Isomeric Complexes Research Articles

Fine tuning dynamic magnetism of dysprosiacarboranyl sandwiches

A series of isomeric sandwich-type dysprosiacarboranyl complexes, including [Na(THF)5][3,2'-(THF)2-3,2'-Dy(1,2-C2B9H11)x(1',7'-C2B9H11)2–x] (o/m-Dy) and [Na(THF)5][2,2'-(THF)2-2,2'-Dy(1,7-C2B9H11)2] (m-Dy) were synthesized by using the isomeric dicarbollide ligands, namely [nido-7,8-C2B9H11]2– and [nido-7,9-C2B9H11]2−. The structural details of o/m-Dy and m-Dy and magnetic dynamics of m-Dy were investigated to compare with the previous study on [Na(THF)5][2,2'-(THF)2-2,2'-Dy(1,2-C2B9H11)2] o-Dy. The bending angles of sandwiched dysprosiacarboranes are straightened so as to improve energy barriers (Ueff) from 430(5) to 591(0) K. Magneto-structural correlations show that the introduction of meta-C sites within the π-electron delocalized heterocyclic ring can effectively shorten the Dy–C2B3 centroid distance and increase the C2B3centroid∙∙∙Dy∙∙∙C2B3centroid bending angle, which is attributed to the differences in electronegativity between C and B atoms on the ring of C2B32–. Therefore, to further enhance the performance of single-molecule magnets (SMMs) on this basis, future endeavors should focus on diminishing the equatorial solvent molecules to make a wider C2B3∙∙∙Dy∙∙∙C2B3 bending angle.

64Cu tumor labeling with hexadentate picolinic acid-based bispidine immunoconjugates.

Discussed are two picolinate appended bispidine ligands (3,7-diazabicyclo[3.3.1]nonane derivatives) in comparison with an earlier described bis-pyridine derivative, which are all known to strongly bind CuII. The radiopharmacological characterization of the two isomeric bispidine complexes includes quantitative labeling with 64CuII at ambient conditions with high radiochemical purities and yields (molar activities >200 MBq/nmol). Challenge experiments in presence of EDTA, cyclam, human serum and SOD demonstrate high stability and inertness of the 64Cu-bispidine complexes. Biodistribution studies performed in Wistar rats indicate a rapid renal elimination for both 64Cu-labeled chelates. The bispidine ligand with the picolinate group in N7 position was selected for further biological experiments, and its backbone was therefore substituted with a benzyl-NCS group at C9. Two tumor target modules (TMs), targeting prostate stem cell antigen (PSCA), overexpressed in prostate cancer, and the fibroblast activation protein (FAP) in fibrosarcoma, were selected for thiourea coupling with the NCS-functionalized ligand and lysine residues of TMs. Small animal PET experiments on tumor-bearing mice showed specific accumulation of the 64Cu-labeled TMs in PSCA- and FAP-overexpressing tumors (standardized uptake value (SUV) for PC3: 2.7±0.6 and HT1080: 7.2±1.25) with almost no uptake in wild type tumors.

Nitrosyl derivatives of the halide-bridged complexes [M2Cp2(μ-X)(μ-PtBu2)(CO)2] (M = Mo, W; X = Cl, I).

The title compounds were prepared as described previously (M = Mo, X = Cl) or by the reaction of the known unsaturated complex [W2Cp2(μ-PtBu2)(CO)4]BF4 with NaI in refluxing 1,2-dichloroethane solution. Reaction of these halide-bridged complexes with NO (1 atm) at low temperature yielded the corresponding dinitrosyl derivatives syn,trans-[M2Cp2X(μ-PtBu2)(CO)(NO)2], with a syn arrangement of Cp ligands relative to the M2P plane, and a transoid arrangement of the halide ligand X relative to the P atom, according to an X-ray study on the ditungsten complex (W−W = 3.113(1) Å). Further decarbonylation of these products at high temperature yielded in both cases the halide-bridged complexes trans-[M2Cp2(μ-X)(μ-PtBu2)(NO)2] as major products, but the minor products were different. For the molybdenum complex, an isomer of the final product, cis-[Mo2Cp2(μ-Cl)(μ-PtBu2)(NO)2], was formed. In contrast, the minor tungsten product, anti,cis-[W2Cp2I(μ-PtBu2)(CO)(NO)2], was an isomer of the parent complex. In addition, trace amounts of the imide cyclopentadienylidene complex [W2Cp(μ-κ:η5-C5H4)I(μ-PtBu2)(NH)(NO)] was also obtained (W−W = 2.9376(2) Å). Density functional theory calculations were used to examine possible routes to the above dinitrosyl complexes, that seem to involve at least three reaction pathways: direct decarbonylation, rearrangement of the MCpX(NO) fragment prior to decarbonylation, and rearrangement of the MCp(CO)(NO) fragment prior to decarbonylation.

