On the Magnetic Coupling and Spin Crossover Behavior in Complexes Containing the Head-to-Tail [Fe^II₂(μ-SCN)₂] Bridging Unit: A Magnetostructural Experimental and Theoretical Study

Abstract

A new dinuclear complex [{Fe(tpc-OBn)(NCS)(μ-NCS)}] (1) based on the tripodal tpc-OBn ligand (tpc-OBn = tris(2-pyridyl)benzyloxymethane), containing bridging μ-κN:κS-SCN and terminal κN-SCN thiocyanate ligands, has been prepared and characterized by single crystal X-ray diffraction, magnetic studies, and DFT theoretical calculations. This complex represents the first example of dinuclear Fe complex with double μ-κN:κS-SCN bridges in a head-to-tail configuration that exhibits ferromagnetic coupling between metal ions (J = +1.08 cm). Experimental and theoretical magnetostructural studies on this kind of infrequent Fe dinuclear complex containing a centrosymmetrically [Fe(μ-SCN)] bridging fragment show that the magnitude and sign of the magnetic coupling parameter, J, depend to a large extent on the Fe-N-C (α) angle, so that J decreases linearly when α decreases. The calculated crossover point below which the magnetic interactions change from ferromagnetic to antiferromagnetic is found at 162.3°. In addition, experimental results obtained in this work and those reported in the literature suggest that large N-Fe distances and bent N-bound terminal κN-SCN ligands favor the high spin state of the Fe ions, while short N-Fe distances and almost linear Fe-N-C angles favor a stronger ligand field, which enables the Fe ions to show spin crossover (SCO) behavior.

Structural Diversity in Ni Chain Coordination Polymers: Synthesis, Structures, Isomerism and Magnetism

“…Even here the experimental value of J was compared with that of other Fe II compounds and the dependence of the exchange constant as function of the, e.g., Fe-N-C angle was additionally investigated by DFT calculations, which also indicate that J increases with increasing Fe-N-C angle. [33] Moreover, for this kind of thiocyanate bridge a value for the Fe-N-C angle of 162.3°was given, at which the exchange should switch from ferromagnetic to antiferromagnetic. [33] However, for nearly all compounds in which, e.g.…”

“…[33] Moreover, for this kind of thiocyanate bridge a value for the Fe-N-C angle of 162.3°was given, at which the exchange should switch from ferromagnetic to antiferromagnetic. [33] However, for nearly all compounds in which, e.g. Mn II , Fe II , Co II or Ni II cations are linked by pairs of thiocyanate anions, the chains are linear and the co-ligands as well as the thiocyanate N and S atoms are trans-oriented.…”

“…In this context it is also noted, that Mekuimemba reported on a Fe compound, in which the Fe II cations are linked by pairs of thiocyanate anions, which exactly corresponds to that arrangement usually found in the corresponding Ni compound. Even here the experimental value of J was compared with that of other Fe II compounds and the dependence of the exchange constant as function of the, e.g., Fe–N–C angle was additionally investigated by DFT calculations, which also indicate that J increases with increasing Fe–N–C angle . Moreover, for this kind of thiocyanate bridge a value for the Fe–N–C angle of 162.3° was given, at which the exchange should switch from ferromagnetic to antiferromagnetic …”

“…Although the magnetic exchange is weaker than that of azide compounds, these anionic ligands show a variety of coordination modes allowing the synthesis of compounds with different coordinations and different dimensionality. [32][33][34][35][36][37][38] With Co(NCS) 2 we have synthesized a number of 1D compounds, in which the metal cations are octahedrally coordinated by four thiocyanate or selenocyanate anions, and the two co-ligands, which in most cases consist of simple pyridine derivatives. In several of these compounds the metal cations are linked by pairs of anionic ligands into linear chains which show slow relaxations of the magnetization, indicative for SCM behavior.…”

Synthesis, Crystal Structures, and Properties of Mn(NCS)2 Coordination Compounds with 4‐Picoline as Coligand and Crystal Structure of Mn(NCS)2

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] Moreover, this ligand is able to mediate a magnetic exchange that can be used to prepare compounds that, depending on the nature of the metal cations and the topology of the coordination network, show very different magnetic properties. [14][15][16][17][18][19][20][21][22][23][24] These are the reasons why we became interested in this class of compounds several years ago. In the course of these investigations, we also have obtained several isomeric or polymorphic modifications that are of special interest, because in this case the chemical composition is constant and all changes in the properties of such compounds can directly be correlated with their structures.…”