Spin fluctuations and orbital ordering in quasi-one-dimensional α-Cu(dca)2(pyz) {dca = dicyanamide = N(CN)2; pyz = pyrazine}, a molecular analogue of KCuF3

The magnetic properties of α-Cu(dca)₂(pyz) were examined by magnetic susceptibility, magnetization, inelastic neutron scattering (INS), muon-spin relaxation (μSR) measurements and by first-principles density functional theoretical (DFT) calculations and quantum Monte Carlo (QMC) simulations. The χ versus T curve shows a broad maximum at 3.5 K, and the data between 2 and 300 K is well described by an S = 1/2 Heisenberg uniform chain model with g = 2.152(1) and J/k_B = −5.4(1) K. μSR measurements, conducted down to 0.02 K and as a function of longitudinal magnetic field, show no oscillations in the muon asymmetry function A(t). This evidence, together with the lack of spin wave formation as gleaned from INS data, suggests that no long-range magnetic order takes place in α-Cu(dca)₂(pyz) down to the lowest measured temperatures. Electronic structure calculations further show that the spin exchange is significant only along the Cu–pyz–Cu chains, such that α-Cu(dca)₂(pyz) can be described by a Heisenberg antiferromagnetic chain model. Further support for this comes from the M versus B curve, which is strongly concave owing to the reduced spin dimensionality. α-Cu(dca)₂(pyz) is a molecular analogue of KCuF₃ owing to d_x2-y2${\text{d}}_{x^2-y^2}$ orbital ordering where nearest-neighbor magnetic orbital planes of the Cu²⁺ sites are orthogonal in the planes perpendicular to the Cu–pyz–Cu chains.     

Syntheses, structures, and dynamic properties of M(CO)2(η-C3H5)(en)(X) (M = Mo, W; X = Br, N3, CN) and [(en)(η-C3H5)(CO)2M(μ-CN)M(CO)2(η-C3H5)(en)]Br (M = Mo, W)

Mononuclear compounds M(CO)₂(η³-C₃H₅)(en)(X) (X = Br, M = Mo(1), W(2); X = N₃, M = Mo(3), W(4); X = CN, M = Mo(5), W(6)) and cyanide-bridged bimetallic compounds [(en)(η³-C₃H₅)(CO)₂M(μ-CN)M(CO)₂(η³-C₃H₅)(en)]Br (M = Mo (7), W(8)) were prepared and characterized. These compounds are fluxional and display broad unresolved proton NMR signals at room temperature. Compounds 1-6 were characterized by NMR spectroscopy at −60 °C, which revealed isomers in solution. The major isomers of 1-4 adopt an asymmetric endo-conformation, while those of 5 and 6 were both found to possess a symmetric endo-conformation. The single crystal X-ray structures of 1-6 are consistent with the structures of the major isomer in solution at low temperature. In contrast to mononuclear terminal cyanide compounds 5 and 6, cyanide-bridged compounds 7 and 8 were found to adopt the asymmetric endo-conformation in the solid state.     

Segregated aromatic π-π stacking interactions involving fluorinated and non-fluorinated benzene rings: Cu(py)2(pfb)2 and Cu(py)2(pfb)2(H2O) (py = pyridine and pfb = pentafluorobenzoate)

The syntheses, physical characterization and crystal structures of two new molecular copper(II) complexes of composition [Cu(C₅H₅N)₂(C₇F₅O₂)₂] (1) and [Cu(C₅H₅N)₂(C₇F₅O₂)₂(H₂O)] (2) (C₅H₅N = py = pyridine and C₇F₅O₂⁻ = pfb = pentafluorobenzoate) are reported. Single-crystal X-ray structure determinations revealed that in 1, the Cu²⁺ ion, which lies on a crystallographic inversion centre, is coordinated to two py molecules and two oxygen atoms from two monodentate pfb anions, resulting in a trans-CuN₂O₂ square planar geometry. In 2, the Cu²⁺ ion is also coordinated to two py and two pfb species in addition to a water molecule in the apical site of a distorted CuN₂O₃ square pyramid. In the crystal packing, both 1 and 2 show segregated aromatic π-π stacking interactions in which (py + py) and (pfb + pfb) ring-pairings are seen, but no (py + pfb) pairings occur. Crystal data: 1: C₂₄H₁₀CuF₁₀N₂O₄, M_r = 643.88, space group , a = 8.0777 (3) Å, b = 8.0937 (3) Å, c = 10.5045 (5) Å, α = 90.916 (3)°, β = 93.189 (2)°, γ = 118.245 (3)°, V = 603.36 (4) Å³, Z = 1. 2: C₂₄H₁₂CuF₁₀N₂O₅, M_r = 661.90, space group , a = 7.5913 (5) Å, b = 15.6517 (6) Å, c = 21.1820 (14) Å, α = 95.697 (4)°, β = 94.506 (2)°, γ = 91.492 (4)°, V = 2495.2 (3) Å³, Z = 4.     

