Search

A strong electron-withdrawing nitro group introduced into the 6-position of 3,5-di-(tert -butyl)-1,2-benzoquinone provides for activation of the sterically blocked Michael addition reaction channel. Addition of amines to the quinone is followed by a concerted 1,2-migration of a tert -butyl group to afford derivatives of 4-amino-3-nitrocyclohexa-3,5-diene-1,2-dione system. The multistep reaction mechanism was examined using DFT computational methods. Image 1 • Michael addition reaction channel blocked in sterically crowded o-quinones is activated. • 3,5-di-(tert -butyl)-6-nitro-1,2-benzoquinone reacts with amines to give cyclohexadienones. • The addition reaction is accompanied by 1,2-shift of a tert- butyl group along the ring. • The multistep mechanism of the reaction is unveiled by the DFT study. [ABSTRACT FROM AUTHOR]

Graphical abstract Bis- o -semiquinonato nickel attach 1,10-phenanthroline (or 2,2′-dipyridine) forming six-coordinate octahedral complexes. Magnetic susceptibility measurements detect that unpaired electrons of high spin nickel(II) interact with whose of o-semiquinones ferromagnetically. DFT calculations support ferromagnetic exchange. Abstract Novel bis- o -semiquinonato nickel complexes (2,2′-bpy)Ni(3,6-DBSQ) 2 (1) and (1,10-phen)Ni(3,6-DBSQ) 2 (2) was synthesized (2,2′-bpy - 2,2′-dipyridine; 1,10-phen - 1,10-phenanthroline; 3,6-DBSQ-anion-radical of 3,6- tert -butyl- o -benzoquinone). Single crystal X-ray diffraction study indicated distorted octahedral environment of nickel atom in both complexes. Variable temperature magnetic susceptibility measurement detected predomination of ferromagnetic exchange interactions between high spin nickel ion and anion-radicals of o-semiquinones. DFT calculations are in a good agreement with experimental structural and magnetic results. [ABSTRACT FROM AUTHOR]

[Display omitted] A one-stage synthesis of paramagnetic Re(I) compounds based on the reaction of [Re(CO) 5 Br] with spin-labeled N -donor heterocycles was developed. Nitronyl nitroxide derivatives of 1 H- imidazole (L1), 1 H- pyrazole (L2), di(1 H -pyrazol-1-yl)methane (L3) and 4-methyl-2-(1 H -pyrazol-1-yl)quinoline (L4) can easily substitute two coordinated CO molecules in [Re(CO) 5 Br], resulting in a series of paramagnetic fac- [Re(CO) 3 (L i) n Br]· x Solv complexes. Single crystal XRD studies showed that the paramagnetic L1-L4 ligands are coordinated by Re(I) through the imine atoms N of the heterocycles. According to SQUID measurements and EPR spectroscopy data, magnetic behavior of [Re(CO) 3 (L1) 2 Br] (1), [Re(CO) 3 (L2) 2 Br] (2), and [Re(CO) 3 (L3)Br] (3) complexes are typical for biradicals, while [Re(CO) 3 (L4)Br] (4) is typical for monoradical. The combination of Re(I) therapeutic properties and contrasting characteristics of nitroxide radicals in diagnostic magnetic resonance imaging, stability and simplicity of synthesis make [Re(CO) 3 (L i) n Br] valuable model objects for material design for theranostics purposes. [ABSTRACT FROM AUTHOR]

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) (NN2Az) and bis(iminonitroxide) (IN2Az) diradicals and their Cu(hfac)2 (hfac=hexafluoroacetylacetonate) complexes were investigated. NN2Az was shown to have an intramolecular ferromagnetic interaction with Jobs/ kB=+10.0 K ( H=−2 J S1 ⋅S2) between (nitronyl nitroxide) spins, whereas IN2Az was estimated to have a much weaker intramolecular magnetic interaction. The reactions of NN2Az and IN2Az with Cu(hfac)2 gave a 1:2 [{Cu(hfac)2}2(NN2Az)] complex and a 1:1 [Cu(hfac)2(IN2Az)] ⋅C6H12 complex, respectively. [{Cu(hfac)2}2(NN2Az)] 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(IN2Az)] exhibited a ferromagnetic exchange interaction ( Jobs-Cu-R/ kB=+114 K) between the CuII spin and the imino-coordinated iminonitroxide spin. [ABSTRACT FROM AUTHOR]

Doubly protonated diazacrown ether cation (1,4,10,13-tetraoxa-7,16-diazoniacyclooctadecane DC H 2 2+ ) was used for the efficient isolation of the homoleptic platinum complexes [Pt(NO 3 ) 6 ] 2- and [Pt(C 2 O 4 ) 2 ] 2- to crystalline solid phases from solutions containing mixtures of related platinum complexes. DC H 2 2+ molecules in nitric acid solution were shown to prevent the condensation of mononuclear [Pt(H 2 O) n (NO 3 ) 6-n ] n−2 species. [ABSTRACT FROM AUTHOR]

