Synthesis, characterization, and catalytic activity of heterometallic ion-pair Ni/Mn and Ni/Zn complexes

Article abstract of DOI:10.1080/00958972.2014.911850

Two new heterometallic compounds, [Ni(bpy)₃][Mn(NCO) ₄]·H₂O (1) and [Ni(phen)₃] ₂[Zn(NCO)₄]₂·4DMSO·H ₂O (2) [bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline], hav

Full text of DOI:10.1080/00958972.2014.911850

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Synthesis, characterization, and
catalytic activity of heterometallic ion-
pair Ni/Mn and Ni/Zn complexes
Nittaya Thuyweanga, Lip Lin Kohb, T.S. Andy Horbc & Somying
Leelasubcharoena
a Materials Chemistry Research Unit, Faculty of Science,
Department of Chemistry and Center of Excellence for Innovation
in Chemistry, Khon Kaen University, Khon Kaen, Thailand
b Faculty of Science, Department of Chemistry, National
University of Singapore, Singapore
c Institute of Materials Research and Engineering, Agency for
Science, Technology and Research, Singapore
Accepted author version posted online: 22 Apr 2014.Published
online: 08 May 2014.
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To cite this article: Nittaya Thuyweang, Lip Lin Koh, T.S. Andy Hor & Somying Leelasubcharoen
(2014) Synthesis, characterization, and catalytic activity of heterometallic ion-pair Ni/
Mn and Ni/Zn complexes, Journal of Coordination Chemistry, 67:7, 1219-1235, DOI:
10.1080/00958972.2014.911850
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Journal of Coordination Chemistry, 2014
Vol. 67, No. 7, 1219–1235, http://dx.doi.org/10.1080/00958972.2014.911850
Synthesis, characterization, and catalytic activity of
heterometallic ion-pair Ni/Mn and Ni/Zn complexes
NITTAYA THUYWEANG†, LIP LIN KOH‡, T.S. ANDY HOR‡§ and
SOMYING LEELASUBCHAROEN*†
†Materials Chemistry Research Unit, Faculty of Science, Department of Chemistry and Center of
Excellence for Innovation in Chemistry, Khon Kaen University, Khon Kaen, Thailand
‡Faculty of Science, Department of Chemistry, National University of Singapore, Singapore
§Institute of Materials Research and Engineering, Agency for Science, Technology and Research,
Singapore
(Received 25 September 2013; accepted 11 March 2014)
Two new heterometallic compounds, [Ni(bpy)3][Mn(NCO)4]·H2O (1) and [Ni(phen)3]2[Zn
(NCO)4]2·4DMSO·H2O (2) [bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline], have been syn-
thesized and characterized. The structures of 1 and 2 were solved by single-crystal X-ray diffraction
analysis. The cationic moieties of [Ni(bpy)3]2+ in 1 and [Ni(phen)3]2+ in 2 show octahedral environ-
ments around Ni(II), whereas the anionic groups of [Mn(NCO)4]2− in 1 and [Zn(NCO)4]2− in 2
exhibit tetrahedral geometry around the Mn(II) and Zn(II), respectively. Both compounds are cata-
lysts in the H/D exchange of salicylaldehyde in DMSO-d6 which takes place under mild conditions
and short reaction time.
Keywords: H/D exchange reaction; Catalysis; Heterometallic complex; Ion pair; Cyanate
*Corresponding author. Email: somying@kku.ac.th
© 2014 Taylor & Francis