Germylene and stannylene (Me2NCH2CH2O)2E as strong σ-donor ligands for transition metal complexes [ML(CO)n] (E = Ge, Sn; M = Cr, Mo, W, n = 4 or 5; M = Fe, n = 4). Synthesis, spectroscopic and theoretical study

A series of germylene and stannylene (Me₂NCH₂CH₂O)₂E (E = Ge, 1; E = Sn, 2) complexes of group 6 metals and iron carbonyls L·M(CO)_n (M = Cr, Mo, W, n = 5 (3-8), n = 4 (9, 10); M = Fe, n = 4 (11, 12)) were prepared. These complexes were characterized by ¹H, ¹³C NMR, FTIR and elemental analysis. Ligand properties of 1 and 2 were compared to PPh₃ and dmiy (N,N′-dimethylimidazolin-2-ylidene) using theoretical calculations (PBE/TZ2P) and FTIR. Ligand dissociation energies increase in the order Ph₃P < 2∼1 < dmiy, while donor strength rise in the order PPh₃ < dmiy < 2 < 1.     

Trimetallic complexes containing 1,1′-Rc′(CC)2 units [Rc′ = ruthenocene-1,1′-diyl, Ru(η-C5H4-)2]

Reactions between 1,1′-(Me₃SiCC)₂Rc′ [Rc′ = ruthenocen-1,1′-diyl, Ru(η-C₅H₄-)₂] and RuCl(PP)Cp′ in the presence of KF gave 1,1′-{Cp(PP)RuCC}₂Rc′ [Cp′ = Cp, PP = PPh₃1, P(m-tol)₃2, dppe 3, dppf 4; Cp′ = Cp^∗, PP = dppe 5]. Compounds 1 and 2 react with tcne to give two diastereomers a/b of the allylic (vinylcarbene) complexes 6 and 7, while methylation of 5 gave the bis-vinylidene [1,1′-{Cp^∗(dppe)RuCCMe}₂Rc′](BPh₄)₂ (8). The X-ray structures of 4, 6b and 8 have been determined. Cyclic voltammograms indicate that there is some electronic communication between the ruthenium end-groups through the Rc′ centre.     

Syntheses and crystal structures of [Bu3SbCr(CO)5], [Bu3BiM(CO)5] (M = Cr, W), and [Bu3BiMnCp′(CO)2] (Cp′ = η-C5H4CH3)

Syntheses and crystal structures of [^tBu₃SbCr(CO)₅] (1), [^tBu₃BiM(CO)₅] [M = Cr (2), W (3)] and [^tBu₃BiMnCp′(CO)₂] (4) (Cp′ = η⁵-C₅H₄CH₃) are reported.     

Insertion reaction of elemental sulfur into the Ln–C bond: Synthesis and characterization of [(C5H4SiMe2Bu)2Ln(μ-SR)]2 (R = Me,Ln = Yb,Er, Dy,Y; R = Bu,Ln = Yb,Dy)

Treatment of (C₅H₄SiMe₂^tBu)₂LnR with 1 equiv of elemental sulfur in toluene at ambient temperature gives dimeric complexes [(C₅H₄SiMe₂^tBu)₂Ln(μ-SR)]₂ [R = Me, Ln = Yb (1), Er (2), Dy (3), Y (4); R = ⁿBu, Ln = Yb (5), Dy (6)]. All these complexes have been characterized by elemental analysis, IR and mass spectroscopies. The structures of complexes 1, 3, 5 and 6 are also determined through X-ray single crystal diffraction analysis, indicating that only one sulfur atom from elemental sulfur inserts into Ln–C σ-bond.     

