reports shown in SI 6. Crystal and refinement
data can be found in Table 2, while selected and bond lengths and angles which are important for
discussion are listed in Table 3. Drawing the crystal structures and packing diagrams was done
using the ORTEP 3v249,50 and Mercury software packages. Thermal ellipsoids in all figures are
drawn at their 50% probability level. All four crystal structures have been deposited into the
CCDC under the following numbers: 1473520 (1), 1473524 (2), 1473518 (3) and 1473523 (4).
Crystal structures of the two organic compounds were deposited as well: HECO – 1473516,
oxamide – 1473522. The PLATON checkCIF reports for all structures are shown at the end of
Supporting Information section in SI 33-40.
51
RESULTS AND DISCUSSION
Syntheses of polynuclear complexes.
Preparation of non-polymeric, molecular complexes of A-type (Scheme 1) is typically
2
-
accomplished as a result of condensation reaction where oxide atoms O in acid residues of
vanadic, molybdic, tungstic acids, for example, are substituted with EO42- (E = Mo, W, or V)
residue to form either isopoly-, or heteropolyacids. One of the examples of such condensations is
dimerization of CrO42- anion in acidic media with the formation of dichromate Cr O anion. At
2-
2
7
first, polymetallic/polynuclear transition metals complexes, that were found to have unusual
magnetic properties including SMM, were obtained by accident when involved in the preparation
organic ligands were hydrolyzed. As the result, complexes contained bridging -hydroxo- -
alkoxo-groups, -oxo atoms, as well as the mixture of anionic and neutral organic ligands and
generated structures possessed a wide range of complexity. Specifically for the oximes-
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containing complexes examples are: Cu - , Cu - Ni - , Mn - polymetallic core as well as
3
27
6
15
-
10
coexistence of HL/L moieties. Conventionally used aliphatic and aromatic mono- and
7
1
dioximes are weak organic acids with pK values above 10, and their ability to form chelate
a
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
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4
4
4
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5
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5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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9
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1
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3
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5
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8
9
0
1
2
3
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8
9
0
knots frequently is not sufficient for the complex formation. Hence, often for the increase of
oximes’ nucleophilicity and their reactivity towards metal centers the deprotonation is required.
-
However, anionic oximes in typically dilute aqueous solutions L generate back protonated HL
-
-
species: L + H O = HL + OH . As the result, more negative charges are required to compensate
2
for a rather significant cumulative positive charge on the metallic core. These counter anions
-
2-
-
72
usually are OH , O , OR or other groups such as, for instance, azide anions. The amount of
these auxiliary groups in the mixed-ligands complexes varies considerably depending on the
nature of the oxime used. In reported herein work we observed a unique situation when
-
-
cyanoximes monoanions of carboxylic esters MeCO and ECO upon de-esterification generated
dianions of the 2-cyano-2-hydroxyimino-acetic acid AACO2- and in that way completely
alleviated the necessity of presence of other auxiliary groups to compensate positive charge of
metal centers in polynuclear complexes.
Syntheses of cyanoximes carboxylic esters and their hydrolysis reactions.
Cyano-hydroxyimino-acetic acid (H AACO) was reported to be an alkaline hydrolytic
2
degradation product of cymoxanil – a fungicide to control late blight in plants. Further
degradation of the H AACO led to the formation of oxalic acid. This degradation was reported to
2
5
2
be pH and temperature dependent, with the rate for the degradation higher in aquatic pH. Metal
ions have been shown to influence the rate of hydrolysis of organic compounds where some
these reactions show pH dependent53,54 and others do not. Some of these reactions represent
metal ion promoted OH- 53-56 and H+ 53,57 catalyzing hydrolysis of esters. The promotion effect of
55
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1
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2
2
2
2
2
2
2
2
2
3
3
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-
divalent metal ion in the OH hydrolysis of esters have been reported to have the rate enhanced
9
54,55,57-59
-
up to 90-10 times.
