Synthesis, crystal structures, spectral and magnetic properties of nickel(II) pyridinecarboxylates with N-heterocyclic ligands

Accepted Manuscript Synthesis, crystal structures, spectral and magnetic properties of nickel(II) pyridinecarboxylates with N-heterocyclic ligands Jozef Miklovič, Alena Packová, Peter Segľa, Ján Titiš, Marián Koman, Ján Moncoľ, Roman Boča, Vladimír Jorík, Hajnalka Krekuska, Dušan Valigura PII: DOI: Reference:

S0020-1693(15)00082-1 http://dx.doi.org/10.1016/j.ica.2015.01.046 ICA 16418

To appear in:

Inorganica Chimica Acta

Received Date: Revised Date: Accepted Date:

14 October 2014 16 December 2014 25 January 2015

Please cite this article as: J. Miklovič, A. Packová, P. Segľa, J. Titiš, M. Koman, J. Moncoľ, R. Boča, V. Jorík, H. Krekuska, D. Valigura, Synthesis, crystal structures, spectral and magnetic properties of nickel(II) pyridinecarboxylates with N-heterocyclic ligands, Inorganica Chimica Acta (2015), doi: http://dx.doi.org/10.1016/ j.ica.2015.01.046

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Synthesis, crystal structures, spectral and magnetic properties of nickel(II) pyridinecarboxylates with N-heterocyclic ligands Jozef Mikloviča,*, Alena Packováa, Peter Segľab, Ján Titiša, Marián Komanb, Ján Moncoľb, Roman Bočaa, Vladimír Joríkb, Hajnalka Krekuskac, and Dušan Valigurab a

Department of Chemistry, Faculty of Natural Science, University of SS Cyril and Methodius, SK-917 01

Trnava, Slovakia b

Institute of Inorganic Chemistry, FCHPT, Slovak University of Technology, SK-812 37, Bratislava, Slovakia

c

Department of Chemistry, University of Szeged, H-6720, Szeged, Hungary

Correspondence e-mail: [email protected]

Abstract The synthesis and characterization of eight new pseudooctahedral nickel(II) aqua-complexes [Ni(2MeSnic)2(L)2(H2O)2] (where 2-MeSnic is 2-methylsulfanylnicotinato and L is furo[3,2-c]pyridine – fpy, 2,3dimethyl-furo[3,2-c]pyridine – Me2fpy, 2-(3-trifluoromethylphenyl)-furo[3,2-c]pyridine – CF3Phfpy, 3,5dimethylpyridine – 3,5-Me2py and iso-quinoline – iq) as well as complexes [Ni(2-MeSnic)2(L)2] (where L is 2methylfuro[3,2-c]pyridine – Mefpy), benzo[4,5]furo[3,2-c]pyridine – Bfpy and iso-quinoline – iq) are reported. Crystal structure of complexes [Ni(2-MeSnic)2(L)2(H2O) 2] (L = fpy and Me2py) was determined by the singlecrystal X-ray structure analysis and that of [Ni(2-MeSnic)2(L)2(H2O)2] (L = Me2 fpy and iq) complexes was determined using X-ray powder diffraction data. The Ni(II) central atom in all four complexes is situated at the centre of symmetry and it is pseudooctahedrally coordinated by two carboxylato oxygen atoms of the unidentate 2-methylthionicotinato ligands, the two pyridine nitrogen atoms of unidentate L, and two oxygen atoms of aqua ligands. The hydrogen atoms of aqua ligands in all four cases form hydrogen bonds. The IR and electronic data of complexes without aqua ligands [Ni(2-MeSnic)2L2] (L = Mefpy, Bfpy and iq) are rather typical for asymmetrically chelating carboxylic groups, unidentate L, as well as pseudooctahedral nickel(II) atoms. Magnetic measurements of [Ni(2-MeSnic)2(fpy)2(H2O)2], [Ni(2-MeSnic)2(3,5-Me2py)2(H2O)2] and [Ni(pydc)(pydm)]⋅H2O (where pydc is pyridine-2,6-dicarboxylate and pydm is pyridine-2,6-dimethanol) revealed that they behave magnetically as typical S = 1 spin systems with large zero-field splitting. These compounds match well and to some extend the range of the magnetostructural D-correlation for hexacoordinate Ni(II) complexes with rather high structural and magnetic anisotropy.

Keywords: Nickel(II) complex, crystal structure, vibrational and electronic spectra, magnetostructural Dcorrelation

1. Introduction A combination of the nitrogen-containing heterocyclic ligands with carboxylato acids is interesting from several points of view. First, nitrogen-based heterocyclic compounds are frequent constituents of biological systems. For instance, the nicotinic acid and its derivatives

are components of several vitamins and drugs [1-3]. On the other hand, metal carboxylates are often used as model compounds for metalloenzymes [4]. They are also interesting from a chemical point of view as the carboxylate ion can coordinate to metals in a number of ways: as a unidentate ligand, as a chelating ligand, as a bridging bidentate ligand, or as a monoatomic bridging ligand. This causes the existence of a rich family of compounds with various structures [5,6]. The pyridincarboxylato ligands coordinates to metal center not only through the carboxylato group, but also via the nitrogen atom of the pyridine ring, giving rise to various structural types: from 1D infinite chains to large 3D porous networks [7,8]. Also the magnetic properties of the metal carboxylates attracted a great interest [9-12]. Synthesis, crystal structure, electronic and magnetic properties of the complex [Ni(2MeSnic)2(H2O)4]⋅4H2O (2-MeSnic is 2-methylsulfanylnicotinate) were reported in a short communication [13]. This complex is used here as a precursor for synthesis of several analogues containing, in addition, an N-heterocyclic ligand. The crystal structure of four new complexes is determined by the X-ray structure analysis. Based on the molecular structure, electronic

