We have devised a new polynucleating porphyrinic ligand, porphyrazine-2,3,7,8,12,13,17,18-octathiolato, (pz)(S-)8, the molecular structure of which may be thought of as a porphyrazine (tetraazaporphyrin) with four dithiolene moieties peripherally fused at the β-positions. Novel star-porphyrazine complexes (R2Sn)4-star-M(pz)(S-)8 (7a: R = t-Bu, M = Ni; 7b: R = n-Bu, M = Ni; 8: R = t-Bu, M = Cu) have been synthesized. Complex 7a crystallizes in the monoclinic space group C2/c with 4 macrocycles and 4 ordered solvent molecules (toluene) in a unit cell of dimensions a = 21.911 (3) Å, b = 21.265 (2) Å, c = 14.882 (3) Å, and υ = 94.44 (2)°. The polynucleating (pz)(S-)8 ligand in 7a coordinates one nickel atom in the central cavity and four tin atoms around the periphery using two thiolate sulfur atoms and one meso nitrogen atom for each tin, thus providing the first example of meso nitrogen coordination observed for a porphyrazine. The crystal structure of model complex 3b-H2O, (aquo)(octakis(methylthio)porphyrazinato)magnesium(II), was also solved: it crystallizes in the orthorhombic space group Pmna with 4 molecules in a unit cell of dimensions a = 14.279 (3) Å, b = 26.403 (6) Å, and c = 8.257 (2) Å. Comparison with the least-squares plane to the porphyrazine core of 3b-H2O and 7a shows that each is nearly planar and that the two have similar bond distances and angles; however, the bond angles involving the sulfur atoms of 7a are changed significantly as a result of coordination to tin. The electronic absorption spectra of 7a, 7b, and 8 show a suppression of the absorbance in the Soret region due to interaction of the Sn with the meso-nitrogen lone-pair and π-orbitals. Addition of halide ions restores the Soret absorption. Halide and pseudohalide ions bind to the Sn atoms of 7b in a two-stage manner, with first one X- and then two X- per Sn coordinating. Halide coordination to Sn is reversed upon dilution for X- = Br-, I-, and SCN-, but not for F-. The evidence suggests that the Sn atoms undergo a cooperative linkage isomerization induced by halide coordination of the second halide per Sn. The EPR spectrum of 1% 8 diluted into diamagnetic host 7a was recorded, and its features are consistent with other square-planar copper porphyrins and phthalocyanines.
ASJC Scopus subject areas
- Colloid and Surface Chemistry