Metallacyclic zinc complexes of alkylidene-linked bitopic bis(pyrazolyl)methane ligands: Unusual exocyclic bridging fluoride ligands

The alkylidene-linked, bitopic bis(pyrazolyl)methane ligands 1,1,3,3-tetrakis(1-pyrazolyl)propane ([CH(pz)(2)](2)CH2; L1; pz = 1-pyrazolyl), 1,1,4,4-tetrakis(1-pyrazolyl)butane ([CH(pz)(2)](2)(CH2)(2); L2), and 1,1,5,5-tetrakis(1-pyrazolyl)pentane ([CH(pz)(2)](2)(CH2)(3); L3) react with Zn(BF4)(2)center dot 5H(2)O in tetrahydrofuran (THF) to afford complexes with the empirical formula [ZnL](BF4)(2) (L = L1 (1), L2 (2), and L3 (3)). H-1 NMR studies indicate that all three complexes are fluxional in solution. Recrystallization of the complexes from acetonitrile yields the crystallographically characterized compounds [Zn(mu-[CH(pz)(2)](2)CH2)(H2O)(CH3CN)](3)(BF4)(6)center dot 2.5CH(3)CN (1a), {[Zn-2(mu(2)-[CH(pz)(2)](2)[CH2](2))(2)(mu(2)-F)](BF4)(3)center dot CH3CN center dot 0.5H(2)O}(infinity) (2a), and [Zn-3(mu-[CH(pz)(2)](2)(CH2)(3))(3)(H2O)(5)](BF4)(6)center dot 4CH(3)CN (3a). Compounds 1a and 3a are trimeric metallacycles in which acetonitrile and water molecules complete the coordination spheres of the octahedral or trigonal bipyramidal Zn2+ ions. Compound 2a consists of one-dimensional chains of dimeric metallacycles connected through the trigonal bipyramidal zinc cations by exocyclic bridging fluoride ligands, the origin of which must be fluoride abstraction from the BF4- counterions. The polymeric chains of 2a are also supported by pi-pi stacking between adjacent pyrazolyl groups, and the compound contains highly ordered solvent molecules that alternate in layers with the intricate gridlike structure of the cationic polymers.