The octaamino cryptand, L2, obtained by tetrahydroborate reduction of the [2+3] condensation product of tris(2-ethy1amino)amine with terephthalaldehyde, acts as a host for pairs of protons or first-series transition-metal cations. An X-ray crystallographic structure determination of [ H,L2I4+ reveals a pair of protons held at opposite ends of the molecule by strong intramolecular hydrogen bonding of each proton to two of the amino nitrogen atoms. Pairs of transition-metal cations co-ordinated to the amino N-donors accommodate mono-and tri-atomic bridging ligands, such as OHor imidazolate, generating weak to moderate antiferromagnetic interaction. Dicopper( 11) p-azido complexes have been prepared where the combination of a large zero-field splitting in t h e ESR spectrum and a near Curie-law dependence of -3.84 (t) 360 183 7.&7.5 (m) 8.40 (s) -3.84 (br s) 183 6.67 (s) 3.53 (br s) 1.55 (br s) 2.53 (br s) L2 CD,CI, 360 298 6.89 (s, 4 H) 3.67 (s, 4 H) 2.0 (br s, 2 H) 2.65 (t, 4 H) CH4L21CCF3S031, (CD,),SO 400 298 7.45 (s, 4 H) 2.80 (s, 4 H) 8.65 (br s) 4.22 (s, 4 H) [Ag,LZ][CF,S03]2 CD3CN 500 298 7.12 (s, 4 H) 2.78 (4 H) 2.9 (br) 3.78' (4 H) 338 7.12 (s, 4 H) 2.80 (4 H) 2.92 3.78' (4 H) [Cu2LZ][CF3S03], CD3CN 500 338 6.89 (4 H) 2.80 2.90 3.90, 3.65 Chemical shifts 6 relative to SiMe,. Overlapped. Assigned on the basis of comparison with the copper(1) spectrum. 323 7.22 (s) 2.90(br s) --3.97 (s) 298 2.80 (s) 2.85 (m) 3.95 (d), 3.53 (1) H E 2.83 (br s) 3.4, 2.1 (br) 2.65 (br s) 2.81 (t, 4 H) 2.61 (t, 4 H) 2.71 (t) 2.95 3.00 (4 H) 3.28, 2.95 3.35 (br t), 2.95 (d) Table 2 Torsion angles (")in [H,L2][CF,S0,], C( 3 1 )-C( 30)-N( 1 )-C( 10) 128.9 C(3O)-N( 1)-C( 10)-C( 11) C( 3 1 )-C( 30)-N( 1 j C ( 23 *) -58.4 -99.2 C(30)-N( 1 )-C(23*)-C(22*) 167.0 C(ll)--C(lO)-N(l)-C(23*) 175.0 C( 10)-N( l)-C(23*)-C(22*) -66.5 N( 1 )-C( 10)-C( 1 1)-N( 12) C( 1 0)-C( 1 1 )-N( 12)-C( 1 3) C( 1 1 )-N( 12)-C( 13)-C( 14) N(12)-C(13)-C(14)-C(15) C( 13)-C( 14)-C( 15)-C( 16) C( 16)-C( 17)-C(20)-N(2 1) C( 20)-N( 2 1 )-C( 22)-C(23) C( 17)-C(20)-N(21)-C(22) N(21)4'(22)-C(23)-N(l*) N(l)-C(3O)-C(31)-N(32) C( 30)-C(3 1 )-N(32)-C(3 3) C(3 1 )-N(32)-C(33)-C(34) N(32)-C(33)-C(34)-C(35) * Symmetry operation +x , y , 1z.-50.1 -167.3 -172.9 115.7 173.4 -112.4 178.4 -153.2 -66.9 -76.9 178.6 106.9 -49.6 L1 *6H,O 70.2 -118.1 -178.6 2.6 -177.1

2-Phenylethnylpyridine reacted with dimethyl acetylenedicarboxylate (DMAD) in the presence of a proton source such as an alcohol to give indolizines having methoxycarbonyl groups at the 2-or 2,3-positions in high yields.

No abstract

A hexaimino cryptand L1 has been obtained by condensation of tris(2-aminoethy1)amine with terephthalaldehyde without template. An X-ray crystal structure determination has been carried out on L1-6H,0 and shows a divergent conformation for the macrocycle in which all six imine nitrogen atoms form hydrogen bonds to water molecules positioned outside the macrobicycle. In the presence of Cu' and Ag' a convergent form of the macrocycle which allows encapsulation of a pair of cations is adopted. Tetra-and di-thiocyanato derivatives [M,L'(NCS),(CIO,),] ( x = 2 or 4, y = 2 or 0) have also been prepared with M = Co, Ni or Cu. In these molecules the thiocyanate ligand adopts a terminal rather than bridging mode. Molecular mechanics and molecular dynamics calculations indicate that at least four different conformations of L1 are likely to be found. Conformational preferences of L' have been established in the gas phase, in water and in the presence of metal ions.

