diazines

As a continuation of our interest in the reactions between methionine- and histidine-containing peptides and dinuclear Pt(II) complexes with six-membered aromatic diazines as bridging ligands, in the present study, we describe synthesis and characterization of three new dinuclear platinum(II) complexes, [[{Pt(en)Cl}.sub.2]([mu]-qx)][Cl.sub.2] x 2[H.sub.2]O (1), [[{Pt(en)Cl}.sub.2]([mu]-qz)][(Cl[O.sub.4]).sub.2] (2), and [[{Pt(en)Cl}.sub.2]([mu]-phtz)] [Cl.sub.2] x 4[H.sub.2]O (3) (qx = quinoxaline, qz = quinazoline, phtz = phthalazine, and en = ethylenediamine).

Three isomeric six-membered aromatic diazines with an additional fused benzene ring, quinoxaline, quinazoline, and phthalazine, were shown as good bridging ligands between two {Pt(en)Cl} units forming dinuclear complexes 1-3.

Djuran, "Gold(III) complexes with monodentate coordinated diazines: an evidence for strong electron-withdrawing effect of Au(III) ion," Polyhedron, vol.

The X-ray data for the corresponding chloride complexes, [[{Pt(en)Cl}.sub.2]([mu]-pydz)][Cl.sub.2] and [[{Pt(en)Cl}.sub.2]([mu]-pz)][Cl.sub.2], confirmed the hidden position of the Pt(II) centers in the pydz-bridged Pt(II) complex caused by their close proximity due to the ortho-positioning of the two diazine nitrogen atoms (the two Pt(II) centers were only 3.2535(4) [Angstrom] apart), compared to the separation of 6.7890(3) [Angstrom] in the analogous pz-bridged Pt(II) dimer.

Besides the resonances corresponding to the benzene ring, those due to the protons of the diazine ring can be detectable in the aromatic region of the [sup.1]H NMR spectra.

Groziak, "Six-membered ring systems: diazines and benzo derivatives," Progress in Heterocyclic Chemistry, vol.

A totally unsaturated membered six-ring containing nitrogen is known as azine [26] or pyridine (1); with two nitrogen atoms it is known as diazine [27], and with a nitrogen at 1,2-position, it is known as pyridine (2), at 1,3position as pyrimidine (3), and at 1,4-position as pyrazine (4) (Figure 1).

Pyrimidines are biologically very important heterocycles and represent by far the most ubiquitous members of the diazine family with uracil (6) and thymine (7) being constituents of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) and with cytosine (8) both being present in Figure 2(b).