Copper Chains Research Articles

DIMERIC COPPER(II) COMPLEXES WITH BRIDGING UNSATURATED CARBOXYLIC LIGANDS. CORRELATION OF pKa VALUES AND MAGNETIC EXCHANGE PARAMETERS

Abstract The copper(II) salts∗ of acrylate, crotonate and 3,3′-dimethyl-acrylate anions exist with reduced magnetic moments. Magnetic susceptibility measurements (80–300 K) revealed the strong antiferromagnetic exchange coupling between the copper(II) ions. Singlet-triplet separation values obtained by least-squares fitting to the modified Bleaney-Bowers equation are equal to −302, −305 and −324 cm−1, respectively. Unusual EPR spectra of these compounds, which, besides lines due to dimeric units, also exhibit the lines characteristic for polymeric copper(II) chains (g ≈2.10) are the basis for discussion of the molecular structures of the compounds.

Structural approach to the behavior of perchlorate as a ligand in transition-metal complexes using EXAFS, IR and Raman spectroscopy. 1. A perchlorate-bridged copper chain with short copper-copper distances in copper(II) perchlorate

Structural approach to the behavior of perchlorate as a ligand in transition-metal complexes using EXAFS, IR and Raman spectroscopy. 1. A perchlorate-bridged copper chain with short copper-copper distances in copper(II) perchlorate

Spectroscopic and magnetic properties of a novel pyrazine-bridged copper(II) chain: [Cu(terpy)(pyz.)](ClO 4) 2

The [Cu(Terpy)(pyz.)](ClO 4) 2 complex (were Terpy = 2,2′:6′,2′'-terpyridine and pyz. = pyrazine) was synthesized and characterized by means of spectral and magnetic properties. UV-visible and EPR spectra indicate a square pyramidal coordination for the copper(II) ion. Magnetic susceptibility measurements, reported in the temperature range 2–125 K, are analyzed in terms of regular and alternating Heisenberg-chain models giving 2J = −4.4 K, g = 2.19 (regular chain) and 2J = −5.6 K, 2J′ = −1.7 K, g = 2.15 (alternating chain). The better agreement obtained with the alternating-chain model allows us to propose a dimerized zig-zag chain structure with the pyz. ligand bridging the copper(II) ions.

Crystal structures and spectroscopic properties of the polymeric adducts formed from Cu(CN) and Cu(NCS) with 2,9-dimethyl-1,10-phenanthroline

The crystal structures of the title adducts, [{Cu(dmphen)(CN)}n](1) and [{Cu(dmphen)(NCS)}n](2)(dmphen = 2, 9-dimethyl-1,10-phenanthroline), consist of one-dimensional zigzag chains of tetrahedral copper(I) atoms linked by cyanide and thiocyanate groups, respectively. Stacks of dmphen molecules are formed by the ‘fitting’ of centrosymmetrical polymeric sequences. Complex (1) crystallizes in space group P21/n with cell dimensions, a= 9.839(4), b= 7.788(2), c= 16.559(7)A, β= 92.33(4)°, and Z= 4; (2) crystallizes in space group Pbca, with cell dimensions, a= 16.283(3), b= 9.485(2), c= 18.115(3)A, and Z= 8. Polarization properties of the i.r. and electronic bands have been determined. Chain formation affects the vibration and bending modes within the zigzag system. In the optical spectrum of both the complexes two bands have been detected : one charge-transfer from dyz of copper to φ9(lowest unoccupied molecular orbital of dmphen), polarized along the short axis (z) of each [Cu(dmphen)]+ mono-complex, and another from dz2 or dx2–y2 of copper to φ9, plane-polarized (xy) because of some vibronic or electronic coupling mechanism operating between the above mentioned mono-complexes stacked in the ‘fitted’ polymeric sequences.

