Adjacent Copper Atoms Research Articles

Polymer complexes: 25. Complexing ability of poly(5-vinylsalicylidene-2-aminopyridine) towards different metal( ii) salts

Mononuclear and binuclear complexes of poly(5-vinylsalicylidene-2-aminopyridine) † † Systematic name: poly[2-(5-vinylsalicylidenimino)pyridine] were prepared by the reaction of the homopolymer with copper( ii), cobalt( ii), nickel( ii), cadmium( ii), dioxouranium( vi) and palladium( ii) salts. Metal( ii) acetates and palladium chloride were found to give mononuclear complexes, while cupric chloride gave a binuclear complex. The polymer complexes have been characterized on the basis of elemental analysis, u.v. and i.r. spectroscopy, and magnetic susceptibility measurements. The stereochemistry and the nature of the complexes are markedly dependent upon the molar ratios of the reactants, the pH of the system and the nature of the anions involved. In all of the complexes the homopolymer was chelated to the metal ion through the nitrogen atom of the azomethine group and the oxygen atom of the phenolic group. The low value of the magnetic moment of the binuclear copper complex is due to an antiferromagnetic interaction between two adjacent copper atoms. The ligand field parameters have been calculated and related to the electronic environments. The electronic absorption of the homopolymer was investigated in organic solvents of varying polarities and buffer solutions of different pH, and the behaviour in the latter has been utilized in calculating the p K a of the phenol group.

Synthesis, crystal structure and magnetic properties of the alternating chain [VO(H2O)5][Cu2(bipym)2(H2O)(SO4)3]·7H2O (bipym = 2,2′-bipyrimidine)

The new compound [VO(H2O)5][Cu2(bipym)2(H2O)(SO4)3]·7H2O 1(bipym = 2,2′-bipyrimidine) has been synthesised and its crystal structure determined by single-crystal X-ray diffraction [monoclinic, space group P21/c, a= 9.944(3), b= 13.928(6), c= 26.275(6)A, β= 99.59(2)° and Z= 4]. Its structure consists of anionic alternating zigzag chains of bipym-bridged copper(II) ions with aqua and sulfato ligands. The electroneutrality is achieved by pentaaquaoxovanadium(IV) cations. The coordination geometry around the copper(II) ions can be described as distorted CuN4O2 octahedral: that around Cu(1) comprises three nitrogens from bipym and an oxygen from sulfate in the basal positions and a nitrogen from bipym and an oxygen of another sulfate group in the axial sites; three nitrogens from bipym and an oxygen from sulfate occupy the equatorial positions around Cu(2), whereas a nitrogen from bipym and an oxygen from water fill the axial sites. The bipyrimidine group joins two adjacent copper atoms acting in a bis(chelating) fashion. The vanadium atom in the pentaaquavanadyl cation is approximately at the centre of an octahedron defined by five oxygens from water molecules and an oxo group. The VIV–O (oxo) bond distance [1.577(5) A] is shorter than that of VIV–O(water)(average 2.025 A). The intrachain copper–copper separations are 5.505(2) and 5.675(2)A. Variable-temperature (4.2–300 K) magnetic susceptibility data were fitted by the alternating-chain spin-exchange model [Ĥ=–J∑(Ŝ2i·Ŝ2i–1+αŜ2i·Ŝ2i+1), α= alternation parameter] and to the usual Bleaney–Bowers expression for a copper(II) pair with the inclusion in both cases of the Curie law for an isolated S=½ species in order to account for the presence of the vanadyl cation. The values of the exchange coupling are discussed in the light of the structural data and compared to those reported for other bipym-bridged copper(II) complexes.

