Some studies in chromium(II) and vanadium(II) chemistry.

Many new compounds of chromium (II), vanadium(II) and iron(II) have been prepared under anaerobic conditions, and their properties investigated by spectroscopic, magnetic and X-ray diffraction techniques, also carried out in the absence of air. An effective method of sealing air-sensitive single crystals in Lindemann capillaries, without the use of a nitrogen box, has been developed from a published apparatus. The new compounds of chromium(II) were [H[2]pipz] [CrCl[4](OH[2])[2] and [H[2]pipz][2] [CrBr[6]]. 2H[2]O where H[2]pipz is doubly protonated piperazine; M[2]CrCl[4] where M=H2[pipz, NPhH[3], o-CH[3]C[6]H[4]NH[3], NH[3](CH[2])[3]H[3]N and NEt[3]H; [N[2]H[6]][2] [CrCl[6]], M[2]CrBr[4] where M=NMe[2]H[2], NPhH[3], n-C[3]H[7]NH[3], n-C[5]H[11]NH[3], n-C[8]H[17]NH[3], and n-C[12]H[25]NH[3]; [H[2]pipz][2][CrBr[6]]; and [C(NH[2])[3]][2][CrBr[4]] 2MeCO[2]H. The dihydrates, hydrazinium hexabromochrornate(II) and guanidinium tetrabromochromate(II) diacetic acid, are magnetically normal while the anhydrous compounds are ferromagnetic except for the piperazinium and triethylammonium tetrachlorochromates(II), hydrazinium hexachlorochromate(II) , and the dimethylammonium and anilinium tetrabromochromates(II) which are antiferromagnetic. From spectral results it has been found that in all compounds the chromium(II) ion is situated in a distorted octahedral environment. Thus, in agreement with the magnetic results, polymeric structures have been assigned to all compounds except the dihydrates which are mononuclear. The polymeric nature of some compounds has been deduced by comparison of their powder photographs with those of corresponding copper(II) compounds of known structures. The crystal structure of a typical ferromagnetic compound [dienH[3]] [CrCl[5]] is reported. A new series of compounds of chromium(II) and iron(II) with hexamethylphosphoramide: CrX[2]. 2HMPA where X=Cl, Br, Cr(BF[4])[2]. 4HMPA and FeX[2].2HMPA where X=Br, I&Fe(BF[4])[2]. 4HMPA has been prepared. These compounds have also been investigated by spectroscopic and magnetic techniques. Chromium(II) compounds are high-spin octahedral while iron(II) compounds are tetrahedral. The structures of iron(II) compounds have been confirmed by Mossbauer spectroscopy, and the isomer shifts are among the highest so far reported for tetrahedral iron(II) compounds. Vanadium(II) chemistry is little known and a series of new complexes of the type, M[2]VBr[4] where M=NPhH[3], NEtH[3], NMe[2]H[2], n-C[8]H[17]NH[3], C(NH[2])[3] has been prepared. The complexes [H[2]pipz][2] [VBr[6]], CsVBr[3] and Cs[2]VCl[4] have also been obtained. The vanadium(II) compounds, unlike many anhydrous tetrabromochromates(II), show antiferromagnetic rather than ferromagnetic behaviour. They probably have polymeric structures in which the vanadium(Il) ion is six co-ordinate