Syntheses, Structural Analyses, and Magneto-Structural Correlations of Three Polymeric Fe(II) Complexes with Azide Ligand

Three new metal−organic polymeric complexes, [Fe(N3)2(bpp)2] (1), [Fe(N3)2(bpe)] (2), and [Fe(N3)2(phen)] (3)
[bpp = (1,3-bis(4-pyridyl)-propane), bpe = (1,2-bis(4-pyridyl)-ethane), phen = 1,10-phenanthroline], have been
synthesized and characterized by single-crystal X-ray diffraction studies and low-temperature magnetic measurements
in the range 300−2 K. Complexes 1 and 2 crystallize in the monoclinic system, space group C2/c, with the following
cell parameters:  a = 19.355(4) Å, b = 7.076(2) Å, c = 22.549(4) Å, β = 119.50(3)°, Z = 4, and a = 10.007(14)
Å, b = 13.789(18) Å, c = 10.377(14) Å, β = 103.50(1)°, Z = 4, respectively. Complex 3 crystallizes in the triclinic
system, space group P1̄, with a = 7.155(12) Å, b = 10.066(14) Å, c = 10.508(14) Å, α = 109.57(1)°, β =
104.57(1)°, γ = 105.10(1)°, and Z = 2. All coordination polymers exhibit octahedral Fe(II) nodes. The structural
determination of 1 reveals a parallel interpenetrated structure of 2D layers of (4,4) topology, formed by Fe(II)
nodes linked through bpp ligands, while mono-coordinated azide anions are pendant from the corrugated sheet.
Complex 2 has a 2D arrangement constructed through 1D double end-to-end azide bridged iron(II) chains
interconnected through bpe ligands. Complex 3 shows a polymeric arrangement where the metal ions are interlinked
through pairs of end-on and end-to-end azide ligands exhibiting a zigzag arrangement of metals (Fe−Fe−Fe angle
of 111.18°) and an intermetallic separation of 3.347 Å (through the EO azide) and of 5.229 Å (EE azide). Variable-temperature magnetic susceptibility data suggest that there is no magnetic interaction between the metal centers
in 1, whereas in 2 there is an antiferromagnetic interaction through the end-to-end azide bridge. Complex 3 shows
ferro- as well as anti-ferromagnetic interactions between the metal centers generated through the alternating end-on and end-to-end azide bridges. Complex 1 has been modeled using the D parameter (considering distorted
octahedral Fe(II) geometry and with any possible J value equal to zero) and complex 2 has been modeled as a
one-dimensional system with classical and/or quantum spin where we have used two possible full diagonalization
processes:  without and with the D parameter, considering the important distortions of the Fe(II) ions. For complex
3, the alternating coupling model impedes a mathematical solution for the modeling as classical spins. With quantum
spin, the modeling has been made as in 2.