Weak Antiferromagnetic Interactions Research Articles

Copper(II) complexes of 1,3-dimethyl-5-(4′/3′-pyridylazo)-6-aminouracil: Structures, redox, magnetic and protein binding properties

Two new monomeric copper(II) complexes based on 1,3-dimethyl-5-(4′/3′-pyridylazo)-6-aminouracil (HL1: 4′-pyridylazo, complex 1: cis-CuIIL12.MeOH; HL2: 3′-pyridylazo, complex 2: cis-CuIIL12.H2O) were synthesized, characterized and investigated for redox, magnetic and protein-binding properties. The complex 1 is in monoclinic space group C2/c, Z = 4 whereas the complex 2 is in triclinic space group P-1, Z = 2. The complexes hold similar structure in solid and solution state as could be infered from the EPR spectra of 1 having well-resolved hyperfine features, g|| > g┴ > ge (g|| =2.20 and g┴ =2.05). The E½ values for oxidative response of Cu(III)/Cu(II) couple are 1.030 V (ΔE = 133 mV) for 1 and 0.982 V (ΔE = 128 mV) for 2, indicating high redox stability of Cu(II) ions in the complex environment. Direct current (DC) variable-temperature magnetic susceptibility measurements on polycrystalline sample of 1 were carried out in the temperature range 1.8-300 K. The magnetic behavior indicates a weak antiferromagnetic interaction between Cu(II) ions in the crystal lattice below 25 K. The study of Bovin Serum Albumin (BSA)-complex interactions reveals that the BSA binds the complexes through the sites of tryptophan residues in 1:1 manner (n = 0.9007 & KA = 1.482 × 104M−1 for 1 and 0.7433 & KA =2.394×103M−1 for 2). Thus, the developed complexes could be treated as muti-functional materials.

Synthesis, crystal structure, Hirshfeld surface analysis and magnetic studies of bis[1,3-dicyclohexyl-2-ethyl isouronium]tetrachlorocobaltate(II)

In this research work, a new inorganic-organic hybrid material bis[1,3-dicyclohexyl-2-ethyl isouronium]tetrachlorocobaltate(II), (C15H29N2O)2CoCl4 has been successfully synthesized and good quality crystals have been grown by slow evaporation solution technique. The structure was determined by single crystal X-ray diffraction at room temperature. This compound crystallizes in the triclinic crystal system with space group Pī. The atomic arrangement of the title compound can be described as an alternation of organic and inorganic layers along the a−axis, which are interconnected via N–H⋯Cl hydrogen bonds. The thermal stability of the grown crystal was evaluated using thermo-gravimetric and differential scanning calorimetric analyses (TG/DSC). The Hirshfeld surface analysis was conducted to investigate intermolecular interactions and associated 2D fingerprint plots, revealing the relative contribution of these interactions in the crystal structure quantitatively. The magnetic susceptibility measurements in the temperature range 2–300 K shows that the complex displays a weak antiferromagnetic exchange interaction at low temperature.

Lanthanide‐Hypophosphite Frameworks with Guanidinium Guest Showing High Proton Conductivity

Main observation and conclusionProton‐conductive metal‐organic frameworks (MOFs) have attracted great attention for their promising application in membrane fuel cells. To explore proton‐conductive MOFs with high performance, here we present four lanthanide‐hypophosphite frameworks with distinct amine guests. These complexes possess a general formula [AH][Gd2(H2PO2)7] (AH = protonated amines). Due to the rich hydrogen bond networks, complex 1 with guanidinium as guest shows high proton conductivity of 1.75 × 10–2 S·cm–1 at a relative humidity of 97% (368 K). We also studied the magnetic properties of complex 1 and reveal that the hypophosphite ligand transfers weak antiferromagnetic interactions between Gd3+ ions.

Solid State Characterization of One‐ and Two‐Electron Oxidized CuII‐salen Complexes with para‐Substituents: Geometric Structure‐Magnetic Property Relationship

AbstractOne‐ and two‐electron oxidized CuII complexes of Schiff base ligands with para‐substituted phenolate moieties were synthesized and characterized. The crystal structure of the one‐electron oxidized methylthio‐substituted complex [Cu(MeS‐salen)]SbCl6 revealed the intermolecular π‐π stacking interaction of the two phenolate moieties with those of the neighboring complex cations to form the one‐dimensional chain. Such a π‐π stacking interaction could not be detected in the two‐electron oxidized complex [Cu(MeS‐salen)](SbCl6)2 and the oxidized methoxy‐substituted complexes [Cu(MeO‐salen)](SbF6)n (n=1, 2). Magnetic study of [Cu(MeO‐salen)]SbF6 showed a weak antiferromagnetic interaction between the CuII ion and phenoxyl radical unpaired electron spins, while [Cu(MeS‐salen)]SbCl6 showed a ferromagnetism. Both of the two‐electron oxidized complexes exhibited a relatively strong magnetic interaction between the two radical electrons, while the signs of the electron spins are different.

