Reversible 100 % Linkage Isomerization in a Single-Crystal to Single-Crystal Transformation: Photocrystallographic Identification of the Metastable [Ni(dppe)(η1-ONO)Cl] Isomer

Exploring the influence of polymorphism and chromophore co-ligands on linkage isomer photoswitching in [Pd(bpy4dca)(NO2)2]

The polymorphic Pd(II)-nitrite complex [Pd(bpy4dca)(NO2)2] (1) (bpy4dca = 2,2’-bipyridine-4,4’-dicarboxylic acid methyl ester) is shown to undergo photoinduced nitro → nitrito linkage isomer switching in two crystal forms, to varying excited...

Enantiopure versus Racemic Mixture in Reversible, Two-Step, Single-Crystal-to-Single-Crystal Transformations of Copper(II) Complexes

The reaction of chiral sodium complexes, ¹_∞ [Na(S-valmetH)]⋅H₂ O (1-S) and ¹_∞ [Na(R-valmetH)]⋅H₂ O (1-R), with copper(II) acetate affords chiral one-dimensional coordination polymers with the formulas ¹_∞ [Cu(S-valmet)(H₂ O)]⋅H₂ O (2-S) and ¹_∞ [Cu(R-valmet)(H₂ O)]⋅H₂ O (2-R) (R/S-valmetH₂ are Schiff base proligands resulting from the condensation reactions between o-vanillin and R/S-methionine). The copper ions are connected by the carboxylato groups belonging to the amino-acid moieties, resulting in infinite chains showing syn-anti out-of-plane bridging mode. The circular dichroism spectra of 1-S, 1-R, 2-S, and 2-R confirm their enantiomeric nature. Compounds 2-S and 2-R undergo a two-step single-crystal-to-single-crystal transformation, with the elimination of the lattice and coordinated water molecules: ¹_∞ [Cu(S-valmet)(H₂ O)]⋅H₂ O (2-S)→¹_∞ [Cu(S-valmet)]⋅H₂ O (3-S⋅H₂ O)→¹_∞ [Cu(S-valmet)] (3-S) and ¹_∞ [Cu(R-valmet)(H₂ O)]⋅H₂ O (2-R)→¹_∞ [Cu(R-valmet)]⋅H₂ O (3-R⋅H₂ O)→¹_∞ [Cu(R-valmet)] (3-R), respectively. During these transformations, every pair of face-to-face chains present in 2-S (or 2-R) has been "zipped up" into a chiral double chain through the removal of the aqua ligands and their replacement by the carboxylato oxygen atoms from the neighboring chain. Consequently, each carboxylato group now bridges three copper ions. The conversion of the single chains, 2-S and 2-R, into the double chains, 3-S and 3-R, is accompanied by a change of the strength of the exchange interactions between the copper ions: weak antiferromagnetic couplings are observed in compound 2-S (J/k_B =-1.23(5) K, H=-2J ΣS_i S_i+1 ) and relatively strong in compound 3-S (J/k_B =-76.0(8) K). When the racemic mixture of the ligands, R,S-valmetH₂ , is employed, in the same experimental conditions, a racemic mixture of mononuclear compounds, [Cu(R,S-valmet)(H₂ O)₂ ]⋅H₂ O (4-RS), is obtained. Compound 4-RS also undergoes a SCSC transformation with the elimination of the lattice and one of the coordinated water molecules, resulting in a racemic mixture of chiral chains, ¹_∞ [Cu(R-valmet)(H₂ O)]⋅¹_∞ [Cu(S-valmet)(H₂ O)] (5-RS). In this compound, the coupling of the copper(II) ions within the chains is weak and ferromagnetic (J/k_B =+0.10(2) K). These results prove that the chirality of the valmetH₂ ligands (optically pure or racemic mixture) plays a key role in the self-assembly process of the copper(II) complexes.

Monitoring photo-induced population dynamics in metastable linkage isomer crystals: a crystallographic kinetic study of [Pd(Bu4dien)NO2]BPh4

We present a detailed kinetic study of photo-induced solid state linkage isomerism in the compound [Pd(Bu₄dien)NO₂]BPh₄ (Bu₄dien = N,N,N',N'-tetrabutyldiethylenetriamine) using in situ photocrystallographic techniques. We explore the key variables that influence the photoconversion and develop a detailed kinetic model for the excitation and decay processes and the temperature dependence of the conversion rates. We show that by varying the temperature the lifetime of the excited state can be varied over orders of magnitude, making these systems ideal test cases for the development of new time-resolved X-ray diffraction methods. The kinetic model is used to build a numerical-simulation tool, which we use to explore the practicalities of pump-probe single-crystal diffraction experiments with minute and second time-resolution.

Understanding solid-state photoswitching in [Re(OMe2-bpy)(CO)3(η1-NO2)] crystals via in situ photocrystallography

Single-crystal-to-single-crystal linkage isomerism is determined in a photoswitchable Re(i)-bpy crystal, shedding new light on the photoactive properties of potential Re(i)-photocatalysts.

Wavelength-selective photoisomerisation of nitric oxide and nitrite in a rhodium complex

Photoinduced linkage isomers (PLIs) of NO and NO₂⁻ are selectively generated by an appropriate choice of irradiation wavelength at low temperature within the same molecular complex [Rh(NO)(NO₂)₂(Bu^t₂PH)₂].