Pyramidal Surroundings Research Articles

Synthesis, crystal structure and magnetic properties of the cyclic tetranuclear compound [Cu4(pz)4(hppa)2(H2O)4] [pz = pyrazolate; hppa = R,S-2-hydroxo-2-phenyl-2-(1-pyrazolyl)acetate

The synthesis, X-ray structure and magnetic properties of the neutral tetranuclear copper(II) complex of formula [Cu4(pz)4(hppa)2(H2O)4] (1) [Hpz = pyrazole and hppa = R,S-2-hydroxo-2-phenyl-2-(1-pyrazolyl)acetate] are reported. Remarkably, the structure of 1 reveals the presence of the S- and R-forms of the new hppa ligand which is formed in situ in the complex reaction between copper(II), pyrazole and phenylmalonate in water:methanol solvent mixture under ambient conditions. The two crystallographically independent copper(II) ions [Cu(1)/Cu(2)] are five-coordinate in square pyramidal surroundings. Three nitrogen atoms, from two pz groups and one hppa ligand and one oxygen atom of the same hppa dianion form the basal plane and a water molecule occupies the apical position at Cu(1) whereas two nitrogen atoms from two pz groups plus one carboxylate- and one hydroxo-oxygen atoms from a hppa ligand build the basal plane and a water molecule fills the apical site at Cu(2). Two types of bridging pathways alternate in the edges of the centrosymmetric cyclic tetracopper(II) unit: a single bis-monodentate pz in the longest edge [3.5850(5) Å] and a double bridge consisting of a hppa ligand adopting the κ2O:κN:κO″ coordination mode and another bis-monodentate pz group in the shortest edge [3.3228(5) Å]. Magnetic susceptibility measurements in the temperature range 50–300 K for 1 show the occurrence of strong antiferromagnetic interactions between the copper(II) ions through the two exchange pathways: J1 = 650(5) cm−1 (across the pz/hppa bridge) and J2 = −200(9) cm−1 (through the single pz linker). These values of the magnetic coupling are analysed and discussed in the light of the literature data of copper(II) complexes where related bridges occur.

A methylenediphosphonate bridged copper(II) tetramer: Synthesis, structural, thermal, and magnetic characterization of [Cu4(H2O)2(phen)4(μ-P2O6CH2)2]·21H2O

A novel tetracopper(II) complex namely, [Cu4(H2O)2(phen)4(μ-P2O6CH2)2]·21H2O (1) was synthesized by using copper(II) chloride, 1,10-phenanthroline (phen), and methylene diphosphonic acid (MDP). The structure of 1 was characterized by single crystal X-ray diffraction and spectroscopy. Compound 1 crystallizes in the triclinic system, P1¯ space group and its crystal structure consists of neutral centrosymmetric tetranuclear copper(II)-methylene diphosphonate units where each peripheral {Cu(phen)(P2O6CH2)}2− fragment adopts the bidentate(Oeq-P-Oeq)/monodentate (Oax) bridging mode towards each of the two inner {Cu(phen)}2+ entities resulting in a “clamshell”-like orientation. The two crystallographically independent copper(II) ions in 1 (Cu1/Cu2) are five-coordinate with two nitrogen atoms from a bidentate phen molecule and two phophonate-oxygens building the basal plane (Cu1/Cu2) and either a water molecule (Cu2) or a phosphonate-oxygen (Cu1) filling the apical position of somewhat distorted square pyramidal surroundings. The values of the intramolecular copper–copper separation are 3.3219(8) and 3.2062(8) Å for Cu1⋯Cu2 and Cu1⋯Cu1i, respectively. Cryomagnetic measurements on a polycrystalline sample of 1 reveal the occurrence of an overall antiferromagnetic behaviour leading to a diamagnetic low-lying spin state. The values of the intramolecular magnetic interactions are J1 = −22.60(4) cm−1 (across the bis-bidentate methylene diphosphonate) and J2 = +4.9(3) cm−1 (through the double-oxo(phosphonate) bridge), the spin Hamiltonian being defined as H = −J1(SCu1·SCu2 + SCu1i·SCu2i) − J2(SCu1·SCu1i). These values are analyzed through simple orbital symmetry considerations and compared with those for related systems in the literature.

