Heterotrimetallic {LnOVPt} complexes with antiferromagnetic Ln-V coupling and magnetic memory.

The new PtVO(SOCR)4 lantern complexes, 1 (R = CH3) and 2 (R = Ph) behave as neutral O-donor ligands to Ln(OR)3 with Ln = Ce, Nd. Four heterotrimetallic complexes with linear {LnOVPt} units were prepared: [Ln(ODtbp)3{PtVO(SOCR)4}] (Ln = Ce, 3Ce (R = CH3), 4Ce (R = Ph); Nd, 3Nd (R = CH3), 4Nd (R = Ph); ODtbp = 2,6-ditertbutylphenolate). Magnetic characterization confirms slow magnetic relaxation behaviour and suggests antiferromagnetic coupling across {Ln-O[double bond, length as m-dash]V} in all four complexes, with variations tunable as a function of Ln and R.

Aqueous Superparamagnetic Magnetite Dispersions with Ultrahigh Initial Magnetic Susceptibilities.

Superparamagnetic nanoparticles with a high initial magnetic susceptibility χo are of great interest in a wide variety of chemical, biomedical, electronic, and subsurface energy applications. In order to achieve the theoretically predicted increase in χo with the cube of the magnetic diameter, new synthetic techniques are needed to control the crystal structure, particularly for magnetite nanoparticles larger than 10 nm. Aqueous magnetite dispersions (Fe3O4) with a χo of 3.3 (dimensionless SI units) at 1.9 vol %, over 3- to 5-fold greater than those reported previously, were produced in a one-pot synthesis at 210 °C and ambient pressure via thermal decomposition of Fe(II) acetate in triethylene glycol (TEG). The rapid nucleation and focused growth with an unusually high precursor-to-solvent molar ratio of 1:12 led to primary particles with a volume average diameter of 16 nm and low polydispersity according to TEM. The morphology was a mixture of stoichiometric and substoichiometric magnetite according to X-ray diffraction (XRD) and Mössbauer spectroscopy. The increase in χo with the cube of magnetic diameter as well as a saturation magnetization approaching the theoretical limit may be attributed to the highly crystalline structure and very small nonmagnetic layer (∼1 nm) with disordered spin orientation on the surface.

Quasi-1D chains of dinickel lantern complexes and their magnetic properties.

Four new quasi-1D Ni2-lantern chain complexes of the form [Ni2(SOCR)4(L)]∞ (R = Ph, L = DABCO (1); R = Ph, L = pyz (2); R = CH3, L = DABCO (3); R = CH3, L = pyz (4)) were prepared from the reaction of [Ni2(SOCR)4(EtOH)], R = CH3 or Ph, with the N,N'-donor bridging ligands pyrazine (pyz) or 1,4-diazabicyclo[2.2.2]octane (DABCO). Reaction of [Ni2(tba)4(EtOH)], (tba = thiobenzoate) with the mono-N donor ligand quinuclidine (quin) gave the discrete Ni2-lantern complex [Ni2(tba)4(quin)] (5), whereas reaction with pyridine led to fragmentation of the lantern and formation of the known [Ni(tba)2(py)2] (6). Single-crystal X-ray diffraction reveals 2-4 to be 1D chain complexes comprising DABCO or pyz ligands which bridge the Ni2-lantern units. Complex 5 forms dimers through two equivalent NiS interactions. The Ni-Ni distances within the Ni2-lanterns are 2.5316(18)-2.595(2) Å for the 1D chain complexes 2-4, and 2.5746(4) Å in the dimeric complex 5, respectively. Comparing the solid state magnetism of 5 to precursor [Ni2(tba)4(EtOH)] demonstrates a change in coupling upon change of capping ligand. Meanwhile, chains 1-4 exhibit magnetic properties consistent with an S = 1 system, due to a mixed valent system where the two Ni centers differ in spin state, while 5 possesses two S = 1 Ni(ii) centers. DFT calculations confirm low-spin S = 0 {NiS4} and high-spin S = 1 {NiO4} centers in each lantern. Fits to the magnetic susceptibility data of the chains suggest a weak antiferromagnetic mean field interaction is present that is largely 1-D in nature, though neither pyrazine nor DABCO promote significant magnetic interaction between neighboring Ni2-lanterns.

Pt-Mg, Pt-Ca, and Pt-Zn Lantern Complexes and Metal-Only Donor-Acceptor Interactions.

Pt-based heterobimetallic lantern complexes of the form [PtM(SOCR)4(L)] have been shown previously to form intermolecular metallophilic interactions and engage in antiferromagnetic coupling between lanterns having M atoms with open shell configurations. In order to understand better the influence of the carboxylate bridge and terminal ligand on the electronic structure, as well as the metal-metal interactions within each lantern unit, a series of diamagnetic lantern complexes, [PtMg(SAc)4(OH2)] (1), [PtMg(tba)4(OH2)] (2), [PtCa(tba)4(OH2)] (3), [PtZn(tba)4(OH2)] (4), and a mononuclear control (Ph4P)2[Pt(SAc)4] (5) have been synthesized. Crystallographic data show close Pt-M contacts enforced by the lantern structure in each dinuclear case. 195Pt-NMR spectroscopy of 1-4, (Ph4P)2[Pt(SAc)4] (5), and several previously reported lanterns revealed a strong chemical shift dependence on the identity of the second metal (M), mild influence by the thiocarboxylate ligand (SOCR; R = CH3 (thioacetate, SAc), C6H5 (thiobenzoate, tba)), and modest influence from the terminal ligand (L). Fluorescence spectroscopy has provided evidence for a Pt···Zn metallophilic interaction in [PtZn(SAc)4(OH2)], and computational studies demonstrate significant dative character. In all of 1-4, the short Pt-M distances suggest that metal-only Lewis donor (Pt)-Lewis acceptor (M) interactions could be present. DFT and NBO calculations, however, show that only the Zn examples have appreciable covalent character, whereas the Mg and Ca complexes are much more ionic.

Thiocyanate-Ligated Heterobimetallic {PtM} Lantern Complexes Including a Ferromagnetically Coupled 1D Coordination Polymer.

A series of heterobimetallic lantern complexes with the central unit {PtM(SAc)4(NCS)} have been prepared and thoroughly characterized. The {Na(15C5)}[PtM(SAc)4(NCS)] series, 1 (Co), 2 (Ni), 3 (Zn), are discrete compounds in the solid state, whereas the {Na(12C4)2)}[PtM(SAc)4(NCS)] series, 4 (Co), 5 (Ni), 6 (Zn), and 7 (Mn), are ion-separated species. Compound 7 is the first {PtMn} lantern of any bridging ligand (carboxylate, amide, etc.). Monomeric 1-7 have M(2+), necessitating counter cations that have been prepared as {(15C5)Na}(+) and {(12C4)2Na}(+) variants, none of which form extended structures. In contrast, neutral [PtCr(tba)4(NCS)]∞ 8 forms a coordination polymer of {PtCr}(+) units linked by (NCS)(-) in a zigzag chain. All eight compounds have been thoroughly characterized and analyzed in comparison to a previously reported family of compounds. Crystal structures are presented for compounds 1-6 and 8, and solution magnetic susceptibility measurements are presented for compounds 1, 2, 4, 5, and 7. Further structural analysis of dimerized {PtM} units reinforces the empirical observation that greater charge density along the Pt-M vector leads to more Pt···Pt interactions in the solid state. Four structural classes, one new, of {MPt}···{PtM} units are presented. Solid state magnetic characterization of 8 reveals a ferromagnetic interaction in the {PtCr(NCS)} chain between the Cr centers of J/kB = 1.7(4) K.