Cobalt(II) and copper(II) in selective coordination of armed ligands: {[(3,5-dimethyl-1 H -pyrazol-1-yl)methyl]amino}acetic acid and {[bis-(3,5-dimethyl-1 H -pyrazol-1-yl)methyl]amino}acetic acid

Two novel ligand pyrazole derivatives AH and BH ( AH = [(3,5-dimethyl-1 H -pyrazole-1- yl)methyl]amino acetic acid, BH = [bis-(3,5-dimethyl-1 H -pyrazole-1-yl)methyl]amino acetic acid) formed simultaneously by the condensation of N -hydroxy methyl-3,5-pyrazole ( 1 ) with glycine (CH 3 COOH) and their cobalt(II) or copper(II) mixed ligand complex, with 3,5-dimethyl-1 H -pyrazole (Pz) have been synthesized and characterized by spectroscopic analysis and X-ray diffraction study. Distorted square pyramidal geometry is observed around copper(II) with two nitrogens (N 1 , N 3 of AH ) in the first plane and third nitrogen (N4 of one pyrazolic ligand) and two oxygen atoms (O 4 and O 1 ) in the second plane. In contrast to Cu(II) cation which coordinates with ligand AH , the Co(II) cation prefers to coordinate with the second ligand BH .


Introduction
Copper is an important and much studied trace element.Quite apart from the biological 1,2 or technological relevance [2][3][4] of copper(II), the attractions of copper(II) to inorganic chemistry researchers can be understood easily, given the user friendliness of copper(II) complexes.These copper complexes are commonly air and moisture stable, having informative and easy-to-obtain UV-vis, 5 E.S.R. spectroscopic 6,7 signatures and also undergo reactions effectively in solution immediately after mixing.The stereochemical flexibility of copper(II) complexes means that they adopt a wider range of coordination geometries than any other transition ions. 7Copper(II) complexes have found possible medical uses in the treatment of many diseases including cancer. 8,9For copper(II) d 9 electronic configuration penta-or hexa-coordination is usually found. 10Thus, one of the prevailing observations is that upon oxidation of copper(I) to copper(II), a large structural change occurs which often is accomplished by solvent coordination.System for which this process does not occur are very rare. 10Several such type of copper complexes reported by taking the substituted 1,10-phenanthroline. [11][12][13][14] The first example of four coordinate copper(II) having a CuN 4 chromophore was investigated by Hathaway. 15Recently examples of four-coordinated copper(II) bearing 1,10-phenanthroline/2,9-dimethyl phenanthroline was investigated. 16,17In these structures the CuN 4 chromophores generally involves a trigonal or tetrahedral distortion from planar.

Synthesis
For a preparative scale reaction, commercially available glycine was reacted with hydroxymethylated pyrozolic precursor 1 leading to a mixture of two compounds AH and BH, the products shown by TLC after a 2-4 days mixing in acetonitrile, as one point.Precipitation in water, filtration of compounds AH and BH, followed by washing with cold water to eliminate solvent and unreacted starting materials (Scheme 1).Although it has been reported by our group that the ligand AH was purified and well characterised with its Cu(II) complex [20], It is too difficult to see on TLC or to separate the ligands AH and BH before their coordination to Cu(II) or Co(II) cations.So no ligands AH and BH gave satisfactory individual spectroscopic analysis.
The IR spectrum of ligand AH (containing BH) shows one large, medium absorption band around 3260 cm -1 , which may be due to a hydrogen bonded υ(NH) in the end structure or υ(OH) in the carboxymethylated/ amine form.Both C=N imine groups are visible at 1580 and 1520 cm - 1 for compound AH and BH.These bands correlate with carboxylated secondary or tertiary amine compounds AH and BH, which usually exhibit a variable band in the region 1690-1640 cm -1 .This compound also shows one strong υ(CO) stretching frequency at ca. 1670 cm -1 .From this we cannot conclude closely that the resulting product of Scheme 1 exists in the all one principal form AH as shown by crystallographic study of CuA complex. 20n the 1 H-NMR spectrum of AH, the chemical shift for C(4) proton apeares at 5.87 ppm, with no coupling to any adjacent atoms.Furthermore, the chemical shift for methylene protons (NH-CH 2 -Pyrazol) appear as doublet at 5.03 ppm, with coupling to proton of adjacent amine group.The second methylene protons (NH-CH 2 -COOH) appear at 2.93 ppm, with coupling to proton of adjacent amine group.
The IR spectrum of the Cu(II) complex CuA shows one large, medium absorption band around 3523/3340/3238 cm -1 which may be due to a hydrogen bonded υ(NH) in the end structure of A or υ(NH) in the monodentate ligand Pz.Both C=N imine groups are visible at 1587 and 1566 cm -1 for compound AH.These bands correlate with carboxylated secondary amine compound AH, which usually exhibit a variable band in the region 1690-1640 cm -1 .This compound also shows one strong υ(CO) stretching frequency at ca. 1613 cm -1 .From this we have concluded that the dissymmetric ligand AH exists in the alone principal form AH as shown in Scheme 1.

