Effects of wavelength and substituents on iron(III) photoreduction in trans-[Fe(R-sal-R‵-en)(CH3OH)(NCS)] complexes

Photoredox reactions in irradiated methanolic solutions of trans-[Fe(R′-sal-R₂-en) (CH₃OH)(NCS)] complexes, where R′-sal-R₂-en^2? are tetradentate open-chain N,N′-1,1-R₂-ethylenebis(R′-salicylideneiminato) ligands (R?=?H or CH₃; R′?=?H, 5-Cl, 5-Br, 3,5-Br₂, 3-OCH₃, 4-OCH₃), have been explored and a mechanism suggested. The complexes are redox-stable in the dark in methanol. Continuous irradiation of solutions in the region of intraligand (IL) or ligand-to-metal charge transfer (LMCT) transitions leads to photoreduction of Fe(III) to Fe(II) and formation of formaldehyde (CH₂O). Formation of polystyrene-containing bonded NCS, when irradiating the complexes in the presence of styrene used as a radical scavenger, indicates that the primary photoreduction of Fe(III) to Fe(II) is accompanied by oxidation of NCS^? to the ^?NCS radical. R′-sal-R₂-en ligands have little effect on the photoinduced redox processes. The quantum yield of Fe(II) formation, Φ_Fe(II), as a quantitative parameter of photoredox efficiency, decreases significantly with increasing wavelength of incident radiation, and is slightly influenced by the peripheral groups, R, of R′-sal-R₂-en.     

The gamma radiolysis of aqueous solutions of ferriciminodiacetate and ferricglycinate

Radiolytic G-values were determined for [−Fe(III)IDA], Fe(II), (−IDA) and CHO-COOH in deoxygenated aqueous solutions of Fe(III)IDA and Fe(III)gly, and in the presence of scavengers, t-butanol, 2-propanol, methanol, sodium formate and O₂. The metal ion was reduced by e^-_aq, H or secondary radicals HO₂, CO⁻₂, CH₂-OH and (CH₃)₂C-OH, while the OH radical did so indirectly through α-hydrogen abstraction from the ligand followed by intramolecular electron transfer. The rate constant k[OH + Fe(III)IDA], determined by the competition kinetics method at pH 2.0, was 1.7 × 10⁸ M^-1 s^-1.     

Photoredox Reactions Occurring in Methanolic Solutions of Iron(III) Azido Complexes with <Emphasis Type="Italic">N,N</Emphasis>′-Ethylenebis (salicylaldiminato) <Emphasis Type="Italic">Schiff</Emphasis> Base Derivatives

Summary. Photoredox reactions occurring in irradiated methanolic solutions of trans-[Fe(N ₂ O ₂ ) (CH₃OH)N₃], where N ₂ O ₂ ^2– are tetradentate open-chain N ₂ O ₂ -Schiff base N,N-ethylenebis(R-salicylaldiminato) or N,N-1-methylethylenebis(R-salicylaldiminato) ligands denoted as R-salen and R-sal(Me)en, respectively (R=H, 5-Cl, 5-Br, 4-OCH₃), have been investigated and their mechanism has been proposed. The complexes are redox stable in the dark. Ultraviolet and/or visible irradiation of methanolic solutions of the complexes induces photoreduction of Fe(III) to Fe(II). As an intermediate, CH₂OH radicals were identified by EPR spin trapping technique. The final product of the photooxidation coupled with the photoreduction of Fe(III) is formaldehyde. The efficiency of the photoredox processes is strongly wavelength dependent and influenced by the peripheral groups R of the tetradentate ligands. Differences between the course of photochemical changes induced by 254nm radiation and the other wavelengths of incident radiation is rationalized by involving azide anions photoreactivity in observed redox changes.     

