An investigation of the MAM angle in compounds of general formula [MLn]2(μ-A)

Experimental and Quantum Mechanical Characterization of an Oxygen-Bridged Plutonium(IV) Dimer

We report the synthesis and characterization of K₄ {[PuCl₂ (NO₃ )₃ ]₂ (μ₂ -O)}⋅H₂ O, which contains the first known μ₂ -oxo bridge between two Pu^IV metal centers. Adding to its uniqueness is the Pu-(μ₂ -O) bond length of 2.04 Å, which is the shortest of other analogous compounds. The Pu-(μ₂ -O)-Pu bridge is characterized by the mixing of s-, d-, and p-orbitals from Pu with the p-orbitals of O; the 5f-orbitals do not participate in bonding. Natural bond orbital analysis indicates that Pu and O interact through one 3c-2e σ_Pu-O-Pu and two 3c-2e π_Pu-O-Pu bonding orbitals and that the electron density is highly polarized on the μ₂ -O. Bond topology properties analysis indicates that the Pu-(μ₂ -O) bond shares both ionic and covalent character. Quantum mechanical calculations also show that the dimer has multiconfigurational ground states, where the nonet, septet, quintet, triplet, and singlet are close in energy. This work demonstrates the interplay between experimental and computational efforts that is required to understand the chemical bonding of Pu compounds.

Heterobimetallic μ-oxido complexes containing discrete V(V)-O-M(III) (M = Mn, Fe) cores: targeted synthesis, structural characterization, and redox studies

Heterobimetallic compounds [L'OV(V)(μ-O)M(III)L]n (n = 1, M = Mn, 1-5; n = 2, M = Fe, 6 and 7) containing a discrete unsupported V(V)-O-M(III) bridge have been synthesized through a targeted synthesis route. In the V-O-Mn-type complexes, the vanadium(V) centers have a square-pyramidal geometry, completed by a dithiocarbazate-based tridentate Schiff-base ligand (H2L'), while the manganese(III) centers have either a square-pyramidal (1 and 3) or an octahedral (2 and 5) geometry, made up of a Salen-type tetradentate ligand (H2L) as established by X-ray diffraction analysis. The V-O-Mn bridge angle in these compounds varies systematically from 155.3° to 128.1° in going from 1 to 5 while the corresponding dihedral angle between the basal planes around the metal centers changes from 86.82° to 20.92°, respectively. The V-O-Fe-type complexes (6 and 7) are tetranuclear, in which the two dinuclear V(μ-O)Fe units are connected together by apical iron(III)-aryl oxide interactions, forming a dimeric structure with a pair of Fe-O-Fe bridges. The X-ray data also confirm the V═O → M canonical form to contribute predominantly on the overall V-O-M bridge structure. The molecules in solution also retain their heterobinuclear composition, as established by electrospray ionization mass spectrometry and (51)V NMR spectroscopy. Electrochemically, these complexes are quite interesting; the manganese(III) complexes (1-5) display three successive reductions (processes I-III), each with a monoelectron stoichiometry. Process I is due to a Mn(III)/Mn(II) reduction (E1/2 ranges between -0.32 and -0.05 V), process II is a ligand-based reduction, and process III (E1/2 = ∼1.80 V) owes its origin to a V(V)O/V(IV)O reduction; all potentials are versus Ag/AgCl. The iron(III) compounds (6 and 7), on the other hand, show at least four irreversible processes, appearing at Epc = -0.20, -1.0, -1.58, and -1.68 V in compound 6 (processes IV-VII), together with a reversible process (process VIII) at E1/2 = -1.80 V (ΔEp = 80 mV). While the first two of these are due to Fe(III)/Fe(II) reductions at the two iron(III) centers of these tetranuclear cores, the reversible reduction at a more negative potential (ca. -1.80 V) is due to a V(V)O/V(IV)O-based electron transfer.

