View PDF VersionPrevious ArticleNext Article
 
DOI: 10.1039/D5NJ02001H (Paper) New J. Chem., 2025, 49, 13007-13014

Uncommon mononuclear pyrazole–pyrazolate complexes of CoII, CuII and Zn†

Marina A. Uvarova *a, Fedor M. Dolgushin a, Konstantin A. Babeshkin a, Nikolay N. Efimov a, Claudio Pettinari b, Igor L. Eremenko a and Sergey E. Nefedov a
aN.S. Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, Leninsky Prosp. 31, 119991 GSP-1, Moscow, Russian Federation. E-mail: yak_marin@mail.ru
bChemistry Interdisciplinary Project (ChIP), School of Pharmacy, University of Camerino, Via Madonna delle Carceri, 62032 Camerino, Italy

Received 12th May 2025 , Accepted 26th June 2025

First published on 27th June 2025

Abstract

Novel mononuclear complexes [M((CF3)2pz)2((CH3)2pzH)2] (M = Zn (1), CoII (2), and CuII (3)) and binuclear complexes [Cu2(μ-(CF3)pz)2((CH3)2pzH)2(OOCBut)2] (4) were prepared by different simple synthetic methods and characterized by single crystal X-ray diffraction analysis. Compounds 1 and 2 have a similar structure with a tetrahedral metal environment, unlike compound 3, in which copper is in a square-planar environment. A copper square planar environment is also found in 4. The structures of the complexes are stabilized by intermolecular (1, 2, and 4) and intramolecular (3) hydrogen bonds. 1 was additionally characterized in solution by 1H NMR. The study of thermal behavior indicated the transformation of 2 into the pyrazolate bridging polymer [Co((CH3)2pz)2]n at 330 °C. Magnetic susceptibility measurements in the ac-magnetic field show the presence of slow field-induced (Hdc = 2500 Oe) magnetic relaxation behavior for the Co-based complex 2.

Introduction

The chemistry of pyrazole has attracted the attention of researchers in the field of coordination chemistry for many years.1,2 Complexes containing pyrazole ligands are efficient and versatile in various fields, including medicine, magnetism, separation, catalysis, optics, luminescence, etc.3,4 Pyrazole complexes having pharmacological, including antifungal,5,6 antibacterial7,8 and antiproliferative,9–15 properties have been reported in the literature. In addition, the pyrazole ligand has relevant coordination capability due to the presence of two nitrogen atoms of different chemical nature, i.e. pyridinic and pyrrolic. Through the unshared pair of electrons of the pyridinic nitrogen atom, pyrazole can coordinate one metal center, but upon deprotonation of the pyrrolic nitrogen, a pyrazolate anion, which can bridge two metal centers, is formed.16 The nucleophilicity of nitrogen atoms and their steric availability can be adjusted by substitution at the 3,5-positions of the cycle.17–19 The introduction of electron-releasing CH3 substituents leads to an increase in the basicity of nitrogen atoms, whereas the electron-withdrawing CF3 substituents lead to an increase in the acidity of the pyrrole fragment, thereby facilitating its deprotonation to form the pyrazolate anion.
image file: d5nj02001h-u1.tif

In most of the cases, the pyrazolate anion is coordinated in the bidentate form, giving pyrazolate-bridging complexes up to pyrazolate bridging polymers.20–28 The formation of mononuclear pyrazolate complexes is not common. The Deacon group managed to obtain homoleptic pyrazolates of La and Ce [La((CH3)2pz)3]n, in which pyrazolate anions are bound to metals featuring six different coordination modes,29,30 forming polymer chains. Only a few mononuclear complexes of d-metals where the anionic pyrazolate is bound in a monodentate form are known.19,31–34 Just one zinc complex {[Zn(tBu2pz)2(tBu2pzH)2]} has been obtained from a protolysis reaction of ZnEt232 and for this reason one of our goals is to define a clear procedure to obtain mononuclear complexes of 3-d metals containing only pyrazole-based ligands acting as anionic and ancillary donors.

Here we describe some methods for the synthesis of new uncommon mononuclear mixed pyrazolate–pyrazole complexes [M((CF3)2pz)2((CH3)2pzH)2] M = Zn (1), CoII (2), and CuII (3) (Scheme 1). When copper, zinc or cobalt acetate is mixed in acetonitrile with both (CF3)2pzH and (CH3)2pzH, the acetates are replaced by the acid fluorinated pyrazolate anions, whereas the more basic 3,5-dimethylpyrazole coordinates the metal center in the neutral form. An alternative method for obtaining 1 and 2 is the reaction of bridged binuclear complexes [M2(μ-(CH3)2pz)2((CH3)2pzH)2(OOCBut)2] (M = Zn and Co) with an excess of (CF3)2pzH. In the case of the copper compound, the reaction leads to the binuclear complex [Cu2(μ-(CF3)pz)2((CH3)2pzH)2(OOCBut)2] (4). The structures of all the compounds obtained were investigated by single-crystal X-ray diffraction analysis. The stability of the Zn compound was studied by solution 1H NMR. Magnetic susceptibility and thermal properties are investigated for the cobalt complex.


image file: d5nj02001h-s1.tif
Scheme 1 Synthetic approach to 1–3.