Synthesis and structural characterization of antimicrobial binuclear copper(II) coordination compounds bridged by hydroxy- and/or thiodipropionic acid

In the present study, two binuclear copper(II) coordination compounds bridged by hydroxy- and thiodipropionic acid have been synthesized. The structure of compounds was determined by X-ray crystallography. The central copper atoms exist in square pyramidal surroundings. Basal plane is formed by nitrogen atoms of amines and oxygen atoms of bridges, whereas apical positions are occupied by oxygen atoms of coordinated water molecules. Temperature dependence study of magnetic susceptibility proved strong antiferromagnetic exchange between copper atoms in hydroxy-bridged complex. These coordination compounds were also tested for their biological activities in vitro. Both coordination compounds exhibit pronounced cytocompatibility in mammalian epithelial cells with no induction of oxidative stress and DNA fragmentation. Moreover, synthesized compounds are hemocompatible and do not alter expression of a marker of multiple cellular stress, p53. On the other hand, both compounds had stimulatory effect on expression of metallothioneins (MT-1/2 and MT-3). Antimicrobial testing on Escherichia coli, Staphylococcus aureus and methicillin-resistant Staphylococcus aureus revealed that both copper compounds exhibit antibacterial activity regardless the cell wall composition. Overall, current work presents a synthesis of Cu(II) coordination compounds with interesting biological behavior and with a promising potential to be further tested in pre-clinical models.

Heterobimetallic One-Dimensional Coordination Polymers MICuII (M = Li and K) Based on Ferromagnetically Coupled Di- and Tetracopper(II) Metallacyclophanes

The synthesis, crystal structure and magnetic properties of the coordination polymers of formula [EDAP{Li6(H2O)8[(Cu2(μ-mpba)2)2(H2O)2]}]n (1) and [(EDAP)2{K(H2O)4[Cu2(μ-mpba)2(H2O)2]}Cl·2H2O]n (2), in which mpba = N,N′-1,3-phenylenebis(oxamate) and EDAP2+ = 1,1′-ethylenebis(4-aminopyridinium) are described. Both compounds have in common the presence of the [Cu2(mpba)2]4− tetraanionic unit which is a [3,3] metallacyclophane motif in which the copper(II) ions are five-coordinate in a distorted square pyramidal surrounding. The complex anion in 1 is dimerized through double out-of-plane copper to outer carboxylate-oxygen atoms resulting in the centrosymmetric tetracopper(II) fragment [Cu4(μ-mpba)4(H2O)2]8− which act as a ligand toward six hydrated lithium(I) cations leading to anionic ladder-like double chains whose charge is neutralized by the EDAP2+ cations. In the case of 2, each dicopper(II) entity acts as a ligand towards tetraquapotassium(I) units to afford anionic zig zag single chains of formula {K(H2O)4[Cu2(μ-mpba)2(H2O)2]}n3n− plus EDAP2+ cations and non-coordinate chloride anions. Cryomagnetic measurements on polycrystalline samples 1 and 2 show the occurrence of ferromagnetic interactions between the copper(II) ions across the –Namidate–(C–C–C)phenyl–Namidate– exchange pathway [J = +10.6 (1) and +8.22 cm−1 (2)] and antiferromagnetic ones through the double out-of-plane carboxylate-oxygen atoms [j = −0.68 cm−1 (1), the spin Hamiltonian being defined as H = − J ( S C u 1 · S C u 2 + S C u 2 i · S C u 1 i ) − j ( S C u 2 · S C u 2 i ) ].

