Electronic equilibrium between the 6A1 and 2T2 states in iron(III) dithio chelates

Abstract

Further results are reported for ferric dithiocarbamate complexes Fe(S&NRZ)s, which lie at the crossover between high-spin (sextet) and low-spin (doublet) states. Magnetic measurements made over a range of temperatures and pressures are used to estimate E, the separation of the zero-point energies of the 2Tz and BA1 states, and AV, the difference between the volumes of the 6A1 and 2 T~ states. The values of E extend over a large range, both positive and negative, for various complexes, while A V is generally 5-6 cm3/mol; this corresponds to an increase of 0.1 A of the Fe-S bond lengths in passing from the 2 T~ to the 6 A~ state. The compounds may be divided into four distinct classes on the basis of their solution magnetic moments (peff); in order of decreasing petf values (and hence decreasing population of the EA^ state), these are: (1) the pyrrolidyl complex where NRz = pyrrolidyl, peff = 5.8 BM; (2) the N,N-di-n-alkyl complexes, peff = 4.3 BM; (3) the N-alkyl, N-aryl complexes, peff = 3.5 BM; (4) the N,N-di-sec-alkyl complexes, peff = 2.5 BM. The RNR angle in the Fe(SzCNR2)s complexes is expected to increase from class 1 through to 4, with a corresponding change in the C-N bond order, which is expected to affect ligand field strength (A) and pelf. Comparisons of the electronic spectra of complexes falling into the various classes and the pressure dependence of the spectral positions and band intensities are used in the assignment of electronic transitions. From the tentative spectral assignments are estimated values of the ligand field strengths and the electronic pairing energies ( r ) , and these are shown to obey the necessary inequality for the crossover situation: A(high spin)

Compounds with intermediate spin. 3. Structure of tris[N,N-bis(2-hydroxyethyl)dithiocarbamato]iron(III) at 150 and 295 K

“…In a compound llke Fe[S2CN(C2H4OH)2] 3 there Introduction. Most solid Fem dithiocarbamates exhibit strongly temperature-dependent magnetic moments (White, Roper, Kokot, Waterman & Martin, 1964;Ewald, Martin, Sinn & White, 1969 is a possibility of hydrogen bonding without including any solvate molecules. We report here the crystal structure of the title compound, (I), at 150 and 295 K and its magnetic moments in the range 80-300 K.…”

Piezo‐ and Photo‐Crystallography Applied to Spin‐Crossover Materials

“…A recent study of the dinuclear complex [[Fe(bpp)(NCS) 2 ] 2 4,4 -bipy]·2MeOH, provides an example of the structural origin of the difference between the thermal-and piezo-SCO features. 60 In this material, the piezo-SCO corresponds to a complete, gradual SCO over a range of 20 kbar while the thermal-SCO corresponds to a partial, abrupt SCO below 120 K. This discrepancy has been attributed to a purely structural phase transition occurring at 161 K that is disfavoured 2 …”

Spin crossover studies in tris(N,N?-dialkyldithiocarbamato)iron(III) complexes

“…There have been conflicting assignments of the m(FeAS) stretching band for the tris(N, N 0 -dialkyldithiocarbamato)iron(III) complexes. Ewald et al [5] assigned two bands in the 300-400 cm )1 region for tris(N,N 0 -dimethyldithiocarbamato) iron(III) to high and low spin states. In a further study of the di-i-propyl substituted complex they observed two well-defined bands of equal intensity at 320 and 365 cm )1 .…”

“…Ewald et al . [5] studied electronic equilibrium between 6 A 1 and 2 T 2 states in iron(III)dithiochelates by magnetic measurements over a wide range of temperatures and electronic and i.r. spectra.…”