Norman V. Duffy

The dependence of Mössbauer parameters on magnetic moments in iron(III) dithiocarbamates

Abstract We have found a linear relationship between the isomer shift and magnetic moment (μeff) (literature values) for a series of iron(III)-dithiocarbamates, Fe (S2CNR2)3. This is the first observation of a regular dependence of the Mossbauer isomer shift on the spin state of iron in a spin-crossover situation. The solid state isomer shift was found to decrease with decreasing solid μeff. This is interpreted as evidence that the back-donation of iron 3d-electrons into empty ligand π-orbitals is more important as the low-spin state is approached. Due to complicating factors, the quadrupole splitting does not show as clear a correlation, but there is a general trend toward greater splitting as the magnetic moment decreases.

The spin 32 state (?) in six-coordinate iron (III). A Mössbauer and EPR investigation

Tris-(4-morpholinecarbodithioato-S,S′) iron (III) (FeM) and its dichloromethane solvate, (FeM·CH2Cl2), have been prepared and their temperature-dependent Mossbauer and EPR spectra have been determined at temperatures between liquid nitrogen and ambient. The Mossbauer spectra of FeM·CH2Cl2 differ considerably from that of FeM and is interpreted in terms of a four-line spectrum at 77 K. The EPR spectra of the two complexes indicate that the lower spin state of FeM·CH2Cl2 populates much more rapidly in the temperature range studied (100–300 K) than does FeM. These results support the postulation of an S = 52 ⇋ S = 12 spin-equilibrium for FeM and a corresponding S = 52 ⇋ S = 32 equilibrium for FeM·CH2Cl2.

Monosubstituted group VIB carbonyls: Mass spectra and bonding

Abstract Nineteen metal carbonyl derivatives of the type M (CO) 5 L (where M = Cr, Mo, or W, and L = trivalent ligands of N, P, As, and Sb, or pyridine) have been prepared and the mass spectra of these compounds and ligands determined. The mass spectral results have been compared to the Graham σ- and π-parameters, a measure of the donor-acceptor properties of these ligands. No significant correlation was found between any major feature of the mass spectra and these Graham parameters. These results are discussed in terms of postulated ionization and fragmentation processes.

Multinuclear NMR of cis-dicarbonylbis(dithiocarbamato)iron(II) complexes in chloroform solution

Abstract The 13 C and 15 SN NMR spectra of eleven cis -Fe(S 2 CNRR′) 2 (CO) 2 complexes, where R and R′ are organic substituents, have been measured at ambient temperature in CDCl 3 (0.08–0.16 M). The 13 C absorptions for the carbonyl ligands correlate well with the force constants for the CO stretching vibrations in CHCl 3 solution. Each of the parameters ( 13 CO absorption and k cis for CO) correlate well with the aqueous solution p K a for + H 2 NRR′, corrected for the phenyl-containing substituents, high p K a values corresponding to high 13 CO absorptions and low k cis CO force constants. [p ]Evidence was found in the 13 C NMR spectra for hindered rotation about the CN bond in S 2 CNC 2 in complexes with higher p K a(corr) values and in the 13 C spectra of the corresponding thiuram disulfides. [p ]The 15 N (natural abundance) NMR spectra for each of the complexes was determined. Each revealed a single sharp absorption in a region of the 15 N NMR spectrum which indicates substantial CN double bond character, as one would expect for coordinated dithiocarbamate ligands.

UV photoelectron spectra of some substituted iron dithiocarbamates

Abstract Photoelectron spectra (He(I)) are reported for several Fe(dtc) 2 (CO) 2 complexes, which, in vapor phase under experimental p.e. spectroscopic conditions, lose their CO and behave as Fe(dtc) 2 (dtc − = N,N′-disubstituted dithiocarbamate anion). p.e. Spectra are not well resolved, but can be interpreted on the ground of a comparison with already known transition-metal diethyldithiocarbamates. Substituent effects due to the groups bonded to the dithiocarbamate nitrogen are particularly large, and their possible mechanisms are discussed.

Multinuclear (1H, 13C, 59Co, 77Se) NMR studies of thioseleno- and diselenocarbamato complexes of cobalt(III) and indium(III) in CDCl3 solution

