Jaime Casabó

Closely related macrocyclic and acyclic tridentate, pyridine derivatives, containing sulphur, and their complexes. Crystal structures of {dichloro-3,10-dithia-16-azabicyclo[l0.3.1]hexadeca-1(16),12,14-triene}copper(II) and [2,6-bis(ethyithiomethyl)pyridine]dichlorocopper(II)

Four closely related, tridentate, pyridine derivatives, containing sulphur, three of them macrocyclic, 3,10-dithia-16-azabicyclo[10.3.1]hexadeca-1 (16),12,14-triene (L1), 3,8- dithia-14-azabicyclo-[8.3.1]tetradeca-1 (14),10,12-triene (L2), 3,7-dithia-13- azabicyclo[7.3.1]trideca-1 (13),9,11 -triene(L3), and one acyclic, 2,6-bis(ethylthiomethyl)pyridine (L4), have been prepared. All contain the same co-ordination elements (NS2) structurally placed in the same fashion, sulphur–methylene–pyridine–methylene–sulphur. Copper complexes of all the ligands and the palladium complex of L1 have also been prepared. The molecular structures of the complexes [CuL1Cl2] and [CuL4Cl2] are described. The latter is monoclinic, space group I2/c, with a= 14.669(6), b= 7.418(4), c= 29.412(8)A, β= 103.03(4)°, and Z= 8. The former is monoclinic, space group P2/a with a= 14.677(9), b= 7.555(1), c= 29.969(4)A, β= 101.00(2)°, and Z= 8. The different reactivity of the macrocycle ligand L1 with respect to that of L4 is discussed.

Ordered bimetallic ferromagnets of chromium(III): [Cr(NH3)6][Cr(CN)6], [Cr(H2O)(NH3)5][Cr(CN)6], and trans-[Cr(en)2(H2O)2]trans-[Cr(en)2(OH)F]2(CIO4)5·2H2O

Abstract The magnetic bahavior of the isomorphous compounds [Cr(NH 3 ) 6 ][Cr(CN) 6 ] and [Cr(H 2 O)(NH 3 ) 5 ][Cr(CN) 6 ] has been studied by means of zero-field susceptibility measurements. The materials order ferromagnetically at 0.60 and 0.38K, respectively. The compounds behave as examples of the ferromagnetic ( S =3/2) Heisenberg body-center-cubic lattice. The susceptibilities have been analyzed and compared to the Pade approximants of the high-temperature series expansion for this model, a remarkably good fit being obtained with exchange constants 0.042 and 0.022 K, respectively. Another bimetallic substance, trans -[Cr(en) 2 (H 2 O) 2 ] trans -[Cr(en) 2 (OH)F] 2 (CIO 4 ) 5 ·2H 2 O, with a dominant Heisenberg ferromagnetic interaction J / k B =0.122 K in one dimension, orders antiferromagnetically at 0.14 K due to a weaker interchain interaction with exchange constant z ′ J ′/ k B =-0.019 K . The three sets of measurements have been carried out on powdered samples for which demagnetization effects are important. The exchange interactions are remarkably weak for such concentrated magnetic materials, yet they are stronger than those found in a number of other such Cr/Cr compounds.

New low-temperature ferrimagnets

The research in Zaragoza and Barcelona has been supported respectively by Grants 3380/83 and 409/84, from the Comision Asesora de Investigacion Cientifica y Tecnica of the Ministerio de Educacion y Ciencia. The research in Chicago has been supported by Grant DMR-85 15224 fromthe SolidState Chemistry Program, Division of Materials Research of the National Science Foundation. Cooperative work has been supported by Grant CCB-8504/001 from the American—Spain Joint Committee for Technical and Scientific Cooperation. One of us (MCM) wants also to acknowledge a postgraduate student fellowship fromthe Ministerio de Educacion y Ciencia.