The thermal behaviour and spectral properties of some long chain copper(II) carboxylates

Results are presented on the temperatures, enthalpies, and entropies of the phase transitions of the even chain length copper(II) carboxylates from decanoate to octadecanoate. The dodecanoate, tetradecanoate and hexadecanoate melt directly from crystal to isotropic liquid. However, with the decanoate and octadecanoate, an intermediate phase is observed between solid and isotropic liquid. Tentative assignments are made on the intermediate phases. Electronic and infrared spectra are reported for the solid copper(II) carboxylates. In both cases, the spectra provide clear evidence for there being at least two copper ions in the head-group region of each copper carboxylate system.

Effect of Bridge Geometry on Exchange Coupling in Ligand-Bridged Copper(II) Dimers and Chains

Abstract The singlet triplet splitting resulting from exchange coupling in three series of ligand-bridged copper(II) complexes is primarily controlled by the angle at the bridging ligand atom and by the length of the superexchange pathway. Magnetic and structural data exist for chloro-, bromo-, and sulfur-bridged complexes. The smooth correlation between the exchange coupling constant J and the quotient of structural parameters φr 0 (where φ is the angle at the bridging ligand atom and r 0, is the long out-of-plane bond distance) may be explained in terms of extended Huckel molecular-orbital theory, but the theory does not permit an explanation why only complexes which obey the simple correlation exist. It is predicted that a family of such structurally and magnetically related complexes should exist.

Temperature effects on EPR spectra of a linear chain copper complex-copper calcium acetate hexahydrate

The observed angular dependence of the electron paramagnetic resonance linewidth in the ab and ac planes of CuCa(AC)2, 6H2O in the temperature interval 77K–12K was explained by considering dipolar interactions along with hyperfine and isotropic exchange interactions in these two planes. It was found that this so called linear-chain copper compound can be better described by a three dimensional paramagnet. The exchange interaction is very nearly isotropic with values Jab = 0.0098 cm−1 and Jc = 0.0103 cm−1. The values of the A⊥ derived from the linewidth fit in the ab plane are 14G at 77K and 60.5G at 1.2K. Due to insufficiency of data in the ac plane, the fit was done with the measured value of A∥. Although the exchange interaction has been found to be temperature independent the hyperfine interaction increases very much at low temperatures. The high temperature (300–460K) EPR spectra are quite different from the low temperature spectra. High temperature differential thermal analyses and thermogravimetric analyses have been carried out and corroborated with the EPR findings.

The Cluster Approach with Effective Field Approximation to Exchange Coupling in Layer-Type Compound Cu(NH3)2CO3

Magnetic susceptibility data on Cu(NH 3 ) 2 CO 3 are analyzed by the effective field approximation in addition to a cluster approach. The layer structure of Cu(NH 3 ) 2 CO 3 consists of carbonate bridged chains of copper (II) ions linked together into sheets by hydrogen bonding. The cluster model of three copper ions under the effective fields gives a nice fit with the experimental data with the intrachain exchange constant of -5.9 K and the interchain exchange constant of 5.5 K. The results are compared with those of the recent investigation by the cluster approach.

Magnetic properties and superexchange in single chloride-bridged copper(II) chain compounds

Magnetic susceptibility data have been measured in the temperature range 1.75 to 60 K for the following structurally characterized, single chloride-bridged copper(II) chain compounds: dichlorobis(dimethyl sulphoxide)copper(II), dichlorobis(imidazole)copper(II), aquo(caffeine)dichlorocopper(II), and dichloro[2-(2′-methylaminoethyl)pyridine]copper(II). The first two compounds exhibit antiferromagnetic intrachain interactions with exchange coupling constants of –6.1 and –2.1 cm–1, respectively, while the second two compounds exhibit ferromagnetic interactions with J values of 0.48 and 1.58 cm–1 respectively. Except for dichlorobis(imidazole)copper(II), which undergoes long-range magnetic ordering below 7.7 K, the exchange coupling constants become more negative as the angle at the chloride bridge increases from 113.6° in dichloro[2-(2′-methylaminoethyl)pyridine]copper(II) to 144.6° in dichlorobis(dimethyl sulphoxide)copper(II).

