and

.


Introduction
The presence of two or more different donor sets in the ligand molecule often allows obtaining polynuclear complexes with such original topologies as helicates, [3]   metallacrowns [4] and molecular grids.
[ 5-8]   Previously it was shown that polydentate Schiff base ligand Hpop (Scheme 1) forms with transition metals ions polynuclear complexes with [2×2] molecular grid topology. [6]Particularly, two donor sets of Hpop contain the donor atoms of different nature which promote the formation of the heterometalic grid-like [Cu 2 Mn 2 (pop) 4 (OAc) 4 ] complex.[7]   Although the preparation of molecular grids, in particular, heterometalic grids, are one-pot reactions, the formation of these complexes is likely a two-step self-assembly process.[6, 7] In the first step the mononuclear, metal-to-ligand 1:2species is formed.In the second step two such mononuclear bis-ligand species are aggregated with two additional transition metal ions to give the tetranuclear molecular grid.The implementation of these steps as separate synthetic stages expands synthetic abilities and can help to control the self-assembly processes.The presence of three alternative donor compartments in HL makes the molecular design of the target polynuclear complexes complicated as any predictions on the topology and structure of the resulting metal complexes seem to be quite speculative and ambiguous.Moreover, the formation of a sole polynuclear species in this case could not be so straightforward as in the case of the ligands typically used for the preparation of molecular grids (like Hpop) in which the number of donor atoms as a rule corresponds to the total number of positions available in the coordination spheres of all metal ions.Consequently, one-pot approach for polynuclear complexes can be complicated in the case of HL (see below) and thus seems to be unjustified.It is more reasonable and important to (i)define the primary donor sets in which metal binding occurs first, resulting in the formation of mononuclear species, and (ii) isolate the corresponding mononuclear complexes for further use as building blocks for the preparation of polynuclear assemblies.Thus, speciation studies in solution and isolation of mononuclear complexes (which a priori should contain vacant donor atoms or even donor compartments) should be regarded as a primary task in studies of donor properties of HL.

Materials
All of the reagents used in this work were of analytical grade and used without further purification.The solution studies were carried out in a MeOH/H 2 O (80:20 w/w) mixture.The ionic strength was fixed at I = 0.1 M with NaClO 4 .The solutions of Cu(II), Ni(II) and Zn(II) were prepared by dissolving M(ClO 4 ) 2 •nH 2 O (M = Cu(II), Ni(II) and Zn(II)) in water and standardized by ICP-AES.Caution!Perchlorate salts combined with organic ligands are potentially explosive and should be handled in small quantity and with the necessary precautions.HClO 4 solution was titrated by standardized NaOH in MeOH/H 2 O solution.Carbonate-free NaOH solution was standardized by titration with potassium hydrogen phthalate.

