Pyridyl-substituted nitronyl nitroxides: comprehensive magnetochemical and quantum chemical study.

A series of pyridyl-substituted nitronyl nitroxides was synthesized and structurally characterized. A comprehensive magnetochemical and quantum chemical study of extended raw of the nitroxides with different substituents R in the pyridine fragment was performed. It was shown, that temperature-dependent magnetic properties are determined by the short contacts between nitroxide groups of adjacent molecules as well as between nitroxide group and methyl substituents in the pseudo axial positions of imidazoline fragments. Quantum chemistry allows to select the appropriate model of exchange cluster for analysis of experimental magnetic data and evaluation of the exchange interaction parameters. For NN-PyCl the "order-disorder" transition was detected by means of low temperature XRD. The difference in the experimental and calculated exchange interaction energies may serve as an indicator of temperature-induced structural rearrangements. For instance, for methyl substituted nitronyl nitroxide NN-PyMe structural transformations and significant changes in exchange interaction energies were observed.

Hysteretic Room-Temperature Magnetic Bistability of the Crystalline 4,7-Difluoro-1,3,2-Benzodithiazolyl Radical.

The title radical R⋅, synthesized by reduction of the corresponding cation R+, is thermally stable up to ~380 K in the crystalline state under anaerobic conditions. With SQUID magnetometry, single-crystal and powder XRD, solid-state EPR and TG-DSC, reversible spin-Peierls transition between diamagnetic and paramagnetic states featuring ~10 K hysteretic loop is observed for R⋅ in the temperature range ~310-325 K; ΔH=~2.03 kJ mol-1 and ΔS=~6.23 J mol-1 K-1. The transition is accompanied by mechanical movement of the crystals, i. e., by thermosalient behavior. The low-temperature diamagnetic P-1 polymorph of R⋅ consists of R⋅2 π-dimers arranged in (…R⋅2…)n π-stacks; whereas the high-temperature paramagnetic P21/c polymorph, of uniform (…R⋅…)n π-stacks. With the XRD geometries, CASSCF and broken-symmetry DFT jointly suggest strong antiferromagnetic (AF) interactions within R⋅2 and weak between R⋅2 for the (…R⋅2…)n stacks; and moderate AF interactions between R⋅ for the (…R⋅…)n stacks. The fully hydrocarbon archetype of R⋅ does not reveal the aforementioned properties. Thus, the fluorinated 1,3,2-benzodithiazolyls pave a new pathway in the design and synthesis of metal-less magnetically-bistable materials.

Ferrocenyl-substituted nitronyl nitroxide in the design of one-dimensional magnets.

By the reaction of M(hfac)2 (M = Mn(II), Co(II), Cu(II), and Zn(II); hfac is the hexafluoroacetylacetonate anion) and ferrocenyl-substituted nitronyl nitroxide (L), we succeeded in the synthesis of stable heterospin complexes: mononuclear [Zn(hfac)2L], trinuclear {[Cu(hfac)2]3L2} and chain polymer [Mn(hfac)2L]n and [Co(hfac)2L]n. The specific steric bulkiness of the ferrocenyl substituent leads to the formation of trans-type coordination polyhedra in the [Mn(hfac)2L]n and [Co(hfac)2L]n chains. The introduction of the ferrocene substituent leads to an effective weakening of intermolecular or interchain magnetic exchange coupling. Ferrimagnetic ordering was observed for one-dimensional complexes [M(hfac)2L]n (M = Mn(II), Co(II)). [Co(hfac)2L]n exhibits features of single-chain magnet behaviour: slow relaxation of magnetization below 13 K is associated with a high coercive field (54 kOe at 2 K).

A Nitronyl Nitroxide-Substituted Benzotriazinyl Tetraradical.