Syntheses, structures, and dynamic properties of M(CO)2(η-C3H5)(L-L)(NCBH3) (M = Mo, W; L-L = dppe, bipy, en)

Compounds M(CO)₂(η³-C₃H₅)(L-L)(NCBH₃) (L-L = dppe, M = Mo(1), W(2); L-L = bipy, M = Mo(3), W(4); L-L = en, M = Mo(5), W(6)) were prepared and characterized. The single crystal X-ray analyses of 2-6 revealed that the cyanotrihydroborate anion bonds to the metal through a nitrogen atom, the open face of the allyl group being pointed toward the two carbonyls (endo-isomer). In compounds 2, 5, and 6, the two donor atoms of the bidentate ligand occupy equatorial and axial positions, respectively. In the solid state structures of compounds 3 and 4 both nitrogen atoms of the bipy ligand occupy equatorial positions. The NMR spectroscopy reveals a fluxional behavior of compounds 1, 2, 5, and 6 in solution. Although the fluxional behavior of compounds 5 and 6 ceased at about −40 °C, that of compound 1 could not be stopped even at −90 °C. Their low temperature conformations are consistent with their solid state structures. Both the endo- and exo-isomers coexist in solution for compounds 3 and 4.     

New ferrocenylmethylphosphines - Preparation, characterisation and coordination chemistry of PH(CH2Fc)2, P(CH2Fc)3 [Fc = Fe(η-C5H5)(η-C5H4)] and their derivatives

The new ferrocenylmethylphosphines PH(CH₂Fc)₂ (1) [Fc = Fe(η⁵-C₅H₅)(η⁵-C₅H₄)] and P(CH₂Fc)₃ (2) and the phosphonium salt [P(CH₂Fc)₃(CH₂OH)]I (3) were synthesised from P(CH₂OH)₃ and [FcCH₂NMe₃]I. [P(CH₂Fc)(CH₂OH)₃]Cl (4) was obtained from P(CH₂Fc)(CH₂OH)₂, CH₂O and HCl. The new phosphines and phosphonium salts were fully characterised by NMR and IR spectroscopy and MS. [Mo(CO)₆] reacts with 1 to give [Mo(CO)₅{PH(CH₂Fc)₂}] (5) in high yield, but attempts to employ 2 as a ligand failed. The reaction of [P(CH₂Fc)₃(CH₂OH)]I (3) and [PH(CH₂Fc)₃]I (obtained in situ from 3 and Na₂S₂O₅) with [WI₂(CO)₃(NCMe)₂] gave the complex salts [P(CH₂Fc)₃(CH₂OH)][WI₃(CO)₄] (6) and [PH(CH₂Fc)₃][WI₃(CO)₄] (7), respectively. [P(CH₂Fc)₄]I (8) was synthesized from PH₂CH₂Fc and [FcCH₂NMe₃]I. Crystal structures were obtained for 1, 3-8.     

Synthesis and structure of the monometallic cationic complex [Cp(CO)2Fe{η-(CH2CHCH2CH3)}]PF6 (Cp = η-C5H5)

The bimetallic carbocation complex [{Cp(CO)₂Fe}₂(μ-C₄H₇)]PF₆ reacted with trifluoroacetic acid to give the mononuclear cationic complex [Cp(CO)₂Fe{η²-(CH₂CHCH₂CH₃)}]PF₆, which formed yellow orthorhombic crystals in the space group P2₁2₁2₁ with a = 7.652(4), b = 13.422(7), c = 14.037(7); α = β = γ = 90.00 and Z = 4. The carbocation is coordinated to the metal in a η²-fashion forming a chiral metallacyclopropane type structure. The β-CH carbon (C9) is disordered over two positions (C9A and C9B), each having about 50% occupancy. This is attributed to there being both the R and S enantioface isomers in equal amounts in the crystal sample. NMR data indicate that the metallacyclopropane structure observed in the solid state is preserved in solution.     