Results and discussion

Synthesis of compounds

When zinc(II) acetate reacts with 2 moles of (CH3)2pzH (3,5-dimethylpyrazole) and 2 moles of (CF3)2pzH (3,5-trifluorodimethylpyrazole) in acetonitrile, replacement of the acetate by the acidic anionic fluorinated (CF3)2pz− and coordination of the basic (CH3)2pzH in the monodentate form are observed. As a result, the mononuclear complex [Zn((CF3)2pz)2((CH3)2pzH)2] (1) is formed in high yield (88%) (Scheme 1). The analogous cobalt complex [Co((CF3)2pz)2((CH3)2pzH)2] (2) is obtained by using the same procedure.

Complexes 1 and 2 are also prepared through the interaction of the previously described pyrazolate-bridging complexes [M2(μ-(CH3)2pz)2(CH3)2pzH)2(OOCBut)2] (M = Zn,35 M = Co36) with an excess of (CF3)2pzH in dichloromethane at room temperature. The formation of the zinc and cobalt complexes is likely accompanied by transfer of H+ from (CF3)2pzH followed by displacement of both (CH3)2pzH and HOOCBut.

When a mixture of copper acetate hydrate and (CH3)2pzH is warmed at 140 °C for three hours, acetic acid is removed and a brick-red powder insoluble in organic solvents is formed. The addition of hexane and (CF3)2pzH yields [Cu((CF3)2pz)2((CH3)2pzH)2] (3).

The reaction of the [Cu((CH3)2pzH)2(OOCBut)2]37 complex with (CF3)2pzH in dichloromethane does not lead to mononuclear [M((CF3)2pz)2((CH3)2pzH)2] as in the case of cobalt and zinc, but leads to the binuclear complex [Cu2(μ-(CF3)pz)2((CH3)2pzH)2(OOCBut)2] (4) in 75% yield. During this exchange reaction, one pivalate anion is replaced by a fluorinated pyrazolate anion, which in 4 bridges two copper atoms forming a dimer in which the pivalate and the heterocyclic (CH3)2pzH are coordinated in a monodentate form in the axial position.

It is worth noting that mononuclear complexes [M((CF3)2pz)2((CH3)2pzH)2] 1–4 are unique in their kind, since the metal atoms are surrounded only by heterocyclic pyrazole and pyrazolate donors.

X-ray structures of 1–3

Compound 1 is a mononuclear complex in which the zinc atom is located in a tetrahedral environment of four nitrogen atoms belonging to two (CF3)2pz anions (Zn–N 1.995(3) Å, 1.998(3) Å) and two coordinated (CH3)2pzH ligands (Zn–N 2.000(3) Å, 2.001(3) Å) (Fig. 1 and Table 1). The structure of the complex is additionally stabilized by two intramolecular N–H⋯N hydrogen bonds between (CF3)2pz and (CH3)2pzH. The parameters of the hydrogen bonds are presented in Table 2. A similar structure with two intramolecular hydrogen bonds was observed previously for [Zn(tBu2pz)2(tBu2pzH)2].32 Single-element pyrazolate coordination is quite rare and in this case is provided by the H bond, as previously observed in [Nd(Me2pz)3-(MepzH)py].38 The lengths of Zn–N bonds in 1 are close to those of similar Zn–N bonds described in ref. 32.
image file: d5nj02001h-f1.tif
Fig. 1 Molecular structure of 1 with representation of atoms via thermal ellipsoids at 30% probability level (only labels of symmetry-independent heteroatoms are given). The minor component of the disordered CF3-groups is omitted for clarity. Dotted lines represent intramolecular hydrogen bonds.
Table 1 Selected distances (Å) for 1–4
Complex/parameter 1 2 3 4
M–N (CF3)2Pz 1.995(3) 2.008(4) 1.992(3) 1.994(2)
1.998(3) 2.019(4) 1.987(3) 2.000(2)
M–N (CH3)2pzH 2.000(3) 2.019(4) 1.985(4) 1.963(2)
2.001(3) 2.023(4) 1.983(4)
M–O 1.940(2)

Table 2 Hydrogen bonds for 1–4
D H A d(D–H)/Å d(H–A)/Å d(D–A)/Å D–H–A/°
a 1 − X, −Y, +Z. b −X, +Y, 1/2 − Z.
1 N6 H6 N2 0.82(5) 2.08(5) 2.793(6) 146(4)
N8 H8 N4 0.80(3) 2.07(3) 2.799(5) 152(3)
2 N6 H6 N4 0.94(4) 1.98(4) 2.812(6) 146(4)
N8 H8 N2 0.82(4) 2.07(4) 2.820(6) 151(4)
3 N6 H6 N4a 0.87(7) 2.05(7) 2.913(5) 170(7)
N8 H8 N2a 0.93(5) 1.95(5) 2.848(5) 160(5)
4 N4 H4 O2b 0.91(3) 1.83(3) 2.733(3) 172(3)

The structure of complex 2 is very similar to that of compound 1. The cobalt atom is in a tetrahedral environment formed by four nitrogen atoms of two (CF3)2pz anions and two (CH3)2pzH molecules (Fig. 2). There is only a slight increase in bond lengths (Co–N 2.008(4) Å–2.023(4) Å). This is the first example of single-element pyrazolate coordination in cobalt compounds.


image file: d5nj02001h-f2.tif
Fig. 2 Molecular structure of 2 with representation of atoms via thermal ellipsoids at 30% probability level (only labels of symmetry-independent heteroatoms are given). The minor component of the disordered CF3-groups is omitted for clarity. Dotted lines represent intramolecular hydrogen bonds.

