Solution and Solid State Characterization of a Cadmium Octaazacryptand Complex

Abstract

The constant for cadmium binding by octaazacryptand L ) N(CH 2 CH 2 NHCH 2 CH 2 NHCH 2 CH 2 ) 3 N was determined by potentiometry; log ML )18.3(1). Calculation of pM values (pM ) -log [M]) show that L has the highest reported binding affinity for cadmium relative to other [2.2.2] polyoxa-polyaza cryptates. Two cadmium cryptate complexes, [CdL](BF 4 ) 2 (1a) and [CdL](OAc) 2 ‚2H 2 O (1b), were synthesized by metalation of the free cryptand. The molecular structures of compounds 1a and 1b were determined by X-ray diffraction. Crystallographic data for 1a: trigonal, P3 h1c, Z ) 2, a ) 9.581(2) Å, c ) 17.003(4) Å, V ) 1351.2(5) Å 3 . Crystallographic data for 1b: monoclinic, C2/c, Z ) 4, a ) 10.500(2) Å, b ) 14.782(3) Å, c ) 19.395(4) Å, ) 99.30(2)°, V ) 2971(1) Å 3 . The cadmium ions in both complexes are eight-coordinate and display similar coordination geometries but different ligand conformations, designated as parallel and oblique. The cadmium coordination sphere is best described as a bicapped octahedron. Through 2D NMR experiments we have found that the Cd is in a symmetric environment and the conformation of the ligand in solution is consistent with the parallel conformation observed in one of the solid state structures. The 113 Cd NMR shift of this eight-coordinate amine complex is 75 ppm relative to 0.1 M aqueous Cd(ClO 4 ) 2 , which correlates with shifts observed for other [2.2.2] cadmium polyoxapolyaza cryptates.

Conformational and coordination plasticity in silver(i) cryptates

“…Ag(1) and Ag(2) each show two weak additional interactions with oxygen atoms of two triflate ions as shown in Fig.3(b). There are long Ag-O contacts in the range 2.857(7)-3.167(7), comparable to the…”

“…4 1 H NMR spectrum of [Ag 2 (L 2 )](CF 3 SO 3 ) 2 3Ј in CD 3 OD at 228 K with integral values indicated below each feature. 19 F MAS-CP resonances are split by over 6 ppm in the cadmium fluoroborate salt, 5, indicating inequivalent siting of anions in the lattice of the cadmium salt, where the crystallographic independence of the two BF 4Ϫ anions has been demonstrated 7. The 19 F spectra of 3 and 4 also show small (≈1 ppm) splitting of the 19 F resonance arising presumably from the coordination inequivalence of the triflate anions mentioned above.Despite the insensitivity of the nucleus, we did succeed in obtaining a 109 Ag MAS spectrum for the trimeric cryptate 4.…”

Bis-tetradentate complexes of Cd(ii) and Hg(ii) with N8coordination: structural and NMR comparisons

“…Bicapped octahedral coordination geometry in N 8 coordinated complexes has only been observed with the ligands investigated here, 23 the related ligand L4 3,4,40 and a bicyclic octaazacryptand. 41 The latter complex had a 2.832(6) Å distance to the capping N and 2.49(2) Å to the octahedral N, both of which are in the range of distances observed for the Cd(II) bis-tetradentate chelates of L1-L4. Furthermore, the average Cd-N bond lengths in 1, 2, 4 and 7 are all approximately 2.55 Å, similar to the averages observed in the full range of structurally characterized N 8 coordinated complexes.…”

Living in a Cage Is a Restricted Privilege

“…30a) [63], and of its complex with Cd II (Fig. 30c) [64]. The cryptand presents an ellipsoidal cavity (the distance between the apical tertiary nitrogen atoms is 6.37 Å ).…”