Monomer−Trimer Isomerism in 3-Substituted Pentane-2,4-dione Derivatives of Nickel(II)

Heterometallic molecular precursors for a lithium-iron oxide material: synthesis, solid state structure, solution and gas-phase behaviour, and thermal decomposition

Three heterometallic single-source precursors with a Li : Fe = 1 : 1 ratio for a LiFeO₂ oxide material are reported. Heterometallic compounds LiFeL₃ (L = tbaoac (1), ptac (2), and acac(3)) have been obtained on a large scale, in nearly quantitative yields by one-step reactions that employ readily available reagents. The heterometallic precursor LiFe(acac)₃ (3) with small, symmetric substituents on the ligand (acac = pentane-2,4-dionate), maintains a 1D polymeric structure in the solid state that limits its volatility and prevents solubility in non-coordinating solvents. The application of the unsymmetrical ligands, tbaoac (tert-butyl acetoacetate) and ptac (1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedionate), that exhibit different bridging properties at the two ends of the ligand, allowed us to change the connectivity pattern within the heterometallic assembly. The latter was demonstrated by structural characterization of heterometallic complexes LiFe(tbaoac)₃ (1) and LiFe(ptac)₃ (2) that consist of discrete heterocyclic tetranuclear molecules Li₂Fe₂L₆. The compounds are highly volatile and exhibit a congruent sublimation character. DART mass spectrometric investigation revealed the presence of heterometallic molecules in the gas phase. The positive mode spectra are dominated by the presence of [M - L]⁺ peaks (M = Li₂Fe₂L₆). In accord with their discrete molecular structure, complexes 1 and 2 are highly soluble in nearly all common solvents. In order to test the retention of the heterometallic structure in solution, the diamagnetic analog of 1, LiMg(tbaoac)₃ (4), has been isolated. Its tetranuclear molecular structure was found to be isomorphous to that of the iron counterpart. ¹H and ⁷Li NMR spectroscopy unambiguously confirmed the presence of heterometallic molecules in solutions of non-coordinating solvents. The heterometallic precursor 1 was shown to exhibit clean thermal decomposition in air that results in phase-pure α-modification of layered oxide LiFeO₂, the prospective cathode material for lithium ion batteries.

Bis(acetylacetonato)bis(pyrazolato)ruthenate(iii) as a redox-active scorpionate ligand

The potential of a new anionic octahedral metal complex [Ru(III)(acac)2(pz)2](-) ((-)) (pzH = pyrazole) as a ligand with a scorpionate coordination behaviour like tris(pyrazolyl)borate (tp) and reversible redox activity is presented. Trinuclear metal complexes, [Ru(III)2Zn(II)(acac)4(pz)4] () and [Ru(II)Ru(III)2(acac)4(pz)4] (), were each synthesized by the reaction of ZnCl2 or Ru3(CO)12 with [Ru(III)(acac)2(pz)(pzH)] (H) that is in situ deprotonated and acts as a precursor of (-). Single-crystal X-ray diffraction studies clarified that (-) acts as a scorpionate ligand; two (-) units in and one unit in function as bidentate ligands with two pyrazolates as pincers, while another (-) unit in functions as a tridentate ligand with one oxygen atom as a tail in addition to the two pyrazolate pincers. Moreover, and showed reversible multi-stage redox behaviours based on the Ru(II)/Ru(III) and Ru(III)/Ru(IV) couples of the (-) units in the cyclic voltammetry (CV) measurements. Based on the X-ray, IR, and CV measurements and the comparison with other Ru(ii) complexes with tp derivatives, the (-) unit was found to act as a redox-active scorpionate with electron withdrawing properties compared to the tp.

Crystal structure of hexa-kis-(μ2-4-tert-but-oxy-4-oxobut-2-en-2-olato)trizinc

The structure of a centrosymmetric trinuclear zinc(II) complex with the formula [Zn{ZnL₃}₂], where L is 4-tert-but­oxy-4-oxobut-2-en-2-olate, is presented.

The title complex, systematic name hexa­kis­(μ₂-4-tert-but­oxy-4-oxobut-2-en-2-olato)-1:2κ⁹O²,O⁴:O²;2:3κ⁹O²,O⁴:O²-trizinc, [Zn₃(C₈H₁₃O₃)₆], syn­the­sized from tert-butyl aceto­acetate and di­ethyl­zinc, consists of trinuclear centrosymmetric mol­ecules of an approximate C_3i symmetry. The three metal cations are arranged in a linear fashion, with the central Zn^II atom located on a centre of symmetry. All three metal cations exhibit a distorted octa­hedral coordination geometry. The terminal Zn^II cations are chelated by three tert-butyl aceto­acetate ligands and these units are connected to the central Zn^II atom by the bridging enolate O atoms.

Monomeric square-planar cobalt(II) acetylacetonate: mystery or mistake?