Brucinium 3,5‐dinitro­benzoate methanol solvate,methanol disolvate and trihydrate

Crystals of brucinium 3,5‐dinitro­benzoate methanol solvate, C₂₃H₂₇N₂O₄⁺·C₇H₃N₂O₆⁻·CH₃OH, (I), brucinium 3,5‐dinitro­benzoate methanol disolvate, C₂₃H₂₇N₂O₄⁺·C₇H₃N₂O₆⁻·2CH₃OH, (II), and brucinium 3,5‐dinitro­benzoate trihydrate, C₂₃H₂₇N₂O₄⁺·C₇H₃N₂O₆⁻·3H₂O, (III), were obtained from methanol [for (I) and (II)] or ethanol solutions [for (III)]. The brucinium cations and 3,5‐dinitro­benzoate anions are linked by ionic N—H⁺⋯O⁻ hydrogen bonds. In the crystals of (I), (II) and (III), the brucinium cations exhibit different modes of packing, viz. corrugated ribbons, pillars and corrugated monolayer sheets, respectively. While in (III), the amide O atom of the brucinium cation participates in O—H⋯O hydrogen bonds, in which water mol­ecules are the donors, in (I) and (II), the amide O atom of the brucinium cation is involved in weak C—H⋯O hydrogen bonds and other brucinium cations are the donors.     

Mechanism of Photoinduced Processes in Solutions of Iodo Iron(III) Complexes Containing Schiff Base Ligands

Summary.  The mechanisms of photoinduced processes occurring in methanolic solutions of trans-[Fe(4-R-benacen)(CH₃OH)I] (4-R-benacen ²⁻ : N,N′-ethylene-bis-(4-R-benzoylacetoneiminato) tetradentate open-chain Schiff bases with R = H, Cl, Br, CH₃, OCH₃, or NO₂) were investigated by electronic absorption spectroscopy and EPR spin trapping. The complexes are redox-stable in the dark both in the solid state and in methanolic solutions. Ultraviolet and/or visible irradiation in methanol induces photoreduction of Fe(III) to Fe(II). No formation of I^˙ or was observed. ^˙CH₂OH radicals and/or solvated electrons were identified in irradiated systems using nitrosodurene or 5,5-dimethyl-1-pyrroline-N-oxide as spin traps. The final product of the photooxidation coupled with the photoreduction of Fe(III) is formaldehyde, the molar ratio of Fe(II) and CH₂O being close to 2:1. The efficiency of the photoredox process is strongly wavelength dependent and influenced by the peripheral groups R of the tetradentate ligands. It is suggested that the primary photoredox step starts from thermally nonequilibrated ligand-to-metal charge transfer excited states. Received May 2, 2001. Accepted May 30, 2001     

A cyanide‐bridged FeII–NdIII bimetallic assembly with a one‐dimensional ladder‐like chain structure

The title complex, catena‐poly[[[(2,2′‐bipyridine‐1κ²N,N′)tris(methanol‐2κO)(nitrato‐2κ²O,O′)‐μ‐cyanido‐1:2C:N‐cyanido‐1κC‐iron(II)neodymium(III)]‐di‐μ‐cyanido‐1:2′C:N;2:1′N:C] methanol solvate], {[Fe^IINd^III(CN)₄(NO₃)(C₁₀H₈N₂)(CH₃OH)₃]·CH₃OH}_n, is made up of ladder‐like one‐dimensional chains oriented along the c axis. Each ladder consists of two strands based on alternating Fe^II and Nd^III centers connected by cyanide bridges. Furthermore, two such parallel chains are connected by additional cyanide cross‐pieces (the `rungs' of the ladder), which likewise connect Fe^II and Nd^III centers, such that each [Fe(CN)₄(bipy)]²⁻ unit (bipy is 2,2′‐bipyridine) coordinates with three Nd^III centers and each Nd^III center connects with three different [Fe(CN)₄(bipy)]²⁻ units. In the complex, the iron(II) cation is six‐coordinated with a distorted octahedral geometry and the neodymium(III) cation is eight‐coordinated with a distorted dodecahedral environment.     

Cobalt(II), nickel(II) and copper(II) complexes of iso­quinoline‐3‐carbox­ylate

The crystal structures of the title complexes, namely trans‐bis­(iso­quinoline‐3‐carboxyl­ato‐κ²N,O)­bis­(methanol‐κO)cobalt(II), [Co(C₁₀H₆NO₂)₂(CH₃OH)₂], and the corresponding nickel(II) and copper(II) complexes, [Ni(C₁₀H₆NO₂)₂(CH₃OH)₂] and [Cu(C₁₀H₆NO₂)₂(CH₃OH)₂], are isomorphous and contain metal ions at centres of inversion. The three compounds have the same distorted octahedral coordination geometry, and each metal ion is bonded by two quinoline N atoms, two carboxyl­ate O atoms and two methanol O atoms. Two iso­quinoline‐3‐carboxyl­ate ligands lie in trans positions, forming the equatorial plane, and the two methanol ligands occupy the axial positions. The complex mol­ecules are linked together by O—H⋯O hydrogen bonds between the methanol ligands and neighbouring carboxyl­ate groups.     