A novel 4f-4d complex resulted from heptacyanomolybdate(III)

A novel 4f-4d complex {[Gd(H2O)3(DMSO)(μ-CN)4]2[Gd(H2O)4(DMSO)3(μ-CN)] [Mo3(CN)21]·3.5H2O]n was prepared by using GdCl3·6H2O and K4[Mo(CN)7]·2H2O as starting material, in which a fancy anion of [Mo3(CN)21]9- is observed and a straight line structure is formed by [Gd2Mo3] trigonal bipyramidal units. Magnetic measurements indicates that very weak antiferromagnetic interaction is operating between Gd(III) ions.

The magnetic properties of multiferroic Ba5Fe3F19−δ

In order to break the contradictory requirements of the outer shell electronic structure for multiferroism in oxide perovskites, multiferroic fluorides were selected to be studied, in which the ferroelectricity and ferromagnetism may both come from the same magnetic ions. Pure phase Ba5Fe3F19−δ powders were prepared by solid state reaction. Energy dispersive X-ray spectroscopy results indicate the deficiency of Fe. The mixed valence states of Fe3+ and Fe2+ are confirmed by X-ray photoelectron spectroscopy. The observation of amplitude and phase hysteresis loops measured by piezoresponse force microscopy indicates the ferroelectricity in Ba5Fe3F19−δ. The temperature dependent magnetization curves show a continuous increase with decreasing temperature, without clear phase transition. However, the temperature dependent inverse magnetic susceptibility (χ) follows the Curie–Weiss law above 150 K with Curie–Weiss temperature of −55 K, suggesting predominantly antiferromagnetic interactions between the Fe ions. The χT decreases with the temperature decreasing from 300 K, indicating the onset of weak antiferromagnetic interaction from temperature above 300 K. No hysteresis loop was observed for the magnetic dependent magnetization curves down to 5 K, indicating the lacking of long-range ordering. A peak was observed in the temperature dependent dielectric constant and dielectric loss at around 257 K, which was strongly suppressed by the application of 5 T magnetic field. The observation of magnetocapacitance effect confirms the magnetoelectric coupling, which originates from the magnetic and structural coupling.

Low-Coordinate Dinuclear Dysprosium(III) Single Molecule Magnets Utilizing LiCl as Bridging Moieties and Tris(amido)amine as Blocking Ligands

A low-coordinate dinuclear dysprosium complex {[Dy(N3N)(THF)][LiCl(THF)]}2 (Dy2) with a double bridging ‘LiCl’ moiety and tris(amido)amine (N3N)3− anions as a blocking ligand is synthesized and characterized structurally and magnetically. Thanks to the use of the chelating blocking ligand (N3N)3− equipped with large steric –SiMe3 groups, the coordination sphere of both DyIII ions is restricted to only six donor atoms. The three amido nitrogen atoms determine the orientation of the easy magnetization axes of both DyIII centers. Consequently, Dy2 shows slow magnetic relaxation typical for single molecule magnets (SMMs). However, the effective energy barrier for magnetization reversal determined from the AC magnetic susceptibility measurements is much lower than the separation between the ground and the first excited Kramers doublet based on the CASSCF ab initio calculations. In order to better understand the possible influence of the anticipated intramolecular magnetic interactions in this dinuclear molecule, its GdIII-analog {[Gd(N3N)(THF)][LiCl(THF)]}2 (Gd2) is also synthesized and studied magnetically. Detailed magnetic measurements reveal very weak antiferromagnetic interactions in Gd2. This in turn suggests similar antiferromagnetic interactions in Dy2, which might be responsible for its peculiar SMM behavior and the absence of the magnetic hysteresis loop.

