Zinc phosphide is the inorganic chemical
compound. It is a grey solid, although
commercial samples are often dark or
even black. It is used as a rodenticide.
Zn3P2 is a semiconductor with a direct
band gap of 1.5 eV. and may have
applications in photovoltaic cells. A
second zinc phosphide is known, with the
stoichiometry ZnP2.
Synthesis and reactions 
Zinc phosphide can be prepared by the
reaction of zinc with phosphorus;
however, for critical applications,
additional processing to remove arsenic
compounds may be needed.
3 Zn + 2 P → Zn3P2
Another method of preparation include
reacting tri-n-octylphosphine with
dimethylzinc.
Zinc phosphide reacts with water to
produce phosphine and zinc hydroxide2):
Zn3P2 + 6 H2O → 2 PH3 + 3 Zn(OH)2
Structure 
Zn3P2 has two forms, a room temperature
tetragonal form which converts to a
cubic form at around 845 °C.  In the
room temperature form there are discrete
P atoms, zinc atoms are tetrahedrally
coordinated and phosphorus six
coordinate, with zinc atoms at 6 of the
vertices of a distorted cube. ZnP2 has
two forms a lower temperature red
tetragonal form and a black monoclinic
form. In both of these there are chains
of P atoms, helical in the tetragonal,
semi-spiral in the monoclinic.
Rodenticide 
Metal phosphides have been used as
rodenticides. A mixture of food and zinc
phosphide is left where the rodents can
eat it. The acid in the digestive system
of the rodent reacts with the phosphide
to generate the toxic phosphine gas.
This method of vermin control has
possible use in places where rodents are
immune to other common poisons. Other
pesticides similar to zinc phosphide are
aluminium phosphide and calcium
phosphide.
Zinc phosphide is typically added to
rodent baits in amount of around
0.75-2%. Such baits have strong, pungent
garlic-like odor characteristic for
phosphine liberated by hydrolysis. The
odor attracts rodents, but has a
repulsive effect on other animals;
However, birds, notably wild turkeys,
are not sensitive to the smell. The
baits have to contain sufficient amount
of zinc phosphide in sufficiently
attractive food in order to kill rodents
in a single serving; a sublethal dose
may cause aversion towards
zinc-phosphide baits encountered by
surviving rodents in the future.
Rodenticide-grade zinc phosphide usually
comes as a black powder containing 75%
of zinc phosphide and 25% of antimony
potassium tartrate, an emetic to cause
vomiting if the material is accidentally
ingested by humans or domestic animals.
However, it is still effective against
rats, mice, guinea pigs and rabbits,
none of which have a vomiting reflex.
Zinc phosphide use in New Zealand 
The New Zealand Environmental Protection
Authority has approved the import and
manufacture of Microencapsulated Zinc
Phosphide for the ground control of
possums. The application was made by
Pest Tech Limited, with support from
Connovation Ltd, Lincoln University and
the Animal Health Board. It will be used
as an additional vertebrate poison in
certain situations. Unlike 1080 poison,
it cannot be used for aerial
application.
Safety 
Zinc phosphide is highly toxic.
References 
External links 
Zinc Phosphide Pesticide Information
Profile - Extension Toxicology Network
EPA Proposed Risk Mitigation Decision
for Nine Rodenticides
Zinc phosphide in the Pesticide
Properties DataBase
Zinc phosphide properties and use in
Michigan
MD0173 - Pesticides in the military