and

infrared

spectra,

magnetic

susceptibility and

magnetization

data,

stereochemistry and mode of ligand coordination in complexes under study is discussed. In addition the crystal structure of [Ni(pydc)(pydm)]⋅H2O as well as its magnetic properties are reported in this communication. Three new complexes were probed for the magnetostructural D-correlation where the axial zero-field splitting parameter D is correlated with the structural tetragonality Dstr. Sketch and abbreviations of pyridinecarboxylates and heterocyclic ligands used in assembling new Ni(II) complexes are presented in Fig. 1.

COO N

N - OOC

SCH 3

COO

O

pyridine-2,6-dicarboxylate (pydc)

2-methylsufanylnicotinate (2-MeSnic)

H 3C

N

-

furo[3,2-c]pyridine (fpy)

H 3C

N H 3C

O

2-methylfuro[3,2-c]pyridine (Mefpy)

N N O

O

2,3-dimethylfuro[3,2-c]pyridine (Me2fpy)

benzo[4,5]furo[3,2-c]pyridine (Bfpy)

N

N

O F3C 2,3-trifluoromethyphenylfuro[3,2-c]pyridine (CF3Phfpy)

iso-quinoline (iq)

CH 3

H 3C N

3,5-dimethylpyridine (3,5-Me2py)

HOH 2C

N

CH 2OH

pyridine-2,6-dimethanol (pydm)

Fig. 1. Sketch and abbreviations of pyridinecarboxylates and N-heterocyclic ligands.

2. Experimental

2.1. Chemical reagents, analysis and physical measurements All chemicals were of reagent grade (Aldrich or Sigma) and used without further purification. Carbon, hydrogen, and nitrogen contents in the complexes were determined by microanalytical methods (Thermo Electron Flash EA 1112). Nickel content was determined

on the double beam atomic absorption spectrophotometer AA-7000 with graphite furnace (Shimadzu) or, after mineralization, by titration with EDTA. Composition of the prepared solid complexes is given in Table S1 (Supplementary material). IR spectra (400 – 4 000 cm-1) were recorded on FT-IR spectrometer (Nicolet 5700, Thermo Scientific) at room temperature (r.t.). Electronic spectra (9 000 – 50 000 cm-1) of the powdered samples in Nujol mull were recorded at r.t. using Specord 200 (Karl-Zeiss). The magnetic data was taken with the SQUID apparatus (MPMS-XL7, Quantum Design) using the RSO mode of detection. The susceptibility taken at B = 0.1 T has been corrected for the underlying diamagnetism and converted to the effective magnetic moment. The magnetization has been measured at two temperatures: T = 2.0 and T = 4.6 K.

2.2. Preparation of the complexes The organic compounds furo[3,2-c]pyridine (fpy), 2-methylfuro[3,2-c]pyridine (Mefpy), 2,3dimethylfuro[3,2-c]pyridine (Me2fpy), benzo[4,5]furo[3,2-c]pyridine (Bfpy) trifluoromethylphenylfuro[3,2-c]pyridine

(CF3Phfpy)

and

2,3-

have been prepared using the

procedures described elsewhere [14-16]. [Ni(2-MeSnic)2(fpy)2(H2O)2] (1), [Ni(2-MeSnic)2(Me2fpy)2(H2O)2] (3) and [Ni(2MeSnic)2(CF3Phfpy)2(H2O)2] (5) Sodium hydroxide (2 mmol) and the equimolar quantity of 2-MeSnicH were dissolved in solvent mixture methanol (10 cm3) and acetonitrile (5 cm3). After dissolving, ligand L was added (2 mmol, L = fpy, Me2fpy, and CF3Phfpy). Prepared solution of the complex 6 was slowly poured to the solution of Ni(NO3)2⋅6H2O (1 mmol) in acetonitrile (10 cm3) and the mixture was stirred at r.t for 1 h. Green precipitate of 5 was filtered off, washed with methanol and dried in vacuum. Solutions of complexes 1 and 3 were left to evaporate slowly at r.t. for a few days. Well shaped blue-green crystals were separated on Büchner funnel, washed with methanol and dried in vacuum. Yield: 1 – 82% (blue, crystalline); 3 – 70% (blue-green, microcrystalline); 5 – 54% (light-green microcrystalline material). [Ni(2-MeSnic)2(Mefpy)2 ] (2), [Ni(2-MeSnic)2(Bfpy)2 ] (4), [Ni(2-MeSnic)2(iq)2] (6), [Ni(2MeSnic)2(iq)2(H2O)2] (7) and [Ni(2-MeSnic)2(3,5-Me2py)2(H2O)2] (8) The complex [Ni(2-MeSnic)2(H2O)4]⋅4H2O [13] (1 mmol) was dissolved in ethanol (10 cm3) and then the solution of the ligand L (2 mmol, L = Mefpy, Bfpy, iq, and 3,5-Me2py) in