Structure and magnetic transitions along with magnetization switching in nanoparticles of CeCr1-xFexO3 (0 ≤ x ≤ 0.1)

Here, we have investigated the structural, magnetic, and bipolar switching properties in CeCr1-xFexO3 (0 ≤ x ​≤ ​0.1) nanoparticles synthesized by one-step solution combustion method. Rietveld and Raman analysis demonstrate an increase in distortion of orthorhombic structure after substitution of Fe3+ ions due to the rotation/tilting of Cr–O6 octahedra. Besides the Néel transition, TN2 ~260 ​K due to antiferromagnetic (AFM) ordering of Cr3+ in x ​= ​0, a new Néel transition, TN1 above TN2 in x ​> 0 is manifested attributing to the weak antiferromagnetic interaction between Cr3+ and Fe3+ moments. Below the Néel transitions, some interesting magnetic features such as compensation temperature, Tcomp and spin reorientation temperature, TSR are observed. Most importantly, a stable bipolar switching of magnetization by varying the external field is demonstrated for x ​= ​0.06 which could be exploited for its potential use in data storage and magnetic switching based nonvolatile magnetic memory devices.

A manganese (II) dimer bearing the reduced derivatives of nitronyl nitroxides

We report the synthesis, magnetic EPR and conducting properties of a new manganese complex [MnII(hfac)2(IMHPhOPh)]2[MnII(hfac)3](IMH2PhOPh) (1), containing the reduced forms (IMHPhOPh and IMH2PhOPh) of the NIT-PhOPh radical (NIT-PhOPh = 2,4‘-benzoxo-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). Magnetic susceptibility studies reveal the presence of weak antiferromagnetic exchange interactions between the metal ions, within the [MnII(hfac)2(IMHPhOPh)]2 unit. The EPR spectra of 1 exhibit simultaneous contributions of both the monomeric [MnII(hfac)3] and dimeric [MnII(hfac)2(IMHPhOPh)]2 species. Conductivity measurements shown that the electrical conduction of 1 is dominated by Ohm’s law, with a conductance value of 1.3(6)×10-9 S/cm.

Spectroscopic Identification of Disordered Molecular Cations in Defect Perovskite‐Like ALn(HCO2)(C2O4)1.5 (Ln=Tb‐Er) Phases

AbstractThis work reports a new series of ALn(HCO2)(C2O4)1.5 (A=[(CH3)2NH2]+ and Ln3+=Tb3+‐Er3+) compounds made solvothermally. These Cmce phases combine monovalent and divalent ligands, which enables a scarce combination of A+ and B3+ cations in a hybrid perovskite‐like compound. The ratio of ligands leads to ordered anion vacancies, which alternate with oxalate linkers along the c‐axis. The A‐site cations are disordered and cannot be identified crystallographically, likely a result of the larger pores of these frameworks compared to the recently reported AEr(HCO2)2(C2O4) phases. Neutron and infrared spectroscopy, supported by elemental composition, enables these cations to be identified as [(CH3)2NH2]+ molecules. Magnetic property measurements suggest these materials have weak antiferromagnetic interactions but remain paramagnetic to 1.8 K.

Crystal structure and magnetic properties of 3,5-pyridinedicarboxylate-bridged Re(II)M(II) heterodinuclear complexes (M = Cu, Ni and Co)

The use of the mononuclear rhenium(II) precursor NBu4[Re(NO)Br4(H2pydc)]·i-PrOH (1) (H2pydc = 3,5-pyridinedicarboxylic acid) as a metalloligand towards Cu(II), Ni(II) and Co(II) afforded three new heterobimetallic complexes [Re(NO)Br4(μ-Hpydc)Cu(4,4′-dmbipy)2]·(CH3)2CO·0.25MeCN (2), [Re(NO)Br4(μ-Hpydc)Ni(dmphen)2]·MeCN (3) and [Re(NO)Br4(μ-Hpydc)Co(dmphen)2]·2H2O (4), respectively [4,4′-dmbipy = 4,4′-dimethyl-2,2′-bipyridine, dmphen = 2,9-dimethyl-1,10-phenanthroline and Bu4N+ = tetra-n-butylammonium]. The crystal structures of 1 and 2 are reported herein together with the cryomagnetic investigation of 1–4 in the temperature range of 2.0–300 K. 1 is a mononuclear compound whose structure is made of [Re(NO)Br4(H2pydc)]- complex anions, tetra-n-butylammonium cations and isopropanol molecules of crystallization. Each rhenium(II) ion in 1 is six-coordinate with four bromide ligands in the equatorial positions and a nitrosyl group and one pyridyl-nitrogen atom from an H2pydc ligand filling the axial sites. 2 is a neutral heterobimetallic compound where the [Re(NO)Br4(Hpydc)]2- complex anion acts as a monodentate ligand towards the [Cu(4,4′-dmbipy)2]2+ complex cation through one carboxylate–oxygen atom. The rhenium(II) ion is six-coordinate in a somewhat distorted octahedral surrounding similar to that in 1. The copper(II) ion in 2 is five-coordinate with four nitrogen atoms from two bidentate 4,4′-dmbipy ligands and one carboxylate–oxygen atom, describing a surrounding intermediate between square pyramidal and trigonal bipyramidal. Compound 1 behaves as a quasi-magnetically isolated spin doublet with weak antiferromagnetic interactions through space Br⋯Br contacts, ligand field, spin–orbit coupling, tetragonal distortion, and covalence effects considered as variable parameters in a successful simulation of the magnetic data. Compounds 2–4 exhibit also weak intramolecular antiferromagnetic interactions (J) covering the range −0.60(1) to −1.50(1) cm−1 with the Hamiltonian being defined as H = -JSReSM, M = Cu (2), Ni (3) and Co (4).