Four coordinated bis-o-semiquinonato nickel complexes interact with pyridine forming five- or six-coordinated compounds. Coordination number and structure of the product depends on the nature of o-quinonato ligand and synthetic conditions. (Py) 2 Ni(3,6-DBSQ) 2 ·Tol has trans-arrangement of pyridine ligands whereas in it analog – (Py) 2 Ni(4,5-N,N′-pipe-3,6-DBSQ) 2 pyridine molecules occupy cis-positions (3,6-DBSQ – anion-radical of 3,6-di- tert -butyl-o-benzoquinone; 4,5-N,N′-pipe-3,6-DBSQ – tricyclic 5,8-di( tert -butyl)-2,3-dihydro-1,4-ethanoquinoxaline-6,7-dione). The structure of six-coordinated compounds is close to octahedral which promotes high values of effective magnetic moments and the predomination of ferromagnetic exchange interactions. In spite of different geometries complexes demonstrate very close magnetic behavior. Using 1:1 stoichiometric ratio allows to obtain five-coordinated nonsolvated square-pyramidal complex (Py)Ni(3,6-DBSQ) 2 with disordered position of pyridine. The last compound has essentially lower magnetic moment compared to six coordinated analogs. Complex reveals strong metal–ligand antiferromagnetic coupling due to deviation of nickel atom out of the bis-o-semiquinonato plane. Pyridine modified in 4-position by nitronyl-nitroxide radical (4-NIT-Py – 2-(4-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) also coordinate to bis-o-semiquinonato nickel precursors forming (4-NIT-Py) 2 Ni(3,6-DBSQ) 2 and (4-NIT-Py) 2 Ni(4,5-N,N′-pipe-3,6-DBSQ) 2 . Nickel complexes containing different types of free radical ligands were obtained for the first time. However two additional spins do not produce significant changes in their magnetic behavior. [ABSTRACT FROM AUTHOR]

Addition of the cyanomethyl anion to the triple bond of the cyano group in 2-cyano-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazol-3-oxide-1-oxyl with the formation of stable ( Z )-3-amino-3-(4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazol-3-oxide-1-oxyl-2-yl)acrylonitrile is reported. The product yield was dependent on the cyanomethyl anion salt counter-ion and was highest in the case of the potassium salt in liquid ammonia. Crystallization provided at least two polymorphs of the synthesized nitroxide according to single crystal X-ray data. ESR spectroscopy revealed delocalization of unpaired electron spin density into the enaminonitrile substituent. The synthesized nitronyl nitroxide is of interest for the preparation of new polyfunctional nitroxides and as polydentate paramagnetic ligands. [ABSTRACT FROM AUTHOR]

The {[Cu(hfac) 2 LR] 2 [Cu(hfac) 2 ]} ∞ chain-polymer complexes with alkyl-pyridyl-substituted nitroxides LR exhibit phase transitions. The transition temperature increases, while the ratio of the volume of cavity, occupied by R, to the volume of R decreases in the series of compounds with R = i -Pr, n -Pr, Et, CP, n -Bu, Me, MeO. [Display omitted] Reaction of Cu(hfac) 2 with pyridyl-substituted nitronyl nitroxides yielded chain-polymer complexes {[Cu(hfac) 2 LR] 2 [Cu(hfac) 2 ]} ∞ , where LR – 2-(4-R-pyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-3-oxide-1-oxyl, R = Me, MeO, Et, n -Pr, i -Pr, n -Bu, and CP (cyclopentyl). X-ray crystallography experiments proved that the solid state of the investigated compounds has centrosymmetric dimers [Cu(hfac) 2 LR] 2 bonded by the Cu(hfac) 2 fragments into chain polymers. The environment of the Cu atoms in the dimeric fragments undergoes structural rearrangement upon temperature variation. Such transformations cause anomalous temperature dependences of µ eff. We established the relationship between the phase transition temperature and the amount of space accessible for pyridine substituent R. In the complexes containing LMe, LMeO, L n-Bu, and LCP substituents R occupy relatively small amount of space, which results in ordering of R and high transition temperatures of these complexes, whereas the presence of the accessible volume for the substituent disordering leads to increased entropy of the high temperature phase, and, therefore, decreased transition temperature of the complexes with LEt, L i-Pr, and L n-Pr. [ABSTRACT FROM AUTHOR]