Typically, metal ion promoted OH catalyzed reactions have been
observed in ester hydrolysis reaction, when there is a functional group present in the ester which
will allow strong interaction with the metal ions that will lead to chelation.53-55,59-62 This can also
be favored by using high metal-to-ligand ratios.58,61 Nucleophilic attack of the OH is made easy
0
1
2
3
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9
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1
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-
6
1
due to the polarization of the carbonyl oxygen by metal ions. The catalysis of nucleophilic
organic reactions by metal ions has been a subject of interest, due to their possible correlations
with biological systems, where they have a role in the mechanism of hydrolytic metalloenzymes,
2
+
63,64
e.g. carboxypeptidase A with a Zn at the active site,
where metal ion may be coordinated to
the carbonyl of the ester and the amide substrate where the Zn2+ coordination polarizes the
carbonyl group of the substrate, thereby increasing its susceptibility to nucleophilic attack.63,64
The majority of the metal complexes formed after these hydrolysis reactions are mononuclear.
Malek et al. (2004) did some experimental and theoretical calculations on the H AACO oxime,
2
65
in order to understand their coordination to metal ions, and Sliva et al. (1998) studied the
Cu(II) and the Ni(II) complexes of prepared pure H AACO, with successes in obtaining the
2
monomeric Cu(II) and Ni(II), as well as only one dimeric Cu(II) (pH > 5) complex of the
2
-
41-43
AACO dianion
reported thus far. In our case, the Ni(II) complexes, made in situ with metal
ion catalyzed hydrolysis of the 2-cyano-hydroxyimino acetic acid ethyl ester (HECO) and 2-
cyano-2-hydroxyimino-acetic acid methyl ester (HMeCO), are dinuclear and trinuclear
-
crystallohydrate metal complexes. In the case of the Cu(II)-MeCO system there are trinuclear
and mononuclear crystallohydrate metal complexes. A similar situation occurred in the past,
-
66
during an attempt to prepare Pd and Pt complexes with the amide-cyanoxime ACO anion. The
overall hydrolysis process for both employed ester-cyanoximes is depicted in Scheme 4. The
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trinuclear Ni(II) complex K [Ni (AACO) (H O) ]·4H O (2) and the trinuclear Cu(II) complex
2
3
4
2
4
2
K [Cu (AACO) ·(H O) ] ·4H O (3) were found to be isostructural (Table 2; Figures 2 and 3).
2
3
4
2
4
2
OH
OH
HMeCO
HECO
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
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4
4
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5
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5
5
5
5
5
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6
0
1
2
3
4
5
6
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8
9
0
1
2
3
4
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9
0
1
2
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9
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3
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0
1
2
3
4
5
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7
8
9
0
N
N
CN
CN
O
O
H C
O
3
C H
O
2
5
2
-Cyano-2-hydroxyimino-acetic acid,
2
-Cyano-2-hydroxyimino-acetic acid,
methyl ester
ethyl ester
metal ions catalyzed hydrolysis:
1
2
) aqueous solutions
) room temperature
OH
N
2
-Cyano-2-hydroxyimino-acetic acid
colorless
CN
4
2,65
H AACO
2
HO
O
O-
N
CN
2-Cyano-2-hydroxyimino-acetate
bright-yellow
AACO2- dianion
-O
O
2-
Scheme 4. Hydrolysis of the cyanoxime esters leading to potent dianionic bridging ligand AACO .
Therefore, based on our experience in current work, and summarizing the literature data, we can
conclude three proven methods of modification and transformation of cyanoximes as shown in
Scheme 5, where path 2 is presented in this study.
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1
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2
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2
2
2
2
2
2
2
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H
NC
HO
R
hydroxamic acids
NH
0
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9
0
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9
0
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0
oxime-group
derivatization:
reduction
4
X = O, S, Se
X
1
2
NC
HO
R
R - group
derivatization
R'
C
R
cyano-group
derivatization
NC
HO
H N
2
N
N
N
OH
amide / thio / seleno
oxime-group
derivatization:
oxidation
3
NC
-O
R
nitro-cyano anions
+
N
O
Scheme 5. Principal ways of modification of cyanoximes, leading to other chelating ligands.
Another peculiar feature of these ester-cyanoximes/transition metals/water systems is the
persistent formation of significant quantities of oxamide, [C(O)NH ] . Oxamide crystals were
2
2
always obtained as a side product from the syntheses of these polynuclear complexes, as
2
+
depicted in Scheme 3, above. When we used Zn cations, the result was the same, with respect
to the oxamide formation, which highlights indifference of the hydrolysis products from 3d
transition metal ions present in the system. A pathway was proposed for the formation of
oxamide, but the mechanism for the formation of this side product is yet to be fully elucidated.
