Hexacyclen complexes of inorganic anions: bonding forces, structure, and selectivity

Abstract

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...

A new hexaaminomacrocycle for ditopic binding of bromide

“…The binding constant is, however, not strong in water as expected, due to the high solvation effect of the competitive polar solvent. The obtained value is in agreement with the results for halide binding in [18]N6,21 however much lower than that observed for bromide or chloride binding in p -xylyl cryptand 22. The presence of methyl group in macrocyclic moiety made the tosylate salt of L (prepared from the reaction of L with four equivalent of TsOH) fairly soluble in non-polar solvent, thus allowing us to measure the binding constant in CDCl 3 .…”

Manifestations of noncovalent interactions in the solid state. 3. X-ray crystal structures of [H4(cyclam)][FeCl5(OH2)](Cl)2 and [H4(cyclam)][CF3COO]4, two network hydrogen bonded solids

“…Nevertheless, polyazamacrocyclic ligands and their complexes are capable of forming ordered solids, but not as a direct result of the ligand engaging in intermolecular interactions (13-1 6). The protonated polyammonium derivatives of cyclam are known but have received much less attention, although complexation of anions by polyammonium and macrocyclic cations has been of interest from structural (17)(18)(19)(20), photochemical (2 l ) , and analytical (22) Strem Chemicals, Inc., and trifluoroacetic acid was purchased from rameters)]'I2 are also presented. Weights based on counting staAldrich Chemical Co. All reagents were used as received.…”

X‐Ray Reflectometry Study of Self‐Assembled Ionic Nanolayers

“…The negatively charged layer-building blocks were such macrocycles as copper(II) phthalocyanine tetrasulfonic acid tetrasodium salt (CuPc), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid tetrasodium salt (DOTA), and mellitic acid hexasodium salt (MA). Azacyclic compounds as cyclen [23] and hexacyclen are known ligands for cations [24] as well as anions if protonated [25]. Metal phthalocyanines are known for their photochemical [26] and conductivity [27] properties.…”