1220
N. Thuyweang et al.
1. Introduction
Hydrogen/deuterium (H/D) exchange processes are powerful methods to evaluate the poten-
tial of a catalyst for substitution of hydrogen by solvent deuterium [1]. Hydrogens from side
chains of a protein that contain –OH, –SH, –NH2, –COOH, –CONH2 groups, and hydro-
gens from amino and carboxylate termini exhibit rapid H/D exchange [2]. H/D exchange is
an important method for characterizing the conformational flexibility of β2-microglobulin
amyloid fibrils at single residue resolution [3]. Furthermore, deuterated products have been
found in drug discovery processes [4]. Therefore, there is interest in selective catalytic H/D
exchange processes for the synthesis of deuterated products. H/D exchange reactions have
been catalyzed by using acid [5], base [6], or transition metals [7]. The processes are usu-
ally performed with D2 or in deuterated organic solvents such as benzene (C6D6), acetone
(C2D6CO), deuterium oxide (D2O), and methanol (CD3OD), and only in very few cases
dimethyl sulfoxide (C2D6SO) can be used [8–12]. The use of heterometallic complexes for
catalyzed H/D exchange has been found in the past decade. Heterometallic systems have
been studied due to the promise of enhanced catalytic reactivity from the cooperative acti-
vation and synergistic interaction of metal centers with differing electronic properties [13].
Heterometallic Rh/Pd and Rh/Pt complexes rapidly catalyze selective H/D exchange of one
of the diastereotopic protons of the dipycolylamine methylene group in the presence of
CD3OD [14]. Mixed metal complexes offer the opportunity for metal–metal cooperation
[15–18]. The π–π stacking interactions between parallel aromatic rings of 2,2′-bipyridine
(bpy) and 1,10-phenanthroline (phen) have been exploited for coordinative assemblies [19,
20]. Recently, new ion-pair complexes containing bipyridine and 1,10-phenanthroline such
as [Ni(bpy)3]2[Ag(CN)2]3Cl·9H2O [21], [Ni(bpy)3][Ni(CN)4]·6H2O·0.5bpy [22], [Ni(bpy)3]
[Fe(CN)5(NO)]·3H2O [23], [Ni(bpy)3][ZnCl(H2PO4)3] [24], [Ni(bpy)3]2[Mo(CN)8]·12H2O
[25], [Ni(bpy)3]2[W(CN)6]·6H2O [25], [Ni(phen)3][MnCl4] [26], and [Ni(phen)2(tmt-Bu)Cl)]
[Zn(tmt-Bu)Cl3] (tmt-Bu = 1-tert-butylimidazole-2-thione) [26] have been reported, but little is
known on cyanate complexes. The present work reports the synthesis of new heterometallic
compounds and a catalytic study of the compounds in the H/D exchange of salicylaldehyde
in DMSO-d6 solvent.
2. Experimental setup
2.1. Materials and general methods
NiCl2·6H2O, NaOCN, and dimethyl sulfoxide (DMSO-h6) were purchased from Sigma-
Aldrich. MnCl2·4H2O, 2,2′-bipyridine, 1,10-phenanthroline, and organic solvents were pur-
chased from CARLO ERBA. Ni(NO3)2·6H2O was purchased from QRëc. Zn
(CH3COO)2·2H2O was purchased from UNIVAR. Salicylaldehyde and DMSO-d6 were pur-
chased from Aldrich. Elemental analyses of carbon, hydrogen, and nitrogen were performed
on a Perkin–Elmer model 2400 elemental analyzer. FT-IR spectra were recorded as KBr
disks from 4000 to 400 cm−1 on a Perkin–Elmer Spectrum One FT-IR spectrophotometer.
Solid-state (diffuse reflectance) electronic spectrum was measured as polycrystalline sample
on a Perkin–Elmer Lambda 2s spectrometer from 8000 to 18,000 cm−1. Thermogravimetric
analyses were carried out on a Pyris Diamond TG-DTA, Perkin–Elmer instrument with a
heating rate of 10 °C min−1 in a flow of nitrogen gas. Melting point was observed in a capil-
lary tube on an Electrothermal 9100.

Ion-pair Ni/Mn and Ni/Zn complexes
1221
1
1
The progress of the reaction was monitored by H NMR spectroscopy at 27 °C. H NMR
spectra were recorded on a Varian Mecury Plus 400 Spectrometer. The organic product was
confirmed by gas chromatography–mass spectrometry (GC–MS) using a Trace GC chro-
matograph equipped with a Finnigan Polaris Q mass spectrometer (Thermo Finnigan,
USA). About 1 μL of the sample was injected into the gas chromatograph using the split-
less mode. Organic products were analyzed with a ZB-5 column (30 m × 0.25 mm i.d.,
0.25 μm film thickness). The oven was programmed with step temperature program starting
at 60 °C for 5 min and increased to 280 °C with a heating rate of 3 °C min−1. Helium gas
was used as carrier gas at a flow rate of 1.0 mL min−1 (constant flow). The GC injector tem-
perature was 200 °C and the transfer line temperature was held at 275 °C. The mass spec-
trometer presented an electronic impact source (EI) to promote electron ionization operated
at the ionization energy of 70 eV and temperature of the ion source of 250 °C.
2.2. Synthesis of [Ni(bpy)3][Mn(NCO)4]·H2O (1)
A methanol solution (5.0 mL) of 2,2′-bipyridine 0.46 g (3.0 mM, 3 eq) was added to a meth-
anol solution (5.0 mL) of NiCl2·6H2O 0.25g (1 mM, 1 eq). The mixture was stirred for 30
min at room temperature followed by adding a solution of NaOCN 0.15g (2.0 mM, 2 eq) in
Table 1. Crystal data and structure refinement parameters for 1 and 2.
Complex
1
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
34H26MnN10NiO5
C88H74N20Ni2O13S4Zn2
1996.07
293(2)
0.71073
768.30
100(2)
0.71073
Orthorhombic
Pbcn
Triclinic
Pī
14.3532(15)
19.972(2)
11.0569(7)
b (Å)
19.1548(11)
c (Å)
23.449(2)
21.5902(13)
α (°)
90
97.5970(10)
β (°)
90
91.0710(10)
γ (°)
90
105.0240(10)
4370.9(5)
2
1.517
1.138
2052
0.56 × 0.40 × 0.20
Volume (Å3)
Z
6722.2(12)
8
1.518
0.994
3144
0.48 × 0.24 × 0.22
1.74–27.49
−14 ≤ h ≤ 18, −25 ≤ k ≤ 25,
−30 ≤ l ≤ 29
45,873
Density (Calcd) (Mg m−3
)
Absorption coefficient (mm−1
F (000)
)
Crystal size (mm3)
Theta range for data collection (°)
Index ranges
1.11–27.50
−14 ≤ h ≤14, −24 ≤ k ≤ 24, −28 ≤ l ≤ 27
Reflections collected
56,499
Independent reflections
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
7703 [R(int) = 0.0459]
0.8109 and 0.6468
Full-matrix least-squares on F2
7703/2/466
1.048
R1 = 0.0430,
wR2 = 0.1020
R1 = 0.0548,
wR2 = 0.1073
0.644 and −0.750
20,062 [R(int) = 0.0361]
0.5629 and 0.4507
Full-matrix least-squares on F2
20,062/15/1177
1.052
R1 = 0.0448,
wR2 = 0.1123
R1 = 0.0564,
wR2 = 0.1178
R indices (all data)
Largest diff. peak and hole (e Å−3
)
1.345 and −0.900