No evidence was found for the existence of a previously reported mononuclear square-planar form of unsolvated cobalt(II) acetylacetonate, Co(acac)(2), in all samples that have been obtained by using a variety of preparative techniques and crystallization conditions. It was confirmed that the structure of tetramer Co(4)(acac)(8), reported back in 1964 by Cotton and Elder, is correct, the synthesis is reproducible, and the bulk material corresponds to single-crystal data. Additionally, the title compound can be isolated in tetranuclear form by reducing cobalt(III) acetylacetonate with cobalt metal in solvent-free conditions or by crystallization from a hexanes solution. At the same time, from noncoordinating halogenated solvents, Co(acac)(2) crystallizes as a trinuclear core molecule, in which all Co atoms also exhibit octahedral coordination. From coordinating solvents such as ethanol, cobalt(II) acetylacetonate was found to appear in the form of its bis-adduct Co(acac)(2)(EtOH)(2). On the basis of observations made in this work and the details presented in the original paper, we suggest that the reported mononuclear structure of square-planar acetylacetonate should likely contain copper instead of cobalt.

Hydrogen-bonding in ethanol adducts to bis(3-R-penta-2,4-dionato)nickel(II) species

Ethanol adducts of bis(3-R-penta-2,4-dionato) nickel(II) have been prepared by recrystallization of the corresponding nickel bisacetylacetonate species from ethanol, and their crystal structures have been determined by X-ray diffraction: R = methyl, C16H30NiO6, a = 5.177(1), b = 9.326(1), c = 9.649(1), a = 95.39(1), beta = 100.04(1), gamma = 97.16(1), space group Ponebar, Z = 1; R = hex-5-enyl, C26H46NiO6, a = 5.176(1), b = 9.677(1), c = 14.458(1), a = 92.333(3), beta = 93.945(4), gamma = 96.011(6), space group Ponebar, Z = 1; R = phenyl, C26H34NiO6, a = 27.399(1), b = 5.349(1), c = 19.827(2), beta = 117.410(7), space group C2/c, Z = 4. The compounds show remarkable differences in their ability to form hydrogen bonds in the solid phase and in solution, depending upon the nature of the substituent in the 3-position of the acetylacetone fragment. Analysis of the strength of hydrogen bonds within the limits of supermolecular approximation based on the results of calculations by DFT method has been carried out and were found to correlate with experimental observations.

Nickel(II) and zinc(II) dibenzoylmethanates: molecular and crystal structure, polymorphism, and guest- or temperature-induced oligomerization

Four forms of nickel(II) and two of zinc(II) dibenzoylmethanates have been isolated and characterized with powder and single-crystal X-ray diffraction analyses, differential scanning calorimetry, magnetic susceptibility measurements, and solid-state 13C cross-polarization/magic angle spinning NMR. Nickel dibenzoylmethanate, Ni(DBM)2 (DBM = PhCOCHCOPh-), forms three polymorphic forms (light-green, brown, and green) and a fourth clathrate form with guest benzene included. The light-green polymorph is metastable. Substituted benzenes induce recrystallization of the polymorph into a stable brown form (C30H22NiO4; a = 26.502(3) A, b = 5.774(1) A, c = 16.456(2) A, beta = 116.03(1) degrees; monoclinic, C2/c; Z = 4). Unlike the other forms, the brown form is diamagnetic and is comprised of monomers of the low-spin [Ni(DBM)2] complex. The Ni(II) is chelated by two DBM ligands in a square planar environment by four donor oxygen atoms. When heated, the brown form transforms to a green form which is stable above 202 degrees C (C90H66Ni3O12; a = 13.819(2) A, b = 16.252(2) A, c = 17.358(2) A, beta = 108.28(1) degrees; monoclinic, P2(1)/n; Z = 2). This polymorph is formed by van der Waals packing of trimers [Ni3(DBM)6] containing linear Ni3 clusters with an Ni-Ni distance of 2.81 A. The cluster is surrounded by six DBM ligands, providing a distorted octahedral environment about each Ni by six oxygen atoms. Benzene stabilizes the trimeric structure at room temperature, forming a [Ni3(DBM)6].2(benzene) inclusion compound (Ni-Ni distance of 2.83 A) with guest benzene molecules located in channels (C90H66Ni3O12 + 2(C6H6); a = 17.670(2) A, b = 20.945(3) A, c=11.209(2) A, beta = 102.57(1) degrees; monoclinic, P2(1)/c; Z = 2). Zinc dibenzoylmethanate has been prepared in two polymorphic forms. The monomeric form contains [Zn(DBM)2] molecules with the zinc center in a distorted tetrahedral environment of four oxygens from the two chelated DBMs (C30H22O4Zn; a = 10.288(2) A, b = 10.716(2) A, c = 12.243(2) A, alpha = 89.19(1) degrees, beta = 75.39(1) degrees, gamma = 64.18(1) degrees; triclinic, P1; Z = 2). Another, dimeric form contains [Zn2(DBM)4] species, with two zinc atoms separated by a distance of 3.14 A and each zinc coordinated by five oxygen atoms (C60H44O8Zn2; a = 25.792(3) A, b = 7.274(1) A, c = 24.307(2) A, beta = 90.58(1) degrees; monoclinic, C2/c; Z = 4). The polymorphic variety of the title complexes and the peculiarities of the Ni(II) and Zn(II) coordination environments are discussed in the context of using the complexes as precursors for new metal complex hosts.