A new heterometallic Cu(II)-Cd(II) complex based on 1,3,5-benzenetricarboxylic acid

A novel heterometallic complex [Cu2Cd2(OH)(BTC)(TMA)(H2O)2]n (1) (H3BTC = 1,3,5-benzenetricarboxylic acid, H4TMA = 2-hydroxytimesic acid) is synthesized and characterized. The crystal structure analysis reveals that two crystallographically independent Cu(II) ions are both five-coordinate in distorted square pyramidal surroundings. And for two Cd(II) ions, Cd1 is six coordinated, displaying a distorted triangular prism; Cd2 is five-coordinated, fabricating a distorted trigonal bipyramid. In 1, the H3BTC ligand is partially oxidized into H4TMA, with bridging mode of μ8- and μ7- for TMA4− and BTC3−, respectively. Thus, 1 presents a 3D structure with (5, 6, 7, 9)-connected net topology.

Copper(ii) assembling with bis(2-pyridylcarbonyl)amidate and N,N′-2,2-phenylenebis(oxamate)

We herein present the synthesis and X-ray structures of five copper(II) complexes of formulae [Cu(bpca)(CF3SO3)(H2O)]·H2O (1), [Cu(bpca)(Phpr)(H2O)]·3/2H2O (2), {[Cu(bpca)]2[Cu(opba)(H2O)]}·H2O (3), {[Cu(bpca)]2(H2opba)}2·6H2O (4) and [Cu(bpca)(EtH2opba)]n (5), where bpca = bis(2-pyridylcarbonyl)amidate, Phpr = 3-phenylpropionate, CF3SO3(−) = triflate (anion of the trifluoromethanesulphonic acid), H4opba = N,N′-1,2-phenylenebis(oxamic acid), and EtH3opba = monoethyl ester derivative of the H4opba. 1 and 2 are mononuclear copper(II) complexes where the copper atom is five-coordinate in distorted square pyramidal surroundings with a tridentate bpca and a water molecule (1)/carboxylate oxygen (2) building the basal plane and a triflate oxygen (1)/water molecule (2) filling the apical position. 3 is a neutral tricopper(II) complex where the [Cu(opba)(H2O)]2− unit acts as a bis-bidentate ligand toward two peripheral [Cu(bpca)]+ fragments. The three crystallographically independent copper(II) ions in 3 are five-coordinate with two nitrogen and two oxygen atoms (inner copper atom)/three bpca-nitrogen and an oxamate oxygen (outer copper atom) building the basal plane plus a water molecule (inner copper)/an oxamate oxygen (outer copper) in the apical position (inner copper atom) of somewhat distorted square pyramidal surroundings. 4 is a centrosymmetric tetracopper(II) compound where four [Cu(bpca)]+ fragments are assembled by two H2opba2− groups adopting an unusual bidentate/bis-monodentate bridging mode. The two crystallographically independent copper(II) ions in 4 are also five-coordinate having the three bpca-nitrogens in basal positions, the other two sites of the distorted square pyramid being filled by two oxygens of either a bidentate oxamate (at one copper centre) or two bis-monodentate oxamates (at the other copper atom). 5 is a zigzag chain of [Cu(bpca)(H2O)]+ units which are connected through the EtH2opba− ligand adopting a bidentate/monodentate bridging mode across the monodeprotonated oxamate group. Each copper(II) ion in 5 is six-coordinate in an elongated octahedral CuN3O3 chromophore. The magnetic properties of 3–5 were investigated in the temperature range 1.9–300 K. 3 exhibits an intermediate intramolecular antiferromagnetic interaction [J = -65.8(2) cm(-1) with the Hamiltonian H = -J(S(Cu1)·S(Cu2) + S(Cu2)·S(Cu3))] which leads to a low-lying spin doublet at low temperatures. A weak antiferromagnetic coupling between the inner copper(II) ions occurs in 4 [J = -2.36(2) cm(-1), H = -JS1·S2)] and a very small intrachain antiferromagnetic interaction is observed in 5 [J = -0.17(1) cm(-1) with H = -J∑(i)S(i)·S(i+1)]. These values are analyzed by means of simple orbital symmetry considerations and compared with those previously reported for parent systems.