1222
N. Thuyweang et al.
deionized water (5.0 mL). After stirring for 30 min, a methanol solution of MnCl2·4H2O
0.20 g (1 mM, 1 eq) was added to the solution and stirred for another 5 h. Red powder pre-
cipitated and was recrystallized in DMSO. Red crystals were obtained after three days by
slow evaporation at room temperature. Yield = 0.47 g (70%). M.p. >250 °C. FT-IR (KBr,
cm−1): 3508 (br), 3081 (w), 2188(s), 1599 (m), 1493 (m), 770 (s) and 621 (m). Anal. Calcd
for NiMnC34H26N10O5: C, 53.15; H, 3.41; N, 18.23%. Found: C, 53.02; H, 3.22; N,
17.73%.
2.3. Synthesis of [Ni(phen)3]2[Zn(NCO)4]2·4DMSO·H2O (2)
About 5.0 mL of methanol solution of 1,10-phenanthroline 0.30 g (1.5 mM, 3 eq) was added
to a methanol solution (5.0 mL) of Ni(NO3)2·6H2O 0.16 g (0.5 mM, 1 eq). The mixture was
stirred for 30 min at room temperature followed by adding a solution of NaOCN 0.07 g
(1.0 mM, 2 eq) in 5.0 mL of DI. After the mixture was stirred for 30 min, a methanol solution
of Zn(OAc)2·2H2O 0.15 g (0.5 mM, 1 eq) was added to the mixture and stirred for 5 h. Red
powder precipitated and was recrystallized in DMSO. Red crystals appeared in three days by
slow evaporation at room temperature. Yield = 73.75%. M.p. >250 °C. Anal. Calcd for
Ni2Zn2C88H74N20O13S4: C, 52.95; H, 3.74; N, 14.03%. Found: C, 53.17; H, 3.53; N, 14.75%.
IR (KBr, cm−1): 3445 (br), 3062 (w), 2208 (s), 1626 (m), 1426 (m), 848 (s), 726 (s).
2.4. Catalytic reaction
[Ni(bpy)3][Mn(NCO)4]·H2O (1) 0.0029 g (0.0038 mM, 3 M%) was dissolved in DMSO-d6
(ca. 0.4 mL) and transferred into an NMR tube. Salicylaldehyde 13.40 μL (0.1260 mM) was
1
injected into the tube and determined by H NMR spectroscopy. The progress of the reac-
1
tion was monitored by H NMR spectroscopy. The product of the H/D exchange reaction
1
was identified by GC–MS analysis. H NMR(DMSO-d6, ppm) δ: 10.23 (1H, CH), 7.65
(1H, Ar–H), 7.49 (1H, Ar–H), 6.98 (2H, Ar–H). EI-MS (70 eV): m/z (rel. int. %): 123(23),
121(100), 65(16).
Figure 1. Diffuse reflectance spectra of 1 and 2.