The geometry of complex 3 differs from those of 1 and 2. In 3, the copper atom, in a square planar environment, is four-coordinated by nitrogen atoms from two (CF3)2pz-anions (Cu–N 1.992(3) Å, 1.987(3) Å) and two (CH3)2pzH molecules (Cu–N 1.985(4) Å, 1.983(4) Å) (Table 1 and Fig. 3a). A square-planar environment is typical for a copper atom due to the strong field of ligands that affects the electronic structure of the copper ion, forcing it to form bonds in one plane, unlike cobalt and zinc, which usually form a tetrahedral or octahedral environment. The nature of hydrogen bonds is quite different from those in 1 and 2. In 3, intermolecular hydrogen bonds between (CF3)2pz and (CH3)2pzH of neighboring molecules aggregate mononuclear complexes into dimers (Table 2 and Fig. 3b). Additionally, the dimers are stabilized by weak π–π interactions between pairwise adjacent (CH3)2pzH fragments with the shortest C–C distance of 3.386(8) Å and distances between the centroids of the pyrazole rings of 3.84 and 4.02 Å. The formation of similar H-linked dimers is observed for square planar pyrazolate Pd34 and Pt complexes.39


image file: d5nj02001h-f3.tif
Fig. 3 Molecular structure of 3 (a) and a fragment of H-bonded molecules in the crystal (b). Non-hydrogen atoms are shown as thermal ellipsoids at 30% probability level, and only labels of symmetry-independent heteroatoms are given.

Complex 4 of composition [Cu2(μ-(CF3)pz)2((CH3)2pzH)2(OOCBut)2] crystallizes into the monoclinic space group C2/c with a solvate molecule of dichloromethane. Compound 4 is a binuclear complex in which two copper atoms positioned at a non-binding distance of 3.3063(7) Å and connected by two bridging (CF3)2pz− anions are coordinated by a monodentate-bound pivalate anion and (CH3)2pzH (Fig. 4). As a result, each copper atom is found in a square planar environment formed by three pyrazolic nitrogen atoms (Cu–N 1.9632(19)–1.9998(17) Å) and one oxygen atom of the carboxylic group (Cu–O 1.9402(16) Å). The structure of the complex is additionally stabilized by unusual “cross” intramolecular hydrogen bonds involving the oxygen atoms of the terminal pivalate anions of one copper atom and the hydrogen atom of the NH group of the (CH3)2pzH molecule coordinated to the other copper atom (Table 2). Analogous hydrogen bonds are found in the similar complex [Cu2(μ-(CH3)2pz)2((CH3)2pzH)2(OOCBut)2].37 The substitution of the bridging (CF3)2pz− anions in 4 with (CH3)2pz− in ref. 37 results in a shortening of the Cu⋯Cu distance to 3.2629(8) Å. It can also be noted that in 4 the bond lengths of copper with bridging (CF3)2pz− Cu–N(CF3)2pz (1.9998(17) Å–1.9942(17) Å) are longer than those in [Cu2(μ-(CH3)2pz)2((CH3)2pzH)2(OOCBut)2] containing a bridging (CH3)2pz− (Cu–N(CH3)2pz 1.952(8)Å–1.977(8)Å), while in 4 the bond lengths between the copper and terminal (CH3)2pzH ligands (Cu–N(CH3)2pzH 1.9632(19)Å) are shorter than those in [Cu2(μ-(CH3)2pz)2((CH3)2pzH)2(OOCBut)2] (Cu–N(CH3)2pzH 2.0041 (5)Å).


image file: d5nj02001h-f4.tif
Fig. 4 Molecular structure of 4. Dotted lines represent intramolecular hydrogen bonds.

The molecular structures of complexes 1–4 are also confirmed by IR spectroscopy. Complexes 1–3, having very similar spectra, show very strong bands due to the valence fluctuations of CF3-groups at 1257 cm−1, 1222 cm−1, and 1117 cm−1 in 1 and at 1254 cm−1, 1218 cm−1, and 1117 cm−1 in 2 and 3. Bands at 2936–2940 cm−1 in 1–4 correspond to the vibrations of the CH3-groups of the heterocyclic pyrazole ligand. Aromatic C–H-stretching vibrations are characterized by the bands at 750–755 cm−1 and 1008–1058 cm−1 (ring fluctuations) in 1–4. In the spectrum of 4, it is also possible to distinguish the C–O vibrations due to the pivalate anions (1553 cm−1). The change in the coordination of the pyrazole ligand from the monodentate in compounds 1–3 to bridging in 4 leads to a slight shift of all characteristic absorption bands (see the ESI,† Fig. S3–S6).

Magnetic properties of 2

The magnetic behavior of complex 2 was investigated under a 5000 Oe dc-magnetic field in the 2–300 K temperature range. The temperature dependences of the magnetic susceptibility (χ) and χT are presented in Fig. 5. The χT value at 300 K (2.91 cm3 K mol−1) is much higher than the spin-only value (1.875 cm3 K mol−1), which indicates an unquenched orbital contribution to the total magnetic moment.
image file: d5nj02001h-f5.tif
Fig. 5 Temperature dependences of magnetic susceptibility (χ) and χT under a 5000 Oe dc-magnetic field.

The χT values decrease linearly up to 2.53 cm3 K mol−1 at 40 K, then a sharper drop in the χT magnitude follows reaching the minimum value of 1.08 cm3 K mol−1 at 2 K. This behavior can arise from the anisotropy of Co2+ ions and the Zeeman effect caused by the applied dc-magnetic field.40 The M(H) and M(H/T) dependences are given in Fig. S1 (ESI†).