Azide‐Bridged Copper(II) and Manganese(II) Compounds with a Zwitterionic Tetrazolate Ligand: Structures and Magnetic Properties

AbstractTwo azide‐bridged coordination polymers, [Cu(mptz)(N3)2] (1) and [Mn(mptz)(N3)2H2O] (2), (mptz = N‐methyl‐4‐pyridinium tetrazolate), were synthesized and crystallographically and magnetically characterized. Compound 1 is a neutral 1D coordination polymer in which the CuII ions, which are in a square pyramidal surrounding, are linked by double end‐on azide bridges in an alternating basal–basal and basal–apical fashion. Compound 2 exhibits a 3D MnII–azide coordination framework with the (10,3)‐b net topology, in which the double end‐on–azide‐bridged dimanganese units are interlinked by single end‐to‐end azide bridges. The magnetic analyses indicated that 1 behaves magnetically as a quasi‐dimer with an S = 1 ground state due to a strong ferromagnetic interaction through the basal–basal azide bridges and a very weak antiferromagnetic coupling through the basal–apical azide bridges. Compound 2 exhibits 3D antiferromagnetic behaviors with TN = 24.0 K, where the end‐to‐end and end‐on azide bridges mediate the antiferromagnetic and ferromagnetic interactions, respectively.

Synthesis, crystal structures and magnetic properties of tricyanomethanide-containing copper(II) complexes

The preparation, crystal structures and magnetic properties of the copper(II) complexes of formula [Cu(pyim)(tcm)(2)](n) (1), [Cu(bpy)(tcm)(2)](n) (2), [Cu(4)(bpz)(4)(tcm)(8)] (3), {[Cu(terpy)(tcm)].tcm}(n) (4) and {[Cu(2)(tppz)(tcm)(4)].3/2H(2)O}(n) (5) [pyim = 2-(2-pyridyl)imidazole, tcm = tricyanomethanide, bpy = 2,2'-bipyridine, bpz = 2,2'-bipyrazine, terpy = 2,2':6',2''-terpyridine and tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine] are reported. Complexes, 1, 2 and 4 are uniform copper(II) chains with single- (1 and 4) and double-(2) micro-1,5-tcm bridges with values of the intrachain copper-copper separation of 7.489(1) (1), 7.520(1) and 7.758(1) (2) and 7.469(1) A (4). Each copper atom in 1, 2 and 4 is five-coordinate with bidentate pyim (1)/bpy (2) and tridentate terpy (4) ligands and nitrile-nitrogen atoms from bridging (1,2 and 4) and terminal (1) tcm groups building a distorted square pyramidal surrounding. The structure of 3 is made up of neutral centrosymmetric rectangles of (2,2'-bipyrazine)copper(II) units at the corners, the edges being built by single- and double-micro-1,5-tcm bridges with copper-copper separations of 7.969(1) and 7.270(1) A, respectively. Five- and six-coordinated copper atoms with distorted square pyramidal and elongated octahedral environments occur in . Compound 5 is a neutral copper(II) chain with regular alternating bis-tridentate tppz and double micro-1,5-tcm bridges, the intrachain copper-copper distances being 6.549(7) and 7.668(1) A, respectively. The two crystallographically independent copper atoms in 5 have an elongated octahedral geometry with three tppz nitrogen atoms and a nitrile-nitrogen atom from a bridging tcm group in the equatorial positions, and two nitrile nitrogen atoms from a terminal and a bridging tcm ligand occupying the axial sites. The investigation of the magnetic properies of 1-5 in the temperature range 1.9-295 K has shown the occurrence of weak ferro- [J = +0.11(1) cm(-1) (2)] and antiferromagnetic interactions [J = -0.093(1) (1), -0.083(1) (4), -0.04(1) and 1.21(1) cm(-1) (3)] across the micro-1,5-tcm bridges and intermediate antiferromagnetic coupling [-J = 37.4(1) cm(-1) (5)] through bis-tridentate tppz. The values of the magnetic interactions are analyzed through simple orbital symmetry considerations and compared with those previously reported for related systems.

