A Systematic Exploration of Nickel(II)/Acetate/Di-2-pyridyl Ketone Chemistry: Neutral and Cationic Tetranuclear Clusters, and a Novel Mononuclear Complex

Reversible PtII-CH3 deuteration without methane loss: metal-ligand cooperation vs. ligand-assisted PtII-protonation

Di(2-pyridyl)ketone dimethylplatinum(ii), (dpk)Pt^II(CH₃)₂, reacts with CD₃OD at 25 °C to undergo complete deuteration of Pt-CH₃ fragments in ∼5 h without loss of methane to form (dpk)Pt^II(CD₃)₂ in virtually quantitative yield. The deuteration can be reversed by dissolution in CH₃OH or CD₃OH. Kinetic analysis and isotope effects, together with support from density functional theory calculations indicate a metal-ligand cooperative mechanism wherein DPK enables Pt-CH₃ deuteration by allowing non-rate-limiting protonation of Pt^II by CD₃OD. In contrast, other model di(2-pyridyl) ligands enable rate-limiting protonation of Pt^II, resulting in non-rate-limiting C-H(D) reductive coupling. Owing to its electron-poor nature, following complete deuteration, DPK can be dissociated from the Pt^II-centre, furnishing [(CD₃)₂Pt^II(μ-SMe₂)]₂ as the perdeutero analogue of [(CH₃)₂Pt^II(μ-SMe₂)]₂, a commonly used Pt^II-precursor.

A tetranuclear nickel cluster isolated in multiple high-valent states

We report a series of high-valent tetranuclear nickel clusters isolated from the chemical oxidation of an all Ni(ii) ([Ni₄]) neutral cluster. Electrochemical analysis of [Ni₄] reveals three reversible sequential oxidations at 0.248 V (1e^-), 0.678 V (1e^-), and 0.991 V (2e^-) vs. Fc/Fc⁺ corresponding to mono-, di-, and tetra-oxidized species, [Ni₄]⁺, [Ni₄]²⁺, [Ni₄]⁴⁺, respectively. Using spectroscopic, crystallographic, magnetometric, and computational techniques, we assign the primary loci of oxidations to the Ni centers in each case, thus resulting in the isolation of the first tetranuclear all-Ni(iii) cluster, [Ni₄]⁴⁺.

Mechanistically Driven Control over Cubane Oxo Cluster Catalysts

Predictive and mechanistically driven access to polynuclear oxo clusters and related materials remains a grand challenge of inorganic chemistry. We here introduce a novel strategy for synthetic control over highly sought-after transition metal {M₄O₄} cubanes. They attract interest as molecular water oxidation catalysts that combine features of both heterogeneous oxide catalysts and nature's cuboidal {CaMn₄O₅} center of photosystem II. For the first time, we demonstrate the outstanding structure-directing effect of straightforward inorganic counteranions in solution on the self-assembly of oxo clusters. We introduce a selective counteranion toolbox for the controlled assembly of di(2-pyridyl) ketone (dpk) with M(OAc)₂ (M = Co, Ni) precursors into different cubane types. Perchlorate anions provide selective access to type 2 cubanes with the characteristic {H₂O-M₂(OR)₂-OH₂} edge-site, such as [Co₄(dpy-C{OH}O)₄(OAc)₂(H₂O)₂](ClO₄)₂. Type 1 cubanes with separated polar faces [Co₄(dpy-C{OH}O)₄(L2)₄] ⁿ⁺ (L2 = OAc, Cl, or OAc and H₂O) can be tuned with a wide range of other counteranions. The combination of these counteranion sets with Ni(OAc)₂ as precursor selectively produces type 2 Co/Ni-mixed or {Ni₄O₄} cubanes. Systematic mechanistic experiments in combination with computational studies provide strong evidence for type 2 cubane formation through reaction of the key dimeric building block [M₂(dpy-C{OH}O)₂(H₂O)₄]²⁺ with monomers, such as [Co(dpy-C{OH}O)(OAc)(H₂O)₃]. Furthermore, both experiments and DFT calculations support an energetically favorable type 1 cubane formation pathway via direct head-to-head combination of two [Co₂(dpy-C{OH}O)₂(OAc)₂(H₂O)₂] dimers. Finally, the visible-light-driven water oxidation activity of type 1 and 2 cubanes with tuned ligand environments was assessed. We pave the way to efficient design concepts in coordination chemistry through ionic control over cluster assembly pathways. Our comprehensive strategy demonstrates how retrosynthetic analyses can be implemented with readily available assembly directing counteranions to provide rapid access to tuned molecular materials.