Synthesis and structural study of complexes of nickel(II) with 4-amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro-l,2,4-tria-zine

Abstract Bis-ligand nickel(II) complexes with 4-amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro-1,2,4-tria-zine have been prepared by reaction between the triazine and the corresponding nickel salt in the 2:1 molar ratio, respectively. Conductance, magnetic, and infrared and visible spectroscopy data have been used for structural assignments. Pseudooctahedral structures are proposed for the complexes with the triazine molecule acting either as a monodentate N-donor ligand or a bidentate N- and S-donor ligand. An X-ray structural determination carried out with [Ni(triazine)2(H2O)2](ClO4)2 shows that the triazine acts as a bidentate ligand via the 4-amino nitrogen and the 3-thioxo sulfur (Ni-S=2.377 A; Ni-N=2.079 A) and the two H2O molecules complete the hexacoordination of nickel(II) (Ni-O=2.135 A).

Single‐crystal ac susceptibility measurements on [Co(NH3)6][CuCl5], a 3D, S=1/2 Heisenberg antiferromagnet

Single‐crystal ac magnetic susceptibilities of [Co(NH3)6][CuCl5] along the three crystallographic axes in the temperature range from 1.1 to 90 K are presented. The magnetic behavior is characteristic of a three‐dimensional antiferromagnet, its ordering temperature being at Tc=3.8 K. Susceptibilty data can be fit to a Heisenberg S=1/2 simple cubic model using high‐temperature series expansions extrapolated with Pade approximants. Good agreement is found for an exchange constant J/kB=−3.13 K and values of g factor ga=2.09, gb=gc =2.04, a,b, and c being the crystallographic axes. This result makes [Co(NH3)6][CuCl5] one of the few examples of a 3D antiferromagnetic Heisenberg S=1/2 model. The magnetic behavior below Tc indicates the existence of crystallographic domains due to the structural transition from cubic to tetragonal symmetry that the system has at about 280 K.

Vibrational spectra and normal coordinate analysis of two isotopomers of the thiosulfate ion

Abstract The Raman spectra of 18 O-thiosulfate ion (S 1 O −2 3 ) in H 1 18 O solution and the IR spectrum of 18 O-sodium thiosulfate in the solid have been obtained. Normal Coordinate calculations fitting all the fundamental wavenumbers of both 16 O and 18 O isotopomers have been carried out transferring the GVFF of the sulfate ion as the starting point and employing a symmetry force field for the least-squares adjustment procedure. A comparison of the results is made with the known force fields for several sulfur compounds.

Bimetallic derivatives of the [M(en)3]3+ ion (M=Cr and Co): A series of compounds with unusual magnetic and structural properties (abstract)

The crystal structure and magnetic susceptibility of a series of [M(en)3]3+ (M=Cr or Co) derivatives are described. In particular, the crystalline structures of (1) [Cr(en)3]3[FeCl6]Cl6⋅H2O, (2) [Co(en)3]3[FeCl6]Cl6⋅H2O, and (3) [Cr(en)3][FeCl6]⋅11H2O are reported. Structural data, in A, for these compounds are as follows: (1) space group R3, a=15.447(4), c=21.060(6), Z=3; (2) space group R3, a=15.346(3), c=20.880(5), Z=3; (3) space group P3c1, a=11.654(3), c=15.508(4), Z=2. The main structural feature of the first two isomorphous materials is that they consist of a three‐dimensional network of triangular antiprisms formed by the [M(en)3]3+ (M=Cr or Co) ions and connected with each other by sharing corners. An [FeCl6]3− ion is placed at the center of each antiprism. Compound (3) contains a sc arrangement of [Cr(en)3]3+ and [FeCl6]3− octahedra. In addition, the magnetic susceptibilities of the above‐mentioned isomorphous compounds and of [M(en)3][FeCl6] (M=Cr and Co) and [Cr(en)3][InCl6] are reported. Whil...

General quadratic force field of the sulfate ion and the relationships between different force fields in tetrahedral molecules

Abstract The General Quadratic Force Field (GQFF) for the sulfate ion SO42− is obtained fitting all the vibrational fundamental wavenumbers of the totally symmetric 16O and 18O isotopomers. The approximations employed in previously reported force fields are discussed. The effects are studied of the redundancy condition on the value of the GQFF force constants expressed both in valence and Urey—Bradley coordinates, and on the relationships between both force fields for tetrahedral XY4 molecules. The a1 and e mode anharmonicity constants and harmonic wavenumbers are obtained.