Magnetic Properties of Cationic Tungsten(IV) Half Sandwich Compounds:  Experimental and Theoretical Study of a Solvent and Ligand Stabilized Singlet Ground State Leading to a Thermally Induced Singlet−Triplet Spin State Interconversion

Abstract

A series of novel neutral tungsten(III) and cationic tungsten(IV) complexes with disubstituted 4,4'-R,R-2,2'-bipyridyl (R(2)-bpy) ligands of the type [CpW(R(2)-bpy)Cl(2)](n+) (n = 0,1) were prepared and characterized by X-ray crystallography. Susceptibility measurements of the tungsten(IV) complexes revealed an intrinsic paramagnetism of these compounds and evidenced different magnetic properties of the dimethylamino and methyl (R = NMe(2), Me) substituted tungsten(IV) compounds in solution and in the solid state. In dichloromethane solution, singlet ground states with thermally populated triplet states were observed, whereas triplet (R = Me) and singlet ground states (R = NMe(2)) were observed in the solid state. Using both experimental and theoretical techniques (DFT) allowed to establish solvation and ligand effects to account for the different magnetic behavior. Thermodynamic parameters were derived for the spin equlibria in solution by fits of the temperature dependent (1)H NMR shifts to the Van Vleck equation and were found to be in excellent agreement with the DFT calculations.

1H NMR, Electron Paramagnetic Resonance, and Density Functional Theory Study of Dinuclear Pentaammineruthenium Dicyanamidobenzene Complexes

“…A contact shift results from the presence of spin density at the resonating nucleus and can be described by using the spin-only equation , normalδ con = A normalC g av normalμ normalB S ( S + 1 ) g normaln normalμ normaln 3 k T where A c is the hyperfine coupling constant, μ B is the Bohr magneton of the electron, g n is the nuclear g -factor, μ n is the nuclear magneton, k is the Boltzmann constant, and T is temperature. Hyperfine coupling constants are usually determined by measuring the temperature dependence of contact shifts. , In this regard, a temperature dependent study (−50 to 25 °C in CD 3 CN) of the nearly diamagnetic complex [{Ru(NH 3 ) 5 } 2 (μ-Me 2 dicyd)][PF 6 ] 4 was attempted to see if the singlet ground state could be completely populated and a diamagnetic spectrum obtained. Instead of a diamagnetic spectrum, we observed an increase in the downfield isotropic shift of the ammine protons, presumably because the triplet state is increasingly populated with decreasing temperature.…”

Synthesis of [(HIPTNCH2CH2)3N]Cr Compounds (HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3) and an Evaluation of Chromium for the Reduction of Dinitrogen to Ammonia

“…We have invoked spin state as a significant problem with respect to binding of dinitrogen to Cr or { Cr } - . Whether spin state can affect reactivity is a question that has been discussed with greater frequency in the literature in the past 10 years. − There seems to be agreement that spin state can affect reactivity, but the degree to which it does depends greatly upon the particular case being considered. As far as simple addition of an even-electron σ-donor/π-acceptor ligand to a metal is concerned, the more weakly binding the ligand (in terms of its combined σ-donor/π-acceptor ability) the more spin state can be a determining factor.…”

Structure, magnetism and colour in simple bis(phosphine)nickel(II) dihalide complexes: an experimental and theoretical investigation

“…Multiple attempts to quantify the solution magnetism using the Evans method were unsuccessful (Evans, 1959); due to the low magnetic moments, only extremely small changes in chemical shift were observed and no quantitative data could be obtained. Sophisticated NMR methods are now available for the interpretation of paramagnetic complexes (Cremer & Burger, 2003;Kö hler, 2011). However, to date with these methods the NMR data could not be fitted to an equilibrium between a paramagnetic (tetrahedral) and a diamagnetic (square planar) complex, as has been done for related systems (Pignolet & Horrocks, 1969).…”