ethanol (5 cm3) was added at r.t. and the mixture was stirred at r.t. for 1 h. Complexes 2, 4 and 8 precipitated during stirring and were filtered off, washed with ethanol and dried at r. t. On the other hand, blue-green well shaped crystals were formed by recrystallization of 8 in 20 cm3 of wet ethanol solution. The solution of 6 was left to evaporate slowly at r.t; the precipitate was separated on Büchner funnel after two days, washed with ethanol and dried in vacuum. Green crystals of 7 were prepared by recrystallization of 6 in 20 cm3 of wet ethanol. Yield: 2 – 73% (blue-green microcrystalline); 4 – 63% (blue-green microcrystalline); 6 – 79% (blue-green microcrystalline); 7 – 58% (green microcrystalline); 8 – 88% (light-blue microcrystalline material). [Ni(pydc)(pydm)]⋅H2O (9) Ni(CH3CO2)2⋅4H2O (1 mmol) was dissolved in water (25 cm3) and the equimolar quantities of 2,6-pyridinedimethanol and pyridine-2,6-dicarboxylic acid (known also as dipicolinic acid) were added after short stirring. The resulting solution was stirred gently heated (up to 60 °C) for 1 h, and then it was left to evaporate slowly. The crystals of 9 appeared after a few days and they were dried in vacuum. Yield: 55% (light-blue microcrystalline material).

2.3. Crystallography The powder diffraction pattern used for the structure determination and Rietveld refinement of 3 and 7 was collected within the 2Θ range 6° – 60° with the step of 0.02° on a transmission diffractometer (STADI-P, STOE) equipped with a curved Ge(111) monochromator in primary beam providing CoKα1 radiation and with a linear PSD. Indexing of diffraction pattern was performed by the DICVOL06 program [17] and the estimated lattice parameters were further refined by the LeBail pattern decomposition method using JANA-2006 [18] Ab initio structure determination from the powder diffraction data was obtained with FOX [19] and restrained Rietveld refinement was carried out with JANA-2006. Data collection for the single crystal crystallography and cell refinement were carried out using Eulerian-gradle four-circle diffractometer (Siemens P4) for 1 and 9, and κ-axis fourcircle diffractometer (Xcalibur 2) with Sapphire 2 CCD detector with graphite monochromated MoKα radiation for 8. The diffraction intensities were corrected for Lorentz and polarization factors. The structure was solved by the direct methods with SHELXS-97 [20] or charge-flipping method with SUPERFLIP [21], and refined by the full-matrix least

squares procedure with SHELXL-2014 (1, 9) [20] or CRYSTALS-14.40 (8) [22]. The semiempirical absorption corrections were made by using ψ-scan method using XEMP [23] or multi-scans method using SCALE3 ABSPACK algorithm within CRYSALISPRO [24]. Geometrical analysis was performed using SHELXL-2014 or CRYSTALS. The positions of all hydrogen atoms have been constrained for all compound using AFIX (SHELXL) or RIDE (CRYSTALS) commands. Final crystal data and structure refinement parameters are given in Table 1. The selected bond distances are given in Table 2. The crystal structures were drawn using the OLEX2 [25] and MERCURY [26] program. Table 1 Crystallographic data for complexes 1, 3, 7, 8 and 9 Complex Chemical formula Mr

1

3

7

8

[Ni(2-MeSnic)2 (fpy)2 (H2 O)2] C28 H26N4NiO8S2

[Ni(2-MeSnic)2 (Me2 fpy)2 (H2 O)2] C32H34N4NiO8S2

[Ni(2-MeSnic)2 (iq)2(H2 O)2] C32H30N4NiO6S2

[Ni(2-MeSnic)2(3,5- [Ni(pydc)(pydm)]⋅H2 O Me2py)2(H2O)2 ] C28H34N4NiO6S2 C14H14N2NiO7

9

669.36

725.5

725.5

645.44

380.98

Triclinic, P

Monoclinic, P21/c

Orthorhombic, Pbca

Triclinic, P

Monoclinic, P21/c

Cell setting, space group T (K)

293

293

293

293

293

a (Å)

6.775(2)

11.307(2)

22.7081(9)

7.3427(5)

6.585(1)

b (Å)

10.368(3)

20.617(4)

19.4432(7)

8.6926(4)

25.608(4)

c (Å)

11.292(7)

7.3769(14)

7.2407(2)

12.2566(5)

8.656(1)

α (°)

85.28(3)

90

90

76.826(3)

90

β (°)

73.26(2)

92.328(4)

90

80.429(5)

96.73(1)

γ (°)

77.91(2)

90

90

81.162(5)

90

V (Å3)

742.5(6)

1718.2(6)

3196.9(2)

745.63(7)

1449.6(4)

Z

1

2

4

1

4

Radiation type

Mo Kα

Co Kα

Co Kα

Mo Kα

Mo Kα

µ (mm−1 )

0.85

-

-

0.84

1.38

Crystal size (mm) Diffractometer

0.32 x 0.28 x 0.22 Siemens P4

powder

powder

0.37 x 0.28 x 0.11

0.45 x 0.23 x 0.20

STOE STADI-P

STOE STADI-P

Xcalibur 2 CCD

Siemens P4

Abs. correction

SADABS

None

None

SADABS

XEMP

Tmin, Tmax

0.379, 0.491

-

-

0.322, 0.668

0.282, 0.519

S

1.003

χ2 = 2.045

χ2 = 2.310

1.007

1.016

R1[F2 > 2σ(F2)], wR2(F2 )

