Single Isomer Heterometallic {Cr^III₆M^II₂} Rings Templated by Tetramethylammonium

Abstract

F 8 (O 2 C t Bu) 16 ] is reported using tetramethylammonium hydroxide pentahydrate as the source of a template, where M = Zn, Mn, Ni, and Co. The metal cores are octagons with metal−metal edges bridged by one fluoride and two carboxylate ligands. The divalent metal ions are found ordered at positions 1 and 5 in the octagon. The tetramethylammonium cations are above and below the metal plane of the ring in the crystal structure. Magnetic studies show antiferromagnetic coupling between the paramagnetic metal ions present, leading to paramagnetic ground states in each case. 1 H NMR spectroscopy confirms that the structure of the {Cr III 6 Co II 2 } ring exists in solution, and electron paramagnetic resonance spectroscopy confirms the magnetic structure of the other three rings.

Synthesis and characterization of heterometallic rings templated through alkylammonium or imidazolium cations

“…The spectra have some features reminiscent of 8, which contains two {Cr 6 } chains and therefore these features could be due to isomer 5A. Other features resemble those seen in an ordered {Cr 6 Zn 2 } structure [Me 4 N] 2 [Cr 6 M 2 F 8 (O 2 C t Bu) 16 ] 9; 30 these features would therefore be due to isomer 5D. Our conclusion is that both these isomers are present, but we cannot exclude the possibility that 5C is present; 5B would include features from a single Cr III centre, 31 and such features are clearly absent.…”

“…This contrasts with a family of {Cr 6 M 2 } rings we reported with tetramethylammonium as the cation. 30 …”

“…This contrasts with a family of {Cr 6 M 2 } rings we reported with tetramethylammonium as the cation. 30 The magnetic study of 4 is a rare example of an open ninemetal chain. The best fit magnetic parameters show J = −3.33 cm −1 , which is significantly smaller than the chromium-chromium exchange interactions found in seven-metal chains but similar to that found for a regular {Cr 9 } ring ( J = −2.7 cm −1 using the same Hamiltonian used here).…”

Hexanuclear {ZnII4FeIII2} and {ZnII4CrIII2} complexes from the use of potentially tetradentate NOO′O′′ Schiff-base ligands

“…x Cr III y )} formulas (x, y are integer numbers) exhibit exciting structural and physical properties, and they have been proposed for various applications 47 including quantum information processing 48 and magnetic refrigeration; 49 and (v) doping of cyclic {Zn II Cr III 7 } molecular nanomagnets into diamagnetic and isostructural hosts allows pulsed X-band EPR studies (including relaxation and nutation experiments on the S = 3/2 ground state), the doping without scrambling of the Cr III and Zn II ions being aided by the kinetic inertness of the former. 50 This work can also be considered as a continuation of the interest of our groups in various aspects of the coordination chemistry of N,O-based Schiff bases.…”

“…Zn II –Cr III complexes attract the interest of the inorganic chemistry community because – among others –: (i) diamagnetic Zn II “metalloligands” can be used in the study of the presence of long-range Cr III ⋯Cr III exchange interactions even if the distance between the paramagnetic metal ions is as long as ∼7 Å; 44 (ii) the simultaneous presence of the two metal ions have resulted in a new trinodal metal–organic material platform comprised of simple and inexpensive triangular, tetrahedral and trigonal-prismatic molecular building blocks, 45 leading to molecular materials with chemical stability (organic solvents, water and bases) and high uptake of CO 2 and H 2 . These properties are desirable in the context of the cost/performance ratio that is needed to develop metal–organic materials for applications; (iii) heterometallic Anderson-type {Zn II 5 Cr III 2 } “wheels” help in the in-depth study of substitutional disorder in the positions of the Cr III and Zn II ions around the outside ring; 46 (iv) heterometallic rings based on generic {(Zn II x Cr III y )} formulas ( x , y are integer numbers) exhibit exciting structural and physical properties, and they have been proposed for various applications 47 including quantum information processing 48 and magnetic refrigeration; 49 and (v) doping of cyclic {Zn II Cr III 7 } molecular nanomagnets into diamagnetic and isostructural hosts allows pulsed X-band EPR studies (including relaxation and nutation experiments on the S = 3/2 ground state), the doping without scrambling of the Cr III and Zn II ions being aided by the kinetic inertness of the former. 50…”