Due to the active development of Co-based molecular magnets in recent years,41 the ac-magnetic susceptibility measurements were performed to determine the possibility of slow magnetic relaxation for complex 2.

In the zero dc-magnetic field, the out-of-phase (χ′′) values of magnetic susceptibility in comparison to in-phase (χ′) values for complex 2 are negligible at 2 K in the ac-frequency range from 10 to 10[thin space (1/6-em)]000 Hz (Fig. 6). The absence of considerable χ′′(ν) signals for complex 2 most likely is attributed to the significant contribution from the quantum tunneling of the magnetization (QTM), resulting in fast relaxation. To minimize the effect of QTM, non-zero dc-fields of up to 5000 Oe have been applied, resulting in the appearance of significant out-of-phase signals on the χ′′(ν) dependences for complex 2. The optimal value of the dc-field strength, corresponding to the minimal relaxation rate, equals 2500 Oe for complex 2 (Fig. S2, ESI†).


image file: d5nj02001h-f6.tif
Fig. 6 Frequency dependences of the real (a) and imaginary (b) components of the ac-magnetic susceptibility for complex 2 in the 2–4.1 K range measured under the optimal 1000 Oe dc-field. Solid lines represent visual guides (a) and fitting using the generalized Debye model (b).

The χ′′(ν) isotherms measured under a 2500 Oe dc-field were approximated using the generalized Debye model. The resulting temperature dependence of relaxation time (τ vs. 1/T) is shown in Fig. 7.


image file: d5nj02001h-f7.tif
Fig. 7 τ vs. 1/T plot for complex 2 under a 2500 Oe dc-field. Blue dashed lines represent fitting using the Orbach relaxation mechanism. Solid red lines represent fitting using the sum of Orbach, Raman and QTM relaxation mechanisms.

In the high-temperature range of 3.9–4.1 K, for complex 2 the τ(1/T) dependence was fitted using the Arrhenius equation (τ = τ0·exp{Δeff/kBT}) corresponding to the Orbach relaxation mechanism, where τ0 and Δeff/kB are the shortest relaxation time and demagnetization energy barrier, respectively. The resulting relaxation parameters for complex 2 in the high-temperature range were calculated as follows: Δeff/kB = 44 (±1) K and τ0 = 3 × 10−10 (± 1 × 10−10) s.

The τ vs. 1/T dependence in the whole temperature range of 2–4.1 K for complex 2 was approximated using the sum of Orbach, Raman (τ−1 = CRamanTnRaman) and QTM (τ−1 = BQTM) relaxation mechanisms with the following set of parameters: Δeff/kB = 44 (fixed) K, τ0 = 3 × 10−10 (fixed), CRaman = 0.08 (±0.04) s−1 K−nRaman, nRaman = 7.8 (±0.6) and BQTM = 156 (±3) s−1. The Orbach relaxation parameter values were set to the values obtained from the high-temperature range approximation to avoid over-parametrization.

Thermal analysis of 2

The thermal behavior of 2 was investigated by the STA method in an argon atmosphere (with simultaneous registration of TG and DSC curves) up to 500 °C. Compound 2 is stable up to 128 °C and the start of its decomposition is accompanied by an endothermic effect at 153 °C (Fig. 8).
image file: d5nj02001h-f8.tif
Fig. 8 TG (blue) and DSC (red) curves of 2.

The main mass loss of 64% corresponds to the removal of two (CF3)2pzH molecules (theoretical value: 62%), which are obtained by protonation of the fluorinated pyrazolate anion, and is accompanied by the formation of a residue (practical value: 35%, theoretical value: 38%).42 The formation of a pyrazolate-bridged polymer is accompanied by an exothermic effect at a temperature of 331 °C. The composition of the residue is confirmed by the elemental analysis data. Such proton exchange between pyrazole fragments is associated with a higher volatility of (CF3)2pzH compared to (CH3)2pzH. Beyond 370 °C, a slow decrease in mass is observed without thermal effects, which indicates the destruction of the pyrazolate anion without the formation of a new phase. The formation of a pyrazolate-bridged copper polymer, [Cu(μ-(CH3)2pz)2]n, has been previously described in ref. 37.

Conclusions

Uncommon mononuclear mixed pyrazole–pyrazolate complexes [M((CF3)2pz)2((CH3)2pzH)2] (M = Zn (1), CoII (2), and CuII (3)) have been synthesized by reactions of copper, zinc and cobalt acetates with (CF3)2pzH and (CH3)2pzH. The acetate anions in the starting metal salts are replaced by acid fluorinated pyrazolate anions, the basic 3,5-dimethylpyrazole being coordinated in a monodentate fashion to the metal center. An alternative method for obtaining 1 and 2 was the reaction of pyrazolate-bridged dinuclear complexes [M2(μ-((CH3)2pz)2((CH3)2pzH)2(OOCBut)2] (M = Zn and Co) with an excess of (CF3)2pzH. When the copper species [Cu((CH3)2pzH)2(OOCBut)2] was employed, the reaction leads to the binuclear complex [Cu2(μ-(CF3)pz)2((CH3)2pzH)2(OOCBut)2] (4). Heating complex 2 above 160 °C leads to the removal of (CF3)2pzH to form the polymer [Co((CH3)2pzH)2]n. Slow relaxation of magnetization in complex 2 occurs through the collective contributions of Orbach, Raman and QTM relaxation mechanisms with the application of a 2500 dc-magnetic field.