Nevertheless, it has been known for a long time that nitriles undergo stepwise hydrolysis to
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carboxylic acids (their ammonium salts to be exact) via formation of amides. However, the
formation of the amide from the oxime moiety represents Beckman re-arrangement which takes
place at acidic conditions. These were inconsistent with our particular reaction conditions during
preparations of complexes carried out at room temperature in aqueous solutions. More studies,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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0
1
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9
0
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1
2
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4
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7
8
9
0
1
3
15
including C, N isotopic labeling, are needed to elucidate the mechanisms of these rather
unusual transformations in aqueous solutions, which end up in a partial hydrolysis of involved
groups to the amide, instead of the carboxylic acid and its ammonium salt.
Crystal Growth.
As we stated in the synthesis section above, no precipitates were formed upon mixing of
ingredients. The clear deep brown solution and green solutions were filtered through a tight glass
wool plug into clear 10 mL capacity polyethylene test tubes where crystals eventually appeared
in abundance. Thus, filtrates were kept in those tubes in a desiccator charged with concentrated
H SO for quite some time until high quality crystals slowly grew up on walls of tubes (SI 1,2).
2
4
It is important to note that the use of glass tubes and beakers for crystallization purposes did not
lead to suitable crystals at all, but plastic tubes with the hydrophobic surface were the correct
choice for a good quality specimen. Wettability of a glass surface with aqueous solutions leads to
the formation of poor quality frost-like crystals “crawling” down the concaved surface of
solution during water evaporation. Numerous microcrystals that formed during such event
represented multiple seeds that prevented the formation of well-shaped large crystals (SI 1,2). At
the same time non-wettable by aqueous solution smooth walls of plastic tubes had convex
surface and this facilitated upon water evaporation slow growth of a good quality much larger
crystals. Another good feature of the use of plastic tubes for crystal growth from aqueous
solutions is much easier and essentially non-destructive removal of crystalline specimen from the
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5
5
5
5
5
5
5
5
5
5
6
tubes. Along with colored crystals of transition metals complexes, large, well-shaped colorless
prisms of the oxamide were also formed. The actual yield of this compound varied between 15 to
~26 %. Again, it turned out that the metal-containing products of these preparations were Cu(II)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2-
and Ni(II) complexes of AACO dianion and oxamide, NH C(O)-C(O)NH . Both resulted from
2
2
the hydrolysis of the starting HMeCO and HECO cyanoximes.
Crystal Structures.
-
[
Ni(AACO)(H O) ] ·H O (1). The X-ray analysis showed that the ECO anions in the presence
2 3 2 2
2
-
of metal ions were hydrolyzed with the generation of the AACO dianion. The Ni(II) ion in
2-
emerald-green complex of AACO is a bimetallic tricyclic complex, with one water molecule
outside the coordination sphere (Figure 1). The crystal and refinement data for this complex are
displayed in Table 2, while selected bond lengths and angles are presented in Table 3. All H-
atoms during structure solution and refinement of 1 were found on the electron density map, and
2-
refined isotropically. The AACO dianions are bound to nickel centers in chelate fashion, using
the nitrogen atoms of the oximes and the oxygen atom of the carboxylate group. Also, the
2
-
AACO dianion acts as a bridge, connecting two Ni centres via N-O bond. Thus, two nickel
2
2-
atoms are bridged in a μ -fashion by the NO group of the AACO , making a six-membered
2
-
metallacycle system with the two nickel centres opposite to each other. The AACO moieties
occupy the equatorial position, coordinating in a trans-anti-configuration (oxime group trans to
the carbonyl group). The axial positions around the Ni(II) ions are each occupied by two water
molecules trans to each other, and an equatorial position is occupied by another water molecule,
creating a distorted octahedral environment around the Ni(II) ion (Figure 1). The vacant
positions in the equatorial plane are occupied by bridging O-atoms (Figure 1).
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9
Table 2. Crystal and refinement data for synthesized bivalent Cu and Ni complexes.
