Reaction of MCl(2) (M = Pd, Pt) with 1 molar equiv of [16]aneSe(4) in refluxing MeCN solution in the presence of TLPF(6) affords the complexes [M([16]aneSe(4))](PF6)(2) in high yield. [Pd([16]aneSe(4))](PF6)(2).2MeCN crystallizes in the monoclinic space group P2(1)/c with a = 10.184(4) Angstrom, b = 10.673(4) Angstrom, c = 13.960(7) Angstrom, beta = 98.01(4)degrees, V = 1502.6 Angstrom(3), Z = 2, and F(000) = 917. The structure shows the Pd-II ion on a center of symmetry at (0, 0, 0), coordinated to a precisely square planar arrangement of the four selenoether donor atoms, with the macrocycle adopting an up,up,down,down configuration, Pd-Se = 2.435(2), 2.428(1) Angstrom. [Pt([16]aneSe(4))](PF6)(2).2MeCN is isomorphous with its Pd-II analogue, giving a = 10.200(7) Angstrom, b = 10.609(6) Angstrom, c = 14.045(8) Angstrom, beta = 98.90(2)degrees, V = 1501.6 Angstrom(3), Z = 2, F(000) = 984, and Pt-Se = 2.420(3), 2.417(3) Angstrom. Variable-temperature Se-77 and Pt-195 NMR studies are described which reveal the occurrence of a dynamic process in solution for [M([16]aneSe(4))](2+), involving interconversion of invertomers. The bis-bidentate model complexes [M(MeSeCH(2)CH(2)CH(2)SeMe)2]- (PF6)(2) have also been prepared by reaction MCl(2) with 2 molar equiv of MeSeCH(2)CH(2)CH(2)SeMe in refluxing MeCN in the presence of TlPF6. Variable-temperature Se-77 and Pt-195 NMR spectroscopic studies on these complexes are compared with those of the macrocyclic tetraselenoether complexes. Cyclic voltammetry of [M([16]aneSe(4))](PF6)(2) in MeCN solution shows no oxidative activity. An irreversible reduction is seen for each complex at E(pc) = -0.90 V for M = Pd and E(pc) = -1.64 V vs Fc/Fc(+) for M = Pt, at a scan rate of 200 mV s(-1).