Croconato-bridged copper(ii) complexes: synthesis, structure and magnetic characterization

Three croconato-bridged Cu(ii) complexes were synthesized and structurally and magnetically characterized.

Coordination behaviour of new dipyridylpyrazole ligands towards ZnCl2and PdCl2fragments. Crystalline structural characterization and multinuclear NMR studies as evidence of linkage and conformational isomers

Novel metal complexes containing dipyridylpyrazole ligands as efficient examples of isomerism are investigated.

Dichlorido{2-[(3,5-diphenyl-1H-pyrazol-1-yl-κN2)methyl]pyridine-κN}palladium(II)

The title compound, [PdCl(2)(C(21)H(17)N(3))], is a member of a sequence of Pd, Pt and Co dichloride complexes bearing polysubstituted (pyrazol-1-ylmethyl)pyridine ligands. It is shown that there is a correlation between the steric bulkiness of the bidentate (pyrazol-1-ylmethyl)pyridine ligands and the Pd-N(pyrazole) distances, i.e. the larger the ligand, the longer the bond. In contrast, no trend is observed between the steric properties of the ligand and the Pd-N(pyridine) bond lengths.

Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal

A detailed description of the procedures utilized in the non-routine X-ray single-crystal structural determination and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallography how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and atomic positional disorder.

Ethyl 3-ferrocenyl-1-(pyridin-2-ylmeth-yl)-1H-pyrazole-5-carboxyl-ate

The title compound, [Fe(C(5)H(5))(C(17)H(16)N(3)O(2))], crystallizes with an essentially eclipsed conformation of the cyclo-penta-dienyl (Cp) rings. The unsubstituted ring is disordered over two positions with the major component being present 90 (1)% of the time. The substituted Cp ring, the pyrazole ring and three atoms of the eth-oxy-carbonyl group form a conjugated π-system. These 13 atoms are coplanar within 0.09 Å.

A New Chiral N,N‘,O-Donor Heteroscorpionate Ligand. Structures of Ni2+, Cu2+, Zn2+ Complexes and Study of Solution Equilibria by Means of 1H NMR/UV−Vis Titrations and EXSY NMR Spectroscopy

The N,N',O-heteroscorpionate ligand 1-(4-methoxy-3,5-dimethyl-pyridin-2-yl)-2-methyl-1-pyrazol-1-yl-propan-2-ol (LOH) was prepared in two high-yield steps. Complexes [M(LOH)2][MCl4] (M2+ = Cu2+ and Zn2+) and [M(LOH)2]Cl2 (M2+ = Ni2+ and Cu2+) were prepared and characterized by X-ray crystallography. The speciation in solution (methanol:water 95:5) of the M2+/LOH systems was investigated by means of spectrophotometric (Ni2+ and Cu2+) and 1H NMR (Zn2+) titrations. The beta1 and beta2 global formation constants for the [M(LOH)]2+ and [M(LOH)2]2+ species were obtained and are in agreement with the Irving-Williams series: Ni2+< Cu2+> Zn2+. The Zn2+/LOH system was studied by means of quantitative 1H-1H EXSY spectroscopy (300 K, mixing time = 0.2-0.8 s), which allows the description of the equilibria occurring between five octahedral [Zn(LOH)2]2+ structural isomers and tetrahedral [Zn(LOH)Cl]Cl species. Exchange constants kijex and associated rate constants kij suggest that two types of interconversion occur: octahedral-octahedral (faster) and octahedral-tetrahedral (slower). DFT calculations (B3LYP/6-311+G(d)) were employed to evaluate the relative stability of the [Zn(LOH)2]2+ isomers, which are comparable for the five complexes with a maximum energy difference of 6.3 kJ/mol.

Ligand design in multimetallic architectures: six lessons learned

Metallosupramolecular chemistry involves the use of combinations of organic ligands and metals for the construction of both discrete and polymeric aggregates. This Account describes some lessons that we have learned about aspects of ligand design in the course of our work in this area. Specifically, we recommend the incorporation of a diverse range of heterocyclic rings and arene cores within the ligands, as well as attention to symmetry considerations, and offer suggestions for the introduction of chirality and flexibility within the ligands and the exploitation of other weak interactions to assist self-assembly processes.