Ion-pair Ni/Mn and Ni/Zn complexes
1223
[Ni(phen)3]2[Zn(NCO)4]2·4DMSO·H2O (2) 0.0076 g (0.0038 mM, 3 M%), Zn
(OAc)2·2H2O 0.0008 g (0.0038 mM, 3 M%), Ni(NO3)2·6H2O 0.0011 g (0.0038 mM, 3 M%),
NiCl2·6H2O 0.0011 g (0.0038 mM, 3 M%), or MnCl2·4H2O 0.0008 g (0.0038 mM, 3 M%)
were used as catalysts in identical reactions.
Figure 2. TGA curves of 1 and 2.
Figure 3. Molecular structure of [Ni(bpy)3][Mn(NCO)4]·H2O (1) with displacement ellipsoids shown at 50%
probability level.

1224
N. Thuyweang et al.
Table 2. Selected bond lengths (Å) and angles (°) for 1 and 2.
1
2
Bond lengths (Å)
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–N(4)
Ni(1)–N(5)
Ni(1)–N(6)
Mn(1)–N(7)
Mn(1)–N(8)
Mn(1)–N(9)
Mn(1)–N(10)
Bond lengths (Å)
Ni(1)–N(6)
Ni(1)–N(3)
Ni(1)–N(2)
Ni(1)–N(1)
Ni(1)–N(4)
Ni(1)–N(5)
Ni(2)–N(12)
Ni(2)–N(9)
Ni(2)–N(8)
Ni(2)–N(7)
Ni(2)–N(11)
2.0842(19)
2.0800(19)
2.075(2)
2.0806(19)
2.0774(19)
2.093(2)
2.067(2)
2.073(2)
2.067(3)
2.040(2)
2.0744(18)
2.0799(17)
2.0833(18)
2.0869(18)
2.1019(18)
2.1170(18)
2.0733(18)
2.0789(17)
2.0803(17)
2.0868(18)
2.0927(18)
Bond angles (°)
N(5)–Ni(1)–N(2)
N(4)–Ni(1)–N(1)
N(3)–Ni(1)–N(6)
N(10)–Mn(1)–N(9)
N(10)–Mn(1)–N(7)
N(9)–Mn(1)–N(7)
N(10)–Mn(1)–N(8)
N(9)–Mn(1)–N(8)
N(7)–Mn(1)–N(8)
N(7)–C(31)–O(1)
N(8)–C(32)–O(2)
N(9)–C(33)–O(3)
N(10)–C(34)–O(4)
169.92(8)
171.27(7)
171.95(7)
103.66(10)
113.64(10)
110.13(10)
112.44(9)
106.14(9)
110.35(9)
178.7(4)
Ni(2)–N(10)
Zn(1)–N(13)
Zn(1)–N(14)
Zn(1)–N(15)
Zn(1)–N(16)
Zn(2)–N(17)
Zn(2)–N(18)
Zn(2)–N(19)
Zn(2)–N(20)
N(1)–C(1)
N(1)–C(12)
N(13)–C(73)
N(14)–C(75)
N(15)–C(77)
N(16)–C(79)
N(17)–C(81)
N(20)–C(87)
N(18)–C(83)
2.1205(17)
1.959(2)
1.960(2)
1.967(2)
1.992(2)
1.956(2)
1.9619(19)
1.970(2)
1.977(2)
1.331(3)
1.356(3)
1.162(3)
1.165(3)
1.165(3)
1.175(3)
1.162(3)
1.158(3)
1.169(3)
177.8(3)
178.8(3)
179.5(3)
2
Bond angles (°)
Bond lengths (Å)
N(19)–C(85)
N(19)–Zn(2)–N(20)
C(73)–N(13)–Zn(1)
C(75)–N(14)–Zn(1)
C(77)–N(15)–Zn(1)
C(79)–N(16)–Zn(1)
C(81)–N(17)–Zn(2)
C(83)–N(18)–Zn(2)
C(85)–N(19)–Zn(2)
C(87)–N(20)–Zn(2)
N(19)–Zn(2)–N(20)
C(73)–N(13)–Zn(1)
109.56(12)
154.94(19)
170.8(2)
1.169(3)
Bond angles (°)
148.6(2)
N(8)–Ni(2)–N(11)
N(7)–Ni(2)–N(10)
N(12)–Ni(2)–N(9)
N(2)–Ni(1)–N(5)
N(1)–Ni(1)–N(4)
N(6)–Ni(1)–N(3)
172.52(7)
172.86(7)
168.32(7)
172.72(7)
172.31(7)
167.91(7)
110.50(9)
111.44(8)
106.81(9)
107.27(9)
110.97(8)
109.36(10)
107.99(10)
109.56(12)
154.94(19)
170.8(2)
147.11(19)
164.58(19)
165.1(2)
143.9(2)
158.9(2)
109.56(12)
154.94(19)
N(14)–Zn(1)–N(15)
N(13)–Zn(1)–N(16)
N(14)–Zn(1)–N(16)
N(15)–Zn(1)–N(16)
N(17)–Zn(2)–N(18)
N(17)–Zn(2)–N(19)
N(18)–Zn(2)–N(19)
N(19)–Zn(2)–N(20)
C(73)–N(13)–Zn(1)
C(75)–N(14)–Zn(1)
C(77)–N(15)–Zn(1)
C(79)–N(16)–Zn(1)
C(81)––N(17)–Zn(2)
C(83)–N(18)–Zn(2)
C(85)–N(19)–Zn(2)
C(87)–N(20)–Zn(2)
148.6(2)
147.11(19)
164.58(19)
165.1(2)
143.9(2)
158.9(2)