Experimental

Materials and methods

Commercial reagents and solvents were used for the synthesis, including 3,5-dimethylpyrazole ((CH3)2pzH, 99% Acros), 3,5-(bis-trifluoromethyl)pyrazole ((CF3)2pzH), 99% Acros), hexane (≥99%), dichloromethane (≥99%), copper acetate monohydrate, zinc acetate dihydrate, and cobalt acetate tetrahydrate (Acros). The complex [Zn2(μ-(CH3)2pz)2((CH3)2pzH)2(OOCBut)2] was obtained in accordance with the method reported in ref. 35, the complex [Co2(μ-(CH3)2pz)2((CH3)2pzH)2(OOCBut)2] was obtained in accordance with the method reported in ref. 36, and the complex [Cu((CH3)2pzH)2(OOCBut)2] was obtained in accordance with the method reported in ref. 37.

IR spectra were recorded in the 400–4000 cm−1 region using a Spectrum-65 PerkinElmer FT-IR spectrometer.

Microprobe analyses were carried out using a Carlo Erba EA 1108 Series CHN elemental analyzer (Center of Collective Use of IGIC RAS).

X-ray diffraction analysis of 1–4 was carried out on a Bruker Apex II diffractometer (MoKα, λ = 0.71073 Å, graphite monochromator, CCD detector). The absorption correction was applied semiempirically using the SADABS program.43 The structures were solved by direct methods using the ShelXS-97 program44 and refined by the full-matrix least-squares method using the ShelXL program45 in the anisotropic approximation for non-hydrogen atoms. Some of the CF3 groups in structures 1 and 2, as well as the tert-butyl group in 4, are positionally disordered over two positions (refinement of disordered groups was carried out using standard DFIX, DANG, and EADP constraints). The hydrogen atoms of the NH groups were located from the difference Fourier maps and included in the refinement in the isotropic approximation without constraints; the positions of other hydrogen atoms were calculated geometrically, and they all were refined in the isotropic approximation in the riding model with Uiso(H) = 1.5Uequiv(C) for methyl groups and Uiso(H) = 1.2Uequiv(C) for other hydrogen atoms. The main crystallographic data and refinement parameters for compounds 1–4 are given in Table S1 (ESI†).

The thermal behavior of the complexes was studied using the simultaneous thermal analysis (STA) technique for parallel recording of TG (thermogravimetry) and DSC (differential scanning calorimetry) curves. The study was performed using an STA 449 F1 Jupiter instrument (“NETZSCH”) in Al-crucibles under a lid with a hole to ensure a vapor pressure of 1 atm during the thermal decomposition of the samples. The rate of heating to 500 °C was 10 °C min−1 under an argon atmosphere (Ar content > 99.998%, O2 < 0.0002%, N2 < 0.001%, water vapor < 0.0003%, and CH4 < 0.0001%).

1H NMR spectra were recorded in CDCl3 at ambient temperature using Bruker AVANCE 300 and 400 spectrometers at 300.1 and 400.1 MHz, respectively, using a solvent as the internal standard (CDCl3, 7.26 ppm; CD3OD, 3.31 ppm). Chemical shifts (δ) and coupling constants (J) are given in ppm and in Hz, respectively. The peak patterns are indicated as follows: (s, singlet; d, doublet; t, triplet; q, quartet; o, octet; m, multiplet; and br., broad).

Magnetic susceptibility measurements were performed using a Quantum Design PPMS-9 susceptometer. For dc susceptibility measurements, a magnetic field of 5000 Oe was applied, and the corresponding measurements were performed in the 2–300 K range. For ac susceptibility measurements of all samples, oscillating ac fields of 5 Oe, 3 Oe and 1 Oe in the frequency ranges of 10–100, 100–1000 and 1000–10[thin space (1/6-em)]000 Hz, respectively, were applied. These settings allowed one both to avoid sample heating at low temperatures (which may occur when the modulation amplitude and frequency are high) and to obtain the best signal-to-noise ratio. All magnetic measurements were performed on polycrystalline samples sealed in polyethylene bags and covered with mineral oil in order to prevent field-induced orientation of crystallites. The paramagnetic components of the magnetic susceptibility χ were determined taking into account both the diamagnetic contribution evaluated from Pascal's constants and the contributions of the sample holder and mineral oil.

Synthesis of complexes

[Zn((CF3)2pz)2((CH3)2pzH)2] (1).
Method 1. 0.1 g (1 mmol) of (CH3)2pzH and 0.2 g (1 mmol) of (CF3)2PzH were added to 0.1 g (0.5 mmol) of zinc acetate dihydrate in 20 ml of acetonitrile and mixed at room temperature for 1 hour. The resulting solution was kept at a temperature of +5 °C for a day. The formed colorless crystals were separated from the mother liquor by decantation and dried in air. 1 was obtained in 88% yield (0.3 g).
Method 2. 0.14 g (0.7 mmol) of (CF3)2PzH were added to 20 ml of dichloromethane solution containing 0.1 g (0.17 mmol) of [Zn2(μ-((CH3)2pz)2((CH3)2pzH)2(OOCBut)2] and mixed at room temperature. The resulting solution was kept at a temperature of +5 °C for a day. The formed colorless crystals were separated from the mother liquor by decantation and dried in air. 1 was obtained in 56% yield (0.13 g).

