Marius Andruh

The interplay of coordinative, hydrogen bonding and π–π stacking interactions in sustaining supramolecular solid-state architectures.: A study case of bis(4-pyridyl)- and bis(4-pyridyl-N-oxide) tectons

Abstract Bis-monodentate ligands, such as bis(4-pyridyl) derivatives and bis(4-pyridyl-N-oxide), are able to generate polymetallic coordination networks with interesting supramolecular solid-state architectures. This review is devoted to high-dimensionality systems, which are extended by combining two or three organizing forces: metal-coordination, hydrogen bonds and π–π stacking interactions. A special emphasis is given to the following molecules, which play the role of linkers and spacers in the construction of extended frameworks: 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethane, trans-1,2-bis(4-pyridyl)ethene, trans-4,4′-azo-pyridine, 4,4′-bipyridyl-N,N′-dioxide.

3d−4f Combined Chemistry: Synthetic Strategies and Magnetic Properties

Heterometallic 3d-4f complexes are of high interest in molecular magnetism: the lanthanide ions bring large and, in most cases, anisotropic magnetic moments. The combination of 3d and 4f metal ions, which differ through their chemistries and stereochemical preferences, leads to a rich variety of heterometal complexes, ranging from discrete entities to 3-D coordination polymers. This paper reviews recent achievements in this field: (i) oligonuclear complexes for studying the nature of the 3d-4f exchange interaction; (ii) construction of single-molecule magnets; (iii) magnetic properties of 3d-4f coordination polymers.

Preparation, crystal structures, and magnetic features for a series of dinuclear (Ni(II)Ln(III)) Schiff-base complexes: evidence for slow relaxation of the magnetization for the Dy(III) derivative

A series of dinuclear [Ni(II)Ln(III)] Schiff-base complexes (using a Schiff-base dicompartmental ligand derived from o-vanillin [H(2)valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)]) with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and a hydroxo-bridged tetranuclear [Ni(II)Yb(III)] are reported. The crystal structures have been solved for 10 dinuclear complexes revealing four arrangements for the dinuclear units, which are modulated by the coordinated solvent molecules and the nitrato-anion interactions. The magnetic behaviors have been investigated, and the nature of the Ni(II)-Ln(III) exchange interaction has been emphasized by comparison with the behavior of the related [Zn(II)Ln(III)] derivatives. This allowed for establishing that the interaction within these compounds is antiferromagnetic with the 4f ions of the beginning of the Ln series and turns ferromagnetic from Gd(III) toward the end of the series. AC susceptibility investigations clearly show the occurrence of slow relaxation processes of the magnetization close to 2 K for the dinuclear [Ni(II)Dy(III)] complex.

Study of the Luminescent and Magnetic Properties of a Series of Heterodinuclear [ZnIILnIII] Complexes

Herein, we report the synthesis, structural investigation, and magnetic and photophysical properties of a series of 13 [Zn(II)Ln(III)] heterodinuclear complexes, which have been obtained employing a Schiff-base compartmental ligand derived from o-vanillin [H(2)valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)]. The complexes have been synthesized starting from the [Zn(valpn)(H(2)O)] mononuclear compound and the corresponding lanthanide nitrates. The crystallographic investigation indicated two structural types: the first one, [Zn(H(2)O)(valpn)Ln(III)(O(2)NO)(3)], contains 10-coordinated Ln(III) ions, while in the second one, [Zn(ONO(2))(valpn)Ln(III)(H(2)O)(O(2)NO)(2)]·2H(2)O, the rare earth ions are nine-coordinated. The Zn(II) ions always display a square-pyramidal geometry. The first structural type encompasses the larger Ln ions (4f(0)-4f(9)), while the second is found for the smaller ions (4f(8)-4f(11)). The dysprosium derivative crystallizes in both forms. Luminescence studies for the heterodinuclear compounds containing Nd(III), Sm(III), Tb(III), Dy(III), and Yb(III) revealed that the [Zn(valpn)(H(2)O)] moiety acts as an antenna. The magnetic properties for the paramagnetic [Zn(II)Ln(III)] complexes have been investigated.

