Structures of anhydrous and hydrated copper(II) hexafluoroacetylacetonate

Crystal structure analyses are reported for anhydrous copper(II) hexafluoroacetylacetonate (Cu(hfac)(2)) and for two of its hydrates. The anhydrous compound (Cu(hfac)(2), 1: P1; at 100 K, a = 5.428(1), b = 5.849(1), c = 11.516(3) A; alpha = 81.47(2), beta = 74.57(2), gamma = 86.96(2) degrees; Z = 1) contains centrosymmetric square-planar complexes with close intermolecular Cu.F contacts. The geometry of the complex is similar to that previously reported for Cu(hfac)(2).toluene. The monoaquo compound (Cu(hfac)(2)(H(2)O), 2: P2(1)/c; at 100 K, a = 10.8300(8), b = 6.5400(6), c = 21.551(3) A; beta = 90.282(8) degrees; Z = 4) consists of square-pyramidal molecules with apical H(2)O ligands, and close-lying F atoms in the sixth coordination sites. The major difference between this structure and the two other polymorphs previously reported is the nature and direction of hydrogen bonds. The yellow-green solid formed from Cu(hfac)(2) with excess H(2)O is identified as the trihydrate. In crystalline form it is the previously unreported [trans-Cu(hfac)(2)(H(2)O)(2)].H(2)O (3: P1; at 150 K, a = 8.3899(3), b = 9.6011(3), c = 11.4852(4) A; alpha = 72.397(2), beta = 79.161(2), gamma = 87.843(2) degrees; Z = 2). There is no conclusive evidence in favor of any solid with the composition Cu(hfac)(2).2H(2)O.     

"Jumping crystals": oxygen-evolving metal-nitroxide complexes

The crystals of heterospin complexes [M(hfac)(2)L(2)] (where M = Cu, Ni, Co, or Mn; hfac = hexafluoroacetylacetonate; and L = nitronyl nitroxide, 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl) were found to make unusual jumping motions. Under ambient conditions, the jumping and various displacements of crystals lasted for several weeks. The mechanical motion was accompanied by the cracking and disintegration of crystals, and a solid [M(hfac)(2)(L(1))(2)] complex with the corresponding imino nitroxide 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-1-oxyl (L(1)) was detected. The jumping was accompanied by the spontaneous elimination of oxygen, the source of which was the nitronyl nitroxyl fragment of coordinated L. An X-ray study of [M(hfac)(2)L(2)] (where M = Cu, Ni, Co, or Mn) showed that the molecular structure of all [M(hfac)(2)L(2)] and their packing in the solid state were identical. The packing of [M(hfac)(2)L(2)] was concluded to be critical to the mechanical effect. In complexes with different stoichiometries or different sets of diamagnetic ligands ([Cu(hfac)(2)L](2), [Cu(hfac)(acac)L]·EtOH, [CuPiv(2)L(2)]·2CH(2)Cl(2), and [Cu(hfac)(2)L(2)Cu(2)Piv(4)]·3C(7)H(8) (where acac is acetylacetonate and Piv is trimethylacetate), or free L), the effect vanished when the packing changed.     

Structural and magnetic behavior of the kinked chain Cu(hfac)2(tan) and its relevance to Cu(NO3)2(tan) (hfac = hexafluoroacetylacetonate; tan = 1,4,5-triazanaphthalene)

When stoichiometric amounts of Cu(hfac)(2).H(2)O and 1,4,5-triazanaphthalene (tan) were combined in methanol, green crystals of Cu(hfac)(2)(tan) were formed. Its structure was determined at low temperature (P2(1)/c; a = 8.3308(4) A, b = 14.8945(7) A, c = 18.3046(10) A, beta = 99.298(2) degrees, V = 2241.5(3) A(3)) and found to consist of a novel kinked-chain arrangement where N atoms on opposite sides of the tan ligand bridge Cu(hfac)(2) moieties together. Long axial Cu-N bonds lead to rather weak (J/k(B) = -0.06(5) K) antiferromagnetic interactions according to a Bonner-Fisher fit of the magnetic susceptibility data. The magnetic behavior demonstrated by Cu(hfac)(2)(tan) contrasts markedly with that of Cu(NO(3))(2)(tan), as reported by Hatfield and co-workers, and is attributed to the differing orientations of the Cu d(x)2(-)(y)2 magnetic orbital.     

