We report the synthesis of nominal 2 and 5 at.% Mn-doped ZnO nanocrystalline particles by a co-precipitation method. Rietveld refinement of x-ray diffraction data revealed that Mn-doped ZnO crystallizes in the monophasic wurtzite structure and the unit cell volume increases with increasing Mn concentration. DC magnetization measurements showed ferromagnetic ordering above room temperature with Hc∼150 Oe for nominal 2 at.% Mn-doped ZnO nanoparticles annealed at 675 K. A distinct ferromagnetic resonance (FMR) signal was observed in the EPR spectra of the 2 at.% Mn-doped ZnO nanoparticles annealed at 675 K. EPR measurements were used to estimate the number of spins participating in ferromagnetic ordering. Of the total Mn present in the 2 at.% Mn ZnO lattice, 25% of the Mn2+ ions were responsible for ferromagnetic ordering, whereas nearly 5% of the Mn2+ ions remained uncoupled (isolated spins). A well resolved EPR spectrum of 5% Mn-doped ZnO samples annealed at 875–1275 K (g = 2.007, A = 80 G, D = 210 G and E = 15 G) confirmed that Mn was substitutionally incorporated into the ZnO lattice as Mn2+. On increasing the temperature of annealing beyond 1075 K an impurity phase emerges in both the 2 and 5 at.% Mn-doped ZnO samples, which has been identified as a variant of (Zn1−XMn(II)X)Mn(III)2O4 with Tc∼15 K. Our results indicate that the observed room temperature ferromagnetism in Mn-doped ZnO can be attributed to the substitutional incorporation of Mn at Zn-sites rather than due to the formation of any metastable secondary phases.

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The geometric and electronic structures of Si(n), Si(n) (+), and AlSi(n-1) clusters (2< or =n< or =13) have been investigated using the ab initio molecular orbital theory under the density functional theory formalism. The hybrid exchange-correlation energy function (B3LYP) and a standard split-valence basis set with polarization functions [6-31G(d)] were employed for this purpose. Relative stabilities of these clusters have been analyzed based on their binding energies, second difference in energy (Delta (2)E) and fragmentation behavior. The equilibrium geometry of the neutral and charged Si(n) clusters show similar structural growth. However, significant differences have been observed in the electronic structure leading to their different stability pattern. While for neutral clusters, the Si(10) is magic, the extra stability of the Si(11) (+) cluster over the Si(10) (+) and Si(12) (+) bears evidence for the magic behavior of the Si(11) (+) cluster, which is in excellent agreement with the recent experimental observations. Similarly for AlSi(n-1) clusters, which is isoelectronic with Si(n) (+) clusters show extra stability of the AlSi(10) cluster suggesting the influence of the electronic structures for different stabilities between neutral and charged clusters. The ground state geometries of the AlSi(n-1) clusters show that the impurity Al atom prefers to substitute for the Si atom, that has the highest coordination number in the host Si(n) cluster. The fragmentation behavior of all these clusters show that while small clusters prefers to evaporate monomer, the larger ones dissociate into two stable clusters of smaller size.

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The dilute magnetic semiconductor oxides (DMSO) are of current interest because of their potential 'spintronics' applications, where the charge and spin degrees of freedom of electrons are used simultaneously for novel memory and optical device applications. [1,2] In particular, Co doped ZnO has attracted considerable interest. [3] There have been a number of reports about the observance of room temperature ferromagnetism in thin films of Zn 1-x Co x O produced by different techniques. [4][5][6][7] Schwartz et al. [8] also observed ferromagnetism above room temperature in aggregated particles of Co doped ZnO, by heat treating (below 200 o C) colloidal quantum dots of Co doped ZnO. However, most recent works on well-characterized polycrystalline Zn 1-x Co x O samples indicate that they are not ferromagnetic at room temperature, [9][10][11][12][13][14] except for an isolated report by Deka et al.. [15] In general, studies on polycrystalline samples have converged on to a conclusion that robust room temperature ferromagnetism (RTF) is not realizable in Co doped ZnO without additional carrier doping. Sato and Katayama-Yoshida [16] predicted Co doped ZnO would become ferromagnetic in the presence of n-type carriers. This was experimentally demonstrated by Schwartz and Gamelin. [17] They were the first to show the reversible cycling of paramagnetic (P) to ferromagnetic (FM) state in Co doped ZnO spin coated films, produced from colloidal nanocrystals, by introducing and removing interstitial Zn (Zn i ), a native n-type defect of ZnO. Later Spaldine, [18] in a computational study, showed only hole doping promotes RTF in Co doped ZnO. This is in contrast with

