and 4-aminopyridine: syntheses, structures, and ...

Monatsh Chem DOI 10.1007/s00706-011-0578-3

ORIGINAL PAPER

Two new nickel(II) carboxylates with 3- and 4-aminopyridine: syntheses, structures, and magnetic properties Brina Dojer • Amalija Golobicˇ • Zvonko Jaglicˇic´ Matjazˇ Kristl • Miha Drofenik

•

Received: 20 May 2011 / Accepted: 12 July 2011 Ó Springer-Verlag 2011

Abstract The synthesis and characterization of two new nickel(II) coordination compounds with 3- and 4-aminopyridine are reported. They were obtained after dissolving Ni(CH3COO)24H2O in different solutions of 3- and 4-aminopyridine. The products were characterized magnetically, structurally by single-crystal X-ray diffraction analysis, and spectrally by FT-IR spectroscopy. Dark green crystals of the polymeric coordination complex {[Ni(O2CCH3)2(3-apy)2]H2O}n were synthesized by the reaction of Ni(CH3COO)24H2O and 3-aminopyridine (3-apy). The molecular structure of this complex consists of a zigzag chain in which nickel(II) ions are connected by bridging 3-aminopyridine ligands. The Ni(II) ion is six-coordinated by three oxygen atoms from two acetate ligands, one chelating and one monodenate, and by three nitrogen atoms from three 3-aminopyridine ligands, one terminal and two bridging ones. The blue crystals obtained by the reaction of Ni(CH3COO)24H2O with 4-aminopyridine (4-apy) consist B. Dojer (&)  M. Kristl  M. Drofenik Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, 2000 Maribor, Slovenia e-mail: [email protected] A. Golobicˇ Faculty of Chemistry and Chemical Technology, University of Ljubljana, Asˇkercˇeva 5, 1000 Ljubljana, Slovenia Z. Jaglicˇic´ Institute of Mathematics, Physics and Mechanics, Jadranska 19, 1000 Ljubljana, Slovenia Z. Jaglicˇic´ Faculty of Civil and Geodetic Engineering, Jamova 2, 1000 Ljubljana, Slovenia M. Drofenik Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

of the monomeric complex [Ni(O2CCH3)2(4-apy)2(H2O)2], in which the ligands possess trans geometry around the Ni(II) ion. The interactions including intra- and intermolecular hydrogen bonds in the crystal structures of both complexes are discussed. Magnetic properties of both compounds were studied between 2 and 300 K giving the result of leff = 3.1 BM in the paramagnetic region. Keywords Nickel(II) acetate tetrahydrate  Aminopyridine  X-ray structure determination  Magnetic properties  Hydrogen bonds

Introduction During the last decade a lot of work has been devoted to the study of mixed carboxylato–pyridine ligand complexes because of their properties in areas such as crystallography, catalysis, and magnetochemistry. Some of the most studied groups in the solid state are copper(II), nickel(II), and cobalt(II) complexes [1–14]. The diversity of these kinds of compounds depends on the carboxylate radical tail and also on the additional N-donor ligand with respect to its size, shape, and substituents. Among the great number of structurally characterised carboxylato-coordinated Ni complexes, there are also a few examples of acetate-coordinated compounds of Ni(II) with 2-aminopyridine [15], 2-pyridinecarboxaldehyde [16], and pyridine [17–20]. Herein we report the syntheses, crystal structures, and magnetic behaviour of new Ni(II) coordination compounds with acetate and 3- and 4-aminopyridine ligands. The aim of our work was to find out how the change of the aminopyridine ligands with different position of the amino substituent affected the crystal structure. We discuss the

123

B. Dojer et al. Fig. 1 ORTEP drawing (with atom labelling scheme) of the structure of compound 1. Ellipsoids are drawn at 50% probability level. The dashed lines represent hydrogen bonding

shown in Figs. 1 and 2. Selected bond distances and angles are displayed in Table 1. The reactions were done under different conditions (temperature, solvent, amounts of the reagents). Description of the structures

Fig. 2 ORTEP drawing (with atom labelling scheme) of molecules of compound 2. Ellipsoids are drawn at 50% probability level

interactions, hydrogen bonding, and metal–ligand coordination. The introduction of hydrogen bonds can be achieved by incorporation of carboxylate groups and aminopyridines into the coordination compounds. Water molecules from the solvent can be incorporated into the structure in coordination mode and tend to form hydrogen bonds with nitrogen and oxygen. Aminopyridines can be used as bridges owing to the possible coordination sites of two lone electron pairs on both nitrogen atoms in one molecule.

