Mol 2 Net Synthesis and Platinum ( II ) Complexes of Different Polyazacyclophane Receptors

The interaction of PtCI4 with different polyazacyclophanes containing a pyridine unit as aromatic spacer has been studied by H and Pt NMR spectroscopy, Analysis of the recorded spectra of D2O solutions containing L and PtCl4 in a 1:1 molar ratio at acidic pH shows the evolution with time of the H and Pt signals. Different crystal structures have been solved by X-ray diffraction analysis. At acidic pHs, the metal ion is coordinated by the central amino group of the macrocyclic cavity and three chloride or bromide atoms, in a square planar geometry. Formation of [Pt(H2L1)Br3]Br (1) and [Pt(H2L2)Br3]Br (2) reveals the rapid substitution of chloride ligands in PtCl4 by bromide ligands. However, as reveals the crystal structure obtained for [PtL3Br2](PtBr4)(H2O) (4), at slightly higher pH values, the metal ion is coordinated through all nitrogen atoms of the macrocyclic cavity and an oxidation to Pt(IV) occurs.


Results and Discussion
Crystals suitable for x-ray diffraction were obtained from K2PtCl4 and L• 3HBr in I:1 molar ratio.In accordance with a behaviour previously reported by Garcí a-España et al., 10   However, as reveals the crystal structure obtained for [Pt IV L3Br2](PtBr4)(H2O) (4), at slightly higher pH values, the metal ion is coordinated through all nitrogen atoms of the macrocyclic cavity and two bromide ligands complete the octahedral geometry, indicating that an oxidation to Pt(IV) occurs.As can be seen in Table 1, the Pt-N bond distances in the [Pt IV L3Br2] 2+ cation are shorter than the obtained for the bromide ligands.Furthermore, the [Pt IV L3Br2] 2+ cations are interconnected through intermolecular hydrogen-bonds with the [PtBr4] 2- anions.This counterion links through hydrogen bonding one of the benzylic amino groups of a unit (Br6-H• • • N2=2.323Å) with the same amino group of the following unit creating chains that are isolated and do not show any kind of interconnection These 195 Pt NMR spectral changes are accompanied by significative variations in the 1 H NMR spectra.The initial 1 H NMR spectrum, which corresponds to the fully protonated free receptor presents, in the aliphatic region, a singlet signal at 4.55 which can be assigned to the benzylic protons, and two triplet signals at 3.20 and 2.95 ppm assigned to the protons of the ethylenic chains.In the aromatic region, a triplet and a doblet signals appear at 8.00 ppm and 7.48 ppm respectively.As the reaction proceeds, although the symmetry is essentially preserved, http://sciforum.net/conference/mol2net-1new signals with more complex spin systems appear.

Materials and Methods
The synthesis of L1-L3 has been carried out by slightly modifications on the general procedures described in literature. 8,9,12All reagents and chemicals were obtained from commercial sources and used as received.Solvents used for the chemical synthesis were of analytical grade and used without further purification.
Synthesis of [Pt(H 2 L1)Br 3 ]Br (1).To an aqueous solution (5 mL) of L1• 3HBr, K2[PtCl4)] in water (5 mL) in a 1.1 molar ratio was added dropwise with stirring.After the mixture was stirred for 2 h at room temperature, it was filtered.Orange crystals suitable for X-Ray analysis were obtained by slow evaporation of the solvent.

Synthesis of [Pt(H 2 L2)Br 3 ]Br (2).
To an aqueous solution (5 mL) of L2• 3HBr, K2[PtCl4)] in water (5 mL) in a 1.1 molar ratio was added dropwise with stirring.After the mixture was stirred for 2 h at room temperature, it was filtered.Orange crystals suitable for X-Ray analysis were obtained by slow evaporation of the solvent.

Synthesis of [Pt(H 2 L1)Cl 3 ]Cl (3).
To an aqueous solution (5 mL) of L1• 3HCl, K2[PtCl4)] in water (5 mL) in a 1.1 molar ratio was added dropwise with stirring.After the mixture was stirred for 2 h at room temperature, it was filtered.Yellow crystals suitable for X-Ray analysis were obtained by slow evaporation of the solvent.

Synthesis of [Pt IV L3Br 2 ](PtBr 4 )(H 2 O) (4).
To an aqueous solution (5 mL) of L3• 3HBr, K2[PtCl4)] in water (5 mL) in a 1.1 molar ratio was added dropwise with stirring..After the mixture was stirred for 2 h at room temperature, it was filtered.Orange crystals suitable for X-Ray analysis were obtained by slow evaporation of the solvent.
NMR Measurements.The 1 H and 13 C NMR spectra were recorded on a Bruker Avance AC-300 spectrometer operating at 299.95 MHz for 1 H.The chemical shifts are given in parts per million referenced to the solvent signal.Adjustments to the desired pH were made using drops of DCl or NaOD solutions.The pD was calculated from the measured pH values using the correlation, pH = pD − 0.4. 13rystallographic analysis Analysis of single crystals was carried out with an Enraf-Nonius KAPPA CCD single-crystal diffractometer (λ =0.71073 Å).The structures were solved with using the program SHELXS-86. 14 program SHELXL-97. 15Molecular plots were produced with either the program MERCURY 16 or ORTEP. 17Crystal data, data collection parameters, and results of analysis are listed in Table 2.  2-. by bromide ligands.The X-ray analysis of the compound shows that interaction of [PtCl4] 2-with L.3HBr in 1:1 molar ratio gives rise to two different complexes as function of the pH, which differ in the location of platinum in the macrocycle.At acidic pH, Pt(ll) binds to the central nitrogen of the macrocycle, while at slightly higher pH values, as the benzylic nitrogens deprotonate, the metal ion can be coordinated by all the nitrogen atoms of the macrocyclic cavity and an oxidation to Pt(IV) occurs.We are currently trying to characterize better these complexes in solution, analyzing the effect of pH changes, as well as trying to obtain information on interaction with nucleobases and oligonucleotides.

Figure 2 .Figure 3
Figure 2. X-Ray crystal structure of the cation [Pt IV L3Br2] 2+ Figure 3 shows the evolution with time of 1 H and 195 Pt NMR spectra of D2O solutions containing K2PtCl4 and L1• 3HCl in 1:1 molar ratio recorded at acidic pH.Initially, the 195 Pt spectrum consists of a signal at -1660 ppm which can be attributed to [PtCI4] 2-. 11After 2 days, a new signal at -2030 ppm appears and can be attributed to a platinum(II) ion coordinated to three chlorides and to a nitrogen atom of the macrocycle,, in accordance with the crystal structure obtained for this receptor, [Pt(H2L1)Cl3]Cl (3).These195  Pt NMR spectral changes are accompanied by significative variations in the 1 H NMR spectra.The initial 1 H NMR spectrum, which corresponds to the fully protonated free receptor presents, in the aliphatic region, a singlet signal at 4.55 which can be assigned to the benzylic protons, and two triplet signals at 3.20 and 2.95 ppm assigned to the protons of the ethylenic chains.In the aromatic region, a triplet and a doblet signals appear at 8.00 ppm and 7.48 ppm respectively.As the reaction proceeds, although the symmetry is essentially preserved, Structure refinement was performed by means of the [http://sciforum.net/conference/mol2net-1