Lead borosilicate glasses having general formulae (PbO)0.5 −x(SiO2)0.5(B2O3)x with 0.0 ≤ x ≤ 0.4 and (PbO)0.5(SiO2)0.5 −y(B2O3)y with 0.0 ≤ y ≤ 0.5 have been prepared by a conventional melt–quench method and characterized by 29 Si, 11 B magic angle spinning (MAS) NMR techniques and infrared spectroscopy, as regards their structural features. From 29 Si NMR results, it has been inferred that with increasing concentration of boron oxide, (PbO)0.5 −x(SiO2)0.5(B2O3)x glasses exhibit a systematic increase in the number of Q4 structural units of Si at the expense of Q2 structural units, along with the formation of Si–O–B linkages. On the other hand, for (PbO)0.5(SiO2)0.5−y(B2O3)y glasses, there is no direct interaction between SiO2and B2O3 in the glass network, as revealed by the 29 Si MAS NMR studies. Boron exists in both trigonal and tetrahedral configurations for these two series of glasses and for the (PbO)0.5(SiO2)0.5−y(B2O3)y series of glasses; the relative concentration of these two structural units remains almost constant with increasing B2O3 concentration. In contrast, for (PbO)0.5−x(SiO2)0.5(B2O3)x glasses, there is a slight increase in the number of BO3 structural units above x = 0.2, as there is a competition between SiO2 and B2O3 for interaction with Pb2+, thereby leading to the formation of BO3 structural units. For both series of glasses, the thermal expansion coefficient is found to decrease with increasing B2O3 concentration, the effect being more pronounced for the (PbO)0.5 −x(SiO2)0.5(B2O3)x series of glasses due to the increased concentration of Q4structural units of silicon and better cross-linking as a result of the formation of Si–O–B-type linkages.

The condensation of bis(2-formylphenyl) telluride 1 with ethane-I ,2-diamine yielded the novel macrocyclic tellurium ligand 2 via metal-free dimerisation. Crystals of 2 are triclinic, space group P i with a = 7.956(3), h = 9.885(2), c = 10.068(2) A, 2 = 1. Hydrogenation of macrocycle 2 provided the corresponding saturated tetraazamacrocycle 3, protonation of which with HBr afforded 4. The co-ordination chemistry of 2 has been studied with 'soft' metal ions such as palladium(1r) and mercury(I1). N,N'-Bis[(2-chlorotelluranyl)benzylidenelethane-1,2-diamine has also been characterised by an X-ray diffraction study, with triclinic space group P i , a = 7.71(1), b = 7.90(1), c = 8.52(1) A and Z = 1.Supramolecular chemistry, which involves the design and synthesis of polytopic macrocyclic and macrobicyclic ligands containing several recognition sites, is a promising area of considerable current interest. Recently there have been extensive studies on the synthesis and ligating behaviour of macrocyclic Schiff bases containing phenol, pyridine, pyrrole, furan and thiophene units.' Very recently the first example of a Schiff-base macrocycle containing a pyridazine unit has been reported., Most of the work in this area has focussed on the design and synthesis of receptors which are selective for 'hard' metal ions. Recently Beer et al., have described the synthesis of several polyazamacrocyclic complexes which incorporate both 'hard' and 'soft' metal ions and contain multiple metallocene redoxactive groups. Interest in macrocycles which contain 'hard' and 'soft' donor atoms to complex both 'hard' and 'soft' metal cations derives from their intrinsic potential for (i) modulation of the redox properties of a complexed 'soft' transition-metal cation upon co-complexation of a 'hard' cation, (ii) allosteric effects and (iii) bimetallic activation and catalysis., Although a few examples of polyazamacrocycles containing 'soft' sulfur ' or phosphorus and 'hard' nitrogen donor atoms are known, to our knowledge neither selenium nor tellurium has been incorporated into a macrocyclic Schiff base. Some homoleptic selenoether macrocycles, however, have been reported. We report here an easy high yield synthesis, structure and co-ordination of a novel tellurium-containing azamacrocycle (see Scheme 1). Experiment a1 Materials and methodsBis(2-formylphenyl) telluride and [PdCl,(NCC,H,)] were prepared by reported procedures. Air-sensitive reactions were carried out under an inert atmosphere. Solvents were purified by standard techniques and were freshly distilled prior to use. Ethane-1,2-diamine (en) (SISCO) was reagent grade and was distilled prior to use. Melting points were recorded in capillary tubes on a Ketari melting point apparatus and are uncorrected. Proton (299.94 MHz), 13C (75.42 MHz) and 12'Te (94.75 MHz) NMR spectra were recorded on a Varian VXR 300s spectrometer. Chemical shifts are cited with respect to SiMe, as internal standard ('H and ' ,C) and Te(S,CNEt,), as external standard (' ,'Te). Elemental analyses were performed on a...