Structure and magnetic properties of a syn-anti carboxylate bridged linear trinuclear copper(II) complex with ferromagnetic exchange interaction

The synthesis, crystal structure and magnetic properties are reported for the trinuclear compound [Cu(H 2O) 4{Cu(HL)(H 2O)(ClO 4)} 2][ClO 4] 2·2H 2O, where HL is the monodeprotonated form of 6-methylamino-1,3-dimethyl-5-[(2′-carboxyphenyl)azo]uracil. The compound crystallizes in the triclinic system, space0 group P 1 , with cell constants a=7.824(3), b=12.278(3), c=13.705(9) Å, α=104.34(3), β=91.80(3), γ=103.37(5)° and Z=1. The structure was solved and refined to R=0.071 ( R w=0.064). The structure consists of trinuclear [Cu(H 2O) 4{Cu(HL)(H 2O)(ClO 4)} 2] 2+ cations, non-coordinated perchlorate anions and crystal water molecules, held together by a network of hydrogen bonds. The central copper is in an elongated octahedral CuO 6 chromophore and the terminal copper atoms in distorted square-pyramidal CuNO 4 chromophores. Adjacent copper atoms are linked by carboxylate groups in a syn-anti conformation. From the magnetic susceptibility measurements, the complex is found to exhibit weak ferromagnetic interaction between nearest-neighbour copper(II) ions. The magnitude and nature of the exchange coupling are discussed on the basis of the structural data.

A novel high nuclearity bimetallic cluster: The crystal structure of [N(PPh 3) 2][Ag 6Cu 7(C 2Ph) 14

An X-ray diffraction study of the high nuclearity complex [N(PPh 3) 2][Ag 6Cu 7(C 2Ph) 14] has shown it to be a novel 13-atom bimetallic anionic cluster [Ag 6Cu 7(C 2Ph) 14] − with two types of copper atoms, one inside the body of the cluster and six on its surface. The surface atoms have a distorted trigonal bipyramidal geometry whereas the internal copper atom is linearly coordinated by two C 2Ph groups in addition to displaying six CuAg bonding interactions with three tetranuclear [Ag 2Cu 2(C 2Ph) 4] subclusters. Thus the internal copper atom essentially exhibits eight-coordination. All the silver atoms have a bent two-coordinate geometry as far as CuAgCu metal bonding is concerned. These atoms are also asymmetrically π bonded to alkyne groups on the phenyl moieties attached to the adjacent copper atoms. This complex represents a new class of Group 1B metal clusters with a bonding pattern not observed previously.

Complexing ability of poly[5-vinylsalicylidene-2-aminopyridine] towards different metal(II) salts

Mononuclear and binuclear complexes of poly (5-vinylsalicylidene-2-aminopyridine) a)were prepared with Copper(II), Cobalt (II), Nickel(II), Cadmium(II), dioxuranium(II) and Palladium(II) salts. The metal (II) acetates and palladium chloride gave mononuclear complexes, while cupric chloride gave a binuclear complex. The polymer complexes have been characterized on the basis of elemental analysis, u.v., i.r. and magnetic susceptibilty. The stereochemistry and the nature of the complexes are markedly dependent upon the mole ratio of the reactants and the anions. In all complexes the homopolymer was chelated to the metal ion via the nitrogen atom of the azomethine group and oxygen atom of the phenolic, group. The low value of the magnetic moment of binuclear copper complexes is due to the antiferromagnetic interaction between two adjacent copper atoms. The ligand field parameters are calculated and related to the electronic environments.

Crystal and molecular structure of di-μ-chlorobis[2-[[[(2-hydroxy-1-naphthyl)methyl]imino]-ethanolato]N,O,O′]di-copper(II) hemihydrate

The structure of the title compound [Cu2Cl2(C13H12NO2)2]·1/2 H2O has been determined from single crystal X-ray diffraction data by direct methods. Full-matrix least-squares refinement of the structural parameters led to conventionalR factor of 0.037 for 4367 intensities above 3σ(I). The compound forms a dinuclear complex with distorted tetragonal-pyramidal geometry at each copper center. The unsymmetrical dimers are formed by weak axial coordination to one copper center by chloride ligands which are in the base plane of the adjacent copper atom. The apical Cu1-C12 and Cu2-C11 distances are 2.788(1) and 3.130(1) A, respectively. The Cu1-Cu2 separation is 3.4995(3) A in the dimers. A disorder of one five-membered chelate ring has been observed. Two alternative positionsa andb of the C26 atom were found and refined with constrained bond lengths. The geometry of the ligand and hydrogen bonds is discussed.

