Sergio Baggio

A new simplifying approach to molecular geometry description : the vectorial bond-valence model

A method to describe, analyze and even predict the coordination geometries of metal complexes is proposed, based on previous well established concepts such as bond valence and valence-shell electron-pair repulsion (VSEPR). The idea behind the method is the generalization of the scalar bond-valence concept into a vector quantity, the bond-valence vector (BVV), with the innovation that the multidentate ligands are represented by their resultant BVVs. Complex n-ligand coordination spheres (frequently indescribable at the atomic level) reduce to much simpler ones when analyzed in BVV space, with the bonus of a better applicability of the VSEPR predictions. The geometrical implications of the BVV description are analyzed for the cases of n=2 and 3 (n=number of ligands), and the validity of its predictions, checked for a large number of metal complexes.

X-ray study of two new cadmium acetato complexes

Two new cadmium acetate compounds, Cd(tpy)(Ac)2·2H2O (1) and Cd2(bbip)2 (Ac)3·0.5S2O8·2H2O (2) (tpy = 2,2′,2′′-terpyridine; bbip = 2,6-bis(benzimidazol-2-yl)pyridine; Ac = acetate), have been synthesized and their crystal structures determined. Compound 1 is monoclinic, P2(1)/n, a = 8.4899(11), b = 23.169(3), c = 10.9224(14) Å, β = 7.493(2)°, V = 2049.1(5) Å3, Z = 4, R = 0.037 for 4552 N i independent reflections and for 1619 N o observed [I>2σ(I) ] reflections. Compound 1 is monomeric, with a heptacoordinate cadmium ion bonded to two bidentate acetate groups and a tridentate tpy; two hydration water molecules complete the formula unit. Compound 2 is triclinic, , a = 10.8412(7), b = 14.4051(9), c = 15.5354(10) Å, α = 82.889(1), β = 77.953(1), γ = 85.805(1)°, V = 2351.73(3) Å3, Z = 2, R = 0.044, N i = 9014, N o = 6837. The binuclear structure has two independent Cd atoms per asymmetric unit, two bbip tridentate ligands (one attached to each cation) and three acetate groups, displaying a range of different coordination features.

Mercury(II) halide complexes with N-donor organic ligands: crystal and molecular structure of HgI2R, R = 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, bipyridine

AbstractThe synthesis, characterization and single crystal X-ray structure of three compounds of general formula HgI2R (R = phen[1], dmph [2] and bpy[3]) are presented. The crystal data for the three compounds are: [1], triclinic, space group P

X-Ray Study of Two Novel Nickel(II)–Thiosulfate Compounds

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X-Ray Study of Two Nickel Complexes Stabilized by the Pentathionate Anion

(#2) a = 7.902(2), b = 9.479(2), c = 10.002(2) Å, α = 91.45(2), β = 111.34(2), γ = 100.82(2)° [2]: monoclinic, space group C2/c (#15) a = 15.670(3), b = 11.640(2), c = 9.730(2) Å, β = 114.57(3)° [3]: triclinic, space group P1¯ (#2) a = 9.472(1), b = 9.507(1), c = 9.023(1) Å, α = 98.46(1), β = 102.89(1), γ = 119.62(1)°. Compounds [1] and [2] are monomers, with highly distorted tetrahedral environments around Hg. In [3], instead, there is a significant intermolecular I···Hg interaction leading to the formation of softly bound dimers linking two pentacoordinated cations. The structure is compared with related ones in the literature.

X-Ray Study of Two ZnII and CdII 2,2'-Dipyridylamine Thiosulfate Compounds

The crystal structures of two transition-metal complexes with different dinitrogenated bases, and the unusual peroxodisulfate anion are presented, Cd(S2O8)(bpy)2·H2O (1) and Hg2(S2O8)(terpy)2(acet)2 (2) (where bpy represents 2,2′-bipyridine, terpy represents 2,2′,2′′-terpyridine, and acet represents acetate). In both structures, though in different ways, the peroxodisulfate group acts as a bridge, giving rise to polymeric linear chains. To our knowledge these are the first structures reported wherein the anion displays such behaviour. The cadmium compound crystallizes with one water molecule of hydration, which intervenes in medium-strength H-bonds, stabilizing the structure. The mercury complex is built up of similar, though independent, chains displaying double Hg–O–Hg bridges spanning Hg···Hg distances of 4.214(1) and 3.911(1) A. The inter-chain link is achieved through weak C–H···O contacts. Compound (1) is triclinic P1–; a 7.213(3), b 9.841(6), c16.371(5) A; α 82.94(4), β 82.31(3), γ 86.32(4)˚; V 1141.6(9) A3; Z 2; conventional R (on F) being 0.0315 for 4019 No observed reflections (I> 2σ(I)). Compound (2) is also triclinic P1–; a 10.653(2), b 12.195(3), c 14.641(3) A; α 88.295(19), β 83.553(18), γ 73.921(19)˚; V 1816.0(7) A3; Z 2; R0.0498; No 6179.

Two hydrates of 2,6-bis­(1H-benzimidazol-2-yl)­pyridine

Two novel nickel thiosulfate complexes have been prepared and their crystal structures determined: NiS2O3(dmph)(H2O)·H2O·CH3OH (1) (dmph = 2,9-dimethyl-1,10-phenanthroline), which to our knowledge is the first pentacoordinated nickel thiosulfate complex described so far, and NiS2O3(dmph) (2), a hexacoordinated complex which displays a thiosulfate binding mode with no precedents in the literature, viz. bridging solely through oxygen. Compound (1) is monoclinic, C2/c, a 26.269(5), b 7.641(3), c 18.381(3) A, β 97.00(2)˚, V 3662(2) A 3 ,Z 8, conventional R (on F) being 0.049 for 2217 No observed reflections (I > 2σ(I)). Compound (2) is also monoclinic, P21/n, a 11.108(2), b 10.955(2), c 11.666(2) A, β 103.32(3)˚, V 1381.4(5) A 3 , Z 4, R 0.036, No 2497.

Tetraaqua(2,2'-bipyridyl-N,N')cadmium(II) sulfate and catena-poly[[[diaqua(2,2'-bipyridyl-N,N')cadmium(II)]-μ-(sulfato-O:O')] hydrate]

The crystal structures of two unreported CdII complexes with different dinitrogenated bases and the unusual peroxodisulfate anion (pds, S2O8 2–) are presented: Cd(pds)(phen)2(H2O)·H2O and Cd(pds)(dmph)2 (phen = 1,10- phenanthroline; dmph = 2,9-dimethyl-1,10-phenanthroline). Both compounds are monomeric. In the first, the anion acts as a monodentate ligand, as in all previously reported structures where it binds to a cation, while in the second it displays novel chelate behaviour. Both structures are stabilized by hydrogen-bonding networks, with mediumstrength interactions mediated by aqua and hydration water molecules in the first case and much weaker ones provided by C–H…O contacts in the second. Compound (1) is triclinic, P1–, a 8.745(3), b 9.260(5), c 17.564(3) A, α 96.80(2), β 101.581(3), γ 105.97(3)˚, V 1316.6(9) A3, Z 2, R 0.044, No 4384. Compound (2) is monoclinic, Cc, a 22.233(12), b 9.566(5), c16.017(8) A, β 123.78(3)˚, V2831(3) A3, Z 4, R 0.024, No 2363.