This dissertation focuses on the exploratory synthesis of compounds that contain
R6ZI12 (R= Ce, Gd, Er; Z=Mn, Fe, Co, C2) clusters with the goal of finding magnetically
interesting compounds. Several new compounds were made via high temperature, solid
state methods and structurally characterized using x-ray diffraction. Compounds that
contain isolated clusters were studied in order to understand the magnetic coupling
between lanthanide atoms.
The exploration of transition metal centered clusters resulted in the discovery of
two new structure types, CsR(R6CoI12)2 (R=Gd and Er) and (CeI)0.26(Ce6MnI9)2. The xray
crystal structure of CsEr(Er6CoI12)2 was solved in the Pa3 – space group with the cell
length 18.063(2) Å at 250K (Z = 4, R1 [I>2σ(I)] = 0.0459). (CeI)0.26(Ce6MnI9)2 was
made by combining KI, CeI3, MnI2 and Ce metal and heating to 850°C for 500 hrs. The
single crystal x-ray structure for (CeI)0.26(Ce6MnI9)2 was solved in the trigonal, P3 – space
group with lattice parameters of a = 11.695(1) Å c = 10.8591(2) Å (Z = 2, R1 [I>2σ(I)] =
0.0895).
The magnetic susceptibilities of hexanuclear gadolinium clusters in the
compounds Gd(Gd6ZI12) (Z = Co, Fe or Mn), CaxGd1-x(Gd6MnI12) and CsGd(Gd6CoI12)2
are reported. The single-crystal structure of Gd(Gd6CoI12) and CaxGd1-x(Gd6MnI12) are
reported here as well. The compound with a closed shell of cluster bonding electrons, Gd(Gd6CoI12), exhibits the effects of antiferromagnetic coupling over the entire range of
temperatures measured (4 - 300 K). Clusters with unpaired, delocalized cluster bonding
electrons (CBEs) exhibit enhanced susceptibilities consistent with strong ferromagnetic
coupling, except at lower temperatures (less than 30 K) where intercluster
antiferromagnetic coupling suppresses the susceptibilities.
Four new compounds containing Gd6C2 clusters have been found: Gd6C2I11,
Gd(Gd6C2I12), CsGd(Gd6C2I12)2 and Cs(Gd6C2I12). Gd6C2I11 and Cs(Gd6C2I12)
crystallized in the P1 space group while Gd(Gd6C2I12) and CsGd(Gd6C2I12)2 crystallized
in the R3 and Pa3 space groups respectively. The magnetic susceptibility data for
Cs(Gd6C2I12) indicate strong intracluster ferromagnetic coupling, but antiferromagnetic
coupling suppresses the susceptibility below 150 K. DFT calculations on CsGd6C2I12
and molecular models indicate that the magnetic coupling between the basal Gd atoms is
stronger than the magnetic coupling involving the axial Gd atoms in the distorted
clusters.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-3128 |
| Date | 15 May 2009 |
| Creators | Sweet, Lucas Edward |
| Contributors | Hughbanks, Timothy |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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