José Martínez-Lillo

Highly Anisotropic Rhenium(IV) Complexes: New Examples of Mononuclear Single-Molecule Magnets

The rhenium(IV) complex (NBu4)2[ReBr4(ox)] (1) (ox = oxalate and NBu4(+) = tetra-n-butylammonium cation) has been prepared and its crystal structure determined by X-ray diffraction. The structure is made up of discrete [ReBr4(ox)](2-) anions and bulky NBu4(+) cations. Each [ReBr4(ox)](2-) anion is surrounded by six NBu4(+) cations, which preclude any significant intermolecular contact between the anionic entities, the shortest rhenium···rhenium distance being 9.373(1) Å. Variable temperature dc and ac magnetic susceptibility measurements and field-dependent magnetization experiments on polycrystalline samples of 1 reveal the occurrence of highly anisotropic magnetically isolated Re(IV) centers (S(Re) = 3/2), which exhibit slow relaxation of the magnetization at very low temperatures in a dc field. Ac measurements conducted on a polycrystalline sample of the complex (NBu4)2[ReCl4(ox)] (2) [compound isostructural to 1 whose structure and dc magnetic susceptibility study were previously reported in Tomkiewicz, A.; Bartczak, T. J.; Kruszyński, R.; Mroziński, J. J. Mol. Struct. 2001, 595, 225] show a similar behavior, both complexes thus constituting new examples of mononuclear single-molecule magnets. High-frequency and -field electron paramagnetic resonance on polycrystalline samples of 1 and 2 and on single crystals of 2 allowed for the determination for the first time of the negative sign and confirmed a significant magnitude and rhombicity (E/D) of the zero-field splitting tensor of the [ReCl4(ox)](2-) and [ReBr4(ox)](2-) centers, originating from a combination of spin-orbit coupling and low molecular symmetry. D and E values of 1 and 2 were estimated through magnetization measurements and theoretically calculated through complete active space and density functional theory methodologies.

Heterotetranuclear Oxalato-Bridged ReIV3MII (M = Mn, Fe, Co, Ni, Cu) Complexes: A New Example of a Single-Molecule Magnet (M = Ni)

The use of the mononuclear species (NBu(4))(2)[Re(IV)Cl(4)(ox)] (NBu(4)(+) = tetra-n-butylammonium cation; ox = oxalate dianion) as a ligand toward fully solvated divalent first-row transition-metal ions affords the tetranuclear complexes (NBu(4))(4)[{Re(IV)Cl(4)(mu-ox)}(3)M(II)] with M = Mn (1), Fe (2), Co (3), Ni (4), and Cu (5). Their structure is made up of discrete [{ReCl(4)(mu-ox)}(3)M](4-) anions and bulky NBu(4)(+) cations. The complexes 2-5 crystallize in the triclinic system with space group P1; 2 and 5 as well as 3 and 4 are isostructural. The Re and M atoms exhibit somewhat distorted ReCl(4)O(2) and MO(6) octahedral surroundings, with the oxalate groups adopting the bis-bidentate bridging mode. Magnetic susceptibility measurements on polycrystalline samples of 1-5 in the temperature range 1.9-300 K show the occurrence of intramolecular antiferromagnetic [J = -1.30 cm(-1) (1)] and ferromagnetic couplings [J = +1.62 (2), +3.0 (3), +16.3 (4), and +4.64 cm(-1) (5)], with the Hamiltonian being defined as H = -J[S(M)(S(Re1) + S(Re2) + S(Re3))]. Compound 4 is the first example of an oxalato-bridged heterometallic species that behaves as a single-molecule magnet with a ground-state spin S = (11)/(2) and D = -0.8(1) cm(-1), as shown by the study of its static and dynamic magnetic properties and a high-frequency electron paramagnetic resonance study on polycrystalline samples together with detailed micro-SQUID measurements on single crystals.

X-Ray structure of [ReCl4(μ-ox)Cu(pyim)2]: a new heterobimetallic ReIVCuII ferrimagnetic chain

A new heterobimetallic ReIVCuII compound has been prepared and its crystal structure determined by single-crystal X-ray diffraction; magnetic susceptibility measurements show that this compound behaves as a ferrimagnetic chain with significant antiferromagnetic interactions between Re(IV) and Cu(II) metal ions.

A self-assembled tetrameric water cluster stabilized by the hexachlororhenate(IV) anion and diprotonated 2,2′-biimidazole: X-ray structure and magnetic properties

A self-assembled tetrameric water cluster stabilized by [ReCl6]2− anions and [H4biim]2+ cations occurs in the new compound [H4biim][ReCl6]·4H2O, which exhibits a weak ferromagnetic coupling between the Re(IV) centers through an unusual ReIV–Cl⋯(H2O)⋯Cl–ReIV pathway.