Ion-pair Ni/Mn and Ni/Zn complexes
1225
2.5. X-ray crystallography
Crystals of 1 and 2 suitable for X-ray crystallographic analysis were obtained from slow
evaporation of a DMSO solution at room temperature. Red block-shaped crystals of 1 and
2 were mounted on quartz fibers for data collection. Diffraction data were collected on a
Brüker AXS APEX diffractometer, equipped with a CCD detector, using graphite-mono-
chromated Mo Kα radiation (λ = 0.71073 Å). The collecting frames of data, indexing reflec-
tion, and determination of lattice parameters and polarization effects were performed with
the SMART suite of programs. Integration of intensity of reflections and scaling was per-
formed by SAINT [27] and empirical absorption correction was performed by SADABS
[28]. Space group determination, structure solution, and least-squares refinements on |F|2
were carried out with SHELXTL [29]. The crystal and refinement data of 1 and 2 are listed
in table 1.
3. Results and discussion
3.1. Synthesis and spectroscopic characterization of 1 and 2
New heterometallic products 1 and 2 were synthesized by a direct method under mild con-
ditions. Compound 1 shows a broad adsorption at 3508 cm−1 due to O–H stretch of water.
The strong peak at 2188 cm−1 is assigned to C=N stretch of cyanate [30]. Medium peaks at
1599 cm−1 are attributed to C=N stretch, whereas a medium peak at 770 cm−1 is assigned
to C–H stretch. This result is assigned to pyridine ring stretching vibrations [24]. Com-
pound 2 shows a broad peak at 3445 cm−1, attributed to O–H stretch of water. The strong
peak at 2208 cm−1 is assigned to C=N stretch of cyanate [30]. The medium peak at
1626 cm−1 is attributed to C=N stretch and the medium peak at 726 cm−1 is assigned to
C–H stretch. The electronic spectra of 1 and 2 are represented in figure 1. The two
Table 3. The comparison of the bond distances (Å) and angles (°) of cations of 1 and 2 with previous research.
Complexes
Bond distances of Ni–N
Bond angles of N–Ni-N
Ref.
[Ni(bpy)3]2[Ag(CN)2]3Cl·9H2O
[Ni(bpy)3][Ni(CN)4]·6H2O·0.5bpy
[Ni(bpy)3][Fe(CN)5(NO)]·3H2O
[Ni(bpy)3][ZnCl(H2PO4)3]
[Ni(bpy)3]2[Mo(CN)8]·12H2O
[Ni(bpy)3]2[W(CN)6]·6H2O
[Ni(phen)3][MnCl4]
[Ni(bpy)3][Mn(NCO)4]·H2O (1)
[Ni(phen)3]2[Zn(NCO)4]2·4DMSO·H2O (2)
2.093(3)–2.096(3)
2.078(3)–2.100(3)
2.072(3)–2.103(3)
2.085(5)–2.089(6)
2.062(13)–2.118(11)
2.039(16)–2.129(16)
2.063(2)–2.144(3)
2.075(2)–2.093(2)
2.0744(18)–2.1170(18)
78.46(10)–95.28 (10)
78.72(11)–79.14(11)
94.35(13)–95.77(13)
78.7(2)–94.8(2)
78.5(5)–96.9(5)
79.2(6)–95.7(6)
79.49(8)–96.39(6)
78.76(8)–95.35(7)
79.57(7)–96.24(7)
[21]
[22]
[23]
[24]
[25]
[25]
[26]
This work
This work
Table 4. Hydrogen bonds (Å) and angles (°) for [Ni(bpy)3][Mn(NCO)4]·H2O (1).
D–H⋯A
d(D–H)
d(H⋯A)
d(D⋯A)
∠(DHA)
O(1W)–H(1WB)⋯O(1)i
O(1W)–H(1WA)⋯O(3)
0.928(19)
0.927(19)
1.92(4)
1.87(3)
2.743(4)
2.737(4)
146(5)
154(5)
Note: Symmetry transformations used to generate equivalent atoms, i: −x + 1/2, −y + 1/2, z − 1/2.