Probing the electronic structure of a copper(ii) complex by CW- and pulse-EPR spectroscopy

The electronic structure of a mononuclear octahedral copper(ii) complex has been studied using CW EPR spectroscopy and other advanced methods including Davies ENDOR and HYSCORE (¹H and ¹³C) spectroscopy.

Tetranuclear Ni(ii) and Co(ii) Schiff-base complexes with an M4O6 defective dicubane-like core: zero-field SMM behavior in the cobalt analogue

Two tetranuclear Ni₄ and Co₄ complexes were prepared and characterized. Their magnetic properties were thoroughly studied and it was revealed that the Co₄ compound behaves as a zero-field single-molecule magnet.

Solvent-induced structural diversity in tetranuclear Ni(ii) Schiff-base complexes: the first Ni4single-molecule magnet with a defective dicubane-like topology

The tetranuclear Ni^IIcomplexes with the Ni₄O₄cubane-like core (1) and the Ni₄O₆defective dicubane core (2) were studied, and the latter identified as a first single-molecule magnet with such topology.

Structure and magnetic properties of a mixed-ligand copper(II) complex

The hydrothermal synthesis of the novel complex poly[[μ2-N(1),N(4)-bis(pyridin-3-yl)naphthalene-1,4-dicarboxamide-κ(2)N(3):N(3')](μ4-phthalato-κ(4)O(1):O(1):O(1'):O(2'))copper(II)], [Cu(C8H4O4)(C22H16N4O2)]n, is described. With the phthalate ligand connecting neighbouring Cu(II) cations, an infinite one-dimensional chain is formed. Adjacent one-dimensional chains are connected by the dicarboxamide ligand, forming an intriguing two-dimensional framework. The magnetic properties and thermal stability of this complex are also described.

Two CoII Compounds Showing Interesting Magnetic Properties Modulated by Supramolecular Interactions

Two new CoII coordination compounds, namely Co[(cis-trans)-L](nip)·H2O (1) and Co[(cis-cis)-L](Hbtc)·2H2O (2) (L = N1,N4-di(pyridin-3-yl)terephthalamide, H2nip = 5-nitroisophthalic acid, H3btc = benzene-1,3,5-tricarboxylic acid), were synthesised hydrothermally and characterised by single crystal X-ray diffraction and direct current magnetic susceptibility measurement. Interestingly, the results disclose somewhat tuneable magnetic properties for compounds 1 and 2, mainly due to the distinct supramolecular interactions.

Synthesis, structure and magnetic properties of phenylhydroxamate-based coordination clusters

The strategic recombination of preformed coordination clusters in the presence of polymodal bridging ligands has successfully led to the characterisation of five new compounds of structural and magnetic interest. Indeed using the dinuclear complex [M2(H2O)(piv)4(Hpiv)4] (M = Co, Ni; Hpiv = pivalic acid) as starting material and reacting it with phenylhydroxamic acid (H2pha) has yielded the four tetrametallic coordination clusters [Co4(Hpha)2(piv)6(Hpiv)4] (1), [Ni4(Hpha)2(piv)6(Hpiv)2(DMF)2] (2), [Co4(Hpha)2(piv)6(EtOH)2(H2O)2] (3), [Ni4(Hpha)2(piv)6(EtOH)2(H2O)2] (4) and the hexanuclear complex [Co6(Hpha)4(piv)8(EtOH)2]·EtOH (5). All the compounds have been structurally characterised revealing a particular binding mode for the hydroxamate ligand. The study of their magnetic properties has been performed and the modelling of these properties has been done using the appropriate hamiltonians for each compound. The experimental data and their modelling show non-zero spin ground states for compounds 4 and 5.