Coordination complexes of 2-(4-quinolyl)nitronyl nitroxide with M(hfac)(2) [M = Mn(II), Co(II), and Cu(II)]: syntheses, crystal structures, and magnetic characterization

Three new complexes of the formula M(2)L(2) derived from 2-(4-quinolyl)nitronyl nitroxide (4-QNNN) and M(hfac)(2) [M = Mn(II), Co(II), and Cu(II)], (4-QNNN)(2).[Mn(hfac)(2)](2) (1), (4-QNNN)(2).[Co(hfac)(2)](2).2H(2)O (2), and (4-QNNN)(2).Cu(hfac)(2).Cu'(hfac)(2) (3), were synthesized and characterized structurally as well as magnetically. Complexes 1 and 2 are four-spin complexes with quadrangle geometry, in which both the nitrogen atoms of quinoline rings and oxygen atoms of nitronyl nitroxides are involved in the formation of coordination bonds. For complex 3, however, the nitrogen atoms of quinoline rings are coordinated with Cu(II) ion to afford a three-spin complex, which is further linked to another molecule of Cu(hfac)(2) (referred to as Cu'(hfac)(2)) to form a 1D alternating chain. The magnetic behaviors of the three complexes were investigated. For complex 1, as the nitronyl nitroxides and Mn(II) ions are strongly antiferromagnetically coupled, consequently its temperature dependence of magnetic susceptibility was fitted to the model of spin-dimer with S = 2, yielding the intradimer magnetic exchange constant of J = -0.82 cm(-1). For complex 2, the temperature dependence of the magnetic susceptibility in the T > 50 K region was simulated with the model of two-spin unit with S(1) = 3/2 and S(2) = 1/2, leading to J = -321.9 cm(-1) for the magnetic interaction due to Co(II).O coordination bonding, D = -16.3 cm(-1) (the zero-field splitting parameter), g = 2.26, and zJ = -3.8 cm(-1) for the magnetic interactions between Co(II) ions and nitronyl nitroxides through quinoline rings and those between nitronyl nitroxides due to the short O.O short contacts. The temperature dependence of magnetic susceptibility of 3 was approximately fitted to a model described previously affording J(1) = -6.52 cm(-1) and J(2) = 3.64 cm(-1) for the magnetic interaction between nitronyl nitroxides and Cu(II) ions through the quinoline unit via spin polarization mechanism and the weak O.Cu coordination bonding, respectively.     

A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.     

Syntheses and magnetic properties of Cu(II)(hfac)2 and Mn(II)(hfac)2 complexes of 4-pyridyl-substituted thioaminyl radicals

Two types of Cu(II)(hfac)2 and Mn(II)(hfac)2 complexes of N-(4-pyridylthio)-4-ethoxycarbonyl-2,6-bis(4-chlorophenyl)phenylaminyl (1) and N-(4-pyridylthio)-2,4,6-tris(4-chlorophenyl)phenylaminyl (2) were prepared and their X-ray crystallographic and magnetic studies were performed. Mixtures of Cu(II)(hfac)2 and 1 and Mn(II)(hfac)2 and 2 in anhydrous heptane-benzene solution gave 1 : 2 complexes of M(II)(hfac)2 (M = Cu, Mn) and 1 or 2 in 73-75% yields. For Cu(II)(hfac)2(1)2 and Mn(II)(hfac)2(2)2 X-ray crystallographic analyses were successfully performed. The magnetic behaviors for the two metal complexes were investigated with a SQUID magnetometer. The analyses for the chimolTvs. T plots of Cu(II)(hfac)2(1)2 were carried out by the numerical diagonalization of the Heisenberg Hamiltonian matrix (4096 x 4096 matrix) for the four repeating units of the complex (12-spin system). The exchange interaction between the copper(II) ion and the thioaminyl radicals is ferromagnetic (J1/kB = +28 K) and the interactions between the complexes is antiferromagnetic (J2/kB = -13 K). The magnetic behavior of Mn(II)(hfac)2(2)2 complexes is well analyzed with the theoretical equation of a 1/2-5/2-1/2 three-spin system taking the intermolecular interaction (theta) into account. The exchange interaction between the Mn(II) ion and the thioaminyl radicals is antiferromagnetic (J/kB = -4.2 K) and theta = -1.0 K. These magnetic behaviors could be well explained in terms of their crystal structures.     