Anal. calc. ZnC20H18N8F12: C 36.18, H 2.73, N 16.88. Found: C 36.87, H 2.56, N 16.11. FT-IR (ATR), ν cm−1: 3435 m, 3139 w, 2934 w, 1576 m, 1547 m, 1530 m, 1502 m, 1423 w, 1376 m, 1352 m, 1296 s, 1224 s, 1259 s, 1194 w, 1157 s, 1128 s, 1080 w, 1050 m, 1014 s, 983 w, 813 s, 750 w, 733 w, 577 w, 428 w. 1H NMR (CDCl3, 400 MHz, 294 K) 2.51 (s, 12 H, (CH3)2pzH), 5.92 (s, 2H, (CF3)2pz), 6.79 (s, 2H, (CH3)2pzH, 14.7 (s, 2H, NH–(CH3)2pzH).

[Co(CF3)2pz)2((CH3)2pzH)2] (2).
Method 1. 0.1 g (1 mmol) of (CH3)2pzH and 0.2 g (1 mmol) of (CF3)2pzH were added to 0.12 g (0.5 mmol) of cobalt acetate tetrahydrate in 20 ml of acetonitrile and stirred for 1 hour. The resulting solution was kept at a temperature of +5 °C for a day. The formed purple crystals were separated from the mother liquor by decantation and dried in air. 2 was obtained in 85% yield (0.28 g).
Method 2. 0.14 g (0.7 mmol) of (CF3)2pzH were added to 20 ml of dichloromethane solution containing 0.1 g (0.17 mmol) of [Co2(μ-((CH3)2pz)2((CH3)2pzH)2(OOCBut)2] and mixed at room temperature. The resulting solution was stored at +5 °C for a day. The purple crystals were separated from the mother liquor by decantation and dried in air. 2 was obtained in 61% yield (0.15 g). Anal. calc. CoC20H18N8F12: C 36.54, H 2.76, N 17.04. Found: C 36.56, H 2.13, N 16.91. FT-IR (ATR), ν/cm−1: 3434 w, 2930 w, 2854 w, 1575 m, 1530 m, 1501 m, 1430 w, 1349 w, 1293 m, 1258 s, 1222 m, 1167 s, 1120 s, 1079 m, 1020 s, 1015 s, 981 w, 815 m, 755 w, 718 w, 430 w.
[Cu((CF3)2pz)2((CH3)2pzH)2] (3). 1.0 g (5 mmol) of aqueous copper acetate was heated at 140 °C with 2 g (20 mmol) of (CH3)2pzH for 3 hours. 40 ml of hexane and 1.0 g (5 mmol) of (CF3)2pzH were then added to the resulting red insoluble substance and stirred under heating for 1 h. The resulting green solution was filtered and kept at room temperature for a day. The formed pink crystals were separated from the mother liquor by decantation. 3 was obtained in 68% yield (2 g).

Anal. calc. CuC20H18N8F12: C 36.29, H 2.74, N 16.92. Found: C 36.59, H 2.55, N 17.11. FT-IR (ATR), ν/cm−1: 3199 w, 3102 w, 2940 m, 2785 w, 1595 s, 1545 m, 1528 w, 1501 w, 1422 m, 1348 m, 1308 m, 1254 s, 1217 s, 1173 w, 1111 s, 1079 m, 1058 w, 1025 m, 1008 s, 978 w, 810 s, 755 m, 733 w, 617 m.

[Cu2(μ-(CF3)pz)2((CH3)2pzH)2(OOCBut)2] (4). 0.1 g (0.5 mmol) of (CF3)2pzH were added to 10 ml of a green dichloromethane solution containing 0.2 g (0.45 mmol) of Cu((CH3)2pzH)2(OOCBut)2 and stirred for an hour at room temperature. 2 ml of hexane were added to the resulting blue solution and kept at +5 °C for a day. The formed blue crystals were separated from the mother liquor by decantation. 4 was obtained in 75% yield (0.2 g).

Anal. calc. Cu2C30H36F12N8O4: C 38.84, H 3.91, N 12.08. Found: C 39.11, H 4.16, N 12.34. FT-IR (ATR), ν cm−1: 3423 s, 2964 m, 2931 m, 1634 m, 1556 s, 1553 s, 1500 w, 1483 m, 1411 w, 1371 s, 1265 s, 1225 w, 1137 s, 1055 w, 1028 s, 810 w, 760 s, 618 w, 433 w.

Author contributions

The manuscript was written through contributions from all authors. M. A. Uvarova – scientific idea, synthesis, and manuscript writing; F. M. Dolgushin – X-ray analysis and manuscript writing; K. A. Babeshkin and N. N. Efimov – study of magnetic properties, C. Pettinari – review of the manuscript and IR and NMR measurements, I. L. Eremenko and S. E. Nefedov – general guidance.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the ESI.† Crystallographic data for 1–3 have been deposited at the Cambridge Structural Data Bank (CCDC 2430824–2430827†).

Acknowledgements

This work was financially supported by the Russian Science Foundation (project no. 22-13-00175-Π). We are grateful to the User Facilities Center of Institute of General and Inorganic Chemistry of the Russian Academy of Sciences for physicochemical measurements (X-ray, thermal analysis, and magnetic measurements).

