Like LaI2 and LaI, LaH2 is probably an electride compound.Due to the large ionic radius and great electropositivity of La3+, there is not much covalent contribution to its bonding and hence it has a limited coordination chemistry, like yttrium and the other lanthanides. Lanthanum oxalate does not dissolve very much in alkali-metal oxalate solutions, and [La(acac)3(H2O)2] decomposes around 500 °C. Oxygen is the most common donor atom in lanthanum complexes, which are mostly ionic and often have high coordination numbers over 6: 8 is the most characteristic, forming square antiprismatic and dodecadeltahedral structures. These high-coordinate species, reaching up to coordination number 12 with the use of chelating ligands such as in La2(SO4)3·9H2O, often have a low degree of symmetry because of stereo-chemical factors.Lanthanum chemistry tends not to involve π bonding due to the electron configuration of the element: thus its organometallic chemistry is quite limited. The best characterized organolanthanum compounds are the cyclopentadienyl complex La(C5H5)3, which is produced by reacting anhydrous LaCl3 with NaC5H5 in tetrahydrofuran, and its methyl-substituted derivatives. History
In 1751, the Swedish mineralogist Axel Fredrik Cronstedt discovered a heavy mineral from the mine at Bastnäs, later named cerite. Thirty years later, the fifteen-year-old Wilhelm Hisinger, from the family owning the mine, sent a sample of it to Carl Scheele, who did not find any new elements within.
Immunohistochemical staining for antibodies against T. whipplei has been used to detect the organism in a variety of tissues, and a polymerase chain reaction-based assay is also available,  which can be confirmatory if performed on blood, vitreous fluid, synovial fluid, heart valves, or cerebrospinal fluid. PCR of saliva, gastric or intestinal fluid, and stool specimens is highly sensitive, but not specific enough, indicating that healthy individuals can also harbor the causative bacterium without the manifestation of Whipples disease, but that a negative PCR is most likely indicative of a healthy individual. Treatment
Treatment is with penicillin, ampicillin, tetracycline, or co-trimoxazole for one to two years. Any treatment lasting less than a year has a relapse rate around 40%. Expert opinion as of 2007 is that Whipples disease should be treated with doxycycline with hydroxychloroquine for 12 to 18 months. Sulfonamides (sulfadiazine or sulfamethoxazole) may be added for treatment of neurological symptoms. Epidemiology
The disease is regarded as extremely rare, with an incidence (new number of cases per year) of one case per million people. The patients are predominantly male (86% in a survey of American patients), although in some countries, the rate of women receiving a diagnosis of Whipples disease has increased in recent years. It occurs predominantly in those of Caucasian ethnicity, suggesting a genetic predisposition in that population. T. whipplei appears to be an environmental organism that is commonly present in the gastrointestinal tract, but remains asymptomatic. Several lines of evidence suggest that some defect—inherited or acquired—in immunity is required for it to become pathogenic.