Dimetallic complexes of acyclic pyridine-armed ligands derived from 3,6-diformylpyridazine

New ternary ligands consisting of an N4 bridging ligand and two terpyridines, and their Co(II) and Ni(II) dinuclear complexes. Structure, redox properties, and reaction with acid

Two ternary ligands consisting of two 2,2′:6′,2′′-terpyridines and one N4-quadridentate μ2,η(2)-bridging ligand were synthesized. The N4 bridge is 1,4-bis(2-pyridyl)phthalazine in ligand 1, and 3,6-bis(2-pyridyl)pyridazine in ligand 2. Two Co(II) dinuclear complexes [(1)Co2(μ-OH)]3+ and [(2)Co2(μ-OH)]3+, and one Ni(II) dinuclear complex [(1)Ni2(μ-Cl)]3+ were obtained. In the crystal structures of [(1)Co2(μ-OH)]3+ and [(1)Ni2(μ-Cl)]3+, two pyridine rings are twisted around the pyridine-phthalazine bonds to avoid steric repulsion between the hydrogen atoms. The pyridine rings also showed a significant tilt from the octahedral coordination plane, which causes the large positive shift of the first reduction potentials. Upon the addition of a proton, the cobalt dinuclear complexes can release one cobalt ion selectively, and the dinuclear complexes can be easily restored by the addition of a tertiary amine.

[(Z)-1-({3-[(3-Aminopropyl)(2-nitrobenzyl)amino]propyl}iminomethyl)naphthalen-2-olato]copper(II) perchlorate

In the title compound, [Cu(C₂₄H₂₇N₄O₃)]ClO₄, the Cu^II atom has a distorted square-planar coordination geometry and is surrounded by an N₃O donor set composed of a secondary amine N, a primary amine H, an imino N and a naphthalen-2-olate O atom. An intra­molecular N—H⋯O hydrogen bond occurs. In the crystal, mol­ecules are held together by inter­molecular N—H⋯O hydrogen bonds, leading to the formation of a three-dimensional network.

(2-Formyl-6-methoxy-phenolato-κO,O)(perchlorato-κO)(1,10-phenanthroline-κN,N')copper(II)

In the title mol­ecule, [Cu(C₈H₇O₃)(ClO₄)(C₁₂H₈N₂)], the Cu^II ion is five-coordinated by two N atoms [Cu—N = 1.995 (3) and 2.022 (3) Å] from a 1,10-phenanthroline ligand, two O atoms [Cu—O = 1.908 (2) and 1.927 (2) Å] from an o-vanillin ligand and one O atom [Cu—O = 2.510 (3) Å] from a perchlorate anion in a distorted square-pyramidal geometry. Three O atoms of the perchlorate anion are rotationally disordered between two orientations, with occupancies of 0.525 (13) and 0.475 (13). In the crystal structure, two mol­ecules related by a centre of symmetry are paired in such a way that the phenolate O atom from one mol­ecule completes the distorted octa­hedral Cu coordination in another mol­ecule [Cu⋯O = 2.704 (2) Å].

Synthesis and Some First-Row Transition-Metal Complexes of the 1,2,4-Triazole-Based Bis(terdentate) Ligands TsPMAT and PMAT

The employment of a strategy based on nucleophilic substitution, rather than Schiff base condensation, for the preparation of 1,2,4-triazole-based ligands has been investigated and has led to the synthesis of two new ligands, 4-amino-3,5-bis{[N-(2-pyridylmethyl)-N-(4-toluenesulfonyl)amino]methyl}-4H-1,2,4-triazole (TsPMAT, 14) and 4-amino-3,5-bis{[(2-pyridylmethyl)amino]methyl}-4H-1,2,4-triazole (PMAT, 15). These are the first examples of bis(terdentate) ligands incorporating the 1,2,4-triazole unit. TsPMAT (14) forms a dinuclear 2:2 complex with Co(BF4)2.6 H2O even when reacted in a metal-to-ligand molar ratio of 2:1. Similarly, the reaction of PMAT (15) with Mn(ClO4)2.6H2O or M(BF4)2.6 H2O (M=Fe, Co, Ni, Zn) in a ligand-to-metal molar ratio of 1:1 has afforded a series of complexes with the general formula [M(II) (2)(PMAT)2]X4. The metal centres in these complexes of TsPMAT (14) and PMAT (15) are encapsulated by two ligand molecules and doubly bridged by the N2 units of the 1,2,4-triazole moieties, which gives rise to N6 coordination spheres that are strongly distorted from octahedral, as evidenced by the X-ray crystal structure analyses of [Co(II) (2)(TsPMAT)(2)](BF(4))(4)6 MeCN (246 MeCN) and [Fe(II) 2(PMAT)2](BF4)4DMF (27DMF). Studies of the magnetic properties of [Co(II) 2(TsPMAT)2](BF4)4.4 H2O (244 H2O), [Mn(II) 2(PMAT)2](ClO4)4 (26), and [Co(II) 2(PMAT)2](BF4)4 (28) have revealed weak antiferromagnetic coupling (J=-3.3, -0.16, and -2.4 cm(-1), respectively) between the two metal centres in these complexes.

