Variable Asymmetric Chains in Transition Metal Oxyfluorides: Structure Second-Harmonic-Generation Property Relationships

Four novel transition metal oxyfluorides, [Zn(pz)(3)][MoO2F4] center dot 0.1H(2)O (1), [Zn(pz)(2)F-2] [Zn(pz)(3)](2)[WO2F4](2) (2), [Cd(pz)(4)][Cd(pz)(4)(H2O)][MoO2F4](2)center dot 0.625H(2)O (3), and [Zn(mpz)(3)](2)[MoO2F4](2) (4) (pz = pyrazole; mpz = 3-methyl pyrazole) have been synthesized. Compounds 1 and 4 contain helical chains. Compound 2 accommodates zigzag chains, and compound 3 has quasi-one-dimensional linear chains. The variable chain structures are found to be attributable to the different structure-directing anionic groups and hydrogen bonding interactions. Compound 4 crystallized in the noncentrosymmetric (NCS) polar space group, Pna2(1), is nonphasematchable (Type I), and reveals a moderate second-harmonic-generation (SHG) efficiency (10 X alpha-SiO2). The observed SHG efficiency of compound 4 is due to the small net polarization occurring from the arrangement of ZnN3F2 trigonal bipyramids. Spectroscopic and thermal characterizations along with calculations for the title materials are reported.