The adducts FeI2 .[16]aneS(4) (1) and FeBr2 .[16]aneS(4) (2) are high-spin iron(II) compounds that may be described as either octahedral or square-planar coordinated complexes. Mossbauer measurements an 1 at various temperatures and applied fields analyzed with the spin-Hamiltonian formalism together with spin-polarized molecular orbital calculations in local density approximation clearly favor the octahedral description, Calculations with different iron-iodine bond lengths elucidate the structural dependence of Mossbauer parameters and orbital energies during the gradual transition from octahedral to square-planar like coordination. A suggestion for the geometry of 2 (d(Fe,Br) = 2.47 Angstrom) is obtained by minimizing the total binding energy. MO calculations provide evidence that unusually large iron-surfur bond distances in 1 and 2 are forced by the size of the macrocycle [16]aneS(4) and are connected with unusually large axial bond distances.