Pentanuclear Compound Research Articles

Metal-Metal Charge Transfer Properties of a Series of Trinuclear Fe2 Ru and Corresponding Pentanuclear Fe2 Ru2 Ag Cyanido-Bridged Complexes.

A series of trimetallic cyanidometal-bridged compounds [Men Cp(dppe)FeII -(μ-NC)-RuII (MeOpy)4 -(μ-CN)-FeII (dppe)CpMen ] - [PF6 ]2 (N[PF6 ]2 , n=0, N =1; n=1, N=2; n=3, N=3; Cp=cyclopentadiene, dppe=1,2-bis(diphenylphosphino)ethane, MeOpy=4-methoxypyridine) and their one- and two-electron oxidized compounds N3+ and N4+ were synthesized and characterized. Meanwhile, a series of corresponding linear cyanido-bridged pentanuclear compounds [Men Cp(dppe)FeIII -(μ-NC)-RuII (MeOpy)4 -(μ-NC)-AgI -(μ-CN)-RuII (MeOpy)4 -(μ-CN)-FeIII (dppe)CpMen ][BF4 ]5 (M[BF4 ]5 , n=0, M=4; n=1, M=5; n=3, M=6) were also obtained and well characterized. The investigations suggest that in the trinuclear system there exists remote interaction between the two Fe centers, but no significant interactions exist across the central silver unit between the metals on the two sides of the silver center in the pentanuclear system. In both the trinuclear N4+ and the pentanuclear M5+ complexes, there exists the neighboring RuII →FeIII MM'CT transitions, and the MM'CT energy in the corresponding trinuclear system is higher than those in the pentanuclear system in which no remote metal-metal interaction occurs. Meanwhile, as the substituted methyl groups on the cyclopentadiene increases, the redox potential of the ruthenium in the trinuclear N4+ series increases, but that in the pentanuclear M5+ complexes decreases.

Dy4, Dy5, and Ho2 Complexes of an N3O2 Aminophenol Donor: A Dy5-µ3-Peroxide Single Molecule Magnet.

The reactivity of the new flexible potentially pentadentate N3O2 aminophenol ligand H4Lr (2,2'-((pyridine-2,6-diylbis(methylene))bis(azanediyl))diphenol) towards different dysprosium salts and holmium(III) nitrate was investigated. Accordingly, this reactivity seems to greatly depend on the metal ion and salt employed. In this way, the reaction of H4Lr with dysprosium(III) chloride in air leads to the oxo-bridged tetranuclear complex [Dy4(H2Lr)3(Cl)4(μ3-O)(EtOH)2(H2O)2]·2EtOH·H2O (1·2EtOH·H2O), while the same reaction just changing the chloride salt by the nitrate one renders the peroxo-bridged pentanuclear compound [Dy5(H2Lr)2(H2.5Lr)2(NO3)4(µ3-O2)2]·2H2O (2·2H2O), where both peroxo ligands seem to come from the fixation and reduction of atmospheric oxygen. However, if holmium(III) nitrate is used instead of dysprosium(III) nitrate, no evidence of a peroxide ligand is observed, and the dinuclear complex {[Ho2(H2Lr)(H3Lr)(NO3)2(H2O)2](NO3)} 2.5H2O (3·2.5H2O) is isolated. The three complexes were unequivocally characterized by X-ray diffraction techniques, and their magnetic properties were analyzed. Thus, while the Dy4 and Ho2 complexes do not show magnet-like behavior even in the presence of an external magnetic field, 2·2H2O is a single molecule magnet, with an Ueff barrier of 61.2 K (43.2 cm-1). This is the first homonuclear lanthanoid peroxide SMM, which also shows the highest barrier among the reported 4f/3d peroxide zero field SMMs to date.

Pentagonal Bipyramid FeII Complexes: Robust Ising-Spin Units towards Heteropolynuclear Nanomagnets.

