Linear Tetranuclear Complex Research Articles

Modulating magnetic anisotropy in linear tetranuclear dysprosium(III) complexes via coordinated anions.

We report the synthesis, structures, and magnetic properties of two novel linear tetranuclear complexes with the general formula [Dy4(Hheb)2(heb)4X2(MeOH)4] (X- = NO3-, OAc-; H2heb = (E)-N'-(1-(2-hydroxyphenyl)ethylidene)benzohydrazide, OAc- = acetate). The rigid ligands (Hheb-/heb2-) incorporate phenoxide groups and bridge the Dy3+ ions in an unusual tetranuclear linear assembly. Notably, we demonstrate through magnetic measurements and theoretical calculations how the anion (X) coordinated at the peripheral Dy3+ centers acts as a switch, significantly changing the magnetic anisotropy of the entire complex. This control over magnetic anisotropy through the selection of the coordinated anion offers a promising avenue for tailoring the functionality of single-molecule magnets.

Anion encapsulation promoted by anion⋯π interactions in rationally designed hexanuclear antiferromagnetic wheels: synthesis, structure and magnetic properties

The reaction of Kpymca (pymca = pyrimidine-2-carboxylato anion) with MX2·6H2O and tmda (N,N,N′,N′-tetramethylethylenediamine) in 1 : 3 : 3 molar ratio, using a MeOH/water mixture (3 : 1) as solvent, afforded the hexanuclear complexes [M6(µ-pymca)6(tmda)6]X6·4H2O (M = NiII, X = ClO4−1, BF4−2; M = CoII, X = ClO4−3). The reaction of pymca with either Cu(ClO4)2·6H2O or Cu(BF4)2·6H2O did not lead to any definite product. However, in the presence of strong coordinating chloride anions the linear tetranuclear complex [Cu4(µ-pymca)3Cl(H2O)](ClO4)4·4.5H2O 4 could be obtained. The structures of 1–3 are very similar and consist of wheel-shaped hexanuclear [M6(µ-pymca)6(tmda)6]6+ cations, with pseudo-D3d symmetry in which the ligand acts in a bis(chelating)/bridging mode. The pyrimidine rings of the ligands converge alternatively above and below the plane of the wheel toward the normal to this plane, leading to the formation of a bowl-shaped capsule, which is occupied by one ClO4− (1 and 3) or BF4− (2) anion. There exist tight contacts between ClO4−/BF4− and the π-electron density of the pyrimidine rings of the ligands. The tetranuclear cations of 4 exhibit a zig-zag linear conformation, in which copper ions are bridged by three bis(chelating)/bridging pymca ligands. Variable-temperature magnetic susceptibility studies reveal that complexes 1 and 4 show moderate antiferromagnetic coupling between the metal ions through the pymca ligands with J = −26.3 cm−1 for 1, and J1 = −16.3 cm−1 and J2 = −43.78 cm−1 for 4. The tetranuclear complex 4 has two different magnetic coupling constants accounting for the external–central (J1) and central–central (J2) copper interactions. The magnitude of the J1 and J2 values for 4 has been discussed on the basis of the geometrical factors affecting the magnetic pathways. Moreover, DFT calculations have been performed to support the relative magnitude of the J parameters in 4. A model accounting for spin–orbit coupling (λ), orbital reduction factors (Ak), axial zero-field splitting (Δ) and magnetic exchange coupling (J) was used to analyse the magnetic data of 3. The values of these parameters after the diagonalisation process were: Ak = 1.15, λ = −122 cm−1, Δ = 650 cm−1 and J = −5.2 cm−1.

Syntheses, structures and magnetism of linear tri- and tetra-copper chains containing anions of N,N′-bis(pyrimidine-2-yl)formamidine

Reaction of Kpmf (pmf(-) = anion of N,N'-bis(pyrimidyl-2-yl)formamidine, Hpmf) with divalent copper salt CuX2 afforded the linear trinuclear complexes of the type [Cu3(pmf)4](X)2 (X = BF4, 1; NO3, 2; ClO4, 3), while reaction of Kpmf with monovalent copper salt CuX gave the linear tetranuclear complexes of the type Cu4(pmf)4X2 (X = Cl, 4; Br, 5). The copper atoms of complexes 1-5 are helically bridged by four pmf(-) ligands, resulting in three different coordination modes for the pmf(-) ligands. In complexes 1-3, one pmf(-) ligand adopts a new coordination mode with the two amine nitrogen atoms chelating to the central copper atom, while the other three feature chelation by one pyrimidyl and one adjacent amine nitrogen atoms. The Cu(II)...Cu(II) distances are 2.729(2) and 2.825(2) A for 1, 2.762(1) and 2.832(1) A for 2 and 2.732(1) and 2.827(1) A for 3. In complexes 4 and 5, the pmf(-) ligands are coordinated to the copper atoms in tetradentate fashion with each nitrogen atom coordinating to one Cu atom. The Cu...Cu distances are 2.580(1) and 2.549(1) A for 4 and 2.582(1) and 2.561(1) A for 5. Antiferromagnetic interactions between the copper ions are observed with calculated g and J values of 2.03(1) and -188(2) cm(-1) for 1, 2.09(1) and -268(3) cm(-1) for 2, and 2.09(1) and -486(2) cm(-1) for 5. By comparing the magnetic data it can be shown that the bonding mode of the pmf(-) ligand is one of the important factors in determining the strengths of the Cu...Cu interactions in linear trinuclear and tetranuclear copper complexes.