Aluminagerma[5]pyramidanes-Formation and Skeletal Rearrangement.

The salt metathesis reaction of dipotassium germacyclopentadienediide with aluminum(III) dichlorides provides either half-sandwich alumole complexes of germanium(II) or aluminylene germole complexes. Their molecular structure and the delocalized bonding situation, revealed by density functional theory (DFT) calculations, are equally described as isomeric aluminagerma[5]pyramidanes with either the germanium or the aluminum atom in the apical position of the pentagonal pyramid. The product formation and the selectivity of the reaction depends on the third substituent of the aluminum dichloride. Aryl-substituents favor the formation of alumole complexes and Cp*-substituents that of the isomeric germole complexes. With amino-substituents at the aluminum atom mixtures of both isomers are formed and the positional exchange of the two heteroatoms is shown by NMR spectroscopy. The alumole complexes of germanium(II) undergo facile reductive elimination of germanium and form the corresponding alumoles.

Aluminagerma[5]pyramidane – Bildung und Gerüstumlagerung

AbstractSalzmetathesereaktionen zwischen Dikaliumgermacyclopentadiendiiden und Aluminium(III)dichloriden ermöglichen die Synthese von Alumol‐Halbsandwichkomplexen des zweiwertigen Germaniums oder von Aluminylen‐Germol‐Komplexen. Deren Molekülstrukturen und ihre delokalisierte Bindungssituation, wie sie durch Dichtefunktionalrechnungen (DFT) belegt wird, erlauben gleichermaßen ihre Beschreibung als isomere Aluminagerma[5]pyramidane mit entweder dem Germanium‐ oder dem Aluminiumatom in der apikalen Position der pentagonalen Pyramide. Die Produktbildung und die Selektivität der Reaktion hängen von dem dritten Substituenten des Aluminiumdichlorids ab. Arylgruppen begünstigen die Bildung von Alumolkomplexen und der Cp*‐Substituent die der isomeren Germolkomplexe. Mit Aminosubstituenten am Aluminiumatom werden Mischungen beider Isomere erhalten, wobei der Austausch der Positionen der beiden Heteroatome im Pyramidan durch NMR Spektroskopie nachgewiesen wurde. Zudem können, ausgehend von Alumolkomplexen des zweiwertigen Germaniums, durch reduktive Eliminierung des Germaniums die entsprechenden Alumole erhalten werden.

6-Bromo-2-hydroxypyridinate-bridged Paddlewheel-Type Dirhodium Complex Isomers: Synthesis, Crystal Structures, Electrochemical Properties, and Structure-Dependent Absorption Properties

Two new paddlewheel-type dirhodium (Rh2) complex isomers, formulated as trans-2,2- and 3,1-forms of [Rh2(bhp)4] (bhp = 6-bromo-2-hydroxypyridinate), were obtained by the reaction of 6-bromo-2-hydroxypyridine with [Rh2(O2CCH3)4(H2O)2] and characterized by NMR, ESI-MS, and elemental analyses. Single crystal X-ray diffraction analyses clarified that the crystal structure of trans-2,2-form takes a conventional paddlewheel-type dimer structure with no axial coordination ligands, i.e., trans-2,2-[Rh2(bhp)4], whereas that of the 3,1-form changed significantly depending on the kinds of solvent used for crystallization processes; dimer-of-dimers-type tetrarhodium complex, i.e., 3,1-[Rh2(bhp)4]2, and a conventional paddlewheel-type dimer complex with an axial DMF ligand, i.e., 3,1-[Rh2(bhp)4(DMF)], were observed. The 3,1-form showed unique absorption changes that were not observed in the trans-2,2-form; the trans-2,2-form showed an absorption band at approximately 780 nm both in the solid state and in solution (CH2Cl2 and DMF), whereas the 3,1-form showed a similar absorption band at 783 nm in CH2Cl2 solution, but their corresponding bands were blue-shifted in solid state (655 nm) and in DMF solution (608 nm). The molecular structures and the origin of their unique absorption properties of these Rh2 complexes were investigated using density functional theory (DFT) and time-dependent DFT (TDDFT).