Parameter
1
2
3
4
Formula
C H N NiO
C H KN Ni1.50O10 C H Cu KN O
C H CuK N O
9
3
8
2
7
6
8
4
6
8
1.50
4
10
6
6
2
4
Formula weight
242.82
423.33
430.57
419.89
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Crystal habit, color
light green block light green block
light bronze needle dark purple prism
Crystal system
Monoclinic
C2/c
Monoclinic
Monoclinic
Monoclinic
Space group
P2 /n
P2 /n
P2 /c
1
1
1
a/Å
16.0508(10)
6.4725(5)
16.5248(13)
90.00
9.750(2)
6.7291(15)
20.616(5)
90.00
9.7412(11)
6.7282(8)
20.585(2)
90.00
8.7730(6)
12.4214(8)
13.1215(8)
90.00
b/ Å
c/ Å
α/°
β/°
114.2450(10)
90.00
90.508(4)
90.00
90.543(2)
90.00
108.3500(10)
90.00
γ/°
V/ Å3
1565.3(2)
8
1352.5(5)
4
1349.1(3)
4
1357.18(15)
4
Z
Dcalcd/g cm-3
F(000)
2.061
2.079
2.120
2.055
992
852
858
836
μ(MoKα)/mm-1
T/K
2.492
2.479
2.757
2.276
120(2)
273(2)
0.71073
1.98-25.00
120(2)
100(2)
λ/ Å
0.71073
2.70-33.02
0.71073
1.98-28.35
0.71073
2.32-32.99
θ range/°
2
2 2
2
2 2
2
2 2
2
2 2
Function minimized
Reflections > 2σ(F2)
Σ w(F -F )
Σ w(F -F )
Σ w(F -F )
Σ w(F -F )
o c
o
c
o
c
o
c
2446
1698
2415
4310
Data/Restraint/parameters 2791/12/150
2380 / 0 / 231
0.0480, 0.1024
0.0779, 0.1169
1.045
3356 / 12 / 237
0.0426, 0.0811
0.0744, 0.0948
1.025
4756 / 9 / 223
0.0242, 0.0574
0.0285, 0.0605
1.002
2
2
R(F), w R (F ) (> 2σ(F )) 0.0269, 0.0570
2
2
R(F), w R (F ) (all data)
0.0342, 0.0630
1.147
2
GOF on F2
Largest peak/hole/ eÅ-3
R.M.S. deviation from
mean/ eÅ-3
0.520/-0.532
0.105
0.777/-0.564
0.144
0.782/-0.901
0.157
0.660/-0.679
0.093
CCDC #
1473520
1473524
1473518
1473523
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2
3
4
5
6
7
8
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
There is also a non-coordinated water molecule that acts as a linker between units of the complex
1
. In the unit cell, the water molecules from each [Ni(AACO)(H O) ] ·H O occupy channels
2 3 2 2
extending along b-direction (SI 7, 8). The inversion centre is in the middle of the Ni-N-O-Ni ring
Figure 1). The shortest Ni···Ni distance is 3.776 Å, which is much greater than the normal
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
metal-metal bond. Geometry details of the distorted [NiO N] octahedron are shown in Figure 1.
5
Hydrogen bonding is essential in the packing of this complex into a crystal, and is shown in SI 9.
It joins dimeric units of 1 into 3D network. Non-coordinated water molecules O7w are
occupying channels running along b-direction in the unit cell. Complex 1 is not isostructural to
the Cu-complex of the same composition (SI 10) reported earlier.
A
B
Figure 1. (A) A fragment of the dimetallic structure of [Ni(AACO)·(H O) ] ·H O (1), (B) Two
2
3 2
2
orthogonal views of the planar Ni N O six-membered ring with its geometrical parameters. The
2
2
2
symmetry operation for the _1 code is: –x, y, -z+1/2.
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Table 3. Selected bond distances and bond angles in studied complexes (the numbering scheme is from crystal structure figures).
