Dodecanuclear 3d/4f-metal clusters with a 'Star of David' topology: Single-molecule magnetism and magnetocaloric properties

A family of interwoven molecular inorganic knots, shaped like the 'Star of David', was prepared by the employment of naphthalene-2,3-diol in 3d/4f-metal cluster chemistry; the isoskeletal dodecanuclear compounds exhibit slow relaxation of the magnetization and magnetocaloric properties, depending on the metal ion.This work was supported by Brock University, NSERC-DG and ERA (to Th.C.S), the Ontario Trillium Foundation (graduate scholarship to D.I.A), the Fundaçao para a Ciencia e a Tecnologia (FCT, Portugal) financial support to REQUIMTE/LAQV (UID/ QUI/50006/2013), the European Synchrotron Radiation Facility (Grenoble, France) (for granting access time to the Swiss Norwegian BM01a beamline under the CH-3613 and CH-3849 research proposals), MINECO (FEDER-MAT2012-38318-C03 to M. E and postdoctoral contract to G. L), and the National Natural Science Foundation of China (grants 21371166, 21331003 and 21221061 to J. T).Peer Reviewe

In Search for Titanocene Complexes with Improved Cytotoxic Activity: Synthesis, X-Ray Structure, and Spectroscopic Study of Bis(η5-cyclopentadienyl)difluorotitanium(IV)

The 1 : 2 reaction of [Ti(η5-C5H5)2Cl2] and AgF in CHCl3/H2O yielded the fluoro analog [Ti(η5-C5H5)2F2] (1) in almost quantitative yield (C5H5 is the cyclopentadienyl group). The coordination about the TiIV atom formed by two fluoro ligands and the centroids of the cyclopentadienyl rings is distorted tetrahedral. The compound crystallizes in the orthorhombic space group C2cm. The lattice constants are a = 5.9055(4), b = 10.3021(5), c = 14.2619(9) Å, and α = β = γ = 90°. The complex has been characterized by elemental analyses and spectroscopic (IR, 1H NMR) data. A structural comparison of the four members of the [Ti(η5-C5H5)2X2] family of complexes (X = F, Cl, Br, I) is attempted

Synthesis, Structural, Magnetic and Computational Studies of a One-Dimensional Ferromagnetic Cu(II) Chain Assembled from a New Schiff Base Ligand

A new asymmetrically substituted ONOO Schiff base ligand N-(2′-hydroxy-1′-naphthylidene)-3-amino-2-naphthoic acid (nancH2) was prepared from the condensation of 2–hydroxy–1–naphthaldehyde and 3–amino–2–naphthoic acid. nancH2 reacts with Cu2(O2CMe)4·2H2O in the presence of Gd(O2CMe)3·6H2O to afford a uniform one-dimensional homometallic chain, [CuII(nanc)]n (1). The structure of 1 was elucidated via single crystal X-ray diffraction studies, which revealed that the Cu(II) ions adopt distorted square planar geometries and are coordinated in a tridentate manner by an [ONO] donor set from one nanc2− ligand and an O− of a bridging carboxylate group from a second ligand. The bridging carboxylato group of the nanc2− ligand adopts a syn, anti-η1:η1:μ conformation linking neighboring Cu(II) ions, forming a 1D chain. The magnetic susceptibility of 1 follows Curie–Weiss law in the range 45–300 K (C = 0.474(1) emu K mol-1, θ = +7.9(3) K), consistent with ferromagnetic interactions between S = ½ Cu(II) ions with g = 2.248. Subsequently, the data fit well to the 1D quantum Heisenberg ferromagnetic (QHFM) chain model with g = 2.271, and J = +12.3 K. DFT calculations, implementing the broken symmetry approach, were also carried out on a model dimeric unit extracted from the polymeric chain structure. The calculated exchange coupling via the carboxylate bridge (J = +13.8 K) is consistent with the observed ferromagnetic exchange between neighbouring Cu(II) centres. © 2023 by the authors. This article belongs to the Special Issue Coordination Chemistry: Current Developments and Future Perspectives — a Themed Issue in Honor of Professor Spyros P. Perlepes on the Occasion of His 70th Birthday) This article contains supplementary material. It is available for download as a supplementary file

Rare nuclearities in Ni(II) cluster chemistry: an unprecedented {Ni12} nanosized cage from the use of N-naphthalidene-2-amino-5-chlorobenzoic acid.

