The synthesis and characterization of seven bis-pyridine and bis-imidazole complexes of iron(II) teoramesitylporphyrinate are reported. X-ray crystal structures of three of the complexes, [Fe(TMP)(4-CNPy)(2)], [Fe(TMP)(3-CNPy)(2)], and [Fe(TMP)(4-MePy)(2)], have been solved and all show parallel axial ligand orientations with nearly planar porphyrinato cores. The Mossbauer spectra of six of the complexes, having pyridine ligands with pK(a)(PyH+) ranging from similar to 1.1 (4-CNPy) to 9.7 (4-NMe2Py), have been determined. The Mossbauer isomer shifts at 120 K are in the range of 0.36-0.45 mm/s, and the quadrupole splittings (Delta E-Q) are in the range of 1.11-1.27 mm/s. Thus, unlike the corresponding Fe(III) complexes, the X-ray structures and Mossbauer spectroscopic parameters of these (tetramesitylporphyrinato)iron(II)-bis (pyridine) complexes are shown to be essentially independent of the basicity and pi donor/acceptor properties of the axial pyridine ligands. These solid-state structural and spectroscopic properties are compared to the thermodynamic properties of the same series of complexes in solution (Nesset, M. J. M.; Shokhirev, N. V.; Enemark, P. D.; Jacobson, S. E.; Walker, F. A. Inorg. Chem. 1996, 35, 5188): The equilibrium constants, beta(2)(II), for binding two ligands to [Fe-II(TMP)(DMF)] are also nearly independent of the basicity of the axial pyridine ligand, although the Fe-III/Fe-II reduction potentials vary strongly with ligand basicity due to the large variation in beta(2)(III), the equilibrium constant for binding two ligands to the Fe(III) complex. Hence, it appears that low-spin d(6) metalloporphyrins have a marked preference for parallel orientation of planar axial ligands, and that the charge asymmetry at the iron nucleus (deduced from Mossbauer quadrupole splittings) and the thermodynamics of ligand binding are unaffected by the electronic properties of the axial ligand. The major reason for the marked preference for parallel ligand orientation for iron(II) porphyrinates appears to be lack of a means of energy stabilization of the ruffled core of the perpendicular orientation.