Reactions of trans, trans-(C6F5)(p-tol 3P)2Pt(C≡C)4Pt(Pp-tol3) 2(C6F5) and diphosphines Ar 2P(CH2)m-PAr2 yield trans,trans-(C6F5)(Ar2P(CH2) mPAr2)Pt(C≡C)4Pt(Ar2P(CH 2)mPAr2)(C6F5), in which the platinum atoms are spanned via an sp and two sp3 carbon chains (Ar/m = 3, Ph/14, 87%; 4, p-tol/14, 91%; 5, p-C6H4-t-Bu/ 14, 77%; 7, Ph/10, 80%; 8, Ph/11, 80%; 9, Ph/12, 36%; only oligomers form for m > 14). Crystal structures of 3-5 show that the sp3 chains adopt chiral double-helical conformations that shield the sp chain at approximately the van der Waals distance, with both enantiomers in the unit cell. The platinum square planes define angles of 196.6°-189.9° or more than a half twist. Crystal structures of 7-9, which have shorter sp3 chains, exhibit nonhelical conformations. Reaction of the corresponding Pt-(C≡C) 6Pt complex and Ph2P(CH2)18PPh 2 gives an analogous adduct (27%). The crystal structure shows two independent molecules, one helical and the other not. Low-temperature NMR data suggest that the enantiomeric helical conformations of 3-5 rapidly interconvert in solution. Cyclic voltammograms of 3-5 show more reversible oxidations than model compounds lacking bridging sp3 chains. These are the only double-helical molecules that do not feature bonding interactions between the helix strands, or covalent bonds to templates dispersed throughout the strands, or any type of encoding. The driving force for helix formation is analyzed.