Influence of isotope substitution on lattice and spin-Peierls-type transition features in one-dimensional nickel bis-dithiolene spin systems

Design of a One-Dimensional Stacked Spin Peierls System with Room-Temperature Switching from Quantum Mechanical Predictions

Planar bis-1,2-dithiolene complex anions of a transition metal (denoted as [M(dithiolato)₂]^- and M = Ni, Pd, or Pt ion) favor forming columnar stacks of anions in the crystal that feature S = 1/2 spin-chains, and such a spin-chain compound often undergoes a spin-Peierls-type transition, making this a promising material for conducting and magnetic switching. However, current examples show the transition temperatures are far too low for most applications. We use quantum mechanics to predict that changing the cation arrangement from the boat-type to the chair-type packing configuration in a spin-Peierls-type [Ni(dithiolato)₂]^- complex will substantially stabilize the antiferromagnetic coupling, dramatically increasing the transition temperature. We estimate that the [Ni(mnt)₂]-based complexes (mnt = maleonitriledithiolate) with chair-type packing of cations will lead to critical temperatures of ∼170, ∼252, and ∼310 K for S-, Se-, and Te-based mnt, respectively. We also suggest how to stabilize the chair-type configurations of these systems.

Investigation of structural and magnetic properties for two one-dimensional platinum-bis-dithiolene spin-Peierls-like transition salts

Two 1-D spin-Peierls-like salts, [1-N-(4′-R-benzyl)pyridinium-d₅][Pt(mnt)₂] (R = Cl or Br), show different isotopic effect, which is related to H-bond pattern.

Two segregated columnar stack platinum-bis-dithiolene molecule solids showing spin-Peierls-type transition above room temperature

Two new one-dimensional (1-D) compounds, [CH3-BzPy][Pt(mnt)2] (1) and [CH3-BzPy-d5][Pt(mnt)2] (2) (CH3-BzPy(+) = 1-N-(4-CH3-benzyl)pyridinium and the pyridine in CH3-BzPy(+) was replaced by pyridine-d5 to give the CH3-BzPy-d5(+); mnt(2-) = maleonitriledithiolate), were synthesized and characterized. 1 and 2 show similar magnetic behavior in 1.8-400 K; they experience a spin-Peierls-type transition around 320 K and show a uniform antiferromagnetic S = 1/2 chain behavior in high temperature (HT) phase, a spin gap feature in low temperature (LT) phase. A symmetry breaking structural phase transition is associated with the spin-Peierls-type transition. Two isostructural compounds crystallize in space group P2(1)/c in HT phase, with a = 12.3066(8) Å, b = 27.0522(18) Å, c = 7.4248(4) Å, β = 104.204(6)° and V = 2396.3(3) Å(3) for 1 versus a = 12.3331(9) Å, b = 27.087(4) Å, c = 7.4501(9) Å, β = 104.149(13)° and V = 2413.3(6) Å(3) for 2 at 353 K, while space group P1[combining macron] in LT phase, with a = 7.3203(10) Å, b = 12.2816(16) Å, c = 26.904(4) Å, α = 88.500(4)°, β = 86.731(4)°, γ = 75.421(4)° and V = 2337.0(5) Å(3) for 1 versus a = 7.3308(8) Å, b = 12.2848(13) Å, c = 26.930(3) Å, α = 88.479(3)°, β = 86.652(4)°, γ = 75.563(3)° and V = 2344.5(4) Å(3) for 2 at 296 K. DSC measurements revealed 1 and 2 showing almost the same T(C). This observation is distinction from the [Ni(mnt)2](-)-based spin-Peierls-type analogues [CH3-BzPy][Ni(mnt)2] and [CH3-BzPy-d5][Ni(mnt)2] where the deuteration leads to T(C) up shifting 2.3 K.