Results and discussion We synthesized and characterized two new coordination compounds: {[Ni(O2CCH3)2(3-apy)2]H2O}n (1) and [Ni(O2CCH3)2(4-apy)2(H2O)2] (2) by the reactions of the corresponding aminopyridine (apy) with Ni(CH3COO)2 4H2O. The molecular structures of both compounds are

123

In compound 1, {[Ni(O2CCH3)2(3-apy)2]H2O}n, the central Ni(II) ion is coordinated by three nitrogen atoms from three 3-aminopyridine ligands (3-apy) and three oxygen atoms from two acetate ligands, one chelating and one monodenate (Fig. 1). Two N atoms correspond to aromatic ring N atoms from two symmetry-independent 3-apy units and one to an amino N atom from a symmetry-related (x - 1/2, -y ? 3/2) 3-apy ligand. The Ni atom has a distorted octahedral geometry. The chelate bond lengths ˚ ) and Ni–O1 (2.1040(16) A ˚ ) are Ni–O2 (2.1710(15) A ˚) longer in comparison to the distance Ni–O3 (2.0400(17) A 2 1 of unidentate binding which is typical for nickel g ,g bis(carboxylates) [21]. The O(1)–Ni–O(2) angle of 61.53(6)° and consequently large O(1)–Ni–N(1) and O(2)– Ni–O(3) angles (100.24(7)° and 107.00(7)°) with large deviations from the ideal 90° are also characteristic values for this type of compound [21]. The nitrogen atom of the amino group is bonded to Ni atom at significantly longer ˚ ) in comparison with nitrogen atoms distance (2.2159(19) A ˚ for of the aromatic rings (2.0627(17) and 2.0821(19) A N1 and N3, respectively). Similar was observed also in bis[(4-aminobenzoic acid-N)-(2,20 -bi-imidazole)]-nickel(II) complex [22]. Such [Ni(O2CCH3)2(3-apy)2] moieties are through bridging 3-apys connected to polymeric chains which run parallel to the a axis. The chains are stabilized by intramolecular N–HO hydrogen bonds donated by the

Two new nickel(II) carboxylates with 3- and 4-aminopyridine ˚ and angles/° for 1 and 2 Table 1 Selected bond lengths/A

Table 2 Hydrogen bonding geometry for 1 and 2 ˚ d(D–H)/A

˚ d(HA)/A

˚ d(DA)/A

N2–H21O2a

0.82(3)

2.20(3)

3.020(2)

179(5)

N2–H22O4

0.96(5)

1.88(5)

2.753(3)

151(3)

2.1033(14)

N4–H41O5b

0.88(6)

2.42(6)

3.217(4)

152(5)

a

2.0646(13)

N4–H42O5

c

0.87(5)

2.18(5)

3.035(4)

170(4)

Ni–O3a

2.1033(14)

O5–H51O4d

0.77(4)

1.98(4)

2.742(3)

173(3)

O5–H52O1e

0.91(4)

1.87(4)

2.778(3)

173(4)

N2–H2DO3c

0.87(3)

2.42(3)

3.234(3)

158(3)

1

2

D–HA

Ni–O1

2.1040(16)

2.0646(13)

Ni–O2

2.1710(15)

Ni–O3

2.0400(17)

Ni–O1 Ni–N1

2.0627(17)

Ni–N1a

2.1140(12)

\(DHA)/°

Ni–N3

2.0821(19)

N2–H2EO1a

0.84(3)

2.33(3)

3.068(2)

147(2)

Ni–N2b

2.2159(19)

O3–H3AO2f

0.82(3)

1.84(3)

2.6416(19)

162(2)

e

0.78(3)

1.95(3)

2.7251(19)

175(3)

O1–C1

1.259(2)

O1–C11 O2–C1

1.272(3)

O2–C11

1.265(3)

O3–C13

1.255(3)

O4–C13

1.2569(3)

N1–C1

1.326(4) 1.341(2)