Syntheses and structures of nickel(II) and copper(II) complexes with biacetyl bis(benzoylhydrazone): one-dimensional self-assembly via π–π interaction and hydrogen bonding

Reactions of Ni(O₂CCH₃)₂·4H₂O and Cu(O₂CCH₃)₂·H₂O with biacetyl bis(benzoylhydrazone) (H₂babh) in alcoholic media afford mononuclear nickel(II) and copper(II) complexes of general formula [M(babh)]. The complexes have been characterized by microanalysis (C, H, N), magnetic susceptibility, and various spectroscopic measurements. X-ray structures of both complexes have been determined. The metal centre in [Ni(babh)] is in square-planar N₂O₂ environment provided by the tetradentate babh²⁻. On the other hand, [Cu(babh)] crystallizes as distorted square-pyramidal [Cu(babh)(CH₃OH)] from methanol. Here the tetradentate babh²⁻ constitutes the N₂O₂ square-base and the O-coordinating methanol occupies the apical site. In the crystal lattice, the molecules of [Ni(babh)] form a one-dimensional π-stacked structure. The [Cu(babh)(CH₃OH)] molecules also form a one-dimensional structure with alternating long and short Cu···Cu distances via intermolecular O–H···N hydrogen bonding and π–π interaction.     

Ruthenium(II) complexes with ferrocene-modified arene ligands: synthesis and electrochemistry

A series of arene-ruthenium complexes of the general formula [RuCl₂{η⁶-C₆H₅(CH₂)₂R}L] with R=OH, CH₂OH, OC(O)Fc, CH₂OC(O)Fc (Fc=ferrocenyl) and L=PPh₃, (diphenylphosphino)ferrocene, or bridging 1,1^′-bis(diphenylphosphino)ferrocene, have been synthesized. Two synthetic pathways have been used for these ferrocene-modified arene-ruthenium complexes: (a) esterification of ferrocene carboxylic acid with 2-(cyclohexa-1,4-dienyl)ethanol, followed by condensation with RuCl₃ · nH₂O to afford [RuCl₂{η⁶-C₆H₅(CH₂)₂OC(O)Fc}]₂, and (b) esterification between ferrocene carboxylic acid and [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}L] to give [RuCl₂{η⁶-C₆H₅(CH₂)₃OC(O)Fc}L]. All new compounds have been characterized by NMR and IR spectroscopy as well as by mass spectrometry. The single-crystal X-ray structure analysis of [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}(PPh₃)] shows that the presence of a CH₂CH₂CH₂OH side-arm allows [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}(PPh₃)] to form an intramolecular hydrogen bond with a chlorine atom. The electrochemical behavior of selected representative compounds has been studied. Complexes with ferrocenylated side arms display the expected cyclic voltammograms, two independent reversible one-electron waves of the Ru(II)/Ru(III) and Fe(II)/Fe(III) redox couples. Introduction of a ferrocenylphosphine onto the ruthenium is reflected by an additonal reversible, one-electron wave due to ferrocene/ferrocenium system which is, however, coupled with the Ru(II)/Ru(III) redox system.     

Bis(triphenylphosphin)iminium-bis(methoxo)phthalocyaninato(2–)ferrat(III) – Synthese und Kristallstruktur

Bis(triphenylphosphine)iminium Bis(methoxo)phthalocyaninato(2–)ferrate(III) – Synthesis and Crystal Structure Chlorophthalocyaninato(2–)ferrate(III) reacts with bis(triphenylphosphine)iminium hydroxide in methanol/acetone solution to yield blue crystals of bis(triphenylphosphine)iminium bis(methoxo)phthalocyaninato(2–)ferrate(III). The complex salt crystallizes as an acetone/methanol solvate (^bPNP)[Fe(OCH₃)₂pc^2–] · (CH₃)₂CO · 1.5 CH₃OH in the triclinic space group P 1 (no. 2) with the cell parameters a = 13.160(5) Å, b = 15.480(5) Å, c = 17.140(5) Å, α = 97.54(5)°, β = 91.79(5)°, γ = 95.44(5)°. The Fe atom is located in the centre of the pc^2– ligand coordinating four isoindole N atoms (N_iso) of the pc^2– ligand and two O atoms of the methoxo ligands in a mutual trans arrangement. The average Fe–O and Fe–N_iso distances are 1.887 and 1.943 Å, respectively. The cation adopts the bent conformation (< P–N–P = 140.4(2)°) with P–N distances of 1.579(3) and 1.575(3) Å.     

