No abstract

The reaction of a multisite coordination ligand, LH, with Cu(II) salts and Ln(NO)·nHO in a 1:2:1 stoichiometric ratio in the presence of triethylamine was found to afford a series of one-dimensional heterometallic [{CuLn(L)(μ-OH)(ClO)(NO)(OH)}(ClO)(HO)] [Ln = Tb(1), Dy(2) and Ho(3), x = 4.25, 5.5, and 5 for 1-3, respectively] coordination polymers. Complexes 1-3 have been characterized by single crystal X-ray crystallography. The detailed study of the magnetic properties has also been performed and compared with the parent [CuLn] molecular analogues. The ac susceptibility measurements for complexes 1-3 confirm their SMM behavior with the following characteristics: Δ/k = 23.4 K, τ = 1.1 × 10 s and Δ/k = 27.9 K, τ = 6.6 × 10 s under 0 and 1200 Oe dc fields, respectively for 1; Δ/k = 8.3 K, τ = 3.1 × 10 s for 2 under 0 dc field. For 3, the fast QTM below 4 K prevents the estimation of the SMM energy barrier. Remarkably, the magnetic and SMM properties of the previously reported molecular [CuLn] analogues are preserved after their assembly in these coordination networks.

The reaction of a Schiff base ligand (LH3) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln10 (Ln = Dy (1), Tb (2), and Gd (3)) and pentanuclear Ln5 complexes (Ln = Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln10 and Ln5 complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes (1-6) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (Ueff) = 16.12(8) K and relaxation time (τo) = 3.3×10(-5) s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out-of-phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: -ΔSm = 26.6 J kg(-1) K(-1) at T = 2.2 K for 3 and -ΔSm = 27.1 J kg(-1) K(-1) at T = 2.4 K for 4, both for an applied field change of 7 T.

Pyridyloxy cyclophosphazenes, spiro-N3P3(O2C12H8)(O-C5H4N-3)4 (L1), dispiro-N3P3(O2C12H8)2(O-C5H4N-3)2 (L2) and dispiro-N3P3(O2C12H8)2(O-C5H4N-4)2 (L3) were prepared and characterized. The crystal structure of L1 was determined which showed that the cyclophosphazene ring is planar. The reaction of L1 with anhydrous copper(II) chloride or silver nitrate afforded L2M4 metallamacrocycles [{L1}2{ClCu(μ-Cl)2CuCl}]2·8CHCl3 (3) and [{L1}2{(DMF)0.5(NO3)0.5Ag}2{Ag(μ2-(O)NO2)(H2O)}2]{μ-[NO3]}·CH3OH (4) respectively. The molecular structure of 3 reveals that two CuCl2 dimers are bridged to each other in a complex metallamacrocycle that involves four metal ions and two ligands. The molecular structure of 4 is similar to that of 3 except for the presence of weak argentophilic interactions between the two Ag(I) centers. Also, a nitrate anion, which is trapped in the centre of the tetrameric assembly, assists in holding two Ag(I) ions together and 4 serves as a single source precursor for silver nanoparticles. The reaction L1 with ZnCl2 and Cd(NO3)2·4H2O afforded the 1D-coordination polymers [{L1}{ZnCl2}2]n·2nCH3OH·2nH2O (5) and [{L1}2{Cd(CH3OH)2(NO3)2}2{Cd(NO3)2(H2O)}]n·3nCH3OH·3nH2O (6) respectively. While in 5 the 20-membered macrocycles are inter-connected directly, in 6 they are bridged by a Cd(II) connector. The reaction of L2 with CoCl2 afforded the 1D-coordination polymer [{L2}2{CoCl2}]n·2nCHCl3 (7) which also contains interconnected 20-membered metallamacrocycles. On the other hand, the reaction of L2 with CuCl2 afforded [{L2}2{ClCu(μ-Cl)}2]n·2nCHCl3·nH2O (8) which is a 1D-coordination polymer that contains {ClCu(μ-Cl)2CuCl} units. The reaction of L3 with CuCl2 and Cd(NO3)2·4H2O afforded [{L3}2{CuCl2}]n·nDMF (9) and [{L3}2{Cd(NO3)2}]n·nCHCl3·nCH2Cl2·nH2O (10) respectively. While 9 is a 2D-coordination polymer containing 48-membered metallamacrocycles, 10 is a 1D-coordination polymer containing interconnected 24-membered metallamacrocycles which possess spirocyclic cadmium ions as nodes.