Synthesis, Crystal Structure and Magnetic Properties of Heterodimetallic ReIVCuII Complexes

AbstractThe two rhenium(IV)‐copper(II) heterometallic complexes [CuLβ][ReCl4(ox)]·DMF (1) and [(CuLα)2Cl][ReCl4(ox)]Cl (2) (Lβ = N‐dl‐5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradeca‐4,11‐diene and Lα = N‐dl‐5,7,7,12,12,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradeca‐4,14‐diene) were synthesized, and the crystal structures of both compounds were determined at 173(2) K. Complex 1 crystallizes in a monoclinic space group P21, with a = 9.365(2) Å, b = 15.150(2) Å, c = 10.776(1) Å, β = 110.01(1)°, Z = 2, whereas 2 crystallizes in an orthorhombic space group Pca21 with a = 16.660(5) Å, b = 16.017(5) Å, c = 17.066(5) Å, and Z = 4. The CuLβ macrocycle cation is approximately planar and coordinated from above and below by [ReCl4(ox)]2– units through the bis(bidentate) oxalato ligands. It features an oxalato‐bridged heterometallic ReIV–CuII zigzag chain, the shortest intrachain metal–metal distances are Re···Cu = 5.568(2) and 5.870(2) Å in the direction of the b axis. The crystal structure of 2 consists of dinuclear complex cations [(CuLα)2Cl]3+ with [ReCl4ox]2– and isolated Cl– as counter anions. Cu atoms in CuLα are only fivefold coordinated in a square pyramidal surrounding, and the cations (CuLα)2+ are connected in pairs by chloride. The intramolecular Cu···Cu separation is 4.885(3) Å, the shortest Re···Cu distance is 7.612(3) Å. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.7–300 K. Compound 1 behaves like a ferrimagnetic CuII‐ReIV dimetallic, one–dimensional chain with intrachain antiferromagnetic coupling. Compound 2 shows weak antiferromagnetic interactions within the CuII–CuII units. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Structural analysis and magnetic properties of the copper(II) dicyanamide complexes [Cu2(dmphen)2(dca)4], [Cu(dmphen)(dca)(NO3)]n and [Cu(4,4′-dmbpy)(H2O)(dca)2] (dca=dicyanamide; dmphen=2,9-dimethyl-1,10-phenanthroline; 4,4′-dmbpy=4,4′-dimethyl-2,2′-bipyridine)

The preparation, crystal structures and magnetic properties of three copper(II) compounds of formulae [Cu2(dmphen)2(dca)4] (1), [Cu(dmphen)(dca)(NO3)]n (2) and [Cu(4,4′-dmbpy)(H2O)(dca)2] (3) (dmphen=2,9-dimethyl-1,10-phenanthroline, dca=dicyanamide and 4,4′-dmbpy=4,4′-dimethyl-2,2′-bipyridine) are reported. The structure of 1 consists of discrete copper(II) dinuclear units with double end-to-end dca bridges whereas that of 2 is made up of neutral uniform copper(II) chains with a single symmetrical end-to-end dca bridge. Each copper atom in 1 and 2 is in a distorted square pyramidal environment: two (1) or one (2) nitrile-nitrogen atoms from bridging dca groups, one of the nitrogen atoms of the dmphen molecule (1 and 2) and either one nitrile-nitrogen from a terminal dca ligand (1) or a nitrate-oxygen atom (2) build the equatorial plane whereas the second nitrogen atom of the heterocyclic dmphen fills the axial position (1 and 2). The copper–copper separations through double (1) and single (2) end-to-end dca bridges are 7.1337(7) (1) and 7.6617(7) (2). Compound 3 is a mononuclear copper(II) complex whose structure contains two neutral and crystallographically independent [Cu(4,4′-dmbpy)(H2O)(dca)2] molecules which are packed in two different layer arrangements running parallel to the bc-plane and alternating along the a-axis. The copper atoms in both molecules have slightly distorted square pyramidal surroundings with the two nitrogen atoms of the 4,4′-dmbpy ligand and two dca nitrile-nitrogen atoms in the basal plane and a water oxygen in the apical position. A semi co-ordinated dca nitrile-nitrogen from a neighbour unit [2.952(6) Å for Cu(2)–N] is in trans position to the apical water molecule in one of the two molecules, this feature representing part of the difference in supramolecular connections in the alternating layers referred to above. Magnetic susceptibility measurements for 1–3 in the temperature range 1.9–290 K reveal the occurrence of weak antiferromagnetic interactions through double [J=−3.3 cm−1 (1), Ĥ=−JŜ1·Ŝ2] and single [J=−0.57 cm−1 (2), Ĥ=−J∑i=1Ŝi·Ŝi+1] dca bridges and across intermolecular contacts [θ=−0.07 K (3)].