0.0505, 0.1202

0.0646, 0.1431

2984a

Rp = 0.0381, Rwp = 0.0535 Rexp = 0.0352, R(F) = 0.0514 2700b

0.0318, 0.0809

No. of reflections / Data points Restrains

Rp = 0.0385, Rwp = 0.0515 Rexp = 0.0361, R(F) = 0.0383 2700b

2389a

2942a

3

47

42

0

3

Parameters

203

98

88

187

217

CCDC no

1013571

1013572

1019466

1013573

1013574

a

No of reflections, b Data Points

3. Results and discussion

3.1. Crystal structure of 1, 3, 7 and 8 The complexes [Ni(2-MeSnic)2(fpy)2(H2O)2] (1) and [Ni(2-MeSnic)2(3,5-Me2py)2(H2O)2] (8) crystallize in the triclinic system with the space group P . The complexes [Ni(2MeSnic)2(Me2fpy)2(H2O)2] (3) and [Ni(2-MeSnic)2(iq)2(H2O)2] (7) crystallize in the monoclinic system with the space group P21/c and orthorhombic system with the space group Pbca, respectively. Molecular structures of these complexes are shown in Fig. 2.

Fig. 2 Molecular structures of complexes 1, 3, 7 and 8

The Ni(II) central atom in all four complexes is situated at the centre of symmetry and it is octahedrally coordinated by two carboxylato oxygen atoms of the 2-methylsulfanylnicotinato ligands at the distance of Ni1–O1 = 1.98 – 2.09 Å, two pyridine nitrogen atoms of fpy (1), Me2fpy (3), iq (7) or 3,5-Me2py (8) at the distance of Ni1–N2 = 2.06 – 2.11 Å, and two oxygen atoms of the aqua ligands at the distance of Ni1–O1W = 2.09 – 2.22 Å (Table 2). The complex 3 is isostructural with the cobalt(II) analogue [Co(2-MeSnic)2(Me2fpy)2(H2O)2] [27].

Table 2 Selected bond lengths (Å) in complexes 1, 3, 7, 8 and 9 1

3

7

8

Ni1 –O1

2.085(3)

2.014(10)

1.983(17)

2.065(2)

Ni1 –N2

2.109(3)

2.085(10)

2.065(12)

2.093(2)

Ni1 –O1W

2.112(2)

2.221(10)

2.215(17)

2.090(2)

Ni1 –N1

1.962(5)

Ni1 –N2

1.992(5)

Ni1 –O1

2.119(4)

Ni1 –O3

2.151(4)

Ni1 –O5

2.110(4)

Ni1 –O6

2.138(4)

9

The complex molecules of 1, 3, 7 and 8 form intramolecular hydrogen bonds O1W– H1W···O2, which lie in bands parallel with a axis (1, 8), b axis (3) or c axis (7), and are connected through intermolecular O1W–H2W···O2 (see Table S2) into 1-D supramolecular chains. Both hydrogen atoms of aqua ligands in all four cases form hydrogen bonds, which are components of supramolecular rings R22(8) [28] (Fig. S1). One of them forms intramolecular hydrogen bonds to the second uncoordinated carboxyl oxygen atoms O1W– H1W···O2 (Table S2). The distances O1W···O2 are in the range 2.54 – 2.65 Å for intramolecular hydrogen bonds and 2.82 – 2.93 Å for intermolecular hydrogen bonds (Table S2). The crystal packing of 1 and 8 are enriched by π-π stacking interactions [29] between pyridine rings of 2-methylsulfanylnicotinato ligands (Figs. S2 and S2) with cg···cg distances of 3.74 and 3.67 Å, and shift-distances of 1.58 and 1.50 Å, respectively.

In the crystal packing of 8 we also observe also π-π stacking interactions [29] between pyridine rings of 3,5-dimethylpyridine ligands (See supplementary Fig. S2) with cg···cg distance of 3.56 Å and shift-distance of 1.13 Å. The crystal packing of 8 show π-π stacking interactions [29] between aromatic rings of neighbouring isoquinoline ligands (See supplementary Fig. S3) with cg···cg distances of 3.78 and 3.69 Å, and shift-distances of 1.19 and 1.22 Å, respectively.

Fig. 3 Molecular structures and hydrogen bonds within crystal structure of complex 9

3.2. Crystal structure of 9 The complex [Ni(pydc)(pydm)]⋅H2O (9) crystallizes in the monoclinic system with the space group P21/c. Its crystal structure consists of complex molecules of [Ni(pydc)(pydm)] and uncoordinated water molecules (Fig. 3). The Ni(II) central atom is hexacoordinated by two carboxylato oxygen atoms [Ni1–O1 = 2.119(4) Å, Ni1–O3 = 2.151(4) Å] and one pyridine nitrogen atom [Ni1–N1 = 1.962(5) Å] from the tridentate dipicolinato ligand, and two hydroxyl oxygen atoms [Ni1–O5 = 2.110(4) Å, Ni1–O6 = 2.138(4) Å] and one pyridine nitrogen atom [Ni1–N2 = 1.992(5) Å] from the tridentate pyridine-2,6-dimethanol (Fig. 3) The complex molecules and uncoordinated water molecules are linked to 2-D supramolecular frameworks through hydrogen bonds (Table S2) between hydroxyl oxygen atoms of the pyridine-2,6-dimethanol and uncoordinated carboxylato oxygen atoms of dipicolinato ligands [O5–H5O···O4 with O5···O4 distance of 2.622(6) Å], between hydroxyl oxygen atoms of pyridine-2,6-dimethanol and uncoordinated water molecules [O6– H6O···O1W with O6···O1W distance of 2.656(6) Å], between uncoordinated water molecules and carboxylato oxygen atoms of dipicolinato ligands [O1W–H1W···O1, O1W–H2W···O5 with O···O distances of 2.700(6) and 2.985(6) Å, respectively] and form double layers (Fig. S5). In the crystal structure of 9 the π-π stacking interactions [29] are observed between pyridine rings of pyridine-2,6-dimethanol with cg···cg distances of 3.58 and 3.40 Å and shiftdistances of 1.77 and 1.23 Å (Fig. S6).