Chemical Evolution of Enzyme-Catalyzed Glycosylation.

ConspectusThe limited availability of structurally well-defined diverse glycans remains a major obstacle for deciphering biological functions as well as biomedical applications of carbohydrates. Despite tremendous progress that has been made in past decades, the synthesis of structurally well-defined complex glycans still represents one of the most challenging topics in synthetic chemistry. Chemical synthesis of glycans is a time-consuming and labor-intensive process that requires elaborate planning and skilled personnel. In contrast, glycosyltransferase-catalyzed enzymatic synthesis provides a more efficient, convenient, low-cost, and sustainable alternative to affording diverse and complex glycans. However, the existing methods are still insufficient to fulfill the increasing demand for specific synthetic glycan libraries necessary for functional glycomics research. This is mainly attributed to the inherent character of the glycan biosynthetic pathway. In nature, there are too many glycosyltransferases involved in the in vivo glycan synthesis, but only a small number of them are available for in vitro enzymatic synthesis. For instance, humans have over 200 glycosyltransferases, but only a few of them could be produced from the conventional bacterial expression system, and most of these membrane-associated enzymes could be overexpressed only in eukaryotic cells. Moreover, the glycan biosynthetic pathway is a nontemplate-driven process, which eventually ends up with heterogeneous glycan product mixtures. Therefore, it is not a practical solution for the in vitro enzymatic synthesis of complex glycans by simply copying the glycan biosynthetic pathway.In the past decade, we have tried to develop a simplified and transformable approach to the enzymatic modular assembly of a human glycan library. Despite the structural complexity of human glycans, the glycoinformatic analysis based on the known glycan structure database and the human glycosyltransferase database indicates that there are approximately 56 disaccharide patterns present in the human glycome and only 16 disaccharide linkages are required to account for over 80% of the total disaccharide fragments, while 35 disaccharide linkages are sufficient to cover over 95% of all disaccharide fragments of human glycome. Regardless of the substrate specificity, if one glycosyltransferase could be used for the synthesis of all of the same glycosidic linkages in human glycome, it will require only a few dozen glycosyltransferases for the assembly of entire human glycans. According to the glycobioinformatics analysis results, we rationally designed about two dozen enzyme modules for the synthesis of over 20 common glycosidic linkages in human glycome, in which each enzyme module contains a glycosyltransferase and a group of enzymes for the in situ generation of a nucleotide-activated sugar donor. By sequential glycosylation using orchestrated enzyme modules, we have completed the synthesis of over 200 structurally well-defined complex human glycans including blood group antigens, O-mannosyl glycans, human milk oligosaccharides, and others. To overcome the product microheterogeneity problem of enzymatic synthesis in the nontemplate-driven glycan biosynthetic pathway, we developed several substrate engineering strategies to control or manipulate the outcome of glycosyltransferase-catalyzed reactions for the precise synthesis of structurally well-defined isomeric complex glycans.

Insight into the anti-proliferation activity and photoinduced NO release of four nitrosylruthenium isomeric complexes and their HSA complex adducts.

Four Ru(II)-centered isomeric complexes [RuCl(5cqn)(Val)(NO)] (1-4) were synthesized with 5cqn (5-chloro-8-hydroxyquinoline) and chiral Val (Val=L- or D-valine) as co-ligand, and their structures were confirmed using the X-ray diffraction method. The cytotoxicity and photodynamic activity of the isomeric complexes and their human serum albumin (HSA) complex adducts were evaluated. Both the isomeric complexes and their HSA complex adducts significantly affected HeLa cell proliferation, with an IC50 value in the range of 0.3-0.5μM. The photo-controlled release of nitric oxide (NO) in solution was confirmed using time-resolved Fourier transform infrared and electron paramagnetic resonance spectroscopy techniques. Furthermore, photoinduced NO release in living cells was observed using a selective fluorescent probe for NO. Moreover, the binding constants (Kb) of the complexes with HSA were calculated to be 0.17-1.98×104 M-1 and the average number of binding sites (n) was found to be close to 1, it can serve as a crucial carrier for delivering metal complexes. The crystal structure of the HSA complex adduct revealed that one [RuCl(H2O)(NO)(Val)]+ molecule binds to a pocket in domain I. This study provides insight into possible mechanism of metabolism and potential applications for nitrosylruthenium complexes.