Compound
Cyanoximate Dianion
Angles, °
Metal Center
Bonds, Å
Bonds, Å
Angles, °
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
C1-N1 = 1.3101(19)
C1-C3 = 1.495(2)
C3-O3 = 1.2486(19)
N1-O1 = 1.3084(17)
C1-C2 = 1.433(2)
C2-N2 = 1.151(2)
C3-O2 = 1.2705(19)
N2-C2-C1 = 176.92(17)
O3-C3-C1 = 118.74(14)
O1-N1-C1 = 117.39(13)
N1-C1-C2 = 122.57(14)
N1-C1-C3 = 117.55(14)
Ni1-O1 = 2.0127(12)
Ni1-O2 = 2.0441(11)
Ni1-O4W = 2.0754(14)
Ni1-O5W = 2.1135(13)
Ni1-O6W = 2.0286(13)
O4W-Ni1-N1 = 90.86(5)
O6W-Ni1-N1 = 171.10(5)
O6W-Ni1-O4W = 91.23 (6)
O4W-Ni1-O5W = 177.99(5)
O2-Ni1-O2 = 173.74(5)
O2-Ni1-O4W = 88.73(5)
O1-Ni1-O5W = 92.93(5)
O2-Ni1-O5W = 89.47(5)
1
C1-N1 = 1.304(7)
C1-C3 = 1.471(9)
C3-O3 = 1.254(7)
C4-N3 = 1.303(7)
C4-C6 = 1.492(8)
C6-O6 = 1.244(7)
C1-C2 = 1.425(8)
C2-N2 = 1.154(7)
C3-O2 = 1.287(7)
C4-C5 = 1.446(8)
C5-N4 = 1.141(7)
C6-O5 = 1.278(7)
N1-O1 = 1.306(6)
N4-C5-C4 = 176.9
N2-C2-C1 = 177.2
Ni1-O1S = 2.290(5)
Ni1-O5 = 1.947(4)
N1-Ni1 = 1.980(5)
Ni1-O2 = 1.959(4)
N3-Ni1 = 1.980(5)
Ni2-O2S = 2.254(5)
Ni2-O1 = 1.977(4)
Ni2-O4 = 1.960(4)
N3-Ni1-N1 = 99.8(2)
O5-Ni1-O2 = 93.15(17)
O5-Ni1-N3 = 83.47(18)
O2-Ni1-N1 = 83.11(18)
O5-Ni1-O1S =100.40(16)
N3-Ni1-O1S = 88.31(19)
O2-Ni1-O1S = 95.07(18)
N1-Ni1-O1S = 89.00(18)
O4-Ni2-O2S = 88.35(17)
O1-Ni2-O2S = 87.00(17)
O4-Ni2-O2S = 91.65(17)
O1-Ni2-O2S = 93.00(18)
C2-C1-C3 = 122.7(5)
C5-C4-C6 = 123.7(5)
O3-C3-O2 = 124.2(6)
O6-C6-O5 = 126.0(6)
N1-C1-C2 = 121.3(6)
N1-C1-C3 = 115.8(5)
N3-C4-C6 = 116.5(5)
N3-C4-C5 = 119.8(5)
C5-C4-C6 = 123.7(5)
2
C4-C5 = 1.443(5)
C4-N3 = 1.300(5)
N3-O4 = 1.305(4)
C3-O2 = 1.278(5)
C3-O3 = 1.230(5)
C6-O5 = 1.275(5)
C6-C4 = 1.495(5)
N4-C5-C4 = 176.9(4)
C5-C4-N3 = 120.7(4)
C4-N3-O4 = 119.0(3)
O6-C6-C4 = 119.6(4)
O6-C6-C5 = 125.6(4)
N2-C2-C1 = 177.2(4)
C2-C1-C3 = 122.6(3)
Cu1-O5 = 1.942(3)
Cu2-O1 = 1.978(3)
Cu2-O1W = 2.250(3)
Cu1-N1 = 1.977(3)
Cu2-O1W = 2.250(3)
Cu1-O2 = 1.960(3)
Cu1-N3 = 1.977(3)
O5-Cu1-O2 = 93.64(11)
O2-Cu1-N1 = 82.88(12)
O2-Cu1-N3 = 175.63(13)
O5-Cu1-O2W = 100.53(12)
N1-Cu1-O2W = 88.87(12)
O4-Cu2-O4 = 180.0
3
O4-Cu2-O1 = 80.43(11)
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2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
C6-O6 = 1.235(5)
C1-C2 = 1.423(5)
O3-C3-C1 = 118.4(3)
O3-C3-O2 = 126.1(4)
Cu2-O4 = 1.962(3)
Cu2-O1 = 1.978(3)
O4-Cu2-O1 = 99.57(11)
O4-Cu2-O1W = 91.75(12)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
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8
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Table 3.
