Metal-metal bonds between metal cations are ubiquitous in coordination complexes, whereas similar bonding characteristics between non-metal and metal cations are not. Here, we report an X-ray crystal structure of a centrosymmetric complex [Ag(m-O3SCF3)2{(4MePyNO)2I}]2 (1-AgI), where the iodine(I) cation forms an unusual 3-centre 4-electron [O–I–O]+ halogen bond with two oxygen atoms from two 4-methylpyridine N-oxide (4MePyNO). The iodine(I) atoms from two [4MePyNO−I−ONPyMe4]+ cations, which, together with the two silver(I) atoms from the paddlewheel [Ag(m-O3SCF3)2]22− structure, establish two unique I+–Ag+ bonds at 2.863(2) Å. This bond length is characteristic of bimetallic coordination bonds such as Au+−Ag+ [2.8553(6) Å], Cu+−Ag+ [2.8616(9) Å], and Pt2+−Ag+ [2.8602(4) Å]. Density Functional Theory calculations unambiguously support the existence of the I+–Ag+ coordination bond between non-metal and metal cations in complex 1-AgI.