N1–C5

1.330(3)

N1–C7

1.345(2)

N2–C2

1.416(3)

N2–C5

1.361(2)

O1–Ni–O2

61.53(6)

O1–Ni–O3

168.44(7)

O1–Ni–N1

100.24(7)

O3–Ni–O3a

88.16(5) 92.32(5) 180.00(10)

O1–Ni–O3a

91.84(5)

O1–Ni–N3 O1–Ni–N2b

91.70(7) 87.91(7)

O2–Ni–O3

107.00(7)

O2–Ni–N1

161.76(7)

O2–Ni–N3

88.37(7)

O1–Ni–N1a

87.69(5)

O2–Ni–N2b

89.50(7)

O3–Ni–N1

91.24(7)

O3–Ni–N1a

91.25(5) 88.75(5)

O3–Ni–N3

89.28(7)

O3–Ni–N2b

90.66(7)

N1–Ni–N3

91.78(7)

N1–Ni–N2b

90.47(7)

N2i–Ni–N3

177.75(7)

Symmetry codes:

a

1.263(2)

N1–C3

a

-x, -y, -z ;

b

O3–H3BO2

x - 1/2, -y ? 3/2, -z ? 1

N2 atom of a coordinated amino group. Each N2 atom is a donor of two intramolecular hydrogen bonds, which are accepted by the O(2) atom of the chelate acetate and by the uncoordinated O(4) atom of the monodenate acetate ligand. The asymmetric unit of the title compound also contains one water molecule which is a donor of two intermolecular

b

Symmetry transformation for acceptors: x ? 1, y, z; -x?1, y ? 1/2, -z ? 1/2; c -x ? 1/2, -y, z - 1/2; d x, y - 1, z; e x - 1/2, -y ? 1/2, -z ? 1; f -x, -y, -z

O–HO hydrogen bonds to O(1) of the chelate and to uncoordinated O(4) atoms, which both belong to the same chain. The oxygen atom of water molecules is also an acceptor of two intermolecular N–HO hydrogen bonds which are donated by an uncoordinated amino group from another two neighbouring chains. In this manner water molecules and polymeric coordination molecules are connected into a 3D structure. The geometry of hydrogen bonds is presented in Table 2. The crystal structure of compound 2 is made up of centrosymmetric mononuclear [Ni(O2CCH3)2(4-apy)2(H2O)2] molecules. The Ni(II) ion is trans-octahedrally coordinated by two oxygen atoms from two unidentate acetate ligands, two water molecules, and two aromatic N atoms of 4-aminopyridine ligands (Fig. 2). As in the analogous compound with pyridine instead of 4-apy, [Ni(O2CCH3)2(py)2(H2O)2] ˚ ) is [20], the bond length of Ni–O from acetate (2.0646(13) A significantly shorter than the Ni–O distance of water ˚ ) and the Ni–N distance (2.1140(12) A ˚ ). (2.1033(14) A Similar also are the bond angles around the nickel atom, which are close to ideal 90° or 180°, respectively. The conformation of the basal plane, consisting of water molecules and acetate ions bonded to Ni, is in both compounds stabilised by two intramolecular hydrogen bonds donated by coordinated water and accepted by an uncoordinated O atom of the acetate ligand. Furthermore in both compounds a water molecule is, through its second H atom, a donor of an intermolecular hydrogen bond accepted by an uncoordinated O atom of a symmetry-related neighbouring complex molecule. In this way 2D layers of hydrogen-bonded complex molecules are formed perpendicular to the longest cell edge. In both compounds the aromatic rings within the complex molecules are coplanar but have significantly different orientations with regard to the acetate ligand. In compound 2 the aforementioned layers of hydrogen-bonded molecules, which are stacked along the c axis, are also hydrogen bonded

123

B. Dojer et al. Fig. 3 Packing diagram of 2 viewed along a axis. Hydrogen bonding is shown by the dashed lines

c

O

b

paramagnetic behaviour. In order to calculate the Curie constant and obtain information about the valence state of Ni ions, the high temperature data (T [ 60 K has been used for fitting) can be described by the Curie–Weiss law: c v¼ : ð1Þ sh