Abstract The proton decoupled 13C NMR spectra of several Co(Se2CNR2)3, Co(SSeCNR2)3, In(Se2CNR2)3 and In(SSeCNR2)3 complexes(where R=organic substituent) have been measured in CDCl3 solution (23–64 mM). Each of the diselenocarbamate complexes exhibits a single peak for the NCSe2 carbon at 188–197 ppm for Co(III) and at 186–198 ppm for In(III) complexes. The alkyl carbons in the position alpha to the amine N also appear as a single peak. The In(SSeCNR2)3 complexes exhibit single peaks for the NCSSe carbons (192–202 ppm), but the alkyl carbons in the position alpha to the amine N appear as two distinct singlets, indicating hindered rotation about the SSeCNR2 bond. The Co(SSeCNR2)3 complexes exhibit four peaks of approximately equal intensity for the NCSSe carbon which is interpreted as evidence for the stereochemical rigidity of the facial and meridional isomers. The alkyl carbons in the position alpha to the amine N appear as six peaks (except for occasional accidental degeneracy) which is interpreted as evidence for hindered rotation about the SSeCNR2 bond in these two isomers. The 1H NMR spectra of these complexes have been measured in CDCl3 solution (30–63 mM). The 1H spectra of Co(Se2CNR2)3 are similar to those reported for Co(S2CNR2)3, but those for the Co(SSeCNR2)3 complexes are further split by hindered rotation about the SSeCNR2 bond rendering each R non-equivalent. The 1H spectra for the various derivatives of In(SSeCNR2)3 and In(Se2CNR2)3 are similar and indicate ra pid D⇄cL interconversion and evidence (in the case of In(SSeCNR2)3) for hindered rotation about the CN bond. The 59Co NMR spectra of the Co(Se2CNR2)3 complexes exhibit signals (6690–7260 ppm) in close agreement with results reported in the literature. The 59Co NMR signals of Co(SSeCNR2)3 are approximately identical to those of the corresponding Co(S2CNR2)3 complexes but are generally at lower field than for the corresponding Co(Se2CNR2)3 complexes. Similar to the dithiocarbamate complexes, there is evidence for a correlation between the 59Co chemical shifts and μeff2 for the corresponding Fe(SSeCNR2)3. The 77Se NMR spectra of these complexes have been measured in saturated CDCl3 solution. The 77Se spectra of the diselenocarbamates exhibits single peaks with In exhibiting a higher chemical shift (approx. 400 ppm) than the corresponding Co complex. This trend is seen in the corresponding thiosclenocarbamates, but the Co derivatives generally exhibit two peaks of approximately equal intensity, indicating the stereochemical rigidity of the fac and mer isomers.

The dependence of Mössbauer isomer shifts on magnetic moments in solvated tris-dithiocarbamates on iron(III)

Abstract The 57Fe room temperature isomer shifts for six solvated tris-dithiocarbamates of iron(III), [Fe(S2CNRR′)3·solvent] are found to obey the same isomer shift vs solid-state magnetic moment linear dependence as the unsolvated complexes. This relationship is independent of the ground-state ( S = 1 2 or S = 3 2 ) in these spin-crossover complexes.

Ligand exchange in tris(diorganodithiocarbomato)iron(III) complexes

Abstract The reported preparations of mixed ligand spincrossover iron(III) dithiocarbamates have been reexamined. Reaction products of NaS 2 CNR′ 2 with either Fe(S 2 CNR 2 ) 3 , Fe(S 2 CNR 2 ) 2 Cl or Fe(S 2 CNR 2 ) 2 NCS and between Fe(S 2 CNR 2 ) 3 and Fe(S 2 CNR′ 2 ) 3 in solution were studied by 1 H NMR and infrared spectrometry and elemental analysis. The results indicate the Fe(S 2 CNR 2 ) 3 is not substitution inert and the product is determined by the relative stabilities and solubilities of the complexes undergoing metathesis. The reported preparations of Fe(S 2 CNR 2 ) 2 ) 2 (S 2 CNR′ 2 ) are apparently in error.

Mössbauer spectra of tris(diorganothioselenocarbamato)- and tris(diorganodiselenocarbamato)iron(III) complexes

Abstract Room temperature 57 Fe Mossbauer spectra of several tris(diorganothioselenocarbamato)- and tris(diorganodiselenocarbamato)iron(III) complexes are reported, along with their room temperature magnetic moments for the solid state. These results are compared to the previously reported diethyl derivatives and to the corresponding monothio- and dithiocarbamates. Each complex exhibited a single, quadrupole-split absorption in its Mossbauer spectrum. Although variations are noted within specific organic substituents, general trends for the average isomer shifts of all ligands are − OSCNR 2 − S 2 CNR 2 ∼ − SSeCNR 2 ∼ − Se 2 CNR 2 , while the typical order of the quadrupole splittings for a given ligand is − OSCNR 2 − S 2 CNR 2 − SSeCNR 2 − Se 2 CNR 2 . For the same organic substituent, the magnetic moments usually decrease in the order − OSCNR 2 > − S 2 CNR 2 > − SSeCNR 2 > − Se 2 CNR 2 . It is noteworthy that higher quadrupole splittings are observed for the symmetric diselenocarbamate iron(III) complexes than for the corresponding thioselenocarbamates.

Convenient, straightforward routes to carbodithioato derivatives of weak nitrogenous nucleophiles

Abstract The N-alkyldithiocarbamate ligands when bidentately-coordinated to the nickel triad elements undergo facile electrophilic substitution reactions with a diversity of electrophiles affording novel carbodithioato derivatives of weak nitrogenous bases, not avail- able by other methods.