Pentagonal bipyramid FeII complexes have been investigated to evaluate their potential as Ising-spin building units for the preparation of heteropolynuclear complexes that are likely to behave as single-molecule magnets (SMMs). The considered monometallic complexes were prepared from the association of a divalent metal ion with pentadentate ligands that have a 2,6-diacetylpyridine bis(hydrazone) core (H2 LN3O2R ). Their magnetic anisotropy was established by magnetometry to reveal their zero-field splitting (ZFS) parameter D, which ranged between -4 and -13 cm-1 and was found to be modulated by the apical ligands (ROH versus Cl). The alteration of the D value by N-bound axial CN ligands, upon association with cyanometallates, was also assessed for heptacoordinated FeII as well as for related NiII and CoII derivatives. In all cases, N-coordinated cyanide ligands led to large magnetic anisotropy (i.e., -8 to -18 cm-1 for Fe and Ni, +33 cm-1 for Co). Ab initio calculations were performed on three FeII complexes, which enabled one to rationalize the role of the ligand on the nature and magnitude of the magnetic anisotropy. Starting from the pre-existing heptacoordinated complexes, a series of pentanuclear compounds were obtained by reactions with paramagnetic [W(CN)8 ]3- . Magnetic studies revealed the occurrence of ferromagnetic interactions between the spin carriers in all the heterometallic systems. Field-induced slow magnetic relaxation was observed for mononuclear FeII complexes (Ueff /kB up to 53 K (37 cm-1 ), τ0 =5×10-9 s), and SMM behavior was evidenced for a heteronuclear [Fe3 W2 ] derivative (Ueff /kB =35 K and τ0 =4.6 10-10 s), which confirmed that the parent complexes were robust Ising-type building units. High-field EPR spectroscopic investigation of the ZFS parameters for a Ni derivative is also reported.

Tetranuclear and Pentanuclear Compounds of the Rare-Earth Metals: Synthesis and Magnetism.

The Schiff-base proligand 4-tert-butyl-2,6-bis-[(2-hydroxy-phenylimino)methyl]phenol (H3L) was prepared in situ from 4-tert-butyl-2,6-diformylphenol and 2-aminophenol. The proligand (H3L) was used with dibenzoylmethane (DBMH) or acetylacetone (acacH) with lanthanides giving compounds with varying arrangements of metal atoms and nuclearities. The tetranuclear compound {[Dy4(L)3(DBM)4][Et3NH]} (1) and pentanuclear compound {[Dy5(μ3-OH)2(L)3(DBM)4(MeOH)4]·4(MeOH)} (2) were obtained from the ligand (L)(3-) and dibenzoylmethane. The tetranuclear compounds {[Dy4(μ4-OH)(L)2(acac)4(MeOH)2(EtOH)(H2O)]·(NO3)·2(MeOH)·3(EtOH)} (3) and {[Ln4(μ3-OH)2(L)(HL)(acac)5(H2O)] (HNEt3)(NO3)·2(Et2O)} (Ln = Tb (4), Dy (5), Ho (6), and Tm (7)) resulted when the ligand (L)(3-) was used in the presence of acetylacetone. In the solid state structures, the tetranuclear compound 1 adopts a linear arrangement of metal atoms, while tetranuclear compound 3 has a square grid arrangement of metal atoms, and tetranuclear compounds 4-7 have a seesaw-shaped arrangement of metal atoms. The composition found from single-crystal X-ray analysis of compound 1 and 3-7 is supported by electrospray ionization mass spectrometry (ESI-MS). The magnetic studies on compounds 1 suggest the presence of weak ferromagnetic interactions, whereas compounds 2-6 exhibit weak antiferromagnetic interactions between neighboring metal centers. Compounds 1, 2, and 3 also show single-molecule magnet behavior under an applied dc field.

Record antiferromagnetic coupling for a 3d/4d cyanide-bridged compound.

The pentanuclear compound [V(II)(tmphen)2]3[Mo(III)(CN)6]2 (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) exhibits a record antiferromagnetic exchange coupling constant of J(V-Mo) = -114 cm(-1). This is the first example of a heterobimetallic cyanide compound with such strong magnetic coupling.