Aminophosphanes with bulky amino groups: Molecular structure, coupling constants 1J(31P, 15N) and 2J(31P, 29Si), and isotope‐induced chemical shifts 1Δ14/15N(31P)

AbstractThe preferred conformation of aminophosphanes with bulky amino groups (1–20) was determined by NMR spectroscopy in solution, in two cases in the solid state (11,17) and in one case (11) by X‐ray crystallography. Trimethylsilylaminodiphenylphosphanes Ph2PN(R)SiMe3 (R = Bu (1), Ph (2), 2‐pyridyl (3), 2‐pyrimidyl (4), Me3Si (5)), amino(chloro)phenylphosphanes Ph(Cl)PNRR′ (R = Bz, R′ = Me (6), R = Bz, R′ = tBu (7), R = Et, R′ = Ph (8)), amino(chloro)tert‐butylphosphanes tBu(Cl)PNRR′ (R = R′ = iPr (9), R = Me, R′ = tBu (10), R = Bz, R′ = tBu (11), R = H, R′ = tBu (12), R = Et, R′ = Ph (13), R = iPr, R′ = Ph (14), R = Bu, R′ = Ph (15), R = Bz, R′ = Ph (16), R = R′ = Ph (17), R = R′ = Me3Si (18)), 3‐tert‐butyl‐2‐chloro‐1,3,2‐oxazaphospholane (19), and benzyl(tert‐butyl)aminodichlorophosphane (20) were studied by 1H, 13C, 15N, 29Si, and 31P NMR spectroscopy. In all cases, the more bulky substituent at the nitrogen atom prefers the syn‐position with respect to the assumed orientation of the phosphorus lone pair of electrons. Many of the derivatives studied adopt this preferred conformation even at room temperature. Numerous signs of coupling constants 1J(31P, 15N), 2J(31P, 13C), and 2J(31P, 29Si) were determined. Low temperature NMR spectra were measured for derivatives for which rotation about the PN bond at room temperature is fast, showing the presence of two rotamers at low temperature. The respective conformation of these rotamers could be assigned by 13C, 15N, and 31P NMR spectroscopy. Isotope‐induced chemical shifts 1Δ15/14N(31P) were determined for all compounds at natural abundance of 15N by using Hahn‐echo extended polarization transfer experiments. The molecular structure of 11 in the solid state reveals pyramidal surroundings of the nitrogen atom and mutual trans‐positions of the tert‐butyl groups at phosphorus and nitrogen. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:667–676, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10084

Syntheses, crystal structures and magnetic properties of chromato-, sulfato-, and oxalato-bridged dinuclear copper(II) complexes