3.3. Spectral data Some characteristic IR bands of the complexes are given in Table 3. The IR spectra of the complexes 1, 3, 5, 7, 8 and 9 show one or two absorption bands in the region 3200 - 3550 cm−1. These bands correspond to the antisymmetric and symmetric OH stretch and confirm the presence of water in these compounds. Moreover, the IR spectra exhibit characteristic bands at ca 870 and 550 cm-1 that are assigned to rocking and wagging modes of the aqua ligands [30]. Both coordinated and uncoordinated water molecules are involved in a system of hydrogen bonds (see crystal structures). The absence of the carboxyl peaks (at about 1680 cm1

) and other characteristic peaks for free acids indicate that the 2-methylsulfanylnicotinic acid

(2-MeSnicH) or pyridine-2,6-dicarboxylic acid (pydcH2) are present in all complexes under study in deprotonated form only. Moreover, the broad bands assigned to the antisymmetric

stretching vibration νas(COO-) and symmetric stretching vibration νas(COO-) of the carboxyl group for the complexes are in the expected regions at about 1600 and below 1400 cm-1, respectively [30]. The difference between the antisymmetric stretch and symmetric stretch ∆, which gives information about carboxylato bonding mode for complexes 1, 3, 5, 7, 8 and 9 could not be determined accurately due to overlap of νas(COO-) with the stretching vibration of the heterocyclic ring. Moreover, the position as well as a considerable splitting of the absorption bands assigned to νas(COO-) of the absorption bands (Table 3) is strongly affected by hydrogen bonding interactions of the carboxylic group with coordinated and uncoordinated water molecules (see crystal structures above). Table 3 Infrared and electronic data (cm-1) for the 2-MeSnicNa and their NiII complexes a Compound

Infrared spectra

Electronic spectra 3

Carboxyl group -

νas(COO ) 2-MeSnicNa [Ni(2-MeSnic)2(fpy) 2(H 2O)2] (1) [Ni(2-MeSnic)2(Mefpy) 2] (2) [Ni(2-MeSnic)2(Me2 fpy)2(H2O)2] (3) [Ni(2-MeSnic)2(Bfpy)2] (4) [Ni(2-MeSnic)2(CF3Phfpy)2(H 2O) 2] (5) [Ni(2-MeSnic)2(iq)2] (6) [Ni(2-MeSnic)2(iq)2(H2O)2] (7) [Ni(2-MeSnic)2(3,5-Me2py)2(H2O)2] (8) [Ni(pydc)(pydm)]•H2O (9)

a

1584vs

b

-

νs(COO )

∆

T2g←3A2g

3

T1g(F)←3A2g

3

T1g(P)←3 A2g

ν1

ν2

ν3

1386vs

198

1578vsb 1561vs 1533vs 1627vs

1375vs,br

c

9 900

16 200

27 300

1382vs,br

245

9 700

26 200

1579vsb 1563s 1543s 1623vs

1375vs,br

c

10 400

15 800 13 300sh 16 500

1378vs,br

245

10 000

26 600

1582sb 1563s 1542s 1621vs

1378vs,br

c

10 000

16 300 13 400sh 16 100

1376vs,br

245

9 900

1579vsb 1561s 1539s 1578vsb 1561s 1538s 1639vs 1608vs 1564vs

1374vs,br

c

9 600

1374vs,br

c

1344vs,br

c

27 400

26 800

15 900 13 300sh 15 800 13300

26 500

10 200

16 100

26 900

9 800 10 900sh

16 400

28 100

26 600

vs very strong; s, strong; br, broad; sh – shoulder. bMixed bands. cNot determined.

The ∆ values bring information about the carboxylic bonding mode for the complexes after comparison with ∆ values of compounds with ionic carboxylic groups. The ∆ value for the sodium 2-methylsulfanylnicotinate is 198 cm-1 (Table 3). The greater ∆ value (245 cm-1) for complexes without aqua ligands [Ni(2-MeSnic)2L2] (L = Mefpy, Bfpy and iq) is rather

typical for asymmetrically chelating carboxylic groups. However, in these cases, the ∆ values are comparable to those complexes with unidentate ligands [31]. The bands observed in the electronic absorption spectra (Table 3) can be assigned to three spin allowed transitions

3

T2g←3A2g,

3

T1g(F)←3A2g and

3

T1g(P)←3A2g in the Oh

symmetry. The maxima of the absorption bands ν1, ν 2 and ν3 for the complexes under study span the interval usually found for pseudooctahedral nickel(II) complexes [32]. Whilst the ν 1, and ν3 bands are symmetrical (except 9), the ν2 bands show a shoulder for complexes 2, 4, 6 and 7. Such a doublet structure has been ascribed to intensity borrowing of the 1Eg←3A2g spin forbidden transition. The second d-d band confirms a considerable tetragonality.