Heterometallic Pentanuclear [Ni4Ln] (LnIII = Gd, Tb, Dy, Ho) Complexes: Accidental Orthogonality Leading to Ferromagnetic Interactions

AbstractThe reaction of 6‐formyl‐2‐(hydroxymethyl)‐4‐methylphenol (LH2) with NiII and LnIII salts afforded a series of heterometallic pentanuclear compounds [Ni4Ln(L)4(OAc)2(MeOH)4](NO3)(MeOH) [LnIII = Gd (1), Dy (2), Tb (3), Ho (4)]. Four dianionic L2– ligands and two acetate anions hold together four NiII and one LnIII ion to form a Ni4Ln core possessing a distorted tetrahedral geometry. All the NiII ions are hexacoordinate (6 O) with a distorted octahedral geometry whereas the LnIII ion is octacoordinate (8 O) with a distorted square‐antiprism geometry. All the NiII ions are connected to the central LnIII ion through μ2 bridging of one deprotonated phenolic oxygen and two deprotonated alkoxy oxygen atoms. The magnetic properties of 1–4 were investigated in the temperature range 2–300 K. The magnetic properties of 1 were fitted by using a Hamiltonian containing isotropic exchange, NiII local zero‐field‐splitting, and Zeeman effects (Ĥ = Ĥexchange + Ĥzfs + Ĥzeeman). The molecular structures of 1–4 reveal that the Ni–O–Ln angle is around 89° whereas the Ni–O–Ni angle is about 96°. Because of this accidental orthogonality, ferromagnetic interactions between the nearest‐neighbor NiII ions and between NiII and LnIII ions have been observed. The observed J values are 0.34 and 1.88 cm–1 between GdIII–NiII and NiII–NiII, respectively.

Five copper(ii) metal–organic coordination complexes with micro-channels based on flexible bis(imidazole) and carboxybenzaldehyde ligands; structural influence of experimental conditions on their frameworks

Five new copper(II) metal–organic coordination complexes, [Cu2(1,2-bix)2(L)4] (1), [Cu(1,3-bix)(L)2]n·nCH3OH·3H2O (2), [Cu(1,3-bix)(L)2]n·nH2O (3), [Cu5(1,3-bix)2(L)6(NO3)2(H2O)2(OH)2]·2H2O (4) and [Cu(1,4-bix)(L)2]n (5), have been synthesized using 4-carboxybenzaldehyde (HL) and 1,n-bis(imidazol-l-ylmethyl)benzene (1,n-bix; n = 2, 3, 4) as ligands. These complexes were structurally characterized by single-crystal X-ray crystallography and further characterized by FT-IR spectroscopy and thermogravimetric analysis (TGA). Complex 1 is a symmetrical binuclear structure, and in compound 2 the 1D ladders are entangled through π–π stacking interactions to generate a 3D network with one-dimensional micro channel. A 3D coordination framework 2 converted to network 3 by just increasing the reaction temperature. Metal–organic polymer 3 is comprised of 1D corrugated double chains structure. Complex 4 has a pentanuclear (Cu5) cluster structure and compound 5 shows a 1D zigzag chain. The magnetic properties of the complexes 1 and 3 are reported briefly.

Pentanuclear {Cr2Ln3} (Ln = Dy, Tb) Heterometallic Clusters Based on an Amino Acid Ligand: Slow Relaxation of Magnetization and Substitution Reactions

AbstractReactions between Ln3+ (Ln = Dy, Tb), Cr3+, and glycine (HGly) in aqueous solution led to two pentanuclear compounds, Na3[Dy3Cr2(HGly)6(μ3‐OH)6(H2O)9]·(ClO4)8·Cl4·14H2O (1) and Na3[Tb3Cr2(HGly)6(μ3‐OH)6(H2O)9]·(ClO4)6·Cl6·6H2O (2). Structural analyses showed that both 1 and 2 have a {Ln3Cr2} compressed trigonal‐bipyramidal skeleton in which an axial Cr3+ ion lies above and below the triangular equatorial plane defined by the three Ln3+ ions. Magnetic measurements indicated that 1 and 2 exhibit single‐molecule magnetic behavior with Ea ≈ 14.1 K and τ0 = 4.2 × 10–8 s for 1 and Ea ≈ 13.0 K and τ0 = 6.4 × 10–7 s for 2. Interestingly, the clusters are soluble in aqueous solution. The two terminal water molecules of 1 can be substituted by two monocoordinated 4,4′‐dipyridyl N,N′‐dioxide (dpyo) molecules to afford [Dy3Cr2(HGly)6(dpyo)2(μ3‐OH)6(H2O)7]·(ClO4)9·15H2O (3) with a three‐dimensional cds network formed through π–π interactions. Magnetic analysis indicated that 3 also displays slow relaxation of the magnetization with Ea ≈ 13.24 K and τ0 = 9.16 × 10–8 s.