Spirocyclic sulfur and selenium ligands as molecular rigid rods in coordination of transition metal centers

A set of analogous chalcogen-containing spirocycles, 2,6-dithiaspiro[3.3]heptane, 2,6-diselenaspiro[3.3]heptane, and 2-thia-6-selenaspiro[3.3]heptane [E(2)C(5)H(8), E = S (1), Se (2), and S/Se (3)], has been prepared and fully characterized by spectroscopic methods and by X-ray diffraction. The structural characterization of 2 was presented by us earlier, while the crystal structures of 1 and 3 are reported here for the first time. Molecules 1-3 are built around the central tetrahedral carbon atom and therefore are nonplanar. The E...E separation ranges from 4.690(1) A in 1 to 4.906(1) A in 2. Molecule 3 has statistically mixed positions of sulfur and selenium atoms in the solid state with all geometric characteristics being intermediate between those of 1 and 2. Compounds 2 and 3 have been tested as molecular rigid rod ligands in coordination reactions with transition metal complexes such as Cu(hfac)(2) (4), cis-Co(hfac)(2).2H(2)O (5), and cis-Ni(hfac)(2).2H(2)O (6) (hfac = hexafluoroacetylacetonate). Several coordination products built of two building blocks, M(hfac)(2) (M = Cu, Co, and Ni) and Se(2)C(5)H(8) (2), have been prepared in crystalline form and structurally characterized. The copper-based product (7) is comprised of the oligomeric units {[Cu(hfac)(2)](3).2mu(2)-Se(2)C(5)H(8)-Se,Se'} built on the axial Cu...Se interactions averaged at 2.909 A. These units are further assembled into 1D polymeric chains via intermolecular Cu...F contacts at 2.829 A. The SSeC(5)H(8) (3) ligand was also used in the reaction with Cu(hfac)(2) to afford an analogue of 7, namely {[Cu(hfac)(2)](3).2mu(2)-SSeC(5)H(8)-S,Se} (8). Complex 8 exhibits statistically mixed positions of the donor sulfur and selenium atoms to give an average axial Cu...S/Se contact at 2.892 A. In contrast to the copper complexes of composition 3:2, the stoichiometries of the isolated cobalt and nickel products are 1:1, [M(hfac)(2).Se(2)C(5)H(8)] (M = Co (9) and Ni (10)). Complexes 9 and 10 exhibit 1D polymer structures having alternating metal units cis-M(hfac)(2) and ligands 2 with intermolecuar M...Se separations of 2.6046(8) and 2.5523(16) A, respectively. In all products 7-10 the initial cis or trans geometry of M(hfac)(2) complexes is preserved and the spiro[3.3]heptane ligands act as bidentate linkers bridging transition metal centers via both donor ends. The magnetic properties of this series of new Cu(II), Co(II), and Ni(II) complexes have been tested by variable-temperature magnetic susceptibility measurements.     

Synthesis and characterization of diverse coordination polymers. Linear and zigzag chains involving their structural transformation via intermolecular hydrogen-bonded, interpenetrating ladders polycatenane, and noninterpenetrating square grid from long, rigid N,N'-bidentate ligands: 1,4-bis[(x-pyridyl)ethynyl]benzene (x = 3 and 4)