Syntheses
Ethyl 2-[1-(3,5-dimethyl)pyrazolyl]-2-hydroxyiminoacetate: A mixture of ethyl 2-chloro-2-hydroxyiminoacetate (906 mg, 6 mmol, synthesized according to [9] and 3,5-dimethylpyrazol (1152 mg, 12 mmol) in 10 ml of chloroform was left for evaporation in the air overnight.The resulting solid residue was recrystallized from water.Yield: 1120 mg (88% and Zn(II).The exact concentration of the ligand was determined using the method of Gran. [10]The potentiometric data were refined with Superquad [11] program, which use nonlinear least-squares methods. [12]The obtained pKw in the solvent mixture used in measurements was -14.42.[13]   Absorption spectra were recorded using a Varian CARY 300 UV-Vis spectrophotometer at 25.0±0.2˚C.The spectrophotometric data were analyzed with SPECFIT [14]   program.pH-dependent UV-Vis titrations were performed in the pH range 2-11.The combined glass electrode (Mettler Toledo InLab Semi-Micro) was prepared as in the case of potentiometric titration calibrated with buffers prepared in MeOH/H 2 O (80:20 w/w) mixture before every measurement. [15]For Ni(II)-HL system, total volume of the solution containing 1:2 and 1:1 molar ratio of Ni(II):ligand was 7 ml.The concentration of the ligand was around 2•10 -3 M. The starting pH was adjusted to around 2 with HClO 4 and the titration was carried out in a cell with 5cm optical path length.
For Cu(II), titrations were performed in a 1 cm cell with 3.2 ml as total volume of the solution containing 1:1, 1:2 and 2:1 molar ratios of Cu(II):ligand.The pH was controlled by addition of HClO 4 .
EPR spectra were recorded on a Bruker ELEXSYS E500 CW-EPR spectrometer equipped with an NMR teslameter (ER 036TM) and frequency counter (E 41 FC) at X-band frequency, at 77K.The solutions for EPR were prepared by using MeOH/H 2 0 mixture (80/20 w/w).The experimental spectra were simulated using WINEPR Simfonia 1. Electrospray ionization mass spectrometry (ESI-MS) data were collected in two series of experiments: (i) using a Jeol JMS-800D device or (ii) a Bruker apex ultra FT-ICR mass spectrometer and a BrukerMicrO-TOF-Q spectrometer (BrukerDaltonik, Germany), equipped with an Apollo II electrospray ionization source with an ion funnel.In the first series the 1-5 complexes were dissolved in methanol (concentration of 10 -4 -10 -6 M).For the second experiment stock solutions were prepared by using MeOH/H 2 O mixture (80/20 w/w) as a solvent.The metal to ligand molar ratios were 1:1, 1:2 and 2:1 and the final pH of the solutions were 2 and 8.The instrument parameters were: dry gas-nitrogen, temperature 200°C, ion source voltage 4500 V, collision energy 10 eV.The instrument was calibrated using the Tunemix mixture (BrukerDaltonik, Germany) in the quadratic regression mode.During both experiments the spectra were recorded in the positive ion mode in the range 100 to 1500 m/z.The overall charge of the analyzed ion was calculated on the base of the distance between the isotopic peaks.For MS spectra analysis, a Bruker Compass DataAnalysis4.0 software was used.

X-ray crystallography
All the measurements were performed using a NoniusKappa CCD diffractometer with a horizontally mounted graphite crystal as a monochromator and Mo Kα radiation.Data were collected and processed using Collect software. [16]The structures were solved and refined using the SHELXS-97 and SHELXL-97 programs, respectively. [17] For structure representation, the Diamond 3 program was used.[18]

Results and discussion
The HL ligand was synthesized from ethyl 2-chloro-2hydroxyiminoacetate in three steps (Scheme 2).Compounds 1-5 were obtained by the reaction between the HL ligand and the corresponding metal salt in methanol, with or without an addition of alkali.[8] Thus, the reaction of HL with zinc (II) and nickel (II) perchlorates gives complexes 1 and 3, respectively, where one of two ligand molecules is deprotonated.The synthesis under the same experimental conditions, but performed with addition of one equivalent of sodium hydroxide, permits to obtain compounds 2 and 4, where both ligand molecules are deprotonated.In the case of copper (II) perchlorate the deprotonation of both ligand molecules occurs without addition of alkali.IR-spectroscopic studies of 1-5show a limited low frequency shift of the ν(NO) band of the oxime group compared to the spectrum of HL (Δν = 20-24 cm -1 stretching mode), which suggests lack of involvement of this group in the coordination. [19]The long wave shift of the ν(CO) Amide I band of the amide group (Δν = 49-64 cm -1 ) indicates the amide O atom coordination.[20, 21]   ESI-MS Spectrometry Complex formation and the compositions of species formed in solution upon mixing HL ligand with Ni(II), Zn(II) and Cu(II)metal ions were first monitored using ESI-MS.Although this technique is not able to distinguish the ionizable protons in the species, the method can be successfully applied to determine the metal-to-ligand stoichiometry directly from the m/z values and has been successfully used by us when previously describing analogous systems. [6] (M = Ni(II), Zn(II) or Cu(II); X + = H + , Na + or K + ) The presence of such equilibrium suggests the possibility of the association of HL-containing mononuclear complexes into more complex supramolecular aggregates.