A Cu(II) coordination framework constructed by the inorganic layer and a bent dipyridyl ligand: Synthesis, structure and magnetic properties

A new Cu(II) coordination framework {[Cu(4-abpt)(μ3-SO42-)(H2O)]·3H2O}∞ (1) based on the Cu–SO42- inorganic layer and the bent dipyridyl ligand was obtained under solvothermal conditions (4-abpt ​= ​4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole). The compound displays a three-dimensional (3D) “pillar-layer” framework, which can be simplified into a 3,5-connected gra topology. Furthermore, the magnetic properties of 1 have been investigated. As a result, compound 1 displays a weak antiferromagnetic interaction among the Cu(II) centers.

Direct Synthesis and Characterization of Copper(II) 1‐Phenyltetrazol‐5‐olates

AbstractThe interaction of 1‐phenyl‐1,4‐dihydro‐5H‐tetrazol‐5‐one (Hpto) with ethylenediamine (en) and metallic copper in ethanol in the open air was found to yield molecular complexes [Cu(en)2(pto)2] (1) or [Cu2(en)2(EtOH)2(pto)4] (2) depending on the reagents ratio. Deprotonated tetrazol‐5‐one, i.e 1‐phenyltetrazol‐5‐olate anion (pto) acts as a monodentate ligand coordinated to the metal via the tetrazole ring N4 atom in mononuclear complex 1, and as a bridging ligand coordinated via the tetrazole ring N4 and N3 atoms in binuclear complex 2. The latter was found to be a paramagnet, with a very weak antiferromagnetic exchange interaction between copper ions.

Magnetic Properties and Second Harmonic Generation of Noncentrosymmetric Cyanido-Bridged Ln(III)-W(V) Assemblies.

One-dimensional zigzag cyanido-bridged coordination polymers have been prepared as a result of self-assembly of lanthanide(III) ions with octacyanidotungstate(V) anions in the presence of N,N-dimethylacetamide (dma). All compounds crystallized in noncentrosymmetric space group P21 with a molecular formula of [LnIII(dma)5][WV(CN)8] [Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5), Tm (6), Yb (7), Lu (8), or Y (9)]. Magnetic studies revealed weak antiferromagnetic interactions through LnIII-NC-WV bridges and the formation of ferrimagnetically coupled chains at very low temperatures. Moreover, temperature dependencies of magnetic susceptibilities were fitted using the crystal field parameters for Ln(III) ions, determined by the ab initio calculations, yielding magnetic coupling constants in the range of -1 to -5 cm-1. The wide optical transparency of 1-9 has been determined using solid state absorption spectroscopy. Samples exhibited second harmonic (SH) generation properties with SH susceptibilities ranging from 4.7 × 10-12 to 9.4 × 10-11 esu due to the presence of nonlinear optical susceptibility tensor elements (χijk) χzxx, χzyy, χzzz, χzxy, χyyz, χyzx, χxyz, and χxzx, corresponding to space group P21. The determined values were also compared with the results of theoretical calculations and previous reports, indicating a potential relationship between the type of lanthanide ion and the SH intensity.

