Zinc complexes of 3-pyrimidinyl-benzo-1,2,4-thiadiazine.

The synthesis of the novel redox active ligand 3-(2′,6′-pyrimidine)-benzo-1,2,4-thiadiazine (pmbtdaH) is reported. The radical pmbtda can be prepared by in situ 1 e − oxidation and its radical character confirmed by EPR spectroscopy, along with DFT calculations of the spin density distribution. Reaction of pmbtdaH with ZnCl 2 ·2H 2 O in a 1:1 mol ratio afforded the dinuclear complex Zn 2 Cl 4 (pmbtdaH) 2 ( 1 ) in which the two trigonal bipyramidal metal centres are linked via μ 2 -bridging Cl − ligands while the pmbtdaH ligand binds in an N,N′-chelate fashion via N(4) and the pyrimidinyl N(1) atom. The outcome of the reaction of pmbtdaH with Zn(hfac) 2 (hfac = hexafluoroacetylacetonate) proved sensitive to the crystallization method; the mononuclear octahedral complex Zn(hfac) 2 (pmbtdaH) ( 2 ) in which the ligand coordinates in a similar N,N′-chelate fashion to that observed in 1 was isolated by layering a concentrated CH 2 Cl 2 solution with hexane. Conversely the same reaction mixture afforded the tetranuclear complex Zn 4 (hfac) 6 (pmbtda ox ) 2 ( 3 ) when left undisturbed in a sealed vial. In 3 the ligand is both deprotonated and oxidized forming an anionic ligand in which there are two potential N,N′-chelate pockets and an additional S-oxide donor. The pmbtda ox − ligand bridges between a Zn(hfac) 2 and a Zn(hfac) unit to form Zn 2 (hfac) 3 (pmbtda ox ). Two such Zn 2 (hfac) 3 (pmbtda ox ) units dimerise through the S-oxide oxygen atom to form a centrosymmetric tetranuclear Zn 4 (hfac) 6 (pmbtda ox ) 2 cluster. The structures of 1 – 3 have been determined by X-ray diffraction, elemental analysis, IR and UV–Vis spectroscopies as well as 1 H NMR spectroscopy for complex 2 . [ABSTRACT FROM AUTHOR]