1226
N. Thuyweang et al.
Figure 4. The hydrogen bonded (dashed lines) chain between water and [Mn(NCO)4]2−, showing the 1-D chain
along the c axis. The [Ni(bpy)3]2+ has been omitted for clarity [symmetry code, i: −x + 1/2, −y + 1/2, z − 1/2].
absorptions peaks occur at 526 and 793 nm for 1 which is similar to 2 (525 and 800 nm).
3
Two absorption bands are assigned as the A2g to 3T1g(F)(ν2) and 3A2g to 3T2g(F)(ν1) transi-
3
3
tions, respectively. The absorption band of the A2g to T1g(p)(ν3) transition is obscured by
the charge transfer band of the diimine ligand. The visible transitions are described as d–d
transitions of the nickel(II) in near octahedral environment [26].
Figure 5. The crystal packing of [Ni(bpy)3][Mn(NCO)4]·H2O (1). [Ni(bpy)3]2+ resides in the vacancies between
anion chains.

Ion-pair Ni/Mn and Ni/Zn complexes
3.2. Thermogravimetric analysis
1227
Thermogravimertric analyses (TGA) of both complexes were carried out on a polycrystal-
line sample. For 1, the total weight loss of 65.0% takes place from 184 to 689 °C (figure 2
(solid line)). The decomposition of the compound occurs in two steps, the first of 18.5%
(Calcd 18.9%) corresponds to loss of one water and three cyanates at 184–297 °C. The sec-
ond drop of 46.4% (Calcd 46.1%) corresponds to loss of one cyanate and two bpy mole-
cules at 297–689 °C. The thermal decomposition of 2 takes place in one step (figure 2
(dashed line)). The observed weight loss of 31.68% (Calcd 32.16%) corresponds to loss of
two 1,10-phenanthroline, one cyanate, two dimethyl sulfoxide, and one water from 217 to
530 °C.
3.3. Crystallographic structure
3.3.1. Crystal structure of [Ni(bpy)3][Mn(NCO)4]·H2O (1). Complex 1 is ionic and con-
sists of a [Ni(bpy)3]2+, [Mn(NCO)4]2−, and a water hydrate (figure 3). Selected bond dis-
tances and angles are given in table 2. The [Ni(bpy)3]2+ is six-coordinate with three
chelating bpy. The Ni–N bond distances are 2.075(2)–2.093(2) Å and in agreement with the
literature value [20–24]. The coordination sphere is slightly distorted from ideal octahedral,
with N–Ni–Ntrans angles varying from 169.92(8)° to 171.95(7)°. The comparison of the
bond distances and bond angles of the cationic moiety with the previous reports is shown
Figure 6. The molecular structure of [Ni(phen)3]2[Zn(NCO)4]2·4DMSO·H2O (2) with displacement ellipsoids
shown at 50% probability level.

1228
N. Thuyweang et al.
Figure 7. 1H NMR spectrum of salicylaldehyde-d1 in the presence of 1.
in table 3. The data of 1 insignificantly differ from those in previous work, which confirms
the octahedral geometry. [Mn(NCO)4]2− is tetrahedral with manganese(II) coordinated with
four N-donating cyanate groups. The same anion was reported in (Et4N)2Mn(NCO)4 but
this complex has not been crystallographically characterized [31]. The Mn–N bond dis-
tances are within the range of 2.040(2) to 2.073(2) Å, similar to the literature values of
2.105(2) Å for [Mn(salen)(NCO)]2 [32]. The N–Mn–N bond angles vary from 103.16(10)°
Figure 8. GC–MS chromatogram of salicylaldehyde in DMSO-d6 in the presence of 1.

Ion-pair Ni/Mn and Ni/Zn complexes
1229
to 112.44(9)° within a tetrahedral geometry. The cyanates are linear, as evident from
N–C–O angles (178.8(3)°–179.5(3)°). In addition, each water is involved in two hydrogen
bonds, formed between hydrogen of water and oxygen of cyanate. The bond distances of
O(1W)⋯O1i and O(1W)⋯O3 are 2.743(4) and 2.737(4) Å, respectively. The bond angles
for O(1W)–H(1WB)⋯O1i and O(1W)–H(1WA)⋯O3 are 146(5)° and 154(5)°, respectively
(table 4). These H-bonding interactions stabilize the structure by linking the dianions and
extending into a 1-D chain along the c axis (figure 4). As shown in the crystal packing,
[Ni(bpy)3]2+ reside in the vacancies between the anion chains (figure 5).
3.3.2. Crystal structure of [Ni(phen)3]2[Zn(NCO)4]2·4DMSO·H2O (2). Molecular struc-
ture of 2 is shown in figure 6 and selected bond distances and angles of 2 are reported in
table 2. Complex 2 is an ion-pair compound built from two [Ni(phen)3]2+ and two
[Zn(NCO)4]2− along with four DMSO and one water as solvents of crystallization in the
asymmetric unit. Two nickel(II) centers are chelated by phen. The Ni–N distances are
2.0744(18)–2.1170(18) and 2.0733(18)–2.1205(17) Å in Ni(1) and Ni(2), respectively.
These bond distances correspond to Ni–N bond distances in [Ni(phen)3][MnCl4] (2.063(2)–
2.144(3) Å) (table 3) [26]. The N–Ni–Ntrans bond angles are 167.91(7)°–172.52(7)°, in
agreement with the literature values [26]. These values deviate from 180 ° due to steric
Figure 9. GC–MS chromatogram of salicylaldehyde in DMSO-h6 in the presence of 1.