Crystal and Molecular Structure of the Discogen bis[1,3-di(p-n-octylphenyl)propane-1,3-dionato]copper(II)

Abstract The transition metal containing discogen bis[1,3-di(p-n-octylphenyl)propane-1,3-dionato]copper(II) crystallizes in the triclinic space group P1. The copper atom lies on an inversion centre and is surrounded by four oxygen atoms in a square planar arrangement. The octyl chains are fully extended in an alltrans conformation. The molecules form a tilted columnar arrangement, the angle of tilt between the disc normal and the column axis being 122°. The column axis coincides with the crystallographic a-axis. In the crystal structure, each column is surrounded by six others. Along the column axis, adjacent copper atoms are separated by 5.821 (3) Å.

Notizen: Kristallstruktur von [Cu4OCl6(CH3CN)4] · 2 CH3CN / Crystal Structure of [Cu4OCl6(CH3CN)4] · 2 CH3CN

The title compound has been prepared by the reaction of CuCl, with hexakis(trimethylsilyl)-benzdiamidine, in boiling acetonitrile in the presence of traces of water, as brown crystals, which were characterized by their IR spectrum as well as by an X-ray structure determination. Space group C 2/c, Z = 4, 2668 observed unique reflexions, R = 0.036. Lattice dimensions at –65 C: a = 879.5(2), b = 2441.1(3), c = 1241.4(3) pm, β = 95.24(3)°. In the structure four copper atoms surround an oxygen atom in a slightly distorted tetrahedral fashion; the chlorine atoms bridge adjacent copper atoms, and each copper atom is thus bound to three chlorine atoms. The nitrogen atoms of the acetonitrile complete the slightly distorted trigonal bipyramid around the copper atoms.

The heteronuclear cluster chemistry of the Group IB metals XIV. The influence of the P(CH 2Ph) 3 ligand on the metal framework structures adopted by mixed-metal clusters containing M{P(CH 2Ph) 3} (M  Cu or Ag) fragments. Crystal structures of [Cu 2Ru 4(μ 3-H) 2(CO) 12{μ-P(CH 2Ph) 2-(η 2-CH 2Ph)}] and [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2

Treatment of a dichloromethane solution of the salt [N(PPh 3) 2] 2[Ru 4(μ-H) 2(CO) 12] with two equivalents of the complex [M(NCMe) 4]PF 6 (M  Cu or Ag) at −30°C, followed by the addition of two equivalents of P(CH 2Ph) 3, affords the novel mixed-metal cluster compound [Cu 2Ru 4(μ 3-H) 2(CO) 12{μ-P(CH 2Ph) 2(η 2-CH 2Ph)}] (77% yield) when M  Cu, whereas the expected product, [Ag 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2] (37% yield), is obtained for M  Ag. When an acetone solution of [N(PPh 3) 2] 2[Ru 4(μ-H) 2(CO) 12] is treated with a dichloromethane solution containing two equivalents of the compound [CuCl{P(CH 2Ph) 3}], in the presence of TlPF 6, a mixture of [Cu 2Ru 4(μ 3-H) 2(CO) 12{μ-P(CH 2Ph) 2(η 2-CH 2Ph)}] (44% yield) and [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2] (12% yield) is produced. Single-crystal X-ray diffraction studies were performed on [Cu 2Ru 4(μ 3-H) 2(CO) 12 {μ-P(CH 2Ph) 2(η 2-CH 2Ph)}] and [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2]. The former cluster exhibits a capped trigonal bipyramidal metal framework structure (CuCu 2.532(2), CuRu 2.585(2)–2.813(1), RuRu 2.790(1)–2.981(1) Å) and the single P(CH 2Ph) 3 group adopts a novel bidentate bonding mode by bridging the two adjacent copper atoms via bonds from its phosphorus atom (CuP 2.199(2) Å) and an η 2-CH 2Ph ring (CuC 2.146(10) and 2.339(12) Å). In marked contrast, [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2] adopts an unusual metal core structure, which consists of a Ru 4 tetrahedron with one edge bridged by a Cu{P(CH 2Ph) 3} unit and a non-adjacent face capped by the second Cu{P(CH 2Ph) 3} group (CuRu 2.589(4)–2.724(4), RuRu 2.760(3)–2.984(4) Å). Infrared and NMR spectroscopic data show that [Ag 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2] exhibits a capped trigonal bipyramidal skeletal geometry, with the silver atoms in close contact. Thus, although the P(CH 2Ph) 3 ligand is evidently too bulky to allow two adjacent Cu{P(CH 2Ph) 3} units to be accommodated in the metal skeleton of [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2], the greater size of the silver atom relative to copper means that the analogous silver-containing species can adopt the metal framework structure which previous work suggests is preferred by clusters of this type. Variable-temperature 31P-{ 1H} and 1H NMR spectroscopic studies demonstrate that all three of the new heteronuclear cluster compounds undergo a number of interesting dynamic processes in solution.