High-spin organic tetraradicals with significant intramolecular exchange interactions have high potential for advanced technological applications and fundamental research, but those synthesized to date possess limited stability and processability. In this work, we have designed a tetraradical based on the Blatter's radical and nitronyl nitroxide radical moieties and successfully synthesized it by using the palladium-catalyzed cross-coupling reaction of a triiodo-derivative of the 1,2,4-benzotriazinyl radical with gold(I) nitronyl nitroxide-2-ide complex in the presence of a newly developed efficient catalytic system. The molecular and crystal structure of the tetraradical was confirmed by X-ray diffraction analysis. The tetraradical possesses good thermal stability with decomposition onset at ∼150 °C under an inert atmosphere and exhibits reversible redox waves at -0.54 and 0.45 V versus Ag/AgCl. The magnetic properties of the tetraradical were characterized by SQUID magnetometry of polycrystalline powders and EPR spectroscopy in various matrices. The collected data, analyzed by using high-level quantum chemical calculations, confirmed that the tetraradical has a triplet ground state and a nearby excited quintet state. The unique high stability of the prepared triazinyl-nitronylnitroxide tetraradical is a new milestone in the field of creating high-spin systems.

N-Alkylimidazol-5-yl-substituted Nitronyl Nitroxides and Their Mononuclear Cu(II) Complexes: Synthesis, Structure and Magnetic Properties.

A novel synthetic approach has been employed to synthesize a series of new nitronyl nitroxides: 2-(1-propyl-1H-imidazol-5-yl)- (Ln-Pr ), 2-(1-isopropyl-1H-imidazol-5-yl)- (Li-Pr ) and 2-(1-butyl-1H-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (Ln-Bu ). The reaction of Cu(hfac)2 with LR in a 1 : 2 ratio yields mononuclear heterospin complexes [Cu(hfac)2 (LR )2 ] (LR =Ln-Pr , Li-Pr , Ln-Bu ), which have a similar crystal structure to the "jumping" crystals [Cu(hfac)2 (LMe )2 ] that exhibit chemomechanical activity. It was shown that an increase in the alkyl substituent R leads to changes in the crystal packing of the molecules and the absence of chemomechanical activity. Furthermore, it was found that two polymorph modifications of the heterospin complex [Cu(hfac)2 (Ln-Pr )2 ] can be obtained, and magnetic properties of [Cu(hfac)2 (Ln-Pr )2 ] strongly depend on the angle between the planes of the paramagnetic fragment O•-N-C=N→O and the imidazole ring in Ln-Pr .

Novel pyridyl-substituted nitronyl nitroxides as potential antiarrhythmic and hypotensive agents with low toxicity and enhanced stability in aqueous solutions.

This study explores the antiarrhythmic and hypotensive potential of pyridyl-substituted nitronyl nitroxides derivatives, uncovering the crucial role of a single carbon moiety of the pyridine cycle alongside radical and charged oxygen centers of the imidazoline fragment. Notably, the introduction of fluorine atoms diminished the antiarrhythmic effect, while the most potent derivatives featured the nitronyl nitroxide pattern positioned at the third site of the pyridine cycle. Gender-dependent responses were observed in lead compounds LCF3 and LMe, with LMe inducing temporary bradycardia and hypotension specifically in female rats, and LCF3 causing significant blood pressure reduction followed by rebound in females compared to milder effects in males. Mechanistic insights point towards ß1 adrenoceptor blockade as an underlying mechanism, supported by experiments on isolated rat atria. This research underscores the interplay between structure, cardiovascular effects and gender-specific responses, offering insights for therapeutic strategies for treating free radical-associated cardiovascular disorders.

Catalytic System for Cross-Coupling of Heteroaryl Iodides with a Nitronyl Nitroxide Gold Derivative at Room Temperature.

A simple and highly effective methodology for the cross-coupling of heteroaryl iodides with NN-AuPPh3 at room temperature is reported. The protocol is based on a novel catalytic system consisting of Pd2(dba)3·CHCl3 and the phosphine ligand MeCgPPh having an adamantane-like framework. The present protocol was found to be well compatible with various heteroaryl iodides, thus opening new horizons in directed synthesis of functionalized nitronyl nitroxides and high-spin molecules.

Perfluoroalkyl Chain Length Effect on Crystal Packing and [LnO8] Coordination Geometry in Lanthanide-Lithium ß-Diketonates: Luminescence and Single-Ion Magnet Behavior.