• Stable nitronyl nitroxides bearing N -fluoroalkylpyrazolyl substituents. • Reversibility of electrochemical oxidation and reduction. • Crystal structures analyzes based on pairwise interaction energies and NO...ON distances. • Packing Motifs and Magneto-Structural Correlations. The aim of the study was to prepare and investigate structure and properties of a new series of stable nitronyl nitroxides bearing N -fluoroalkylpyrazolyl substituents. According to cyclic voltammetry data, a paramagnet with a difluoromethyl substituent can reversibly undergo electrochemical oxidation and reduction. In contrast, radicals with fluorinated ethyl substituents are electrochemically oxidized reversibly, but their electrochemical reduction is quasi-reversible. Molecular and crystal structures of the nitroxides were confirmed by single-crystal X-ray diffraction analysis. The crystal structures of the radicals were studied quantitatively in terms of pairwise interaction energies and energy framework analysis. Analysis of the energies of molecular pairs revealed that in crystalline phases of all nitroxides, the binding is the strongest in dimers assembled via C–H...O interactions of nitroxide O atoms with pyrazole and/or alkyl H atoms. Other dimers are formed predominantly by C–H...π interactions, and in some cases, their binding energy is almost equal to that for the aforementioned ones. The above contacts are complemented short contacts C–H...A and others, which predetermine the final crystal packing of radicals. A consequence of their packing is the geometry of relative arrangement of nitroxide groups and, above all, distances O...O between the oxygen atoms of the paramagnetic centers. These distances were found to exceed the sum of van der Waals radii; consequently, in solid phases of the paramagnets, weak antiferromagnetic exchange interactions are predominant (| J/k B | ≤ 2.74 K, H = – 2J·S 1 S 2. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis, structure and photoluminescence of a group of substituted 2-pyrazolylquinolines, including a spin-labelled derivative, are described. A comparative study of photoluminescence from the synthesized compounds demonstrates that introduction of a nitronyl nitroxide radical group results not only in the expected reduction in photoluminescence from the pyrazolylquinoline moiety, but also gives rise to a new red photoluminescence band (maximum at 692nm in acetonitrile) from the radical fragment. [Copyright &y& Elsevier]

Abstract: It has been shown that the reaction of Ni(allyl)2 with (2,6-diisopropylphenyl)diazabutadiene gives the imino-amide Ni complex (1). The imino-amide moiety of this complex undergoes some complicated rearrangements resulting in spontaneous formation of a paramagnetic π-allyl Ni(I) complex. Nickel complexes formed in the system have been studied with ESR, FTIR, 2D NMR, and mass spectrometry. The structure of complex 1 was studied with X-ray diffraction. [Copyright &y& Elsevier]

Abstract: Solid heterospin compounds based on Cu(hfac)2 complexes with a new group of nitronyl nitroxides bearing different azine-N-oxide substituents at position 2 of the 2-imidazoline ring (L n ) were studied. The major factor responsible for the change in the magnetic characteristics of the [Cu(hfac)2L1] complex with triazine nitronyl nitroxide with temperature was shown to be the specific pairwise packing of heterospin molecules with the dominant antiferromagnetic exchange between the radical fragments of adjacent molecules. For complexes of Cu(hfac)2 with 1-oxoazin-2-yl-substituted nitronyl nitroxides L2 and L4, 7-membered metallocycles were obtained, although they form rarely. It was shown that polymer chains formed in the solid complex with spin-labeled pyrazine-N-oxide [(Cu(hfac)2)3(L3)2] due to the cross-linking of {(Cu(hfac)2)2(L3)2} binuclear fragments via the bridging [Cu(hfac)2]. [Copyright &y& Elsevier]

It is shown that SNH approach opens new possibilities in the synthesis of polyfunctional nitronyl and imino nitroxides. It is found that the interaction of 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl lithium salt Li1 with 3,6-diaryl-1,2,4-triazines leads to formation of the corresponding triazines bearing nitronyl nitroxide or imino nitroxide substituent at position 5 of the heterocycle. The reaction of Li1 with pyridazine-N-oxide gives rise to nitroxide with buten-3-ynyl substituent 5. Spin-labeled 5 could be readily transformed by the use of 1,3-dipolar and nucleophilic addition reactions, as well as oxidative coupling, that gives a large group of new paramagnets: 2-(1H-pyrazol-5-yl)vinyl-, 2-ethynylcyclopropyl-, 2-(3-(ethoxycarbonyl) isoxazol-5-yl)vinyl-, 1-(pyrrolidin-1-yl)but-3-ynyl-substituted nitronyl nitroxide and a diradical - 2,2'-((1E,7E)-octa-1,7-dien-3,5-diyne-1,8-diyl)bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl). The new nitroxides were characterized by X-ray single crystal data, ESR and static magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

Polymer-chain complexes Cu(hfac)2LR represent an interesting type of molecular magnets exhibiting thermally induced and light-induced magnetic switching, in many respects similar to a spin crossover. In the majority of these compounds the polymer chain consists of alternating oneand threespin units composed of copper(ll) ions and nitronyl nitroxides. The principal one-dimensional structure of the complexes has previously been assumed to play a key role in the observed magnetic anomalies. Using Q-band electron paramagnetic resonance (EPR) spectroscopy, we have reliably demonstrated that these complexes are indeed one-dimensional in the sense of the topology of their exchange channels; however, the magnetic chains spread across the structural polymer chains and consist solely of spin triads of nitroxide-copper(ll)-nitroxide. Using four selected examples of complexes Cu(hfac)2LR, we have found the exchange coupling values between spin triads of neighboring polymer chains to range from <1 to ca. 10 cm-1. This conclusion could only be reached due to the selective probing of oneand three-spin units by EPR and correlates perfectly with both previous magnetic susceptibility data and quantum chemical calculations performed in this work. These findings give new insights into the cooperativity effects and mechanisms of magnetic anomalies in the Cu(hfac)2LR family of molecular magnets. [ABSTRACT FROM AUTHOR]

