Ni4 tetrahedra

Interaction of I2 with concentrated NH3 solution at room temperature gives black crystals of (NI3-NH3) , n = 1, 3, 5, that are explosive when dry. The crystals have zigzag chains of NI4 tetrahedra sharing comers with NH3 molecules linking the chains together. Pure NI3 has been made as red-black explosive, volatile crystals by interaction of boron nitride with IF in CFC13.73... 

In NI3 NH3, slightly distorted NI4 tetrahedra are linked by shared comers into indefinite I-N-I-N-I chains (d(N Ibridge) 230 pm, d(N Item) 214 pm). Ammonia forms a charge transfer complex with the terminal iodine atoms (d(N r NH3)253 pm). 

Concentrated aqueous ammonia reacts with I2 at 25° to give black, explosive crystals of NI3 NH3. With liquid ammonia, more complex reactions occur. The structure of NI3-NH3 contains zig-zag chains of NI4 tetrahedra sharing corners, with NH3 molecules lying between the chains and linking them together.43 The mixed halide NC1F2 (b.p. —67°) is relatively stable. 

La2Ni4 octahedra, La2Ni2 tetrahedra, and Ni4 tetrahedra. The unit cell is doubled along the c axis because of the formation of a super-lattice, which is a consequence of long range correlations between occupied and unoccupied Ni4 tetrahedra. 

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