Structural Variety, Isomerism, and Interconversions of Polynuclear Samarium Complexes with Reduced 9,10-Phenanthrenequinone Ligand

Structural Variety, Isomerism, and Interconversions of Polynuclear Samarium Complexes with Reduced 9,10-Phenanthrenequinone Ligand

From loose to tight: unveiling bond stretch isomerism in π-complexes of Li, Na and K.

The study investigates the phenomenon of bond stretch isomerism (BSI) in complexes formed between alkali metals (Li, Na, K) and various non-aromatic, aromatic hydrocarbons, as well as heteroaromatic systems. The research employs density functional theory (DFT) calculations to optimize complex geometries and analyze their electronic structures using molecular electrostatic potential (MESP), charge, and spin density analyses. The results reveal that these complexes can exist in two distinct configurations: 'loose' long-bond isomers (lbi) that retain the original hydrocarbon geometry and 'tight' short-bond isomers (sbi) that undergo geometrical distortion upon complexation, with sbi generally being more stable. The interconversion between lbi and sbi occurs through a transition state. The study highlights the crucial role of electron transfer in BSI, with sbi involving valence electron transfer from the metal to the hydrocarbon, leading to zwitterionic radical complexes. In contrast, lbi exhibit a slight electron density transfer from the hydrocarbon to the metal. The presence of low-energy transition states between lbi and sbi suggests a dynamic shuttling mechanism for alkali metals, particularly Li, on hydrocarbon surfaces. The study identifies Li complexes as potential candidates for anode materials in batteries due to their stability and electron transfer properties, offering valuable insights into the design of advanced materials for energy storage applications.

Understanding structural isomerism in organoiridium picolinamidate complexes and its consequences on reactivity and biological properties

Insights into structural isomerization in organoiridium picolinamidate complexes were obtained through experimental studies and density functional theory calculations.

Conformational equilibria in acrolein-CO2: the crucial contribution of n → π* interactions unveiled by rotational spectroscopy.

Using gas phase Fourier-transform microwave spectroscopy complemented by theoretical analysis, this study delivers a comprehensive depiction of the physical origin of the 'n → π* interaction' between CO2 and acrolein, one of the most reactive aldehydes. Three distinct isomers of the acrolein-CO2 complex, linked through a C⋯O tetrel bond (or n → π* interaction) and a C-H⋯O hydrogen bond, have been unambiguously identified in the pulsed jet. Relative intensity measurements allowed estimation on the population ratio of the three isomers to be T1/T2/C1 ≈ 25/5/1. Advanced theoretical analyses were employed to elucidate the intricacies of the noncovalent interactions within the examined complex. This study not only sheds light on the molecular underpinnings of n → π* interactions but also paves the way for future exploration in carbon dioxide capture and utilization, leveraging the fundamental principles uncovered in the study of acrolein-carbon dioxide interactions.

Dinuclear tricarbonylrhenium(I) complexes: impact of regioisomerism on the photoluminescence properties.

Dinuclear Re(I) complexes have proportionally been much less studied than mononuclear analogues. In particular, very little information is available about their solid-state emission properties. In this work, two structural isomers of dinuclear complexes (Bi-Re-metaPhe and Bi-Re-paraPhe), which differ by the relative position of the coordination spheres on a central phenyl ring, were synthesized and compared with each other and with the parent mononuclear compound (Mono-Re-Phe), from a theoretical and experimental point of view. In solution, the electronic, electrochemical and spectroscopic properties of the dinuclear complexes were almost identical, and rather close to those of the monomer. In the solid state, the photoluminescence (PL) efficiency of dimers was not higher than that of the monomer, but a clear mechanoresponsive luminescence (MRL) effect appeared only for the former ones. The positional isomerism influenced the amplitude of this effect, as well as the aggregation-induced emission (AIE) properties in a water-acetonitrile mixture. This study reveals the importance of positional isomerism to modulate the emission properties in the solid state. It also shows the advantage of dinuclear structures to access new MRL-active materials.

