Yes you can but.... That board is technically CrossfireX capable, but the PCIE 2.0 slot is limited to x4 speed. Essentially, the card in the 3.0 slot would have the maximum x16 PCIE-3.0 bandwidth allotted by the Intel H97 chipset, but the bandwidth of the card in the 2.0 slot would be lessened quite a bit in comparison. Such a setup wouldn't achieve ideal Crossfire performance, but there would be a gain in performance. Typically, you can expect a R9 280x Crossfire configuration to scale upwards of 70- to 90-percent (sometimes nearing 100-percent) in many titles. A Crossfire setup using your motherboard would not yield the same levels of Crossfire scaling due to the slightly limited bandwidth of the 2nd card.
What you'd ideally want for a Crossfire or SLI configuration is a board that has two identical x16 slots, which would then split the x16 into a x8 + x8 configuration. MSI's Z77A-G45 and above boards have such a setup - they all use two PCIE-3.0 x16 slots. (So do many boards from other manufacturers.)
Lastly, you could potentially run into further bandwidth limitations for the 2nd card since it shares its 4-lanes (x4) with the remaining PCIE-x1 slots. Should you make use of additional cards in those slots, you would end up taking away some of the already slightly limited bandwidth.