A Rare μ-Hydroxo-Bridged Species. Synthesis, Structure, and Properties of μ-Hydroxo(tetraphenylporphyrinatomanganese(III))(phthalocyaninato(azido)chromium(III)), [(TPP)Mn−O(H)−CrPc(N3)]

A novel ditetrapyrrolic, heteroleptic, and heterometallic (Mn-Cr) mu-hydroxo-bridged complex has been prepared, and its structural and general properties have been studied. The species mu-hydroxo(tetraphenylporphyrinatomanganese(III))(phthalocyaninato(azido)chromium(III)), [(TPP)Mn-O(H)-CrPc(N3)], isolated as a chloronaphthalene (ClNP) solvate, has been structurally characterized by single-crystal X-ray work. The two (TPP)Mn and CrPc(N3) fragments are held together by the bridging mu-hydroxo ion with long Mn-O [1.993(5) A] and Cr-O [1.976(5) A] bond distances and a Mn-O(H)-Cr angle of 163.7(3) degrees . The five-coordinate Mn center in the (TPP)Mn fragment is displaced from the TPP rigorously planar central N4 core by 0.128 A, and the environment is typical of a Mn(III) high-spin site. The six-coordinate Cr(III) in the CrPc(N3) moiety lies practically in the plane of the phthalocyanine macrocycle (displacement toward the azido group: 0.054 A). The average Mn-N(pyr) and Cr-N(pyr) bond distances are 2.011(6) and 1.982(6) A, respectively, and the Mn-Cr bond distance is 3.929(2) A. The porphyrin and phthalocyanine rings are in an almost eclipsed position [5.16(2) degrees ], and the mean planes of the two macrocycles form a dihedral angle of 5.79(4) degrees. Crystal data for [(TPP)Mn-O(H)-CrPc(N3)].2ClNP, C76H45CrMnN15O.2C10H7Cl: a = 16.645(3) A, b = 17.692(4) A, c = 25.828(5) A, alpha = 90 degrees , beta = 98.79(3) degrees , gamma = 90 degrees , space group P2(1)/c (No. 14), V = 7517(3) A(3), Z = 4, R1 = 0.086, and wR2 = 0.267. IR and UV-vis-near-IR spectral and room temperature magnetic susceptibility data of the [Mn-Cr] species are also presented.

Ammonolysis of mono(pentamethylcyclopentadienyl) titanium(IV) derivatives

Ammonolyses of mono(pentamethylcyclopentadienyl) titanium(IV) derivatives [Ti(eta5-C5Me5)X3] (X = NMe2, Me, Cl) have been carried out in solution to give polynuclear nitrido complexes. Reaction of the tris(dimethylamido) derivative [Ti(eta5-C5Me5)(NMe2)3] with excess of ammonia at 80-100 degrees C gives the cubane complex [[Ti(eta5-C5Me5)]4(mu3-N)4] (1). Treatment of the trimethyl derivative [Ti(eta5-C5Me5)Me3] with NH3 at room temperature leads to the trinuclear imido-nitrido complex [[Ti(eta/5-CsMes)(mu-NH)]3(mu3-N)] (2) via the intermediate [[Ti(eta5-C5Me5)Me]2(mu-NH)2] (3). The analogous reaction of [Ti(eta5-C5Me5)Me3] with 2,4,6-trimethylaniline (ArNH2) gives the dinuclear imido complex [[Ti(eta5-C5Me5)Me])2(mu-NAr)2] (4) which reacts with ammonia to afford [[Ti(eta5-C5Me5)(NH2)]2(mu-NAr)2] (5). Complex 2 has been used, by treatments with the tris(dimethylamido) derivatives [Ti(eta5-C5H5-nRn)(NMe2)3], as precursor of the cubane nitrido systems [[Ti4(eta5-C5Me5)3(eta5-C5H5-nRn)](mu3-N)4] [R = Me n = 5 (1), R = H n = 0 (6), R = SiMe3 n = 1 (7), R = Me n = 1 (8)] via dimethylamine elimination. Reaction of [Ti(eta5-C5Me5)Cl3] or [Ti(eta5-C5Me5)(NMe2)Cl2] with excess of ammonia at room temperature gives the dinuclear complex [[Ti2(eta5-C5Me5)2Cl3(NH3)](mu-N)] (9) where an intramolecular hydrogen bonding and a nonlineal nitrido ligand bridge the "Ti(eta5-C5Me5)Cl(NH3)" and "Ti(eta5-C5Me5)Cl2" moieties. The molecular structures of [[Ti(eta5-C5Me5)Me]2 (mu-NAr)2] (4) and [[Ti2(eta5-C5Me5)2Cl3(NH3)](mu-N)] (9) have been determined by X-ray crystallographic studies. Density functional theory calculations also have been conducted on complex 9 to confirm the existence of an intramolecular N-H...Cl hydrogen bond and to evaluate different aspects of its molecular disposition.