A Theoretical Study on Au(I) Decorated Isomeric Triazine Complexes as a New Class of Hydrogen Storage Materials

A Theoretical Study on Au(I) Decorated Isomeric Triazine Complexes as a New Class of Hydrogen Storage Materials

Complex isomerism influencing the textural properties of organometallic [Cu(salen)] porous polymers: paramagnetic solid-state NMR characterization and heterogeneous catalysis.

Although organometallic porous polymer networks are recognized as promising heterogeneous catalysts, the relationship between ligand/monomer geometry and network parameters is usually not well understood due to the lack of atom-resolved characterization methods for the amorphous network matrix. In this work, a series of copper(II) salen-type metal complexes was synthesized, using trans- and cis-1,2-diaminocyclohexane segments, and thoroughly characterized by single-crystal X-ray diffraction and solution- and solid-state NMR spectroscopy. Terminal ethynyl groups of the complexes were then transformed into polyacetylene chains by coordination chain-growth homopolymerization, resulting in highly porous (458-655 m2 g-1) organometallic polymer networks with a copper(II) ion content of about 12 wt%. The presence of paramagnetic copper(II) moieties in these complexes and respective polymer networks required the application of tailored NMR techniques, which together with X-ray crystallography and DFT calculations of the paramagnetic NMR shifts made it possible to investigate the differences in the complex geometry in liquid, powder and crystalline form and compare it with the complex geometry in polymer networks. All prepared organometallic polymer networks were also tested as heterogeneous catalysts for styrene oxidation with uncommonly high substrate conversions and compared with their low-molecular-weight analogues. The high reusability of such heterogeneous polymer-based catalysts was also proven.

Confinement of p‐Xylene in the Pores of a Bilanthanide Metal–Organic Framework for Highly Selective Recognition

AbstractThe rapid and accurate sensing of p‐xylene, an essential raw material with a multi‐billion‐dollar market, in xylene mixture is of great significance in industry; however, the highly similar molecular structures, energy levels, and spectral characteristics of xylene isomers make the selective recognition extremely challenging. Metal–organic frameworks (MOFs) exhibiting tailorable pores and potential binding sites provide prospects for xylene sensing but a comprehensive understanding of the pore effect is still elusive, primarily due to the intricacies involved in the sensing process. Herein, we reported a robust bilanthanide MOF NKU‐999‐EuTb with precisely engineered pores to accommodate p‐xylene, of which the binding sites were confirmed by single crystal X‐ray diffraction and dynamic magnetic susceptibilities. NKU‐999‐EuTb exhibits high‐performance in selective recognition for p‐xylene towards its isomers. Through a systematical study, it was revealed that absorbing p‐xylene into the pores governs the sensing performance. This work provides insights for developing advanced sensing materials for complex isomers.

Confinement of p-Xylene in the Pores of a Bilanthanide Metal-Organic Framework for Highly Selective Recognition.

The rapid and accurate sensing of p-xylene, an essential raw material with a multi-billion-dollar market, in xylene mixture is of great significance in industry; however, the highly similar molecular structures, energy levels, and spectral characteristics of xylene isomers make the selective recognition extremely challenging. Metal-organic frameworks (MOFs) exhibiting tailorable pores and potential binding sites provide prospects for xylene sensing but a comprehensive understanding of the pore effect is still elusive, primarily due to the intricacies involved in the sensing process. Herein, we reported a robust bilanthanide MOF NKU-999-EuTb with precisely engineered pores to accommodate p-xylene, of which the binding sites were confirmed by single crystal X-ray diffraction and dynamic magnetic susceptibilities. NKU-999-EuTb exhibits high-performance in selective recognition for p-xylene towards its isomers. Through a systematical study, it was revealed that absorbing p-xylene into the pores governs the sensing performance. This work provides insights for developing advanced sensing materials for complex isomers.

Absolute configuration assignment of highly fluorinated carboxylic acids via VCD and MRR spectroscopy

