A [3]Rotaxane Containing {Ti₇Ga} Rings Linking CuII: Synthesis, Structure, and Spectroscopic Studies

We report the synthesis of extended hybrid organic‐inorganic rotaxanes based on (pyCH 2 NH 2 CH 2 CH 2 py)[Ti IV 7 Ga III O 8 (O 2 C t Bu) 16 ] ( 1 ) and (pyCH 2 NH 2 CH 2 py)[Ti IV 7 Ga III O 8 (O 2 C t Bu) 16 ] ( 3 ) building blocks, containing an anionic macrocycle and doubly pyridyl‐terminated secondary ammonium threads. Reaction of 1 and 3 with [Cu(hfac) 2 ] (hfac = 1,1,1,5,5,5‐hexafluoroacetylacetonate) gives {[Cu(hfac) 2 ] 3 [ 1 ] 2 } ( 2 ) and {[Cu(hfac) 2 ] 2 [ 3 ]} ( 4 ), respectively, which are characterized by single‐crystal X‐ray crystallography. The products are controlled by the differing steric demands imposed by the two arms of the thread. The structure of 2 is an extended [3]rotaxane, with two molecules of 1 binding to a central [Cu(hfac) 2 ] molecule via the longer arm of the thread, and two [Cu(hfac) 2 ] units terminating the structure at the shorter arm. The structure of 4 , where both arms of the thread are short, is an extended [2]rotaxane terminated by two molecules of [Cu(hfac) 2 ]. The Cu…Cu…Cu fragment in 2 is linear, with the central Cu lying on an inversion center and with a separation between the terminal copper ions of 31.3 Å. Double Electron‐Electron Resonance (DEER; also known as PELDOR) spectroscopy proves that the [3]rotaxane structure remains intact in solution, detecting both terminal…center and terminal…terminal Cu…Cu interactions, with orientation‐selective measurements demonstrating that there is a rearrangement of the structure at the terminal positions on dissolution.