Four dinuclear copper(II) complexes of formula [Cu2(bpca)2(H2O)3(CrO4)]·H2O (1), [Cu2(bpca)2(H2O)3(SO4)]·H2O (2), [Cu2(bpca)2(H2O)2(C2O4)]·2H2O (3), and [Cu2(bpca)2(C2O4)] (4) [bpca=bis(2-pyridylcarbonyl)amide anion] have been synthesized and their magnetic behavior has been investigated as a function of temperature. The structures of 1–3 have been determined by single-crystal X-ray diffraction, whereas the structure of 4 was already known. The structures of this family of complexes are made up of neutral chromate-O1,O1′ (1), sulfate-O1,O1′ (2) and oxalate-O1,O2:O1′,O2′-bridged (3 and 4) dinuclear copper(II) units. The two copper atoms within the dinuclear unit of the isomorphous compounds 1 and 2 show different surroundings: they exhibit distorted square pyramidal (Cu(2)) and octahedral (Cu(1)) surroundings with the three bpca-nitrogen atoms and either a chromate (1)/sulfate (2)-oxygen atom (Cu(2)) or a water-oxygen atom (Cu(1)) defining the equatorial positions, whereas the axial sites are occupied by a water molecule (Cu(2) and Cu(1)) and a chromate (1)/sulfate (2)-oxygen atom (Cu(1)). Each copper atom of the centrosymmetric compound 3 is six-coordinated with the three bpca-nitrogen atoms and an oxalate-oxygen forming the equatorial plane, whereas the axial positions are occupied by the other oxalate-oxygen and a water molecule. Complex 4 is also centrosymmetric, each copper atom exhibiting a distorted square pyramidal surrounding. The equatorial plane is the same as in 3, and an oxalate-oxygen occupies the axial position. The intramolecular copper-copper distances are 3.660(1) Å (1), 3.747(1) Å (2) and 5.631(1) Å (3) (5.442(1) Å in 4). The magnetic study of 1–4 reveals the occurrence of weak intramolecular antiferro- (1 and 2) and ferromagnetic (3 and 4) interactions. The magnitude and nature of the magnetic coupling through these extended bridges are analyzed and discussed in the light of the available structural data.

CaBa2Cu2FeO6 Phase: Synthesis, Structure, and Mössbauer Spectra

A new phase CaBa2Cu2FeO6 was synthesized by the ceramic procedure (vacuum, 930°C) from Ca2Fe2O5 and BaCuO2 intermediates. The phase is tetragonal and has a 123 structure with unit cell parameters a = b = 0.4089(3) nm, c = 1.2330(8) nm. Based on the Mossbauer data it is concluded that the iron atoms are in the Fe(3+) state and occupy only the Cu(2) sites, i.e., have tetragonal pyramidal surroundings.

Tetrasupersilyl-tristannaallene and -tristannacyclopropene (tBu3Si)4Sn3 – Isomers with the Shortest Sn=Sn Double Bonds to Date

The dark blue, air- and moisture-sensitive, thermolabile tristannaallene R*2Sn=Sn=SnR*2 (5) (R* = SitBu3) is prepared by reaction of Sn(OtBu)2 or Sn[N(SiMe3)2]2 with R*Na in pentane/benzene at –25°C. The dark red-brown, air-sensitive, moisture-insensitive, and thermostable cyclotri-stannene R*4Sn3 (6) with a –R*Sn=SnR*– moiety as part of a Sn3 ring is obtained from the reaction of Sn(OtBu)2 or Sn[N(SiMe3)2]2 with R*Na in pentane at 25°C or from the isomerization of 5 at room temperature (τ1/2 = 9.8 h). According to the result of X-ray structural analyses the Sn3 framework of chiral 5 is bent (156°) and the terminal Sn atoms have pyramidal surroundings. The SnSn double bonds in 5 (2.68 A) are shorter than those found for the hitherto structurally investigated distannenes (2.77–2.91 A). Even shorter is the double bond in 6 (2.59 A). The unsaturated Sn atoms here have nearly planar surroundings in perfect analogy to the carbon atoms in CC double bonds. The SnSn double bond in 6 can therefore be considered as the first “true” Sn=Sn bond. The structures of 5 and 6 can be deduced also from 119Sn- and 29Si-NMR studies in solution.