Crystal structure and magnetic properties of dinuclear iron(III) complex with ONNO-donor ligand

A new dinuclear Fe(III) complex, [Fe(5-MeOL1)(OH)_0.86(CH₃O)_0.14]₂?2(CH₃OH), [H₂-5-MeOL1 = N,N′-bis(5-methoxy-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine], 1 has been synthesized and characterized by single crystal structure analysis. The structure of 1 consists of two Fe(III) centers with one tetradentate schiff base ligand (N₂O₂) which are bridged by dihydroxo/dimethoxo groups to yield a Fe₂O₂ core. Complex 1 exhibits weak antiferromagnetic exchange interaction between Fe(III) ions with J = ?0.21 cm^–1.     

Dioxygen activation with a cytochrome P450 model. Characterization and electrochemical study of new unsymmetrical tetradentate Schiff-base complexes with iron(III) and cobalt(II)

Salicylaldehyde or 5-bromosalicylaldehyde react with 2,3-diaminophenol to give two unsymmetrical Schiff-bases H₂L¹, H₂L², respectively. With Fe(III) and Co(II), these ligands lead to four complexes: Fe(III)ClL¹, Fe(III)ClL², Co(II)L¹, Co(II)L². The structures of these complexes were determined by mass spectroscopy, infrared and electronic spectra. Cyclic voltammetry in dimethylformamide (DMF) showed irreversible waves for both ligands. In the same experimental conditions, Fe(III)ClL¹ exhibited a reversible redox couple Fe(III)/Fe(II) while the three other complexes showed quasi-reversible systems. The behavior of some of these complexes in the presence of dioxygen and the comparison with cytochrome P450 are described.     

Dinuclear copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with an unsymmetrical exchange fragment

New dinuclear copper(II) complexes with azomethines and hydrazones, which were produced by condensation of substituted salicylaldehyde derivatives with 1,3-diaminopropan-2-ol or carbo(thiocarbo) hydrazide, were studied. The structures of the [Cu₂L(μ-CH₂ClCOO)(CH₃OH)]·(CH₃OH) (L = C₁₇H₁₅N₂O₃) and [Cu₂L²(Cl₃CCO)(CH₃OH)]·H₂O (L² = C₃₂H₄₂N₄O₃) complexes were established by X-ray diffraction. The magnetic properties of these complexes, including the influence of the nature of the substituents in the ligands on exchange interactions, were studied.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 592–596, March, 2005.     

Coordination‐directed one‐dimensional coordination polymers generated from a new oxadiazole bridging ligand and HgX2 (X = Cl,Br and I)

A new 1,3,4‐oxadiazole bridging bent organic ligand, 2,5‐bis{5‐methyl‐2‐[(4‐pyridyl)methoxy]phenyl}‐1,3,4‐oxadiazole, C₂₈H₂₄N₄O₃, L, has been used to create three novel one‐dimensional isomorphic coordination polymers, viz. catena‐poly[[[dichloridomercury(II)]‐μ‐2,5‐bis{5‐methyl‐2‐[(4‐pyridyl)methoxy]phenyl}‐1,3,4‐oxadiazole] methanol monosolvate], {[HgCl₂(C₂₈H₂₄N₄O₃)]·CH₃OH}_n, catena‐poly[[[dibromidomercury(II)]‐μ‐2,5‐bis{5‐methyl‐2‐[(4‐pyridyl)methoxy]phenyl}‐1,3,4‐oxadiazole] methanol monosolvate], {[HgBr₂(C₂₈H₂₄N₄O₃)]·CH₃OH}_n, and catena‐poly[[[diiodidomercury(II)]‐μ‐2,5‐bis{5‐methyl‐2‐[(4‐pyridyl)methoxy]phenyl}‐1,3,4‐oxadiazole] methanol monosolvate], {[HgI₂(C₂₈H₂₄N₄O₃)]·CH₃OH}_n. The free L ligand itself adopts a cis conformation, with the two terminal pyridine rings and the central oxadiazole ring almost coplanar [dihedral angles = 5.994 (7) and 9.560 (6)°]. In the Hg^II complexes, however, one of the flexible pyridylmethyl arms of ligand L is markedly bent and helical chains are obtained. The Hg^II atom lies in a distorted tetrahedral geometry defined by two pyridine N‐atom donors from two L ligands and two halide ligands. The helical chains stack together via interchain π–π interactions that expand the dimensionality of the structure from one to two. The methanol solvent molecules link to the complex polymers through O—H...N and O—H...O hydrogen bonds.     