Selected bond distances and bond angles in the metallic complexes (continued).
Compound
Cyanoximate Dianion
Metal Center
Bonds, Å
Angles, °
Bonds, Å
Angles, °
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
C2-N2 = 1.142(5)
C1-C3 = 1.491(5)
N1-O1 = 1.302(4)
N1-C1-C2 = 121.7(3)
C5-C4-C6 = 123.3(3)
O6-C6-O5 = 125.6(4)
Cu2-O1W = 2.250(3)
O1-Cu2-O1W = 93.23(12)
O4-Cu2-O1W = 88.25(12)
O1-Cu2-O1W = 86.77(12)
O1-Cu2-O1W = 93.23(12)
O1W-Cu2-O1W = 180.0
O5-Cu1-N1 = 170.26(13)
O5-Cu1-N3 = 83.17(12)
N1-Cu1-N3 = 99.79(13)
O2-Cu1-O2W = 95.24(11)
N3-Cu1-O2W = 88.29(13)
O1-Cu2-O1 = 180.0
3
(cont.)
C1-N1 = 1.3140(18)
C1-C3 = 1.4952(19)
C3-O3 = 1.2361(17)
C4-N3 = 1.3247(18)
C4-C6 = 1.4826(19)
C6-O6 = 1.2481(17)
C1-C2 = 1.432(2)
C2-N2 = 1.151(2)
C3-O2 = 1.2839(17)
C4-C5 = 1.432(2)
C5-N4 = 1.149(2)
C6-O5 = 1.2841(17)
N1-C1-C2 = 121.92(13)
C2-C1-C3 = 122.22(12)
O3-C3-O2 = 124.97(13)
O2-C3-C1 = 114.86(12)
N3-C4-C6 = 116.01(12)
N4-C5-C4 = 179.67(17)
O6-C6-C4 = 119.84(12)
N1-C1-C3 = 115.84(12)
N2-C2-C1 = 178.38(16)
O3-C3-C1 = 120.16(13)
N3-C4-C5 = 121.80(12)
C5-C4-C6 = 122.17(12)
O6-C6-O5 = 123.94(13)
O5-C6-C4 = 116.23(12)
O1-N1-C1 = 121.79(12)
Cu1-O2 = 1.9388(11)
Cu1-N3 = 1.9784(12)
Cu1-O1W = 2.2141(11)
Cu1-O5 = 1.9659(10)
Cu1-N1 = 2.0020(12)
O2-Cu1-O5 = 169.61(5)
O5-Cu1-N3 = 83.69(5)
O5-Cu1-N1 = 97.21(5)
O2-Cu1-O1W = 101.20(4)
N3-Cu1-O1W = 96.67(5)
O2-Cu1-N3 = 95.23(5)
O2-Cu1-N1 = 82.86(5)
N3-Cu1-N1 = 174.31(5)
O5-Cu1-O1W = 89.19(4)
N1-Cu1-O1W = 88.97(5)
C1-N1-Cu1 = 110.58(9)
O1-N1-Cu1 = 127.33(9)
4
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
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3
3
3
3
3
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6
K [Ni (AACO) (H O) ]·4H O (2). The reaction of the HMeCO ligand in the presence of KOH
2
3
4
2
4
2
2
-
and Ni(II) salt leads to hydrolysis of the HMeCO ligand yielding the AACO dianion. The
compound crystallized as fine thin yellow plates of the trimetallic complex with AACO2-
dianions. The crystal and refinement data for the complex are shown in Table 2. Selected bond
lengths and angles for this structure are summarized in Table 3. There are two types of Ni(II)
centres in this complex: one with the coordination number five (Ni1), and one six-coordinated
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
-
(
Ni2) (SI 11, 12). The Ni1 has two AACO dianions, coordinated using the nitrogen atom of the
oxime and oxygen atom of the carboxylate group to form a five-membered metallacycle. These
nickel centres have an axial water molecule, thereby creating a square-based, pyramidal
environment. There is, however, longer electrostatic contact to this metal center from O3 atoms
from the carboxylate group of the closest neighboring molecule (SI 13). The Ni2 center has four
oxygen atoms from four N-O groups of four oximes in the equatorial positions, bridging it with
the Ni1 centres. There are also two trans axial water molecules, creating an octahedral
2-
configuration around the Ni(II) centre (Figure 2). The coordination mode of the AACO ion to
the Ni1 centres is in trans-anti-configurations and the ligand moieties, coordinating oppositely to
the nickel centres, are cis to each other. The ligand displays two coordinating modes: chelating
2
2
(
κ ), and bridging (µ ). The overall structure of the complex at the Ni1 centre is cis (Figure 2).
