The crystal and molecular structures of two tetracyclines, anhydrotetracycline hydrobromide ( I ) and 6-demethyl-7chlorotetracycline hydrochloride (11) have been determined by x-ray diffraction techniques. Aromatization of the C ring of tetracyclines gives I but also destroys any useful therapeutic value. In contrast I I has excellent antibacterial properties. The crystals of I monohydrate are orthorhombic, space group P212121 with unit cell dimensions of a = 19.562 (2). b = 16.586 (2), and c = 6.796 (2) A. Crystals of I I as the trihydrate are monoclinic, space group P21, with cell dimensions of a = 9.219 ( I ) , b = 11.634 ( I ) , c = I 1.240 ( I ) A; /3 = 102.39 (4)". Although the conformation of I is similar to that of 11, significant differ-
Reaction of tri-t-butylphosphine with nickel(i1) bromide in alcoholic solution yields green [But3PH] [(But,P) NiBr,]. Conductivity, magnetic-susceptibility, and electronic spectral measurements, and X-ray single-crystal analysis indicated the structure to be the same in solution as in the solid state. Crystals are monoclinic, space group Cc, with cell dimensions a = 24.069( 3), b = 13.896(4), c = 18.739(2) 8, p = 148.91 (I)', Z = 4. The structure w a s solved by conventional heavy-atom methods and refined to R 0.088 for 1839 observed reflexions. Structure1 data for the paramagnetic anion, which has nearly C,, symmetry (excluding the butyl groups), particularly reflezt the bulkiness of the But3P ligand; mean dimensions: Br-Ni-Br 108.7". P-C 2.02(10) and Ni-Br 2.38(2) 8, and a Ni-P bond length of 2.48(1) 8. The P(2)-H bond of the cation lies near the pseudo C3 axis of the anion so that Ni * * * P(2) is 4.48 8, with P(2) * Br 4.27-4.31 8 . These interion contacts indicate strong ion-pairing interaction in the solid-state structure. The calculated Ni-PBut, cone angle is 180 f 2' .EXTENSIVE investigations 1, on nickel@) phosphine complexes of the type [Ni(PR,),X,] have been principally concerned with the various factors which influence the adoption of a planar (diamagnetic) or a tetrahedral
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