Hybrid Polyfunctional Systems Based on Nickel(II) Isonicotinate

AbstractSeveral metal–organic frameworks of nickel(II) were obtained starting from the molecular complex 1, [Ni(OH2)4(4‐pyc)2] (4‐pyc = 4‐pyridinecarboxylate or isonicotinate). By using different reaction conditions, two polymorphs of the anhydrous complex [Ni(4‐pyc)2]n (2a and 2b) and the polynuclear compound [Ni5(OH2)3(4‐pyc)10]n (3) were obtained in very high yield. All of the compounds were characterized by elemental analysis and spectroscopic data. The crystal structure determination of compounds 2b and 3 was also carried out. Structural and topological analysis of these new structural types and other related ones were performed. It was found that compounds 2a and 2b are a rare case of coordination framework isomers. Thermogravimetric studies indicate that compounds 2b and 3 lose the pore‐allocated solvent molecules at moderate temperatures without any significant structural change, and at higher temperatures, compounds 1 and 3 are transformed into 2a. Textural parameters that characterize the microporous networks for 2b and 3 were obtained by nitrogen‐adsorption measurements. For both samples, the micropore size distribution indicates cylindrical pores with diameters of 0.85 (2b) and 0.90 nm (3). The values of Brunauer–Emmett–Teller and Langmuir surface areas are 178 and 185 m2 g–1 for compound 2b, and 995 and 982 m2 g–1 for compound 3. Micropore volumes are 0.065 and 0.350 cm3 g–1 for 2b and 3, respectively. The magnetic properties of compounds 1, 2a, and 2b are consistent with the presence of zero‐field splitting and a small antiferromagnetic coupling between the metal atoms. The magnetic properties of the pentanuclear compound 3 were analyzed by considering one monomer with zero‐field splitting caused by axially distorted NiII octahedral compounds, and two dimeric fragments with magnetic interactions within each dimetallic unit.

Anion mediated formation of different Schiff bases from the same precursors and their nickel(II) complexes with different nuclearity

Two nickel(II) complexes, [Ni2 (H2O)4](NO3)2 (1) and [Ni5 (OAc)6(OH)2] · 5.5H2O (2), have been synthesized and structurally characterized by X-ray crystallographic study, where L1 and L2 represent 2-formyl-4-methyl-6-(1-(2-aminomethyl)piperidine)-iminomethylphenolate and 4-methyl-2,6-bis(1-(2-aminomethyl)piperidine)-iminomethylphenolate, respectively. One-pot reactions between 2,6-diformyl-4-methylphenol with 1-(2-aminoethyl)piperidine, in the presence of nickel(II) nitrate and nickel(II) acetate, afforded in situ [1 + 1] and [1 + 2] condensation leading to Schiff-bases HL1 and HL2, and to 1 and 2 of different nuclearity. Both processes were conducted under the same reaction conditions in anhydrous EtOH. Preferential attainment of bi- or pentanuclear compounds is mediated by the anion of the Ni(II) salt. Complex 1 is formed by two unsymmetrical tridentate L1 chelating in a head-tail fashion to make a centrosymmetric phenoxido-bridged Ni(II) dimer. Two waters complete octahedral coordination. Conversely in 2, two [Ni2(OAc)L2]+ units, having a syn-syn bidentate bridging acetate, embrace a third Ni through bridging acetate and μ3-hydroxide, giving rise to an adduct of C2 symmetry where the compartmental ligand planes form a dihedral angle of ca. 82°. The catecholase activity of these complexes were explored and both complexes effectively catalyze the conversion of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ).