Functionalized perfluoroalkyl lithium ß-diketonates (LiL) react with lanthanide(III) salts (Ln = Eu, Gd, Tb, Dy) in methanol to give heterobimetallic Ln-Li complexes of general formula [(LnL3)(LiL)(MeOH)]. The length of fluoroalkyl substituent in ligand was found to affect the crystal packing of complexes. Photoluminescent and magnetic properties of heterobimetallic ß-diketonates in the solid state are reported. The effect of the geometry of the [LnO8] coordination environment of heterometallic ß-diketonates on the luminescent properties (quantum yields, phosphorescence lifetimes for Eu, Tb, Dy complexes) and single-ion magnet behavior (Ueff for Dy complexes) is revealed.

2-Imidazoline Nitroxide Derivatives of Cymantrene.

The 2-imidazoline nitroxide derivatives of cymantrene-2-(η5-cyclopentadienyl)tricarbonylmanganese(I)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (NNMn) and 2-(η5-cyclopentadienyl)tricarbonylmanganese(I)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl (INMn) were synthesized. It was shown that NNMn and INMn exhibit a sufficiently high kinetic stability both in solids and in solutions under normal conditions. Their structural characteristics, magnetic properties and electrochemical behavior are close to Re(I) analogs. This opens the prospect of using paramagnetic cymantrenes as prototypes in the design of Re(I) half-sandwiched derivatives for theranostics, where therapy is combined with diagnostics by magnetic resonance imaging due to the contrast properties of nitroxide radicals.

Re(i)-nitroxide complexes.

Spin-labeled cyrhetrenes [(NNCp)Re(CO)3] and [(INCp)Re(CO)3], where NNCp is nitronyl nitroxide 2-(η5-cyclopentadienyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl and INCp is the corresponding imino nitroxide, were synthesized and characterized by EPR, CV, XRD, magnetochemistry and quantum chemistry methods. The correlations between different arrangements of paramagnetic centers and the magnetic exchange interactions for three polymorphs of [(NNCp)Re(CO)3] were studied. It was concluded that high kinetic stability of nitroxide-substituted cyrhetrenes is a promising feature of compounds for the creation of multifunctional contrast agents.

Single Crystal X-ray Diffraction Studies of Two Polymorphic Modifications of the Dicarbonyl-o-Semiquinonato Rhodium Complex at Different Temperatures. Destruction Stimulated by Cooling Versus Stability.

It was found that the dicarbonyl-rhodium-o-semiquinonate complex (which thread-like crystals can bend reversibly under light/warm activation) can form two polymorphic modifications: isometric prisms (1) and sticks (2). Some thin sticks can bend as mentioned above. X-ray diffraction studies of polymorphic modifications at different temperatures were carried out. It was found that crystals 1 are destructed after cooling to 110 K as opposed to crystals 2. In turn, the reversible phase transition is detected in 2. In both polymorphic modifications, stack packaging motifs through the direct Rh-Rh bond are observed. The principal difference between packages of polymorphic modifications is that molecules 1 in the adjacent stacks are shifted relative to each other along the stack, in contrast to crystal 2. It was found that different packing of stacks leads to different anisotropic compression of crystals 1 and 2 during cooling, which is a key factor of their stability. Using the molecular invariom approach, the nature of the chemical bonds and charge distribution was investigated; the energy of the Rh-Rh bonds was estimated.

(Pyrrole-2,5-Diyl)-Bis(Nitronyl Nitroxide) and-Bis(Iminonitroxide): Specific Features of the Synthesis, Structure, and Magnetic Properties.

In contrast to diradicals connected by alternant hydrocarbons, only a few studies have addressed diradicals connected by nonalternant hydrocarbons and their heteroatom derivatives. Here, the synthesis, structure, and magnetic properties of pyrrole-2,5-diyl-linked bis(nitronyl nitroxide) and bis(iminonitroxide) diradicals are described. The diradicals show characteristic electron spin resonance spectra in dilute glassy solutions, from which conclusions about the presence of distinct conformations, their symmetry, and interspin distance were made. X-ray diffraction analysis of the diradicals revealed that paramagnetic moieties lie in the plane of the pyrrole ring, because of the formation of an intramolecular hydrogen bond, ONO…HN, with O…H distances of 2.15-2.23 Å. The N-O groups participating in the formation of H-bonds have greater bond lengths (~1.29 Å) as compared with nonparticipating groups (~1.27 Å). The nitronyl nitroxide and iminonitroxide diradicals showed an intramolecular antiferromagnetic interaction, with J = -77.3 and -22.2 cm-1, respectively (H = -2JS1S2).

