Manganese tetraphenylporphyrin bromide and iodide. Studies of structures and magnetic properties

Manganese tetraphenylporphyrin bromide and iodide Mn(TPP)X (X = Br, 2; I, 3; TPP²⁻ = meso-tetraphenylporphyrinate) are synthetic analogs of Mn(III) geoporphyrins. Crystal structures of 2 and 3 with chloroform in the lattices, Mn(TPP)Br·CHCl₃ (2·CHCl₃), Mn(TPP)I·CHCl₃ (3·CHCl₃), Mn(TPP)I·CDCl₃ (3·CDCl₃ in a different space group from 3·CHCl₃), Mn(TPP)I·1.5CHCl₃ (3·1.5CHCl₃), and 2 with dichloromethane in the lattice, Mn(TPP)Br·CH₂Cl₂ (2·CH₂Cl₂), have been determined by single-crystal X-ray diffraction at 100 K or 298 K. Hirshfeld surface analyses of the crystal structures of 2·CHCl₃, 2·CH₂Cl₂, 3·CHCl₃, 3·CDCl₃ and 3·1.5CHCl₃ have been performed. Surprisingly the Mn(III)–Br and Mn(III)–I bonds in Mn(TPP)X (2–3) are about 0.2 Å (8%) longer than Fe(III)–Br and Fe(III)–I bonds in S = 5/2 Fe(TPP)X (X = Br, 4; I, 5), although both Mn(III) and Fe(III) ions have the same radii. Magnetic properties of 2 and 3 have been studied by direct current (DC) and alternating current (AC) susceptibility measurements, high-field electron paramagnetic resonance (HFEPR), and inelastic neutron scattering (INS). With four unpaired electrons in Mn(TPP)X (X = Br, 2; I, 3), the bromide complex 2 in 2·CDCl₃ possesses easy-axis anisotropy, as does the chloride analog Mn(TPP)Cl (1), with the axial (D) and rhombic (E) zero-field splitting parameters of D = –1.091(3) cm⁻¹ and |E| = 0.087(2) cm⁻¹. The iodide complex 3 in 3·CDCl₃ becomes easy-plane with D = +1.30(1) cm⁻¹ and |E| = 0.010(5) cm⁻¹. Axial ZFS parameters D change from −2.290(5) cm⁻¹ in 1, reported earlier, to −1.091(3) cm⁻¹ in 2 and +1.30(1) cm⁻¹ in 3.