Syntheses and Magnetostructural Investigations on Kuratowski-Type Homo- and Heteropentanuclear Coordination Compounds [MZn4Cl4(L)6] (MII= Zn, Fe, Co, Ni, or Cu; L = 5,6-Dimethyl-1,2,3-benzotriazolate) Represented by the NonplanarK3,3Graph

Homo- and heteropentanuclear coordination compounds [MZn(4)Cl(4)(L)(6)] (M(II) = Zn, Fe, Co, Ni, or Cu; L = 5,6-dimethyl-1,2,3-benzotriazolate) were prepared containing mu(3)-bridging N-donor ligands (1,2,3-benzotriazolate), which are structurally related to the fundamental secondary building unit of Metal-organic Framework Ulm University-4 (MFU-4). The unique topology of these T(d)-symmetrical compounds is characterized by the nonplanar K(3,3) graph, introduced into graph theory by the mathematician Casimir Kuratowski in 1930. The following "Kuratowski-type" compounds were investigated by single-crystal X-ray structure analysis: [MZn(4)Cl(4)(Me(2)bta)(6)].2DMF (M(II) = Zn, Fe, Co, and Cu; DMF = N,N'-dimethylformamide) and [MZn(4)Cl(4)(Me(2)bta)(6)].2C(6)H(5)Br (M(II) = Co and Ni; C(6)H(5)Br = bromobenzene). The mu(3)-bridging benzotriazolate ligands span the edges of an imaginary tetrahedron, in the center of which a redox-active octahedrally coordinated M(II) ion is placed. Four Zn(II) ions are located at the corners of the coordination units. Each Zn center is bound to a monodentate Cl(-) anion and three N-donor atoms stemming from different benzotriazolate ligands. The fact that open-shell redox-active M(II) ions can be introduced selectively into the central octahedral coordination sites is unambiguously proven by a combination of magnetic measurements, UV-vis spectroscopy, and energy-dispersive X-ray and inductively coupled plasma atomic emission spectrometry analysis. The phase purity of all compounds was checked by powder X-ray diffractometry, IR spectroscopy, and elemental analysis. The electronic spectra and magnetic properties of the compounds are in complete agreement with their structures determined from single-crystal data. Thermogravimetric analysis shows that all compounds possess a high thermal stability up to 673 K. The pentanuclear compounds retain their structural integrity in solution, as evidenced by time-of-flight mass spectrometry analysis and comparative solution and solid-state diffuse-reflectance spectroscopy. High stability paired with the presence of redox-active metal ions and Lewis-acidic Zn centers renders Kuratowski-type compounds structural and functional models for future MFU-4-type bi- and multifunctional heterogeneous catalysts.

Photoswitchable Heterotrimetallic Chain Based on Octacyanomolybdate, Copper, and Nickel: Synthesis, Characterization, and Photomagnetic Properties

Taking into account the general interest in photoswitchable nanomagnets, we present an original synthetic route to well-defined photoswitchable heterotrimetallic complexes. Our strategy demonstrates the feasibility of using a "molybdenum-copper" switchable complex with terminal cyanide ligands as relevant synthons for the rational design and synthesis of heterotrimetallic photoswitchable molecular architectures. Starting from a pentanuclear compound based on an octacyanometalated precursor, [MoIV(CN)4(CNCuII(Me2en)2)4]4+, and a [NiII(cyclam)]2+ assembling building block, we succeeded in synthesizing a photoswitchable heterotrimetallic chain, denoted as {NiMo2Cu7}n. The compound has been characterized by single-crystal X-ray diffraction, UV-vis and IR spectroscopies, and powder magnetic and photomagnetic susceptibility measurements. Before irradiation, the compound behaves as a paramagnet with eight independent spin carriers (CuII d9, S = 1/2, and NiII d8, S = 1). After irradiation, a long-lived metastable state persists until relatively high temperature (120 K) and is thermally reversible.

Combined Studies on the Surface Coordination Chemistry of Benzotriazole at the Copper Electrode by Direct Electrochemical Synthesis and Surface‐Enhanced Raman Spectroscopy

