INTERCALATION OF AMINOPHENYL-SUBSTITUTED AND PYRIDINIUM-SUBSTITUTED PORPHYRINS INTO ZIRCONIUM HYDROGEN PHOSPHATE - EVIDENCE FOR SUBSTITUENT-DERIVED ORIENTATIONAL SELECTIVITY

Aminophenyl- and pyridinium-substituted porphyrins were intercalated into the alpha phase of zirconium hydrogen phosphate (alpha-ZrP) by exchanging the porphyrins into the p-methoxyaniline (PMA) preintercalated compound Zr(O3POH)2.2PMA (alpha-ZrP.2PMA). Porphyrin exchange reactions with alpha-ZrP and its ethanol intercalate were unsuccessful. Powder X-ray diffraction patterns of p-H2TAPP- and H2TMPyP-exchanged alpha-ZrP.2PMA revealed complete conversion of the starting material to phases with interlayer spacings near 17 angstrom, corresponding to a guest layer thickness of ca. 11 angstrom. The p-H2TAPP derivative was found to partially convert over several weeks to alpha-ZrP and a 24-angstrom phase material. The large interlayer spacing cannot be accounted for by a porphyrin monolayer and is tentatively assigned to a porphyrin bilayer in which the heme planes are tilted relative to the host lamellae. Conversely, intercalation of alpha-ZrP-2PMA with the a,a,a,a, a,alpha,a,beta and alpha,beta,alpha,beta atropisomers of o-H2TAPP afforded multiphasic products with interlayer spacings of 13, 17, 19-20, and 25 angstrom. The relative intensities of the phases were highly dependent on the atropisomer, with the alpha,alpha,alpha,alpha isomer forming mainly a 19-angstrom phase and o-alpha,beta,alpha,beta-H2TAPP forming predominantly a 17-angstrom phase. In order to determine the orientations of porphyrins comprising the 17- and 19-20-angstrom phases relative to the host lamellae,p-CuTAPP and o-alpha,alpha,alpha,alpha-CuTAPP intercalation complexes were prepared, and anisotropic EPR spectra of uniaxially ordered thin films oriented at 0 and 90-degrees relative to the applied magnetic field were recorded. The EPR spectra of the p-CuTAPP-exchanged host displayed little orientational dependence, consistent with tilting of the heme macrocycles near 45-degrees relative to the host lamellae. Conversely, the EPR spectra of uniaxially ordered films of the o-alpha,alpha,alpha,alpha-CuTAPP-exchanged host exhibited a strong orientation dependence, with the perpendicular component of the Cu(II) signal dominating the spectrum in samples oriented at 90-degrees relative to B0 and the parallel component predominating in films oriented at 0-degrees relative to B0, indicating that the porphyrins were highly oriented parallel to the host layers. Together, the XRD and EPR data suggest that the guest morphology of the p-TAPP derivatives consisted of a monomolecular porphyrin layer in which the heme planes were tilted nearly 45-degrees relative to the host lamellae, whereas o-alpha,alpha,alpha,alpha-TAPP derivatives predominantly assembled into a porphyrin bilayer in which the heme macrocycles lay parallel with the host sheets. The preferred porphyrin orientations are discussed in terms of maximization of electrostatic and hydrogen-bonding interactions between the host and guest.