Tuning the formation of dicarboxylate linker-assisted supramolecular 1D chains and squares of Ni(ii) using coordination and hydrogen bonds

Diverse metal organic coordination networks generated under the same reaction conditions are reported. Further association of these with hydrogen bonding networks of lattice water, coordinated water and uncoordinated oxygen atoms of the carboxylate groups generate supramolecular assemblies of higher dimensions.

In search of 3d/4f-metal single-molecule magnets: Nickel(II)/lanthanide(III) coordination clusters

The importance of 3d/4f-metal cluster chemistry is outlined, and the employment of 2-pyridyl ketone- and 2-pyridyl oxime-based ligands for the preparation of low-nuclearity NiII/LnIII complexes (Ln = lanthanide) is reviewed. The synthetic utility of the “metal complexes as ligands” and “one-pot” approaches is critically discussed. The small nuclearity of the products permits the in-depth analysis of their magnetic properties.

trans-Dichloridobis[(6-nicotinoyl-2-pyridyl-κN6)(3-pyridyl-κN)methanone]copper(II)

In the title complex, [CuCl₂(C₁₇H₁₁N₃O₂)₂], the Cu^II ion is located on an inversion center. It exhibits a distorted octa­hedral coordination geometry defined by two chloride anions at trans sites and four 3-pyridyl N atoms at equatorial sites from two (6-nicotinoyl-2-pyrid­yl)(3-pyrid­yl)methanone ligands. The (6-nicotinoyl-2-pyrid­yl)(3-pyrid­yl)methanone ligand can be viewed as having two pendant 3-pyridyl rings attached to a central pyridyl skeleton via separate carbonyl bridges, acting in a κ²N,N′-chelating mode with its 3-pyridyl N atoms bound to the Cu^II ion. The pendant 3-pyridyl rings make a dihedral angle of 80.76 (5)°. In the crystal, mol­ecules are linked through inter­molecular C—H⋯π and C—H⋯O inter­actions, forming a three-dimentional framework.

Trinuclear first row transition metal complexes of a hexapyridyl, trialkoxy 1,3,5-triarylbenzene ligand

Trinuclear complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) were synthesized using a ligand architecture based upon a 1,3,5-triarylbenzene core decorated with six pyridines and three alkoxide moieties. Characterization via X-ray diffraction, NMR, and magnetism studies is discussed.

Defective dicubane-like tetranuclear nickel(II) cyanate and azide nanoscale magnets

Four tetrameric nickel(II) pseudohalide complexes have been synthesized and structurally, spectroscopically, and magnetically characterized. Compounds 1-3 are isostructural and exhibit the general formula [Ni(2)(dpk·OH)(dpk·CH(3)O)(L)(H(2)O)](2)A(2)·2H(2)O, where dpk = di-2-pyridylketone; L = N(3)(-), and A = ClO(4)(-) for 1, L = NCO(-) and A = ClO(4)(-) for 2, and L = NCO(-) and A = NO(3)(-) for 3. The formula for 4 is [Ni(4)(dpk·OH)(3) (dpk·CH(3)O)(2)(NCO)](BF(4))(2)·3H(2)O. The ligands dpk·OH(-) and dpk·CH(3)O(-) result from solvolysis and ulterior deprotonation of dpk in water and methanol, respectively. The four tetramers exhibit a dicubane-like core with two missing vertexes where the Ni(II) ions are connected through end-on pseudohalide and oxo bridges. Magnetic measurements showed that compounds 1-4 are ferromagnetic. The values of the exchange constants were determined by means of a theoretical model based on three different types of coupling. Thus, the calculated J values (J(1) = J(2), J(3), and D) were 5.6, 11.8, and 5.6 cm(-1) for 1, 5.5, 12.0, and 5.6 cm(-1) for 2, 6.3, 4.9, and 6.2 cm(-1) for 3, and (J(1), J(2), J(3), and D) 6.9, 7.0, 15.2, and 4.8 cm(-1) for 4.