Speciation studies
Free ligand.In order to evaluate the coordination properties of the studied HL ligand toward metal ions, first the acid-base properties of this ligand were determined.The deprotonated form of the ligand, [L] -, may attach three protons in the measured pH range, and the protonation constants determined are presented in Table 1.The first constant (logK 1 = 8.77) corresponds to the protonation of oxime O -group, the second (logK 2 = 2.98) and the third (logK 3 = 1.81) of the pyridine and pyrazole N atoms.The determination of microconstants and assignment of the successive protonation constants logK 2 and logK 3 to particular protonation site was not the goal of the work and was not studied in detail.
Although slightly lower, logK 1 and logK 2 agree with the corresponding oxime and pyridine protonation constants determined for Hpop ligand. [6]It should be emphasized that HL  2).
In the spectrophotometric titration carried out for Ni(II)-HL in molar ratio 1:1 and 1:2, the d -d transitions centred at 864 nm (Table 1), present in the entire range of pH, suggest octahedral coordination of the Ni(II) ions (Figure S4).3A).
Using UV-Vis spectroscopy, we observed d-d transitions centred at 685 nm, which showed only small hypso-and hyperchromic shifts above pH 5.5 (Table 2, Figure S7).Such characteristics may indicate that in [CuL] + copper coordination is realized via two nitrogen donors, from the pyridine ring and from the azomethine group, and completed by an oxygen atom from amide group.
In dimeric complexes an additional nitrogen atom from the pyrazole ring may support the copper binding (as observed in X-ray structure of 6, Figure 7).Also EPR parameters strongly support the model based on monomeric and dimeric species (Figure S6).[CuL] + complex is characterized by A II = 156.1 G and g II = 2.25, while the spectra of dimeric species are distinguished by the presence of three g factor values: g x = 2.25, g y = 2.12 and g z = 2.03, what points toward the pentacoordination of Cu(II), and the geometry of the complex being intermediate between the square pyramid and the trigonal bipyramid (Figure7). [22]To distinguish between the two geometries, geometric parameters τ (Equation 2) and R (Equation 3) were calculated: where α is N(2)-Cu(1)-N( 12) and N( 6 species.[23]   The values of τ (τ Cu1 = 0.09, τ Cu2 = 0.05) and R (R = 0.64) parameters indicate the geometry of the distorted square pyramid with less than 10% share of the trigonal bipyramide. [23] The potentiometric titrations performed for 1:2 Cu(II) to ligand molar ratio suggested the formation of the [CuL] + mononuclear species up to pH 5. 2-biscomplexes(Table 2, Figure 3B).The maximum of absorption spectra moves from 685 nm (ε = 110 M -1 cm -1 ), through 574 (ε = 165 M -1 cm -1 ), up to 554 nm (ε = 285  S6) may be the result of a decrease in the symmetry of the complex.It has to be underlined that present speciation is different to the one previously observed for Cu(II):Hpop system, where only biscomplexes were formed along the entire pH range.[6]   The solution studies carried out for an excess of Cu(II) over HL ligand (2:1 and 3:2 molar ratio) show that metal ion complexation again starts with the formation of the [CuL] + complex, and is followed by polynuclear Cu 3 L 2 H x species (Table 2, Figure 3C).The distinct increase of the d-d transitions energy up to 630 nm indicate involvement of additional nitrogen donors in copper coordination (Figure S7).The disappearance of EPR signal confirms the formation of polynuclear species (Figure S6).

