Exploring supramolecular self-assembly of metalloporphyrin tectons by halogen bonding. 2

In expansion of earlier observations, one Sn^IV(L)₂, one oxo-V^IV, and nine oxo-Mo^V(L) new porphyrin compounds (L = anionic axial ligand) have been synthesized and structurally characterized by single crystal X-ray diffraction analysis to probe the occurrence of halogen bonds in crystalline metalloporphyrin assemblies. The [Sn(TIPP)(p-NO ₂-phenolate)₂] six-coordinate system (TIPP = dianion of 5,10,15,20-meso-tetrakis(4-iodophenyl)porphyrin) (1) exhibits weak I⋯O interactions, stimulating further studies with the oxo-Mo/V porphyrin scaffolds. The domed complex [V(O)(TIPP)] (2) crystallizes in a chiral space group and shows short O⋯π contacts along the polar axis, but no distinct halogen bonds. In [Mo(O)(TIPP)(L)] (L = 1-hydroxybenzotriazolate (3), 5-bromonicotinate (4), pyrimidine-5-carboxylate (5), 4-iodobenzoate (6), 2-chlorobenzoate (7)) diverse (O⋯I, N⋯I, I⋯I) halogen bonds and halogen-bonding-type contacts have been observed, depending upon the nature of the axial ligand attached to the Mo center. In analogous compounds with TBrPP, [Mo(O)(TBrPP)(L)] (TBrPP = dianion of 5,10,15,20-meso-tetrakis(4-bromophenyl) porphyrin, L = 5-bromonicotinate (8), isonicotinate (9)), directional halogen interactions involving bromine have not been detected. Intermolecular N⋯I halogen bonding has also been observed when the N-donor sites were positioned on the porphyrin periphery and the iodine acceptor on the axial ligand as in [Mo(O)(T⁴pyP)(4-iodobenzoate)] (10) (T⁴pyP = dianion of 5,10,15,20-meso-tetrakis(4-pyridyl)porphyrin). An attempt to induce the formation of halogen bonded chain assemblies through I⋯O interaction between the axial oxo and iodine sites of adjacent species in [Mo(O)(TTP)(4-iodobenzoate)] (11) (TTP = dianion of 5,10,15,20-meso-tetrakis(p- tolyl)porphyrin) has not been successful.