Multifrequency Nuclear Magnetic Resonance as an Efficient Tool To Investigate Heterospin Complexes in Solutions.

We report a multifrequency nuclear magnetic resonance (NMR) study of heterospin complexes [Eu(SQ)3Ln], where SQ is 3,6-di(tert-butyl)-1,2-semiquinone, L is tetrahydrofuran (THF), pyridine (Py), or 2,2'-dipyridyl (Dipy), and n is the number of diamagnetic ligands. Multifrequency NMR experiments allowed us to determine the effective paramagnetic shifts of the ligands (L = THF or Py) and the chemical equilibrium constant for [Eu(SQ)3(THF)2]. In addition, we have found a strong magnetic field effect on the NMR line broadening, giving rise to very broad NMR lines at high magnetic fields. We attribute this effect to broadening under fast exchange conditions when the NMR spectrum represents a homogeneously broadened line with a width proportional to the square of the NMR frequency difference of the free and bound forms of L. Consequently, the line width strongly increases with the magnetic field. This broadening effect allows one to determine relevant kinetic parameters, i.e., the effective exchange time. The strong broadening effect allows one to exploit the [Eu(SQ)3(THF)2] complex as an efficient shift reagent, which not only shifts unwanted NMR signals but also broadens them, notably, in high-field NMR experiments. We have also found that [Eu(SQ)3Dipy] is a thermodynamically stable complex; hence, one can study [Eu(SQ)3Dipy] solutions without special precautions. We report an X-ray structure of the [Eu(SQ)3Dipy]·C6D6 crystals that have been grown directly in an NMR tube. This shows that multifrequency NMR investigations of heterospin compound solutions not only provide thermodynamic and kinetic data for heterospin species but also can be useful for the rational design of stable heterospin complexes and optimization of synthetic approaches.

Ligand Structure Effects on Molecular Assembly and Magnetic Properties of Copper(II) Complexes with 3-Pyridyl-Substituted Nitronyl Nitroxide Derivatives.

Reaction of Cu(hfac)2 with methyl- and bromo-3-pyridyl-substituted nitronyl nitroxides (L R ) leads to assemble a diverse set of coordination complexes: mononuclear [Cu(hfac)2L 2-Me ], binuclear [{Cu(hfac)2}2(H2O)L 2-Me ], trinuclear [{Cu(hfac)2}3(L 6-Br )2], pentanuclear [{Cu(hfac)2}5(L 2-Me )2], and [{Cu(hfac)2}5(L 2-Me )4], cocrystals [Cu(hfac)2(L 2-Br )2]·[Cu(hfac)2(H2O)2] and [Cu(hfac)2(L 2-Br )2]·2[Cu(hfac)2H2O], one-dimensional polymers [Cu(hfac)2L 2-Br ] n and [Cu(hfac)2L 6-Br ] n , and cyclic dimers [Cu(hfac)2L 5-Me ]2, [Cu(hfac)2L 5-Br ]2, and [Cu(hfac)2L 6-Me ]2. The molecular structures of the obtained complexes are strongly affected by the substituent type and its location in the pyridine heterocycle. Occupation of the second position of the pyridine ring increases the steric hindrance of both imine and nitroxide coordination sites of L 2-R , which is favorable for the formation of various conformers and precipitation of complexes with different molecular structures. The pentanuclear [{Cu(hfac)2}5(L 2-Me )2] and [{Cu(hfac)2}5(L 2-Me )4] complexes do not have prior analogues and are valuable model objects for investigation of the mechanism of formation of various coordination polymers. The arrangement of long Cu-ONO bonds in {CuO6} square bipyramids due to the weakening nitroxide donor site in complexes, based on L 2-Me , L 2-Br , and L 6-Br ligands, results in ferromagnetic exchange interactions between spins of Cu2+ ions and nitroxides. Complexes with substituents that do not considerably affect the coordination ability of ligands (L 5-Me , L 5-Br , and L 6-Me ) exhibit strong antiferromagnetic exchange interactions between spins of Cu2+ ions and nitroxides.