X-ray analysis
Mononuclear complexes.All the reported mononuclear complexes 1-5 are crystallized in P-1 space group with very close unit cell parameters (Table 3).The compounds 1 and 3 have similar ionic structures, which consist of the [M(L)(HL)] + (M = Ni(II) or Zn(II)) complex cation, perchlorate anion and two methanol solvent molecules (Figure 4).The perchlorate anion in structures 1 and 3 is disordered over two near positions; the distance between Cl atoms of two such positions is less than 0.7 Å.The compounds 2, 4 and 5 have similar molecular structures, which consist of the neutral complex species [M(L) 2 ] (M = Cu(II), Ni(II) or Zn(II)) and methanol solvent molecules (Figure 4).Thus, compounds 1-5 reveal two structural types: molecular and ionic.The elements of crystal structures are connected by the extensive systems of hydrogen bonds.Selected bond lengths and angles are collected in Table 4.

The complex species [M(L)(HL)]
+ and [M(L) 2 ] include two ligand molecules and reveal similar structures.One or two ligand molecules are singly deprotonated in [M(L)(HL)] + and [M(L) 2 ], respectively.Note that the deprotonation occurs at the azomethine group, the amide nitrogen is deprotonated although it is not involved in the metal coordination.[26] Both ligand molecules are coordinated in a tridentate {N pyridine , N azomethine , О amide } mode, thus forming two fused five-membered chelate rings.The central atoms have the distorted octahedral coordination arrangements with N 4 O 2 chromophores.Interestingly, in both complex species such an efficient donor as the oxime group remains uncoordinated and protonated, in spite of the fact that it can be involved in the chelate ring formation with the neighbouring pyrazole or amide nitrogen atoms.Presumably, the bis-chelating mode observed in 1 and 3 provides the most efficient donor set for primary metal binding.The Cu-N bond distances in 5 are in the range 1.9299(10)-2.2059(12)Å, Cu-O 2.0024(9)-2.3844(10)Å.The Zn-N and Zn-O bond lengths in the compounds 3 and 4 are comparable to the ones in previously reported zinc complexes with the pyridine and oxime groups complexed to the metal ion.[25, 27]   Bond angles O-M-O`, O-M-N, N-M-N` are typical for the pseudooctahedral coordination environment [28] (Table 2).
N( 7)C( 19)C( 20)N( 8) and M(1)N( 8)N( 9)C( 22)O(3) are almost planar.The deviations of the metal atoms from the mean plane formed by the other four atoms in the ring are less than 0.08Å.Bond lengths N-N', N-C and C-O of the azomethine group of HL are typical for the protonated moieties of these type (Table 4).At the same time the N-N', N-C and C-O bond lengths of L indicate values typical for the deprotonated azomethine group.The C=N and N-O bond lengths in the oxime moieties clearly indicate that the oxime groups exist in the nitroso rather than isonitroso form and are typical protonated oxime groups in the amide derivatives of 2-hydroxyiminopropanoic acid. [29] In the [M(L)(HL)] + cation the azomethine oxygen atom is situated in an anti-position with respect to the oxime N atom in the case of HL and in syn-position in the case of L. There is a similar arrangement in of [M(L) 2 ] molecule: one of the azomethine O atoms is situated in an anti-position with respect to the oxime N atom, another one -in syn-position.Note, that the free oxime group is normally located in antiposition to the amide group which was earlier shown in the structures of the free Hpop ligand [30] and related amide derivatives of 2-hydroxyiminopropanoic acid [31] .Hydrogen bond parameters of 1-5 are collected in Table 4.The crystal packing of 2, 4 and 5 is similar to the crystal packing of 1 and 3. Two [M(L) 2 ] molecules and two methanol molecules due hydrogen bonds form supramolecular units, which have similar structure to analogous units of 1 and 3 (Figure 5).These units are connected by O-H•••N hydrogen bonds into columns spreading along the a-axis (Figure 6, Scheme 3).
Binuclear Cu(II) complex.The compound 6 is crystallized in P-1 space group and has ionic structure, which consists of the complex cation [Cu 2 (L) 2 (DMF) 2 ] 2+ (Figure7), the perchlorate anion and two DMF solvent molecules.The elements of crystal structure are connected by the extensive systems of hydrogen bonds.Selected bond lengths and angles are collected in Table 6.2+ are singly deprotonated via the amide nitrogen atoms; the oxime groups are protonated and non-involved in coordination.The Cu-N bond distances in 6 are in the range 1.9388(12)-2.0164(12)Å, Cu-O -1.9865(10)-2.1472(11) Å, what is typical for tetragonal-pyramidal complexes of copper with similar ligands. [23]The distance between the two copper atoms  6).The C=N and N-O bond lengths are typical for the non-coordinated nondeprotonated oxime groups in the nitroso form.[22-26]   In both ligand molecules of [Cu 2 (L) 2 (DMF) 2 ] 2+ the azomethine oxygen atom is situated in an anti-position with respect to the oxime N atom.The NC(=NOH)C(=O)NH fragments are not planar; the torsion angles O amide -C-C-N oxime are 154.8(1)°and 156.9(1)°.Hydrogen bond parameters of 6 are collected in Table 7. 2+ is connected with two neighbouring cations through two hydrogen bonds, in which the oxime O atom acts as donor and the amide N atom acts as acceptor.Due to these hydrogen bonds in the crystal packing of 6(Figure 8) the columns spreading along the ac diagonal are formed.In a series of mononuclear complexes  [24] , but at the same time in the structures of 1-5 half of ligand molecules are deprotonated.Thus, the The present work is devoted to the synthesis of new polydentate ligand 2-[1-(3,5-dimethyl)pyrazolyl]-2hydroxyimino-N'-[1-(2-pyridyl)ethylidene]aceto-hydrazide (HL) (Scheme 1) containing several donor functions of different nature (vide supra), and the preparation of a series of complexes on its basis.Similarly to Hpop, HL ligand possess two different donor sets, i.e. the pyridine plus azomethine (A) and oxime (B) having common amide O atom; also includes an additional donor set (C) formed by the pyrazole N and oxime O atoms.
26 program and Doubletnew (EPR OF S=1/2) program by Dr. Andrew Ozarowski, National High Field Magnetic Laboratory, University of Florida.

