the compound trans-nbcl/sub 2/(dpm)/sub 2/, hdpm=2,2,6,6-tetramethylheptane-3,5-dione, has been prepared and the molecular structure determined in each of two crystalline polymorphs by x-ray diffraction. the visible spectrum and the epr spectrum have been measured and a fenske-hall calculation performed. the combined results give a reasonable and internally consistent picture of the electronic structure of the molecule. the homo is a b/sub 3g/-orbital (predominantly d/sub yz/), while the two lowest-lying unoccupied orbits (ca 16000 cm/sup -1/ higher) are b/sub 2g/(=d/sub xz/) and a/sub g/(=d(x/sup 2/-y/sup 2/)) orbitals, all in the d/sub 2h/-symmetry. the b/sub 3g/=b/sub 2g/ and b/sub 3g/=a/sub g/ transitions are observed at 588.4 and 626.7 nm. the epr spectrum in solution is a decet: the measured value of (g) is 1.930 and (a/sub iso/) is 149 g. for the crystalline polymorph 1 the crystal data are' orthorhombic (p2/sub 1/2/sub 1/2/sub 1/), a=13.649(3)aa, b=18.166(4)aa, c=11.425(4)aa, v=2833(2)aa/sup 3/ and z=4. polymorph 2 is monoclinic (p2/sub 1//n) with a=12.288(5)aa, b=9.226(4)aa, c=12.545(4)aa, beta=94.24(3) degrees, v=1418(2)aa/sup 3/ and z=2 the molecule in 2 is centrosymmetric with virtual d/sub 2h/-symmetry. in 1 there are distortions in the chelate plane postulated to be due to packing forces. the two forms have comparable averaged values of interatomic dimensions