Magneto-structural studies of a one dimensional Mn(II) coordination polymer derived from a flexible polydentate ligand

The polydentate ligand LHμ contains bipyridine, hydrazone and oxime functionalities and reacts with Mn(CH3COO)2·4H2O to afford an alternating one dimensional chain comprising Mn(II) ions, [{Mn2(LH)(CH3COO)3(CH3OH)2}·CH3OH]n(1). The structure of 1 contains two Mn(II) ions in the asymmetric unit; Mn1 adopts an unusual pentagonal bipyramidal coordination geometry comprising an [N3O4] donor set, while Mn2 adopts a more conventional octahedral geometry coordinated by an [NO5] donor set. The two manganese ions within the dinuclear unit are connected to each either via Ohydrazone and syn-syn Oacetate bridges. These dinuclear units are then linked by anti-anti Oacetate bridges, affording a magnetic 1-D alternating chain topology. Magnetic studies on 1 reveal the presence of weak antiferromagnetic interactions via Ohydrazone and acetate bridges. The magnetism of 1 was modelled using a dimer model [Ĥ = −2JŜ1Ŝ2], with inter-dimer exchange modelled using a mean field term (zJ’) to afford g = 2.046 ± 0.002, J/k = -1.03 ± 0.02 cm−1 and zJ’ = −0.06 ± 0.01 cm−1.

Crystal structure and magnetic study of the complex salt [RuCp(PTA)2-μ-CN-1κC:2κN-RuCp(PTA)2][Re(NO)Br4(EtOH)0.5(MeOH)0.5

A new RuII-ReII complex salt, μ-cyanido-κ2 C:N-bis-[(η5-cyclo-penta-dien-yl)bis(3,5,7-tri-aza-phosphaadamantane-κP)ruthenium(II)] tetra-bromido-(ethanol/methanol-κO)nitrosylrhenate(II), [Ru(CN)(C5H5)2(C6H12N3P)4][ReBr4(NO)(CH4O)0.5(C2H6O)0.5] or [RuCp(PTA)2-μ-CN-1κC:2κ2 N-RuCp(PTA)2][Re(NO)Br4(EtOH)0.5(MeOH)0.5] (PTA = 3,5,7-tri-aza-phosphaadaman-tane) was obtained and characterized by single-crystal X-ray diffraction, elemental analysis and infrared spectroscopy. The title salt was obtained by liquid-liquid diffusion of methanol/DMSO solutions of (NBu4)[Re(NO)Br4(EtOH)] and [(PTA)2CpRu-μ-CN-1κC:2κ2 N-RuCp(PTA)2](CF3SO3). The RuII and ReII independent moieties correspond to a binuclear and mononuclear complex ion, respectively. A deep geometrical parameter analysis was performed, and no significant differences were found with earlier reports containing similar mol-ecules. The magnetic properties were investigated in the temperature range 2.0-300 K, and the complex behaves as a quasi-magnetically isolated spin doublet with weak anti-ferromagnetic inter-actions.

4f-π Molecular Hybrid Exhibiting Rich Conductive Phases and Slow Relaxation of Magnetization.

Cooperation between single-molecule magnets and electrical conductivity holds promise for preparing high-density magnetic devices; however, there are only a few reports so far. Here we report a 4f-π-based molecular hybrid, k-(ET)5Dy(NCS)7(KCl)0.5 (1) (ET = bis(ethylenedithio)tetrathiafulvalene, NCS- = thiocyanate), which undergoes slow relaxation of the magnetization and electrical conductivity. Unlike common ET-based conductive salts, K+ ions were intercalated into ET layers and coordinated with ET radicals. We found that the ET charges were sensitive to temperature, resulting in rich conductive phases at 75-300 K. In particular, the upturn in conductivity with a clear hysteresis loop was explained by the formation of partially oxidized states with charges close to 0.5+, which accounts for a metallic state. From the results of electronic structure calculations, the hole concentration increased to 125 K, which is consistent with a partially oxidized state upon cooling. The weak antiferromagnetic interactions accompanied by a dual magnetic relaxation process below 4 K are closely associated with the weak 4f-π interactions.

Effect of the Alkaline Metal Ion on the Crystal Structure and Magnetic Properties of Heterometallic GdIII-VIV Complexes Based on Cyclobutane-1,1-Dicarboxylate Anions