The long, rigid ligands 1,4-bis[(3-pyridyl)ethynyl]benzene (L1) and 1,4-bis[(4-pyridyl)ethynyl]benzene (L2) were used in the synthesis of 10 new organic-inorganic coordination frameworks, each of them adopting different structural motifs. Synthesis, single-crystal X-ray structure determination, and spectroscopic and thermogravimetric analyses are presented. The reactions between M(NO3)2 x xH2O; M = Cd(II), Cu(II), and Co(II); x = 3-6 and Cu(hfac)2 x H2O [hfac = bis(hexafluoroacetylacetonato)] with L1 afforded the following one-dimensional zigzag chain structures: [Cd(C20H12N2)0.5(NO3)(CH3OH)]n (1, monoclinic, C2/c; a = 7.586(1) A, b = 23.222(1) A, c = 13.572(1) A, beta = 92.824(1), Z = 4); [{Cu(C20H12N2)(NO3)2(CH3OH)} x CH3OH]n (2, orthorhombic, P2(1)2(1)2(1); a = 8.589(1) A, b = 15.766(1) A, c = 17.501(1) A, Z = 4); [Co(C20H12N2)2(NO3)2(H2O)2] (5, triclinic, P1; a = 7.493(1) A, b = 8.948(1) A, c = 14.854(1) A, alpha = 100.427(1), beta = 97.324(1), gamma = 110.901(1), Z = 1); [Cu(C20H12N2)(hfac)2]n (4, monoclinic, C2/c, a = 18.828(1) A, b = 14.671(1) A, c = 13.427(1) A, beta = 90.447(1) degrees, Z = 4). Moreover, the minority phase compound formed from Cu(NO3)2 x 3H2O and L1 yielded a metallocyclic chain structure, [Cu(C20H12N2)(NO3)]n (3, triclinic, P; a = 8.728(1) A, b = 10.018(1) A, c = 11.893(1) A, alpha = 109.991(1), beta = 97.109(1), gamma = 115.542(1), Z = 1). In addition to the dinuclear coordination complex 5, all other polymeric structures (1-4) from L1 are composed of interpenetrating 2D and 3D cross-linked zigzag chains via hydrogen-bonding interactions. The reactions between M(NO3)2 x xH2O; M = Cd(II), Cu(II), and Co(II); x = 3-6 and Cu(hfac)2 x H2O [hfac = bis(hexafluoroacetylacetonato)] and L2 were dependent on the nature of the metal center and resulted in the formation of four different interpenetrating and noninterpenetrating compounds (6-10): [Co(C20H12N2)1.5(NO3)2]n (6, triclinic, P; a = 14.172(1) A, b = 15.795(1) A, c = 18.072(1) A, alpha = 115.380(1), beta = 101.319(1), gamma = 93.427(2), Z = 4), which consists of T-shaped building blocks assembled into three-dimensional interpenetrating polycatenated ladders; [Cd(C20H12N2)2(NO3)2]n (7, monoclinic, I2/a; a = 11.371(1) A, b = 20.311(2) A, c = 15.240(2) A, beta = 100.201(2) degrees, Z = 4), which adopts a two-dimensional noninterpenetrating square-grid motif; [Cu(C20H12N2)(hfac)2]n (8, monoclinic, I2/a; a = 11.371(1) A, b = 20.311(2) A, c = 15.240(2) A, beta = 100.201(2) degrees, Z = 4), composed of three sets of distinct one-dimensional linear chains; [Cu(C20H12N2)(EtOH)(NO3)2] [Cu(C20H12N2)1.5(NO3)2] x 2EtOH (9, triclinic, P; a = 12.248(2) A, b = 13.711(3) A, c = 18.257(4) A, alpha = 108.078(4) degrees, beta = 97.890(4) degrees, gamma = 103.139(5) degrees, Z = 2) and [Cu(C20H12N2)(MeOH)(NO3)2] [Cu(C20H12N2)1.5(NO3)2] x 2MeOH (10, triclinic, P; a = 12.136(1) A, b = 13.738(2) A, c = 17.563(3) A, alpha = 107.663(3) degrees, beta = 94.805(4) degrees, gamma = 104.021(4) degrees, Z = 2). Both 9 and 10 stack into infinite interpenetrating ladders through bundles of infinite chains and are described in our preliminary communication.     

Double half-cubane copper(II) complexes available from copper(II) 1,1,1,5,5,5-hexafluoropentane-2,4-dionate dissolved in formamides

Tetranuclear copper(II) complexes were obtained after simply dissolving [Cu(hfac)2] in formamide-methanol mixed solvents (Hhfac=1,1,1,5,5,5-hexafluoropentane-2,4-dione). X-Ray diffraction studies revealed that they possessed a tetranuclear double half-cubane core sandwiched with two trianionic ligands from 2,4,6-tris(trifluoromethyl)tetrahydropyran-2,4,6-triol (H3ttpt). Complexes [Cu4(ttpt)2(hfac)2(dmf)2.5], [Cu4(ttpt)2(tfa)2(def)4], and [Cu4(ttpt)2(hfac)2(H2O)4](fa) were prepared from N,N-dimethylformamide(dmf)-MeOH, N,N-diethylformamide (def)-MeOH, and formamide(fa)-MeOH (Htfa=trifluoroacetic acid), respectively. A possible mechanism is proposed where a templated aldol-type reaction takes place between hfac and 1,1,1-trifluoroacetonate. Magnetic measurements revealed the presence of antiferromagnetic interaction in the Cu4O6 core.     