Copper(II)-promoted oxidation of mercaptocarboxylic acids. The characterization of disulphide- and oxalate-containing products. Crystal structures of [{Cu(bipy)(2,2′-dtdp)}n]·3nH2O and [{Cu(bipy)(3,3′-dtdp)}n]·2nH2O (bipy = 2,2′-bipyridine, dtdp = dithiodipropanoate)

The reaction of 2- and 3-mercaptopropanoic acids with an aqueous solution of 2,2′-bipyridine (bipy) and copper(II) acetate dihydrate (molar ratio 1 : 2 : 1) under aerobic conditions yields the copper(II) disulphide complexes [{Cu(bipy)(2,2′-dtdp)}n]·3nH2O (2,2′-dtdp = 2,2′-dithiodipropanoate) and [{Cu(bipy)(3,3′-dtdp)}n]·2nH2O (3,3′-dtdp = 3,3′-dithiodipropanoate). Both complexes have been structurally characterized by single-crystal X-ray crystallography. Crystals of the complex [{Cu(bipy)(2,2′-dtdp)}n]·3nH2O are triclinic, space group P, with a= 8.598(5), b= 10.378(6), c= 11.205(6)A, α= 96.43(5), β= 94.34(4), γ= 91.16(5)°, and Z= 2. The structure consists of crystallographically equivalent Cu(bipy)2+ units linked by 2,2′-dtdp ligands into infinite chains. The lattice water molecules participate in a hydrogen-bonding network that connects the 2,2′-dtdp ligands in adjacent chains. Each copper atom has a distorted square-pyramidal co-ordination geometry with the two bipy nitrogen and two carboxylate oxygen atoms in equatorial positions [Cu–N(1) 1.998(6), Cu–N(2) 2.008(6), Cu–O(1) 1.925(5), and Cu–O(3) 1.981 (5)A]. An apically bound disulphide sulphur completes the co-ordination sphere. The Cu–S distance [2.678(2)A] is considered to be at the short end of the range expected for axial Cu–S (disulphide) bond lengths. Crystals of the complex [{Cu(bipy)(3,3′-dtdp)}n]·2nH2O are monoclinic, space group P21/n, with a= 9.686(4), b= 9.409(3), c= 21.231 (4)A, β= 102.0(2)°, and Z= 4. The structure consists of crystallographically equivalent Cu(bipy)2+ centres linked by 3,3′-dtdp ligands into infinite zigzag chains. The chains are connected into sheets via carboxylate oxygen atoms which asymmetrically bridge adjacent copper atoms from neighbouring chains. The sheets are connected via a network of hydrogen bonds involving the lattice water molecules and carboxylate oxygen atoms. The copper atoms are in an irregular six-co-ordinate environment. The bipy nitrogens and two carboxylate oxygens occupy an approximate square plane [Cu–N(1) 1.988(3), Cu–N(2) 1.995(4) Cu–O(1) 1.934(3), and Cu–O(3) 1.961 (3)A]. Axial bonding is achieved by a bridging carboxylate oxygen [Cu–O(3′) 2.231 (4)A], which is also linked equatorially to an adjacent copper atom, and a weakly bound carboxylate oxygen (Cu–O(4) 2.826(5)A]. In contrast to the above results, the reaction of sodium mercaptoacetate with 2,2′-bipyridine and copper(II) acetate dihydrate results in desulphurization of the mercaptoacetate and formation of a ternary oxalate (OX) complex [Cu(bipy)(OX)]·2H2O.