Unusual structural types in nickel cluster chemistry from the use of pyridyl oximes: Ni5, Ni12Na2, and Ni14 clusters

Syntheses, crystal structures, and magnetochemical characterization are reported for the three new nickel(II) clusters [Ni(14)(OH)(4)(N(3))(8)(pao)(14)(paoH)(2)(H(2)O)(2)](ClO(4))(2) (1), [Ni(12)Na(2)(OH)(4)(N(3))(8)(pao)(12)(H(2)O)(10)](OH)(2) (2), and [Ni(5)(ppko)(5)(H(2)O)(7)](NO(3))(5) (3) (paoH = pyridine-2-carbaldehyde oxime, ppkoH = di-2-pyridyl ketone oxime). The reaction of Ni(ClO(4))(2).6H(2)O with paoH and NBu(n)(4)N(3) in H(2)O/MeCN in the presence of NEt(3), gave 1 in 65% yield. Complex 2 was obtained in 60% yield from the reaction of NiCl(2).6H(2)O with paoH and NaN(3) in H(2)O/MeCN in the presence of NaOH. The reaction of Ni(NO(3))(2).6H(2)O with ppkoH in EtOH in the presence of LiOH afforded complex 3 in 75% yield. The complexes all contain novel core topologies. The core of 1 comprises a central Ni(4) rhombus between two Ni(5). Complex 1 is the largest metal/oxime cluster discovered to date, as well as the first Ni(II)(14) coordination complex and the largest Ni(II)/N(3)(-) cluster. Complex 2 has a Ni(12)Na(2) topology that is very similar to that of 1, but with two central Ni(II) atoms of 1 replaced with Na(I) atoms. The core of 3 consists of four Ni(II) atoms forming a highly distorted tetrahedron, with the fifth Ni(II) atom lying almost on one of the edges. Variable-temperature, solid-state dc susceptibility and magnetization studies were carried out on complexes 1-3, and these were complemented with ac susceptibility data for 1 and 2. Fitting of the obtained M/(Nmu(B)) vs H/T data by matrix diagonalization and including axial zero-field splitting (D) gave ground-state spin (S) and D values of S = 6, D = -0.12(3) cm(-1) for 1 and S = 3, D = -0.20(5) cm(-1) for each of the two essentially noninteracting S = 3 Ni(6) subunits of 2. The data for 3 indicate antiferromagnetic exchange interactions and an S = 1 ground state. A simple 2-J model was found to be adequate to describe the variable-temperature dc susceptibility data. The combined work demonstrates the ligating flexibility of pao(-) and ppko(-), and their usefulness in the synthesis of polynuclear Ni(x) clusters with or without the presence of ancillary ligands.

Bis(di-2-pyridylmethane-diol-κN,O,N')nickel(II) dinitrate

The title compound, [Ni(C₁₁H₁₀N₂O₂)₂](NO₃)₂, consists of an Ni^II atom coordinated by two tridentate chelating di-2-pyridylmethane­diol [(2-py)₂C(OH)₂] ligands. The Ni^II atom is located on an inversion center. The geometry around the Ni^II atom is distorted octa­hedral. The gem-diol (2-py)₂C(OH)₂ ligand adopts the coordination mode η¹:η¹:η¹. The Ni—N and Ni—O bond lengths are typical for high-spin Ni^II in an octa­hedral environment [Ni—N = 2.094 (2) and 2.124 (3) Å, and Ni—O = 2.108 (3) Å]. One of the hydr­oxy H atoms is split over two positions which both inter­act with the nitrate anion. The occurence of different O—H⋯O hydrogen bonds leads to the formation of a layer parallel to the (101) plane.