Preparation of a copper ion complex of sterically congested diphenyldiazomethanes having a pyridine ligand and characterization of their photoproducts

To show that persistent high-spin polycarbenes can be realized by utilizing hetero spin systems, two diphenyldiazomethanes having pyridyl groups, i.e., bis{4-(4-pyridyl)-2,6-dimethylphenyl}diazomethane (4,4'-DPy-1-N(2)) and {2,4-di(4-pyridyl)-6-bromophenyl}(2,6-dimethyl-4-tert-butylphenyl)diazomethane (2,4-DPy-1-N(2)), were prepared. Triplet carbenes, 4,4'-DPy-1 and 2,4-DPy-1, generated by photolysis of the corresponding diazomethanes were characterized by spectroscopic means (ESR and UV/vis in matrix at low temperatures and laser flash photolysis in solution at room temperature). The results showed that they were fairly persistent. Magnetic properties of the photoproducts from a 1:1 complex between DPy-1-N(2) and Cu(hfac)(2) (hfac = hexafluoroacetylacetonate) were characterized by ESR and a superconducting quantum interference device (SQUID) magneto/susceptometer. The field dependences of magnetization for the complexes, expressed by using M versus H/T plots, were analyzed in terms of the Brillouin function to be S = 6.80 (F = 0.60) for the 1:1 complex of 4,4'-DPy-1 and Cu(hfac)(2) and S = 3.71 (F = 0.73) for the 1:1 complex of 2,4-DPy-1 and Cu(hfac)(2) at 2.0 K. Thus, it has been demonstrated that a high-spin species is actually generated in the photoproducts and that the complexed carbenes showed significant stability.     

Ferromagnetic versus antiferromagnetic exchange interactions in tetrathiafulvalene-based 3d/4f heterobimetallic complexes

(TTF-salphen)M compounds (TTF-salphen(2-)=4,5-bis(propylthio)tetrathiafulvalene-N,N'-phenylenebis(salicylideneimine) dianion; M=Cu(II) and Ni(II)) have been treated with Ln(hfac)(3)·2H(2)O precursors (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion; Ln=Gd(III), Tb(III), and Dy(III)) to elaborate unprecedented 3d/4f TTF-based heterobimetallic complexes of formula [(TTF-salphen)MLn(hfac)(3)]. All the structures of these compounds have been resolved by X-ray diffraction on single crystals. The structures of these complexes are formed by a TTF-salphen(2-) ligand coordinated to the 3d metal ions in the inert tetradentate N(2)O(2) site. The Ln(hfac)(3) fragment is coordinated to the (TTF-salphen)M one through the two phenolate bridges. Even if the complexes are similar in both Cu(II) and Ni(II) families, the crystal packing is different. In the first case, dimers of TTF-salphen(2-) donors constitute the organic network. In the other case, a reminiscent organic network is observed with S···S contacts. The photophysical properties of [(TTF-salphen)CuDy(hfac)(3)] (3) in chloroform solution highlight the redshift of the TTF→salphen charge transfer (400 cm(-1)) relative to the analogue excitations in (TTF-salphen)Cu, which attest to the stability of these structures in solution. Static magnetic measurements have allowed us to quantify the ferromagnetic interactions (J=+1.29 cm(-1)) between Cu(II) and Gd(III) in the [(TTF-salphen)CuGd(hfac)(3)] complex. Finally, an empirical method that consists of the comparisons of the magnetic properties of [(TTF-salphen)CuTb(hfac)(3)] with [(TTF-salphen)NiTb(hfac)(3)] and [(TTF-salphen)CuDy(hfac)(3)] with [(TTF-salphen)NiDy(hfac)(3)] has established that ferromagnetic interactions take place between Cu(II) and Tb(III) ions, whereas unusual antiferromagnetic interactions have been identified between Cu(II) and Dy(III) ions.     

Preparation of copper ion complexes of sterically congested diaryldiazomethanes having a pyridine ligand and characterization of their photoproducts

To realize fairly stable high-spin polycarbenes by utilizing heterospin systems comprising 2p spins of organic radicals and 3d spins of magnetic metal ions, we prepared dianthryldiazomethanes having two pyridyl groups at the 2,2'- or 2,7-positions, that is, bis[10-(4-tert-butyl-2,6-dimethylphenyl)-2-(4-pyridyl)-9-anthryl]diazomethane (2,2'-DPy-1-N(2)) and [10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl][(10-(4-tert-butyl-2,6-dimethylphenyl)-2,7-di(4-pyridyl)-9-anthryl]diazomethane (2,7-DPy-1-N(2)). The triplet carbene DPy-(3)1 generated by photolysis of DPy-1-N(2) was characterized by ESR and UV-vis spectroscopy in a matrix at low temperature as well as by time-resolved UV-vis in solution at room temperature. The results showed that the triplet carbene DPy-(3)1 was destabilized to some extent as opposed to the parent triplet carbene before pyridination, but it was still fairly persistent, having a half-life of more than 30 min in solution at room temperature. Photoproducts from the complex between DPy-1-N(2) and Cu(hfac)(2) were characterized in a similar manner, and the results suggested that the generated carbene centers interacted magnetically with the Cu(II) ion to form a high-spin species with significant thermal stability. The fact that no significant signals due to the isolated triplet carbene DPy-(3)1 were observed suggested that the pyridine moiety binds with Cu(hfac)(2) in a nearly quantitative manner under these cryogenic conditions. Magnetic measurements of the photoproduct using a superconducting quantum interference device (SQUID) magneto/susceptometer were performed to determine the spin state of the complex. The temperature dependence of the molar paramagnetic susceptibility indicated the presence of ferromagnetic interaction. The field dependences of magnetization for the complexes, expressed using M versus H/T plots, were analyzed in terms of the two-component Brillouin function to be S = 3.18 (F = 0.66) and S = 0.02 (F = 0.23) for the 1:1 complex of 2,7-DPy-1 and Cu(hfac)(2) and S = 2.70 (F = 0.33) and S = 0.49 (F = 0.11) for the 1:1 complex of 2,2'-DPy-1 and Cu(hfac)(2).     

