Aromaticity of an Unsaturated N‑Heterocyclic Stannylene (HCRN)₂Sn^II As Studied by Optical Spectra and Quantum Chemistry. Comparison in the Series (HCRN)₂E^II, E = C, Si, Ge, Sn (R = <i>t</i>‑Bu or Dip)

The degree of π-electron delocalization in a series of unsaturated N-heterocyclic compounds containing divalent group-14 atoms, (HCRN)₂E^II (E = C, Si, Ge, Sn), has been estimated by applying different experimental and theoretical criteria (vibrational and UV–vis spectroscopy, nucleus-independent chemical shifts, and isomerization stabilization energies). All of the methods used confirmed the aromaticity of these heterocyclic molecules involving six π electrons, and most of the methods indicated that the aromaticity increases in going from the silylene to the stannylene

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. We report the synthesis and characterization of [{FeIII(tpa)}2spiro](PF6)2 (1), [{FeIII(tpa)}2Br4spiro](PF6)2 (2), and [{FeIII(tpa)}2thea](PF6)2 (3) (tpa = tris(2-pyridylmethyl)amine, spiroH4 = 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-5,5′,6,6′-tetraol, Br4spiroH4 = 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-4,4′,7,7′-tetrabromo-5,5′,6,6′-tetraol, theaH4 = 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene), utilizing non-conjugated bis(catecholate) bridging ligands. In the solid state, magnetic and structural analysis shows that 1 remains in the [HS–HS] state, while 2 and 3 undergo a partial SCO interconversion upon cooling from room temperature involving the mixed [LS–HS] state. In solution, all complexes undergo SCO from [HS–HS] at room temperature, via [LS–HS] to mixtures including [LS–LS] at 77 K, with the extent of SCO increasing in the order 1 2 3. Gas phase density functional theory calculations suggest a [LS–LS] ground state for all complexes, with the [LS–HS] and [HS–HS] states successively destabilized. The relative energy separations indicate that ligand field strength increases following spiro4– 4spiro4– 4–, consistent with solid-state magnetic and EPR behavior. All three complexes show stabilization of the [LS–HS] state in relation to the midpoint energy between [LS–LS] and [HS–HS]. The relative stability of the [LS–HS] state increases with increasing ligand field strength of the bis(catecholate) bridging ligand in the order 1 2 3. The bromo substituents of Br4spiro4– increase the ligand field strength relative to spiro4–, while the stronger ligand field provided by thea4– arises from extension of the overlapping π-orbital system across the two catecholate units. This study highlights how SCO behavior in dinuclear complexes can be modulated by the bridging ligand, providing useful insights for the design of molecules that can be interconverted between more than two states

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. We report the synthesis and characterization of [{FeIII(tpa)}2spiro](PF6)2 (1), [{FeIII(tpa)}2Br4spiro](PF6)2 (2), and [{FeIII(tpa)}2thea](PF6)2 (3) (tpa = tris(2-pyridylmethyl)amine, spiroH4 = 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-5,5′,6,6′-tetraol, Br4spiroH4 = 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-4,4′,7,7′-tetrabromo-5,5′,6,6′-tetraol, theaH4 = 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene), utilizing non-conjugated bis(catecholate) bridging ligands. In the solid state, magnetic and structural analysis shows that 1 remains in the [HS–HS] state, while 2 and 3 undergo a partial SCO interconversion upon cooling from room temperature involving the mixed [LS–HS] state. In solution, all complexes undergo SCO from [HS–HS] at room temperature, via [LS–HS] to mixtures including [LS–LS] at 77 K, with the extent of SCO increasing in the order 1 2 3. Gas phase density functional theory calculations suggest a [LS–LS] ground state for all complexes, with the [LS–HS] and [HS–HS] states successively destabilized. The relative energy separations indicate that ligand field strength increases following spiro4– 4spiro4– 4–, consistent with solid-state magnetic and EPR behavior. All three complexes show stabilization of the [LS–HS] state in relation to the midpoint energy between [LS–LS] and [HS–HS]. The relative stability of the [LS–HS] state increases with increasing ligand field strength of the bis(catecholate) bridging ligand in the order 1 2 3. The bromo substituents of Br4spiro4– increase the ligand field strength relative to spiro4–, while the stronger ligand field provided by thea4– arises from extension of the overlapping π-orbital system across the two catecholate units. This study highlights how SCO behavior in dinuclear complexes can be modulated by the bridging ligand, providing useful insights for the design of molecules that can be interconverted between more than two states