1230
N. Thuyweang et al.
constraints arising from the shape of the ligand. From table 3, the bond distances and bond
angles of the cationic group correspond to those of the previous reports which support octa-
hedral geometry. The Zn–N bond distances for [Zn(NCO)4]2− are within the ranges 1.959
(2)–1.992(2) Å and 1.956(2)–1.977(2) Å in Zn(1) and Zn(2), respectively. The results corre-
spond to literature values of Zn–N bond distances (1.985(6) Å) [33]. The N-Zn-Ntrans bond
angles are 106.81(9)–111.44(8)°, suggesting tetrahedral geometry [34].
3.4. Catalytic activity
The H/D exchange of salicylaldehyde in the presence of 1 or 2 was studied at room temper-
1
ature. The reaction was monitored using H NMR spectroscopy. The hydroxyl proton peak
at 10.67 ppm disappeared within 5 min and other peaks remained unchanged in the presence
of 1 (figure 7). This reaction indicates H/D exchange of salicylaldehyde. To confirm the cat-
alytic product, GC–MS analysis was carried out. As shown in figure 8, the product ion
mass spectrum of m/z 123 at retention time 21.09 min produces fragment ions at m/z 121
and 65. The ion at m/z 121 resulted from loss of a deuterium from fragment ion at m/z 123.
The ion at m/z 65 corresponds to formation of [M-C5H5]+. Based on the molecular weight
information of salicylaldehyde, which has a mw of 122, an increase of 1 Da suggests that
only 1 active H in its structure is exchanged with deuterium. The identical reaction was also
studied by using DMSO-h6. The product ion mass spectrum of m/z 122 at the retention time
of 19.40 min shows fragment ions at m/z 121 and 65 (figure 9). The ion at m/z 121 is
formed by losing a hydrogen from the fragment ion at m/z 122. The presence of the frag-
ment ion at m/z 65 suggests the formation of [M-C5H5]+. This result corresponds to the free
salicylaldehyde which has a mw of 122.
Figure 10. 1H NMR spectrum of salicylaldehyde-d1 in the presence of 2.

Ion-pair Ni/Mn and Ni/Zn complexes
1231
The molecular weight of the salicylaldehyde increases 1 Da resulting in the slow mobility
1
of the substance and an increase of the retention time [35]. The GC–MS analysis and H
NMR spectroscopy also confirm the H/D exchange reaction. 2 was also used as a catalyst
1
in the H/D exchange reaction. From H NMR data (figure 10), the proton peak at 10.67 ppm
completely disappeared within 5 min. In addition, the GC–MS chromatogram of the
reaction in DMSO-d6 appeared at retention time of 19.07 min (figure 11). When DMSO-h6
was used instead of DMSO-d6, the GC–MS chromatogram of the reaction occurred at the
retention time of 17.12 min (figure 12). Chromatogram patterns are similar to those of the
reaction in the presence of 1 which was described previously. A proposed mechanism for
the H/D exchange reaction of salicylaldehyde is shown in figure 13. The salicylaldehyde is
coordinated to the catalyst generating A. After that, oxygen of DMSO abstracts a proton
from the hydroxyl group of salicylaldehyde to form B [36]. Subsequently, the oxyanionic
site abstracts a deuterium from DMSO yielding the deuterated products C and D. Hetero-
metallic compounds dissolved in DMSO should be dissociated into [Ni(bpy)3]2+ and
[Mn(NCO)4]2− for 1 and [Ni(phen)3]2+ and [Zn(NCO)4]2− for 2. Considering the steric
effect of the metal center, which resulted in the catalytic activity, the tetrahedral geometry
of the anion is less sterically crowded than the octahedral geometry of the cation, which
should be the active site for the catalysis. In addition, both bpy and phen are bidentate
ligands and unlikely to dissociate giving a vacant site for the substrate to coordinate. To test
the role of the catalytic part, [Ni(bpy)3]Cl2·5.5H2O [37] and [Ni(phen)3]Cl2·7H2O [38] were
Figure 11. GC–MS chromatogram of salicylaldehyde in DMSO-d6 in the presence of 2.