References

  1. (a) R. Mukherjee, Coord. Chem. Rev., 2000, 203(1), 151–218 CrossRef CAS ; (b) S. I. Gad, M. S. Altowyan, M. A. Abu-Youssef, A. El-Faham, A. Barakat and R. M. A. Halcrow, J. Chem. Soc., Dalton Trans., 2009, 12, 2059–2073 Search PubMed .
  2. M. V. Lunagariya, K. P. Thakor, R. R. Varma, B. N. Waghela, C. Pathak and M. N. Patel, MedChemComm, 2018, 9, 282 RSC .
  3. (a) K. Karrouchi, E. B. Yousfi, N. K. Sebbar, Y. Ramli, J. Taoufik, Y. Ouzidan, M. Ansar, Y. N. Mabkhot, H. A. Ghabbour and S. Radi, Int. J. Mol. Sci., 2017, 18, 2215 CrossRef PubMed ; (b) R. Tatikonda and A. Yousri, Appl. Organomet. Chem., 2025, 39(1), e7772 CrossRef ; (c) M. Hirahara, A. Iwamoto, Y. Teraoka, Y. Mizuno, Y. Umemura and T. Uekita, Inorg. Chem., 2024, 63(4), 1988–1996 CrossRef CAS PubMed ; (d) M. Guin, S. Halder, S. Chatterjee and S. Konar, J. Mol. Struct., 2022, 1270, 133949 CrossRef CAS .
  4. J. Reedijk, Heterocyclic nitrogen-donor ligands, Comprehensive coordination chemistry, 1987, vol. 2, pp. 73–98 Search PubMed .
  5. S. Abdolmaleki, M. Ghadermazi, A. Fattahi, S. Shokraii, M. Alimoradi, B. Shahbazi and A. R. J. Azar, J. Coord. Chem., 2017, 70, 1406 CrossRef CAS .
  6. D. Ajo, A. Bencini and F. Mani, Inorg. Chem., 1988, 27, 2437 CrossRef CAS .
  7. M. A. Uvarova, M. V. Novikova, V. A. Eliseenkova, D. E. Baravikov, O. B. Bekker, E. V. Fatushina, M. A. Kiskin, I. L. Eremenko and I. A. Lutsenko, Russ. J. Coord. Chem., 2023, 49(10), 680–687 CrossRef CAS .
  8. T. Harit, F. Malek, B. El Bali, A. Khan, K. Dalvandi, B. P. Marasini, S. Noreen, R. Malik, S. Khan and M. I. Choudhary, Med. Chem. Res., 2012, 21, 2772 CrossRef CAS .
  9. A. Chauhan, P. K. Sharma and N. Kaushik, Int. J. Chem. Technol. Res., 2011, 3, 11 Search PubMed .
  10. F. K. Keter, S. Kanyanda, S. S. L. Lyantagaye, J. Darkwa, D. J. G. Rees and M. Meyer, Cancer Chemother. Pharmacol., 2008, 63(1), 127–138 CrossRef CAS PubMed .
  11. N. V. Kulkarni, A. Kamath, S. Budagumpi and V. K. Revankar, J. Mol. Struct., 2011, 1006, 580–588 CrossRef CAS .
  12. M. A. Uvarova, D. E. Baravikov, F. M. Dolgushin, T. M. Aliev, K. O. Titov, O. B. Bekker and I. A. Lutsenko, Inorg. Chim. Acta, 2023, 121649 CrossRef CAS .
  13. M. A. Uvarova, I. A. Lutsenko, M. A. Shmelev, S. E. Nefedov, O. B. Bekker, A. I. Lashkin, V. O. Shender and I. L. Eremenko, New J. Chem., 2024, 48(2), 717–723 RSC .
  14. M. A. Uvarova, F. M. Dolgushin, K. A. Babeshkin, N. N. Efimov, N. V. Gogoleva, D. N. Nebykov, A. V. Lagutina, A. O. Panov, V. M. Mokhov, O. B. Bekker, K. O. Titov, I. A. Lutsenko and I. L. Eremenko, Inorg. Chim. Acta, 2025, 575, 122445 CrossRef CAS .
  15. G. L. Monica and G. A. Ardizzoia, Prog. Inorg. Chem., 1997, 46, 151–238 Search PubMed .
  16. S. Trofimenko, Prog. Inorg. Chem., 2007, 34, 115–210 Search PubMed .
  17. M. A. Uvarova and S. E. Nefedov, Russ. J. Coord. Chem., 2022, 48(9), 565–571 CrossRef CAS .
  18. M. A. Uvarova and S. E. Nefedov, Mendeleev Commun., 2024, 34(1), 54–56 CrossRef CAS .
  19. N. Masciocchi, G. A. Ardizzoia, S. Brenna, G. L. Monica, A. Maspero, S. Galli and A. Sironi, Inorg. Chem., 2002, 41(23), 6080–6089 CrossRef CAS PubMed .
  20. A. A. Titov, O. A. Filippov, A. F. Smol’yakov, A. A. Averin and E. S. Shubina, Mendeleev Commun., 2021, 31(2), 170–172 CrossRef CAS .
  21. M. A. Uvarova, M. A. Shmelev and S. E. Nefedov, Russ. J. Coord. Chem., 2024, 50, 1029–1036 CrossRef CAS .
  22. H. R. Dias, S. A. Polach and Z. Wang, J. Fluorine Chem., 2000, 103(2), 163–169 CrossRef CAS .
  23. H. V. R. Dias, H. Diyabalanage, N. B. Jayaratna, D. Shaw, C. V. Hettiarachchi and D. Parasar, Eur. J. Inorg. Chem., 2019, 3638–3644 CrossRef CAS .