3.4. Magnetic data The complexes [Ni(2-MeSnic)2(fpy)2(H2O)2] (1), [Ni(2- MeSnic)2(3,5-Me2py)2(H2O)2] (8), and [Ni(pydc)(pydm)]•H2O (9) behave magnetically as typical S = 1 spin systems with zerofield splitting (Figs. 4 - 6). At the room temperature, the effective magnetic moment adopts values of µeff = 3.2 − 3.3 µB (see Table 4) that decreases linearly down to 30 − 10 K; then it drops down and at the lowest temperature of the data taking (1.9 K) it adopts values of µeff = 2.4 – 2.6 µB. The room-temperature value yields an estimate of µ eff / µ B = g av [ S ( S + 1)]1/ 2 = 2.82 for gav = 2.0; it indicates an increased value of the g-factors. The magnetization per formula unit M1 = M mol / NA µB = g av S is M1 = 1.8 – 2.2 at B = 7 T and T = 2.0 K; this is a

fingerprint of a considerable single-ion anisotropy reflected into the axial zero-field splitting parameter D.

4 B = 0.1 T

T = 2.0 K 2

Mmol/(NAµB)

6

2

χmol/(10-6 m3 mol-1)

µeff/µB

3

1

5 4

T = 4.6 K 1

3 2 1 0 0

10

20

30

40

0

0 0

50

100

150

200

250

0 1 2 3 4 5 6 7

300

B/T

T/K

Fig. 4. Magnetic functions for complex 1 : left – temperature dependence of the effective

magnetic moment (inset – molar magnetic susceptibility), right – field dependence of the magnetization per formula unit. Lines – fitted.

4 B = 0.1 T

2

T = 2.0 K

Mmol/(NAµB)

5

2

χmol/(10-6 m3 mol-1)

µeff/µB

3

1

4

T = 4.6 K 1

3 2 1 0 0

10

20

30

40

0

0 0

50

100

150

200

250

300

T/K

0 1

2 3 4

5 6

7

B/T

Fig. 5. Magnetic functions for complex 8 : left – temperature dependence of the effective

magnetic moment (inset – molar magnetic susceptibility), right – field dependence of the magnetization per formula unit. Lines – fitted.

2

4 B = 0.1 T

T = 2.0 K

Mmol/(NAµB)

5

2

χmol/(10-6 m3 mol-1)

µeff/µB

3

1

4

T = 4.6 K

1

3 2 1 0 0

10

20

30

40

0

0 0

50

100

150

200

250

300

T/K

0 1 2 3 4 5 6 7 B/T

Fig. 6. Magnetic functions for complex 9 : left – temperature dependence of the effective

magnetic moment (inset – molar magnetic susceptibility), right – field dependence of the magnetization per formula unit. Lines – fitted.

The magnetic data has been fitted using the spin Hamiltonian
Hˆ k ,l = D(Sˆz2 − S 2 / 3)−2 + E (Sˆx2 − Sˆy2 )−2 +µB Bm ( g x sin ϑk cos ϕl Sˆx + g y sin ϑk sin ϕl Sˆy + g z cos ϑk Sˆz )−1

(1)

for directions a = z, x. Here the axial zero-field splitting parameter D and its rhombic counterpart E occur along with the Zeeman term. The Zeeman term needs averaging over a number of grid points (k, l) distributed uniformly over a sphere (210 points at one hemisphere). The generated energy levels for three magnetic fields Bm enter the partition function from which the magnetization and magnetic susceptibility are obtained through the formulae of the statistical thermodynamics [33]. In the crystal structures of the studied complexes, significant intermolecular interactions (hydrogen bonds and/or π−π stacking) have been identified (see sec. 3.1 and ESI). Therefore, the susceptibility data was corrected for the molecular-field correction (zj). Eventually, also the temperature-independent magnetism (χTIM) has been considered, thus the correction is χ corr = χ mol /[1 − ( zj / N A µ 0 µ B2 ) χ mol ] + χ TIM . The latter term accounts to the uncompensated

underlying diamagnetism and the temperature-independent paramagnetism, along with the signal of the sample holder. The susceptibility and magnetization data sets have been fitted simultaneously by applying a joint error functional F = R ( χ ) × R ( M ) that accounts uniformly for the susceptibility and magnetization data. An advanced fitting procedure using a genetic algorithm has been applied. The optimization routine converged to the set of magnetic parameters that are collected in Table 4. As can be seen, the D-parameter is negative for all complexes and this observation can be rationalized in terms of the magnetostructural D-correlation [34]. According to this relationship, the geometry of a compressed tetragonal bipyramid, to which the chromophore {NiO4N2} of the studied complexes belongs to (structural parameter Dstr < 0, for more details see ref. 34) causes negative magnetic D-values (labeled as Dmag in the correlation). The gfactor asymmetry is essential. To verify this forecast, the values of Dmag parameter and the Dstr parameter were correlated and the resulting correlation for a number of Ni(II) complexes is plotted in Fig. 7. The largest structural tetragonality in this correlation is possessed by complex 9 (Dstr = −24.3 pm) which is reflected in its substantial Dmag value (−12.7 cm−1). This is due to the large deviation of the Ni-O and Ni-N distances from its typical values (see ref. 34). In complexes 1 and 8 the tetragonal distortion is lower, Dstr = −7.9 (1) and −7.4 (8) pm. It can be concluded that the complexes under study (1, 8 and 9) belonging to the class with the {NiO4N2} chromophore span the prediction interval of the previously published correlations [13, 34].