Fig. 4 Magnetic susceptibility v and product vT (insets) as a function of temperature for 1 and 2. Solid lines in inset are fits with Eq. (2) for corresponding compounds

via N–HO intermolecular hydrogen bonds into a 3D supramolecular architecture, which is shown in Fig. 3. The donor of these hydrogen bonds is the amino group of 4-apy and the acceptors are a water molecule and a coordinated O from an acetate ligand of a neighbouring layer. In the pyridine analogue, in which there are no amino groups, the interaction among the hydrogen-bonded layers is predominately of van der Waals kind. The nitrogen atom N2 of the amino group is a donor of two intermolecular hydrogen bonds: one to the carboxylate O1 and one to the water O3 atom. Magnetic measurements The susceptibility v(T) of both complexes monotonically increases as temperature decreases from 300 to 2 K. The inset in Fig. 4 shows the product vT as a function of temperature T. From room temperature to around 60 K the product vT is approximately constant revealing a

123

The obtained Curie constant is similar for both samples C = 1.20 emu K mol-1. The corresponding effective moment is leff = 3.1 BM. This agrees well with the expected theoretical spin-only value for a noninteracting S = 1 magnetic ion of Ni2? [23]. With decreasing temperature below 60 K the product vT starts to decrease smoothly for both samples. The decrease of the product vT can be attributed to a zero-field splitting of Ni2? ion with d8 configuration in axially distorted octahedral surroundings as follows from the structural determination. The magnetic susceptibility parallel to the magnetic field is then [24]   D 2 2 exp  kR T 2NA gz lB  ; vs ¼ kB T 1 þ 2 exp  D kB T

whereas perpendicular to it is   D 2 2 1  exp  kB T 2NA gx lB  ; vx ¼ D 1 þ 2 exp  D kD T

where NA is the Avogadro number, lB Bohr magneton, kB Boltzmann constant, and D is zero-field splitting energy. For the polycrystalline sample we used in the experiment, the average susceptibility v was measured: v ¼ ðvz þ 2vx Þ=3:

ð2Þ

Assuming gz = gx = g, the results of fitting procedures (solid lines in inset in Fig. 4) are parameters g = 2.19

Two new nickel(II) carboxylates with 3- and 4-aminopyridine

and D = 3.6 cm-1 for 1 and g = 2.13 and D = 10.0 cm-1 for 2.

Table 3 Experimental data for the X-ray diffraction studies on compounds 1 and 2 1

2

IR spectra C14H20NiN4O5 C14H22NiN4O6

Formula

The IR spectra of the compounds were compared with each other and with the information found in the literature [25]. There are some differences between the compounds in the NH2 stretching region. In the IR spectrum of compound 1 the stretching vibration at 3,423 cm-1 was assigned as mas(NH2) and that at 3,341 cm-1 as ms(NH2), and in the spectrum of compound 2 the vibrations observed at 3,436 and at 3,352 cm-1 can be assigned as mas(NH2) and ms(NH2). The bands around 3,000 cm-1 are assigned to the stretching modes of the water molecules for both compounds. In the range 1,650–1,590 cm-1 some NH2 deformation vibrations occurred (1: 1,644, 1,609 cm-1; 2: 1,650, 1,625 cm-1). Some peaks in the region 1,610– 1,400 cm-1 (1: 1,536, 1,456 cm-1; 2: 1,519, 1,421 cm-1) can be assigned to ring breathing vibrations. Stretching vibrations centred at about 1,550 cm-1 are assigned to the symmetric mode of the acetate groups, and those at about 1,400 cm-1 to the asymmetric mode (1: ms = 1,548, mas = 1,421 cm-1; 2: ms = 1,553, mas = 1,420 cm-1). There are some differences between the compounds, due to the bidentate and monodentate acetate groups. Peaks are also observed at about 1,340–1,250 cm-1, where C–N stretching vibrations can be observed. Some ring vibrations in the region between 900 and 700 cm-1 can be assigned to 3- (810, 796 cm-1) and 4-aminopyridine (830, 840 cm-1).