Relationship between the thermally induced reorientations of aromatic solvate molecules in Cu(hfac)2-nitroxide breathing crystals and the character of the magnetic anomaly

A new group of "breathing" crystals has been synthesized. These are aromatic solvates of the copper(II) hexafluoroacetylacetonate complex with spin-labeled pyrazole Cu(hfac)(2)L·0.5Solv, where L is 2-(1-butyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl and Solv is benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, styrene, o-xylene, m-xylene, p-xylene, 1,4-bis(trifluoromethyl)benzene, 1-methyl-4-ethylbenzene, 1-methyl-4-vinylbenzene, 1,4-diethylbenzene, 1,2,3-trimethylbenzene, or 1,2,4-trimethylbenzene. The main feature of Cu(hfac)(2)L·0.5Solv single crystals is their remarkable mechanical stability and ability to undergo thermally induced structural rearrangements accompanied by spin-crossover-like phenomena. The structures of Cu(hfac)(2)L·0.5Solv solvates are similar and based on mutually parallel {Cu(hfac)(2)L}(∞) heterospin chains with a "head-to-head" motif. The localization of voids with guest molecules being the same in all crystals, the temperature dependence of the effective magnetic moment (μ(eff)) for Cu(hfac)(2)L·0.5Solv is determined by the structure of the guest molecules, along which the polymer chains are "gliding" when the temperature changes. When the temperature decreased from 300 to 100-50 K, μ(eff) decreased, abruptly or gradually, from 2.7-2.4 to ~1.8 β for the majority of Cu(hfac)(2)L·0.5Solv except the solvates with benzene, toluene, and 1,4-bis(trifluoromethyl)benzene. When Cu(hfac)(2)L·0.5C(6)H(6) and Cu(hfac)(2)L·0.5CH(3)-C(6)H(5) were cooled to 50 K, μ(eff) decreased to ~2.1-2.2 β. When Cu(hfac)(2)L·0.5(1,4-(CF(3))(2)-C(6)H(4)) was cooled to 50 K, μ(eff) initially decreased from ~2.7 to 1.9 β and then abruptly increased to ~2.4 β. A single-crystal X-ray diffraction analysis of each solvate within a temperature range wider than the range of magnetic anomaly temperatures revealed a complex interrelated dynamics of the aromatic solvent guest molecules and heterospin chains. The dynamics largely depended on the orientation of the solvent guest molecules relative to the polymer chains. An analysis of the thermally induced phase transformations revealed a relationship between the structural rearrangement of Cu(hfac)(2)L·0.5Solv and the form of the magnetic anomaly on the μ(eff)(T) curve and between the structural rearrangement of the solvate and the temperature of the magnetic effect.     

单晶硅上化学气相沉积铜薄膜的机理研究

A versatile metal-organic chemical vapor deposition (MOCVD) system was designed and constructed. Copper films were deposited on silicon (100) substrates by chemical vapor deposition (CVD) using Cu(hfac)2 as a precursor. The growth of Cu nucleus on silicon substrates by H2 reduction of Cu(hfac)2 was studied by atomic force microscopy and scanning electron microscopy. The growth mode of Cu nucleus is initially Volmer-Weber mode (island), and then transforms to Stranski-Rastanov mode (layer-by-layer plus island).The mechanism of Cu nucleation on silicon (100) substrates was further investigated by X-ray photoelectron spectroscopy. From Cu2p, O1s, F1s, Si2p patterns, the observed C=O, OH and CF3/CF2 should belong to Cu(hfac) formed by the thermal dissociation of Cu(hfac)2. H2 reacts with hfac on the surface, producing OH. With its accumulation, OH reacts with hfac, forming HO-hfac, and desorbs, meanwhile, the copper oxide is reduced, and thus the redox reaction between Cu(hafc)2 and H2 occurs.     

