High-Spin Metal Complexes Containing a Ferromagnetically Coupled Tris(semiquinone) Ligand

Abstract

The tris-bidentate ligand 1,3,5-tris(5'-tert-butyl-3',4'-dihydroxyphenyl)benzene ((TBCat)(3)Ph) was synthesized. The reaction of this molecule in basic solution with two paramagnetic acceptors, i.e., a nickel(II)minus signtetraazamacrocyclic ligand complex (Ni(CTH)) (CTH = dl-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) and manganese(II)-hydrotris[3-(4'-cumenyl)-5-methylpyrazolyl]borate (Mn(Tp(Cum,Me))), yielded two complexes whose analytical formulas are consistent with those of trinuclear complexes. Spectroscopic and magnetic measurements suggest that these derivatives contain divalent metal ions coordinated to the tris(semiquinone) form of the ligand. Analysis of the magnetic data shows that the pi-connectivity of the ligand enforces ferromagnetic coupling between the three semiquinone units of the molecule, giving rise to complexes with S = 9/2 (M = Ni(II)) and S = 6 (M = Mn(II)) ground states. The coupling within the tris(semiquinone) unit is quite large (J = -26 cm(-1) for the nickel(II) derivative and J = -40 cm(-1) for the manganese(II) one, using the general exchange Hamiltonian H = sigma J(ij)S(i)S(j)), and it is of the same order of magnitude as that observed in an analogous series of bis(semiquinone) complexes that we recently reported.

Synthesis of and structure–property relationships in zinc complexes of bis‐metaphenylene semiquinone biradical species

“…The decrease of the χ T data at very low temperatures (below 5 K) was accounted for with a Weiss correction, using the expression χ eff = χ/(1– ϑχ), where ϑ = 2 zJ ′/( Ng 2 β 2 ) . The origin of J ′ can be ZFS, intermolecular interactions, saturation effects, or some combination of these . The curve fit results are seen in Table .…”

“…New paramagnetic ligands are of general interest in both organic and inorganic chemistry as components of sensors, switches, and molecular spintronics . Previous research in our group has shown that both conformation and substituents can modulate spin density and exchange coupling in Bis(Zn II (SQ)Tp Cum,Me ) biradical ligand complexes .…”

“…New paramagnetic ligands are of general interest in both organic and inorganic chemistry as components of sensors, switches, and molecular spintronics. [1][2][3][4][5][6][7][8] Previous research in our group has shown that both conformation and substituents can modulate spin density and exchange coupling in Bis(Zn II (SQ)Tp Cum,Me ) biradical ligand complexes. [9][10][11] The design of novel, functionalized semiquinone (SQ) ligands containing electron-withdrawing, electron-donating, and conjugating substituents enables investigation of multiple structure-property relationships and building blocks for new materials.…”

Transition metal complexes with bulky 4,6-di-tert-butyl-N-aryl(alkyl)-o-iminobenzoquinonato ligands: Structure, EPR and magnetism

“…Cobalt complexes Co(ISQ L1 ) 2 Cl (19) (21) and Co(ISQ L2 ) 2 Cl (22) were synthesized by different methods. Co(ISQ L3 ) 2 Cl (21) was formed as a product of reaction between bis-ligand specie Co(ISQ L3 ) 2 (56, Section 6.5) and CH 2 Cl 2 [53].…”

“…Selected structural data on M(ISQ) 2 X and M(ISQ) 2 L types complexes are shown in Table 2 The electronic spectra of all M(ISQ) 2 X type complexes (19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32) are characterized by a very intense broad absorption with maximum in the range 700-850 nm (with ε ∼ 0.3-1.2 × 10 4 M −1 cm −1 ) and another in the range 450-700 nm (with ε ∼ 0.8-1.5 × 10 4 M −1 cm −1 ). There have been no detailed assignment of these bands.…”