Experimental All starting compounds and solvents were used as purchased. Infrared spectra were recorded on a Perkin–Elmer Spectrum 100 spectrometer. Elemental analyses were carried out on a Perkin–Elmer 2400 CHN analyser at the University of Ljubljana. Magnetic properties of both modifications were studied with a Quantum Design MPMS-XL-5 SQUID magnetometer at the University of Ljubljana (Institute of Mathematics, Physics and Mechanics). catena-(l2-3-Aminopyridine-N,N’)-(acetato-O,O’)(acetato-O)-(3-aminopyridine-N)-nickel(II) hydrate, {[Ni(O2CCH3)2(3-apy)2]H2O}n (1, C14H20NiN4O5) Solid 3-aminopyridine (0.282 g, 3.0 mmol) was slowly added to a mixed tetrahydrofuran/methanol solution (5 cm3 ? 5 cm3) of 0.249 g nickel acetate tetrahydrate (1.0 mmol). The solution was refluxed for about 2 h. After filtration and slow cooling, the solution was left in the air until most of the solvent was evaporated. The sample was

-1

Fw/g mol

383.03

Crystal size /mm

0.30 9 0.22 9 0.30 9 0.30 9 0.12 0.15 Green Blue

Crystal colour

401.07

Crystal system

Orthorhombic

Orthorhombic

Space group ˚ a/A

P212121

Pbca

9.8241(2)

11.8385(2)

˚ b/A ˚ c/A

11.0429(2)

8.7974(1)

15.8954(4)

16.8254(2)

a/°

90

90

b/°

90

90

c/° ˚3 V/A

90

90

1,724.44(6)

1,752.33(4)

Z

4

4

Calcd density/g cm-3

1.475

1.520

F(000)

800

840

h range/°

1.00–27.48

2.42–27.47

No. of collected reflns No. of independent reflns

10,876 3,882

29,108 2,001

Rint

0.047

0.030

No. of reflns used

3,882

2,001

No. parameters

243

133

R[I [ 2r(I)]a

0.029

0.0323

wR2 (all data)b

0.078

0.1208

Goof, Sc

1.06

1.15

Maximum/minimum residual ?0.28/-0.28 ?1.27/-0.44 ˚ -3 electron density/e A P P a R = ||F Fo| i o| h- |Fc||/ nP  2 Ph  2 2 io1=2 b 2 w Fo wR2 = w Fo  Fc2 = nPh  i o1=2  2 c S= w Fo2  Fc2 =ðn  p where n is the number of reflections and p is the total number of parameters refined

put in the fridge and left there for 2 days. The dark green crystalline product of 1 was dried in a desiccator over KOH. Yield: 0.273 g (71.2%). trans-Bis(acetato-O)-bis(4-aminopyridine-N)-diaqua-nickel(II), [Ni(O2CCH3)2(4-apy)2(H2O)2] (2, C14H22NiN4O6) Solid nickel acetate tetrahydrate (0.373 g, 1.5 mmol) was slowly added to a solution of 0.282 g 4-aminopyridine (3.0 mmol) in a mixture of methanol (2.5 cm3) and dichloromethane (2.5 cm3). The obtained solution was heated and stirred at about 50 °C for 3 h. After filtration, the solution was put in the refrigerator and the crystalline product separated in 1 day. The crystals of 2 were dried in a desiccator over KOH. Yield: 0.388 g (64.5%).

123

B. Dojer et al.

X-ray crystallography Crystal data and refinement parameters of compounds 1 and 2 are listed in Table 3. The X-ray intensity data were collected at room temperature with a Nonius Kappa CCD diffractometer equipped with graphite-monochromated Mo ˚ ). The data were processed by Ka radiation (k = 0.71072 A using DENZO [26]. The structures were solved by direct methods (SIR-97) [27] and refined by a full-matrix leastsquares procedure based on F2 using SHELXL-97 [28]. Magnetic measurements The magnetic susceptibility of both complexes was investigated between 2 and 300 K in a constant magnetic field H = 1,000 Oe with a Quantum Design MPMS-XL-5 SQUID susceptometer. The temperature-dependent susceptibilities v = M/H are shown in Fig. 4. The data were corrected for sample holder contribution and temperatureindependent magnetic susceptibility of inner shell electrons (Larmor diamagnetism) as obtained from Pascall’s tables [24]. Acknowledgments The authors thank the Ministry of Higher Education, Science and Technology of the Republic of Slovenia for support, Daniel Korpar for help with the laboratory work, and Marta Kasunicˇ for some measurements.

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