Synthesis and Structure of Solvent-Free Hexameric Magnesium Tri(tert-butyl)silylphosphandiide.

Hexameric magnesium tri(tert-butyl)silylphosphandiide crystallizes with a hexagonal Mg6P6 prism and is a rare example of a solvent-free phosphandiide of a hard main group metal. The magnesium atoms show a coordination number of 3 in a trigonal pyramidal surrounding.

Bis(alkylzink)substituiertes Phosphan und Sulfan sowie deren schweren Homologen des Typs E[ZnC(SiMe 3) 3] 2 (E=PSi iPr 3, AsSi iPr 3, S, Se, Te)

The reaction of lithium tri isopropylsilylphosphanide 1a and -arsanide 1b with tris(trimethylsilyl)methylzinc chloride 2 yields bis[tris(trimethylsilyl)methylzinc]tri isopropylsilylphosphandiide 3a and -arsandiide 3b, respectively. The pnictogen atoms are in a trigonal pyramidal surrounding, and the CZnP as well as the CZnAs moieties are bent. Due to the steric crowding, a bis(alkylzinc) substituted amine was not detected, but the metathesis reaction of lithium tri isopropylsilylamide with 2 gives tris(trimethylsilyl)methylzinc tri isopropylsilylamide 4. The reaction of the compounds 3a and 3b with elemental chalkogenes yields the substitution of the i Pr 3SiP and i Pr 3SiAs fragments by sulfur ( 5), selenium ( 6) and tellurium ( 7). Bis[tris(trimethylsilyl)methylzink] sulfide 5 crystallizes as a dimeric molecule with a folded Zn 2S 2 cycle in the syn/ anti configuration. The syn-(Me 3Si) 3CZn moiety shows weak Lewis acid–base interactions with the transannular sulfur atom. Crystallographic data of 3b: triclinic, P 1 ̄ , a=1198.68(8), b=1377.58(8), c=1628.8(2) pm, α=91.434(6)°, β=108.340(7)°, γ=113.767(4)°, Z=2, wR 2=0.1305 on F 2 values for 7787 reflections.

Synthese sowie Vergleich der spektroskopischen parameter und molekülstrukturen von Bis(tetrahydrofuran-O)magnesium-bis[bis(trimethylsilyl)phosphanid] und -arsanid

The reaction of Magnesium n/ sec-dibutanide with bis(trimethylsilyl)phosphane, respectively -arsane in THF yields derivatives of the type [(Me 3Si) 2E] 2Mg · 2THF (E  P, As). Magnesium-bis[bis(trimethylsilyl)phosphanide] · 2THF crystallizes in the monoclinic space group C2/ c with a = 1861.7(3) pm, b = 976.0(3) pm, c = 1921.2(3) pm, β = 109.67(1)° and Z = 4. The homologous arsanide crystallizes in the triclinic space group P 1 ̄ with a = 980.7(2) pm, b = 1266.1(2) pm, c = 1437.6(2) pm, α = 78.29(1)°, β = 88.02(2)°, γ = 70.28(1)° and Z = 2. In both compounds the magnesium atoms are coordinated distorted tetrahedrally, the pnictogen atoms display pyramidal surroundings.

ESR evidence for structural rearrangements occurring upon MoO 3 reduction

Reduction of polycrystalline MoO 3 in the course of heat treatment in vacuo has been studied by means of ESR. The formation of two different Mo(V) centers has been identified: center A with g x = 1.946, g y = 1.960, g z = 1.868; and center B characterized by g x = 1.943, g y = 1.954, g z = 1.878. Center B exhibited a well-resolved hyperfine structure resulting from naturally abundant odd isotopes of Mo: A x = 3.2mT, A y = 3.0mT, A z = 7.0mT. Species A formed at an early stage of reduction has been identified as Mo(V) in rhombically distorted square pyramidal surrounding, whereas center B appearing in strongly reduced samples shows a distorted octahedral coordination. The results have been interpreted in terms of the crystallographic shear mechanism.