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Complexes of protonated hexacyclen ( C I Z H~~N~) with NO,-, CI-, C104-, and Br-are found by conductometry and pH potentiometry to have the compositions H4LX3+ (where L = hexacyclen, X = anion). Formation constants with these anions at 25 OC are determined by pH potentiometry. A H and AS for the NO3-and C1-complexes as well as the acid dissociation of H4L4+ are derived from the temperature-dependent equilibrium constants. The results indicate that although the NO,complex is more stable the CIapparently forms stronger bonds to H4L4+. Bonding in these complexes is discussed in terms of ionic H bonding and solvent ordering effects. X-ray crystallographic study of H4L(NO3),Cl2.2H20 supports the proposed bonding mechanism.The selective binding of inorganic and organic anions by macrocyclic ligands is a recently reported phenomenon.'s2 In many cases the host ligand species feature protonated amine groups of the type (RR'R''N+H), (where y > 2), and it has generally been assumed that electrostatic and ionic hydrogen-bonding interactions provide the bonding forces in these complexes. The shape and size of the macrocycle cavity are presumed to influence the bonding interactions and so to account for selectivity.In the present work we wish to elucidate the factors which influence these complexation reactions by means of a study of the cyclic hexamine 1,4,7,10,13,16-hexaazacyclooctadecane (hexacyclen, L) complexes of nitrate, perchlorate, chloride, and bromide ions. The study utilizes pH-potentiometric and conductometric measurements designed to determine the nature, formation constants, and thermodynamic properties of the complexes. Also an X-ray crystallographic determination provides information about structure and bonding. Experimental MethodsMaterials. All chemical reagents and solutions were purified or were reagent grade.Hexacyclen hemihydrate, C12H,oN6-0.5H,0, was prepared from the commercial trisulfate salt purchased from either Aldrich or Parish Chemical Co. Weighed portions of the salt were used to prepared 0.5 M solutions of the polyamine and these were treated with an equivalent amount of solid BaCO,. After the resultant slurry was mixed for 2 h at 80 OC, the filtered hot solution was dried with a rotary evaporator. The waxy product purified by vacuum sublimation yielded pure white crystalline hexacyclen-hemihydrate (L.0.5H20): NMR HN,S 2.02 (l), H C ,~, 2.70 (4); mass spectrum, m / e parent peak 259. Anal. Calcd C, 53.70; H, 11.64; N, 31.68. Found: C, 53.20; H, 11.29; N, 31.54. Hexacyclen hexahydrochloride and hexahydrogennitrate salts were prepared directly from the concentrated filtrate solution above by addition of a large excess of the appropriate acid. The product was recrystallized from a fresh portion of the 6 M acid and then air-dried. The crystals were Ci,H3N6.6HCI.3H20 (H&C16.3H20) and Ci2H30N6.6H-Registry No. L, 296-35-5; L.6HC1, 58105-91-2; L.6HN03, 81294-Supplementary Material Available: Table of thermal parameters (1 page). Ordering information is given on any current masthead page.17-9; L.2HNO...

The mitotic spindle inhibitor colchicine, C22H25NO6, crystallizes as a dihydrate in space group P21, a = 17.08, b = 10.70, c = 13.88 A, fl = 117.9 °, Z = 4(C22H25NO6.2H20)/unit cell. The crystal structure was solved by a multiple-solution direct method in which unknown starting phases ~l are represented using 'magic integers': tp I = mix. An appropriate choice of integers m I and sampling of the variable x allows a drastic reduction in computing time and a great increase in structure-solving capability compared to the widely used method in which all unknown phases are permuted among the four values 45, 135, 225, 315 °. The crystal structure of colchicine dihydrate was refined by least squares to R = 0.052 for 2322 observed X-ray reflections. The two independent colchicine molecules have very similar conformations in the crystal. The troponoid rings have alternating bond lengths, and are not precisely planar. These rings make dihedral angles with the planar benzene rings of 53 ° in one molecule of eolchicine, 51 o in the other. The four independent water molecules are all found in a distinct region in the crystal, which is held together by a complex hydrogenbond network. Two methoxy-group O atoms of colchicine act as hydrogen-bond acceptors, the one on the troponoid ring participating in a bifurcated hydrogen bond.Colchicine (I), the principal active substance of the autumn crocus, has a remarkable range of biological effects. The most studied of these is its arrest of mitosis, believed to result from the specific strong binding of eolehicine to the protein tubulin, preventing the assembly of tubulin into mierotubules which form the mitotic spindle (Soifer, 1975). Colchicine is also capable of relieving the pain of gout (for which it has been used since ancient times), of inducing polyploidy * Present address:

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