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

Four novel transition metal oxyfluorides, [Zn(pz)3 ][MoO2 F4 ]·0.1H2 O (1), [Zn(pz)2 F2 ][Zn(pz)3 ]2 [WO2 F4 ]2 (2), [Cd(pz)4 ][Cd(pz)4 (H2 O)][MoO2 F4 ]2 ·0.625H2 O (3), and [Zn(mpz)3 ]2 [MoO2 F4 ]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, Pna21 , is nonphase-matchable (Type I), and reveals a moderate second-harmonic-generation (SHG) efficiency (10 × α-SiO2 ). The observed SHG efficiency of compound 4 is due to the small net polarization occurring from the arrangement of ZnN3 F2 trigonal bipyramids. Spectroscopic and thermal characterizations along with calculations for the title materials are reported.