The self-assembly reaction between NiI2, benzoic acid (PhCO2H) and the Schiff base chelate, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in the presence of the organic base triethylamine (NEt3), has resulted in the isolation and the structural, spectroscopic, and physicochemical characterization of the dodecanuclear [Ni12I2(OH)6(O2CPh)5(nacb)5(H2O)4(MeCN)4]I (1) cluster compound in ~30%yield. Complex 1 has a cage-like conformation, comprising twelvedistorted, octahedral NiII ions that are bridged by five 3-OH, one -OH, an I in 55% occupancy, five PhCO2 groups (under the 1: 1: , 1: 2: 3 and 2: 2: 4 modes), and the naphthoxido and carboxylato O-atoms of five doubly deprotonated nacb2 groups. The overall {Ni12} cluster exhibits a nanosized structure with a diameter of ~2.5 nm and its metallic core can be conveniently described as a series of nine edge- or vertex-sharing {Ni3} triangular subunits. Complex 1 is the highest nuclearity coordination compound bearing the nacbH2 chelate, and a rare example of polynuclear NiII complex containing coordinating I ions. Direct current (DC) magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the NiII ions, while photophysical studies of 1 in the solid-state showed a cyan-to-green centered emission at 520 nm, upon maximum excitation at 380 nm. The reported results demonstrate the rich coordination chemistry of the deprotonated nacb2 chelate in the presence of NiII metal ions, and the ability of this ligand to adopt a variety of di erent bridging modes, thus fostering the formation of high-nuclearity molecules with rare, nanosized dimensions and interesting physical (i.e., magnetic and optical) properties

Use of the 2-Pyridinealdoxime/N,N′-Donor Ligand Combination in Cobalt(III) Chemistry: Synthesis and Characterization of Two Cationic Mononuclear Cobalt(III) Complexes

The use of 2-pyridinealdoxime (paoH)/N,N′-donor ligand (L-L) “blend” in cobalt chemistry has afforded two cationic mononuclear cobalt(III) complexes of the general type [Co(pao)2(L-L)]+, where L-L = 1,10-phenanthroline (phen) and 2,2′-bipyridine (bpy). The CoCl2/paoH/L-L (1 : 2 : 1) reaction system in MeOH gives complexes [CoIII(pao)2(phen)]Cl·2H2O (1·2H2O) and [CoIII(pao)2(bpy)]Cl·1.5MeOH (2·1.5MeOH). The structures of the complexes were determined by single-crystal X-ray crystallography. The CoIII ions are six-coordinate, surrounded by three bidentate chelating ligands, that is, two pao− and one phen or bpy. The deprotonated oxygen atom of the pao− ligand remains uncoordinated and participates in hydrogen bonding with the solvate molecules. IR data of the complexes are discussed in terms of the nature of bonding and the known structures

A general synthetic route for the preparation of high-spin molecules: Replacement of bridging hydroxo ligands in molecular clusters by end-on azido ligands

Abstract A general method of increasing the ground-state total spin value of a polynuclear 3d-metal complex is illustrated through selected examples from cobalt(II) and nickel(II) cluster chemistry that involves the dianion of the gem-diol form of di-2-pyridyl ketone and carboxylate ions as organic ligands. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions, by the end-on azido ligand, which is a ferromagnetic coupler

Molecular nanoscale magnetic refrigerants: A ferrimagnetic {Cu II 15GdIII 7} cagelike cluster from the use of pyridine-2,6-dimethanol

