Zn Distance Research Articles

Distribution of chalcogen atoms in ZnSSe and ZnMgSSe: an EXAFS study

Extended X-ray absorption fine structure (EXAFS) measurements were performed to investigate the local bonding structure in ZnSxSe1 − x (x = 0.06) and Zn1 − xMgxSySe1 − y (x = 0.18, y = 0.2) with zincblende structure. It is found that the first nearest neighbor SZn distance and the second nearest neighbor SS distance remain close to those in ZnS with zincblende structure. This implies a deviation from Vegard's law in these compounds. The second nearest neighbor structure around sulphur shows that the ratio of the number of sulphur atoms to that of selenium is proportional to the respective molar ratio both in ZnSSe and in ZnMgSSe. These results indicate that there is no clustering in ZnSSe and that chalcogen atoms are also distributed with negligible clustering in ZnMgSSe.

Dimeric Bis(μ-propionato-O:O')bis[bis(nicotinamide-N)(propionato-O)zinc(II)

Two bidentate-bridging propionate ligands connect two Zn II atoms [Zn-O(3) 2.040(8) and Zn― O(4)(-x, -y, -z) 2.059(4)A] forming a dimeric [Zn 2 (C 3 H 5 O 2 ) 4 (C 6 H 6 N 2 O) 4 ] complex. The coordination around each Zn II atom is trigonal bipyramidal. A monodentate propionate anion completes the trigonal basal plane [Zn―O(1) 2.072 (3) A] and two unidentate nicotinamide ligands occupy the apical positions [Zn―N(11) 2.192(5) and Zn―N(21) 2.174 (4) A] of the coordination sphere of each Zn II atom. The Zn...Zn distance is 3.900(1)A.

Zinc co-ordination in the DNA-binding domain of the yeast transcriptional activator PPR1

The structure of the native zinc form of the DNA binding domain in the yeast transcriptional activator PPR1 was investigated by extended X-ray absorption fine structure (EXAFS). By carrying out the EXAFS measurements at 11k we were able to demonstrate explicitly the proximity of the two zinc ions ( ZnZn distance = 3.16 ± 0.03 A ̊ ) and the presence of bridging cysteine ligands. The results show that the six cysteine residues co-ordinate two zinc ions in a two-metal ion cluster. PPR1 is the first member of this class of protein for which such information has been obtained.

Dinuclear zinc(II) complexes of a Robson macrocycle

Dinuclear zinc(II) complexes of the Robson macrocycle H2L, derived from the cyclocondensation of 2,6-diformyl-4-methylphenol and propane-1,3-diamine have been synthesised and their crystal structures determined. The compound Zn2(L)(ClO4)2·2H2O crystallises in the monoclinic space group P21/a(C52h no. 14) with a= 14.755(15), b= 12.348(12), c= 16.825(17)A, β= 105.80(3)° and Z= 4. The crystal structure consists of two independent pairs of dinuclear zinc complexes (molecules 1 and 2). Molecule 1 contains two six-co-ordinate zinc(II) with an intermetallic distance of 3.166 A, and molecule 2 has two five-co-ordinate zinc(II) with a Zn ⋯ Zn distance of 3.177 A. The compound [Zn2(L)(N3)2] crystallises in the monoclinic space group P21/c(C52h′ no 14) with a= 7.733(5), b= 11.865(6), c= 14.466(4)A, β= 90.86(4)° and Z= 2. The two zinc atoms are five-co-ordinate and are separated by 3.333 A.

Some unusual organo-zinc and -mercury compounds. The crystal structures of the compounds [(HOMe 2Si)(Me 3Si) 2C] 2Zn, [(MeOMe 2Si)(Me 3Si) 2C] 2Zn, and [(MeOMe 2Si)(Me 3Si) 2C] 2Hg

The preparation of the novel mercurial [(MeOMe 2Si)(Me 3Si) 2C] 2Hg is described. X-ray diffraction studies show that the molecules of this compound and its zinc analogue are centrosymmetric (and the CMC linkage thus linear), but in the former OMe group is directed away from the metal atom whereas in the latter it lies in towards the metal, with an O⋯Zn distance of 2.93 Å. In crystals of [(HOMe 2Si)(Me 3Si) 2C] 2Zn there is hydrogen bonding between the two oxygen atom within each molecule, and hydrogen bonding between two molecules to give discrete dimers. Because of the hydrogen bonding the CZnC linkage is slightly bent (the angle is 175.9(1)°), and the geometries of the two [(HOMe 2Si)(Me 3Si) 2C] 2C groups are significantly different.

Crystal structure and physico-chemical properties of bis(μ-methylphenylphosphinato) zinc(II)·dioxane {Zn[OP(CH 3)(C 6H 5)O] 2} n·nC 4H 8O 2

The structure of {Zn[OP(CH 3)(C 6H 5)O] 2} n·nC 4H 8O 2 has been determined by three dimensional single-crystal X-ray techniques. This polymer crystallizes in the space group P4 2/ m with two formula units in a cell of dimensions a = 10.725(4) Å, c = 9.229(4) Å, V = 1061.6 Å 3 and d c = 1.45 g/ml. Least-squares refinement of 432 independent reflections gives a final R factor of 3.6%. The structure consists of polymeric chains of tetrahedral zinc atoms linked by double phosphinate bridges. The ZnZn distance is 4.614 Å. The dioxane molecules are distributed between the chains at normal Van der Waals distances. IR and NMR evidence suggests that the amorphous form of the parent polymer {Zn[OP(CH 3)(C 6H 5)O] 2} n has essentially the same backbone structure.

EPR Determination of the Nearest-Neighbor Exchange Constant for Mn2+ Pairs in KZnF3

The electron paramagnetic resonance of exchange-coupled pairs of Mn2+ ions has been observed in Mn2+ doped KZnF3, a cubic perovskite. The Mn/Zn ratio used was approximately 0.01. The angular dependence of the pair spectrum indicates that the pair axes are along the three equivalent 〈100〉 directions. Thus the pairs are nearest magnetic neighbors and are expected to be antiferromagnetically coupled. At 4.2°K, only the S = 1 and S = 0 states are significantly occupied and the spectrum which arises from pairs in the S = 1 state is adequately explained by the spin Hamiltonian H=gβH·S+DSz2+AS·(I1+I2),with g = 2.004, | D | = 2.996 kG. From the linewidths of the unresolved hyperfine sets, A∼50 G is found. For a nn Mn2+ pair separated by the normal Zn–Zn distance (4.06 Å) in KZnF3, the dipolar contribution is expected to be D = −3.11 kG, indicating that any local distortion is small. From the temperature dependence of the S = 1 lines in the region 1.5°–25°K, the exchange constant Jnn (Hex=JS1·S2) is found to be +9.9°±0.6°K. This is compared with macroscopic measurements of J in antiferromagnetic KMnF3 and optical measurements in KZnF3:Mn.