Dimers and chains of {3d–4f} single molecule magnets constructed from heterobimetallic tectons

A tetranuclear complex and a 1-D coordination polymer with a ladder-like topology have been obtained by connecting [Ni(II)Dy(III)] nodes with dicarboxylato ligands: [Ni₂(valpn)₂Dy₂(III)(pdca)₂(NO₃)(H₂O)₆](NO₃)·4H₂O 1, and (∞)¹[Ni₂(H₂O)₂(valpn)₂Dy₂(tfa)₃]·4CH₃CN 2 (valpn²⁻ = the dianion of the Schiff base resulting from reacting o-vanillin with 1,3-propanediamine; pdca²⁻ = the dianion of 2,6-pyridinedicarboxylic acid; tfa²⁻ = the dianion of the terephthalic acid). The magnetic measurements show a ferromagnetic interaction between Ni(II) and Dy(III), and that both compounds behave like SMM with strong tunnelling. The barrier of 2 (17.4 K) is higher than that of 1 (13.6 K).

A Mixed-Valence and Mixed-Spin Molecular Magnetic Material: [MnIIL]6[MoIII(CN)7][MoIV(CN)8]2⋅19.5 H2O

Long-range ferromagnetic ordering at 3 K is observed for the title compound, which may be considered as a fully localized mixed-valence species (Mo(3+) and Mo(4+)) as well as a mixed-spin species (low-spin and high-spin Mn(2+) ions). Its two-dimensional structure consists of heart-shaped 48-membered rings, and each ring contains 16 metal centers (see picture).

Crystal engineering of hybrid inorganic–organic systems based upon complexes with dissymmetric compartmental ligands

This paper illustrates the versatility of mono- and heterobinuclear complexes with dissymmetric compartmental ligands in designing molecular and supramolecular heterometallic systems. Mononuclear complexes with side-off bicompartmental ligands derived from o-vanillin act efficiently, through their empty compartment, as hydrogen-bond receptors and as second coordination sphere ligands. These Schiff- bases are also suitable for synthesizing 3d-3d′ and 3d-4f heterobinuclear complexes. Both 3d-3d′ and 3d-4f complexes can be employed as nodes in obtaining coordination polymers with various dimensionalities and network topologies, as well as interesting magnetic and optical properties.

[Cr(phen)(ox)2]−: a versatile bis-oxalato building block for the design of heteropolymetallic systems. Crystal structures and magnetic properties of AsPh4[Cr(phen)(ox)2]·H2O, [NaCr(phen)(ox)2(H2O)]·2H2O and {[Cr(phen)(ox)2]2[Mn2(bpy)2(H2O)2(ox)]}·6H2O