Containing‐PMBP N2O2‐donors transition metal(II) complexes: Synthesis,crystal structure,Hirshfeld surface analyses and fluorescence properties

Three newly designed containing‐PMBP N₂O₂‐donors complexes, [Co(L¹)(CH₃OH)₂] ( 1 ), [{Zn(L²)(CH₃OH)(H₂O)}₃] ( 2 ) and [Cu₄(L²)₄]?2CHCl₃ ( 3 ), have been synthesized and structurally characterized using elemental analyses, infrared and UV–visible spectroscopies and single‐crystal X‐ray diffraction. X‐ray crystal structure determinations revealed that 1 consists of one Co(II) atom, one completely deprotonated (L¹)^2? unit and two coordinated methanol molecules. Complex 2 consists of three Zn(II) atoms, three completely deprotonated (L²)^2? units, three coordinated methanol molecules and three coordinated water molecules. However, 3 includes four Cu(II) atoms, four completely deprotonated (L²)^2? units and two crystallization chloroform molecules. The Co(II) and Zn(II) atoms in the structures of 1 and 2 adopt slightly distorted octahedral geometries. While, Cu(II) atoms in 3 can be best described as adopting slightly distorted square planar geometries. Complex 2 is a novel structure, and the ratio of H₂L² to Zn(II) atom is 3:3. In addition, two‐, three‐ and three‐dimensional supramolecular structures were constructed for 1 , 2 and 3 . Most importantly, Hirshfeld surface analysis of 1 , 2 and 3 was conducted and fluorescence properties were investigated.     

Magnetism and crystal structure of an N3O3‐coordinated iron(II) complex

The reaction of [FeL(MeOH)₂] {where L is the tetradentate N₂O₂‐coordinating Schiff base‐like ligand (E,E)‐diethyl 2,2′‐[1,2‐phenylenebis(nitrilomethylidyne)]bis(3‐oxobutanoate)(2−) and MeOH is methanol} with 3‐aminopyridine (3‐apy) in methanol results in the formation of the octahedral complex (3‐aminopyridine‐κN¹){(E,E)‐diethyl 2,2′‐[1,2‐phenylenebis(nitrilomethylidyne)]bis(3‐oxobutanoato)(2−)‐κ⁴O³,N,N′,O^3′}(methanol‐κO)iron(II), [Fe(C₂₀H₂₂N₂O₆)(C₅H₆N₂)(CH₄O)] or [FeL(3‐apy)(MeOH)], in which the Fe^II ion is centered in an N₃O₃ coordination environment with two different axial ligands. This is the first example of an octahedral complex of this multidentate ligand type with two different axial ligands, and the title compound can be considered as a precursor for a new class of complexes with potential spin‐crossover behavior. An infinite two‐dimensional hydrogen‐bond network is formed, involving the amine NH group, the methanol OH group and the carbonyl O atoms of the equatorial ligand. T‐dependent susceptibility measurements revealed that the complex remains in the high‐spin state over the entire temperature range investigated.     