Artificial amino acids in nickel(II) and nickel(II)/lanthanide(III) chemistry

The synthesis and magnetic properties of five new homo- and heterometallic nickel(II) complexes containing artificial amino acids are reported: [Ni(4)(aib)(3)(aibH)(3)(NO(3))](NO(3))(4)·3.05MeOH (1·3.05MeOH), [Ni(6)La(aib)(12)](NO(3))(3)·5.5H(2)O (2·5.5H(2)O), [Ni(6)Pr(aib)(12)](NO(3))(3)·5.5H(2)O (3·5.5H(2)O), [Ni(5)(OH)(2)(l-aba)(4)(OAc)(4)]·0.4EtOH·0.3H(2)O 6(4·0.4EtOH·0.3H(2)O), and [Ni(6)La(l-aba)(12)][La(2)(NO(3))(9)] (5; aibH = 2-aminoisobutyric acid; l-abaH = l-2-aminobutyric acid). Complexes 1 and 4 describe trigonal-pyramidal and square-based pyramidal metallic clusters, respectively, while complexes 2, 3, and 5 can be considered to be metallocryptand-encapsulated lanthanides. Complexes 4 and 5 are chiral and crystallize in the space groups I222 and P2(1)3, respectively. Direct-current magnetic susceptibility studies in the 2-300 K range for all complexes reveal the presence of dominant antiferromagnetic exchange interactions, leading to small or diamagnetic ground states.     

Synthesis and Characterization of a Bis(&mgr;-beta-diketonato)bis((1,2,5,6-eta)-1,5-dimethyl-1,5- cyclooctadiene)disilver Complex. An Intermediate in the Synthesis of an Isomerically Pure (beta-Diketonato)((1,2,5,6-eta)-1,5-dimethyl-1,5-cyclooctadiene)copper(I) Complex

Dimethyl-1,5-cyclooctadiene (DMCOD) is synthesized by the Ni-catalyzed dimerization of isoprene and consists of 80% 1,5-dimethyl-1,5-cyclooctadiene (1,5-DMCOD) and 20% 1,6-dimethyl-1,5-cyclooctadiene (1,6-DMCOD). Reaction of Hhfac (1,1,1,5,5,5-hexafluoro-2,4-pentanedione) with Ag(2)O in the presence of DMCOD results in the formation of isomeric Ag(I) species. Repeated recrystallizations yield an isomerically pure compound ((1,5-DMCOD)Ag(hfac))(2) that was characterized by X-ray crystallography and (1)H and (13)C NMR and IR spectroscopy. X-ray crystallography revealed a dinuclear complex with a short Ag-Ag spacing (3.0134(3) ? at -150 degrees C and 3.0278(5) ? at -20 degrees C) and bridging hfac ligands (&mgr;(2) bonding). The overall geometry around the Ag atoms is a deformed tetrahedron with two short Ag-O bonds (2.375 ? average) and two Ag-diene bonds. The methyl groups of the 1,5-DMCOD ligand are pointed toward the center of the molecule. Decomposition of the silver complex in a biphasic HCl (1 M)/CH(2)Cl(2) mixture liberates isomerially pure 1,5-DMCOD; this diene is subsequently used to synthesize isomerically pure (1,5-DMCOD)Cu(hfac). The latter compound was characterized by (1)H and (13)C NMR and IR spectroscopy and is a useful liquid precursor for Cu CVD. Crystallographic data: C(30)H(34)Ag(2)F(12)O(4), monoclinic, P2(1)/c (No. 14), Z = 4; at -150 degrees C, a = 12.428(1) ?, b = 11.071(1) ?, c = 24.520(2) ?, beta = 101.98(1) degrees; at -20 degrees C, a = 12.597(1) ?, b = 11.191(1) ?, c = 24.641(2) ?, beta = 102.08(1) degrees.     