The new complexes of formula AsPh4[Cr(phen)(ox)2]·H2O (1), [NaCr(phen)(ox)2(H2O)]·2H2O (2) and {[Cr(phen)(ox)2]2[Mn2(bpy)2(H2O)2(ox)]}·6H2O (3) (AsPh4=tetraphenylarsonium cation; phen=1,10-phenanthroline; ox=oxalate dianion; bpy=2,2′-bipyridine) have been prepared and characterized by single-crystal X-ray diffraction. The structure of 1 consists of discrete [Cr(phen)(ox)2]− anions, tetraphenylarsonium cations and uncoordinated water molecules. The chromium environment in 1 is distorted octahedral with Cr–O bond distances between 1.959(3) and 1.947(3) A and Cr–N bonds of 2.083(4) and 2.072(4) A. The angles subtended at the chromium atom by the two oxalates are 83.6(2) and 83.3(1)° whereas the N–Cr–N angle is 79.9(2)°. The [Cr(phen)(ox)2]− unit of 1 is also present in 2 and 3 but it accomplishes different coordination functions, acting as a bridging (2) or terminal (3) ligand. 2 has a layered structure made up of oxalato-bridged bimetallic CrIII–NaI helical chains that are interconnected through centrosymmetric Na2O2 units. The two oxalates of [Cr(phen)(ox)2]− in 2 are bis-chelating within the bimetallic chain but one of them is in addition monodentate towards a sodium atom of a neighbouring chain, yielding a sheetlike structure. The sodium atom in 2 has a distorted octahedral geometry with five Na–O(ox) bonds ranging from 2.453(5) to 2.319(4) A and the sixth position being occupied by an aqua ligand with Na–O(w)=2.384(6) A. The intralayer chromium–sodium and sodium–sodium separations through bridging oxalate in 2 are 5.560(4) and 3.643(8) A, respectively. The structure of 3 consists of neutral tetranuclear Cr2IIIMn2II units in which two terminal [Cr(phen)(ox)2]− entities act as monodentate ligands towards a central oxalato-bridged manganese(II) dimer. Each manganese atom is six-coordinated as MnN2O4: two nitrogen atoms of a chelating bpy, one aqua ligand and three oxalate oxygens build a distorted octahedron around the manganese atom. The Mn–O(ox) and Mn–N(bpy) bond lengths vary in the ranges 2.219(12)–2.160(13) and 2.33(2)–2.14(2) A, respectively. The intramolecular chromium–manganese separation [5.507(5) and 5.502(5) A for Cr(2)···Mn(2) and Cr(1)···Mn(1)] is somewhat shorter that the manganese–manganese one [5.703(2) A]. The magnetic properties of 1–3 have been investigated in the temperature range 1.9–300 K. Very weak antiferromagnetic interactions between the chromium centers are observed in 1 and 2 in agreement with their crystal structures. In the case of 3, significant intramolecular antiferromagnetic interactions between the adjacent chromium(III) and manganese(II) ions ( j=−1.1 cm−1, through the chelating/monodentate oxalato) and between the two manganese(II) ions (J=−2.2 cm−1, through the bis-chelating oxalato) occur, the Hamiltonian being defined as Ĥ=−JŜMn1· ŜMn2−j[ŜCr1·ŜMn1+ŜCr2·ŜMn2].

Temperature Switch of LMCT Role: From Quenching to Sensitization of Europium Emission in a ZnII―EuIII Binuclear Complex

The synthesis, structural investigation, and photophysical properties of a new heterobinuclear complex, [Zn(H(2)O)(valpn)Eu(NO(3))(3)], are reported [H(2)valpn = 1,3-propanediylbis(2-iminomethylene-6-metoxy-phenol)]. In the absence of the antenna-type sensitization of europium emission at room temperature, the strongest metal-centered emission was obtained following excitation into the (7)F(0)-(5)D(2) transition at 535 nm. In contrast, at 80 K, the strongest emission of europium was obtained by exciting into the maximum of a high-intensity, low-lying ligand-to-metal charge-transfer band (LMCT) located at approximately 425 nm. The overall temperature-induced changes of the photophysical properties of europium were assigned to the relative location of the LMCT and (3)pi pi* ligand states to the europium excited levels. The results may explain the lack of the antenna effects reported for some of the europium complexes with this type of ligand.

Dodecanuclear [CuII6GdIII6] Nanoclusters as Magnetic Refrigerants

A novel dodecanuclear complex, [{(HL)(L)(DMF)Cu(II)Gd(III)(DMF)(H(2)O)}(6)]·6DMF (1; DMF = N,N-dimethylformamide), has been obtained using the ligand resulting from the condensation of 3-formylsalicylic acid with hydroxylamine (H(3)L). The exchange interaction between the phenoxo-bridged Cu(II) and Gd(III) ions is weak ferromagnetic (J = +1.01 cm(-1)). The combination of a high-spin ground state with small anisotropy leads to a significant magnetocaloric effect [-ΔS(m)(0-7 T) = 23.5 J K g(-1) K(-1) at ∼2 K].