Kristall- und Molekülstruktur eines „linearen“ Festkörpers mit drei verschiedenen Metallsträngen: [Pt(dapn)2] [Pt(dapn)2Br2] [(Cu3Br5)2] (dapn = 1.2-Diaminopropan)/Crystal and Molecular Structure of a Linear Chain Solid with Three Different Metal Chains: [Pt(dapn)2][Pt(dapn)2Br2][(Cu3Br5)2] (dapn = 1,2-diaminopropane)

Abstract The compound {[Pt(dapn)2][Pt(dapn)2Br2]}(Cu3Br5)2, which was prepared by oxidation of Pt(dapn)2Br2 with CuBr2, crystallizes in the orthorhombic space group Bmmb (D2h 17), a = 5.617(4) Å, b = 16.206(6) Å, c = 22.00(1) Å, Z = 2. The experimentally determined density is 3.22 g · cm-3 (calculated 3.40). The structure has been determined by Patterson and Fourier methods from single crystal diffractometer data and refined by least squares to R = 0.085 for 485 independent reflections. Crystals of the title compound contain halide-bridged copper and platinum chains.

Exchange interactions in halide-bridged chains of copper(II). Cu(Rpy)2X2

Exchange interactions in halide-bridged chains of copper(II). Cu(Rpy)2X2

Interdimer exchange in linear chain copper acetate-pyrazine

Interdimer exchange in linear chain copper acetate-pyrazine

Criticism of the use of the Ising model to describe linear chains of antiferromagnetically coupled copper(II) ions

Major disadvantages of the use of the anisotropic Ising model to describe strong antiferromagnetic coupling in infinite linear chains of copper(II) ions are discussed with particular reference to cupric oxalate.

Magnetic behavior of linear chain copper(II) complexes—II: Dihalobispyridinecopper(II) complexes

The temperature dependence of the magnetic susceptibility between 115 and 370°K has been determined for fourteen 1:2 addition complexes formed from copper(II) halides and pyridine or a substituted pyridine. The susceptibility-temperature data has been fit to the Curie-Weiss Law and values of φ in the range −9 to −43°K have been determined. From a knowledge of the structure of the complex the Weiss constant can be used to estimate the magnitude and sign of the exchange interaction. These results are compared with those obtained previously for 1:1 addition complexes formed from copper(II) chloride and bidentate heterocyclic amines. Plausable mechanisms for spin exchange in the two types of complexes are discussed.

Magnetic and electrical properties of coordination polymers formed with copper and rubeanic acid

AbstractA crystalline form of a rubeanato‐copper coordination polymer has been synthesized by a solid‐solid reaction. The electrical and magnetic properties of the crystalline form have been studied and compared with the properties of the normally synthesized amorphous form. Molecular structures are proposed for both forms, which are consistent with the resistivity of the samples. Infrared spectra support the proposed structures. In particular, the static magnetic susceptibility was measured in a temperature range from 100–380°K. Typical values at room temperature are: 271 × 10−6 c.g.s.‐e.m.u. for the crystalline form and 236 × 10−6 c.g.s.‐e.m.u. for the amorphous form. The d.c. resistivities at room temperature are 1010 and 4 × 104 Ω‐cm. for the crystalline and amorphous forms, respectively. Also the temperature variation of the ESR absorption was studied. The anomalous behavior of the magnetic susceptibility, i.e. (1) it exhibits very low value, and (2) it exhibits essentially no temperature dependence, requires a new magnetic model to be set forth. Three models are considered: (1) Copper aceta e model, (2) One‐dimensional Heisenberg model, (3) “Equiinteraction” model. Either the second and third model may be employed to explain the behavior as seen. By these models, the effective number of the magnetic copper chain is estimated as nine.