Cyclic M2(RL)2 coordination complexes of 5-(3-[N-tert-Butyl-N-aminoxyl]phenyl)pyrimidine with paramagnetic transition metal dications

5-(3-(N-tert-Butyl-N-aminoxyl)phenyl)pyrimidine (RL = 3NITPhPyrim) forms isostructural cyclic M2(RL)2 cyclic dimers with M(hfac)2 (M = Mn, Co, Cu; hfac = hexafluoroacetylacetonate). Mn2(hfac)4(RL)2 exhibits strong antiferromagnetic Mn-RL exchange, with weak ferromagnetic exchange (0.7 cm(-1)) between Mn-RL units that is consistent with a spin polarization exchange mechanism. The magnetic moment of Co2(hfac)4(RL)2 at higher temperatures is consistent with strongly antiferromagnetic exchange within the Co-NIT units and tends toward zero below 50 K at lower magnetic fields. Cu2(hfac)4(RL)2 shows more complex behavior, with no high-temperature plateau in chiT(T) up to 300 K but a monotonic decrease down to about 100 K. The Cu(II)-nitroxide bonds decrease by 0.2-0.3 A over the same temperature range, corresponding to a change of nitroxide coordination from axial to equatorial. This thermally reversible Jahn-Teller distortion leads to a thermally induced spin state conversion from a high-spin, paramagnetic state at higher temperature to a low-spin state at lower temperature. This spin state conversion is accompanied by a reversible solid-state thermochromic change between dull yellow-brown at room temperature and green at 77 K.     

2D and 3D Cu(hfac)2 complexes with nitronyl nitroxide biradicals

Reactions between Cu(hfac)2 and nitronyl nitroxide biradicals 1,4-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]butane (L4) and 1,8-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]octane (L8) gave respectively a framework compound [Cu(hfac)2]2L4 and a layered polymer compound [Cu(hfac)2]2L8. The framework of [Cu(hfac)2]2L4 consists of 66-membered condensed metallocycles. Inside the framework, the structure has macrohelixes (pitch approximately 25 A) extending along the [001] crystallographic direction. All the helixes have the same direction of winding; the crystals, therefore, are optically active, the structure corresponding either to P-isomer (P4(1)2(1)2) or to M-isomer (P4(3)2(1)2). The long distances between the Cu atoms and the O atoms of the coordinated >N-O groups (Cu-O 2.351-2.467 A) are responsible for ferromagnetic exchange interactions in Cu2+-O-N< and >N-O-Cu2+-O-N< exchange clusters.     

Ni(II) and hs-Fe(II) complexes of a paramagnetic thiazyl ligand, and decomposition products of the iron complex, including an Fe(III) tetramer

Synthesis and structural, magnetic and electrochemical characterization of the Ni(hfac) 2(pyDTDA) and the Fe(hfac) 2(pyDTDA) complexes are reported (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-; pyDTDA = 4-(2'-pyridyl)-1,2,3,5-dithiadiazolyl). Unlike the previously reported Mn(II) and Cu(II) complexes, but similar to the Co(II) complex, the Ni(II) and Fe(II) complexes are not dimerized in the solid state, allowing for magnetic coupling between the metal ion and paramagnetic ligand to be readily obtained from solid state magnetic measurements: Ni complex, J/k B = +132(1) K, using H = -2 J{ S Ni. S Rad} and g Ni = 2.04(2) and g Rad = 1.99(2); Fe complex, J/k B = -60.3(3) K, using H = -2 J{ S Fe. S Rad} and g av = 2.11(2). The iron complex is unusually unstable. A thermal decomposition product is isolated wherein the coordinated pyDTDA ligand appears to have been transformed into a coordinated 2-(2'-pyridyl)-4,6-bis(trifluoromethyl)pyrimidine. The iron complex also yields a solution decomposition product in the presence of air that is best described as an oxygen bridged iron(III) tetramer with two hfac ligands on each of three iron atoms and two oxidized pyDTDA ligands chelated on the fourth.     

Structural and Magnetic Properties of 2p‐3d‐4f Hetero‐Tri‐Spin Chains Comprising [{Cu(hfac)2‐Radical}2] Dimers and Ln(hfac)3 (hfac=hexafluoroacetylacetonate)

A new family of 2p‐3d‐4f hetero‐tri‐spin complexes [Ln(hfac)₃{Cu(hfac)₂(NIT‐3 PyPh)}₂] (Ln=Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ); NIT‐3 PyPh=2‐[4‐(3‐pyridinylmethoxy)phenyl]‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide; hfac=hexafluoroacetylacetonate) have been synthesized. Four complexes possess a 1D chain structure in which two radical ligands join two Cu(hfac)₂ molecules to form a [{Cu(hfac)₂‐rad)}₂] dimer cycle and the dimer rings are linked by Ln(hfac)₃ units. Magnetic studies show that ferromagnetic exchange couplings exist between the coordinated NO groups of radical ligands and metal ions. Field‐induced slow relaxation of the magnetization was observed in the Tb and Dy compounds.