Crystallographic description of phases in the Y-Ba-Cu-O superconductor.

Single-crystal x-ray techniques were used to determine two structures that comprise the Y-Ba-Cu-O superconductor. A green phase has the orthorhombic ${\mathrm{Y}}_{2}$${\mathrm{BaCuO}}_{5}$ structure. An opaque phase (${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathrm{x}}$, 0\ensuremath{\le}x\ensuremath{\le}1.0) is tetragonal (a=3.859 A\r{}, c=11.71 A\r{}; space group P4\ifmmode\bar\else\textasciimacron\fi{}m2;Z=1). The structure is related to a 1:1:3 AB${\mathrm{O}}_{3}$ perovskite: Ba and Y order in A sites and Cu is in B sites. Systematic oxygen vacancies between adjacent copper atoms lead to a fivefold-coordinate Cu in proximity to Y and a twofold-coordinate Cu in the vicinity of the Ba site.

The Crystal Structure of Bis(2,2′-bipyridine)-catena-μ-tetrafluoroborato-copper(II) Tetrafluoroborate

Abstract The crystal structure of the title compound was determined by means of the X-ray diffraction technique. The crystal is triclinic, space group P\barl, a=11.288(8), b=15.186(17), c=7.368(4) Å, α=74.93(3), β=78.23(3), γ=65.92(3)°, and Z=2. The structure was solved by the heavy-atom method and refined by the least-squares method to R=0.068 for 3678 non-zero reflections. The crystal is composed of BF4− ions and polymeric chains of [Cu(BF4)(bpy)2+] in which a tetrafluoroborate ion bridges two adjacent copper atoms through its two fluorine atoms. The coordination polyhedron around the copper atom is a tetragonally distorted octahedron; the four nitrogen atoms of bipyridine molecules in the equatorial plane are arranged in a flattened tetrahedral manner (average Cu–N=1.99 Å) and the two axial Cu–F distances are 2.566(6) and 2.662(4) Å. In both bipyridine molecules, the two pyridine rings are twisted slightly from each other; the interplanar angle is 3.1° in one bipyridine ligand and 10.2° in the other.

Catena-diaquabis-μ-(nicotinato-N-oxido)copper(II) tetrahydrate: structural, thermogravimetric and IR properties

An unstable copper(II) complex with nicotinic acid N-oxide {[Cu(N-nicO) 2(H 2O 2)]·$H 2O} n has been prepared and its crystal and molecular structure determined from three dimensional X-ray diffraction data. The crystals belong to the monoclinic space group P2 1. The cell parameters are a = 4.84(1), b = 27.55(7), c = 6.77(1) Å, β = 106.08(17)°, D o = 1.79, D c = 1.72 Mg m −3 and Z = 2. The structure was refined to a final R-value of 0.087. The copper complex is polymeric. Nicotinato N-oxido ligands are bonded bidentately through one carboxylato oxygen and the N-oxido oxygen atom, forming a double bridge between adjacent copper atoms. The central copper atoms have elongated octahedral geometry, such that the axial copperN-oxido oxygen distances (2.577(6) and 2.468(6) Å) are longer than equatorial copper-oxygen distance (average value 1.937 Å). The decomposition of the complex has been followed thermogravimetrically and IR spectra of intermediates have been run. Lattice water begins to be released at room temperature and at about 83°C only aqua ligands are left. The final fast decomposition of the complex begins at about 250°C.

