Preparation of Site-Differentiated Mixed Ligand and Mixed Ligand/Mixed Metal Metallacrowns

Abstract

Assembly reactions that can prepare reliably regioselective metallamacrocyclic complexes have been a target in the development of metallacrowns. To this end, a series of mixed ligand and mixed ligand/mixed metal metallacrowns have been synthesized in high yield and structurally characterized. Two distinct connectivities have been observed in these types of metallacrowns. The monomeric, vacant metallacrown with mixed ligand composition [12-MC(Ni(II)N(Hshi)2(pko)2-4)] (1a) shows the connectivity pattern [-O-Ni-O-N-Ni-N-]2 while the other Ni metallacrowns, [12-MC(Ni(II)N(shi)2(pko)2-4)] (2a) and the coupled [12-MC(Ni(II)N(shi))2(pko)2-4)][12-MC(Ni(II)N(shi))3(pko)-4)] (3a) fused metallacrowns as well as the mixed metal Mn-Ni metallacrown [12-MC(Ni(II)Mn(III)N(shi)2(pko)2-4)] (4a), follow the pattern [-Ni-O-N-]4. Also, three distinct arrangements of the chelate rings around the metal ions have been observed. The syntheses are completely general, allowing for the substitution of different ligands into the metallacrown core. Compounds 1 and 4 show the 6-5-6-5-6-5-6-5 arrangement, compounds 2 and 3(1) the 6-6-5-5-6-6-5-5, and the 3(2) component the 6-6-5-5-6-5-6-5. The obtained structures can be rationalized by balancing the charge at each metal site in the metallacrown. Variable temperature magnetic susceptibility measurements show that exchange interactions for all the compounds are weak and dominantly antiferromagnetic (e.g., 2a gives an exchange coupling of J = -1.2 cm(-1) with g = 2.2). In solution, the metallacrowns are shown to be stable both to decomposition and ligand exchange.

Metal complexes of the third-generation quinolone antimicrobial drug sparfloxacin: Structure and biological evaluation

“…For all the metal ions a default parameter set with R * = 2.20 Å and e * = 0.02 kcal mol À1 was used, since the van der Waals interactions are not expected to play a major role in such bonded representations as in octahedral complexes. Metal-ligand bond lengths were corrected in the final models using harmonic restraints with equilibrium values extracted from crystallographic data of similar compounds [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] (Tables S1, S3, S5, S7, S9). Non-bonded interactions were calculated in vacuo with no cutoff and the electrostatic energy term was treated using bond dipoles.…”

“…The final structures of the transOc isomers (Scheme 3A) exhibit lower average energies than the other isomers (trans3, cis3, transOp and transOw) by more than 1.7 kcal mol À1 . The energy of the complex has been minimized after the appropriate distance restraints (Table S7) of NiAO bonds [26][27][28][29][30][31][32] for the transOc model with the lowest energy and the structure of the predicted most stable isomer (a transOc isomer) has been obtained (Fig. 2B).…”

Inter-conversion of 15-MC-5 to 12-MC-4 manganese metallacrowns: structure and bioactivity of metallacrowns hosting carboxylato complexes

“…The cavity size of metallacrowns compares well to that of organic crown ethers. [14], [15][16][17] inverse- [18,19], [20][21][22][23], [24], [25], [26], [24], [27] metallacrowns with Mn III , Fe III , Ni II , Cu II and V V O, metal ions, stacking metallacrowns [28][29][30] as well as a variety of dimers and fused metallacrowns [16,20,31,32] have been reported to date. Metallacrowns are typically prepared using hydroxamic acids and/or ketonoximic acids as constructing ligands (Scheme 1), while suitable organic molecules such as picoline-tetrazolylamides [33], diethyl ketipinate [30], 3-hydroxy-2pyridone [34] or 3-thione-1,2-dithione-4,5-dithiolato [35] have also been used.…”

Synthesis, crystal structure and bioactivity of a novel 18-metallacrown-6 [Mn6(H2O)6 (anshz)6]·10DMF

“…One, two or three dimensions of networks of metallacrown could be connected via facial interactions and anion bridging [6]. To this day, metallacrowns, with Mn(III), Fe(III), Ni(II), Cu(II), Zn(II), Ga(III) and V(V)O metal ions, [7], [8][9][10][11][12], [13][14][15][16], [17], [18], [19], ] [17], [20], stacking metallacrowns [21][22][23] as well as a variety of dimers and fused metallacrowns [9,13,24,25] have been reported. Metallacrowns are typically prepared using hydroxamic acids and/or ketonoximic acids as constructing ligands (Scheme 1(a)), while suitable organic molecules such as salicylhydrazides [19,20,26], picoline-tetrazolylamides [27], diethyl ketipinate [23], 3-hydroxy-2-pyridone [28] or 3-thione-1,2-dithione-4,5-dithiolato [29] have also been used.…”