The diprotonated, bishydroperchlorate forms of three isomeric beta-oct
aalkyl-substituted tetrapyrrolic macrocycles, namely, etioporphyrin II
(1), etioporphycene (2), and etiocorrphycene (3), have been character
ized both in chloroform solution, by UV/visible spectroscopy and H-1 a
nd proton-correlated 2D N-15 NMR methods, and in the solid state, by s
ingle-crystal X-ray diffraction analyses. In the solid state, in marke
d contradistinction to what is observed for the corresponding free-bas
e forms, the macrocyclic portion of these salts were found to be disto
rted significantly from planarity with the two perchlorate counteranio
ns being held above and below the average N-4 plane by N-H ... O hydro
gen bonds in all three cases. In solution, H-1 and proton-correlated 2
D N-15 NMR experiments reveal molecular ions of relatively high symmet
ry (D-2h, D-2h, and C-2v in the case of 1 .(HClO4)(2), 2 .(HClO4)(2),
and 3 .(HClO4)(2), respectively) as would be anticipated on the basis
of the solid-state results. These same NMR analyses, while revealing s
light differences between the three salts in the NH and meso H-1 NMR s
pectral regions, also serve to confirm the generalized congeneric natu
re of 1 .(HClO4)(2), 2 .(HClO4)(2), and 3 .(HClO4)(2) and support the
assignment of the latter two species as being porphyrin-like salts. UV
/vis analyses further support this conclusion; in all three instances,
strong Soret- and Q-like transitions are observed in dichloromethane
that are both distinct from each other (lambda(max) = 404, 549, 570, 5
93; 388, 409, 599, 666; and 419, 559, 604 for 1 .(HClO4)(2), 2 .(HClO4
)(2), and 3 .(HClO4)(2), respectively) and from those of the correspon
ding free-base forms (lambda(max) = 396, 496, 530, 565, 619; 382, 570,
617, 657; and 410, 509, 539, 574, 628 for 1, 2, and 3 respectively).
Protonation experiments were carried out by exposing dichloromethane s
olutions of the isomers to aqueous perchlorate/perchloric acid solutio
ns of differing pH. These studies reveal that while porphycene 2 adds
two protons readily and concurrently, becoming 50% diprotonated when e
xposed to perchlorate/perchloric solutions with a pH of around 3.6, po
rphyrin 1 and corrphycene 3 are protonated in a stepwise manner; they
become 50% monoprotonated when exposed to perchlorate/perchloric solut
ions of pH approximate to 3.7 and 3.9, respectively, and diprotonated
at pH less than or equal to 0.8 and 1.3, respectively.