Reactions of diferrocenyl dichalcogenides with [W(CO)5(THF)]: X-ray crystal structures of Fc2Te2 and [W2(μ-SeFc)2(CO)8] (Fc = [Fe(η-C5H5)(η-C5H4)])

Treatment of [W(CO)₅THF] with diferrocenyl diselenide, Fc₂Se₂, yielded the novel metal-metal bonded tungsten(I) complex, [W₂(μ-SeFc)₂(CO)₈] (1: Fc = ferrocenyl, [Fe(η⁵-C₅H₅)(η⁵-C₅H₄)]), which was characterised by NMR and IR spectroscopy, mass spectrometry, and X-ray crystallography. The corresponding tellurium derivative could not be prepared by an analogous route. The X-ray crystal structure of Fc₂Te₂ has also been determined.     

Centrosymmetric [Mn2(CO)6(μ-thpymS)2] (thpymS = tetrahydropyrimidine-2-thionato) as a synthon to mixed-metal clusters

Reaction of [Mn₂(CO)₉(NCMe)] with tetrahydropyrimidine-2-thione (thpymSH) at 25 °C furnishes the mono- and dinuclear complexes [Mn(CO)₄(κ¹:η¹-SCNHC₃H₆NCO)] (2) and [Mn₂(CO)₆(μ-thpymS)₂] (1), respectively. Carbon-nitrogen coupling is observed in compound 2 resulting in the formation of κ¹:η¹-SCNHC₃H₆NCO ligand while compound 1 adopts a centrosymmetric structure. Reaction of 1 with [Os₃(CO)₁₀(NCMe)₂] at 80 °C affords the mixed Mn-Os cluster [MnOs₃(CO)₁₃(μ₃-thpymS)] (3) which possesses a butterfly skeleton of four metal atoms whereas with Ru₃(CO)₁₂ at 110 °C gives the mixed Mn-Ru complex [MnRu₃(CO)₁₄(μ₄-S)(κ¹:η¹-thpym)] (4). In contrast, treatment of 1 with Fe₃(CO)₁₂ at 80 °C furnishes two triiron complexes [Fe₃(CO)₉(μ₃-S)(μ₃-κ¹:η¹-C₄H₆N₂)] (5) and [Fe₃(CO)₈(μ₃-S)₂(η¹-C₄H₈N₂)] (6). The former also results from the direct reaction of thpymSH with Fe₃(CO)₁₂ and reacts with H₂S to afford 6. The molecular structures of all these new complexes have been determined by X-ray diffraction studies.     

Reactions of Cu3(dppm)3(μ3-OH)(ClO4)2 (dppm = bis-(diphenylphosphino) methane) with Soft Heterocumulenes

The reaction of [Cu₃(dppm)₃(μ₃-OH)](ClO₄)₂ (1) with heterocumulenes (XCS; X = NPh, NMe and S) has been studied. The μ₃-OH ligand inserts into PhNCS and MeNCS only in the presence of methanol. Insertion products are formed in accord with earlier observations made with copper(I)-aryloxides. On heating, the insertion products convert to a S bridged cluster [Cu₄(dppm)₄(μ₄-S)](ClO₄)₂ (8), having a tetrameric core. However, in the reaction with CS₂, 1 is converted to 8 even at room temperature in the presence of methanol. On the other hand, the dimeric complex [Cu₂(dppm)₂(CH₃CN)₄](ClO₄)₂, reacts with CS₂ to give (diphenylphosphinomethyl)-diphenylphosphine sulfide, Ph₂P-CH₂-P(S)Ph₂ (dppmS), which forms the complex [Cu(dppmS)₂]ClO₄ (9). A single crystal X-ray crystallographic study of 9, the first copper(I) complex of dppmS has been taken up to confirm the mono-oxidation of the dppm ligand and the nuclearity of the complex. Reactions of complex 1 with heterocumulenes and with elemental sulfur, are compared.     