THE method described by Blom and Edelhausenl for determining carbon dioxide, involving absorption in acetone or pyridine followed by titration with sodium methoxide in methanolpyridine solution with thymol blue as indicator, has several disadvantages. These include the obnoxious nature of pyridine, the necessity for purifying it before use2 and the inflammability of acetone, particularly since it may be used in the vicinity of combustion furnaces. Moreover, the high proportion of methanol in the titrant interferes with the sharpness of the end-point because of its acidic behaviour in non-aqueous media.Fritz3 has discussed the merits of other compounds, such as formdimethylamide, ethylenediamine and n-butylamine, as solvents for acidic substances in general, and concludes that formdimethylamide is an excellent solvent for many acids and for their sodium and potassium salts, is suitable for use in titrations with visual indicators and is superior to either ethylenediamine or n-butylamine.Fritz and Keen4 have proposed alkaline methoxide in benzenemethanol solution as titrant for acids dissolved in non-aqueous media. The amount of methanol is kept to the minimum required to give a homogeneous solution and, since potassium methoxide requires less methanol for this, it gives sharper end-points than sodium methoxide.It is commercially available of sufficient purity to require no further treatment and is much less inflammable than acetone. The use of potassium methoxide in benzenemethanol as titrant and the replacement of thymol blue by the one-colour indicator, thymolphthalein, has considerably improved the

Some of the factors, including choice of absorbent, indicator and titrant, that affect the determination of carbon dioxide by non-aqueous titrimetry are examined experimentally. The results of this examination are used to give a procedure that is recommended for the determination of milligram amounts of carbon dioxide.The method involves absorption of the carbon dioxide in a 5 per cent. v/v solution of ethanolamine in formdimethylamide, followed by titration with standard tetrabutyl ammonium hydroxide in benzenemethanol solution t o a visual end-point with thymolphthalein indicator. EXPERIMENTAL ABSORPTION AND RETENTION OF CARBON DIOXIDE-The reactions of a number of amines with carbon dioxide were examined by passing the gas sequentially into undiluted samples of diethylamine, diamino-ethane, butylamine, benzylamine, cyclohexylamine and ethanolamine.

Much of the current interest in macrocyclic coordination chemistry stems from the hope that unusual geometric relationships imposed on the metal ions by the macrocyclic donor set may be transformed into unusual bonding situations. In the particular case of binuclear macrocyclic complexes, attention is directed a t the bridgingligand coordinated between metal ions held in the macrocyclic cavity. Where this ligand is constrained within a restricted cavity, there is the hope of observing unusual bridging modes associated perhaps with enhanced ligand reactivity, thus modelling the role of substrate in an enzyme-catalyzed reaction. In such situations there is also interest in the degree of interaction between paramagnetic centers, which in the limit of strong interaction could lead to the binuclear pair acting as one unit in multielectron redox processes. There are many metalloproteins whose function is associated with the occurrence of metal centers in pairs. The atoms in the natural bimetallic site may be identical as, for example, the Cu---Cu site in hemocyanin or the Fe---Fe site in hemerythrin, or they may be different as in the Cu---Zn pair in superoxide dismutase or the Cu --Fe pair in cytochrome c-oxidase ( I ) .Despite the biological importance of the binuclear site, and research emphasis focusing on the biomimetic approach, few teaching experiments are available that involve the synthesis and characterization of binuclear complexes. The exercises that are described in this paper involve the use of a macrocyclic ligand designed to hold a pair of metal ions in fairly close (4-5 A) proximity; the restrictions imposed by the coordination site are responsible for the unusual mode of coordination of a small hridging substrate, and for the generation of heterobinuclear complexes.These features of the coordination chemistry of the easily prepared (2) macrocyclic ligand L1 contribute to a useful open-ended project experiment for the inorganic teaching laboratory a t or above second-year university level. Among other things, the experiment illustrates the way in which use of the large ion Pb2+ directs the Schiff-base condensation reaction toward formation of a "double"macrocycle by [2 + 21 condensation (i.e., using 2 mol of diamine and 2 mol of dicarbonyl) under mild conditions and in high yield. I t also illustrates the transmetallation process whereby Pb2+ is replaced by a smaller ion (i.e., the series of first transition series ions Mn(I1)-Cu(I1)).The main results of the experiment fall under three headings:(1) The product of template synthesis, Pb2L1(NCSk, contains the rare "short" N-only thiocyanate bridge, whose presence is easily demonstrated by IR spectroscopy. (2) Transmetallation of PbzL1(NCS)~ with Co(I1) or Cu(I1) salts yields hornobinuclear products. Magnetic and ESR measurements reveal spin equilibrium in the dicobalt and weak antiferromagnetie interaction in the dicopper complex. (3) Transmetallation of Ph2L1(NCS)~ with Mn(II), Fe(II), or Ni(I1) salts yields heterobinuclear complexes.The experiment will...

Cascade Complexes of an Octaaza Cryptand: Coordinated Azide with Linear M-NNN-M Geometry. -The title ligand (I), prepared by reduction of the known corresponding hexaimino cryptand, acts as a host for pairs of protons or transition-metal cations. The increased flexibility implicated by the six saturated C-N links permits incorporation of a range of bridging ligands such as OH-, imidazolate or azide, so that the dependence of magnetic interaction on the nature of the bridge can be studied. The results reveal a near linear alignment of the M-NNN-M assembly. -(DREW, M. G. B.; HUNTER, J.; MARRS, D. J.; NELSON, J.; HARDING, C.; J.