RESUMO
Porous materials resembling zeolites that are composed of organic and inorganic building units were synthesized and characterized. Control of pore and channel size was achieved by using different-sized cations. The metal-assembled, anionic cage molecule, Co(4)1(2)(8-), with a hydrophobic cavity and four carboxylate rich arms, was used as a structural unit for the formation of materials with pores and channels. When assembled into a solid material with dications (Mg(2+), Ca(2+), Sr(2+), and Ba(2+)), Co(4)1(2)(8-) arranges into sheets of cages linked together by cations. The series of materials based on Co(4)1(2)(8-) and containing alkaline earth cations was characterized using X-ray crystallography. The magnesium material packs with cages close together, has small channels, and has cation-carboxylate linkages in three dimensions. The calcium material has cages packed with voids between them and has 5 x 10 A channels and 10 x 21 A pores. The strontium and barium materials also pack with voids between the cages and similarly to each other. They have 11 x 13 A and 11 x 11 A channels and 10 x 27 A and 9 x 27 A pores, respectively. Each of these materials has many (20-50) solvent water molecules associated with each cage. The associated water can be removed from and adsorbed by the materials. The heat of water binding has been measured to be -52 kJ/mol (Mg(4)Co(4)1(2)); -47 kJ/mol (Ca(4)Co(4)1(2)); -48 kJ/mol (Sr(4)Co(4)1(2)); -49 kJ/mol (Ba(4)Co(4)1(2)).
RESUMO
A series of macrocyclic tetraazacrown ethers containing two pyridine, quinoline, 8-hydroxyquinoline, or 8-aminoquinoline sidearms has been prepared. Crab-like cyclization of bis(alpha-chloroacetamide)s and diamines followed by reduction of the cyclic diamides was used to synthesize the selected crown ethers containing two unsubstituted macroring nitrogen atoms. The preparation of the macrocycles with sidearms was accomplished by reductive amination of the proper aldehydes with the crown ethers using sodium triacetoxyborohydride (NaBH(OAc)(3)) as the reducing agent. The 8-hydroxyquinoline- and 8-aminoquinoline-containing macrocycles were synthesized by reductive amination of 8-acetoxyquinoline-2-carboxaldehyde or 8-nitroquinoline-2-carboxaldehyde followed by removing the acetate groups or reducing the nitro groups to amino groups, respectively. Complexation of ligand 22 with Cu(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), and Pb(2+) was evaluated potentiometrically in aqueous solution (0.10 M Me(4)NCl) at 25 degrees C. Ligand 22 formed very stable complexes with these metal ions. The UV-vis spectra of 22 and its complexes were examined in an aqueous acetic acid buffer solution (pH 5). The 22-Cu(2+) complex provided a new absorption band at 258 nm.
RESUMO
New 5-chloro-8-hydroxyquinoline (CHQ)-substituted aza-18-crown-6 (4), diaza-18-crown-6 (1), diaza-21-crown-7 (2), and diaza-24-crown-8 (3) ligands, where CHQ was attached through the 7-position, and aza-18-crown-6 (11) and diaza-18-crown-6 (10) macrocycles, where CHQ was attached through the 2-position, were prepared. Thermodynamic quantities for complexation of these CHQ-substituted macrocycles with alkali, alkaline earth, and transition metal ions were determined in absolute methanol at 25.0 degrees C by calorimetric titration. Two isomers, 1 and 10, which are different only in the attachment positions of the CHQ to the parent macroring, exhibit remarkable differences in their affinities toward the metal ions. Compound 1 forms very stable complexes with Mg(2+), Ca(2+), Cu(2+), and Ni(2+) (log K = 6.82, 5.31, 10.1, and 11.4, respectively), but not with the alkali metal ions. Ligand 10 displays strong complexation with K(+) and Ba(2+) (log K = 6.61 and 12.2, respectively) but not with Mg(2+) or Cu(2+). The new macrocycles and their complexes have been characterized by means of UV-visible and (1)H NMR spectra and X-ray crystallography. New peaks in the UV spectrum of the Mg(2+)-1 complex could allow an analytical determination of Mg(2+) in very dilute solutions in the presence of other alkali and alkaline earth metal cations. (1)H NMR spectral and X-ray crystallographic studies indicate that ligand 10 forms a cryptate-like structure when coordinated with K(+) and Ba(2+), which induces an efficient overlap of the two hydroxyquinoline rings. Such overlapping forms a pseudo second macroring that results in a significant increase in both complex stability and cation selectivity.
RESUMO
The synthesis and physical characterization of oxo-bridged [Cr(2)(tmpa)(2)(&mgr;-O)(X)](n)()(+) complexes (tmpa = tris(2-pyridylmethyl)amine) containing a variety of complementary ligands (X = CO(3)(2)(-), PhPO(4)(2)(-), HS(-)) are described, with the objective of understanding factors underlying variations in the antiferromagnetic coupling constant J. We also present the crystal structure of [(tmpa)Cr(&mgr;-O)(&mgr;-CO(3))Cr(tmpa)](ClO(4))(2).2H(2)O, for comparison with previous findings on [(tmpa)Cr(&mgr;-O)(&mgr;-CH(3)CO(2))Cr(tmpa)](ClO(4))(3). The carbonate-bridged complex crystallizes in the monoclinic space group P2(1)/c with a = 11.286(10) Å, b = 18.12(2) Å, c = 20.592(12) Å, beta = 95.99(5) degrees, and V = 4190 Å(3) and Z = 4. Asymmetric tmpa ligation pertains, with apical N atoms situated trans to bridging oxo and acido O atoms. Key structural parameters include Cr-O(b) bond lengths of 1.818(6) and 1.838(6) Å, Cr-OCO(2) distances of 1.924(7) and 1.934(7) Å, and a bridging bond angle of 128.3(3) degrees. Several attempts to prepare oxo, amido-bridged dimers were unsuccessful, but the nearlinear [Cr(tmpa)(N(CN)(2))](2)O(ClO(4))(2).3H(2)O complex was isolated from the reaction of dicyanamide ion with [Cr(tmpa)(OH)](2)(4+). In contrast to the behavior of analogous diiron(III) complexes, antiferromagnetic coupling constants of [Cr(2)(tmpa)(2)(&mgr;-O)(X)](n)()(+) dinuclear species are highly responsive to the X group. Considering the complexes with X = CO(3)(2)(-), PhPO(4)(2)(-), HS(-), SO(4)(2)(-), and RCO(2)(-) (10 R substituents), we find a reasonably linear, empirical relationship between J and oxo bridge basicity, as measured by pK(a) (Cr(OH)Cr) values in aqueous solution. While there is no theoretical basis for such a correlation between solid-state and solution-phase properties, this relationship demonstrates that CrOCr pi-bonding contributes significantly to antiferromagnetic exchange. Thus, J tends to become less negative with increasing &mgr;-O(2)(-) basicity, showing that greater availability of a bridging oxo group lone pair toward the proton, with decreasing CrOCr pi-interaction, reduces the singlet-triplet gap.