AbstractThe surface coordination chemistry of benzotriazole (BTAH) on a Cu electrode was investigated by electrochemical synthesis of surface complexes and in situ electrochemical surface‐enhanced Raman spectroscopy (SERS) in nonaqueous solution. Two different surface complexes were prepared in solution with or without triphenylphosphane (PPh3). A new mixed‐valence Cu–N cluster compound containing BTAH was synthesized by direct electrochemical oxidation of Cuin nonaqueous solutions with PPh3. The final product, Cu5Cl(BTA)5(PPh3)4 was crystallized and characterized by microanalysis and Raman spectroscopy together with X‐ray crystallographic determinations. The complex crystallized in a monoclinic space group (P21/n) with lattice parameters a = 16.739(2) Å, b = 18.919(2) Å, c = 31.042(4) Å, β = 103.194(3)°, V = 9571.0(19) Å3, R1 = 0.0704, wR2 = 0.1643. The results showed that the complex was a pentanuclear compound. The central CuII atom is coordinated to four equatorial and one axial BTA– ligands to form a distorted tetragonal pyramidal coordination polyhedron, whereas each surrounding CuI ion is in a distorted tetrahedral environment. The in situ SERS studies revealed that the BTA– ion was coordinated to a Cu surface through its two N atoms of the triazole ring to form a surface polymer complex of [Cu(BTA)]n, which suppressed the dissolution and oxidation of Cu effectively. The introduction of PPh3 blocked the surface coordination of BTAH with the electrode, and a complex of BTA– and PPh3 with Cu was formed in the bulk solution.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Control of Magnetic Properties through External Stimuli

In our Review, we described only work of D. M. Adams et al. (J. Am. Chem. Soc. 1993, 115, 8221–8229) as an example of solid-state valence tautomerism (p. 2154). However, we should note that solid-state valence tautomerism has also been reported by G. A. Abakumov et al. (Dokl. Akad. Nauk SSSR 1993, 328, 332–335). Furthermore, the pioneering works of G. A. Abakumov et al. in which metal–ligand electron transfer in o-semiquinonic copper complexes was first reported are not cited (Dokl. Akad. Nauk SSSR 1982, 266, 361–363; Dokl. Akad. Nauk SSSR 1989, 304, 107–111). It has been suggested that our interpretation of photomechanical effects on p. 2158 is wrong. We proposed that bending is induced by the expansion of the irradiated region of the crystals. If this were the case, irradiation of the opposite side of the crystal should cause bending in the other direction. However, the crystal actually bends according to its own axis, and the bending is independent of the side from which the crystal is irradiated. Furthermore, the title of Chapter 3.1 on p. 2162 should read “Metal-to-Metal Charge Transfer in FeCo Pentanuclear Compounds”.

Synthesis, structures and magnetic properties of pentanuclear and trinuclear heterometallic complexes with bended and linear cyano-bridges (tren = tris(2-aminoethyl)amine)

The reaction of [Cu(tren)(OH 2)](ClO 4) 2 with KCN gave a mononuclear complex [Cu(tren)(CN)](ClO 4) ( 1) (tren = tris(2-aminoethyl)amine). Using 1 as a building block, one pentanuclear compound, [{Cu(tren)(NC)} 4Ni](ClO 4) 6 ( 2) and two trinuclear complexes, [{Cu(tren)NC} 2Co(tren)](ClO 4) 5 · 2H 2O ( 3), [{Cu(tren)CN} 2NiL](ClO 4) 4 ( 4) (L = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) were prepared and characterized by single crystal X-ray analysis. In 1, Cu(II) atom adopts a distorted trigonal bipyramidal (TBP) geometry. In 2, the Ni(II) atom occupies the center of the pentanuclear compound with a square-planar coordination geometry. In 3, the six-coordinated Co(III) atom presents a distorted octahedral geometry with four nitrogen atoms from tren and two carbon atoms of bridged cyano groups in cis-positions. In 4, the nickel atom is located in an inversion center and coordinated with two [(tren)CuCN] + moieties through cyano-bridging ligands. Magnetic susceptibility measurements of 2– 4 show that the magnetic interactions between the heterometallic ions are antiferromagnetical coupling through the cyano bridges with g = 2.25, J = −0.142 cm −1 and J′ = −0.167 cm −1 for 2, g = 2.06, J = −0.094 cm −1 for 3, and g = 2.20, J = −33.133 cm −1 for 4. The correlations between the structures and the J values are discussed.

