Copper(II) complexes with neutral bis(pyrazolyl)methane ligands: The influence of steric hindrance on their structures and properties

Binding Interactions in Copper, Silver and Gold π-Complexes

The copper(I), silver(I), and gold(I) metals bind π‐ligands by σ‐bonding and π‐back bonding interactions. These interactions were investigated using bidentate ancillary ligands with electron donating and withdrawing substituents. The π‐ligands span from ethylene to larger terminal and internal alkenes and alkynes. Results of X‐ray crystallography, NMR, and IR spectroscopy and gas phase experiments show that the binding energies increase in the order Ag<Cu<Au and the binding energies are slightly higher for alkynes than for alkenes. Modulation of the electron density at the metal using substituents on the ancillary ligands shows that the π‐back bonding interaction plays a dominant role for the binding in the copper and gold complexes.

Crystal structure of chlorido-(η 5-pentamethylcyclopentadienyl)-((bis-pyrazol-1-yl)methane-κ2 N,N′) rhodium(III) hexafluorophosphate. (C17H23ClN4RhF6P)

C17H23ClN4RhF6P, monoclinic, P21/c (no. 14), a = 10.6954(2) Å, b = 15.3868(3) Å, c = 12.6130(2) Å, β = 90.5590(10)°, V = 2075.60(7) Å3, Z = 4, R gt(F) = 0.0296, wR ref(F 2) = 0.0727, T = 100(2) K.

Structures and Properties of Dinitrosyl Iron and Cobalt Complexes Ligated by Bis(3,5-diisopropyl-1-pyrazolyl)methane

Two dinitrosyl iron and cobalt complexes [Fe(NO)2(L1”)](BF4) and [Co(NO)2(L1”)](BF4) are synthesized and characterized, supported by a less hindered bidentate nitrogen ligand bis(3,5-diisopropyl-1-pyrazolyl)methane (denoted as L1”), are surprisingly stable under argon atmosphere. X-ray structural analysis shows a distorted tetrahedral geometry. Spectroscopic and structural parameters of the dinitrosyl iron and cobalt complexes are consistent with the previous reported {Fe(NO)2}9 and {Co(NO)2}10. Two N–O and M–N(O) stretching frequencies and their magnetic properties are also consistent with the above electronic structural assignments. We explored the dioxygen reactivities of the obtained dinitrosyl complexes. Moreover, the related [FeCl2(L1”)], [Co(NO3)2(L1”)], and [Co(NO2)2(L1”)] complexes are also characterized in detail.

X-ray crystallographic insights into post-synthetic metalation products in a metal-organic framework

Post-synthetic modification of metal-organic frameworks (MOFs) facilitates a strategic transformation of potentially inert frameworks into functionalized materials, tailoring them for specific applications. In particular, the post-synthetic incorporation of transition-metal complexes within MOFs, a process known as 'metalation', is a particularly promising avenue towards functionalizing MOFs. Herein, we describe the post-synthetic metalation of a microporous MOF with various transition-metal nitrates. The parent framework, 1: , contains free-nitrogen donor chelation sites, which readily coordinate metal complexes in a single-crystal to single-crystal transformation which, remarkably, can be readily monitored by X-ray crystallography. The presence of an open void surrounding the chelation site in 1: prompted us to investigate the effect of the MOF pore environment on included metal complexes, particularly examining whether void space would induce changes in the coordination sphere of chelated complexes reminiscent of those found in the solution state. To test this hypothesis, we systematically metalated 1: with first-row transition-metal nitrates and elucidated the coordination environment of the respective transition-metal complexes using X-ray crystallography. Comparison of the coordination sphere parameters of coordinated transition-metal complexes in 1: against equivalent solid- and solution-state species suggests that the void space in 1: does not markedly influence the coordination sphere of chelated species but we show notably different post-synthetic metalation outcomes when different solvents are used.This article is part of the themed issue 'Coordination polymers and metal-organic frameworks: materials by design'.

Synthesis and structural diversity of d10 metal coordination polymers constructed from new semi-rigid bis(3-methyl-1H-pyrazole-4-carboxylic acid)alkane ligands

Three isomeric ligands, and four d¹⁰ metal CPs were synthesized, varying from 1D to 2D, together with achirality to chirality variation.

Hydrotris(triazolyl)borate complexes as functional models for Cu nitrite reductase: the electronic influence of distal nitrogens

Hydrotris(triazolyl)borate (Ttz) ligands form CuNO(x) (x = 2, 3) complexes for structural and functional models of copper nitrite reductase. These complexes have distinct properties relative to complexes of hydrotris(pyrazolyl)borate (Tp) and neutral tridentate N-donor ligands. The electron paramagnetic resonance spectra of five-coordinate copper complexes show rare nitrogen superhyperfine couplings with the Ttz ligand, indicating strong σ donation. The copper(I) nitrite complex [PPN](+)[(Ttz(tBu,Me))Cu(I)NO(2)](-) has been synthesized and characterized and allows for the stoichiometric reduction of NO(2)(-) to NO with H(+) addition. Anionic Cu(I) nitrite complexes are unusual and are stabilized here for the first time because Ttz is a good π acceptor.

Heteroscorpionate-based Co2+, Zn2+, and Cu2+ complexes: coordination behavior, aerobic oxidation, and hydrogen sulfide detection

The coordination behavior and reactivity of the phenol-substituted bis(pyrazolyl)methane ligands, (3,5-(t)Bu(2)-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L1-H) and 2-phenol-bis(3,5-Me(2)-pyrazol-1-yl)methane (L2-H) have been investigated in the metal complexes (L1-H)CoCl(2) (1), (L1-H)ZnCl(2) (2), (L3)CuCl(2) (3), (L2)(2)Co(2)Cl(2) (4) (L2-H)ZnCl(2) (5), and (L2-H)CuCl(2)·H(2)O (6). The mononuclear tetrahedral cobalt complex 1 was isolated and fully characterized by X-ray single crystal diffraction and (1)H NMR spectroscopy and relaxometry. The neutral L1-H is κ(2)-coordinated to the metal center whereas the not coordinated hydroxy-phenyl group is involved in extended intermolecular hydrogen bonds. Aerobic oxidation of L1-H was observed in the reaction of this ligand with CuCl(2) to yield the para-quinone derivative L3 (L3 = 2-(t)Bu-6-(bis(3,5-Me(2)-pyrazol-1-yl)methyl)cyclohexa-2,5-diene-1,4-dione). Upon oxidation L3 resulted κ(2)-coordinated to the tetrahedral Cu(II) metal center, affording 3. The reaction of L2-H with CoCl(2)·6H(2)O produced the elimination of 1 equiv of hydrochloric acid and the formation of the binuclear complex 4 in which one cobalt is in an octahedral environment featuring two κ(3)-coordinated deprotonated ligands whereas the second cobalt center is detected in tetrahedral coordination geometry, bound to the octahedral cobalt via two phenoxo bridging moieties. Interestingly L2-H, (3-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L4-H), or (5-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L5-H) were not oxidized in the reaction with CuCl(2). The reaction of the ligand L2-H with ZnCl(2) and CuCl(2)·2H(2)O yielded the κ(2)-coordinated tetrahedral complex 5 and the square planar complex 6, respectively. The application of the cobalt complex 1 as molecular dosimeter for H(2)S was explored and compared to that of the zinc analogue 2. Density functional theory (DFT) calculations and NMR experiments to assess the possible mechanisms of H(2)S detection by both 1 and 2 are also described.