Dimetallic complexes of a structurally versatile pyridazine-containing Schiff-base macrocyclic ligand with pendant pyridine arms

The new [2 + 2] Schiff-base macrocyclic ligand L2, containing pyridazine head units and pyridine pendant arms, was synthesised as [Ba(II)2L2(ClO4)4(OH2)] 1 from the barium(II) ion templated condensation reaction of 3,6-diformylpyridazine and N1-(2-aminoethyl)-N1-(methylene-2-pyridyl)-ethane-1,2-diamine. Subsequent transmetallation reactions of 1 with copper(II), iron(II) and manganese(II) perchlorates led to the formation of [Cu(II)2L2](ClO4)4.2MeCN 2, [Fe(II)2L2(MeCN)2](ClO4)4 3 and two manganese complexes, 4 and 5, with the same formula, [Mn(II)2L2(MeCN)(OH2)](ClO4)4, but slightly different crystal structures, respectively. Single-crystal X-ray structural analyses reveal the variety of structures which can be supported by L2 in order to meet the coordination environment preferences of the incorporated metal ions. The barium(II) ions in 1 have an irregular ten-coordinate geometry whereas the copper(II) ions in 2 have a square pyramidal geometry and the iron(II) ions in 3 have an octahedral geometry, while in 4 and 5 every manganese(II) ion is seven-coordinate and the environment can be best described as distorted pentagonal bipyramidal. In 1, 4 and 5 the pyridazine moieties bridge the metal centres [Ba(1)...Ba(2) 4.9557(3)A 1; Mn(1)...Mn(2) 4.520(1)A 4; Mn(1)[dot dot dot]Mn(2) 4.3707(8)A 5] but this is not observed in the copper(II) and iron(II) complexes, 2 and 3, in which the metal ions are well separated [Cu(1)...Cu(2) 5.9378(6)A 2; Fe(1)...Fe(2) 5.7407(12)A 3]. In the cyclic voltammogram of [Cu2(II)L2](ClO4)4.2MeCN 2 in MeCN vs. Ag/AgCl two separate reversible one-electron transfer steps are observed [E(1/2)=0.04 V, DeltaE= 0.12 V and E(1/2)= 0.20 V, DeltaE=0.12 V; K(c)=510; in this system E(1/2)(Fc+/Fc)=0.42 V and DeltaE(Fc+/Fc)=0.08 V]. The other complexes cannot be reversibly reduced/oxidised.

Synthesis and crystal structure of tetra- and hexanuclear uranium(iv) complexes with hexadentate compartmental Schiff-base ligands

Treatment of UCl4 with the hexadentate Schiff bases H2Li in thf gave the expected [ULiCl2(thf)] complexes [H2Li=N,N'-bis(3-methoxysalicylidene)-R and R = 2,2-dimethyl-1,3-propanediamine (i= 1), R = 1,3-propanediamine (i= 2), R = 2-amino-benzylamine (i= 3), R = 2-methyl-1,2-propanediamine (i= 4), R = 1,2-phenylenediamine (i= 5)]. The crystal structure of [UL4Cl2(thf)] (4) shows the metal in a quite perfect pentagonal bipyramidal configuration, with the two Cl atoms in apical positions. Reaction of UCl4 with H4Li in pyridine did not afford the mononuclear products [U(H2Li)Cl2(py)x] but gave instead polynuclear complexes [H4Li=N,N'-bis(3-hydroxysalicylidene)-R and R = 1,3-propanediamine (i= 6), R = 2-amino-benzylamine (i= 7) or R = 2-methyl-1,2-propanediamine (i= 8)]. In the presence of H4L6 and H4L7 in pyridine, UCl4 was transformed in a serendipitous and reproducible manner into the tetranuclear U(iv) complexes [Hpy]2[U4(L6)2(H2L6)2Cl6] (6a) and [Hpy]2[U4(L7)2(H2L7)2Cl6][U4(L7)2(H2L7)2Cl4(py)2] (7), respectively. Treatment of UCl4 with [Zn(H2L6)] led to the formation of the neutral compound [U4(L6)2(H2L6)2Cl4(py)2] (6b). The hexanuclear complex [Hpy]2[U6(L8)4Cl10(py)4] (8) was obtained by reaction of UCl4 and H4L8. The centrosymmetric crystal structures of 6a.2HpyCl.2py, 6b.6py, 7.16py and 8.6py illustrate the potential of Schiff bases as associating ligands for the design of polynuclear assemblies.