Pressure-Controlled Migration of Paramagnetic Centers in a Heterospin Crystal.

A study of the single-crystal-to-single-crystal transformation induced by temperature variation for the chain polymer Cu(II) complex with nitronyl nitroxide showed that an increase in the hydrostatic pressure of up to ∼0.07 GPa completely changes the intracrystalline displacements of molecules relative to one another. This, in turn, significantly affects the interaction energy of the unpaired electrons of the paramagnetic centers and hence the form of the temperature dependence of the magnetic susceptibility χT. The cooling of crystals under normal conditions causes a rearrangement of the intrachain exchange clusters {>N-•O-Cu(II)-O•-N<} accompanied by a shortening of the distances between the paramagnetic centers. This changes the character of exchange interactions and generates multistage spin transitions. An increase in the hydrostatic pressure leads to a drastic change in the O···O distances between the nitroxyl fragments of adjacent chains, an increase in the antiferromagnetic exchange between them, and complete suppression of spin transitions.

Simultaneous Introduction of Two Nitroxides in the Reaction: A New Approach to the Synthesis of Heterospin Complexes.

A new approach to the synthesis of multispin compounds has been developed, namely, the simultaneous introduction of two different stable nitroxides (nitronyl nitroxide and imino nitroxide) in a reaction with a metal ion. An important characteristic of the new method is that nitronyl nitroxide and imino nitroxide introduced in the reaction with the metal are the products of different series; i.e., the nitronyl nitroxide molecule differs from the imino nitroxide molecule not only in one additional oxygen molecule per molecule but also in another substituent in the side chain of the organic paramagnet. This possibility was demonstrated on the synthesis of multispin compounds [Ni2(A1)(L2)2(Piv)(MeOH)], [Ni2(L1)(A2)2(Piv)(H2O)], [Co2(A1)(L2)2(Piv)(MeOH)], and [Co3(L1)2(A2)2(Piv)2], in which Ln and An differ in the substituent in the phenyl ring. The number of multispin compounds that can be synthesized by the proposed method is almost unlimited. The heterospin complexes of transition metals with coordinated nitronyl nitroxide and imino nitroxide in one molecule contain energy-different exchange interaction channels that differ in both magnitude and sign, as confirmed by the quantum-chemical analysis of exchange channels in [Ni(B1)(B2)2](NO3)2. The series of mixed-radical complexes may include compounds with nontrivial magnetic properties such as [Co2(A1)(L2)2(Piv)(MeOH)], which experiences bulk magnetic ordering below 3.5 K.

Light-Induced Spin State Switching and Relaxation in Spin Pairs of Copper(II)-Nitroxide Based Molecular Magnets.

Similar to spin-crossover (SCO) compounds, spin states of copper(II)-nitroxide based molecular magnets can be switched by various external stimuli including temperature and light. Although photoswitching and reverse relaxation of nitroxide-copper(II)-nitroxide triads were investigated in some detail, similar study for copper(II)-nitroxide spin pairs was still missing. In this work we address photoswitching and relaxation phenomena in exchange-coupled spin pairs of this family of molecular magnets. Using electron paramagnetic resonance (EPR) spectroscopy with photoexcitation, we demonstrate that compared to triad-containing compounds the photoinduced weakly coupled spin (WS) states of copper(II)-nitroxide pairs are remarkably more stable at cryogenic temperatures and relax to the ground strongly coupled spin (SS) states on the scale of days. The structural changes between SS and WS states, e.g., differences in Cu-Onitroxide distances, are much more pronounced for spin pairs than for spin triads in most of the studied copper(II)-nitroxide based molecular magnets. This results in higher energy barrier between WS and SS states of spin pairs and governs higher stability of their photoinduced WS states. Therefore, the longer-lived photoinduced states in copper(II)-nitroxide molecular magnets should be searched within the compounds experiencing largest structural changes upon thermal spin transition. This advancement in understanding of LIESST-like phenomena in copper(II)-nitroxide molecular magnets allows us to propose them as interesting playgrounds for benchmarking the basic factors governing the stability of photoinduced states in other SCO and SCO-like photoswitchable systems.

(Azulene-1,3-diyl)-bis(nitronyl nitroxide) and (Azulene-1,3-diyl)-bis(iminonitroxide) and Their Copper Complexes.