Linear Metal−Metal-Bonded Tetranuclear M−Mo−Mo−M Complexes (M = Ir and Rh): Oxidative Metal−Metal Bond Formation in a Tetrametallic System and 1,4-Addition Reaction of Alkyl Halides

Reaction of Mo2(pyphos)4 (1) with [MCl(CO)2]2 (M = Ir and Rh) afforded linear tetranuclear complexes of a formula Mo2M2(CO)2(Cl)2(pyphos)4 (2, M = Ir; 3, M = Rh). X-ray diffraction studies confirmed that two "MCl(CO)" fragments are introduced into both axial sites of the Mo2 core in 1 and coordinated by two PPh2 groups in a trans fashion, thereby forming a square-planar geometry around each M(I) metal. Treatment of 2 and 3 with an excess amount of tBuNC and XylNC induced dissociation of the carbonyl and chloride ligands to yield the corresponding dicationic complexes [Mo2M2(pyphos)4(tBuNC)4](Cl)2 (5a, M = Ir; 6a, M = Rh) and [Mo2M2(pyphos)4(XylNC)4](Cl)2 (7, M = Ir; 8, M = Rh). Their molecular structures were characterized by spectroscopic data as well as X-ray diffraction studies of BPh4 derivatives [Mo2M2(pyphos)4(tBuNC)4](BPh4)2 (5b, M = Ir; 6c, M = Rh), which confirmed that there is no direct sigma-bonding interaction between the M(I) atom and the Mo2 core. The M(I) atom in 5 and 6 can be oxidized by either 2 equiv of [Cp2Fe][PF6] or an equimolar amount of I2 to afford Mo(II)2M(II)2 complexes, [Mo2M2(X)2(tBuNC)4(pyphos)4]2+ in which two Mo-M(II) single bonds are formed and the bond order of the Mo-Mo moiety has been decreased to three. The Ir(I) complex 5a reacted not only with methyl iodide but also with dichloromethane to afford the 1,4-oxidative addition products [Mo2Ir2(CH3)(I)(tBuNC)4(pyphos)4](Cl)2 (13) and [Mo2Ir2(CH2Cl)(Cl)(tBuNC)4(pyphos)4](Cl)2 (15), respectively, although the corresponding reactions using the Rh(I) analogue 6 did not proceed. Kinetic analysis of the reaction with CH3I suggested that the 1,4-oxidative addition to the Ir(I) complex occurs in an SN2 reaction mechanism.

Linear and cyclic tetranuclear copper(i) complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine

The reaction of Kpmf (pmf = anion of N,N[prime or minute]-bis(pyrimidyl-2-yl)formamidine, Hpmf) with CuSCN afforded the complexes K[Cu4(pmF)3(SCN)2], 1, and Cu(4)(pmf)4, 2. Reaction of 1 with [(n-Bu)4N]PF6 in THF gave the complex [(n-Bu)4N][Cu4(pmf)3(SCN)2], 3. Their structures were characterized by X-ray crystallography. Complexes 1 and 3 are the first linear tetranuclear complexes containing only Cu(I) atoms, while complex 2 is cyclic. The four Cu(I) atoms of complexes 1 and 3 are helically bridged by three tetradentate pmf- ligands. The [Cu4(pmf)3(SCN)2]- anions of 1 show weak interactions with adjacent [K(THF)5]+ cations through the sulfur atoms, forming infinite chains which are subjected to a series of intermolecular pi-pi interactions. In complex 2, the pmf- ligands are coordinated to the copper atoms in bidentate fashion through the two central amine nitrogen atoms, leaving the pyrimidine nitrogen atoms uncoordinated. Unexpected fluxional behaviors were observed for complexes 1 and 3 in solution. By the DNMR analysis, the free energy of activation (DeltaGc(not equal)) for the exchange is 12.8 kcal mol(-1) at 278 K (T(c)), and the rate constant of exchange (K(c)) is 470 s(-1) for 1. The DeltaGc(not equal) and Kc are 12.6 kcal mol(-1) at 273 K and 433 s(-1), respectively, for 3.