Abstract: Unprecedented selective reactions of β-halo-β-trifluoromethylstyrenes with secondary amines under different conditions were discovered. Depending on the electronic properties of the starting styrenes and the reaction parameters, two pathways were found. With neat secondary amines a series of α-trifluoromethyl-β-aryl enamines were prepared in high yields. In contrast, the reactions of the mentioned styrenes with the same amines in polar solvents by substitution of all halogen atoms gave vinylogous guanidinium salts. Possible reaction mechanisms are discussed. [Copyright &y& Elsevier]

Abstract: Chain complex of copper(II) hexafluoroacetylacetonate with pyrazole-substituted nitronyl nitroxide containing exchange-coupled copper(II)–nitroxide clusters has been studied using electron paramagnetic resonance (EPR) spectroscopy. The structural rearrangements at low temperatures induce spin transitions in one half of the copper(II)–nitroxide clusters and effectively lead to reversible diamagnetic dilution. This results in significant changes of EPR spectra and allows us to obtain the value of dipole–dipole interaction in exchange-coupled spin pair as well as the value of exchange interaction between neighboring pairs. [Copyright &y& Elsevier]

Abstract: It was established that the reactions of pyrazol-3-yl-substituted nitronyl nitroxide (HL 1) and pyrazol-3-yl-substituted imino nitroxide (HL 3) with Cu(II) acetate lead to self-assembly of the Cu4(OH)2(OAc)4(DMF)2(L1)2 tetranuclear and Cu2(OAc)2(H2O)2(L3)2 dinuclear complexes, respectively. The reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted nitronyl nitroxide (HL 2) gave unexpected solid Cu2(H2O)2(L6)2 ·2DMF, in which L 6 is a deprotonated 5-carboxy-pyrazol-3-yl-substituted nitronyl nitroxide, formed as a result of cleavage of an ester bond in the starting HL 2. A similar transformation of the paramagnetic ligand was observed in the reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted imino nitroxide (HL 4). It led to the formation of Cu2(DMF)2(L7)2, where L 7 is deprotonated 2-(5-carboxy-1H-pyrazol-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide. An X-ray diffraction study indicated that in Cu4(OH)2(OAc)4(DMF)2(L1)2 and Cu2(OAc)2(H2O)2(L3)2, the L 1 and L 3 paramagnetic ligands perform the bridging cyclic tridentate function, while in Cu2(H2O)2(L6)2 ·2DMF and Cu2(DMF)2(L7)2, the paramagnetic L 6 and diamagnetic L 7 are bridging bicyclic tetradentate ligands. The magnetic behavior of complexes with coordinated nitronyl nitroxide – Cu4(OH)2(OAc)4(DMF)2(L1)2 and Cu2(H2O)2(L6)2 ·2DMF is dictated by the dominant antiferromagnetic exchange interactions, which is confirmed by quantum-chemical data. The magnetic susceptibility of Cu2(OAc)2(H2O)2(L3)2 reflects the competition between the antiferromagnetic and ferromagnetic components, of which the latter is due to electron coupling in the Cu(II)←N=C–N∸O exchange channels. EPR data confirm the results received from static magnetic measurements for multispin solids. [Copyright &y& Elsevier]

Thermally induced spin transitions in a family of heterospin polymer chain complexes of Cu2+ hexafluoroacetylacetonate with two pyrazole-substituted nitronyl nitroxides are studied using electron paramagnetic resonance (EPR) spectroscopy. The structural rearrangements at low temperatures induce spin transitions in exchange-coupled spin triads of nitroxide-copper(II)-nitroxide. The values of exchange interactions in spin triads of studied systems are typically on the order of tens to hundreds of inverse centimeters. The large magnitude of exchange interaction determines the specific and very informative peculiarities in EPR spectra due to the predominant population of the ground state of a spin triad and spin exchange processes. The variety of these manifestations depending on structure and magnetic properties of spin triads are described. EPR is demonstrated as an efficient tool for the characterization of spin transitions and for obtaining information on the temperature-dependent sign and value of the exchange interaction in strongly coupled spin triads. [ABSTRACT FROM AUTHOR]

