Bridge-Dependent Donor-Metal-Acceptor-Metal-Donor (D-M-A-M-D) Systems: From Charge Transfer to Electron Transfer in Dioxolene-Ge-Diimine Complexes.

Synthesis and structural characterization of a family of germanium-dioxolene complexes with ditopic N-donor ligands (L-L) (L=1,2-bis(pyridin-2-ylmethylene)hydrazine L=1,6-bis-(pyridin-2-yl)-2,5-diaza-1,5-hexadiene, L=N,N-bis(pyridin-2-ylmethylene)-1,4-benzenediamine, L=N,N-bis(pyridin-2-ylmethylene)-(biphenyl)-4,4-diamine, L=2,2'-azopyridine) is reported. The reaction of germanium bis-catecholate with bridging ligands L - L, differing by the nature of the linker between pyridine sites gives rise to dinuclear digermanium complexes (36CatGe)L (36Cat=dianion of 3,6-di-tert-butylcatechol) 1-4 of DMAMD type (donor-metal-acceptor-metal-donor) with a charge transfer in the UV-Vis region. In opposite, the interaction of the 36CatGe with 2,2'-azopyridine (L) results in the two-electron transfer from the donor 36Cat ligands to the azopyridine bridge forming stable open-shell complex 5 [(36SQ)(36CatGe)](L) (36SQ=radical-anionic semiquinonate ligand).

Molecular Twist-Induced Single-Crystal Isomerization and Valence Tautomeric Transitions in a Cobalt-Dioxolene Complex.

A mononuclear valence tautomeric (VT) complex, [Co(pycz)(Sq)(Cat)] (1-trans), where pycz = 9-(pyridin-4-yl)-9H-carbazole, Sq⋅ = 3,5-di-tert-butyl-semiquinonato, and Cat = 3,5-di-tert-butyl-catecholato, is synthesized in the trans configuration, which undergoes one-step valence tautomeric transition above room temperature. Remarkably, 1-trans can transform into its isomeric structure, [Co(pycz)(Sq)(Sq)] (1-cis), at temperature above 350 K in a single-crystal-to-single-crystal way by in situ molecular twist, and the resulting 1-cis exhibits a pronounced two-step VT transition during magnetic measurements that is rare for mononuclear VT complexes. Such drastic solid-state structural transformation is reported in VT compounds for the first time, which is actuated by a crystal surface's melting-recrystallization induced phase transition process.

Controlling Spin Crossover in a Family of Dinuclear Fe(III) Complexes via the Bis(catecholate) Bridging Ligand.

Spin crossover (SCO) complexes can reversibly switch between low spin (LS) and high spin (HS) states, affording possible applications in sensing, displays, and molecular electronics. Dinuclear SCO complexes with access to [LS-LS], [LS-HS], and [HS-HS] states may offer increased levels of functionality. The nature of the SCO interconversion in dinuclear complexes is influenced by the local electronic environment.

Magnetically bistable cobalt-dioxolene complexes with a tetradentate N-donor base.

Synthesis and magnetic characterization of a family of cobalt-dioxolene complexes [(MeTPA)Co(36-DBCat)] (1), [(MeTPA)Co(36-DBCat)](PF) (2) and [(MeTPA)Co(diox-(OMe))](BPh) (3) (MeTPA = bis(6-methyl-2-pyridyl)methyl-(2-pyridylmethyl)amine; 36-DBCat = dianion of 3,6-di--butylcatechol; diox-(OMe) - 2,5-di--butyl-3,3,4-trimethoxy-6-oxocyclohexa-1,4-dienolate) is reported. The neutral complex 1 is found to form hexa- (CoON, 1a) and pentacoordinated (CoON, 1b) isomers. Variable temperature single crystal X-ray diffraction analysis of 1a and 1b clearly indicates the presence of the high-spin divalent metal ion and the dianionic catecholate form of the dioxolene ligand.

Spin transitions in ferric catecholate complexes mediated by outer-sphere counteranions.

A family of ionic ferric catecholate complexes 1-4 bearing a disubstituted 3,6-di--butyl-catecholate ligand (3,6-DBCatH) and tetradentate tris(2-pyridylmethyl)amine (TPA) was prepared and its spin transitions were investigated. Variation of the outer-sphere counteranions (PF, BPh, ClO, BF) is accompanied by changes in the magnetic behavior of the compounds under consideration. The crystal structures of complexes 1, 3 and 4 were determined by single crystal X-ray diffraction analysis at 100 K and 293 K.