The employment of pyridine-2,6-dimethanol in 3d/4f metal cluster chemistry has resulted in a new {CuII15GdIII7} cagelike molecule with a beautiful structure and an overall ferrimagnetic behavior with an appreciable ground-state spin value. The compound shows a satisfactory magnetocaloric effect with −ΔSmmax = 22.2 J kg−1 K−1.This work was supported by the CICYT (Project CTQ2012-30662) and Excellence in Research ICREA-Academia Award (to A.E.), the MINECO (Grant MAT2012-38318-C03 to M.E. and G.L.), an EU Marie Curie IEF (Grant PIEF-GA-2011-299356 to G.L.), the ARISTEIA Action (Project code 84, acronym MAGCLOPT) of the Operational Programme “Education and Lifelong Learning”, cofunded by ESF and National Resources (to S.P.P.), and the NSERC Discovery Grant (to T.C.S.).Peer Reviewe

A New {Dy₅} Single-Molecule Magnet Bearing the Schiff Base Ligand <i>N</i>-Naphthalidene-2-amino-5-chlorophenol

A new {Dy5} cluster compound has been synthesized and structurally characterized from the initial use of the Schiff base ligand N-naphthalidene-2-amino-5-chlorophenol (nacpH2) in coordination chemistry. The 1:1 reaction between Dy(hpd)3∙2H2O and nacpH2, in a solvent mixture comprising CH2Cl2 and MeOH, afforded orange crystals of [Dy5(OH)2(hpd)3(nacp)5(MeOH)5] (1) in 70% yield, where hpd&#8722; is the anion of 3,5-heptadione. The {Dy5} complex can be described as two vertical {Dy3(&#956;3-OH)}8+ triangles sharing a common vertex; such a metal topology is unprecedented in 4f-metal cluster chemistry. Direct current (dc) magnetic susceptibility studies revealed the presence of some weak ferromagnetic exchange interactions between the five DyIII ions at low temperatures. Alternating current (ac) magnetic susceptibility measurements at zero applied dc field showed that complex 1∙3MeOH∙CH2Cl2 exhibits temperature- and frequency-dependent out-of-phase signals below ~20 K, characteristics of a single-molecule magnet (SMM). The resulting relaxation times were used to construct an Arrhenius-type plot and determine an effective energy barrier, Ueff, of 100 K for the magnetization reversal. The application of a small dc field of 200 Oe resulted in the surpassing of the quantum tunneling process and subsequently the increase of the Ueff to a value of 170 K. The reported results are part of a long-term program aiming at the preparation of structurally and magnetically interesting lanthanide complexes bearing various Schiff base chelating/bridging ligands

New insights in Mn–Ca chemistry from the use of oximate-based ligands: {Mn\u3csup\u3eII/III\u3c/sup\u3e22Ca2} and {Mn\u3csup\u3eIV\u3c/sup\u3e2Ca2} complexes with relevance to both low- and high-valent states of the oxygen-evolving complex

The initial use of quinoline-2-aldoxime (qaoH) and 2,6-diacetylpyridine dioxime (dapdoH2) in heterometallic Mn–Ca chemistry has afforded a mixed-valence {MnII/III22Ca2} cluster containing several {Mn4CaOx} subunits and a ‘butterfly’-like {MnIV2Ca2} complex, respectively. The one-pot reaction of Mn(O2CPh)2·2H2O and Ca(O2CPh)2·H2O with qaoH and NEt3 in a 1:1:1:1 molar ratio in a solvent mixture comprising MeCN/MeOH gave complex [Mn22Ca2O14(OH)4(OMe)6(O2CPh)22(qao)2(MeCN)2(H2O)4](OH)2 (1; 6MnII/16MnIII) in 20% yield. A similar reaction with that of 1, albeit with Mn(O2CPh)2·2H2O and Ca(NO3)2·4H2O in the presence of dapdoH2 and NEt3, in a molar ratio of 1:1:2:2 in MeCN/MeOH, led to the smaller nuclearity complex [Mn2Ca2(OMe)2(NO3)2(dapdo)4] (2; 2MnIV) in 40% yield. The reported compounds demonstrate structural and magnetic relevance to both low- and high-valent states of the OEC