Core protonation of meso-tetraphenylporphyrin with tetrafluoroboric acid: unusual water-mediated hydrogen bonding of H4tpp2+ to the counterion

N-Protonation of meso-tetraphenylporphyrin (H2tpp) with tetrafluoroboric acid gives a hydrated porphyrin dication of the formula [H4tpp](BF4)2·2H2O·CHCl3, in which the saddled [H4tpp]2+ moiety is hydrogen bonded to the counterions through the two water molecules. Apparently, the formation of this unusual porphyrin diacid serves to optimize the hydrogen bonding. Rather than the tetrafluoroborate ion hydrogen bonding to the two N–H’s of [H4tpp]2+, the water molecules interact with [H4tpp]2+ and then with the BF 4 - counterions. The average pyrrole tilt angle with the N4 plane is 23.37° and an essentially saddled porphyrin core structure, with insignificant ruffling of the porphyrin core, is observed.