The basal distances around Ni1 (in the range 1.947-1.980 Å, Table 3) are shorter than the apical
one (2.254 Å), and confirm that the environment around Ni1 is a slightly distorted square-base
pyramid (SI 13). The equatorial bond lengths around Ni2 (1.960(4) and 1.977(4) Å) are also
shorter than the axial ones (2.254(5) Å), and show that the environment of the Ni2 is an
elongated octahedron (SI 12). The metal ion is in a special position (inversion center) with SOF
= 0.5. These two nickel centres (Ni1 and Ni2) are not on the same plane (SI 14). The dihedral
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angle of the basal and equatorial planes is 26.11° (Figure 2.B). Neither of the two Ni1 centres are
on the same plane, but are on fairly parallel planes, with an offset of 1.288 Å (SI 14). There are
also two potassium counter-ions, surrounded by four water molecules. The potassium ions have
electrostatic interactions with the carboxylate oxygen, carbonyl oxygen, oxygen atoms of the
water molecules, as well as longer contacs with nitrile groups. The nitrile groups are practically
linear; the N4-C5-C4 and N2-C2-C1 bond angles are 177.3° and 178.1°, respectively. Extensive
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
and rather complex H-bonding between H O molecules both coordination water to Ni-centers
2
and outer-sphere crystallization water, play essential role in organization of the structure (SI 15).
A
B
Figure 2. (A) Asymmetric unit of K [Ni (AACO) ·(H O) ]·4H O (2) showing the numbering
2
3
4
2
4
2
scheme; long electrostatic contacts with alkali metal cation are shown as dashed lines. (B)
-2
+
Structure of the [Ni (AACO) (H O)4] dianion with K counter ions and associated water
3
4
2
molecules being omitted for clarity.
K [Cu (AACO) (H O) ]·4H O (3). This compound also represents a product of hydrolysis of
2
3
4
2
4
2
the ester (OEt) group in HECO cyanoxime, in the presence of KOH. The complex crystallizes as
a clear, light bronze-brown, needle-like specimen. The crystal and refinement data for this
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2
3
4
5
6
7
8
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
complex are presented in Table 2, while selected bond lengths and angles are listed in Table 3.
This crystal specimen was a 4-component rotational twin. Only the first, main domain was used
for structure solution/refinement, with details presented in the CIF. The compound
K [Cu (AACO) (H O) ]·4H O (3) is isostructural to K [Ni (AACO) (H O) ]·4H O (2), and
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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9
0
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9
0
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2
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9
0
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2
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4
5
6
7
8
9
0
2
3
4
2
4
2
2
3
4
2
4
2
contains a trimeric Cu complex (Figure 3A), very similar to that described above for 2. The
3
bond distances around Cu1 and Cu2 (Table 3) confirm that they present, respectively, a distorted
square-base and an elongated octahedral environment, as the Ni1 and Ni2 centers in compound
2
. The Cu2 atom is also in a special position (inversion center), with SOF = 0.5 (SI 16). The
C6-O5 and C6-O6 bond lengths (1.275(5) Å and 1.235(5) Å, respectively) are closer to the
2
expected values for C(sp )-O, confirming the resonance in the carboxylate anion. The nitrile
2-
groups of the oppositely coordinated AACO ions to the Cu1 centres have different bond lengths
(C5-N4 = 1.134(5) Å and C2-N2 = 1.142(5) Å. The C4-N3 and N3-O4 bond distances (1.300(5)
and 1.305(5) Å, respectively) as well as the C1-N1 and N1-O1(1.308(5) and 1.302(5) Å,
respectively), and are all typical of the deprotonated oxime form. The two Cu1 centres are
located on parallel planes with an offset of 1.294 Å, as observed in the nickel analog 2. The
dihedral angle between the basal plain of Cu1 and the equatorial plane of Cu2 is 26.38° (SI 16).