Nonexponential Relaxation of the Metastable State of the Spin-Crossover System [Fe(L)2](ClO4)2·H2O [L = 2,6-Bis(pyrazol-1-ylmethyl)pyridine]

The relaxation of the metastable state of the spin-crossover compound [Fe(L)(2)](ClO(4))(2).H(2)O, with L = 2,6-bis(pyrazol-1-ylmethyl)pyridine, populated by the LIESST (light induced excited spin state trapping) effect, has been investigated by magnetic measurements. The time dependence of the relaxation curve at several temperatures, starting from different initial states, is in the shape of stretched exponentials, and the thermal variation of the photostationary state under constant photoexcitation is progressive and reversible. These features are satisfactorily modeled by considering noninteracting two-level systems with a distribution of activation energies. A suggested origin for the distribution is the conformational flexibility of the nonplanar heterocyclic ligands. The effect of the intensity distribution during the LIESST process is also accounted for in a simple way.

Chiral Heterocyclic Ligands. X. Synthesis and Metal Complexes of Hindered and Chiral 2,2′-Bipyrimidines

The first examples of 2,2′-bipyrimidine ligands incorporating bulky or chiral substituents have been prepared by nickel(0)-mediated homo-coupling reactions of chloropyrimidines. The 4,4′-di-(tert-butyl) derivative 2 and the chiral derivative 5, with 4,5-fused bornane groups, have been shown to form mononuclear metal complexes in which they coordinate through the less hindered nitrogen donors.

Structural and Magnetic Properties of Three One-Dimensional Azido-Bridged Copper(II) and Manganese(II) Coordination Polymers

Three one-dimensional (1D) azido-bridged coordination polymers of formula [Cu(L)(N3)2]n (1), [Cu2(Me-L)(N3)4]n (2), and [Mn(L)(N3)2]n (3) have been synthesized and structurally characterized, and their magnetic properties studied, where L and Me-L are 2-(pyrazol-1-ylmethyl)pyridine and 2-(3-methylpyrazol-1-ylmethyl)pyridine, respectively. Compound 1 consists of 1D chains in which the Cu(II) ions with a square pyramidal geometry are alternately bridged by an end-to-end (EE) and an end-on (EO) azido ligands, both adopting a basal-apical disposition. Compound 2 exhibits an unprecedented chain topology built via three different kinds of EO azido bridges. Four Cu(II) ions in the square pyramidal environment are alternately bridged by single and double EO bridges to form a tetranuclear cyclic ring, and neighboring rings are interlinked by double EO bridges to generate a "chain of rings". The intraannular double azido ions are disposed between metal ions in a basal-basal fashion, and the other two kinds of azido ions adopt the basal-apical disposition. Compound 3 consists of 1D concave-convex chains in which cis-octahedrally coordinated Mn(II) ions are alternately bridged by double EE and double EO bridges. There exist pi-pi interactions between the ligands bound to the neighboring Mn(II) ions bridged by the EO bridges. Temperature- and field-dependent magnetic analyses reveal alternate ferromagnetic interactions for 1, dominating ferromagnetic interactions for 2, and alternating ferro- and antiferromagnetic interactions through the EO and EE azido bridges for 3, respectively.

Synthesis of Novel Chiral Diazole Derivative Ligands for the Enantioselective Addition of Diethylzinc to Benzaldehyde

The high-pressure-promoted reaction of epoxides with pyrazoles and imidazoles provided access to a variety of chiral diazole derivative ligands such as 11-23. Furthermore, chiral pyrazoles 26 and 27, which have a primary alcohol side chain, were also prepared from (+)-camphopyrazole 4. Each of these chiral diazole ligands was used for the catalytic enantioselective addition of diethylzinc to benzaldehyde. The best results were obtained for 16 and 18: 93% ee was achieved in both cases, and reversed asymmetric induction was observed. A plausible mechanism for this efficient asymmetric induction is offered on the basis of X-ray crystallographic data.