A series of heterometallic GdIII-VIV compounds were synthesized by the reaction of VOSO4·3H2O with cyclobutane-1,1-dicarboxylic acid salts M2(cbdc) (M = Na, Rb, Cs). The new compounds were formed by [Gd(VO)2(cbdc)4(H2O)8]− trinuclear anionic units that were similar in composition but differed in structure, depending on the nature of the alkali metal cation incorporated in the crystal structure of the compound. In the case of Na+, the {GdV2}− units were characterized by identical V···Gd distances and were linked into the 1D-polymeric chain [NaGd(VO)2(cbdc)4(H2O)10]n (1). In the systems with Rb+ and Cs+, the V···Gd distances were different, and the {GdV2}− units were linked into the 3D-framework {[RbGd(VO)2(cbdc)4(H2O)10]·2.5H2O}n (2) and the octanuclear molecule {[CsGd(VO)2(cbdc)4(H2O)11]·5H2O}2 (3), respectively. According to dc-magnetic measurements, the VIV and GdIII ions were ferromagnetically coupled in compound 1 (JVGd = 0.163 ± 0.008 cm−1), while in compounds 2 and 3, ferro- and weak antiferromagnetic exchange interactions were observed (JVGd = 0.989 ± 0.028 and −0.089 ± 0.008 cm−1 for 2, 0.656 ± 0.009 and −0.050 ± 0.004 cm−1 for 3). Analysis of the EPR spectra of 1 revealed the presence of weak magnetic anisotropy of GdIII ions (D ~ 0.08 cm−1 and E/D ~ 0.1–0.15). Ac-susceptibility measurements showed an occurrence the field-induced slow relaxation of magnetization in 1–3.

Two-Dimensional Copper Coordination Polymer Assembled with Fumarate and 5,5’-Dimethyl-2,2’-bipyridine: Synthesis, Crystal Structure and Magnetic Properties

[[Cu(fum)(dmb)]·H2O]n (1) (fum = fumarate; dmb = 5,5’-dimethyl-2,2’-bipyridine) was obtained by a self-assembly solution reaction, at ambient conditions, and characterized by elemental analysis, IR spectroscopy and X-ray single crystal diffraction. Crystallographic studies show that 1 crystallizes in a triclinic system with a P-1 space group, with a = 8.2308(2) A, b = 9.7563(2) A, c = 10.3990(2) A; α = 80.3444(4)°, β = 77.9517(4)°, γ = 82.0440(5)°; V = 800.45(3) A3. The Cu(II) centers are five-coordinated with a distorted square pyramidal configuration. The formation of a two-dimensional (2D) array in 1 can be explained by the presence of two different coordination modes in the fumarate ligand: μ-η1:η0 and μ2-η2:η0, both in a bridging monodentate manner, the latter generating distinctive rhombic-dinuclear units. The thermal stability of 1 has also been analyzed. Magnetic measurements revealed that this polymer exhibits weak antiferromagnetic ordering. [[Cu(fum)(dmb)]·H2O]n, exhibiting weak antiferromagnetic interactions, displays a two-dimensional array comprised of rhombic dinuclear units, where the carboxylate moieties of fumarate bridging ligand displays monodentate and oxo-bridging coordination modes connecting two Cu centers.

Magnetic Switching in Vapochromic Oxalato-Bridged 2D Copper(II)-Pyrazole Compounds for Biogenic Amine Sensing

A new two-dimensional (2D) coordination polymer of the formula {Cu(ox)(4-Hmpz)·1/3H2O}n (1) (ox = oxalate and 4-Hmpz = 4-methyl-1H-pyrazole) has been prepared, and its structure has been determined by single-crystal X-ray diffraction. It consists of corrugated oxalato-bridged copper(II) neutral layers featuring two alternating bridging modes of the oxalate group within each layer, the symmetric bis-bidentate (μ-κ2O1,O2:κ2O2′,O1′) and the asymmetric bis(bidentate/monodentate) (μ4-κO1:κ2O1,O2:κO2′:κ2O2′,O1′) coordination modes. The three crystallographically independent six-coordinate copper(II) ions that occur in 1 have tetragonally elongated surroundings with three oxygen atoms from two oxalate ligands, a methylpyrazole-nitrogen defining the equatorial plane, and two other oxalate-oxygen atoms occupying the axial positions. The monodentate 4-Hmpz ligands alternatively extrude above and below each oxalate-bridged copper(II) layer, and the water molecules of crystallization are located between the layers. Compound 1 exhibits a fast and selective adsorption of methylamine vapors to afford the adsorbate of formula {Cu(ox)(4-Hmpz)·3MeNH2·1/3H2O}n (2), which is accompanied by a concomitant color change from cyan to deep blue. Compound 2 transforms into {Cu(ox)(4-Hmpz)·MeNH2·1/3H2O}n (3) under vacuum for three hours. The cryomagnetic study of 1–3 revealed a unique switching from strong (1) to weak (2 and 3) antiferromagnetic interactions. The external control of the optical and magnetic properties along this series of compounds might make them suitable candidates for switching optical and magnetic devices for chemical sensing.