Scheme 2 .
Scheme 2.Synthetic route to the HL ligand.
Ni(II) and Zn(II) complexes.According to the potentiometric titrations, for Ni(II) and Zn(II) ions the stoichiometry of the complexes formed in solution were different for experiments performed in 1:1 and 1:2 metal to ligand molar ratios.In equimolar solutions only oligomeric species were found, starting from [Ni 3 L 3 H 2 ]2+ and [Zn 3 L 3 H 3 ] 3+ , for Ni(II) and Zn(II) and Hpop were measured under different experimental conditions (MeOH/H 2 O 80/20 w/w and DMSO/H 2 O 10/90 v/v, respectively), thereby precluding direct comparison of the data.However, the decrease of the protonation constants of HL ligand may come from an inductive effect of the pyrazole group.

Table 1 .
Potentiometric and spectroscopic data for proton and M(II) complexes of HL predominating the solution in pH range 2-5.5, and followed by [Cu 2 L 2 H -1 ]+ and [Cu 2 L 2 H -2 ] (Table2, Figure Cu(II) complexes.Calculations based on the potentiometric data obtained for equimolar solutions of Cu(II) and HL indicate the formation of monomeric and dimeric species, i.e. starting with [CuL] +

Table 2 .
Potentiometric and spectroscopic data for Cu(II) complexes of HL

Table 7 .
Hydrogen bond parameters of 6.Each complex cation [Cu 2 (L) 2 (DMF) 2 ] 1-5obtained in solid state the corresponding metal ion has a distorted octahedral coordination arrangement N 4 O 2 formed by two ligand molecules.HL molecules are coordinated in the protonated or the singly deprotonated form via the pyridine and the azomethine nitrogen atoms and the amide oxygen atom.Such coordination mode is typical for mononuclear complexes based on already described polynucleating azomethine ligand Hpop: Zn[pop] 2 ·2H 2 O and Zn[(Hpop)Cl 2 ]·2H 2 O [21, 24] .It is important to note that the reaction of Hpop with ZnCl 2