Unsaturation in binuclear cyclopentadienylchromium carbonyl thiocarbonyls: Viability of (η-C5H5)2Cr2(CS)2(CO)3 in contrast to (η-C5H5)2Cr2(CO)5

The cyclopentadienylchromium carbonyl thiocarbonyls Cp₂Cr₂(CS)₂(CO)_n (n = 4, 3, 2, 1) have been studied by density functional theory using the B3LYP and BP86 functionals. The lowest energy Cp₂Cr₂(CS)₂(CO)₄ structure can be derived from the experimentally characterized unbridged Cp₂Cr₂(CO)₆ structure by replacing the two terminal carbonyl groups furthest from the Cr-Cr bond with two terminal CS groups. The two lowest energy Cp₂Cr₂(CS)₂(CO)₃ structures have a single four-electron donor η²-μ-CS group and a formal Cr-Cr single bond of length ∼3.1 Å. In contrast to the carbonyl analogue Cp₂Cr₂(CO)₅ these Cp₂Cr₂(CS)₂(CO)₃ structures are viable with respect to disproportionation into Cp₂Cr₂(CS)₂(CO)₄ and Cp₂Cr₂(CS)₂(CO)₂ and thus are promising synthetic targets. The lowest energy Cp₂Cr₂(CS)₂(CO)₂ structures have all two-electron donor CO and CS groups and short CrCr distances around ∼2.3 Å suggesting the formal triple bonds required to give the chromium atoms the favored 18-electron configurations. These Cp₂Cr₂(CS)₂(CO)₂ structures are closely related to the known structure for Cp₂Cr₂(CO)₄. In addition, several doubly bridged structures with four-electron donor η²-μ-CS bridges are found for Cp₂Cr₂(CS)₂(CO)₂ at higher energies. The global minimum Cp₂Cr₂(CS)₂(CO) structure is a triply bridged triplet with a CrCr triple bond (2.299 Å by BP86). A higher energy singlet Cp₂Cr₂(CS)₂(CO) structure has a shorter Cr-Cr distance of 2.197 Å (BP86) suggesting the formal quadruple bond required to give each chromium atom the favored 18-electron configuration.     

A series of multinuclear homo- and heterometallic complexes with bridging tellurolato ligands derived from [CpIr(CO)(TeTol)2] (Cp = η-C5Me5, Tol = p-tolyl)

Reactions of [Cp^∗Ir(CO)(TeTol)₂] (1; Tol = p-tolyl) with certain organometallic Pd(II), Pt(II), Ir(III), Rh(III), and Ru(II) species afforded IrPd, IrPt, IrPt₂, Ir₂, IrRh, IrRu₃, and IrRu complexes having tellurolato-bridged dinuclear or trinuclear cores. This finding demonstrates that 1 is a versatile precursor to synthesize a variety of multinuclear homo- and heterometallic μ-tellurolato complexes, whose chemistry is still less advanced as compared with that of μ-thiolato complexes.     

夹心化合物Ni(C5H5)2的Xα研究

用Xα方法计算了Ni(C5H5)2的电子能级与归一化电荷,讨论了夹心化合物成键的特点,并用过渡态方法分析Ni(C5H5)2的光电子能谱及紫外可见吸收光谱,结果与实验相符。     

Synthesis,structural characterisation and thermal decomposition of a new organic–inorganic hybrid material (C5H14N2)[Cu(SO4)2(H2O)4] · H2O

The crystal structure of copper sulfate templated by 2-methylpiperazine, (C₅H₁₄N₂)[Cu(SO₄)₂(H₂O)₄] · H₂O, was investigated using single crystal X-ray diffraction data. At room temperature, it crystallises in the monoclinic P2₁/n space group with the following unit-cell parameters: a = 6.9153(1), b = 23.1295(3), c = 10.4472(1) Å, β = 104.227(1)°, V = 1619.75(4) Å³ and Z = 4. The Cu^II cation adopts a slightly distorted octahedral geometry, arising from four water molecules and two sulfate tetrahedra leading to the formation of [Cu(SO₄)₂(H₂O)₄] units. The structure consists of isolated [Cu(SO₄)₂(H₂O)₄]²⁻ anions, 2-methylpiperazinediium cations (C₅H₁₄N₂)²⁺ and water molecules connected by a three-dimensional hydrogen-bond network. The thermal decomposition of the precursor, studied by thermogravimetry and temperature-dependent X-ray powder diffraction, proceeds through four stages giving rise to the copper oxide.     

