Exploring Supramolecular Self-Assembly of Metalloporphyrin Tectons by Halogen Bonding. 2

Abstract

In expansion of earlier observations, one SnIV(L)2, one oxo–VIV, and nine oxo–MoV(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-NO2-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.