Structure of bis-(4-methylpyridine)dichlorocopper(II): a dislocated linear chain

The crystal and molecular structure of bis(4-methylpyridine)dichlorocopper(II), Cu(C 6H 7N) 2Cl 2, has been determined from three-dimensional photographic X-ray data obtained from a twinned and highly mosaic crystal. The complex crytallizes in space group P2 1/c of the monoclinic system with two formula units in a cell of dimensions a = 9.745(7), b = 3.932(4), c = 19.035(9) Å, β = 111.8(2)°. The observed diffraction pattern, however, is nearly consistent with orthorhombic symmetry and the space group Cmma. The chain axis is parallel to the monoclinic crystallographic b-axis, and the twinning occurs perpendicular to this axis; the twinning causes dislocations in the chain by limiting the chain lengths to the sizes of the ordered crystal domains along the chain axis. The geometry at each copper atom is (4 + 2) tetragonally-elongated octahedral, the in-plane ligands being two trans-nitrogen atoms [CuN =2.07(3) Å] and two trans-chlorine atoms [CuCl =2.35(1) Å]. The axial ligands are symmetry-related chlorine atoms, which are in-plane ligands of the adjacent copper atoms in the chain, the axial CuCl and CuCu′ distances being 3.19(1) and 3.932(4) Å, respectively. Each chain is very similar to that found in the analogous pyridine complex, but the arrangement of the chains in the crystal is more like that in the thiazole complex Cu(thz) 2Cl 2.

The Crystal Structure of Perchlorato-bis(2,2′-bipyridine)copper(II) Perchlorate, [Cu(ClO4)(bipy)2]ClO4

Abstract The structure of bis(2,2′-bipyridine)copper(II) perchlorate, Cu(bipy)2(ClO4)2, has been determined from three-dimensional X-ray data collected by the photographic method. The compound forms triclinic crystals with a=7.44(1), b=14.93(1), c=15.32(1) Å, α=136.3(0.1), β=103.7(0.1), γ=83.2(0.1)°, and Z=2 in the space group P\bar1. The structure was solved by the usual Patterson and Fourier techniques and was refined by the least-squares method to an R value of 0.134. The crystal is composed of an infinite chain of [Cu(ClO4)(bipy)2+]∞ and ClO4−; a perchlorate ion in the chain bridges two adjacent copper atoms through its two oxygen atoms. Roughly speaking, the coordination polyhedron around the copper atom is a tetragonally-distorted octahedron; the four nitrogen atoms of bipyridine molecules are arranged in a flattened tetrahedral manner (average Cu–N=1.99 Å), the least-squares plane of these atoms making an equatorial plane, while the polar positions are occupied by the two oxygen atoms of perchlorate anions, the Cu–O distances being 2.45 and 2.73 Å. The two pyridine rings are twisted slightly to each other in both of the bipyridine molecules; the dihedral angle between the pyridine planes is 13° in one bipyridine ligand and 4° in the other.

Some studies in inorganic complexes. XXIII. Reactions of copper(II) with chelating heterocyclic bases

Studies have been made of copper(II) complexes of the ligands 2- aminomethyl-pyridine, 2-methylaminomethylpyridine, 2-aminomethyl-6- methylpyridine, and 2-(2-aminoethyl)pyridine. Various hydrated and anhydrous copper(II) complexes with the anions sulphate, nitrate, halide, and perchlorate were obtained with copper(II) ion to ligand in stoicheiometric ratios of 1 : 1 and 1 : 2 and several instances of water molecule and anion attachment to the coordination sphere are reported. Certain sulphate complexes are considered to be of the bridged type, others have sulphate coordinated to the� copper(II) atom by unidentate attachment, and some of the halide complexes are thought most probably to be dimers based upon double halogen to copper bridging. But there are no instances of bridging by metal-metal bonding between adjacent copper atoms since all magnetic moment values for the copper atoms in the complexes are either normal or only very slightly lower than normal. Physical methods used in the elucidation of structures included measurements of molecular conductances in suitable organic solvents, solubility observations, infrared and visible absorption spectrophotometry, pyrolysis methods, and measurements of magnetic susceptibility. Complex cations in aqueous solution were characterized by visible spectrophotometry. ��� A majority of the solid complexes isolated are described for the first time; where complexes have previously been recorded additional physical investigations have been made.