[M(dipicH2)(H2O)3], M = Ni,Cu, Zn (dipicH2 = dipicolinic acid) – A combined crystallographic,spectroscopic and computational study

Cationic metal complexes of dipicolinic acid (dipicH₂) are stabilized by [Ce(dipic)₃]²⁻ ions in the three isomorphous crystals [M(dipicH₂)(OH₂)₃][Ce(dipic)₃] · 3H₂O (M = Ni, 1; Cu, 2; Zn, 3). Magnetic dilution provided by the bulky anions leads to well-resolved EPR spectra in polycrystalline samples of 2. The cations have 4+2 coordination, the carbonyl atom of the carboxylic acid groups coordinating weakly from trans positions. In the case of 2 this steric distortion is augmented by Jahn–Teller distortion. All the three structures are satisfactorily modelled by calculations based on density functional theory (DFT). The switch of the Jahn–Teller axis upon deprotonation of the complex, leading to the neutral species Cu(dipic)(H₂O)₃, is also reproduced by DFT. Electronic transition energies as well as the g-tensor component of the d⁹ complex obtained are in good agreement with experiment. However, the calculated hyperfine coupling constants are in error. DFT also fails to satisfactorily account for the electronic transition in the d⁸ ion in 1.     

Are closed clusters expected from the (n + 1) skeletal electron pairs rule in alanes and gallanes? A DFT structural study of AnHn + 2 (A = Al, Ga, and n = 4-6)

It has been suggested recently that the alanes Al_nH_n + 2 can be treated by the polyhedral skeletal electron pair theory (PSEPT) of Wade and Mingos (W-M) as it was successful for their borane congeners such as B_nH_n + 2, well known as the deprotonated B_nH_n²⁻. To do so, the neutral Al_nH_n + 2 have been considered as Al_nH_n²⁻ + 2H⁺. The additional hydrogens donate their electrons to the Al_nH_n polyhedral framework and according to the n + 1 electron pairs rule; these clusters should have closo-polyhedral structures. In this work the homologous gallanes, the structures and stabilities of Ga_nH_n + 2 are studied at high levels of calculational theory and we investigated the applicability of the W-M rule to the alanes and gallanes A_nH_n + 2 (n = 4-6; A = Al, Ga). It will be shown that the presence of bridging hydrogen atoms reduces the compactness of the corresponding polyhedron and so these species do not have the closed structures. The computations were performed at B3LYP/6-311+G(d,p), BPW91/6-311G(d,p) and B3LYP/6-311+G(3df,2p) levels of theory. Our interest in these compounds includes their potential use as hydrogen storage species and future clean sources of energy.     

A general route for the synthesis of hydrido-carboxylate complexes of the type MH(CO)(κ-OCOR)(PPh3)2 [M = Ru,Os; R = CH3, CH2Cl,C6H5, CH(CH3)2] and their use as precatalysts for hydrogenation and hydroformylation reactions

The synthesis and solid-state IR, ¹H and ³¹P{¹H} NMR spectroscopic characterization of complexes of the type MH(CO)(κ³-OCOR)(PPh₃)₂ [M = Ru, Os; R = CH₃, CH₂Cl, C₆H₅ and CH(CH₃)₂] are reported in this paper. These compounds were obtained by reaction of the respective cationic complex [MH(CO)(NCMe)₂(PPh₃)₂]BF₄ with the sodium salt of the corresponding carboxylic acid in a 1:1 v/v dichloromethane/methanol solution at room temperature. The spectroscopic data of these complexes and some DFT calculations reveal an octahedral geometry with a bidentated carboxylate, two equivalent triphenylphosphines in a mutually trans positions, a linear hydride and a linear carbonyl both in the cis-positions of the coordination sphere. The catalytic results indicate that these complexes are efficient and regioselective precatalysts for the quinoline hydrogenation and for the hydroformylation of 1-hexene, under mild reaction conditions (130 °C and 4 atm H₂ and 120 °C and 15 atm H₂/CO, respectively). For benzothiophene hydrogenation, the osmium complexes showed low activities whereas the analogous ruthenium complexes were catalytically inactive under somewhat more drastic reaction conditions to those of the quinoline hydrogenation (140 °C and 10 atm H₂).