1232
N. Thuyweang et al.
1
synthesized and used in the catalytic reaction. From H NMR spectra, the O–H peak of sali-
cylaldehyde is unchanged after 5 h, suggesting that the anionic moiety plays the key role in
the catalytic process. The same ion of 1 and 2 in previous reports, such as [Ni(bpy)3]2[Ag
(CN)2]3Cl·9H2O
[21],
[Ni(bpy)3][Ni(CN)4]·6H2O·0.5bpy
[22],
[Ni(bpy)3][Fe
(CN)5(NO)]·3H2O [23], [Ni(bpy)3][ZnCl(H2PO4)3] [24], [Ni(bpy)3]2[Mo(CN)8]·12H2O [25],
[Ni(bpy)3]2[W(CN)6]·6H2O [25], and [Ni(phen)3][MnCl4] [26], have not been studied in
catalysis.
However, reaction without complex shows no reaction even after 24 h at room tempera-
ture. In order to test the efficiency of the metal salts, the catalytic ability of various metal
1
salts were examined for the H/D exchange of salicylaldehyde. H NMR spectra are shown
in figure 14 and the results are summarized in table 5. The reaction in the presence of Zn
(OAc)2·2H2O takes place immediately, suggested from the decrease in the intensity of the
hydroxyl proton peak. After 6 h, the hydroxyl proton peak remains as a broad peak. The
identical reaction in the presence of Ni(NO3)2·6H2O, NiCl2·6H2O or MnCl2·4H2O shows
no catalytic ability. The hydroxyl proton of salicylaldehyde remains unchanged. From the
result, heterometallic compounds 1 and 2 are efficient catalysts in the H/D exchange of sali-
cylaldehyde under mild conditions and short reaction times.
Figure 12. GC–MS chromatogram of salicylaldehyde in DMSO-h6 in the presence of 2.

Ion-pair Ni/Mn and Ni/Zn complexes
1233
Figure 13. A proposed mechanism for the H/D exchange reaction of salicylaldehyde.
Figure 14. The 1H NMR spectra of the H/D exchange of salicylaldehyde in the presence of 1, 2, Zn(OAc)2·2H2O,
MnCl2·4H2O, NiCl2·6H2O, or Ni(NO3)2·6H2O.

1234
N. Thuyweang et al.
Table 5. The H/D exchange reaction of salicylaldehyde in the presence of 1, 2, Zn(OAc)2·2H2O, MnCl2·4H2O,
NiCl2·6H2O or Ni(NO3)2·6H2O.
Entry
Catalysts
Time
1
2
3
4
5
6
[Ni(bpy)3][Mn(NCO)4]·H2O (1)
[Ni(phen)3]2[Zn(NCO)4]2·4DMSO·H2O (2)
Zn(OAc)2·2H2O
MnCl2·4H2O
NiCl2·6H2O
5 min
5 min
5 min, within 6 h peak at 10.67 ppm shows a broad
No reaction
No reaction
No reaction
Ni(NO3)2·6H2O
Note: Condition: Catalyst 3 M% in DMSO-d6, salicylaldehyde 0.0126 mM.
4. Conclusion
Two new heterometallic compounds, [Ni(bpy)3][Mn(NCO)4]·H2O (1) and [Ni(phen)3]2[Zn
(NCO)4]2·4DMSO·H2O (2), were synthesized under mild conditions. The cationic moieties
of [Ni(bpy)3]2+ and [Ni(phen)3]2+ show octahedral geometry, whereas the anionic [Mn
(NCO)4]2− and [Zn(NCO)4]2− exhibit tetrahedral geometry. The two compounds are power-
ful catalysts in the H/D exchange of salicylaldehyde in a DMSO-d6 under mild conditions
and short reaction times.
Supplementary material
CCDC 882848 and 936776 contain the crystallographic data for 1 and 2, respectively.
These data can be obtained free of charge from The Cambridge Crystallographic Data Cen-
ter via E-mail: deposit@ccdc.cam.ac.uk or www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
This work was financially supported by Khon Kaen University under Incubation Researcher Pro-
ject and the Center of Excellence for Innovation in Chemistry (PERCH-CIC). We are grateful to
Miss Tan Geok Kheng and Hong Yimian (National University of Singapore) for the solution of
the crystal structure. We wish to acknowledge the support of the Khon Kaen University Publica-
tion Clinic, Research and Technology Transfer Affairs, Khon Kaen University, for their assis-
tance.
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