Heterospin complexes [Cu(SQ)2Py]-C7H8, Cu(SQ)2DABCO, and [Cu(SQ)2NIT-mPy]-C6H6, where Cu(SQ)2 is bis(3,6-di-tert-butyl-o-benzosemiquinonato)copper(II), DABCO is 1 ,4-diazabicyclo(2,2,2)octane, and NIT-mPy is the nitronyl nitroxide 2-(pyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide- 1-oxyl, have been synthesized. The molecules of these complexes have a specific combination of the intramolecular ferro- and antiferromagnetic exchange interactions between the odd electrons of Cu(ll) and SQ ligands, characterized by large exchange coupling parameters ∣J∣ ≈ 100–300 cm-1. X-ray and magnetochemical studies of a series of mixed-ligand compounds revealed that an extra ligand (Py, NIT- mPy, or DASCO) coordinated to the metal atom produces a dramatic effect on the magnetic properties of the complex, changing the multiplicity of the ground state. Quantum chemical analysis of magnetostructural correlations showed that the energy of the antiferromagnetic exchange interaction between the odd electrons of the SQ ligands in the Cu(SQ)2 bischelate is extremely sensitive to both the nature of the extra ligand and structural distortions of the coordination unit, arising from extra ligand coordination. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of [Co6(O)2Piv10Thf3H2O]·1.5Thf, where and Thf=tetrahydrofuran, with nitroxides 2,4,4,5,5-pentamethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (NIT-Me) and/or 2,4,4,5,5-pentamethyl-4,5-dihydro-1H-imidazole-1-oxyl (Im-Me) leads to simultaneous transformation of both the polymetallic core and the nitroxides. New polynuclear complexes: , , , , L6[Co6(O)4Piv9(H2O)2]·2HPiv, , ,, and have been synthesized and characterized by X-ray crystallography; in these complexes, L1-L5 are modified molecules of the starting NIT-Me and/or Im-Me: Display Omitted [Copyright &y& Elsevier]

Abstract: An effective procedure has been developed for the synthesis of the potassium salt of 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide-2-carboxylic acid K(1). The salts of 4,4,5,5-tetramethyl-1-oxyl-4,5-dihydro-1H-imidazole-2-carboxylic acid X(2) are kinetically much more stable than K(1). Due to this, a series of heterospin complexes Cu(2)2(CH3OH)2, Cu(2)2(H2O)2, Cu(2)2, Co(2)2(CH3OH)2, Ni(2)2(H2O)2, Ni(2)2(py)2, and Ni(2)2(dipy)·H2O were isolated. For K(2), Cu(2)2(CH3OH)2, and Ni(2)2(py)2, crystal and molecular structure has been determined. For Cu(2)2 and Ni(2)2(bipy), cooperative magnetic ordering has been recorded at 16.6 and 4.6K, respectively. [Copyright &y& Elsevier]

Abstract: A series of mixed-metal solid solutions M x Cu1− x (hfac)2L (M=Mn, Ni, and Co) liable to undergo thermally induced spin transitions have been synthesized. The structure and magnetic properties of the compounds have been investigated. By varying the metal to be incorporated in the complex (Mn, Ni, or Co) and the value of x, one can control the character of the magnetic anomaly. [Copyright &y& Elsevier]

Abstract: Synthetic procedures have been developed to prepare heterospin compounds based on the [Mn6(O)2Piv10] polymetallic nucleus, where , and nitronyl nitroxides NIT-R, where R=H, Et, p-Py, n-butyl-pyrazole: [Mn6(O)2Piv10(NIT-H)4]·0.5CH2Cl2, [Mn6(O)2Piv10(NIT-Et)3HPiv]·0.5C7H16, [Mn6(O)2Piv10(NIT-Et)4], [(EtOAc)3Mn6(O)2Piv10(Ac–Ac)Mn6(O)2Piv10(EtOAc)3], [Mn6(O)2Piv10(Me2CO)2(H2O)], [Mn6(O)2Piv10(NIT-p-Py)4], [Mn6(O)2Piv10(NIT-p-Py)4]·0.5C7H16, [Mn6(O)2Piv10(NIT-p-Py)2(H2O)], [Mn6(O)2Piv10(NIT-n-Bu-Pz)2(HPiv)2], and [Mn6(O)2Piv10(NIT-n-Bu-Pz)(Thf)(H2O)]·C6H14. The structure of these compounds has been studied. To obtain highly dimensional structures demands structural complementarity of the [Mn6(O)2Piv10] and NIT-R nuclei, which is only possible when R=CH3. [Copyright &y& Elsevier]

Methods for the synthesis of a new family of nitronylnitroxides, iminonitroxides, and their precursors with 2-hydroxyphenyl or 3-hydroxypyridin-2-yl substituents in the side chain have been developed. Five heterospin chelates of Cu(II) with deprotonated iminonitroxides have been isolated. Their structure and magnetic properties have been studied. In all complexes, ferromagnetic intramolecular exchange interactions take place (J∼40–350 cm−1). [Copyright &y& Elsevier]

A new Gd III complex with the tridentate chelating redox ligand 2,4,6,8-tetrakis( tert -butyl)-9-hydroxyphenoxazinone was synthesized and studied by X-ray crystallography, ESR spectroscopy and magnetic measurements. The rigid tricyclic framework of the ligands ensures the formation of a nine-coordinate environment of Gd III surrounded by three nitrogen and six oxygen atoms in the form of a tricapped trigonal prism. [ABSTRACT FROM AUTHOR]

Investigates by way of a study, the magnetic susceptibility of nickel complexes. Synthesis of the complexes; Description of the structures of the complexes; Magnetic measurements of the complexes.

