[scifan]

How many isomers does dicarbonylbis(trimethylphosphine)platinum(0) have?

[cheese (MSW)]

Years ago a member of my research group accidentally made this cmpd!  And it is a liquid.  We never investigated it further which was sad.
(I'll tell you how we made it for a beer!)
Because it is Pt(0) it is probably tetrahedral (C&W) and there is only one form of Pt(PMe3)2(CO)2: two ν(C≡O) IR <2000 cm^-1
(let me guess ~1960 and ~1920 cm_1?; PMe3 strong σ donor); H-NMR equivalent Hs but a doublet (JPH).
Less likely is it square planar and you can have cis-Pt(PMe3)2(CO)2 with the same spectroscopic properties as the tet form.
trans-Pt(PMe3)2(CO)2: one ν(C≡O) IR around the value of the lower energy band in the cis. ; H-NMR again equivalent Hs
but you get a triplet.  It is called a virtual triplet (the P atoms are not magnetically equivalent).  Our guy had two CO stretches in the IR 

[scifan]

Thanks
Love to know how he made this compound!

So there are 3 isomers? Tetrahedral arrangement and cis and trans for square planar arrangement?

[cheese (MSW)]

Yes that's correct: tet, cis and trans sq planar, but since it is Pt(0) almost certainly tet.
F. A. Cotton, G. Wilkinson, C. A. Murillo, M. Bochmann Advanced Inorganic Chemistry 6th ed (1999). p 1065.
I know realize that what she made was PtMe2(CO)2  (Pt(II) cis isomer).  We were working on cis-Pt(PR3)2Me2
[in collaboration with an NMR guy:solid state P/(JPt-195) NMR)] but she knocked the PMe3 groups off as I recall and
the PtMe3(CO)2 was so volatile it went into the lig N2 trap!