Ruthenium‐Cluster‐Mediated Activation of All Bonds of a Methyl Group of 6,6′‐Dimethyl‐2,2′‐bipyridine and 2,9‐Dimethyl‐1,10‐phenanthroline: Transformation of the Latter into a 2‐Alkenyl‐9‐methyl‐1,10‐phenanthroline Ligand

The treatment of [Ru3(CO)12] with 6,6'-dimethyl-2,2'-bipyridine (Me2bipy) or 2,9-dimethyl-1,10-phenanthroline (Me2phen) in THF at reflux temperature gives the trinuclear dihydride complexes [Ru3(mu-H)2(mu3-L1)(CO)8] (L1 = HCbipyMe 1 a, HCphenMe 1 b), which result from the activation of two C-H bonds of a methyl group. The hexa-, hepta-, and pentanuclear derivatives [Ru6(mu3-H)(mu5-L2)(mu-CO)3(CO)13] (L2 = CbipyMe 2 a, CphenMe 2 b), [Ru7(mu3-H)(mu5-L2)(mu-CO)2(CO)16] (L2 = CbipyMe 3 a, CphenMe 3 b), and [Ru5(mu-H)(mu5-C)(mu-L3)(CO)13] (L3 = bipyMe 4 a, phenMe 4 b) can also be obtained by treating 1 a and 1 b with [Ru3(CO)12]. Compounds 2 a and 2 b have a basal edge-bridged square-pyramidal metallic skeleton with a carbyne-type C atom capping the four Ru atoms of the pyramid base. The structures of 3 a and 3 b are similar to those of 2 a and 2 b, respectively, but an additional Ru atom now caps a triangular face of the square-pyramidal fragment of the metallic skeleton. The most interesting feature of 2 a, 2 b, 3 a, and 3 b is that their carbyne-type C atoms were originally bound to three hydrogen atoms in Me2bipy or Me2phen and, therefore, they arise from the unprecedented activation of all three C-H bonds of C-bound methyl groups. The pentanuclear compounds 4 a and 4 b contain a carbide ligand surrounded by five Ru atoms in a distorted trigonal-bipyramidal environment. They are the products of a series of processes that includes the activation of all bonds (three C-H and one C-C) of organic methyl groups, and are the first examples of complexes having carbide ligands that arise from C-bonded methyl groups. The alkenyl derivatives [Ru5(mu5-C)(mu-p-MeC6H4CHCHphenMe)(CO)13] (5 b), [Ru5(mu-H)(mu5-C)(mu-p-MeC6H4CHCHphenMe)(p-tolC2)(CO)12] (6 b), and [Ru5(mu-H)(mu5-C)(mu-PhCHCHphenMe)(PhC2)(CO)12] (7 b) have been obtained by treating 4 b with p-tolyl- and phenylacetylene, respectively. Their heterocyclic ligands contain an alkenyl fragment in the position that was originally occupied by a methyl group. Therefore, these complexes are the result of the formal substitution of an alkenyl group for a methyl group of 2,9-dimethyl-1,10- phenanthroline.

Cyano-bridged Fe(II)–Cu(II) bimetallic assemblies: honeycomb-like and pentanuclear structures

A 2D honeycomb-like compound [Fe(CN)6{Cu(apn)}3]n(ClO4)2n(H2O)4n (1) (apn=N-(3-aminopropyl)-1,3-propanediamine) and a pentanuclear compound [Fe(CN)6{Cu(dmen)2}4](ClO4)4 (2) (dmen=N,N-dimethylethylenediamine) have been prepared and characterized. In the synthesis, the use of ferricyanide or ferrocyanide yielded identical products due to reduction of Fe(III) ion to Fe(II) in water. For 1, all cyanide groups of ferrocyanide are bonded to six Cu(II) ions of which two symmetry-related Cu atoms are linked to nitrogen atoms of cyanide ligands bound to the neighboring Fe(II) center, resulting in the honeycomb structure. The variations of the geometries around Cu(II) centers are between ideal trigonal bipyramidal and square pyramidal structures, which may arise from the relative structural arrangements of flexible apn ligands. For 2, all the Cu(II) ions can be seen as square pyramidal geometries composed of basal least-squares planes from four dmen nitrogen atoms and apical nitrogen atoms from cyanide bridge. The Cu–NC angle around Cu centers in 2 is 127.9(7)°, much acuter than that of 1, which is presumably associated with steric interactions between the bulky methyl groups of the dmen ligands on the neighboring Cu ions. Both compounds exhibit very weak antiferromagnetic interactions in the low temperature range.

Formation of two diverse classes of poly(amino-alkoxide) chelates and their mononuclear and polynuclear lanthanide(III) complexes.