Table 4 Magnetic parameters for complexes under study a Complex

a

gz

gx

D/hc

E/hc

(zj)/hc

χTIM/10−9

/cm−1

/cm−1

/cm−1

m3 mol−1

R(χ)

R(M)

1

2.279

2.241 −4.98

0

−0.06

−2.2

0.019

0.042

8

2.249

2.199 −7.84

0

−0.09

1.7

0.012

0.008

9

2.478

2.169 −12.7

0.13

−0.06

3.1

0.022

0.027

Estimated errors: 0.01 for g-factors, 1.0 cm−1 for the D-parameter.

15 Regr

10

95% Conf 95% Pred

Dmag/cm

-1

5 0 -5

1 8

-10 9

-15 -20 -30

-20

-10

0

10

20

Dstr/pm

Fig. 7. Enlarged magnetostructural D-correlation for hexacoordinate Ni(II) complexes.

Correlation: Dmag[cm−1] = −0.69 + 0.59Dstr[pm], R2 = 0.89.

4. Conclusions

We have presented the synthesis, structural and magnetic study of five new pseudooctahedral nickel(II) complexes: [Ni(2-MeSnic)2(fpy)2(H2O)2] (1 ), [Ni(2-MeSnic)2(Me2fpy)2(H2O)2] (3), [Ni(2-MeSnic)2(iq)2(H2O)2] (7), [Ni(2-MeSnic)2 (3,5-Me2py)2(H2O)2] (8) and [Ni(pydc) (pydm)]•H2O (9). In the crystal structures of the aqua-complex molecules of 1 , 3, 7 and 8 ,

significant intermolecular interactions (hydrogen bonds and/or π−π stacking) lead into 1-D supramolecular chains. The complex molecules and uncoordinated water molecules of 9 are linked into 2-D supramolecular frameworks through hydrogen bonds. Three complexes (1, 8 and 9) have been magnetically characterized (temperature dependence of magnetic susceptibility and field dependence of magnetization), and on the basis of these measurement, it can be concluded that these complexes behave as typical S = 1 spin systems with a substantial Ising-type magnetic anisotropy. Spin Hamiltonian analysis of the magnetic data gave the zero-field splitting parameter D that has been correlated with the structural tetragonality parameter Dstr of the studied complexes. These new complexes clearly span the prediction interval of the previously published correlations and confirm the assumption that the negative ZFS parameter D (Ising-type magnetic anisotropy) of the Ni(II) can be tuned by the tetragonal compression of the pseudooctahedral chromophore.

Acknowledgments

Grant Agencies (Slovakia: VEGA 1/0073/13, VEGA 1/0233/12, VEGA 1/0472/13, APVV0014-11) are acknowledged for the financial support.

References

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[25] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann. J. Appl. Crystallogr. 42 (2009) 339. [26] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L. Rodriguez-Monge, R. Taylor, J. van de Streek, and P.A. Wood. J. Appl. Crystallogr. 41 (2008) 466 [27] P. Segľa, J. Miklovič, D. Mikloš, V. Mrázová, L. Krupková, D. Hudecová, Z. Ondrušová, J. Švorec, J. Moncol, M. Melník. Transition Met. Chem. 34 (2009) 15. [28] J. Bernstein, R.E. Dave, L. Shimoni, N.L. Chang. Angew. Chem. Int. Ed. Engl. 34 (1995) 1555. [29] C. Janiak. J. Chem. Soc., Dalton Trans. (2000) 3885. [30] K. Nakamoto. Infrared and Raman spectra of inorganic and coordination compounds, 6th edn., part B, Wiley, New York, (2009) pp 58, 64. [31] N.W. Alcock, J. Culver, S.M. Roe. J. Chem. Soc. Dalton Trans. 1992 (1992) 1477. [32] A.B.P. Lever. Inorganic electronic spectroscopy, 2nd edn. Elsevier, Amsterdam, 1984, p 554. [33] R. Boča, A Handbook of Magnetochemical Formulae. Elsevier, Amsterdam, 2012. [34] J. Titiš, R. Boča. Inorg. Chem., 49 (2010) 3971.

Supplementary Material Synthesis, crystal structures, spectral and magnetic properties of nickel(II) pyridinecarboxylates with N-heterocyclic ligands.

Jozef Miklovič, Alena Packová, Peter Segľa, Ján Titiš, Marián Koman, Ján Moncol, Roman Boča, Vladimír Jorík, Hajnalka Krekuska, and Dušan Valigura.