In contrast to diradicals connected by alternant hydrocarbons, only a few studies on those connected by nonalternant hydrocarbons have been reported. The syntheses, structures, and magnetic properties of azulene-1,3-diyl linked bis(nitronyl nitroxide) (NN2 Az) and bis(iminonitroxide) (IN2 Az) diradicals and their Cu(hfac)2 (hfac=hexafluoroacetylacetonate) complexes were investigated. NN2 Az was shown to have an intramolecular ferromagnetic interaction with Jobs /kB =+10.0 K (H=-2JS1 ⋅S2 ) between (nitronyl nitroxide) spins, whereas IN2 Az was estimated to have a much weaker intramolecular magnetic interaction. The reactions of NN2 Az and IN2 Az with Cu(hfac)2 gave a 1:2 [{Cu(hfac)2 }2 (NN2 Az)] complex and a 1:1 [Cu(hfac)2 (IN2 Az)]⋅C6 H12 complex, respectively. [{Cu(hfac)2 }2 (NN2 Az)] showed strong intramolecular antiferromagnetic interactions (J1-Cu-R /kB ≈-800 K, J2-Cu-R /kB ≈-500 K) between the CuII spins and the coordinating NN spins, whereas [Cu(hfac)2 (IN2 Az)] exhibited a ferromagnetic exchange interaction (Jobs-Cu-R /kB =+114 K) between the CuII spin and the imino-coordinated iminonitroxide spin.

Reaction of Paramagnetic Synthon, Lithiated 4,4,5,5-Tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide, with Cyclic Aldonitrones of the Imidazole Series.

It was shown that dipole-stabilized paramagnetic carbanion lithiated 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide can be attached in a nucleophilic manner to either isolated or conjugated aldonitrones of the 2,5-dihydroimidazole 3-oxide and 2H-imidazole 1-oxide series to afford adducts the subsequent oxidation of which leads to polyfunctional mono- and diradicals. According to XRD, at least two polymorphic modifications can be formed during crystallization of the resulting paramagnetic compounds, and for each of them, geometric parameters of the molecules are similar. An EPR spectrum of the diradical in frozen toluene has a complicated lineshape, which can be fairly well reproduced by using X-ray diffraction structural analysis and the following set of parameters: D=14.9 mT, E=1.7 mT; tensor a((14) N)=[0.260 0.260 1.625] mT, two equivalent tensors for the nitronyl nitroxide moiety a((14) N)=[0.198 0.198 0.700] mT, and g≈2.007. According to our DFT and ab initio calculations, the intramolecular exchange in the diradical is very weak and most likely ferromagnetic.

A Copper-Nitroxide Adduct Exhibiting Separate Single Crystal-to-Single Crystal Polymerization-Depolymerization and Spin Crossover Transitions.

A complex cascade of solid-state processes initiated by variation of temperature was found for the heterospin complex [Cu(hfac)2L(Me/Et)] formed in the reaction of copper(II) hexafluoroacetylacetonate [Cu(hfac)2] with stable nitronyl nitroxide 2-(1-methyl-3-ethyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L(Me/Et)). The cooling of the compound below 260 K initiated a solid-state chemical reaction, which led to a depolymerization of chains and formation of a pair heterospin complex [Cu(hfac)2L(Me/Et)2][[Cu(hfac)2]3L(Me/Et)2]. Further decrease in temperature below 144 K led to a spin transition accompanied by a drastic decrease in the effective magnetic moment from 2.52 to 2.24 µB. When the compound was heated, the order of effects was reversed: at first, the magnetic moment abruptly increased, and then the molecular fragments of the pair cluster united into polymer chains. Two hysteresis loops correspond to this cascade of temperature-induced structural transformations on the experimental dependence µeff(T): one at high (T↑ = 283 K and T↓ = 260 K) and the other at low (T↑ = 161 K, T↓ = 144 K) temperature. The spin transitions were also recorded for the [[Cu(hfac)2]3L(Bu/Et)2] and [[Cu(hfac)2]5L(Bu/Et)4] molecular complexes, which are models of the trinuclear fragment of the {[Cu(hfac)2]3L(Me/Et)2} pair cluster.