Factors that influence aggregation of lanthanide(III) (Ln(III)) ions to form polynuclear complexes were studied utilizing 1-aziridineethanol as a versatile source of macrocyclic and acyclic chelates. The facile ring-opening cyclo-oligomerization of 1-aziridineethanol leads to the formation of a series of polyaza cyclic oligomers (series A). In the presence of ethylenediamine, a competing N-alkylation reaction occurs to produce a new class of acyclic ligands (series B). The cyclo-oligomerization of four 1-aziridineethanol units is the most favorable process, leading to the formation of the 12-membered cyclen-type macrocycle, H(4)L(1) (1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraaza-cyclododecane). Ring-opening cyclo-oligomerization of 1-aziridineethanol in the presence of Ln(III) ions produces self-assembled mononuclear, tetranuclear, and pentanuclear compounds of H(4)L(1). In the presence of ethylenediamine, oligomerization of 1-aziridineethanol results in a dinuclear complex of an acyclic poly(amino-alkoxide) H(2)L(2). The coordinative unsaturation of (i) the alkoxy sites of [H(x)L(1)](x)(-)(4) (where x < 4) and (ii) Ln(III) ions in coordination numbers less than nine are critical factors in the formation of the polynuclear Ln(III) complexes. The identities of mononuclear, dinuclear, tetranuclear, and pentanuclear complexes herein discussed were established by X-ray crystallography.

Structural diversity of cyanide-bridged bimetallic clusters based on hexacyanometallate building blocks

Four new cyanide-bridged bimetallic complexes, with different geometries and nuclearities, have been synthesized and characterized by single crystal X-ray crystallography. The trinuclear compound {〚Zn(bpy) 2(OH 2)〛 2〚Fe(CN) 6〛}Cl ( 1)·2 MeOH·12 H 2O crystallizes in the triclinic space group P 1 , with a = 12.010(2) Å, b = 16.316(3) Å, c = 16.325(3) Å, α = 97.47(3)°, β = 92.14(3)°, γ = 92.43(3)°, V = 3166(1) Å 3 and Z = 4. The tetranuclear compound {〚Zn(phen) 2〛 2〚Fe(CN) 6〛 2} 2– ( 2) cocrystallizes with 〚Zn(bpy) 3〛 2+ and 32 H 2O molecules in the monoclinic space group C2/ c with a = 42.047(8) Å, b = 13.541(2) Å, c = 28.781(5) Å, β = 120.23(3)°, V = 14158(4) Å 3 and Z = 2. The pentanuclear compound {〚Zn(bpy) 2(H 2O)〛〚Zn(bpy) 2〛 2〚Fe(CN) 6〛 2}( 3)·23 H 2O crystallizes in the triclinic space group P 1 with a = 15.308(3) Å, b = 17.496(4) Å, c = 20.050(4) Å, a = 64.25(3)°, β = 72.96(3)°, γ = 88.50(3)°, V = 14158(4) Å 3 and Z = 5. The decanuclear compound {〚Zn(phen) 2〛〚Fe(CN) 6〛} 2{〚Zn(phen) 2〛〚Zn(phen) 2(OH 2)〛〚Fe(CN) 6〛} 2( 4)·4 MeOH·26 H 2O crystallizes in the monoclinic space group C2/ c, with a = 48.14(1) Å, b = 13.585(3) Å, c = 34.131(7) Å, β = 112.05(3)°, V = 20689(7) Å 3 and Z = 4. The unusual geometries discovered in this mixed Fe(III)/Zn(II) chemistry provide excellent models for the design of high-spin cyanide-bridged transition-metal clusters.

Heteronuclear thiocyanate-bridged compounds of the type (NiL) 3[M(NCS) 6] 2 (M=Fe(III), Cr(III); L=5,6,12,13-Me 4-[14]-4,11-dieneN 4)

The complexes of the general formula (NiL) 3[M(NCS) 6] 2 (where L=5,6,12,13-Me 4-[14]-4,11-dieneN 4, M=Fe(III) ( 1), Cr(III) ( 2)) were obtained and their magnetic and spectroscopic properties characterized. For the compound (NiL) 3[Fe(NCS) 6] 2, the crystal structure was determined and X-ray analysis showed that it forms a linear pentanuclear compound NiFeNiFeNi in which the peripheral nickel(II) ions are five-co-ordinate. Magnetic studies for both compounds showed the existence of structural differences between them.