Synthesis, Structure and Characterizations in Solid State and Solution of Dinuclear Pentacoordinated FeII and MnII Complexes and of a Linear Tetranuclear FeIII Complex Obtained with the Ligand N,N,N′,N′‐Tetrakis[(6‐methyl‐2‐pyridyl)methyl]propane‐1,3‐diamine

AbstractTwo neutral complexes [(L634M)Fe2Cl4]·2H2O·2CHCl3 (1) and [(L634M)Mn2Cl4]·CH3CN (2) have been synthesized {L634M = N,N,N′,N′‐tetrakis[(6‐methyl‐2‐pyridyl)methyl]propane‐1,3‐diamine} and their molecular structures established by X‐ray crystallography. Both structures are similar, with each metal center in a trigonal‐bipyramidal environment. No magnetic coupling is observed between the metal centers. UV/Vis spectra and cyclic voltammograms were recorded in CH2Cl2 and CH3CN solutions. Both complexes are stable in CH2Cl2, whereas only 2 is stable in CH3CN. On the contrary, 1 is in equilibrium with another FeII species in CH3CN. When this last solution is aerated, monocrystals of the neutral linear tetranuclear complex [(L634M)Fe4(μ‐O)3Cl6]·2CH3CN (3) can be isolated. Its structure is unusual with two FeIII ions pentacoordinate and the two others tetracoordinate with only chloro ligands and oxo bridges. The magnetic properties reveal that two consecutive metal centers are strongly antiferromagnetically coupled. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Reductive Formation of Straight Linear Metal−Metal Bonded Tetranuclear Complexes X−M−Mo−Mo−M−X from X2M···Mo−Mo···MX2Supported by Four Tridentate 6-Diphenylphosphino-2-pyridonate Ligands (M = Pd, Pt; X = Cl, Br, I)

Straight linear tetranuclear complexes have been prepared by using pyphos ligand (pyphos = 6-diphenylphosphino-2-pyridonate), which has unique coordinating sites comprised of three kinds of elements, i.e., phosphine, nitrogen, and oxygen atoms, in almost linear fashion. The starting complex is the quadruply bonded dinuclear molybdenum(II) complex, Mo2(pyphos)4 (1), which was prepared by the reaction of Mo2(OAc)4 with sodium salt of pyphos. Single crystal X-ray analysis revealed that 1 consists of quadruply-bonded Mo2 and trans-arranged diphosphine at both axial position of Mo2 core. Thus, transition metal can be expected to be placed at both axial positions of Mo2 core. Thus, treatment of 1 with Pd(II) and Pt(II) complexes gave rise to tetranuclear complexes of the general formula, Mo2Pd2X4(pyphos)4 (2) and Mo2Pt2X4(pyphos)4 (4) (a: X = Cl; b: X = Br; c: X = I). Single crystal X-ray analysis of 2a, 2b, and 4a revealed the structure of complexes 2 and 4 that consist of M(II)···MoMo···M(II) skeleton supported by four pyphos ligands. They have quadruply-bonded Mo2 core and no bonding between a M(II) atom and a Mo atom. Treatment of 2 and 4 with reducing reagents, photoirradiation, or thermal reduction resulted in the formation of metal−metal bonded tetranuclear complexes Mo2Pd2X2(pyphos)4 (6) and Mo2Pt2X2(pyphos)4 (7) (a: X = Cl; b: X = Br; c: X = I), respectively. All of them were characterized by single crystal X-ray analysis, which revealed that they consist of M(I)-MoMo-M(I) skeleton supported by pyphos ligands. The bond lengths between M(I) and Mo are short enough to be formally regarded as a single M(I)-Mo bond, while the longer Mo−Mo distance compared to that of 1, 2, and 4 indicated that the Mo−Mo bond of 6 and 7 are formally triple (π2δ component). The electrochemical study indicates that all the atoms in the M−Mo−Mo−M system are electronically strongly coupled to allow an effective 2-electron redox process, and thus the chemical reduction of 2 and 4 readily gives 6 and 7, respectively.

Reactions of monoazadienes with metal carbonyl complexes. XII. Reactions of the linear tetranuclear ruthenium complex Ru4(CO)10(CH3C:C(H)C(H):N-iso-Pr)2 with oxidizing reagents. Syntheses of halide-bridged [Ru(CO)2X(CH3C:C(H)C(H):N-iso-Pr)]2 and fac-Ru(CO)3X(CH3C:C(H)C(H):N-iso-Pr)

The linear tetranuclear complex Ru 4 (CO) 10 (CH 3 C=C(H)C(H)=N-i-Pr) 2 (1), containing two η 5 -azaruthenacyclopentadienyl systems, reacts with oxidizing reagents (I 2 , Br 2 , NBS, CCl 4 ) at elevated temperatures (40-90°C) in heptane or benzene to give the new dimeric halide-bridged organoruthenium (II) complexes

ChemInform Abstract: Platinum in the Unusual Oxidation State +2.75: A Linear Tetranuclear Complex with the Model Nucleobase 1‐Methylthymine.

AbstractThe oxidation of the diplatinum(II) complex (I) with Ce(IV) leads via different, spectroscopically identified oxidation steps to the diplatinum(III) end product.

Platinum in the Unusual Oxidation State + 2.75: A Linear Tetranuclear Complex with the Model Nucleobase 1‐Methylthymine

Platinum in the Unusual Oxidation State + 2.75: A Linear Tetranuclear Complex with the Model Nucleobase 1‐Methylthymine