A heteropentanuclear oxalato-bridged [Re(IV)4Gd(III)] complex: synthesis, crystal structure and magnetic properties.

The compound (NBu(4))(5)[Gd(III){Re(IV)Br(4)(μ-ox)}(4)(H(2)O)]·H(2)O (1), with intramolecular antiferromagnetic coupling, is the first Re(iv) system incorporating a 4f ion.

Metamagnetic behaviour in a new Cu(II)Re(IV) chain based on the hexachlororhenate(IV) anion.

A new chloro-bridged heterobimetallic Cu(II)Re(IV) chain of formula {Cu(pyim)(Him)2ReCl6}n·MeCN (·MeCN) has been prepared and magnetostructurally characterised. Compound is the first example of the [Re(IV)Cl6](2-) anion acting as a metalloligand towards a paramagnetic metal ion.

Spin canting in Re(IV) complexes: magnetic properties of [ReX4(bpym)] ( X = Cl and Br; bpym = 2,2′-bipyrimidine)

The mononuclear complexes [ReCl4(bpym)] (1) and [ReBr4(bpym)] (2) (bpym = 2,2′-bipyrimidine) are weak ferromagnets. Magnetic ordering occurs below 7.0 (1) and 20.0 K (2) and good hysteresis loops are observed for the two compounds at 2.0 K. A spin-canting phenomenon, i.e., a non-strict linearity of the individual spins aligned in an anti-parallel way by intermolecular antiferromagnetic coupling occurring in many Re(IV) complexes, accounts for these magnetic features which are unusual in molecular solids such as 1 and 2.

A cationic and ferromagnetic hexametallic Mn(III) single-molecule magnet based on the salicylamidoxime ligand

The salicylamidoxime-based complex [Mn6(μ3-O)2(H2N-sao)6(py)6(EtOH)2](ClO4)2·4EtOH (1·4EtOH) constitutes the first example of a cationic and ferromagnetic member of the oxime-based family of [Mn(III)6] single-molecule magnets.

Self-assembly of a chiral carbonate- and cytidine-containing dodecanuclear copper(II) complex: a multiarm-supplied globular capsule.

A dodecanuclear copper(II) globular-shaped structure has been obtained with the cytidine nucleoside and the templating carbonate anion. It shows receptor properties through anion-cation and multiple anion-pi interactions toward ClO 4 (-) as well as an overall antiferromagnetic coupling.

Cubane-Type CuII4 and MnII2MnIII2 Complexes Based on Pyridoxine: A Versatile Ligand for Metal Assembling

By using Vitamin B6 in its monodeprotonated pyridoxine form (PN-H) [PN = 3-hydroxy-4,5-bis(hydroxymethyl)-2-methylpyridine], two tetranuclear compounds of formula [Mn4(PN-H)4(CH3CO2)3Cl2]Cl·2CH3OH·2H2O (1) and [Cu4(PN-H)4Cl2(H2O)2]Cl2 (2) have been synthesized and magneto-structurally characterized. 1 crystallizes in the triclinic system with space group P1 whereas 2 crystallizes in the orthorhombic system with Fdd2 as space group. They exhibit Mn(II)2Mn(III)2 (1) and Cu(II)4 (2) cubane cores containing four monodeprotonated pyridoxine groups simultaneously acting as chelating and bridging ligands (1 and 2), three bridging acetate ligands in the syn-syn conformation (1), and two terminally bound chloride anions (1 and 2) plus two coordinated water molecules (2). The electroneutrality is achieved by the presence of chloride counterions in both compounds. Tri- [Mn(1) and Mn(3)] and divalent [Mn(2) and Mn(4)] manganese centers coexist in 1, all being six-coordinate with distorted Mn(1/3)O6 and Mn(2/4)O5Cl octahedral surroundings, respectively, the equatorial Mn-O bonds being about 0.2 Å shorter at the former ones. The two crystallographically independent copper(II) ions in 2 are five-coordinate in somewhat distorted CuO5 [Cu(1)] and CuO4Cl [Cu(2)] square pyramidal geometries. The values of the intracore metal-metal separation cover the ranges 3.144(1)-3.535(1) (1) and 2.922(6)-3.376(1) Å (2). The magnetic properties of 1 and 2 were investigated in the temperature range 1.9-300 K, and they correspond to an overall antiferromagnetic behavior with susceptibility maxima at 5.0 (1) and 65.0 K (2). The analysis of the magnetic susceptibility data showed the coexistence of intracore antiferro- and ferromagnetic interactions in the two compounds. Their values compare well with those existing in the literature for the parent systems.