The polycyclic oxygen-containing spiro-heterocycles 6-oxa-2,9-diazadispiro[4.1.4.1]dodeca-1,8-diene-4,11-dione 2,9-dioxide and 3,3a,6,6a-tetrahydrospiro(furo[2,3-c]pyrrole-2,3’-pyrrol)-4’(5’H)-one 1’,5-dioxide were formed in the reactions of 2,4-dihydro-3H-pyrrol-3-one 1-oxide with benzaldehyde. [Copyright &y& Elsevier]

• New method for preparation of derivatives of 3 H -phenoxazin-3-one was studied. • The condensation reaction of 3 H -phenoxazin-3-one with arylamines was studied. • Redox activity of 3 H -phenoxazin-3-one studied by cyclic voltammetry. • Reduction of 3 H -phenoxazin-3-one affords its stable radical anion and dianion. • Very rare for radical anions intense fluorescence was detected. A sterically crowded 6,8-di-(tert -butyl)-3 H -phenoxazin-3-one 3 was prepared by coupling 3,5-di-(tert -butyl)- o -benzoquinone with p -aminophenol. The molecular structure of 3 was established with the aid of X-ray crystallography and the redox activity studied using cyclic voltammetry and ESR spectroscopy. The reduction of 3 with a potassium mirror led to the formation of persistent radical anion 3a and dianion 3b which were characterized by their absorption and luminescence spectra. [ABSTRACT FROM AUTHOR]

The article discusses the temperature dependence of the exchange interaction among copper(II) ion and nitroxide ligands in "breathing" crystals Cu(hfac)2LR. High-field EPR is a convenient tool to study temperature dependence and the results makes these crystals makes them an interesting compounds in research regarding creation of molecular-magnetic switches and spin devices.

Spontaneous solvent-controlled solid-state transformations were observed for a series of polymeric chain solvates [Cu(hfac) 2 L Pr ]·0.5Solv (Solv = (CH 3 ) 2 CO, THF, CH 2 Cl 2 , CH 2 Br 2 , CHCl 3 ) with 2-(1-propyl-1 H -imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-3-oxide-1-oxyl (L Pr ) under ambient conditions. The conversion of powdered polymeric chain [Cu(hfac) 2 L Pr ]·0.5THF and [Cu(hfac) 2 L Pr ]·0.5(CH 3 ) 2 CO complexes, accompanied by the loss of solvent molecules, occurs completely to binuclear [Cu(hfac) 2 L Pr ] 2 within a day. On the other hand, in the case of [Cu(hfac) 2 L Pr ]·0.5Solv (Solv = CH 2 Cl 2 , CH 2 Br 2 , CHCl 3 ), the partial transformation into a desolvated 1D polymer [Cu(hfac) 2 L Pr ] or its mixture with [Cu(hfac) 2 L Pr ] 2 takes much longer time. The magnetic behavior of the isostructural solvates is highly sensitive to the included solvent molecules. The complexes with THF, CH 2 Cl 2 , CH 2 Br 2 , and CHCl 3 undergo a transition to a magnetically ordered state below 4 K, a phenomenon reported for the first time for the polymeric chain Cu(II) complexes with a "head-to-tail" motif. [Cu(hfac) 2 L Pr ]·0.5THF and [Cu(hfac) 2 L Pr ]·0.5(CH 3 ) 2 CO undergo a spin transition at 190 K, which is induced by the transformation of the Cu atom environment. In the case of the THF solvate, the increase in the distances between the Cu and oxygen atoms leads to enhanced ferromagnetic exchange interactions, while in the acetone solvate, the nitroxide coordination type changes from axial to equatorial at certain coordination sites, resulting in the emergence of strong antiferromagnetic exchange.

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 P2 1 /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., (© 2024 Wiley-VCH GmbH.)

A simple and highly effective methodology for the cross-coupling of heteroaryl iodides with NN-AuPPh 3 at room temperature is reported. The protocol is based on a novel catalytic system consisting of Pd 2 (dba) 3 ·CHCl 3 and the phosphine ligand Me CgPPh 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.

Spin-labeled cyrhetrenes [(NNCp)Re(CO) 3 ] and [(INCp)Re(CO) 3 ], where NNCp is nitronyl nitroxide 2-(η 5 -cyclopentadienyl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H -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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

We report a multifrequency nuclear magnetic resonance (NMR) study of heterospin complexes [Eu(SQ) 3 L n ], 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) 3 Dipy] is a thermodynamically stable complex; hence, one can study [Eu(SQ) 3 Dipy] solutions without special precautions. We report an X-ray structure of the [Eu(SQ) 3 Dipy]·C 6 D 6 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.