Chiral analysis has become a crucial step in studying the stereospecific synthesis of Active Pharmaceutical Ingredients (APIs). Both Vibrational Circular Dichroism (VCD) and Molecular Rotational Resonance (MRR) spectroscopy are capable of determining absolute configurations (ACs) via comparison of experimental and calculated data. In this regard, each technique has its own caveats. In VCD analysis, accurate prediction of the normal modes as well as rigorous conformational searches of both the analyte and potential (self-)aggregation products are required to optimally match experimental spectra. In MRR analysis, chiral species are resolved through complexation with a chiral tag to prepare spectrally distinct diastereomeric complexes. Although individual complex isomers can be distinguished, spectral assignments need to be matched to unique isomer geometries for unambiguous AC assignment. In this work, the ACs of two highly fluorinated carboxylic acids were successfully assigned using VCD and MRR spectroscopy. In the VCD analysis, the M06-2X functional was demonstrated to be superior to B3LYP and B3LYP-GD3 in accurately predicting the C–F normal modes and both monomeric and dimeric spectral contributions were observed. In a similar analysis with broadband MRR, most experimentally identified geometries had more than one possible computational match. Nevertheless, careful consideration of the chiral tag, as well as additional isomer assignments, resulted in successful assignment of the AC. This comparative study demonstrates the power of contemporary VCD analysis and the unique contributions of MRR to the analytical toolbox.

Cryo-IR spectroscopy and cryo-kinetics of cluster N2 adsorbate complexes of tantalum cluster cations Ta5-8.

We present an IR-PD study of tantalum cluster adsorbate complexes [Tan(N2)m]+, abbreviated (n,m), n = 5-8. We utilize infrared spectroscopy of isolated and size selected clusters as prepared and characterized by a cryogenic tandem ion trap setup, and we augment our experiments with quantum chemical simulations at the level of density functional theory. The cluster adsorbate complexes (n,m) reveal vibrational bands above 2000cm-1, which indicate end-on coordinated μ1-N2 oscillators, and bands below 2000cm-1, which indicate side-on μ2-κN:κN,N coordinated ones. We observe a general increase in spectral complexity and an inhomogeneous broadening, mainly towards the red, at certain points of N2 loading m, which originates from an increasingly higher amount of double and triple N2 coordination at Ta sites, eventually at all of them. Other than the small tantalum clusters Tan+, n = 2-4, the IR-PD spectra of the initial N2 adsorbate species (n,1), n = 5-8, provide strong evidence for a lack of spontaneous N2 cleavage. Spontaneous N2 cleavage by Tan+, n = 5-8, seems suppressed. Therefore, the ability of a small Ta cluster to cleave dinitrogen disappears with one more tantalum core atom. The study of stepwise N2 adsorption on size selected Tan+, n = 5-8 clusters revealed adsorption limits m(max) of [Tan(N2)m]+ that are independent of cluster size within this size range. Cryo-adsorption kinetics at 26K allowed for kinetic fits to consecutive N2 adsorption steps, and the fits revealed significant N2 desorption rates upon higher N2 loads, and the cluster adsorbate complexes eventually reached equilibrium. Some enhanced N2 desorption rates point towards likely adsorbate shell reorganization, and there is also some evidence for the coexistence of isomeric cluster adsorbate complexes.

Selective Crystallization of Linkage Isomers, [RhIII(NCS)(SCN)5]3- and [RhIII(SCN)6]3-, to Investigate Structural Trans Influence and Thermal Stability.

Linkage isomers of homoleptic complexes, [RhIII(SCN)6]3- and [RhIII(NCS)(SCN)5]3-, formed in aqueous solution were successfully separated by employing methyltriphenylphosphonium (MePPh3+) and 1-ethylquinolinium (EtQu+) ions as countercations, respectively. The single-crystal X-ray analysis of (MePPh3)3[RhIII(SCN)6] (1) indicated that all of the SCN- ligands coordinate to the RhIII ion by S atoms with an octahedral symmetry, where the average bond length of Rh-S is 2.374(7) Å. On the other hand, the RhIII ion of (EtQu)3[RhIII(NCS)(SCN)5]·H2O (2) is coordinated by five S atoms and one N atom of the SCN- ligands with a C4v symmetry. Structural trans influence was observed in the shorter bond length of Rh-S at the trans position of Rh-N. The Rh-S bond length is 2.3398(13) Å significantly shorter than those of 1 by ca. 0.04 Å, although DFT calculations based on the crystal structures indicated that the effective bond order of Rh-N is higher than those of Rh-S. Thermal stability examination by thermogravimetric and differential thermal analyses (TG/DTA) and IR spectroscopy indicated that the linkage isomerization of [RhIII(SCN)6]3- to [RhIII(NCS)(SCN)5]3- proceeded after melting around 174 °C. These results clearly indicate that [RhIII(NCS)(SCN)5]3- is thermodynamically more stable than [RhIII(SCN)6]3- in solid states, although further linkage isomerization hardly occurs.