Because of isostructural nature of Cu complex 3 to the above Ni complex 2, details of the crystal
packing for 3 will not be discussed. Again, extensive H-bonding involving all water molecules is
essential for the crystal lattice formation and is very similar to that shown for the complex 2.
This crystal structure features an extensive 3D network of hydrogen bonds tabulated and shown
later on in SI 20.
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2
3
4
5
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7
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9
A
B
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
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5
5
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5
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5
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0
1
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9
0
1
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9
0
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0
1
2
3
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5
6
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8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3. (A) The asymmetric unit in K [Cu (AACO) (H O) ]·4H O, showing the atomic
numbering scheme. (B) Coordination around the Cu2 atom in the structure, showing the
connectivity of potassium counter ions to the [Cu (AACO) (H O) ] dianion; long electrostatic
contacts around K are indicated as dashed lines.
2
3
4
2
4
2
2
-
3
4
2
4
+
K [Cu(AACO) (H O)]·2H O (4). Self-standing crystal structure of this complex has been
2
2
2
2
7
0
reported by Golenya et al in 2012, which we found during manuscript preparation. No other
characterization of this compound was ever carried out. Also, it turned out that presented in this
paper our structural determination of the complex 4 was more accurate. Similarly, to reported
here other compounds, this compound is a hydrolysis product of the HECO cyanoxime ligand
2
-
that led to the formation of the AACO dianion, although, in contrast with 2 and 3, this complex
is a monomer. The crystal was obtained as a clear, dark black-purple, prismatic specimen. The
crystal and refinement data are shown in Table 2, while selected bonds and angles are presented
in Table 3. This complex contains a dianion formed by a Cu(II) center connected to two AACO2-
+
anions and one H O molecule. There are two charge-balancing K cations, and two non-
2
coordinated to transition metal water molecules (Figure 4). The alkali metal cations form rather
elegant layers with geometry around them showed in SI 19. The shortest interaction distance
between two K2 ions on a side of the molecule with O2 and O4 atoms facing them is 3.992 Å,
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2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
+
while the shortest K cyanoxime dianion distances are between K1 and O1(nitroso) and K1---
2
-
O5(carboxyl) groups at 2.894 Å and 2.883 Å respectively. The AACO ions are coordinated to
the metal ion using the nitrogen atoms of the nitroso groups (N1and N3) and the oxygen atoms
of the carboxylate groups (O2 and O5), forming an unexpected trans-complex in contrast to
0
1
2
3
4
5
6
7
8
9
0
1
2
3
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5
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9
0
1
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0
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9
0
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2
3
4
5
6
7
8
9
0
2
-
complexes 2 and 3. The AACO ions adopt a trans-anti-conformation, as in 2 and 3. The Cu(II)
ion has a trans-CuN O basal plane, with an axial water molecule, to form a distorted square-
2
2
pyramidal coordination geometry (Figure 4).
Figure 4. The ASU in the structure of K [Cu(AACO) ·H O]·2H O (4). Clearly shown is the
trans-geometry of the chelating AACO anion in the complex. Dotted lines show electrostatic
2
2
2
2
-2
contacts.
The basal bond lengths (in the range 1.939-2.002 Å, table 3) are shorter than the axial one
(2.2141 Å). Upon analysis of the unit cell content and packing of 4 into the crystal it was found
2-
that the two square-pyramidal units of [Cu(AACO) (H O)] are closely spaced in a back-to-back
2
2
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2
3
4
5
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7
8
9
fashion (SI 17). The bases of pyramids facing each other at a distance of 3.057 Å are co-planar,
+
and being joint by K2 cations form a “sandwich” with related via inversion center components
having the Cu1---Cu1 distance of 3.535 Å (Figure 5, SI 18).
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
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3
3
3
3
3
4
4
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4
4
4
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4
4
4
5
5
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5
5
5
5
5
5
5
6
0
1
2
3
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5
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7
8
9
0
1
2
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5
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9
0
1
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9
0
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2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
A
B
Figure 5. Two orthogonal views (A – side, B - top) of the K [Cu(AACO) )(H O) ] fragments
2
4
2
2
making an intermolecular “sandwich” dimer in the structure of 4.
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