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) 2 L 2-Me ], binuclear [{Cu(hfac) 2 } 2 (H 2 O)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 (H 2 O) 2 ] and [Cu(hfac) 2 (L 2-Br ) 2 ]·2[Cu(hfac) 2 H 2 O], one-dimensional polymers [Cu(hfac) 2 L 2-Br ] n and [Cu(hfac) 2 L 6-Br ] n , and cyclic dimers [Cu(hfac) 2 L 5-Me ] 2 , [Cu(hfac) 2 L 5-Br ] 2 , and [Cu(hfac) 2 L 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-O NO bonds in {CuO 6 } 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 Cu 2+ 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 Cu 2+ ions and nitroxides., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

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.

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 [Ni 2 (A 1 )(L 2 ) 2 (Piv)(MeOH)], [Ni 2 (L 1 )(A 2 ) 2 (Piv)(H 2 O)], [Co 2 (A 1 )(L 2 ) 2 (Piv)(MeOH)], and [Co 3 (L 1 ) 2 (A 2 ) 2 (Piv) 2 ], in which L n and A n 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(B 1 )(B 2 ) 2 ](NO 3 ) 2 . The series of mixed-radical complexes may include compounds with nontrivial magnetic properties such as [Co 2 (A 1 )(L 2 ) 2 (Piv)(MeOH)], which experiences bulk magnetic ordering below 3.5 K.

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-O nitroxide 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.

Spin-labelled compounds are widely used in chemistry, physics, biology and the materials sciences but the synthesis of stable high-spin organic molecules is still a challenge. We succeeded in synthesising heteroatom analogues of the 1,1,2,3,3-pentamethylenepropane (PMP) diradicals with two nitronyl nitroxide (DR1) and with two iminonitroxide (DR2) fragments linked through the C(sp2) atom of the nitrone group. According to magnetic susceptibility measurements, EPR data and ab initio calculations at the (8,6)CASSCF and (8,6)NEVPT2 levels, DR1 and DR2 have singlet ground states. The singlet–triplet energy splitting (2J) is low (J/k=−7.4 for DR1 and −6.0 K for DR2), which comes from the disjoint nature of these diradicals. The reaction of [Cu(hfac)2] with DR1 gives rise to different heterospin complexes in which the diradical acts as a rigid ligand, retaining its initial conformation. For the [{Cu(hfac)2}2(DR1)(H2O)] complex, sufficiently strong ferromagnetic interactions (J1/k=42.7 and J2/k=14.1 K) between two coordinating CuII ions and DR1 were revealed. In [{Cu(hfac)2}2(DR1)(H2O)][Cu(hfac)2(H2O)], the very strong and antiferromagnetic (J/k=−416.1 K) exchange interaction between one of the coordinating CuII ions and DR1 is caused by the very short equatorial CuO bond length (1.962 Å).

Metal complexation reactions of N-t-butyl-N-oxidanyl-2-amino(nitronyl nitroxide) diradical (1) with M(hfac)2 (M: Mn or Cu) were investigated. These reactions were found to be very sensitive to the type of metal ion employed. Complex [Mn(hfac)2·1], consisting of Mn(hfac)2 and diradical 1, was readily prepared by mixing the components. However, the reaction of Cu(hfac)2 with 1 or N-t-butyl-N-oxidanyl-2-amino(iminonitroxide) diradical (2) involved the reduction of the diradical to the N-t-butyl-N-oxidanide-2-amino(iminonitroxide) radical anion (3) and finally produced the polymer-chain complex [Cu2(hfac)2·32·Cu(hfac)2]n. The structures of these complexes were elucidated by X-ray analysis, and their magnetic properties were investigated in detail. The temperature dependence of χpT (χp: magnetic susceptibility) for [Mn(hfac)2·1] exhibited a strong antiferromagnetic interaction (H = -2JS1·S2, J/kB = -217 K) between the Mn(II) spin (S = 5/2) and the diradical 1 spin (S = 1). However, the χpT-T plots for [Cu2(hfac)2·32·Cu(hfac)2]n indicated the presence of several magnetic interactions: a large ferromagnetic interaction (J/kB = 510 K) between iminonitroxide 3 and the imino-coordinating Cu(II) atom, a moderately large ferromagnetic interaction (J/kB = 58 K) between the iminonitroxide and (iminonitroxide oxygen)-coordinating Cu(hfac)2, and a weak antiferromagnetic interaction (J/kB = -1.4 K) between the two Cu(hfac)-3 moieties within a Cu2O2 square.

Polymer-chain complexes Cu(hfac)(2)L(R) represent an interesting type of molecular magnets exhibiting thermally induced and light-induced magnetic switching, in many respects similar to a spin crossover. In the majority of these compounds the polymer chain consists of alternating one- and three-spin units composed of copper(II) ions and nitronyl nitroxides. The principal one-dimensional structure of the complexes has previously been assumed to play a key role in the observed magnetic anomalies. Using Q-band electron paramagnetic resonance (EPR) spectroscopy, we have reliably demonstrated that these complexes are indeed one-dimensional in the sense of the topology of their exchange channels; however, the magnetic chains spread across the structural polymer chains and consist solely of spin triads of nitroxide-copper(II)-nitroxide. Using four selected examples of complexes Cu(hfac)(2)L(R), we have found the exchange coupling values between spin triads of neighboring polymer chains to range from <1 to ca. 10 cm(-1). This conclusion could only be reached due to the selective probing of one- and three-spin units by EPR and correlates perfectly with both previous magnetic susceptibility data and quantum chemical calculations performed in this work. These findings give new insights into the cooperativity effects and mechanisms of magnetic anomalies in the Cu(hfac)(2)L(R) family of molecular magnets.