Metal complexes as ligands. VII. Copper bromide complexes with bidentate schiff bases

A series of new binuclear copper(II) complexes has been prepared by the reaction of copper(II) bromide with bis(N-R-salicylaldimino) copper(II) complexes, where R is a normal or branched alkyl, or a phenyl group. The room temperature magnetic moments are considerably below the «spin-only» values, due to antiferromagnetic exchange interactions between adjacent copper atoms. The ligand field absorption spectra are in keeping with only one type of copper atom, indicating that the environment about each of the two copper atoms is the same. These properties are explained in terms of a trans structure ▪ for these binuclear complexes derived from bidentate salicylaldimines, as opposed to the cis structure for the analogous derivatives of tetradentate salicylaldimines. This trans structure is analogous to that proposed earlier for copper chloride complexes with bidentate Schiff Bases. The magnetic moments and the ligand field absorption spectra are not very sensitive to the size of the R- group on the nitrogen, indicating that the steric effect of these groups is fairly small, as expected for the proposed structure. The copper bromide complexes are less stable, and lower melting, than the chloride complexes. The ligand field absorption bands are at lower energies in the bromide than in the chloride complexes; this is interpreted in terms of a difference in ligand field strength as well in stereochemistry.

Metal Complexes as Ligands. VI. Antiferromagnetic Interactions in Trinuclear Complexes Containing Similar and Dissimilar Metals

The magnetic properties of a series of discrete trinuclear transition-metal complexes derived from tetradentate Schiff bases have been investigated over the temperature range 80°–400°K. The complexes contain the groupings of metals CuMCu where M is Cu(II), Ni(II), Co(II), Fe(II), and Mn(II), and the three metal atoms are linked by oxygen bridges. For each grouping of metals, the observed magnetic moments are subnormal, and decrease markedly with decreasing temperatures. These magnetic properties are explained in terms of antiferromagnetic interactions between the central metal atom M and the adjacent copper (II) atoms. The magnetic moments calculated on the basis of this model of discrete antiferromagnetism are found to be in good agreement with the experimental results. Mutual interactions between the terminal copper atoms apparently exist to only a small degree or not at all.

Crystal Structure of Cu2Cl4(CH3CN)2, Cu3Cl6(CH3CN)2, and Cu5Cl10(C3H7OH)2

The crystal structures of three red complexes of copper (II) chloride with the molecular formulas Cu2Cl4(CH3CN)2, Cu3Cl6(CH3CN)2, and Cu5Cl10 (C3H7OH)2 have been determined. Each compound contains discrete molecules in which the copper atoms and their ligands lie essentially in a plane. Within each molecule, adjacent copper atoms are bridged by two chlorine atoms equidistant from the copper atoms. Each copper atom forms four bonds, with Cu–Cl≃2.3 Å while Cu–O or Cu–N bonds are just less than 2.0 Å. Bond angles are approximately 90°. In all cases the organic molecules are bonded to copper atoms in positions which are trans for the entire molecule. Molecules are bridged together by longer Cu–Cl bonds which vary from 2.6 to 3.2 Å.

Isotropic Exchange Integral for Cupric Acetate Monohydrate Crystals

MOOKHERJI1 from his magnetic studies on cupric acetate monohydrate crystal predicted that there is some sort of exchange interaction between adjacent copper atoms. But in the absence of either crystallographic data or diamagnetic dilution data he could not say whether the interaction forces were of Kramers' super-exchange type acting through intermediate oxygen atoms, or whether direct spin interaction occurred. Later, from an examination of anomalous behaviour of cupric acetate monohydrate towards magnetic susceptibility and paramagnetic resonance absorption, Bleaney and Bowers2 concluded that there is some form of strong coupling between unpaired electrons on adjacent copper atoms through exchange forces. Van Niekerk and Schoening3 from X-ray analysis showed that cupric acetate monohydrate is a new type of complex having the formula Cu2(CH3COO)4.2H2O. The Cu-Cu distance is 2.64 A, showing that there is direct interaction between the copper ions, because the distance for super exchange of Kramers type (Cu-Cu distance) should be of the order of 4 A. Figgis and Martin4 have shown that exchange integral J = l.6 kTc, where Tc is critical temperature at which Δχ/δT = 0 (χ being the gram molecular susceptibility).