Dinuclear cobalt and nickel complexes of a mercaptoacetic acid substituted 1,2,4‐triazole ligand: syntheses,structures and urease inhibitory studies

Because of its versatile coordination modes and strong coordination ability, the mercaptoacetic acid substituted 1,2,4‐triazole 2‐{[5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐3‐yl]sulfanyl}acetic acid ( H₂L ) was synthesized and characterized. Treatment of H₂L with cobalt and nickel acetate afforded the dinuclear complexes {μ‐3‐[(carboxylatomethyl)sulfanyl]‐5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐4‐ido‐κ²N¹,N⁵:N²,O}bis[aqua(methanol‐κO)cobalt(II)] methanol disolvate, [Co₂(C₉H₆N₄O₂S)₂(CH₃OH)₂(H₂O)₂]·2CH₃OH ( 1 ), and {μ‐3‐[(carboxylatomethyl)sulfanyl]‐5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐4‐ido‐κ²N¹,N⁵:N²,O}bis[diaquanickel(II)] methanol disolvate dihydrate, [Ni₂(C₉H₆N₄O₂S)₂(H₂O)₄]·2CH₃OH·2H₂O ( 2 ), respectively. Complex 1 crystallized in the monoclinic space group P2₁/c, while 2 crystallized in the tetragonal space group I4₁/a. Single‐crystal X‐ray diffraction studies revealed that H₂L is doubly deprotonated and acts as a tetradentate bridging ligand in complexes 1 and 2 . For both of the obtained complexes, extensive hydrogen‐bond interactions contribute to the formation of their three‐dimensional supermolecular structures. Hirshfeld surface analysis was used to illustrate the intermolecular interactions. Additionally, the urease inhibitory activities of 1 , 2 and H₂L were investigated against jack bean urease, where the two complexes revealed strong urease inhibition activities.     

Bis[bis­(methoxy­carbimido)amine‐κ2N,N′]bis­(perchlorato‐κO)copper(II) bis­[bis­(methoxy­carbimido)amine‐κ2N,N′]bis­(methanol‐κO)copper(II) bis­(perchlorate) methanol disolvate

The title compound, [Cu(ClO₄)₂(C₄H₉N₃O₂)₂][Cu(C₄H₉N₃O₂)₂(CH₄O)₂](ClO₄)₂·2CH₃OH, comprises two independent Cu^II species lying on different inversion sites. In the Cu complexes, a distorted octa­hedral geometry arises (from basic square‐planar N₄ coordination) from the weak coordination of two perchlorate ions (as Cu—O) in one species and two methanol mol­ecules in the other (also as Cu—O). Inter­actions between the O atoms of the perchlorate anions or methanol groups and the imide or amine NH groups afford an extensive inter­molecular hydrogen‐bonding network.     

Solution Properties of Azidokojatoiron(III) Complexes

The formation of iron(III) complexes with chelating azidokojate anions L⁻ was investigated in aqueous solutions as a function of the pH and the c(Fe³⁺):c(HL) molar ratio. Based on the stability constants, the distribution among the above complexes, [Fe(H₂O)₆]³⁺, and [Fe(H₂O)₅(OH)]²⁺ were calculated in solutions of various compositions. The complexes are redox stable in aqueous solutions both in the dark and in visible laboratory light. Properties of the investigated azidokojic acid and its iron(III) complexes are compared with those required for therapeutic applications as alternative iron chelators.     

New structures in the bi­pyridine–copper(II) nitrate–methanol system: [(bpy)2Cu(NO3)]NO3·CH3OH and [(bpy)2Cu(NO3)]NO3

Reaction of 2,2′‐bi­pyridine (bpy) and copper(II) nitrate in methanol results in two complexes, namely light‐blue bis(2,2′‐bi­pyridine)­nitrato­copper(II) nitrate methanol solvate, [Cu(NO₃)(C₁₀H₈N₂)₂]NO₃·CH₃OH, (I), which is unstable in air, and the product of its decomposition, catena‐poly­[[[bis(2,2′‐bi­pyridine)copper(II)]‐μ‐nitrato‐O:O′] nitrate], {[Cu(NO₃)(C₁₀H₈N₂)₂]NO₃}_n, (II). The crystal structures of both compounds were determined from one crystal at room temperature. Later, the structure of (I) was redetermined at low temperature. In (I) and (II), the Cu atom is coordinated by two bpy and one or two nitrate ions, respectively. The second nitrate ion in (I), along with the methanol solvent mol­ecule, is found in the outer coordination sphere, not bonded to Cu. The nitrate in (I) is chelating, while in (II), it bridges (bpy)₂Cu complexes, forming a one‐dimensional chain structure. The Cu cation in (II) lies on a twofold axis and the uncoordinated NO₃^? ion is located close to a twofold axis and is therefore disordered. Compound (I) converts into (II) upon loss of solvent.