We show that the S(N)(H) approach opens up new possibilities in the synthesis of hetaryl-substituted nitronyl nitroxides. The reaction of 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl lithium salt with pyridine-, pyrimidine-, pyrazine-, isoquinoline-, phthalazine-, quinoxaline-, and 1,2,4-triazine-N-oxides readily gives rise to the corresponding paramagnetic hetarenes. The reaction of this salt with quinoxaline-1,4-dioxide enabled the synthesis of the first nitronyl nitroxide biradical with two spin-labeled fragments in the vicinal positions of the heteroaromatic cycle; the persistent biradicals of this type were not known earlier. The characterizations of all persistent radicals obtained by S(N)(H) synthetic strategy include X-ray crystal structures, EPR investigation, and static magnetic susceptibility measurements.

We succeeded in synthesizing of a whole family of isostructural solvates of the copper(II) hexafluoroacetylacetonate complex with pyrazolyl-substituted nitronyl nitroxide (L): Cu(hfac)2L x 0.Solv. The main feature inherent in nature of Cu(hfac)2L x 0.5 Solv single crystals is their incredible mechanical stability and ability to undergo reversible structural rearrangements with temperature variation, accompanied by anomalies on the mu(eff(T)) dependence. Structural investigation of the complexes over a wide temperature range before and after the structural transition and the ensuing magnetic phase transition showed that the spatial peculiarities of the solvent molecules incorporated into the solid govern the character of the mu(eff(T)) dependence and the temperature region of the magnetic anomaly. Thus, doping of crystals with definite solvent molecules could be used as an efficient method of control over the magnetic anomaly temperature (T(a)). The investigation of this special series of crystals has revealed the relationship between the chemical step and the magnetic properties. It was shown that "mild" modification of T(a) for Cu(hfac)2L x 0.5 Solv required a much smaller structural step than the typical change of one -CH2- fragment in a homologous series in organic chemistry. Quantum-chemical calculations with the use of X-ray diffraction data allowed us to trace the character of changes in the exchange interaction parameters in the range of the phase transition. In the temperature range of the phase transition, the exchange parameter changes substantially. The gradual decrease in the magnetic moment, observed in most experiments during sample cooling to T(a), is the result of the gradual increase in the fraction of the low-temperature phase in the high-temperature phase.

Reactions between Cu(hfac)2 and nitronyl nitroxide biradicals 1,4-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]butane (L4) and 1,8-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]octane (L8) gave respectively a framework compound [Cu(hfac)2]2L4 and a layered polymer compound [Cu(hfac)2]2L8. The framework of [Cu(hfac)2]2L4 consists of 66-membered condensed metallocycles. Inside the framework, the structure has macrohelixes (pitch approximately 25 A) extending along the [001] crystallographic direction. All the helixes have the same direction of winding; the crystals, therefore, are optically active, the structure corresponding either to P-isomer (P4(1)2(1)2) or to M-isomer (P4(3)2(1)2). The long distances between the Cu atoms and the O atoms of the coordinated >N-O groups (Cu-O 2.351-2.467 A) are responsible for ferromagnetic exchange interactions in Cu2+-O-N< and >N-O-Cu2+-O-N< exchange clusters.

The copper(II) complex formation equilibria of N-(2-carboxyethyl)chitosans with three different degrees of substitution (DS = 0.42, 0.92, and 1.61) were studied in aqueous solution by pH-potentiometric and UV-spectrophotometric techniques. It was demonstrated that the complexation model of CE-chitosans depends on DS: the [Cu(Glc-NR(2))(2)] complexes are predominant for two lower substituted samples ("bridge model", log beta(12) = 10.06 and 11.6, respectively), whereas the increase of DS leads to formation mainly of the [Cu(Glc-NR(2))] complexes ("pendant model", log beta(11) = 6.41). As a model for copper complexation with a disubstituted residue of CE-chitosan, the complex of N-methyliminodipropionate [CuMidp(H(2)O)].(H(2)O) was synthesized and structurally characterized by XRD. The unit cell consists of two crystallographically nonequivalent Cu atoms having slightly distorted square pyramidal coordination; Midp constitutes the basal plane of the pyramid and acts as a tetradentate NO(3) chelate-bridging ligand by the formation of two six-membered chelate rings (average Cu-O 1.99 A, Cu-N 2.04 A) and a bridge via carbonyl O atom (average Cu-O 1.99 A), an apical position is occupied by a water molecule (average Cu-Ow 2.30 A).