  24. A. Cingolani, S. Galli, N. Masciocchi, L. Pandolfo, C. Pettinari and A. Sironi, J. Am. Chem. Soc., 2005, 127, 6144–6145 CrossRef CAS PubMed .
  25. M. A. Yakovleva, E. V. Kushan, N. S. Boltacheva, V. I. Filyakova and S. E. Nefedov, Russ. J. Inorg. Chem., 2012, 57(2), 181–192 CrossRef CAS .
  26. C. Pettinari, A. Tăbăcaru and S. Galli, Coord. Chem. Rev., 2016, 307, 1–31 CrossRef CAS .
  27. C. Di Nicola, F. Marchetti, A. Tombesi, S. Xhafa, P. Campitelli, M. Moroni and C. Pettinari, New J. Chem., 2023, 47(41), 19047–19056 RSC .
  28. G. B. Deacon, C. M. Forsyth, A. Gitlits, B. W. Skelton and A. H. White, Dalton Trans., 2004, 1239–1247 RSC .
  29. D. Werner, U. Bayer, N. E. Rad, P. C. Junk, G. B. Deacon and R. Anwander, Dalton Trans., 2018, 47(17), 5952–5955 RSC .
  30. M. A. Uvarova and S. E. Nefedov, Russ. J. Coord. Chem., 2022, 48(12), 909–915 CrossRef CAS .
  31. N. E. Rad, P. C. Junk, G. B. Deacon, I. V. Taidakov and J. Wang, Aust. J. Chem., 2020, 73, 520–528 CrossRef CAS .
  32. C. C. Quitmann and K. Müller-Buschbaum, Z. Anorg. Allg. Chem., 2005, 631(6–7), 1191–1198 CrossRef CAS .
  33. G. A. Ardizzoia, G. L. Monica, S. Cenini, M. Moret and N. Masciocchi, J. Chem. Soc., Dalton Trans., 1996, 7, 1351–1357 RSC .
  34. E. V. Amel’chenkova, T. O. Denisova and S. E. Nefedov, Russ. J. Inorg. Chem., 2006, 1218–1263,  DOI:10.1134/S0036023606080110 .
  35. T. O. Denisova and S. E. Nefedov, Russ. Chem. Bull., 2003, 52, 775–777 CrossRef CAS .
  36. T. O. Denisova, E. V. Amel’chenkova, I. V. Pruss, Zh. V. Dobrokhotova and O. P. Fialkovskii, Russ. J. Inorg. Chem., 2006, 51(7), 1020–1064 CrossRef .
  37. G. B. Deacon, C. M. Forsyth, A. Gitlits, R. Harika, P. C. Junk, B. W. Skelton and A. H. White, Angew. Chem., Int. Ed., 2002, 41, 3249 CrossRef CAS PubMed .
  38. K. Umakoshi, T. Kojima, K. Saito, S. Akatsu, M. Onishi, S. Ishizaka and Y. Ozawa, Inorg. Chem., 2008, 47(12), 5033–5035 CrossRef CAS PubMed .
  39. C. Benelli and D. Gatteschi, Chem. Rev., 2002, 102, 2369–2387,  DOI:10.1021/cr010303r ; H. Zhao, N. Lopez, A. Prosvirin, H. T. Chifotides and K. R. Dunbar, Dalton Trans., 2007, 878–888,  10.1039/b616016f ; S. P. Petrosyants, K. A. Babeshkin, A. V. Gavrikov, A. B. Ilyukhin, E. V. Belova and N. N. Efimov, Dalton Trans., 2019, 48, 12644–12655,  10.1039/c9dt02260k .
  40. D. Cabrosi, C. Cruz, V. Paredes-García and P. Alborés, Dalton Trans., 2023, 52(1), 175–184 RSC ; Z. Hooshmand, J. X. Yu, H. P. Cheng and M. R. Pederson, Phys. Rev. B, 2021, 104(13), 134411 CrossRef CAS ; P. E. Kazin, M. A. Zykin, L. A. Trusov, A. A. Eliseev, O. V. Magdysyuk and R. E. Dinnebier, Chem. Commun., 2017, 53(39), 5416–5419 RSC ; E. Zorina-Tikhonova, A. Matyukhina, I. Skabitskiy, M. Shmelev, D. Korchagin, K. Babeshkin and I. Eremenko, Crystals, 2020, 10(12), 1130 CrossRef .
  41. M. K. Ehlert, S. J. Rettig, A. Storr, R. C. Thompson and J. Trotter, Can. J. Chem., 1990, 68(9), 1494–1498 CrossRef CAS .
  42. L. Krause, R. Herbst-Irmer, G. M. Sheldrick and D. Stalke, J. Appl. Crystallogr., 2015, 48, 3 CrossRef CAS PubMed .
  43. G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Adv., 2015, 71, 3 CrossRef PubMed .
  44. G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Adv., 2008, 64, 112 CrossRef CAS PubMed .
  45. O. V. Dolomanov, L. J. Bourhis and R. J. Gildea, et al. , J. Appl. Crystallogr., 2009, 42, 339 CrossRef CAS .

Footnote

† Electronic supplementary information (ESI) available. CCDC 2430824–2430827. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5nj02001h
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2025
Click here to see how this site uses Cookies. View our privacy policy here.