X-Ray crystallography
A blue irregular prismatic crystal of {[Cu(A)(Pz)](NO 3 ).H 2 O} n was mounted on a glass fiber and used for data collection.Cell constants and an orientation matrix for data collection were obtained by least-squares refinement of the diffraction data from 23 reflections in the range of 1.04 < θ < 24.93° on an Enraf Nonius MACH3 automatic diffractometer. 21Data were collected at 293 K using CuK(α) radiation (λ = 0.70930 Å) and the ω /2θ-scan technique, and corrected for Lorentz and polarization effects. 22A semi-empirical absorption correction (Psi-scans) was made. 23RKAT USA, Inc.
The crystal structure analysis of the title compound, {[Cu(II)(C 5 H 8 N 2 )(Pz)](NO 3 ).H 2 O} 2 , reveals that the copper(II) ion lies in a distorted square pyramidal with N3O2 copper(II) environment.It is possible that the O atoms of the nitrate group are involved in intra-and intermolecular hydrogen bonding.The continuity of the present complex structure (Fig. 2) shows dimer consisting of two copper atoms and two (A) anions.The two halves of the dimer are related by a crystallographic twofold axis.Each L-anion binds one copper atom at its two nitrogen and one oxygen atoms, and the second copper of the dimer at one of its carboxyl oxygen atoms.The copper atoms are 5-coordinated distorted square pyramidal.The atom Cu forms bonds to the nitrogen atoms N(1), N(3) of LH, N(4) of one pyrazolic ligands and to a carboxyl oxygen atom O(4) and O(1) of the other AH molecule of the dimer.There is also a weaker bond between the copper and oxygen O(6) of the NO3 anion (Fig. 3).In the five coordinate structures, the AH molecules occupy the basal plane.The pyrazolic ligands display axial coordination.The base of each distorted square pyramidal unit is occupied by N(1), N(3) and O(4) atoms, with a optical position is occupied by the O(1) atom of the second LH ligand.Similar geometry is suggested in [Cu(PMDT)(bipy)](ClO 4 )2 and [Cu(PMDT)(phen)](ClO 4 ) 2 complexes. 18n contrast to the dissymmetric tridentate N,N,O-ligand AH, the new tetradentate N,N,N,Oligand BH would have a symmetric charge distribution.Therefore, the most probable complexed form for BH contains a hemilabile bond (Co-OCO).These results prompt several pertinent observations: (i) This new type of armed tetradentate ligand can furnish an interesting model for preparing large series of organometallic catalysors with various metals because the hemilabile character of metal-carboxylate bond is generally present in large catalytic reactions; (ii) The unsaturated electronic configuration of both Cu(II) and Co(II) enables us to prepare various complexes for organic catalysis, redox and magnetic materials; and (iii) Functionalised polydentate ligands can easily be prepared from glycine and other amino-acid precursors.
ARKAT USA, Inc.  26 where Pz is 3,5-dimethyl-pyrazole.In the chloride compound, the Cu(II) atom displays a distorted octahedral coordination, while in the perchlorate and nitrate compounds, the Cu(II) coordination geometry is described as distorted square-pyramidal.Since the properties of the two compounds AH and BH were different, it was difficult to separate the two compounds simultaneously.To have a clear idea about the polymeric aspect of complex Co(B), the ORTEP view for the continuity of the complex cation of [Co(B)(OH 2 )] + has been added here as shown in Figure 3.

Conclusions
Using the standard TLC technique with a single of solvent system and a silicate gel or alumina of the solid phase, but the separation of them could be achieved by selective coordination of Cu(II) with AH or Co(II) with BH.The present results of our studies indicate that the coordination technique by varying metallic cation is a powerful and selective technique for the separation of armed ligands AH and BH.
As a perspective, the use of the ligands AH and BH represents a new selective way for the synthesis of polymeric copper(II) or Co(II) complex containing hemilabile bond Cu-O or Co-O.Moreover, they are soluble in the reaction mixture and could catalyse reactions which are impossible to perform with the M(II)Cl-L complexes.The metal could also be changed and act as a template and allow the notoriously difficult catalysis suggested previously.We will try to relate the redox potentials of the analogous complexes to their possible biocatalytic activity.
The synthetic methodology adopted for the preparation of these present complexes may be useful in fine tuning the structural features to get more accurate Cu 2 Cu 2 SOD and Co 2 Co 2 superoxidase dismutase (SOD) models for the active site.The SOD like activity evaluation will reveal modes with this important enzymatic activity.
In conclusion, a combined crystallographic and spectroscopy approach is useful not only to give the complete characterization of the new complexes, but also it will help to correlate their structural features with possible biological activation.

Scheme 1 .
Scheme 1. Synthesis of the ligands AH and BH.

Figure 3 .
Figure 3. ORTEP view for the continuity of the complex cation of [Co(B)(OH 2 )] + .The hydrogen atoms have been omitted for clarity.