Syntheses, structures and electrochemistry of [Zn(L1)2](BF4)2•2H2O and [Zn(L1)(TpR)]BF4 (L1=1-(pyrid-2-yl)-3-{2′,5′-dimethoxyphenyl}pyrazole; [TpR]-=tris-{3-arylpyrazolyl}borate)

dComplexation of hydrated Zn(BF4)(2) by 1-{pyrid-2-yl}-3-{2',5'-dimethoxyphenyl}pyrazole (L-1) in MeCN, followed by layering with Et2O, affords a white polycrystalline material analysing as [Zn(L-1)(2)] (BF4)(2). 2H(2)O (1). Reaction of 1 with K[Tp(Ph)], K[TPTol] or K[TPPhF] ([Tp(Ph)]- = tris-{3-phenylpyrazolyl}borate; [Tp(Tol)](-) = tris-{3-[4-methylphenyl]pyrazolyl}borate [Tp(PhF)](-) = tris-{3-[4-fluorophenyl]-pyrazolyl}borate) in 4:1 CH2Cl2:MeCN gives [Zn(L-1)(Tp(Ph))]BF4 (2), [Zn(L-1)(Tp(Tol))]BF4 (3) and [Zn(L-1)(Tp(PhF))]BF4 (4) in low-to-moderate yields. The single crystal structure of 2 shows a five-coordinate zinc ion, with a very distorted square-pyramidal geometry. A variable temperature NMR study of 2 in CD2Cl2 demonstrates a fluxional process involving libration of the L-1 ligand within one 'wedge' of the [Tp(R)](-) tripod. Cyclic voltammograms of 1-3 in CD2Cl2/0.5 M (NBu4PF6)-P-n, or MeCN/0.1 M (NBu4PF6)-P-n each show one irreversible L-1-based oxidation at E-pa = + 1.0-1.1 V versus ferrocene/ferrocenium, and two principle daughter waves at E-pc = 0.0 V and E-1/2 = - 0.5 V. This differs from the cyclic voltammograms of their previously published copper-containing analogues, which do not show oxidative EC reactivity. The reasons for these differences, and the nature of the decomposition products of zinc-coordinated [L1-](+), are discussed. (C) 2000 Elsevier Science Ltd All rights reserved.