Current Inorganic Chemistry (Discontinued) - Volume 3, Issue 2, 2013

The syntheses, structures and magnetic properties of seven new iron complexes, [Fe4O2(sao)4(tacn)2]·2MeOH·H2O (1·2MeOH·H2O), [Fe4O2(Me-sao)4(tacn)2]·2MeCN (2·2MeCN), [Fe4O2(Etsao) 4(tacn)2]·MeOH (3·MeOH), [Fe9/NaO4(Et-sao)6(hmp)8]·3MeCN·Et2O (4·3MeCN·Et2O), [Fe4(Et-sao)4(hmp)4]·Et-saoH2 (5·Et-saoH2), [Fe4(Ph-sao)4(hmp)4]·2MeCN (6·2MeCN) [Fe9/O3(sao)(pdm)6(N3)7(H2O)] (7), stabilised with salicylaldoxime (saoH2) or derivatised salicylaldoxime (R-saoH2) ligands in conjunction with either 1,4,7-triazocyclononane (tacn), 2-(hydroxymethyl)pyridine (hmpH) or 2,6-pyridinedimethanol (pdmH2) are discussed.

The initial employment of 1,3-propanediol (pdH2) in the synthesis of 3d/4f metal clusters has afforded a new family of tetranuclear [Mn2Ln2O2{(CH3)3CCO2}8{(CH3)3CCO2H}2(pdH2b)2] (Ln = Dy, 1; Gd, 2; Ho, 3) complexes. Compounds 1-3 represent new additions to the small family of MnIII 2Ln2 clusters possessing planar or diamond-like cores. Variable-temperature, dc and ac magnetization measurements were performed on compounds 1-3 and revealed the existence of very weak antiferromagnetic exchange interactions between the metal centers leading to a ground state spin value S = 5 in case of 2·2(CH3)3CCO2H·2H2O.

To study quantum spin systems, we have investigated the magnetic properties of a one-dimensional chain magnet, (MV)[CuCl3]2 (MV = 1,1’-dimethyl-4,4’-bipyridinium). The chain structure of [Cu2C16]∞ is represented as an alternating inplane/ out-of-plane bridging system. From the analysis of magnetic susceptibility, we revealed the alternating ferro- /antiferromagnetic couplings in the chain, and estimated the two exchange coupling parameters between copper ions as J1/kB = –18.08(3) K and J2/kB = +1.33(17) K (defined as H = –2 Σ(Ji Si-1 ·Si + J2 Si .Si+1)). Additionally, the DFT calculations were performed, giving the exchange coupling constants as –16.78 K and +1.86 K. The calculated values are in good agreement with the experimental results. EPR spectra below 7 K revealed the triplet spin state in the copper(II) chain, indicating clearly the intrinsic ferromagnetic coupling, while the antiferromagnetic is dominant. It is concluded that (MV)[CuCl3]2 shows the quantum fluctuated one-dimensional spin system having alternating ferro- and antiferromagnetic couplings.

The discovery of a series of lanthanide complexes behaving as Single Molecule Magnets (SMMs) has resulted in the rapid expansion of this field in the past few years. In this review, we focus on dysprosium-based SMMs assembled from versatile hydrazone ligands. The studies on a series of Dy2 complexes and Dy6 triangular prism indicate that the Dy2 unit with hula hoop-like geometry represents an excellent building block for the assembly of polynuclear dysprosium complexes. Structural and magnetic investigations on such system suggest that the hydrazone ligands are suitable candidates to construct robust dysprosium-based SMMs and to probe their relaxation dynamics.

The pairing of metal-based electrons to form metal-metal bonds in paddlewheel complexes would suggest that this chemistry is limited to diamagnetic complexes. However, a wide variety of paramagnetic complexes exist in this geometry. Whether obtained by oxidation or reduction of the divalent dinuclear species, as a result of degeneracy or neardegeneracy of their metal-based molecular frontier orbitals, or due to unpaired electrons in extended metal atom chains, paramagnetic paddlewheel complexes can be found in each group of the transition series. This review will present some of these molecules, their polynuclear analogues, and their use in supramolecular and extended architectures, with an emphasis on electronic structure.

Reported cases of the influence of guest molecules absorption/desorption on magnetic properties of porous coordination polymers (PCP) of transition metals are reviewed. Interaction of PCPs with guest molecules can modify magnetic susceptibility in wide temperature range, as well as can lead to change of the magnetic ordering or spin-crossover temperature and other magnetic characteristics. The reasons of such influence can be divided into several groups – guest molecule coordination to metal ion or decoordination; formation or cleavage of bonds in the group, which transmits exchange interactions between metal ions; or change of bond lengths or angles in coordination polymer because of crystal lattice adaptation to the guest molecule.

The “unsuccessful” synthesis of the non-commercially available ‘Dy(O2CPh)3’ precursor from the stoichiometric reaction of Dy(NO3)3·5H2O with 3 equivalents of NaO2CPh in MeCN/H2O has led instead to the “successful” isolation and structural characterization of the 1-D coordination polymer [Dy4(O2CPh)12(H2O)8]n·2n(PhCO2H)·n(MeCN) (1·2n(PhCO2H)·n(MeCN)) in excellent yields (∼90%). The one-dimensional double-chain structure of 1 was resulted from the linkage of two parallel chains by syn,anti-1:η1:µ PhCO2 - groups. The lattice structure of 1 is further extended to a 2-D network through hydrogen bonding and Π-Π stacking interactions. The observation of out-of-phase (χ"M) ac susceptibility signals suggested that 1 might be a molecular nanomagnet, and this was confirmed by single-crystal magnetization vs. dc field sweeps that exhibited hysteresis, the diagnostic property of a magnet.

This review summarizes recent developments in the field of single-molecule magnets derived from paramagnetic cyanometalate complexes supported by pyrazolylborate ancillary ligands. This review describes developments between 2002 and 2013 and is restricted to descriptions of molecular cyanometalate precursor complexes, their magnetic polynuclear single-molecule magnet derivatives, and common structural archetypes.