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

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.