Table S1 Analytical data for the complexes Compounds

Empirical formula

Formul a wt.

wi,calc/mass % wi,found/mass %a C

H

N

S

Ni

[Ni(2-MeSnic)2(fpy)2(H2O)2] (Complex 1)

C28H26NiN4O 8S2

669.36

50.24 50.63

3.92 3.96

8.37 8.52

9.58 9.64

8.77 8.29

[Ni(2-MeSnic)2(Mefpy)2] (Complex 2) [Ni(2-MeSnic)2(Me2fpy) 2(H2O)2] (Complex 3)

C30H26NiN4O 6S2

661.38

C32H34NiN4O 8S2

725.45

54.48 54.47 52.98 53.25

3.96 3.73 4.72 4.42

8.47 8.85 7.72 8.17

9.69 9.23 8.84 8.53

8.87 8.41 8.09 8.45

[Ni(2-MeSnic)2(Bfpy)2] (Complex 4) [Ni(2-MeSnic)2(CF3Phfpy)2(H2O)2] (Complex 5)

C36H26NiN4O 6S2

733.45

C42H32NiN4O8F6S2

957.55

58.95 58.64 52.68 52.35

3.57 3.60 3.37 3.45

7.64 7.18 5.85 5.93

8.74 8.27 6.70 6.58

8.00 7.53 6.13 6.04

C32H26NiN4O4S2

653.40

C32H30NiN4O6S2

689.43

58.82 58.46 55.75 55.44

4.01 3.81 4.38 4.11

8.57 8.24 8.13 8.01

9.81 9.62 9.30 9.02

8.98 9.34 8.51 8.84

[Ni(2-MeSnic)2(iq)2] (Complex 6) [Ni(2-MeSnic)2(iq)2(H2O)2] (Complex 7)

[Ni(2-MeSnic)2(3,5-Me2py)2(H2O)2] C28H34NiN4O6S2 645.41 52.10 5.31 8.68 9.93 9.09 (Complex 8) 52.41 4.89 9.03 9.45 8.62 [Ni(pydc)(pydm)]•H2O C14H14NiN2O7 380.96 44.14 3.70 7.35 15.40 (Complex 9) 44.11 3.55 7.17 15.25 a) Microanalysis results obtained with maximum deviation: C ± 0.39, H ± 0.42, N ± 0.46, S ± 0,48, Ni ± 0.48

Table S2 Parameters of hydrogen bonds (Å,°) for complexes 1, 3, 7-9. H···A

D···A

D–H···A

O1W–H1W···O2

1.83

2.641(4)

173

O1W–H2W···O2i

2.13

2.849(4)

147

O1W–H1W···O2

1.85

2.618(10)

179

O1W–H2W···O2ii

2.03

2.821(10)

176

O1W–H1W···O2vii

1.82

2.541(5)

147

O1W–H2W···O2viii

2.32

2.841(5)

122

O1W–H1W···O2

1.86

2.650(4)

163

O1W–H2W···O2iii

2.30

2.928(4)

134

O1W–H1W···O1iv

1.91

2.700(6)

161

O1W–H2W···O5v

2.27

2.985(6)

146

O5–H5O···O4vi

1.83

2.622(6)

162

O6–H6O···O1Wvi

1.84

2.656(6)

176

1

3

7

8

9

Symmetry codes: (i) 1-x, -y, -z; (ii) -x, 2-y, 1-z; (iii) 2-x, 1-y, 1-z; (iv) x+1, y, z; (v) x+1, 1.5-y, z-1/2; (vi) x-1, y, z; (vii) x, y, z+1; (viii) 1-x, 1-y, 2-z.

Fig. S1 Hydrogen bonds within crystal structure of complex 1

Fig. S2 The π···π stacking interaction within crystal structure of 1. The symmetry of two neighbouring pyridine rings of 2-methylsulfanylnicotinate ligands is 1-x, -y, -1-z. Hydrogen atoms are omitted for clarity.

Fig. S3 The π···π stacking interaction within crystal structure of 7. The symmetry of two neighboring pyridine rings of 2-methylsulfanylnicotinate ligands is 2-x, 1-y, -z, and two neighboring pyridine rings of 3,5dimethylluthidine ligands is 1-x, -y, 1-z. Hydrogen atoms are omitted for clarity.

Fig. S4 The π···π stacking interaction within crystal structure of 7. The symmetry of two neighboring isoquinoline ligands are x, 3/2-y, 1/2+z; and x, 3/2-y, -1/2+z. Hydrogen atoms are omitted for clarity.

Fig. S5 The double layer forming complex and water molecules within crystal structure of 9.

Fig. S6 The π···π stacking interaction within crystal structure of 9. The symmetry of two neighboring pyridine rings of 2,6-bis(hydroxymethyl)pyridine ligands is -x, 1-y, 1-z, and 1-x, 1-y, 1-z. Hydrogen atoms are omitted for clarity.

Graphical abstract

4

D/hc = 7.84 cm1

B = 0.1 T

2

T = 2.0 K

Mmol/(NAB)

5

2

mol/(10-6 m3 mol-1)

eff/B

3

1

4

1

3 2 1 0 0

10

20

30

40

0

0 0

50

100

150 T/K

200

250

300

0 1 2 3

B

Five new pseudooctahedral nickel(II) complexes have been prepared, structurally and magnetically characterized. For three complexes the zero-field splitting parameter D has been extracted from SQUID measurements and correlated with the structural tetragonality parameter Dstr. These complexes span the prediction interval of the previously published correlations and confirm the assumption that the negative ZFS parameter D of the Ni(II) can be tuned by the tetragonal compression of the pseudooctahedral chromophore.

HIGHLIGHTS •

Eight new 2-methylsulfanylnicotinatonickel(II) complexes prepared and characterized

•

X-ray diffraction and structure description of four new pseudooctahedral complexes

•

Magnetic properties of three complexes determined

•

Increased magnetic anisotropy correlated with structural distortion of chromophore